CI vs. RPM

[Gary Kubisch]

With a 525 limit in Pro Stock and a 70 Skylark that will never get below 3300lbs w/ driver.
What theory is best for this approach?
Max CI or smaller CI to save as much weight as possible?

The best BB Buick heads will go 360-400 on the intake at .700 lift.
This is with port volume in the 250cc range.

I'm don't really think these engine will see much by going to the larger CI,Am I better to build it like a large CI SBC?

A little "brand-x" challenge for you while I wait on parts.....

[Chris Uratchko]

Gary,

Pro Stock gives a huge weight break for Buicks. You can weigh 3175 with 525 inchs, and a nostalgia weight break. Since you can't get below 3300, you need to stick with the largest CID possible. Also, it's 8.5 lbs/cid penalty for addition cubes, up to 565 inchs. So you can add an additional 14 cubes for free.... 540 basically....

On those heads, what is the min cross sectional area with a 400 cfm port? Volume don't do me any good as I don't know the port length. Also what is the short turn like? How high is the port raised off the deck? What is the port length? What is the runner length in a good intake? Can't answer anything about rpm without knowing all the details.

On the flip side of the coin, if I had a light weight car, I'd build something small CID for those heads. Ever hear the phrase, a small engine makes a bad head look good??? I'm not saying your heads are bad, but they're not what a Dart Pro1 BBC head is, nor a Victor Glidden SBF head is in terms of capability. A 400 inch engine would be interesting for that head you're talking about. Then the fight becomes making the crankshaft LIGHT!!

Really that's your battle even for the Big inch deal. Get that crank light and make that your first priority. Don't care what it takes, make it light, and get the rod journals into a honda bearing size or at least a small journal sbc size. I'm saying this because I know what Cagle went through with his Buick engine. Obviously I'm talking big dollar crank, but to even waste a second of thought on the class you need concentrate on some of this stuff before you even get the credit card out. Crank, Block, Heads/Intake. Get those out of the way first. The rest is easy stuff.

[Staged70Lark]

Chris,

Gary and I are Buick racers!! I will try to answer as many of the questions you asked with as much detailed information as possible.

My Buick heads flow 220@.300 and 355 @.650 lift on the intake side and 185@.300 and 263@.650 on the exhaust. I beleive the valve angle is 14 degrees. I personally cannot get the heads to continue to gain air over .650 lift on the intake side. I believe when the valve is extended out into the cylinder it begins to interfere with the cylinder wall. The valves in my heads are a 2.200 intake and a 1.75 exhaust. The venturi at the base of the valve seat is set at 88% of the valve diameter.

The smallest cross sectional area in our heads are at the top of the short turn. The total amount of area is 2.83 square inches. The port entrance is 2.375 tall and 1.200 wide. The total volume of the port in this cylinder head is 260 ccs.

When porting a cylinder head I try to keep the short turn radius the same as the valves radius. The port floor at the top of the short turn is around 1.180 from the deck of the cylinder head.

The cylinder head port length is close to 5.25 long.
Intake runner length is close to 8.5 inches long.

You speak of lightweight parts. I have recently contacted Bryant and Winneburg (spelling??) to make a nice crankshaft for us. Presently I use a Moldex crank that is 4.500 stroke. With a bobweight of 1684 grams (4.350 bore, 10.575 deck height) and the crank ways a whopping 77 lbs. This has main bearing diameters of 3.250 and rod journals of 2.100. This is WAYYY to heavy. Now you understand why I have been looking elsewhere.

Another option for us is to stay with a stock crank of 3.900 which weighs in at 72 lbs and then lathe balance to the light bobweight. I have never done this but I am thinking I could get the stock crank down to 65 lbs.

I hope this information is usefull. If you have any other questions please ask. And thanks in advance for your help.

Thanks Again

[Chris Uratchko]

Man oh man.... 2.8 inch min cross section with a 2.200 valve. That's tight for that size valve. Seems like you should have a little more cross section in there, as the 355 cfm seems low for that size valve. As you said it might be shrouded by the wall. What is the highest lift you tested the head?

A 70 pound crank just ain't gonna do for an n/a engine. Have you considered bushing the main tunnel in the block for smaller bearings? It's not that outlandish an idea.

If you're stuck with that kind of main I picture a big ol'e gun drill down the crank centerline. I can't imagine you'd have to hold Bryants hand in getting a light crank. I don't see why this crank can't be around 50 pounds honestly. Or less. I have a 3.75 stroke crank that is 38 pounds. The crank guy can get creative with the counterweights, the gun drilling, and the throws. Get the rod journals to 2.00", not 2.100.

[Staged70Lark]

Chris,

Our 455 Buick cranks are EXTREMELY close to a 440 Chrysler crank. I was told by Bryant that they can build a crank for us with a 4.400 stroke that would be 60 to 65 lbs. I would be happy taking off another 12 to 17 lbs.

How much ET is there to gain by taking off another 15 lbs from the crank?

Also going back to Gary's original question. With our cylinder head limitation what is the best way to build our Buick engine? Big CID or Small CID?

We are presently looking into bore housing spacers. Or maybe some day we will see a new block. :roll: Do you know of anyone who does a nice job with lightening up a crankshaft?



I can say that my 535 CID in a 2850 lb car has gone a best of 8.78@153mph at 2000 ft of density altitude at Norwalk. The new car has gone 8.10@167mph but its new and dont have much time so I dont have much detailed info.

[Chris Uratchko]

Just had a passing thought. Have you considered dropping the valve size in the intake port? Something that might bring the throat from 88 percent to around 90-91 percent? This would also unshroud the valve some from the cylinder wall. Obviously your stuff is running good but I was just reading again and thought I'd throw that out there.

As for lightening up a crank, I would think Bryant would be a great choice. They are good at keeping their dates. Most other crank shops are a gamble.