Cam and Valve Spring Question
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=36235
Printed Date: October-07-2024 at 8:25pm
Topic: Cam and Valve Spring Question
Posted By: Jeremiah2001
Subject: Cam and Valve Spring Question
Date Posted: June-05-2015 at 12:50am
In the middle of a 351W engine rebuild. Of course I couldn't leave well enough alone.
My head were cracked so I found a set of rebuilt GT40P heads.
They came with a set of new trick flow valve springs # TFS-2500100.
Seat Pressure 115 @ 1.800
Open Pressure 315 @ 1.200
Max lift of .540
Ive also ordered a Cam Research Ski Cam which I believe has the following specs.
intake lift .49
exhaust lift .49
intake duration 278
exhaust duration 282
Intake duration @.050 216
Exhaust duration @ .050 220
lobe separation 112
recommended seat pressure 95lb
recommended open pressure 295lb
I'm a novice but It appears the valve springs have a higher rating than recommended by the cam card. Will these work? Of course I will call Cam Research but you guys are wizards so what do you think?
Thanks Jeremiah
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Replies:
Posted By: oldcuda
Date Posted: June-05-2015 at 2:11am
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Is that a flat tappet cam? If so that's a bit too much spring pressure.Don't forget to use the proper oil for break-in NOT the additives.
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Posted By: mamigacz
Date Posted: June-05-2015 at 10:45am
I my opinion, that spring would be a good fit for that cam. With a .49” lift you are only get an open height of 1.31” (1.8” - .49”). At 1.31” you will get an open pressure of 280lb. I can show you the math if you want.
Too much open pressure is hard on the cam.
Too little open pressure and you might experience valve float.
Your only 6% less than the recommended open pressure (280lb vs 295lb). If you were zinging this engine past 6000 RPM you might have a valve float issue. But you are going to be maxing out around 5000 PRM. Also, being a little high on the seat pressure (115lb vs 95lb) is better than being low.
The next thing is to make sure the installed height of the springs is 1.8” Are you using the stock GT40P valves? If you are, pay close attention to the exhaust install height. I remember having to buy special keepers that raised the install height.
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Posted By: mamigacz
Date Posted: June-06-2015 at 10:03am
I found this article from hot rod magazine, which explains the exhaust valves on the GT40P heads.
http://www.hotrod.com/how-to/engine/1409-how-to-upgrade-your-ford-gt40p-heads/" rel="nofollow - hot rod mag article
If you have to buy a bunch of parts to make these trick flow springs work, it might be worth while to buy a new set of springs from cam research. I wish I would of. I think the spring kit was $100 three years ago.
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Posted By: Jeremiah2001
Date Posted: June-09-2015 at 5:13pm
Thanks Everyone for the replies. I called cam research with the specs.
They believe these will work just fine. They suggested I have the machine shop double check the pressure of the springs just to make sure.
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