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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old December 7th, 2021, 04:15 PM
Prowbar Prowbar is offline
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Default The fuel efficient GMC V6

Here's something I've been tinkering with for a while. I've been reading that old post from James Cleary and he mentions outstanding fuel economy from an engineering standpoint. Well, as we know, these V6's are anything but fuel-efficient.

Which got me wondering, is it possible to improve the mileage on these V6's? I believe so, by reducing the internal friction that these have. The main advantage we already have is 2 cylinders less than a V8, meaning less friction.

Some ideas I had: (which apply to a 305E)
1. Custom (longer) connecting rods and the use of 4.250" big block Chevy pistons with thin, low tension, piston rings. Modern materials make this possible. This would reduce the massive friction of the thick piston rings and the large piston skirts.
The longer connecting rods are needed because of the higher wrist pin location.

Does anything know what length the stock rods are, and what the deck height is?

2. Another advantage is the compression gain, with a flattop or even a slight dome design. Up to 9.5-10:1 static. Maybe even higher, given the rod ratio.

The disadvantage would be to have everything rebalanced.

Of course, the mains and rod diameters are larger on a V6 than a comparable engine, adding to the friction, which is a given. But I have a hunch this (different piston) will improve the efficiency of the engine significantly.

Reducing additional friction could be done by the switch to a roller camshaft.

Another idea is to change the intake manifold, but I'm not sure how good or bad these are. Optimized and equal fuel distribution to all cylinders is the idea.

I'm no engine builder, just a student on the subject, but I'd love to hear your ideas. It is not my idea to write off the base design, just some thoughts to improve on it.

Last edited by Prowbar; December 7th, 2021 at 05:11 PM.
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  #2  
Old December 7th, 2021, 04:45 PM
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FetchMeAPepsi FetchMeAPepsi is offline
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Default Re: The fuel efficient GMC V6

I can't help, but if someone were to design and build a piston that helped with mileage and efficiency, and was a drop-in replacement for ours, I'd buy 12 of them for the two engines I have.
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  #3  
Old December 7th, 2021, 05:22 PM
Prowbar Prowbar is offline
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Default Re: The fuel efficient GMC V6

Quote:
Originally Posted by FetchMeAPepsi View Post
I can't help, but if someone were to design and build a piston that helped with mileage and efficiency, and was a drop-in replacement for ours, I'd buy 12 of them for the two engines I have.
That is a great idea; omit the whole BB chevy piston and longer rod and design a piston with the same weight and wrist pin height, which uses the thinner piston rings, ups the compression by removing the dish, and reduces friction by reducing the large piston skirts...

Also, different diameters could be designed and manufactured for the 351, 401, and 478 engines. This would also do away with the 3 compression ring design which definitely adds to the internal friction.
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Old December 8th, 2021, 02:03 PM
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Default Re: The fuel efficient GMC V6

Quote:
Originally Posted by Prowbar View Post
Here's something I've been tinkering with for a while. I've been reading that old post from James Cleary and he mentions outstanding fuel economy from an engineering standpoint. Well, as we know, these V6's are anything but fuel-efficient.

Which got me wondering, is it possible to improve the mileage on these V6's? I believe so, by reducing the internal friction that these have. The main advantage we already have is 2 cylinders less than a V8, meaning less friction.

Some ideas I had: (which apply to a 305E)
1. Custom (longer) connecting rods and the use of 4.250" big block Chevy pistons with thin, low tension, piston rings. Modern materials make this possible. This would reduce the massive friction of the thick piston rings and the large piston skirts.
The longer connecting rods are needed because of the higher wrist pin location.

Does anything know what length the stock rods are, and what the deck height is?

2. Another advantage is the compression gain, with a flattop or even a slight dome design. Up to 9.5-10:1 static. Maybe even higher, given the rod ratio.

The disadvantage would be to have everything rebalanced.

Of course, the mains and rod diameters are larger on a V6 than a comparable engine, adding to the friction, which is a given. But I have a hunch this (different piston) will improve the efficiency of the engine significantly.

Reducing additional friction could be done by the switch to a roller camshaft.

Another idea is to change the intake manifold, but I'm not sure how good or bad these are. Optimized and equal fuel distribution to all cylinders is the idea.

I'm no engine builder, just a student on the subject, but I'd love to hear your ideas. It is not my idea to write off the base design, just some thoughts to improve on it.
Stock rod length: 7.17825" C-C;
Piston Deck Height 0.000"
Not for sure on the Piston Dished Volume but I believe it is around 10CC.

Plans for my 305:
To increase the compression ratio I am planning on offset grind the crankshaft to increase the stroke, going from stock journal size to 0.030" undersize. Then mill the head of the piston (will be 0.030" oversize) to get it back to a zero deck height, this will remove most of the dished from the head of the piston.

Also in the works I have been flow testing the heads to improve the flow. Been getting mixed results from this. Still in progress. I will be targeting high swirl and all the flow I can get. Stock head has no swirl and badly shrouded valves.

