Inliners International Forums General Discussion Bench racing short stroke GMC RPM's?

I'm building a short stroke 270 engine and am wondering what others have found a PROPERLY built engine will reliably wind to.
The stroke is still very long but with properly prepped rods: polished then peened and balanced with ARP fasteners and the counterweights weighted to go with the piston weights etc.?
Have others found it necessary to fab steel main caps?
I only wound the standard stroke 270 I built without the special treatments to 5000 and it held together so I expect lots more as stated.
This is for a track roadster I dug out of a backyard here in California.
Roar

Sounds like a cool project.

I've heard rumor on here of people winding the long stroke engines (270,302) beyond 7K with proper prep, at Bonneville.

Might want to find the people doing that though and see what they reccomend.

Is that the short stroke 270 like in the 'California Bill' book?

The main limiting factors that will keep you from be able to buzz these engines very high is a relatively poor flowing cylinder head, and camshaft selection. Most of the high revving engines that others have been able to achieve this with are using the very pricy 12 port aluminum heads, or with the stock heads ported to the max and much larger race profile camshafts or both. Even the stock heads ported step by step in the California Bill book are still only able to reach the low 200 CFM range on the intake ports. Other 21st century techniques used by others have so far been able to get these heads a little higher into the 230 CFM range, and along with a custom camshaft have been able to get these engines to turn beyond 5000 RPM. With the newer cam technology and cylinder head development that is currently available, the sky is the limit, but it also is very expensive. All the high tech ARP bolts and polished beams don't help out much with RPM when you have a 10 pound piston on the end of the rod trying to pull it in half. The rest of the engine as well has to be modified to endure the extra RPM also. The only way to get a much lighter piston for the GMC's, is to install a much longer connecting rod, so a custom compression height piston can be made that eliminates a lot of the piston mass. Both are very costly. In the rare chance you can even find a cam company that has a stock type cam core to grind you a decent cam profile with, the only other alternative is to regrind a stock one, but you are limited as too how much bigger you can regrind it. I have been working with a camgrinder to develop some brand new billet roller cams for the entire early(Chevy and GMC) and late(250/292)engines, as well as any other inline possible from the Flathead 6's to the Straight 8 Buicks and Pontiacs, and everything in between, and are available now with just a phone call. So before long it will be possible to have a 21st century vintage engine in a lot of ways....

Somewhere here there is a thread where we began to discuss this. Using a 228/248 crank the stroke is 3 13/16. with a bore of 3 15/16 that gives you 279 ci. To do this with stock height pistons .095 has to be milled either from the head or the deck. This is from California Bill's book and it was his favorite street combo. Somewhere I read that this could turn 7,500 rpm. That seems like a lot. I used to shift my 270 at 5,500 regularly and it would turn 6,000 but it lost power before it got there. I don't know how or why it would go that high but it did. It would only do it in first and second gears when I was running 4.11s. I have thought of doing his to a 302 for a supercharged engine. Just so 5,000 to 5,500 would be in it's comfort zone. Of course we know that these are not high winding engines but 5,500 is not that much.

I've built a 321 cid GMC (302+0.125" bore)in a HAMB dragster and turn it 6200 all the time. In fact the dragster is traction limited and the engine spends most of it's time on the rev limiter. The engine has stock 308 cid Hudson rods which are 1.25" longer than the GMC. I had a custom piston made by JE that weighs 500 grams. I saved about 1.25 POUNDS per cylinder with this combination!!!! I also run a SB Chevy Fluidamper (fits perfectly).

I had Dema Elgin grind the cam. It made 346 HP @ 5600 and 347 TQ @ 4500.

We ported the 302 head (#883 IIRC) and it flows 264 cfm @ 0.600
on the intake but only 144 cfm on the exhaust @ 0.400. All flow was @ 28". The head has 2.02/1.6 SB Chevy valves.

The dyno testing was done with zoomie headers which I've since replaced with a 1 3/4" 4x1 header. The TQ increase was unreal.

I also drive the distributor and BB Chrysler oil pump off the front of the engine. Works great. I'd attach pictures if I knew how.

Ron (goldenri@aol.com)

here you go ron.

Thanks for the picture. One of these days I'm going to master this computer and become smarter than it is.

Ron

[quote=Ron Golden One of these days I'm going to master this computer and become smarter than it is.

Ron [/quote]

I used to think that same thing. I don't any more!