Max fuel economy for the 6.5TD

Good Day!

Interesting! It would be quite simple to drive the Wastegate Actuator Solenoid with a closed-loop servo controller, to control the wastegate of a 94-on truck at whatever temp you would like. This actually came up a number of years ago, but never went anywhere. You'd probably want to terminate the Solenoid wires with a resistor, & would certainly have to have at least a boost fooler, so the PCM would think the boost was staying in an acceptable range.

I sure wish I could have pursued this, but never had the time. It sure would have been fun... :(

Of course, none of this applies to me now. I'm bailing on my two 95s, having just bought a 93, which of course doesn't have PCM-control for the wastegate. That's in fact one of the reasons I went backwards to a 93 - there's only two wires to the IP.

Blessings!

i'm supposing the choice of stock pistons over 18 to 1's is because were not chasing power but efficiency...higher c.r = better volumetric efficiency and therefore better burn equates eventually to better mpg....
you cant have power and economy...you have to make a choice or compromise with shi##y mileage.acceleration up to speed is a big user of fuel because we all get up to speed at a different rate. i doubt i'll ever see 20 mpg in this truck despite being on imperial gallons.if we could 'knock off' half the cylinders electronically (compression and fuel delivery)when at cruising speeds you might see better figures but this engine just cant do that.i got the best mpgs out of my truck the day i bought it and drove it home with a badly split vac pipe, had no problems other than the odd puff of black smoke but since i fixed it and i'm getting a closed wastegate and normal boost conditions, i havent seen those kind of figures since. maybe welding shut the factory wastegate and bolting on a massive wastegate/shunt pipe would get your preturbo backpressure/temps down and allow you to run with it wide open so no boost ...or am i barking up the wrong tree here ......?

i suggestedthe same thing long time back, got laughed at,.
i proposed a solenoid with a switch that dumped the boost at cruise throttle position, dropping drive pressure to zero and switched back to full boost when needed for power,.

There is now the school of thought that the different turbo's available and being used on the 6.5 will get up to 2mpg better fuel mileage because the drive pressures are lower than a GM turbo,.

Nick

If the boost sensor doesnt see any boost figures then wont the fuel programming 'ride' on a different part of the fuel 'map' and not follow max boost/max power part of the map? unless its designed to put the fuel in anyway to hell if youve got the boost or not ,hence the black smoke..i suppose i'll have to try this 'boost dump' out for myself to see if theres any logic to this logic .i wonder if the programming produced by the chip tuners could use this to gain some extra mpg's in the cruising rpm range depending on your gearing/load with zero boost showing.would be interesting to find out...everybody seems to be chasing max power most of the time.
if the standard turbo's still produces some boost even with the wastegate fully open , as ive read on here,then surely the wastegate isnt big enough for this particular application but big enough by design to retain some boost/turbo speed so it comes back on song when you stab the throttle.
i'm supposing the original design remit was to find the middle ground but i think the 6.5n/a engines do better on fuel because their map is centred around their breathing without a turbo and thereby dont need the 'extra fuel' so naturally run better mpg's...
If by chance Mr Kennedy is reading this drivel,and if by chance he decided to experiment by overlaying 2 or more chips into a switching unit attached to the dash.... I'd definitely buy into this..i'd love power on demand and economy 99% of the time..isnt this what the newer tech programmers do anyway?....is it worth investing any time/effort into this Mr K? or am i just dreaming one step too far ?? you could call it a K-DOG programmer (or something else) you must have a few standard chips laying about doing nothing to try it out??? standard , mild tune with boost dump,tow tune and max power...??? just a daft thought

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Originally Posted by stezloco