I had already modified the intake manifold to be equal to the Magnum engine and had installed the Holley 2 barrels carb. I need to schedule time on the chassis dyno, this will show the change from the totally stock dyno reading.
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Old December 8th, 2021, 02:24 PM
Prowbar Prowbar is offline
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Default Re: The fuel efficient GMC V6

Quote:
Originally Posted by James View Post
Stock rod length: 7.17825" C-C;
Piston Deck Height 0.000"
Not for sure on the Piston Dished Volume but I believe it is around 10CC.

Plans for my 305:
To increase the compression ratio I am planning on offset grind the crankshaft to increase the stroke, going from stock journal size to 0.030" undersize. Then mill the head of the piston (will be 0.030" oversize) to get it back to a zero deck height, this will remove most of the dished from the head of the piston.

Also in the works I have been flow testing the heads to improve the flow. Been getting mixed results from this. Still in progress. I will be targeting high swirl and all the flow I can get. Stock head has no swirl and badly shrouded valves.

I had already modified the intake manifold to be equal to the Magnum engine and had installed the Holley 2 barrels carb. I need to schedule time on the chassis dyno, this will show the change from the totally stock dyno reading.
Thanks James. What would the compression ratio be after you've performed the modifications? How much displacement do you gain?

Looking at a picture, indeed, those valves are shrouded pretty bad. Should be better on the larger bore engines, if they have larger chambers?

Custom pistons are expensive, but do you see any gains in my idea? Maybe it is possible to modify a standard piston by machining to up the compression and reduce friction.
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Old December 8th, 2021, 05:24 PM
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Default Re: The fuel efficient GMC V6

Quote:
Originally Posted by Prowbar View Post
Thanks James. What would the compression ratio be after you've performed the modifications? How much displacement do you gain?

Looking at a picture, indeed, those valves are shrouded pretty bad. Should be better on the larger bore engines, if they have larger chambers?

Custom pistons are expensive, but do you see any gains in my idea? Maybe it is possible to modify a standard piston by machining to up the compression and reduce friction.
After all of the modifications, compression ratio would be around 8.75 (stock is 7.5:1). Displacement should be around 310 ci.

Gains and expenses in your idea, with custom made parts anything possible.
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Old December 8th, 2021, 09:07 PM
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Default Re: The fuel efficient GMC V6

Some where there is a thread that I read where someone turn the rod journals and used connecting rods and I believe the piston too out of a Hemi. The engine was able to turn 5,000 rpm.

I have personal seen at a swap meet where there was a V12 that used a crank trigger and individual coils for each spark plug for the ignition.
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Last edited by duallyjams; December 8th, 2021 at 09:12 PM.
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  #8  
Old December 9th, 2021, 06:20 AM
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AZKen AZKen is offline
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Default Re: The fuel efficient GMC V6

Maybe just spend that risky $8000 development cash on gas for a stock 305E. The difference between 12 MPG and 15 MPG is about 5 cents per mile.

A 700r4 and a 3.08 differential is another option.

What would be the reason for reconstructing a 305E instead or installing GM: 5.3 V8 @ 21 MPG highway...or other modern motor. Lots of good used motors out there if you want a restomod style GMC.

Maybe this is just a "what if" post. Not sure. This kind of talk on 6066Club is messing with Mother Nature and Father Time.

(I am a closet V8 guy)

Last edited by AZKen; December 9th, 2021 at 06:58 AM.
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  #9  
Old December 9th, 2021, 04:06 PM
POWERSTROKE POWERSTROKE is offline
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Default Re: The fuel efficient GMC V6

Another possibility is to get a big time sponsorship from a TV show about fixing up rare old pickup trucks with a large parts budget, for your custom pistons with plasma ceramic coated piston tops, anti-friction coatings on the piston skirts, low tension rings, custom grind cam, roller cam followers, roller rocker arms, and today there's no reason NOT to run EFI, except for the cost of the aftermarket system.

Another thing that hurts these 60 year old trucks is they are so heavy. Everything is heavier than the same part on a new truck.

Hope you guys have success in achieving your goal!
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Old December 9th, 2021, 04:56 PM
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FetchMeAPepsi FetchMeAPepsi is offline
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Default Re: The fuel efficient GMC V6

Quote:
Originally Posted by POWERSTROKE View Post
Another possibility is to get a big time sponsorship from a TV show about fixing up rare old pickup trucks with a large parts budget, for your custom pistons with plasma ceramic coated piston tops, anti-friction coatings on the piston skirts, low tension rings, custom grind cam, roller cam followers, roller rocker arms, and today there's no reason NOT to run EFI, except for the cost of the aftermarket system.

Another thing that hurts these 60 year old trucks is they are so heavy. Everything is heavier than the same part on a new truck.

Hope you guys have success in achieving your goal!
Haha! now that's the ticket! Call up ol' Garage Squad or someone and hover over them so they don't just throw crap in there and call it done like a lot of these shows do.

I can't believe out of all our members, that no one is independently wealthy enough to finance something like this. Where's Jay Leno when you need him?
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