Max fuel economy?

[convert2diesel]

Moondoggie:

Yes you are correct. There has been lots done to make these trannies more durable, and to allow them to standup to some incredible punishment. For an overdrive tranny that doesn't need electronic assistance to operate (with the possible exception of the lock-up) it would fill the bill for most use.

What I was trying to accomplish was incorporating the concept of "gear splitting". In an attempt to use this engine in it's naturally aspirated state to tow more then a light boat trailer.

It is very important to keep this engine within a very small torgue band of 1,600 to 2,200 RPMs. While this is possible with a 4 speed (8 speeds with aux tranny), the resultant double overdrive is way too low at highway speeds. If I go to an underdrive, the first gear under could be used to pull stumps out of the field and generally not useful.

That sent me looking for a 3 speed tranny, with a lock-up torgue convertor, that could handle the out-put of the 6.2, and then add the overdrive aux tranny.

My local guy said he could build up any tranny I want, but I was looking for anyone who had experience with the 350"C" behind our engines.

MP:

While I doubt the numbers the Corvette guy is getting, it illustrates what I was trying to get at. Namely lower the HP requirements and these engines do quite well in the economy department.

Would be very interesting to see one of these with 7,500 lbs of Airstream hung on the back . With 4 1/2 in of clearance I wonder if he could even get it into the campsite without leaving his oilpan at home.

Dan:

Man after my own. This is number four for me. Got tired trying to get any power out of the 5.7s though they did get great mileage, so am now doing the 6.2/6.5. This is the best one yet (knock on wood). Short of some logistical problems that are easily solved, it was reasonably painless. Now on to a 93 Fleetwood .

A belated Merry Christmas to all

Bill

[Dieselmania]

Moondoggie:

Yes you are correct. There has been lots done to make these trannies more durable, and to allow them to standup to some incredible punishment. For an overdrive tranny that doesn't need electronic assistance to operate (with the possible exception of the lock-up) it would fill the bill for most use.

What I was trying to accomplish was incorporating the concept of "gear splitting". In an attempt to use this engine in it's naturally aspirated state to tow more then a light boat trailer.

It is very important to keep this engine within a very small torgue band of 1,600 to 2,200 RPMs. While this is possible with a 4 speed (8 speeds with aux tranny), the resultant double overdrive is way too low at highway speeds. If I go to an underdrive, the first gear under could be used to pull stumps out of the field and generally not useful.

That sent me looking for a 3 speed tranny, with a lock-up torgue convertor, that could handle the out-put of the 6.2, and then add the overdrive aux tranny.

My local guy said he could build up any tranny I want, but I was looking for anyone who had experience with the 350"C" behind our engines.

MP:

While I doubt the numbers the Corvette guy is getting, it illustrates what I was trying to get at. Namely lower the HP requirements and these engines do quite well in the economy department.

Would be very interesting to see one of these with 7,500 lbs of Airstream hung on the back . With 4 1/2 in of clearance I wonder if he could even get it into the campsite without leaving his oilpan at home.

Dan:

Man after my own. This is number four for me. Got tired trying to get any power out of the 5.7s though they did get great mileage, so am now doing the 6.2/6.5. This is the best one yet (knock on wood). Short of some logistical problems that are easily solved, it was reasonably painless. Now on to a 93 Fleetwood .

A belated Merry Christmas to all

Bill

My dad had an '82 caprice with a 5.7 diesel, 350c tranny with a lockup torque converter, and 3.08:1 rear axle ratio ...it got 35mpg running 65-70 on I-40 going from Jackson Tn to Cookeville Tn and back. A few months later, the 5.7 stripped the head bolt threads out of the block ( blowing the head gasket ) and the car got parked. If I hadn't moved to Oklahoma, I was going to replace the 5.7 with a 6.2

[Dan Wilson]

The problem with the 350C may be that it uses the varable vacuum of the gas engine to determine the shift points. The 200C 2004r and 700r4 use a cable that monitors the throttle position. The 82 Cad that I did has the original 2004r that was behind the 350 Diesel. Got to be gental in 2nd gear or it slips the band. Got lots of torqe. Once you get in 3rd and od no problem. First gear is no problem.
Dan

[convert2diesel]

Dan:

How did you ever get a BOC type tranny to marry up to a 6.2? Lucky you didn't take out forth gear. I tried that combination but could never get the right adaptor plate.

The 400 equipped 6.2 had a vacuum regulator attached to the passenger side of the throttle arm. This should be sufficient to regulate the 350. Failing that, this would be a fairly simple control to fabricate.

Jbell:

Will try to scan it in tommorow and send the chart to you. By the way, if you think the DMax is dependant on computers, wait till you see what is attached to the VM Moterie that the Jeep will be getting. This engine has been very successful in Europe for a number of years and gets great mileage, but don't let anything happen to it. Has been known to create spontanious wallet combustion when repairs are needed. Will stick with the tried and true for now.

Bill

[catmandoo]

convert lots of them had the dual bolt pattern.

[convert2diesel]

Catmandoo:

Could be a regional thing. Up here in the great white north, all the 200s I have come across attached to the older 5.7s were the BOC style only. Only wished I had known then about the dual style. Would have saved me a bunch of time and energy.

Bill

[jbell]

spontaneous wallet consumption? Sounds worse than a 50% off sale that my wife attends.

Yea, tried and true, perkins 354T, 12valve 6BT, my 6AT, and a few old hercules that are around, and now my newest toy, my NA6.2 sub. I looked hard for a herc 3.7dt for my jeep, before I found my 6AT. Love my 6AT, wish cummins hadn't killed it, after they bought onan. (It's my mpg king)
My tacoma is over 310,000 and probably will be in need of a diesel repower in the next 100,000. (Always In pursuit of mpg, and the wonderful smell of a diesel....) Any tried and true for it? (other than the toy 3L?) Don't think a 6.2 would fit....

