GMC 302 inline 6 maximum effort Bonneville engine

[COMP461]

I have taken on another crazy program.
The car is a top-shelf Modified roadster chassis and this motor is currently in the car. The records are fairly developed and there is a lot of ideas I have.
Classes are XXO GMR XXO is engine glass G is for Gasoline Mis is modified and R is Roadster.
So the car can run event fuel which I believe is VP C16 in Gas or anything including nitrous is Fuel class.
Then you step up to Blown classes with both fuels so a total of 4 classes with the basic engine. XXO GMR, XXO FMR XXO BGMR, and XXO BFMR.

I look at the crank and there are only 4 main bearings yuck. I am thinking the block needs the main girdle, wonder if anyone ever did a 7 main conversion.

The head is the Wayne Aluminum head, we have a few of those, I see a lot of room for improvement


The car has a magneto and mechanical fuel injection

whay are some ideas , need your thoughts

[panic]

Do you have the 12 port cam as well (some heads have OEM valve positions, some are I E I E etc.)? Rockers?
Never heard of 7 mains, $$$.
IMHO none of the alloy heads have a good chamber shape, some are vertical valves, some are "plank" (chamber in the dome). I'd look into making a closed chamber wedge out of it with inclined & parallel valves.
Longer rods to get the piston weight down.
No serious work on the case volume or oil control has been posted TIKO.
I'm writing something on the slightly similar 235" Chevy (block pretty close, head not so much): http://victorylibrary.com/235BK.htm

[PackardV8]

Go over to the H.A.M.B. and look up Rich Fox. He ran a 302" there for several years and is one of the old heads. Tell him Jack sent you.

[jed]

As panic suggested you NEED the 12 port head. your project needs to start there.

[dannobee]

Didn't Cotton Perry run that engine, or a variant of it in H/MP way back when (Late 70's)? It was the first engine that I ever heard of with 1" of valve lift.

[jed]

You might want to look at this 12 port head.
BPE ported Howard/Wayne/Arias 12 Port GMC inline 6cyl
head fits 1952-60 302 CID GMC truck engines.

[tenxal]

Didn't Cotton Perry run that engine, or a variant of it in H/MP way back when (Late 70's)? It was the first engine that I ever heard of with 1" of valve lift.

It was 292-based, not the GMC 302 style.

[panic]

I have pictures of a Wayne head, shows 6 downdraft intake ports in pairs (adjacent, not siamese), 6 individual horizontal exhaust ports, vertical valves, with the 1 chamber a "stadium" shape (stretched circle with parallel sides) and 2 quench surfaces above & below the valve seats, and the other a "plank" (flush) type. Both may use the original or any aftermarket cam, since the valve positions match OEM. Sorry, no text details or source.

[PackardV8]

Would require two very different pistons. Which would you choose?

I'd be inclined to try the no-chamber head, as it wouldn't be shrouded and would allow for a custom piston dish which could put the squish right at the spark plug.

Other thoughts?

[pdq67]

I have pictures of a Wayne head, shows 6 downdraft intake ports in pairs (adjacent, not siamese), 6 individual horizontal exhaust ports, vertical valves, with the 1 chamber a "stadium" shape (stretched circle with parallel sides) and 2 quench surfaces above & below the valve seats, and the other a "plank" (flush) type. Both may use the original or any aftermarket cam, since the valve positions match OEM. Sorry, no text details or source.

What is actually the diffence between these two heads?

One has the chamber in the head and the other in the piston??

To me, it seems like, "6 one way, and 1/2 a dozen, the other way"?

pdq67

[COMP461]

we have several Wayne heads, the car is complete and has not been run for 12 years but has run faster than the current record

We have extensive experance in advanced engine rogram, I' trying to get in to the mind set of who ever built this engine and car 30 years ago

[pdq67]

Where does the Buick Straight 8 fit in here?

pdq67

[Truckedup]

The Buick 8 is not capable as the GMC.
I messed around with a 302 Gmc 20 years ago but it was a street engine using a modified stock head . At that time some talked of N/A 302's with the best parts and tuning making 600 hp for limited duration racing....with the 4 mains and I believe stock cranks?

[COMP461]

the 4 main is one of the potential problems. I can fix the 4 main cams with an H13 tool steel core. and hollow 8 mm titanium valves. This should get spring requirements down dramatically.

What kind of RPMs does this engine survive at? I think ultralight rods and pistons will help.

[PackardV8]

the 4 main is one of the potential problems. I can fix the 4 main cams with an H13 tool steel core. and hollow 8 mm titanium valves. This should get spring requirements down dramatically.

What kind of RPMs does this engine survive at? I think ultralight rods and pistons will help.

For true; every part can be lightened and or made stronger. Old straight six Jaguars with 4.20" stroke are being raced today at RPM which would have flown to flinders back when. The GMC are only a 4" stroke and think of what we're turning V8s of the same stroke.

If everything is right, four main bearings should be enough for five miles. The Novi V8s ran 500 miles at Indy making 750 horsepower with only three main bearings.

The one problem V8s do not have are harmonics. Straight sixes are known to require extraordinary efforts to keep the flywheel in place. Has anyone ever tried running one at Bonneville without a flywheel? Think sprint cars and push starts; on the salt push starts are the norm.

The one problem with the GMC is the loooong pushrods. While cam-side valve train weight is not the problem that valve-side weight is, to make a pushrod that long strong enough for modern higher intensity cam profiles and higher RPM requires a large diameter.

jack vines