Boost/Compression Ratio Calculator

http://rbracing-rsr.com/compression.htm

The link above is for a boost psi to compression ratio calculator. I ran a couple and was quite surprised at what I got!

1) A typical stock 6.5L
You are running 8 PSI of boost at an altitude of 1000 feet. Your motor's static compression is 21.2 :1. At this boost level and altitude your effective compression ratio is 32.54 :1, and without altitude correction your compression ratio would be 32.74 :1.

2) Reduced 18:1 CR and 15 PSI boost
You are running 15 PSI of boost at an altitude of 1000 feet. Your motor's static compression is 18 :1. At this boost level and altitude your effective compression ratio is 36.17 :1, and without altitude correction your compression ratio would be 36.37 :1.

Do these seem correct!? Can our 6.5s (or any diesel) handle this CR!? I was a bit shocked at the effective CR. I came upon this because I was wondering what is the effect of boost to CR. I knew it had to go up but, still I am very shocked.

Another way of looking at this by "first level approximation" is:
15psi = 2 atmospheres
8psi ~= 1.5 atmospheres

18 CR x 2 atmospheres = 36 CR
21.2 CR x 1.5 atmoshperes = 31.8 CR

So, I believe the calculator is accurate! I would never have thought that any engine would be able to handle a 32 much less a 36 CR. This is why it is necessary to reduce the typical 6.5L CR from 21.2 to ~18 to run 15psi of boost.

Those who run their stock CR of 21.3:1 at 15 psi:

Quote:

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You are running 15 PSI of boost at an altitude of 1000 feet. Your motor's static compression is 21.3 :1. At this boost level and altitude your effective compression ratio is 42.83 :1, and without altitude correction your compression ratio would be 43.03 :1.

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That's why lowering the 6.5 CR to 18:1 improves durability..... :) Now, imagine what would happen if you raised CR above stock...

Jim

So why lower the static compression ratio and run more boost when the end result is the same?

Randy

more boost = more combustion O2 avilable. Add a corresponding amount of additional fuel and you have a more powerful combustion event. Even though the dynamic compression ratio remains the same +/- , the lower height of the 18-1 piston crown creates a larger effective combustion chamber volume, which is now packed with the same density of air/fuel as the smaller area that was provided by the stock piston compression height.

Same DCR + Same A/F Density+ more A/F Volume = bigger bang per power stroke

Ennybody compare that to 3000psi combustion pressures?

No problem, as long as that pressure rise occurs at the right time!;)

Quote:

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Originally Posted by robscarab

more boost = more combustion O2 avilable. Add a corresponding amount of additional fuel and you have a more powerful combustion event. Even though the dynamic compression ratio remains the same +/- , the lower height of the 18-1 piston crown creates a larger effective combustion chamber volume, which is now packed with the same density of air/fuel as the smaller area that was provided by the stock piston compression height.

Same DCR + Same A/F Density+ more A/F Volume = bigger bang per power stroke

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Nicely said! Although the fuel-air "density" isn't the same, but the fuel-air ratio is - unless as you mentioned, more fuel and more air is introduced. Without more fuel/air, with the larger volume, the density is decreased. The fuel-air mixture has, however, the same energy content, but it will be slightly less efficient than at the higher compression ratio. But this will decrease BMEP (Brake Maximum Effective Pressure) in the cylinders, which reduces piston head pressures and does, in fact contribute to longevity at the cost of a slight decrease in efficiency. With a bit more fuel/air, the power will be nearly the same, but still with less stress on piston crowns and skirts.

Compression ratio is a compromise - higher CR results in higher theoretical efficiency, but at the cost of longevity - and sometimes it's too high, such that decreasing it raises efficiency. Which is why I elected to get my new engine with 18:1 pistons. And fuel economy is up 15% over the original GM 6.5L TD.

For an IDI (InDirect Injected) diesel to produce clean cold starts with short glow cycle times, and to produce fewer cold start emissions, the CR has to be somewhere at/above 20:1. The precups/prechambers cool the charge on a cold engine. A DI (Direct Injected) diesel (like the current Duramax, Cummins, PSD) starts well cold at a lower CR. So, a higher CR was an IDI cold start compromise.

I did a short tech piece on the Isuzu C240 I-4 2.4L diesel recently. It too is an IDI engine that has 20:1 CR. Its 3.0L DI siblings are, on the other hand, just over 18:1 CR.