[84 Convert]

My $0.02 on fuel quality vs. economy...On my last job, I drove many miles in a '94 Dodge flatbed dually loaded with tools. I could get fuel here in western WA at the Pacific Pride stations and would get ~16mpg. But fuel at Pac. Pride in OR and I would get ~20mpg! only thing different was the fuel. I repeated this performance at least three times. Driving style was the same as I have a hereditary abnormality...my right leg and foot bones consist entirely of LEAD. Oh, yeah and OR driving invariably involved climbing one pass or another. Logging roads always a part of the mix.

Gregg

[G. Gearloose]

Spotted a old Buick GN yesterday , thought that would be a sweet ride with a 6.x..and 3" duals..

[Dan Wilson]

If i remeber right i did get an adapter from TCI Racing trans co. They have lots of adaptors. http://www.powerandperformancenews.c...&Store_Code=TC
Good idea to use the 400 shifting parts with 350C. I believe I have seen dual pattern 350C's.
Dan

[convert2diesel]

Jbell:

Didn't get a chance to do your chart today but will work on it. As per the Tacoma, if that guy up north could shoe horn a 6.2 into a Vette, anything is possible.

84 Convert:

Fuel quality may not be the problem. Could it be that the station in Wasington was still pumping winter fuel? I find a 10% to 15% decrease in mileage using the 20% kerosine mix we use up here as winter diesel (#1). Also could it be a difference in altitude? Just guessing here.

G. Gearloose:

Having just survived fabricating a 3 inch single on the Roadmonster I can't even envision doing it twice on the same car . That also begs the question...To what benifit would dual 3 in be. I would think 2 1/2 would be more then enough. No to mention that most of the system you could buy off the shelf.

Dan:

Now that I am using the 6.2, my tranny options are more universal and I don't have to work around the problems normally associated with the 200R4.

MP:

Getting back to the topic at hand, I know I have just spent the last week advocating lowering the HP requirements as opposed to tweeking the engine but I will now digress.

Almost without exception, anyone I know that have either installed a puffer or purchased their truck with one on has said the same thing. Namely the mileage at normal speeds has been 2 to 5 MPG less then the equivalent free breather. After reading the other posts this seems to be a universal complaint.

Could it be that the combination of exhaust restriction and intake air restriction at low boost pressures are effecting the performance? Perhaps the following would work:

1. Install a seperate "Swanger Air" intake and filter directly into the manifold, bypassing the turbo, with a wieghted air door designed to close at anything over atmospheric pressure allowing the turbo to pressurise the sytem when needed.

2. Install a larger exhaust by-pass to reduce back pressure when turbo not required.

3. Manually switched vacuum source to the wastegate, allowing the driver to activate (or de-activate) the turbo.

Especially on the older 6.2s or the converted NA 6.5s this arrangement should return these engines to thier original selfs but would retain the turbo when it is really needed.

Just some thoughts

Bill

[G. Gearloose]

3" was just to peg the coolometer, plus Dr. Lee is a fan of the 3" with crossover,and appears to attribute a portion of his good performance to it.

I concur a tru dual 2.5" with crossover could be adequate strictly reguarding milage.

[More Power]

Personally, I think the light-load fuel economy for a TD is very close to that of N/A. If you need the extra power provided by a turbo, it would be worth the trade-off, in my opinion. However.....

The biggest problem with a turbocharger for a strictly fuel economy rig is the nut behind the wheel. Unless there's an individual out there with a lot more willpower than myself, a typical TD owner will accelerate harder, drive faster and use the power more often than when driving N/A. This hurts fuel economy.

Other drawbacks for a TD include cost and complication for an otherwise simple to maintain engine. But, after towing a 14' camp trailer with an N/A 6.2L for several years, I know how important a TD is when towing. Headwinds and hills are not a lot of fun for an N/A.

MP

[Stage1]

Again I am building/reconstucting a 84' Blazer and am interested in your thoughts on goal for engine RPMs at 65 MPH? Blazer will not be used for towing much, however, hills are part of the roads here. Review of comments has me thinking about the range of 1800 to 2200. Origionally thinking about 2200 before this thread started, is 1800 hard on the engine because of loads caused by going up hills, etc? How much fuel is saved by 1800 vs 2200?
I must also admit, enjoy putting the right foot down once in a while for that diesel fuel tank high.
thanks,
Les

[84 Convert]

In this case I seriously doubt winter fuel. The stations I was using are mostly used by semi-trucks, so fuel turnover is rapid. Also, this was happening in the middle of summer.

Gregg

[Salemone]

I have not seen any reference to the benefit of reduced pumping losses when using a turbo. The back pressure in front of the turbo is free. The back pressure after the turbo may be more of a
parasitic factor.

Is there any scientific proof that a properly
sized turbo will not increase your mileage by
reducing pumping losses and providing an oxygen
rich condition allowing complete burning of all the fuel in the chamber.

[Salemone]

MP,
The power plant I would pick for max fuel mileage
regardless of the vehicle would be:

6.2 - stock compression- GM wastegated turbo-
DB 2829 Injection Pump calibrated for 1983 C
engine. (can be turned down in a "CAR" vs "truck")

6.2= smallest displacement.
GM turbo= low end boost (reduces pumping losses)
DB 2928 IP= Less hp to run.

My $.02
Salemone

[More Power]

Salemone, Good choice! I would also add a gear drive timing set, balanced rotating assembly, and matched ports.

MP

[jbell]

Thanks Convert2Diesel

[Ratau]

MP

Very interesting topic, what is your final conclusion?

Most off the replies suggested tall gears (3.08).

I get