If the boost sensor doesnt see any boost figures then wont the fuel programming 'ride' on a different part of the fuel 'map' and not follow max boost/max power part of the map? unless its designed to put the fuel in anyway to hell if youve got the boost or not ,hence the black smoke..i suppose i'll have to try this 'boost dump' out for myself to see if theres any logic to this logic .i wonder if the programming produced by the chip tuners could use this to gain some extra mpg's in the cruising rpm range depending on your gearing/load with zero boost showing.would be interesting to find out...everybody seems to be chasing max power most of the time.
if the standard turbo's still produces some boost even with the wastegate fully open , as ive read on here,then surely the wastegate isnt big enough for this particular application but big enough by design to retain some boost/turbo speed so it comes back on song when you stab the throttle.
i'm supposing the original design remit was to find the middle ground but i think the 6.5n/a engines do better on fuel because their map is centred around their breathing without a turbo and thereby dont need the 'extra fuel' so naturally run better mpg's...
If by chance Mr Kennedy is reading this drivel,and if by chance he decided to experiment by overlaying 2 or more chips into a switching unit attached to the dash.... I'd definitely buy into this..i'd love power on demand and economy 99% of the time..isnt this what the newer tech programmers do anyway?....is it worth investing any time/effort into this Mr K? or am i just dreaming one step too far ?? you could call it a K-DOG programmer (or something else) you must have a few standard chips laying about doing nothing to try it out??? standard , mild tune with boost dump,tow tune and max power...??? just a daft thought

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Sounds good, but no. Combustion gasses drive the turbine. The gasses come from fuel. More fuel = more drive pressure. More drive pressure = more boost. Not the other way around. Late model high-tech Diesels, such as the Duramax, have a MAF active in the fuel mapping. They are able to "limit" initial fuel volume, and increase it as MAF sensed air volume increases. The EFI 6.5L doesn't do this. The fuel you get is "mapped" according to throttle position and RPM, in a static model. This is why black smoke is the result of too little air (boost) for whatever reason. They smoke because there is too much fuel for the O2 available.

N/A 6.5L's get better mileage, mostly in part, due to its lack of baggage. The turbo on TD engines causes a significant amount of parasitic loss in the inlet/outlet path. It takes additional fuel to overcome the loss, thus lower mileage. All else equal, more power or more economy....Pick one.

Now, on the lines of improving cruise mileage, I've often thought of a "bypass" system the would essentially make a TD engine N/A when more power isn't needed. This would require a compressor bypass, and an "open wastegate" ability. Easier on a Duramax LB7, because it has active MAF sensing, preventing excess fuel at higher throttle positions. Maybe I'll put it to the test sometime.

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Originally Posted by DmaxMaverick

I've often thought of a "bypass" system the would essentially make a TD engine N/A when more power isn't needed.

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Can you say "Turbo Lag"? ;)

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Originally Posted by JohnC

Can you say "Turbo Lag"? ;)

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Actually, that could be a thing of the past. With a bypass, you'd get full N/A intake air off idle, and about the RPM the boost would normally spool (the engine speed, not the normal lag time), the turbine could be nearly wound up. Close the bypass, and instant boost. With wastegate closed, you'd still have the exhaust gas restriction of the turbine, but I think that's better than a restriction at both ends. It would take some refinement to smooth it out, but I think it could work.

:DI think weve just come up with a brilliant new invention ...should we call it a SUPERCHARGER ?.... its catchy .....he he

Going by what youve already said about the fuelling being fixed and dictated by a 2 d map ie throttle position and rpm (but with no facility to measure load) you'd still need a suitable map to carry out the mod to reduce the fuelling at cruising speed whilst bypassing the turbo altogether..and you'd be stuck with just that ..1 map, unless some clever so and so takes up the crazy idea of layering chips which are switchable between normal /towing/cruising with bypass/max power..thats 4 layers.....essentially a programmer??
' is this even possible Mr Scott?'
'aye Cap'n but I'll have to check with Mr Spock first'
you'd need 2 very good sealing butterfly valves , one in a seperate intake branch to open up to a k+n say...and another to open up the 'bypass' loop in the exhaust...? thats totally do-able but I'm dead stop at the multi layer chip thing.
any more crazy thoughts???
To the Bat-cave......