Diesel farm tractors with DI diesels (of those I've seen the data for) run at anywhere between 15 and 18:1 CR. The Duramax/PSD/Cummins ran at 17.5-18:1 (the LMM Duramax is now at 16.8:1). The marine 5.9L Cummins runs with 15:1 CR. And so on...

Tractor, industrial and marine diesels are usually run at high load for extended periods, and tend to have a lower CR for improved durability. Certainly, tractors, OTR diesels, marine diesels and so on are also designed with efficiency in mind. If a higher CR was a better compromise (for efficiency), they'd all have a higher CR. They don't because of increasing durability issues with increasing CR.

Jim

PS - Here's a question for the thinkers out there.... What effect does CR have on crankshaft harmonics?

The reason I selected the 18-1 pistons is so I could safely run higher boost while towing. I have increased the amount of fuel injected per power stroke by "turning up" my DB2 and installing marine injectors. The only time I will benefit from these mods is when I am accellerating a load or pulling it up a grade at cruise. I chose the comprimise of less efficient low boost performance and harder starting. If I was not using this rig exclusively for towing than I would have stayed with the stock compression ratio. If I had a half ton used for running around town empty,I personally would not go with lower compression. I live in Canada where we have periods of very cold temps and starting a 6.5 at -35C can be a challange at the best of times!

Please tell me can you make up for the loss of efficiency with the lower CR by introducing propane injection? Thanks.

Quote:

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Originally Posted by tomtaylor

Please tell me can you make up for the loss of efficiency with the lower CR by introducing propane injection? Thanks.

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No. Propane is just another fuel. Propane injection only adds to volume of fuel(s) already in the combustion. Adding more/other fuels until the combustion process uses all the available O2 available can be advantageous from an economic standpoint (if the alternative fuel is significantly less expensive than the primary fuel), but offers little more than that. Also, consider that almost all fuels (capable of being used in an internal combustion engine) other than #2 Diesel have a significantly lower BTU potential (translates to less "efficient"). Mixing alternative fuels into any engine may have an economic advantage, but you'll have to consider all the costs involved. Most often, the ROI (Return On Investment) is far beyond what you will actually ever achieve.

None of this will change the "efficiency" of a charge-air system. The principals, function and science are very simple. X amount of exhaust gas energy will produce X amount of charge-air energy. On the charge-air side, you will hit a wall on compressor efficiency, at which point, it will fall off exponentially (the value of the fuel input compared to the output power depart very quickly). None of this takes into consideration the mechanical limitations of the platform involved (the point an efficiency increase start breaking things).

Thanks for the feedback on fuel types

In reading here about Dynamic vs Static compression ratio the conversation sounds more like cylinder pressure than compression ratios. Isn't Dynamic CR only affected by cam profile?

if that is true then DCR is cool to understand but wouldn't really matter since we can't change it unless we are out grinding custom cams as we don't have a plethora cam options like a SBC 350?

Was just talking to a guy that says ethanol inj will have a dramatic impact on fuel economy. He claims it burns the fuel more completely producing more power. Anyone trying this, any truth to it?

Quote:

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Originally Posted by tomtaylor

Was just talking to a guy that says ethanol inj will have a dramatic impact on fuel economy. He claims it burns the fuel more completely producing more power. Anyone trying this, any truth to it?

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If you aren't making smoke, you are burning all the fuel. Adding more fuel (such as ethanol) will only increase power up to the point it uses all the remaining O2. Adding #2 up to that point will yield more power. Once it begins making smoke, you have crossed that line, and are pushing incompletely burned fuel out the pipe.

The only way to burn "more completely" is to improve atomization and distribution within the combustion chamber. Adjusting (optimizing) the combustion event timing can help, to some degree. Late model Diesels (Duramax, Cummins, PS) achieve this by increasing the fuel injection pressure (10X), and optimize the fuel duration (also with multiple injection events) and timing dynamically controlled by a computer.

Once again, adding ethanol is adding fuel. Adding fuel will take advantage of available O2. Nothing more. Using a more costly, less efficient (lower BTU) fuel to use up extra air is a cost, in the end. If your goal is economy, this is a net loss, no matter how long your test period is.

Quote:

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Originally Posted by tomtaylor

Was just talking to a guy that says ethanol inj will have a dramatic impact on fuel economy. He claims it burns the fuel more completely producing more power. Anyone trying this, any truth to it?

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Like DmaxMaverick said, if alcohol was cheaper than diesel (by cost per BTU, not volume), there might be an economic advantage to its use.

