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Senior Member
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806 Posts
Discussion Starter · #1 ·
Hi Gordon,

I recently purchased a MK 3.1, with a 5.0 roller motor installed and running. It has EFI, with AFR 165 heads, 1.6 roller rockers and a custom grind camshaft. I'm converting to Weber carbs, so I purchased the Comp Cams 35-491-8 camshaft. Can you look at the following specs and tell me if you see any red flags as far as PTV clearance? I appreciate your expertise.

Current camshaft=

Lobe lift Int .354 Ex .354
Valve lift 1.6 ratio Int .566 Ex .566
Duration @ .050" lift Int 218 Ex 224
Lobe separation 110
Recommended Int Centerline 107

Valve timing at .050 lift Int- Open 2 BTDC Close 36 ABDC
Ex- Open 45 BBDC Close (-1) ATDC


Comp Cam=

Valve lift 1.6 ratio Int .571 Ex .565
Duration @ .050 lift Int 222 Ex 224
Lobe separation 115


Thanks, Mike
 

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Pro FFR Builder and Moderator
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14,823 Posts
The big question is what pistons are in the engine. If they are stock 5.0 pistons anything above .530 lift is going to be a real problem. The other thing is those heads have a safe lift rating of .550 but it's really lower than that so doing a valve job and changing springs would be in your best interest.
 

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Pro FFR Builder and Moderator
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14,823 Posts
Reading a bit more of your post a couple things I see in the new profile. The 115 center if fine but it have very little duration which is going to cost you some top end power. The webers will like it.
 

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Senior Member
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806 Posts
Discussion Starter · #4 ·
Cam clearance

Thanks Gordon,

This motor is a fresh build, by what was described as a well known high performance engine builder in Texas. I know that the head hardware was all upgraded for certain. I'm not certain about the pistons, but the seller said it's stock bore.

This motor ran incredibly strong and quick, with a ton of low end torque, with 308 rear gears (I'm upgrading to 355's). So, can we assume that something was done with the pistons, due to the high lift on the current camshaft? I know the sheet on the camshaft is from FlowTech Induction

In the meantime, I'll try to get a hold of the forum member that I bought the car from and get more info.

Mike
 

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Senior Member
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806 Posts
Discussion Starter · #5 ·
No new information...

Gordon,

It appears that the seller has dropped off the forum. He has not responded to my request for more information.

I'm confident that this motor was professionally built, and remember the seller stating that the valve train was upgraded to withstand the existing camshaft.

So, looking at the specs on both these camshafts, and ASSUMING the valve train is upgraded, any issues jumping out at you?

Because I ran the existing motor through some hard runs (this go-kart & motor only has 10 miles on it) prior to tearing the car apart. It seems likely to me that some clearancing was already done.

Thanks for your help,

Mike
 

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Pro FFR Builder and Moderator
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If you've run this engine with the old cam I don't see any issues with the new cam.
 

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Senior Member
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Discussion Starter · #7 ·
Camshafts

Thanks very much Gordon!

Mike
 
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