I have been thinking of going to the SE forged pistons and changing my cams to get more torque at the lower RPMs.My previous build had cast 103 pistons.89 cc ported heads and andrew 50 cams with a .030 head gasket.Not much low end power and hard to control at low speeds like in town.So i was told that even if you have 10.0-1 compression your corrected compression depends on cam choice,What is a good steetable corrected comp. on pump gas.I also found a web site that lets you pick differant variables.to get the right comp. check it out. Big Boyz Head Porting.com Then go to calculators and open twin cam calculators.

 

Hey, Bagger, thanks for the link. That is the best explanation I've seen. I read American Iron Mag and am often amused by the articles showing how you can increase torque and hp. Almost always the trade-off is higher peak output for lower output in the low-to-mid rpm range. I want a torque curve that builds quickly, flattens out, and stays flat as far as possible up the rpm range. It sounds like the Big Boyz understand.

 

Thanks for the link. Gives me more ideas for this winter's project.

 

I thought it was interesting that differant cams can change the comp. so much.Anyone running the andrews 31 or 37 in a 103" what do ya think?

 

Cams do not change the compression ratio, that is a ratio of cylinder+dome cc's /dome cc's. They do however affect cranking pressure and a good psi for a nice reliable not gas picky motor would be about 190. You can call it corrected cr or dynamic cr but it is just really cranking pressure.

 

From what I can gather, 190 is getting close to the limit. I'm just over 190 on mine and had to pull some timing in certain rpm/tps combinations. No running problems at any rpm after the tune though.

 

it has to do with ow much overlap (LSA- lobe seperation angle) the cam has built in. Less overlap builds more pressure, more overlap, less
I puuled this from Chevy High Perf:


Lobe-Separation Angle (LSA)
This measurement indicates the angle, in camshaft degrees, between the maximum lift points on the intake lobe and the exhaust lobe. Lobe separation is usually calculated by adding the intake centerline and the exhaust centerline, then dividing by two. For example, a cam with a 106-degree intake centerline and a 114-degree exhaust centerline has an LSA of 110 degrees [(106 + 114) / 2 = 110]. Overlap
Overlap is the amount of time, measured in crankshaft degrees, that both the intake valve and the exhaust valve are open. This situation happens at the end of the exhaust stroke and the beginning of the intake stroke. Increasing duration or decreasing lobe-separation angle--or doing both--increases overlap. A cam with an exhaust closing point of 4 degrees ATDC and an intake opening point of 8 degrees BTDC has 12 degrees of overlap.

 

Thanks man

 

255's have nice torque curve. The intake closes quick and low overlap.

 

Thanks for the info.