Water/alcohol injection can be advantageous for other reasons (i.e. to cool the intake air charge). This can be helpful to reduce detonation in a gas engine, or it can be used to reduce EGT in a diesel. For either engine, its not so much about economy, but more about power.

That said, if someone was selling water/alcohol injection systems, and the diesel fuel costs at the pump were high, they might try to make the case about fuel economy to make the sale. Ask them to provide verifiable data... I'm just saying...

Quote:

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Originally Posted by tomtaylor

Thanks for the feedback on fuel types

In reading here about Dynamic vs Static compression ratio the conversation sounds more like cylinder pressure than compression ratios. Isn't Dynamic CR only affected by cam profile?

if that is true then DCR is cool to understand but wouldn't really matter since we can't change it unless we are out grinding custom cams as we don't have a plethora cam options like a SBC 350?

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Compression Ratios, static and dynamic directly correlate to cylinder pressure ratios. Which when combined with Combusting fuel correlate to cylinder pressure. In a naturally aspirated induction system, your DCR will always be less than your SCR.

With Forced induction you can increase the DCR over the SCR with the added benefit of having more Oxygen available for the fuel to use to combust.

DCR can be controlled as the calculator More power posted by increasing the level of boost. or mechanically altering your SCR Via increasing the combustion chamber volume size which is commonly done by shaving pistons down, using thicker gaskets, or using pistons which have the wrist pin placement raised on the skirt thereby shortening the stroke of the piston.

Custom cams and grinds for diesel motors are not very prevalent because almost always they will move the power band further up into the rpm range given the same timing correlation of the valve events to a stock motor. Retarding or advancing the cam to bring it back into a useable RPM range is often not practicle With the relatively small piston to valve clearance in a diesel motor. Due to the sheer mass of the components and already high cylinder pressures within a diesel motor RPM's are typically 3/4 to half of what a gasoline motor operates off of so any work to adjust the level down to an area where it is most useable becomes fruitless as parts will start contacting.

With forced induction this becomes even less important as you are increasing the engines ability to intake air which is where most of your power over stock grinds comes from with custom camshafts in Gas motors.

All of that being said If you were able clearance the pistons around the valves and change the overlap and allow the exhaust valve to hang open a bit longer it seems that some more power could be made. But would it increase your DCR and therefore your Pressure ratio to a point where things start breaking?

A simple way to visualise it assuming that a compression ratio is Adiabatic (Thermal dynamics phrase which doesnt take into effect heat introduced outside of the heat of compression as that math is overly complicated for this example). Your pressure ratio with a Compression ratio of 10:1 would be 25.12:1 CR of 15:1 would be 44.31:1 CR of 20:1 would be 66.29:1 CR of 25:1 would be 90.61:1 and a CR of 35:1 would be 145.11:1

Actual cylinder pressure when taking into account the combustion is hard to figure accurately without measuring it as so many different factors effect it. If you could figure the PSI of a metered amount of diesel combusting you can than get a general ideal of the cylinder pressure and its relatationship to compression above by using a simple formula.

So how hard is it to start when cold with 18 to 1 pistons? Are we talking 20 seconds of cranking? What glow plugs/relay parts are best to start a 18 to 1 motor? Could bad injection pump timing affect its ability to start easily (DB-2)?

Peculiar issue.... I have a '93 that was running to much boost. I believe I burned up a couple pistons. A compression test showed low numbers~150psi. The truck started great with the low compression test numbers and still ran with less power. Finally I swapped in a 18 to 1 long block, and now it cranks for 20 or 30 seconds before wanting to fire. All the components were swapped directly off the old motor onto the new motor, pump, hi pop injectors, glow stuff etc....

Anyone have any insight on why its so hard to start? Maybe I got some glow wiring screwed up?

Quote:

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Originally Posted by BigFj40

So how hard is it to start when cold with 18 to 1 pistons? Are we talking 20 seconds of cranking? What glow plugs/relay parts are best to start a 18 to 1 motor? Could bad injection pump timing affect its ability to start easily (DB-2)?

Peculiar issue.... I have a '93 that was running to much boost. I believe I burned up a couple pistons. A compression test showed low numbers~150psi. The truck started great with the low compression test numbers and still ran with less power. Finally I swapped in a 18 to 1 long block, and now it cranks for 20 or 30 seconds before wanting to fire. All the components were swapped directly off the old motor onto the new motor, pump, hi pop injectors, glow stuff etc....

