I'm sorry for my ignorance, but I've read a few threads stating that the stock TPI heads all crap out at around .375 lift. What is it that causes this stall?

I should do a search, but what are typical flow numbers for the TPI heads?

Along with what you have asked I would also like to know if putting different rocker with a higher lift would have much of an affect.

obviousely no expert....but if the .375 lift limit is the limit, the tiny change to the 'ramp rate' AT the valve would net hardly any power at all.

I think a cam swap based on duration is the way to go....



but what part of the design causes this stall at such low lift?

If the head crap out at .375 lift why does the '85 305 have .415 lift. I have very little knowledge of cams and heads.

Not sure about the iron heads, but the Corvette heads flow fine to .500". They defintely do not stop at .375". Flow at .400" is 26 CFM more than .300". (160 to 186)

iron tpi heads will not tolerate more than .470"-.480" of lift without the valve hitting the guide. not a good thing.

I put a zz4 cam in my 91 z28 350 and it has .510 lift on the exhaust side and I didnt have any problems.

What are we talking about?

Where the most CFM occures at what lift on the head?

Or how much lift the cam can have before problems with the head?

I've never heard a 350 TPI head peaking at .375 lift in terms of airflow.

Did you have your heads flowed?

Whoever told you that a stock iron head doesn't flow well over .375 is full of crap. Period.

And the valve doesn't hit the gide. It never does. Unless your vailtrain geometry is screwed up and the rocker is pulling or pushing the valve stem up against the gide. The retainers hit the gide if your trying to run a lot of lif on a stock head.

that's what i meant. oops.