I guess I thought you were bypassing the turbine, since that's just as restrictive...

Yes, initially. It would have to be brought online eventually, shortly before more power is needed. With exhaust gasses already flowing, the turbine should spool up very quickly, like a brake stand. If all you are doing is tooling around and more power isn't needed, of course the WG would remain open. It would have to be in concert with the intake bypass. An unrestrained compressor will cause overspeed of the turbo, with the turbine engaged. I think the key will be either a throttle position limit while in "low power" mode on older models, or the MAF could manage that on later models. It's a rough idea, but I think it could work. The question is, will it be practical? I doubt there will be a ROI. Maybe.... Or just for fun.

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The EFI 6.5L doesn't do this. The fuel you get is "mapped" according to throttle position and RPM, in a static model. This is why black smoke is the result of too little air (boost) for whatever reason. They smoke because there is too much fuel for the O2 available.

Now, on the lines of improving cruise mileage, I've often thought of a "bypass" system the would essentially make a TD engine N/A when more power isn't needed. This would require a compressor bypass, and an "open wastegate" ability.
unquote
So how would you deal with the fuel being delivered without boost with your bypass fitted? sounds great by the way ,ive already built one in my head.
just the fuelling to sort out now then?
i'm wondering since the chips are a plug in item anyway, why not jack one in beside the master with multiple switches for each connection and switch them all over before you turn on the ignition so no voltage on/off spikes, then you'd have 2 available maps , one could be a N/ASP map ,as you'd need for your bypass conversion, the other a power map of your choice....? why wouldnt that work, its not rocket surgery ,just a matter of experimentation and a spare N/ASP chip???? ISNT IT????

I drove a 3.42 geared NA 6.2L (1500-series 4x4 pickup) for several years. With a 700R4 automatic and driven for fuel economy at 65-mph it would routinely deliver 23-24 mpg.

I eventually installed a Banks turbo kit. It was very difficult to keep the speed down and not "use" the turbo, but when I did drive it for fuel economy, it only decreased about 1-mpg to 22-23 mpg. So, not a big difference, if I could force myself to drive for fuel economy.

The Banks turbo was the non-wastegated variety, which was pretty free-flowing. That turbo required about 2500-rpm and a fair amount of throttle to spool it to 7-10-psi boost pressure. At a 65-mph unloaded cruise on level highways (about 1800-rpm), the turbo produced no or virtually no boost. Turbine drive pressure was pretty low.

Rather than swap chips/programs, installing a larger, more free-flowing turbo might accomplish more, easier.

Jim

Just throwing out an idea. Back when Ford first installed a turbo on their Binder Engine, it did not meet California regs, specifically on transition emissions. To meet the regs, Ford installed an aneroid in the dome of the DB2 that essentially restricted rack travel until upper deck pressure exceeded a certain level. This makes sense as very little throttle movement is required to make the DB2 go full rack.

If one was to combine this aneroid with a two position wastegate actuator we could theoretically have an engine that could operate at part rack (lower fuel flow) and only allow the turbo to spool to .5 to 1 lb of upper deck pressure (pick up some VE) and when needed, transition back to full wastgate control and full rack travel for power.

This could all be controlled manually with a couple of electrically actuated vacuum relays, controlled by a switch on the dash, or driven through an older TPS switch that was used on the older 400 equipped 6.2.

That should produce NA or better economy due to maintaining slightly positive upperdeck pressure but with restricted fuel flow but still give you full power when and if it's needed. This method would work even better on the center mounted turbo engines (much lower exhaust restriction) and a 4911 pump.

Just a thought.