Anyone have any insight on why its so hard to start? Maybe I got some glow wiring screwed up?

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Where a 21:1 6.2/6.5 will start normally down to +20 degrees F with 8 seconds of glow, an 18:1 needs 15 or a few more seconds of glow to start more or less normally. Your engine block heater is your friend. With an hour or two of block heat, the 18:1 will start normally with 10-12 seconds of glow time down to about as low a temp as required (lower 48).

Jim

A lot of the engines ability to start is atributable to the condition of the engines mechanical condition, Glow plugs, injectors and the IP.

A couple years ago we had some NASTY winter weather with temps down in the low single digits (+5) Cold for us anyway.

Our 94 Burb 6.5 that was left out in the cold with no block heat would fire right off with one standard glow cycle and then twist its tail.

This was a standard compression 6.5 with the engine having been rebuilt a year prior.

The glows were the stock ones that came in the 94 trucks.

A friend has an 18:1 enigne and uses 60G plugs. His truck starts a tad balky even in 35F weather (fresh engne)

More glow time on some 60G plugs and the issue is not a big one.

Get those glow plugs really warm.

The condition of the Squirts is very important to good clean, easy starts.

Squirts that are low on POP pressure and that dont spray a nice fine mist of fuel will result in a very hard starting engine.

Squirts with POPs set at 2000 or so and a lovely fine cone of mist when they let fly will make things work really well.

Our 94 Burb sounded like a very UNHAPPY powerstroke when started in those low temps.

Have fun

Missy

Quote:

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Originally Posted by More Power

Where a 21:1 6.2/6.5 will start normally down to +20 degrees F with 8 seconds of glow, an 18:1 needs 15 or a few more seconds of glow to start more or less normally. Your engine block heater is your friend. With an hour or two of block heat, the 18:1 will start normally with 10-12 seconds of glow time down to about as low a temp as required (lower 48).

Jim

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How did you increase your glow time? Did you buy an adjustable glow controller relay?

Ok since I have all of you guys on the same page (sort of) about CR does anyone have any suggestions on the best way to obtain a 19:1 CR on a new P400 6.5 engine? Is there only two ways to do this as of this date? Machine piston crowns or machine the block deck? If I intend on running an HX 35 @ 20 to 25 lbs of boost do I need to go to 18:1 CR? How much efficiency and or fuel mileage will I loss going with 18:1? I feel that with the envelope being pushed and the present day and future improvement of the DB2 and or the DB4 pumps that it will be much easier to increase boost pressures (than change CR) to match fuel input by tuning the turbo (such as changing turbine and compressor wheels & housings) and the HX 35 has many different choices to increase air charge much further than the 6.5 structural integrity can withstand, even the P400. Or even better if you could fit a 351VGT with a Fleece controller on one of these would be even better but I'm not sure that could be made to fit in a DD and retain the A/C and Heater assembly. I guess the platform and use has alot to do with the settup like Robscarab says, a half ton grocery getter could probably run 20lbs of boost with 20:1 CR in a P400 but my 3/4 ton 4X4 Suburban towing will probably need the 18:1 CR if I want it to live. I guess I am just looking for verification of what I am allready thinking by some of you others with a little more experience with these motors than I and or any info on any 19:1 CR pistons that I don't now about or should I really just go with the 18:1 s for longevity? I have a size 13 shoe and two 5.9 Cummins 12 valve trucks and one 5.9 common rail (all 3 turned up) so I'm sure when I step out of one of those into my Burb it's going to be real hard to have a lite foot. Oh and after seeing that dodge IC in one of these I'm thinking of replacing my spearco with the dodge mounted behind the grill but I'm not sure the gains will be worth the expense, we'll see when I get my grill off, but my Burb is big and black and needs all the A/C it can get so I'm not sure I want to cut down the condenser.
I appreciate any and all comments and opinions
Thanks, Dave

This Fascination with high boost on the 6.5 is really an interesting subject.

The 6.5,even the P400 was never ment to run those high boost pressures.

The end result is going to be trouble that you are not going to like.

The P400 has a great bottom end now and the metalurgy in the block and heads has been improved too.

The issue is that there is still the same number of head bolts and these engines still use the same head gaskets that have been around for a few years now.

Running boost levels of 20 PSI is a one way trip to engine destruction, not if but when.

The Dmax, the Cummins and the Power Stroke have a little different layout in the heads and can handle more boost.

