Joel5.0

[sm=youreright.gif] think about it for a sec.........don't look at peak numbers..... wouldn't having a "useless" peak lift cause the "usable" lift number to be reached earlier in the valve events....... ...would it make a difference in power???????......there are some good examples.......

AdderMk2

well sure they work great on our mostly stock or mild cars.... but they arent GREAT....

Trying to use them on a car with 580-620 lift wouldnt be a very good idea... because they wont flow well.


But myself personally, the only reason I wouldnt use them, is the inconvience of the spark plug location.

grabbem88

first of all you don't always need lift to make power...my cam has small lift numbers and it screams..

tell ya what..like joel said...there are very good examples of what gt40's potential are...total package not peak values.


if you look at my peak numbers on my dyno sheet you would say something was wrong,but take it to the track and cut bottom 12's all day long..you would probably be scratching your head

my77stang

well said.

when your trying to be able to get more lift from your heads without mechanical limitations the first step is the springs, followed in at a close second by having the guides machined down. otherwise the retainers will be smashing the valve seals or worse hit the top of the guide.

gspfunk

On the stock bottom end, you're "usually" limited to ~.530 max lift, if you are playing it safe. (<--not the end-all, say-all; but a decent guidelineto follow.Claying it up should be a must, IMHO!!)

As mentioned, the P heads don't flow as well over .500 lift, due to the 1.46 exhaust valves....do some work and upgrade the valves and you'll have a helluva set of heads.

Upgrading springs and valvetrain should be a given if you're working with stock components. I went w/ a Crane valve spring kit good to .550 lift for my ported E7's, even though I'm only running the E cam. Stock components aren't trustworthy and are 14+ years old on top of that.....

Joel5.0

Total valve lift IS NOT a cause for any PtV problems....you could have a cam with .600" lift and not have any PtV issues.....by the same token, you could have another cam with .480" lift and have the piston hit the valves. It's the OVERLAP you have to check......when BOTH valves are open anywhere from .016" to .157", cam spec dependent (not lift)...and the piston is at Exhaust-TDC.....again, the valve lift = PtV problems is wrong ....when any of the valves is at full lift, the piston is >1.5" below the deck.........agree on the measuring part though.....

my77stang

+1 on that too. even if you dont have the cash to get all new valves, the intakes are exposed to alot less heat than the exhaust valves and if you have the 1.84 intakes because they are GT-40 heads you can just get new exhaust valves in a 1.60 or even a 1.50 size along with some machine pocket porting on the intake and exhaust and you'd be quite happy with the outcome.

btw...
http://www.carbdford.com/tech/headflow.htm

Joel5.0

But wait....I see them flowing better than the stock GT40's...and a few aftermarkets on the exhaust side, albeit the smaller exh valve.......it should be caused by other aspects of their design.....

my77stang

well everyone knows the P's flow better than the regular 40's

the point was that with a little ex side work 40's OR the 40P's flow can be increased easily

gspfunk

The comparisons I've seen agree w/ what you're saying, but only up to .500 or so lift. The P heads dohave redesigned and improved exhaust runners, but they used the stock E7 size valves, IIRC. At .500 lift, the valve size seems to become the hinderance. The GT40's have 1.54 exh valves, and, even w/ the thermactor bumps in place, the larger valves allow more airflow.

That is what I've gathered from the info I've read/researched, but may not be the entire scenario....other factors may contribute as well.....