Bill

Thanks Jim,
on larger turbo's ...
i bought an HX35W from the USA from an ozzy bloke who screwed me by sending it over in bits (! ? ! ? ! ) ultimately damaging the compressor wheel and bending the shaft slightly on the journey thro' sh#t packaging (i think that was the intent from the start)...dont get me started on that one..I still rage about it, i ended up buying a recon centre section for the same money again so i'm into this thing now for a lump i'd never get back if i sold it.
I was going to fit this but was put off by the articles i read about pushing the power band further up the rev range thereby defeating my primary aim, to get more mpg out of this truck if at all possible.It actually has more than enough power to pull as it is (I'm used to weedier jap trucks and Landrovers tho') I should give myself a firm kick, I said i wasnt going to spend this money, but I have. I'd need a power chip/g/box shift-point change to match this turbo's character. for all the info ive read about chips and turbos, i dont recall if theres info about a chip combined with an HX35W,and the results,( my memorys letting me down here,)??? any ideas,is there???
If, as has been said, the 2d mapping puts the fuel in anyway, then i'm going to be missing the air to burn the fuel and will run dirtier, still not achieving the objective. I still like the idea of 1 chip for economy, the other for Max power/towing ability.I pulled my own chip yesterday out of curiosity mainly to record the no's and have a look at the connections with a view to doing what ive already suggested, i see no technical reason why this cannot be done and wonder if the gains would weigh up against the cost of a 'heart bypass' so to speak.would need to get hold of an 'F' code non-turbo chip/or ECM, if there is such a thing. If anybody reading this can tell me any possible pitfalls with the idea , i'm all ears.
your decent mpg's were probably down to the combination of setup you had on that engine, i.e. lighter truck,gearing, small precups, mech pump, high power band in the rev range (did you up the fuel @ the pump or leave as standard to better burn what was there/run cleaner??)
I'm stalled as to where to go with this one, or not at all.It'll still take £££'s to complete it, i'm halfway there i suppose.
still might get a chip (who's chip tho'??)if i get the right advice from somebody else's experience with the same truck.(always preferred)
I have the lead/GMtech programme from Engh Motors on a netbook i keep specifically for the task and wondered whether to buy his chip or not but had no data from him or reports from anybody using his chip, so i put off. Mr Kennedy says 60 hp is the realistic figure anyway ,and thats roughly what they claim.Is there a way of checking my chip no's to see if it has been changed already ??? how would i know?
recently bought a set of 4 hummer H2 wheels/tyres 315's x17...fun trying to get these to clear the fronts, fitted straight onto the hubs (and were hubcentric!) looks as tho i could use a 3" lift now though, i have 2" wheel spacers on the rear to balance the look ...will be moving my bumper forward and cutting the lower spoiler and fill in panel as well...these taller tyres might get me a few more mpg, ...just need to look for that vssb thingy now...
fun n' games eh......

I actually talked to Gale Banks about his 6.2 turbo kit, and mentioned that the turbo didn't spool till about 2500-rpm and with quite a bit of throttle. I was expecting to see boost more of the time.

Gale's response was that "the power will be there when you need it."

Of course, he was right. My truck drove more or less just like it did without a turbo, and delivered almost identical fuel mileage in light load driving. But, the power was there to pull grades, pass or accelerate. It just took the turbo a couple seconds to spool before the power became available.

So... theoretically, reducing turbine drive pressure to look for more mpgs can be done by installing a larger turbo. But, you'll still have a turbo for those times when you need more power. As Gale said, "the power will be there when you need it."

Yes, I did "Turn up the Pump" during the Banks 6.2L turbo kit install. I don't believe that affected fuel economy. It takes a certain amount of fuel to move a vehicle down the highway, no matter whether turbo'ed or not, no matter where the fuel rate screw is set to. The maximum fuel rate was increased, which means fuel economy would be affected only when using the additional fuel. The delivered fuel rate during normal light load driving shouldn't change.

Jim

So this thread was necro'd about a year ago, but after reading everything I thought I would chime in with my situation as well.