The fact that you have an IDI engine (precup) is one issue and the lack of more head bolts is the other.

The P400 was never meant to handle 20 ++PSI Boost, the P400 was designed to create a useable platform that could produce around 300-325 HP and 500 Ft lb torque at most and do it over the long haul.

I would leave the compression as it comes from AMG change the turbo out to reduce the backpressure on the drive side and then run about 14-15 PSI absolute max with no more than 1000F EGT showing at the Ports.

SO turn up the fuel or chip it depending on if your using a DB2 or a DS4 until the black smoke just starts to show at WOT on a pull.

As has been mentioned, BLACK smoke is $$$$$$$$$ going up the stack thats not making HP, Only heat.

Now, there are a couple ways to reduce compression ratio.\
Cut the tops of the pistons, or use a piston that has a wrist pin C/L thats slightly higher (lowers the piston in the hole)

You do not cut the block unless the block deck has been damaged or worn from time and use.\

There are .010" thicker gaskets but these are designed to be used when the deck has been cut, to restore the head to the standard location and also to keep the comp ration right.

A stock engine in the mid /late 90's vintage will have only about .045-.050 clearance between the piston and the head at TDC.

The late engines (AMG) are at 19:1 compression ration.

This is a great place to be unless you are planning on putting this thing on a 8% grade with the throttle wide open and keep it there for half a day, all while pulling 10,000 pounds.

My suggestions are not made because I dont like BOOST, I do like keeping an engine together far more than wrenching on them.

A well built 6.5 with things working right can do 300-320 HP and live.

This can be done handily with boost pressures no more than 15 PSI and EGT's kept in check.

Your new P400 has limitations. Live with them and you will be happy, step out on the edge of the envelope and you will find a place you dont want to be.

Its called MELTVILLE :eek:

Above 15 PSI the need for an aftercooler come into view really quick.

The 6.5 was just not designed to do more than what I have spoken of.

Your P400 is not going to make a D max nervous and only give a good running powerstroke of the 97 vintage a bit of a tussle.

Sorry about the bucket of cold water on the campfire, but I hate to see a fella plunk down the $$$$$$$$$$$ for a new P400 and then send it off to destruction.

At the power levels spoken of the P400 should be able to serve really well for 250K miles or more with some care.

The head gaskets are still the fuse, even on these engines.

Been with this engine family since 82 when they came out and owned a bunch of them. Broke some too.

Hope this helps.

Missy

Thanks for the reply Missy, as always I value your input and advice, can you tell me where you recieved the information that the P400 comes with 19:1 CR? The only reason I ask is that just two weeks ago I was told by Ron Taylor of W.W. Williams that the P400 came with a 20.2:1 CR and that a lower CR was not available and this information came directly from Brad Bee of AM General in an email dated 11/09/11. I would be tickled pink if they came with a 19:1 CR, I think I will have to try and call Brad Bee directly this week and verify this again. On the other hand, hasn't Ron Schoolcraft been successfull running 20 to 25 lbs of boost with his engine without failure and I believe he did quite well in one of the last pulloffs with his Suburban or am I mistaken, has it blown? I know you have more experience than I and are more up to date as to what others are doing with the 6.5 performance scene, so please correct me if I am wrong. All I do know is that 15 lbs of boost is not enough boost to clear up the black smoke with my exsisting Peninsular DB2 Marine pump putting out less than 90 Cubic millimeters of fuel per stroke and I am reading and getting told how many others are getting more than 100 cubic millimeters of fuel per stroke out of some DS4 and DB4 pumps. Therfore if it is true and you can actually get this kind of fuel out of these pumps then I want to be able to use that fuel and put it to power and not black smoke, and my present tune tells me that if I can't give it more boost then I can't use one of these pumps putting out that kind of fuel, but yet others are? So they say.
Like I said, I value your experience and advice and I will let you know if I find out anything different from AM GENERAL this week.
Thanks Again, Dave

Hmmmmmm

Seeems that we have conflicting information coming down the pipeline.

I was told that the P400 were 19:1.

OOOOOK well even 20:1 is not anything to worry about.

The black smoke should clear with 15 PSI and no more the 90 cube mm of fuel.

Which turbo are you using now ??? The issue I see here is that you need to get the air flow into the engine and out again.

Let us know which turbo your using.

I saw in your last post that you were planning to use an HX 35 ???

