Will GT40 Heads Handle A Big Cam?? - Mustang Evolution

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Old 10-26-2011, 02:52 AM   #1
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Will GT40 Heads Handle A Big Cam??

Im currently working with a stock 302 besides the basic bolt-ons (CAI, Pulleys, Headers etc.)....I came across a brand new Edelbrock RPM Performer Cam from a friend who I traded with for 24lb injectors..but anyways the cam specs are .496/.520 lift with 290/300 Duration pushing against flat tappet hydraulic lifters....My question is how would a cam this size perform with gt40 heads. I also have matching edelbrock sure seat valve springs retainers,seals, and locks that will be replacing the stock valve springs on the gt40 if its worth the swap from the stock e7 heads. Help Me Out!!
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Old 10-26-2011, 09:18 AM   #2
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That cam will work well with those heads. You will need to check your ptv clearance.
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Old 10-26-2011, 10:20 AM   #3
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Yeah that should be a good swap, I just got upgraded valve spring and retainers put in mine. Cost like 105 from our local shop for the changeover
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Old 10-27-2011, 01:19 PM   #4
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Is there any other or more simple way to check my ptv without havin to put clay on my pistons?
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Old 10-27-2011, 03:00 PM   #5
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Re: Will GT40 Heads Handle A Big Cam??

no other way
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Old 10-28-2011, 11:59 AM   #6
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Re: Will GT40 Heads Handle A Big Cam??

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Originally Posted by 90Stang_5.0 View Post
Is there any other or more simple way to check my ptv without havin to put clay on my pistons?
It can be done with the engine assembled, but it is not really easier.

You will need to bring the piston on the cylinder you are checking up to TDC using a brass piston stop tool that threads into the spark plug hole. These tools are usually included in camshaft degreeing sets, but they can also be purchased separately

First set up a dial indicator on the valve spring retainer with the valve closed and then rotate the engine in its normal direction until that valve is fully opened. Record the distance the valve moves.

Bring the piston in that cylinder back up to TDC using the tool described above.
Remove the rocker arm, valve keepers, retainer and spring. With the piston on TDC the valve should not drop too far into the cylinder.

Set up the dial indicator on the valve tip again with the valve held up in the closed position. Slowly move the valve down until contact with the piston is made. Record that number.

You know from your first measurement how far the rocker arm opens the valve.
From your second measurement you know how far it is to the top of your piston. Subtract the first measurement from the second to see how far away your piston is when the valve is fully opened and the piston is at TDC.

It can be done, but the hassles of checking each valve in each cylinder this way and the time involved make it easier to pull the head and clay the pistons.
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Old 10-28-2011, 12:15 PM   #7
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Quote:
Originally Posted by Trojan Horse

It can be done with the engine assembled, but it is not really easier.

You will need to bring the piston on the cylinder you are checking up to TDC using a brass piston stop tool that threads into the spark plug hole. These tools are usually included in camshaft degreeing sets, but they can also be purchased separately

First set up a dial indicator on the valve spring retainer with the valve closed and then rotate the engine in its normal direction until that valve is fully opened. Record the distance the valve moves.

Bring the piston in that cylinder back up to TDC using the tool described above.
Remove the rocker arm, valve keepers, retainer and spring. With the piston on TDC the valve should not drop too far into the cylinder.

Set up the dial indicator on the valve tip again with the valve held up in the closed position. Slowly move the valve down until contact with the piston is made. Record that number.

You know from your first measurement how far the rocker arm opens the valve.
From your second measurement you know how far it is to the top of your piston. Subtract the first measurement from the second to see how far away your piston is when the valve is fully opened and the piston is at TDC.

It can be done, but the hassles of checking each valve in each cylinder this way and the time involved make it easier to pull the head and clay the pistons.
Peak opening will probably occur before tdc, dont forget about the duration.
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Old 10-28-2011, 01:02 PM   #8
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Re: Will GT40 Heads Handle A Big Cam??

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Peak opening will probably occur before tdc, dont forget about the duration.
True, but any contact will most likely happen with the piston at TDC when it and the valves are closest proximity.
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Old 10-28-2011, 02:42 PM   #9
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Quote:
Originally Posted by Trojan Horse

True, but any contact will most likely happen with the piston at TDC when it and the valves are closest proximity.
I know, I know that's why it's best to use clay.
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Old 10-28-2011, 04:18 PM   #10
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Re: Will GT40 Heads Handle A Big Cam??

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I know, I know that's why it's best to use clay.
Not sure I understand your reasoning here.
A dial indicator is much more accurate than clay and if you have the piston at its highest possible point then you will get the most accurate reading.
Clay is sufficient, but not all that accurate.
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Old 10-28-2011, 05:45 PM   #11
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Quote:
Originally Posted by Trojan Horse

Not sure I understand your reasoning here.
A dial indicator is much more accurate than clay and if you have the piston at its highest possible point then you will get the most accurate reading.
Clay is sufficient, but not all that accurate.
But your valves won't be fully open at tdc. The intake valve is at max lift after the piston has moved down some, so measuring ptv at tdc would be wrong.