My truck is very stock on the outside... no Chicken Lights, stock mirrors, no bug shield, and nothing else that would increase the Aerodrag on the truck. I have fairly large tires, about 32x10x16.5 in US measurements, and hardly ever tow anything larger than a 150lb boat on a Sunfish Trailer. (speaking of which, I need a new sunfish trailer, if anyone has one laying around) My mods include a Turbo-Master set to Heath Specs, a performance chip from Heath Diesel, newer glowplugs, new PMD on a FSDCooler, removed Air Intake Ring, and don't have anything blocking the radiator or bumper holes in the winter (though I know I should.)

At 65mph in Overdrive, I'm running at ~1950RPM, and in Summer I get about 21mpg highway and 18 in the city. In Winter, with Primrose Winter Power fuel additive, the best I've seen is 17MPG on the highway and 15 in the city. I don't know my final gear ratio, but I think it calculates out to about a 3.42 rear end, as I got a 3.10 calculation from my Overdrive RPM. When I checked it without overdrive, I was hitting about 2400RPM at 65 in third gear, and it just didn't sound very nice so I have only run that way once for the purpose of testing.

I would like to get up to 24mpg without spending a crapton of money on the mods, as the truck already has 221,000 miles on it. I still have thoughts of doing a Cummins 4BT swap eventually for the magical 35MPH they are advertised to get in these trucks, but I'm pretty sure it would be cheaper in the long run - even with increased repair costs - to buy an older mercedes 300D or VW TDI when my engine decides to go the way of the dodo. I know that's blasphemous to say in here... but our trucks are becoming more rare, and harder to find parts and replace big ticket items.

Drag, have you adjusted the VSSB for the slightly larger tire size? I think what you have is about equal to 265/75/16?

For a few years now, I've been toying with the idea of adding a front "skirt" under the bumper. Kind of like a big air dam. I was thinking of making to within 6" of the ground. Maybe use some steel L-channel bolted to the underside of the bumper, then plywood for the vertical section - but it would need to be braced so it didn't just fold in on itself at speed. I haven't looked at it any further than that, though. Wanna give it a go?:)

Drag, I think your tire size is about equivalent to my 265/75/16's (stock is 245) but I don't get MPG near that - but I suppose part of that is because of the larger vehicle and whether or not you have the larger rear end and 8-bolts. Have you adjusted your VSSB (or whatever a '94 has) for tires? Otherwise, your speedo and odometer aren't reading correct.

If you jack up one wheel... make a mark on the driveshaft and rotate the tire once. Count how many times the driveshaft rotates. ~ 3-1/2 would give you the 3.42, ~3-3/4 would make it a 3.73.

Or, as long as a PO hasn't changed it, just look at the RPO code list in the glovebox. GU6=3.42 and GT4=3.73.

OK, on to the more interesting stuff...

For quite a few years I've thought about adding a large air dam under the front bumper. It wouldn't be pretty, but it would at least give me an idea if it works. My thought was to use some 1-1/2" or 2" L-channel mounted to the bottom of the bumper, and then attach plywood to the vertical section of the L-channel. Extend the plywood to within about 6" of the ground. Add some support rods from the plywood to the undercarriage so the thing doesn't blow away at speed.

That's about as far as I've gone, though - more just theory than anything else. Wanna give it a go and see what happens?:)

I just returned from an 800+ mile trip, and pulled down the best MPG to date with my 95 Tahoe.

Averaging 68 mph on the freeway I hit 18.67 MPG. Normally I average closer to 17.5 MPG. I've never really taken any long trips with this vehicle without some sort of trailer or heavy gear, so I've never really got to see what she'd do solo.

Also, take into consideration that the old Tahoe was loaded down with three passengers and lots of luggage; and she still did all this with over 264K on the clock! :D

We had actually planned to take my wife's minivan, but at the last minute, the engine started puking oil into the coolant. So now I get to see what I have to do with a Chrysler 3.3L with only 160K on her.

But old faithful was standing by ready to go and didn't let us down!

Casey