If you are using a GM unit now, therein lies part of the issue.

My DaHooooley has a latest Heath chip installed and that one will allow a DS4 to deliver everything it can pump.

Under a hard pull I will see some smoke, but more of a gray haze than BLACK

If you are "Rolling Coal" then you are over fueling.

The best spot is just to just have a hint of black when working it hard.

NOT dense fog of black smoke.

If your stack is clear you can stand more fuel and it will make power with it.

If your turbo drive side is not allowing a free flow out of the cylinders then the 15 PSI boost is a moot point.

Another ?????

I reread your post, what are you using for an exhaust system ???

3 inch down into a 3-1/2 inch system or a 4 incher will do everything that can be done.

Absolutely no cats here either if you want the max flow.

The big bottleneck on the 6.5 is the turbo driveside on the GM turbos.

The convoluted flow in and around the turbine and then a hard turn to get out and into the down pipe causes issues.

A friend of mine has a 6.5 Burb with a Turbo off a 5.9 cummins that he has grafted on ????

so far it seems to work great.

Airflow though the engine is the key with these old IDI engines.

18:1 Pistons has been proven to extend engine life when running the 6.5 under extremely hard use.

Penninsular did many many dyno tests and the 6.5 will fail when subjected to full power for extended periods.

The pistons will overheat and start scuffing the cylinder walls.

The 18:1 ratio reduces the peak burn temperature.

Now keep this in mind, you can't make the sort of power that the boat boys are making as you don't have an endless supply of COLD water to carry away the heat.

About 300-310 maybe 320 is it. You need a good clean aluminum radiator and the HO pump and dual stat Xover too. The Kennedy Fan and clutch is a must too.

The heat will kill the thing long before you can ever really get a good start on making more HP that the 310 Range.

If you look at the Little Toy Hauler trucks like the Freightliner
sport truck you will see a HUGE radiator up front.

Look at the radiators in the class 8 trucks that are kicking down 600 HP
The things are huge and the fans will suck in every bug for 20 miles.

The cooling system on the 6.5 Burbs/trucks is /was designed for 190/200 HP and even this number can push the system to the edge of the envelope, especially when the radiator gets a few years under its belt.

The 6.5 given the fuel and the ability to shed the heat can produce near 400 HP but not in a truck, at least not an live long.

If you want a Sprinter, you can get the ponies for a short time and then get off it.

The problem is, that once the horse is let run, the temptation is to let it run. FRY VILLE next exit comes into view.


As far as the 18:1 compression goes, the easy way is to swap in a set of lower Compression pistons.

Don't fool around with thicker gaskets and other such stuff. Just step up, buy the slugs and swap them into the beast.

As far a glow times to aid in cold starts, there is much here in the forum about extended glow cycles.

Keep us in the loop

Missy

Dave,

The DS/DB pumps generate their highest mm3 output at about 2000-rpm. It tapers off to some degree at higher engine speeds. Probably has something to do with rate of pumping plunger recharge - not able to keep up at higher speeds. The marine DBs have slightly better flow rates above 2700+, which means they should be able to produce more horsepower (rpm is a factor in the numbers). I'd have to see the data sheets from a calibrated Stanadyne flow bench to be convinced of 100+mm flow from any DS/DB. I have the Stanadyne spec sheets for the DS and DB2 & DB4. None approach 100, at any rpm.

The original LB7 Duramax was rated at 91mm at 3400-rpm to deliver 300 horsepower, but it has a high-pressure common rail, which means fuel delivery is less affected by higher engine speeds.

Clear up the smoke... I plan to install a modified Holset HX35W on our newest 6.5 project... This one is efficient at 15-20 with cool EGTs, where the GM turbos are not - too restrictive. I'm not doing this (Holset) for ultimate power, but for better efficiency and fuel economy.