---------- Post added at 05:45 PM ---------- Previous post was at 05:45 PM ----------

Also not disputing the dial indicators accuracy.
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Old 10-28-2011, 06:11 PM   #12
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Quote:
Originally Posted by 93slowstang

But your valves won't be fully open at tdc. The intake valve is at max lift after the piston has moved down some, so measuring ptv at tdc would be wrong.

---------- Post added at 05:45 PM ---------- Previous post was at 05:45 PM ----------

Also not disputing the dial indicators accuracy.
But dosnt the move back down faster than the valve does.so it should be out of the way.
Ps I'm not sure on this ,just asking
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Old 10-28-2011, 07:45 PM   #13
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Quote:
Originally Posted by dreamstang

But dosnt the move back down faster than the valve does.so it should be out of the way.
Ps I'm not sure on this ,just asking
Yes.
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Old 10-29-2011, 12:57 AM   #14
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Re: Will GT40 Heads Handle A Big Cam??

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Originally Posted by 93slowstang View Post
But your valves won't be fully open at tdc. The intake valve is at max lift after the piston has moved down some, so measuring ptv at tdc would be wrong.

---------- Post added at 05:45 PM ---------- Previous post was at 05:45 PM ----------

Also not disputing the dial indicators accuracy.
If the piston is moving away as the valve is going to fully open position then there wouldn't ever be an issue.
The valve train moves at 1/2 the speed of the crankshaft, so the piston would "outrun" the valve at a very handy margin.
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Old 10-29-2011, 01:45 AM   #15
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I think that's where valve size, valve reliefs, and camshaft timing come into play
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Old 10-29-2011, 07:55 PM   #16
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Re: Will GT40 Heads Handle A Big Cam??

definatnely clay the pistons....

i ran .529 lift with gt40-p heads and shattered two pistons and punched a hole in a cumbustion chamber.
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Old 10-29-2011, 08:32 PM   #17
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I know this isn't my thread but.is it necessary to check ptv clearance going from 1.6 to 1.7 roller rockers.b303 and gt40 p .
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Old 10-29-2011, 08:45 PM   #18
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Quote:
Originally Posted by dreamstang
I know this isn't my thread but.is it necessary to check ptv clearance going from 1.6 to 1.7 roller rockers.b303 and gt40 p .
That will give you a .510 lift. You should be able to get away without claying yours, but I would to be safe.
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Old 10-29-2011, 08:54 PM   #19
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Re: Will GT40 Heads Handle A Big Cam??

i only chimed in cause he said he would running .520 on the exhaust side.
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Old 10-29-2011, 08:59 PM   #20
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Quote:
Originally Posted by 93slowstang

That will give you a .510 lift. You should be able to get away without claying yours, but I would to be safe.
ok thanx.
my buddy is parting out his bronco so i can get them really cheap. they are the anodized blue aluminum comp cams
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Old 11-01-2011, 06:11 PM   #21
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Quote:
Originally Posted by svtlx
definatnely clay the pistons....

i ran .529 lift with gt40-p heads and shattered two pistons and punched a hole in a cumbustion chamber.
I recently asked a technician about my ptv clearance and he said i would be fine if i just place shims on the valve springs....he didnt have time to explain why where or how i can do this....never actually heard of it...Anybody wna educate me?
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Old 11-01-2011, 06:29 PM   #22
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Re: Will GT40 Heads Handle A Big Cam??

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I recently asked a technician about my ptv clearance and he said i would be fine if i just place shims on the valve springs....he didnt have time to explain why where or how i can do this....never actually heard of it...Anybody wna educate me?
Shimming valve springs will help you get the proper installed height and seat pressure, but I don't see how that is going to insure proper PTV clearance.
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Old 11-01-2011, 09:20 PM   #23
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Re: Will GT40 Heads Handle A Big Cam??

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Shimming valve springs will help you get the proper installed height and seat pressure, but I don't see how that is going to insure proper PTV clearance.
maybe he meant rocker arm shims???? still not helping alot though...
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Old 11-01-2011, 09:28 PM   #24
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Re: Will GT40 Heads Handle A Big Cam??

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maybe he meant rocker arm shims???? still not helping alot though...
I don't have a clue what he is talking about.
Only thing that I can think of is that he is thinking about trying to reduce the valve lift, which would seriously hurt the performance.
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Old 11-01-2011, 10:03 PM   #25
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Quote:
Originally Posted by Trojan Horse

I don't have a clue what he is talking about.
Only thing that I can think of is that he is thinking about trying to reduce the valve lift, which would seriously hurt the performance.
Yea maybe thats what he was talkn about but shimming the rocker arms would just be taking a step backwards....im just gunna keep it simple and go with the clay method...im jus hopin i dnt run into any problems nd have to end up fly cuttin the pistons....thnx 4 all tha help
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Old 11-02-2011, 02:01 AM   #26
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I ran a trickflow stage 3 cam with almost .600 on the lift with some E7 heads.
Ran great, no issues.
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Old 11-02-2011, 02:19 AM   #27
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I ran a trickflow stage 3 cam with almost .600 on the lift with some E7 heads.
Ran great, no issues.
If the stock head runs good with a big cam I think ima stick to th E7's and just get them ported which i heard pretty much matches it up to the flow a stock gt40 will give you....itll save me time nd money...thnx
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Old 11-02-2011, 04:12 AM   #28
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Yea man. Not a problem.
Glad I could help
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