Boost/Compression Ratio Calculator

[Robyn]

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

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

[spdgofast]

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

[Robyn]

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

[More Power]

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

[spdgofast]

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

[More Power]

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

[Robyn]

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