Jim

Hey Jim, as we have spoke before, if the P400 comes with 19:1 pistons I'll leave it and tune accordingly, if not I think I'm going to put 18:1 s in it and then play with the tuning and I think I will be able to add more fuel IF IN FACT THERE IS A PUMP PUTING OUT MORE THAN 90 MM. I agree with you and I have my spec sheet but there sure are alot of claims of 100 to even 120 mm of fuel output most claiming from a DS4, I couldn't get mine to do that so that is why I converted it to a DB2, so I'd have to see it to believe it but who am I? I just want to be able to get MORE POWER if infact someone can get a DB4 to put out more fuel than my DB2. And Missy I presently tuned with a GM 8 turbo with a Spearco IC, a 3" DP and 4" to muffler then 5" muffler on back, so yes you are correct if I just added an HX 35 to my present setup 15 psi of boost may be enough I just don't want to have to pull the motor and change pistons later if a better pump is produced. Nor do I want to pull it because I overboosted or overfueled either. I am really hoping that you are correct and the P400 comes with the 19:1 CR so I won't have to go into the motor and I think the DB2 that I have now will work great with that CR and a HX 35 and it will save me some $ to maybe put that Dodge IC that I have taking up space in my shop in it. Oh! then it will be able to handle more fuel, It's a viscious cycle this diesel power thing Jim got me started on back in 95 when I bought my Burb.

As always, Thanks for your time and input, Dave

As far as I know, the P400 engines are all 20.2:1 CR, unless AMG is offering something different as a special run for Peninsular. Talk to Matt-at-Peninsulardiesel.com He'd know for sure, because the 18:1 CR is his baby.

Jim

I will make a suggestion here.

If this were MY project

I would go pretty much as you are going, except that I would not spend the $$$$ on the 18:1 pistons on a brand new engine has cost some serious $$$

The 20.2:1 slugs are not going to be an issue unless you are planning to run this rig at a constant heavy load for miles and miles on end with maximum power demand.

The 18:1 pistons came into being due to Penninsulars use of the 6.5 in large boats.

A boat is always on a pull (uphill both ways) and when subject to hauling said boat along at a good rate of speed the load can be really heavy.

The testing that was done showed that the stock 21:1 compression resulted in too much peak combustion heat that caused piston seazure.

In a truck you are not likely to have any of these issues.

The secret is to tune the engine to make a good reasonable power level and maintain the intake air temp and of course the biggy, the exhaust temps.

Now, running a DB2 pump will allow you to fool with the timing easier than a DS4.

Slightly advanced timing will yield lower EGT's while slightly retarded timing will see an increase in the EGT.

Too far either way from nominal is not good.

Make really sure that your POP pressures on your injectors are all as close to identical as your IP/ injector guys can get them.

A top flight set of squirts not only promotes easy starting, better fuel economy and EGT's, having nearly identical squirts also helps eliminate tortional vibes due to cyl-cyl timing variations.

If you have slight POP pressure differences such at 100-150 PSI it changes the actual time that the particular cylinder fires in comparison to the one before or after it.

On my last 6.5 engine, I spec'd the injectors at 2000 PSI which is a tad low for a DS4 but still within specs.

All the injectors were spot on at 2000 PSI (cost me a tad extra for the fiddling) but the engine ran exceptionaly smooth at idle and all the way through the RPM range.

Injector setup can have a marked effect on EGT too. A poor set of squirts can send the EGT right off into the Ozones.

The secret is a nice clean "POP" at the right pressure with a clean well defined spray "cone" of fuel and a clean crisp fuel cut off.

Poor injectors are probably one of the biggest causes of starting issues, poor fuel economy, rough running and high EGT's (other than overfueling)

Stay away from "marine injectors" especially those advertising 40 plus HP gains.

A stock factory injector as used in these engines can pass all the fuel that any of the pumps spoken of here can provide.

Much of the Hooopla on the Marine injectors is derived from the fact that just replacing the old worn out stock injectors makes such a huge difference in power that the sellers credit their "Marine Squirts" as the reason for the power gain.

Many things to consider here.


If it were me, I would really think long and hard as to whether you really will benefit from the 18:1 pistons.


Just some thoughts.


Missy

Hey Missy, not much time right now but a P400 from AMG comes with no warranty but Matt SAYS that Peninsular will give a one year warranty on an 18:1 motor. Trust me, I'd rather leave it alone, and I got real excited when you said that they came with 19:1s in them but that's not the case. I thought of puting .010 head gaskets on it with the stock pistons but I'm afraid of failure. If I put 18:1 s in it and I just add fuel and boost untill I get a "clean burn" and 20lbs max boost and I'm thinking it will live. I would like it to take 25lbs of boost just incase a real HO DS4 gets developed. DIS in grand rapids is working on it slowly because I donated a perfectly good DB4 pump housing for them to play with. My Marine DB2 with marine injectors feeds a good amount of fuel but HP to me is like a gun "It's better to have it and not need it than to need it and not have it". I could reconvert it back to a DS4 and put one of these programmers that claim 120 cubic mm of fuel but I think I would have to witness one of them on a test stand puting out that kind of fuel 24/7 for a year steady before I'll do that. What do you think about that Jim? DS4, 120 cubic mm per stroke?
Thanks Again
Happy Holidays
Dave

Sounds good on the 1 year warranty.

