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i am looking into buying some gt40p cylinder heads for my 91 mustang and already have a cam ground out for .512 lift. i read some where that its max is .500 so im a little concerned. i would appreciate any feedback, thank you
 

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both wrong..lift has very little to do with PTV clearance..its in the duration/overlap of the cam

FWIW,i have my GT40P heads shaved .010" and i run a bcam with 1.72 rockers which gives me .516" lift,and i have miles of clearance...

89coupe said:
when the Intake valve is opening, the piston is heading down in the bore, drawing the intake charge in. On the exhaust, the valve is open when the piston is down, but the piston chases the valve closed. But at peak lift, the valve is not close to the piston.
 

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The limitation of lift is determined by the length of the valves and the valve springs used, which should match/support the camshaft profile total net lift specifications +a .060" gap from springs coil bind specification. IOW..... you should not use the stock valve springs with an aftermarket cam.

And what need4spd90 said........ total valve lift has nothing to do with possible PtV issues.
 

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Your valve springs usually determine your max lift, I think anything over .520 in the Gt40s is going to be a waste of time without some good port work.
 

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If that cam has anything less then 290 duration and you use that with stock pistions and 1.6 rockers your PTV clearence should be fine but make sure when you are swapping the heads to check it to be safe, it only takes 10 mins to check and possibly save you alot of time and money. The thing i am pretty sure of is that you will need to upgrade the valve springs, and possibly have to get a different length pushrod.
 

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What about clearance with 93 cobra heads, e cam and 1.7 rr's?
 

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Cobra heads are gt40s, What is the lobe lift on the e cam?
 

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I think I found it, the lobe lift is .311, with 1.7s the would be .529 lift. I think. I just started learnig the math with cams a rockers.
 

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I have the cam card. Lift is .498/.498 so with 1.7 rr's it'll be .528/.528. I've read that maximum lift on regular gt-40s is .544/.544
 

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make sure when you are swapping the heads to check it to be safe, it only takes 10 mins to check and possibly save you alot of time and money.

right on :bigthumbsup

and 88gt306---have you not read any of this thread????

the max lift is determined by the valve springs you are using. Piston to Valve clearance has nothing to do with max valve lift

and an Ecam with 1.7's will have .529" lift

.498/1.6= .311
.311 x 1.7= .529

look at joel..he's using an X cam with 1.72 rockers..thats like .582" lift...stock bottom end..valves not hitting pistons..WHY? because of the DURATION..not the lift
 

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I have gt40p's with a x303 cam if that helps.
right..and the Xcam is like a grown up B cam..very similar Duration..lots more lift..and thats why you have no problems
 

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right on :bigthumbsup

and 88gt306---have you not read any of this thread????

the max lift is determined by the valve springs you are using. Piston to Valve clearance has nothing to do with max valve lift

and an Ecam with 1.7's will have .529" lift

.498/1.6= .311
.311 x 1.7= .529

look at joel..he's using an X cam with 1.72 rockers..thats like .582" lift...stock bottom end..valves not hitting pistons..WHY? because of the DURATION..not the lift
Not arguing with you or nothing but I was taught that lift is lobe lift and duration is the side to side length of the lobe. So when a cam says it has .500/.500 lift, exactly what is being measured? And I'm using frpp's single valve springs so with those valv springs and e cam with 1.7s, so what should my lift be?
 

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so, by what I've read, unless I get a cam with crazy duration, I'll be fine with upper .500s in lift?
I'm looking to eventually upgrade to a Box-R series intake and Trick Flow's stage 2 cam which is .542/.563 lift and 293/290 adv duration and 224/232 duration at .050.
What is advertised duration?
 

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Sorry but I just need more information. Seems like duration would mean length of time the valve is open. And lift Is lobe lift. Please explain more please.
 

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Most of the time, advertised lift is not lobe lift. It is valve lift with a standard rocker arm ratio (1.6ish) rocker arm. Usually lobe lift will be in the upper .200s or lower .300s. You then multiply lobe lift by rocker arm ratio to get valve lift. Duration is how long the valve is open. There is advertised duration, which I'm not sure exactly what that is, then duration at .050, which is how long it is open beyond .050 lift. It is only at max lift for a moment, most of the duration is either spent opening or closing.
If I am wrong on any of this, someone please correct me.
 

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Ok I see what you mean but the duration lift and PTV clearance thing is still confusing me.so the duration at the very top middle is lobe lift right??? Somebody clarify please
 

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What about clearance with 93 cobra heads, e cam and 1.7 rr's?

I know that the E cam with gt-40 heads and 1.6 rockers you should'nt have a problem with PTV clearance, but with that cam you are getting really close to the max lift for the stock springs on those heads so IMO i would upgrade the spring. Since you want to upgrade the rocker to 1.7 that will change what the cam specs for the lift on spec sheet. The rocker ratio that the E cam specs are set to is 1.6 which makes it a .498 lift. When you go to the 1.7 ratio it ups it to .529 lift which is getting pretty close for stock PTV clearance. So if you use those rockers IMO you should definitely check your PTV clearance and upgrade the springs in the heads.
 

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I'll have to try to find it, but I think it was popular hot rodding that covered the build. It was a 347 making 800 some horsepower NA. The amazing part was they were revving it to almost 10k with around 13:1 compression and almost a full inch of valve lift.
 
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