Brett

How does a lobe separation aide in making power with an engine with forced induction? What would be the difference between 112 and 114 degrees of lobe separation? This is one of the shady spots I have about cam knowledge.

I returned my whole LT4 Hot cam kit and decided to go with what is turning out to be an all-Crane valvetrain. What I need to do now is pick a cam. For me it is a toss-up between the Comp Cams 305-8 and 306-8 for the LT1. Here are the specs...

220/230 .544/.544 114 #305 with 1.6rr's
230/244 .510/.540 112 #306 with 1.5rr's
or .544/.577 with 1.6rr's but I think I'd stick to 1.5's with the 306 cam.

Anyway, the car is geared with 3.73s, has 1 3/4" headers, will be getting a 2400tc, and the heads are being cleaned up and worked on a bit, and of course I will be using a D-1sc next year. The displacement will either be 350 or 355 depending on if I can find a new block or only used ones.

The car will be daily-driven. Gas milage is not a concern. We have emissions in this state and I think think the 305 'might' clear it but not sure about the 306. The two conflicting ideas I have are power vs. drivability. Where I live isn't like any large city and the driving is usually pretty easy, but I don't want the car to surge or be too extreme for the street. I like a car that is a little hairy to drive but most of the power will be coming from positive manifold pressure

I dunno, what are your thoughts on these cams? Anyone ever use one, or something with a similar grind?

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1991 RS LT1
every imaginable bolt-on, and an all-forged 355 on the way with an ATI following in '01

2000 C5 Coupe
black/black 6-spd, optional polished rims, 'mostly' stock....

"So what DOES the back of a Mustang look like?"

[This message has been edited by Brett (edited September 19, 2000).]

askulte

The quick answer is that that forced induction well, forces the air in much faster and harder. The reason for overlap is that it takes time for air to begin moving and also stop moving. Since the blower/turbo will be actively pushing the air in, rather than the engine just sucking it, it will fill the cylinder that much quicker. If your exhaust valve is open (overlap period) then your intake charge will go right out the exhaust port, killing emmissions, fuel economy, and some power (since all your air/fuel mixture isn't being burned). I hope this helps!

BTW - If you want to learn more, get David Vizard's book on Small Block Chevy Valvetrains. He has a whole chapter on forced induction cams



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Andris Skulte
Skulte Performance Designs
Z28tt-89 IROC T56 DFI Twin Turbo
http://www.skulte.com