As far as I know there is not a DS4 that can shove over 90 cube mm of fuel.

There is a lot of Myth and just plain BS out there about all this stuff.

The HO DB2 stuff that Penninsular has to offer is good stuff.
They have gone the extra mile, done the testing on the dyno and can back up any and all claims on what they sell.

Good luck with whatever you decide to do.

The P400 is a good foundation to start with for sure.

Missy

1. This is what I have... The HO DB2 stuff that Penninsular has to offer is good stuff.
They have gone the extra mile, done the testing on the dyno and can back up any and all claims on what they sell

2. This I believe... There is a lot of Myth and just plain BS out there about all this stuff.


3. They are working on this... a DS4 that can shove over 90 cube mm of fuel.

Quote:

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Originally Posted by More Power

For an IDI (InDirect Injected) diesel to produce clean cold starts with short glow cycle times, and to produce fewer cold start emissions, the CR has to be somewhere at/above 20:1. The precups/prechambers cool the charge on a cold engine. A DI (Direct Injected) diesel (like the current Duramax, Cummins, PSD) starts well cold at a lower CR. So, a higher CR was an IDI cold start compromise.

I did a short tech piece on the Isuzu C240 I-4 2.4L diesel recently. It too is an IDI engine that has 20:1 CR. Its 3.0L DI siblings are, on the other hand, just over 18:1 CR.

Diesel farm tractors with DI diesels (of those I've seen the data for) run at anywhere between 15 and 18:1 CR. The Duramax/PSD/Cummins ran at 17.5-18:1 (the LMM Duramax is now at 16.8:1). The marine 5.9L Cummins runs with 15:1 CR. And so on...

Tractor, industrial and marine diesels are usually run at high load for extended periods, and tend to have a lower CR for improved durability. Certainly, tractors, OTR diesels, marine diesels and so on are also designed with efficiency in mind. If a higher CR was a better compromise (for efficiency), they'd all have a higher CR. They don't because of increasing durability issues with increasing CR.

Jim

PS - Here's a question for the thinkers out there.... What effect does CR have on crankshaft harmonics?

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Pretty sure changing CR will affect the frequency in some if not all critical vibration orders.
Most of the engines I worked with in my Navy career were good sized like 16 ton that's where a great deal of my diesel education comes from.
In relation to crankshaft torsional vibrations one of my favorite engines used a crankshaft torsional vibration absorber (Fairbanks Morse 38 ND 8-1/8 OP) engine.
The absorber insisted of a hub with plates and free floating pins of different diameters and weights. Great component. Better to absorb than dampen.
I know there is a similar unit for gassers called the Rattler.
Is one available for the 6.2/6.5 to your knowledge and what is your opinion on dampen vs absorb.
New here and seeing that your knowledge and ability to express it make you well worth following
Thank you

Quote:

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Originally Posted by 86 CUCV

Pretty sure changing CR will affect the frequency in some if not all critical vibration orders.
Most of the engines I worked with in my Navy career were good sized like 16 ton that's where a great deal of my diesel education comes from.
In relation to crankshaft torsional vibrations one of my favorite engines used a crankshaft torsional vibration absorber (Fairbanks Morse 38 ND 8-1/8 OP) engine.
The absorber insisted of a hub with plates and free floating pins of different diameters and weights. Great component. Better to absorb than dampen.
I know there is a similar unit for gassers called the Rattler.
Is one available for the 6.2/6.5 to your knowledge and what is your opinion on dampen vs absorb.
New here and seeing that your knowledge and ability to express it make you well worth following
Thank you

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Thanks for your comments.

Generally, a damper recommendation depends on the owner.

For example, if the owner plans to own the same vehicle for some number of years, then I'd recommend the Fluidampr. It's a little pricey, but it does a better job of damping, and it never-ever wears out or deteriorates over time. Plus, you could sell the damper if you needed to, to recoup some of the cost.

Most owners are best served by using the original equipment GM/AMG damper, if a replacement becomes necessary. Avoid the cheap imports like the plague. A genuine piece will cost ~$100 and an import will cost about half that.

I don't know of any other aftermarket type dampers for these engines - a "Rattler", for example. Jim