Allright, here's the dilemna; I'm new to road racing engines, and I'm building a motor for a guy that is limited to 355 inches. The car is about 2,500 lbs, and will be geared to match whatever the engine needs.

The rules: no more than 355 inches and one 4bbl carb, and a modest budget- relatively speaking. We're looking to keep up with a couple 304" Katech powered cars . Anything else goes, and this needs to be high rpm, high hp motor. Little concern will be given to anything below 4500 rpm. It will be a solid roller with 220-235 cc heads- I'm interested in the aluminum Pro heads right now. Compression is unlimited, and will be somewhere on the far side of 13:1. I'm looking at a rod length of 6" to maybe 6.125" to reduce piston speed at the projected 8,000 rpm redline.

So... the only thing left is this: do I build a normal 4.030x 3.484, or do I build a 4.155x 3.25? Cost will be close either way, as I'll be using a bowtie block and Callies crank.

Based on what I know about big bore, small stroke engines I think the 4.155x 3.25 would be the best combination, but figured I'd ask here.

 

There ya go......put in the 6.125 rods also

have fun

 

You got it on the nose!!

~Mike

 

Definetely big bore short stroke.

 

what's the budget??? I can see an all-aluminum big-block with 4.5x2.79 = 354.98ci. Super-short stroke - should be able to pull 9Krpm pretty easily...
You'll get more flow out of big block heads than small block heads will have any chance of matching, and the aluminum will keep the BB on par with SB weight!
Be sure to get a short deck BB as well to trim even more weight, since you won't need much height to fit a short stroke/long rod...
Remember to always opt for a longer rod over a taller piston - it'll keep your weight down even more which is vital in racing.

 

What class is he running exactly? Might be able to give eh... more specific suggestions then

 

I'll ask next time he's in the shop. Stands in my mind it's GT2, but I wouldn't bet ten cents on it.

 

The large bore and a 6.25" rod.

With something like the CNC bowtie block you can get that all done with room to spare. Hell I ran a 6.25" rod with a 3.500 stroke with no problems.

BTW what heads are you looking at?



Those are from Weld Tech and they are right up there with everything else in that CC range. On top of that you could look at the AFR 215's the CNC versions of that are actually around 235cc's

Why not go with 18 deg heads?

You can get some awesome 18 heads in the 240 range.

Bret

 

Nope the SBC with the 183 lbs block would still weight less, and would have a shorter Center of Gravity. On top of that the BBC heads are too big port wise, it's not always CFM but velocity, especially in road racing.

Bret

 

Right now I'm looking at the Pro Action heads. I haven't seen them on a bench, but I have a set of small iron heads from them at the shop, and I like the way their castings look. If I hired a porter, it would be Skarodom and his motley gang.

I am checking, but I believe that only 23* heads are allowed.

 

Allright, I talked to Andy last night. The class is GT1, and he's looking for a mill similar to what's run in Trans Am series.

Some new concerns: Throttle blade is limited to 1 11/16" per hole on a "750 cfm" carb. He's checking into whether 18* heads are allowed, but it's likely they are not.

The issue is this: would a built 750 carb starve a 353 to the point that a 304 would be a better option? My mind tells me that the 353 would be better because it would have more area under the curve below say 6,000 rpm.

Either way, he pretty much gave us the go-ahead last night. He's going to run the 355 we built for the rest of the year and start on the new one this fall.

 

If the rule is for 23* heads only you are going to want to run some raised runner heads.......dart, AFR, pro action, even GM makes them

 

That throttle blade size is really big. You should be fine with that. If you want the best go with a braswelll carb. www.braswell.com that will be more than enough to feed your engine. BTW Winston cup uses a "750" and they get 800hp

If you are allowed cubes take them, the 304 has no advantages over the 355.

BTW how much money is this guy willing to spend?

Seriously e-mail me. (I would hope that my customer was not on here reading this!) My last naturally aspiriated endurance engine put out 520 ft lbs out of a 365 cube small block, I can definately give you some help.

Bret

 

Bret I appreciate the offer to help, and will send an email shortly!

The guy that will be buying this engine knows that we have never built an engine of this type and that I'm looking for help wherever I can find it. Why wouldn't I want him to know that I'm doing all I can to put together the best combination I can? Our shop does 70% stock rebuilds and machining and the rest is mild street/ strip stuff. FWIW, I'm making approximately $0 on this project for my time. It's all about learning for me....

 

Yes and No. Depends upon the runner size. There are some really good non raised runner heads in 23 deg for chevy.