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Cam valve lift difference? 

 

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 Post subject: Cam valve lift difference?
Posted: Sun Feb 12, 2006 2:20 pm 
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I am trying to gain an understanding of what, if any, differences there are between cams that have an equal amount of valve lift such as the E303 which has .498 @ IN and .498 @ EX and compare it to, say, a Crane 2031 which has .513 @ IN and .529 @ EX.
What is the effect on the cam when the valve lift is equal and when they're not equal? Anything at all or is it completely irrelevant?

 

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Posted: Sun Feb 12, 2006 3:49 pm 
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It just changes the intake/exhaust flow bias.

i.e. if your exhaust is restricting your combo, a cam with more lift and/or duration on the exhaust lobes could make more power.

More bias on the exhaust can help for cars running n20 or superchargers. Turbo cars are a different story though.
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Posted: Sun Feb 12, 2006 4:03 pm 
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So for GT40P heads, which have a more efficient burning combustion chamber but smaller exhaust ports, should I be considering the flow bias, e.g. selecting a cam that has more bias towards the exhaust? Or won't it make a difference either to stock or ported GT40P's?

 

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Posted: Sun Feb 12, 2006 8:14 pm 
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GT40p's flow pretty good on the exhaust side, better than the GT40 heads at least.

I don't know enough about cam design to be totally honest. Not enough to make a recommendation either way.

There are plenty of good threads on Corral about cam design for the 5.0L. Knowledgable guys like Ed Curtis who frequent the forums.

Whats your combo, and what are you looking for out of it?
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Posted: Sun Feb 12, 2006 8:36 pm 
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Sure, my application will have:

Cobra intake manifold
GT40P heads ( most likely with a little porting to match the lower Cobra intake and Pacemaker PH4000 headers )
65mm TB
24lb injectors
73mm MAF
cam
matching ratio roller rockers.

This will all be running with a stock ECU and a stock auto transmission.

The cam is of course one of the harder items for me to pick so that it complements the rest of the package. The type of cam I want is one that has the power and torque developing evenly across the RPM range, from low to high RPM and not just up high. I understand the overall effect of low and high duration, lift and lobe separation and how they affect the cam performance in general but I wouldn't mind stretching my knowledge a bit further if I can.
So, cam selection is the last item for me to nail down and I have four cam profiles that currently interest me, though there isn't much between them.
I'm open to suggestions.

 

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Last edited by Vic on Sun Feb 12, 2006 10:04 pm, edited 1 time in total.

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Posted: Sun Feb 12, 2006 8:55 pm 
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GT40P heads still are fairly weak on the exhaust side compared with aftermarket heads (good for a factory head though), and respond really well to a exhaust biased cam. You will see that all the modern design windsor cams (Crane 2030, 2031, TFS1 and many of the Comp cams) have an exhaust bias.
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Posted: Sun Feb 12, 2006 9:58 pm 
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Well that makes selection a lot easier to deal with, I can rule out the XE270HR then.
In fact Grant, would this flow bias coupled with the GT40P heads be a main consideration why many folks select either the 2031, 2030 or the TFS1? Because these cams' do have this IN / EX bias and that it works so well with the smaller exhaust ports on the GT40P??

 

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Posted: Sun Feb 12, 2006 10:22 pm 
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Exactly, these cam designs have proven themselves many times in the US and Australia with GT40P heads.
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Posted: Mon Feb 13, 2006 12:41 am 
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Lift [over .520] mainly is good for high flowing heads..Much more than .500 lift is not such an advantage with Gt p heads..For heavy car and tall rear ratio's I wouldn't go anymore agressive than 2031 or 218 / 220 exh @50..Even then you need to check valve to piston clearance..Std valves should be o/k but double springs are a must...
The Crane cam is possibly made for aftermarket heads also...But its a good al round cam..Lumpy but evens out when load comes on ...

 

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Posted: Mon Feb 13, 2006 3:22 am 
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Just a quick one on piston to valve clearances, Ive got a set of E7TE's which have been extensively ported, and I also have a set of Ferrea SS valves for them. The prob is that the Ferrea's are 1.92"/1.6" vs the std 1.78"/1.45". I know that the AFR 165's run fine with the std cam and higher rocker ratio on the 1.92"/1.6" valves however the chambers appear a little deeper however smaller chamber/better squish area than the E7TE's do. Has anyone tried the combo that Im doing and if so how did you go? Did you have to fly cut the pistons?

 

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