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Will someone please explain to me how I can safely know if I can use a CompCams #FF 296 BR-8 mech roller (260/268 duration @ 050, valve lift .726"/.726", LS of 108) cam in my 460? The block has 10.315" deck height, 75cc Edelbrock heads, Eagle 4.14" crank, 6.80" Eagle rods & JE flat-top w/eyebrow pistons. Right now, I don't know my piston-to-deck measurement.

I'd like to be fairly certain it'll work without having to BUY the cam first - If I do buy it & clay it with a single piston & find out it's too tight, I still own the pistons & cam! Yes, my concern is about having enough needed valve/piston clearance. I've never run anything with that much lift before - talk to me,guys. Thanks in advance for your help, Ryan

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Steve
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209.140.201.69 clearance
No score for this post March 26 2001, 8:04 AM

I had very similar prediciment. I have 466 (with Eagle H-beams & steel crank), JE SRP flat tops with (2) reliefs, and am running Crane solid roller with 255-265 at .050 and 670 lift. (The cam has .720 lift with 1.7 rockers but I am running 1.6 to knock it down to .670). I too had great concerns about piston to valve and you never will know until you clay it. But I called JE tech and guy has some program or chart or whatever and asks you your max lift, dur at .050 and LSA, deck height & intake valve dia and tells you if you are close. This assumes Edelbrock heads use identical geometry to Ford heads. In my case he said I would have NO problem. Id have about .150 he said. I am claying it this week when I get heads back. Incidentally the relief in these JE pistons are 2.350 dia by .250 deep. The reason I chose SRP over JE is they expand less with heat and have an exhaust relief as well. Same price and same manufacturer.

Steve

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StickBBF
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205.158.104.42 Good Point...
No score for this post March 27 2001, 8:32 AM

Steve,
Did you go with the 1.6 rockers for concern of valve-to-piston contact?

I probably should of went with the SRP pistons too, but "live & learn" for me since I already have them.

Thanks for the pointers, Ryan

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Mike R.
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32.97.239.14 cam
No score for this post March 26 2001, 8:05 AM

My brother ran that exact cam with trw L2443NF pistons and police interceptor heads with 466 cubic inches. He did the clay test and had plenty of clearance. My guess is you will have enough clearance, but I would absolutely plan on doing the clay test to make sure. If it doesn't have enough clearance it's easy enough to get the pistons flycut for larger reliefs and it only costs about $50. That's probably the safest plan you can follow.

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StickBBF
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205.158.104.42 Fly-cut Pistons...
No score for this post March 27 2001, 8:38 AM

Mike R,
I will clay the setup, just to be sure. That's also a good idea to be prepared to send the pistons back for fly-cutting some...
How much clearance whould you recommend as a minumim between the valves and piston?
How much can the shop cut from top of the piston before it's "too much"? Thanks for your pointers,,, Ryan

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Steve
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209.140.201.41 Cam
No score for this post March 27 2001, 8:49 AM

I went with 1.6 because I felt that .67 lift is where I want to be. I had numbers in mind when looking for a cam and .650 was the range. I just felt that .720 was alot and would reduce the longevity of the motor etc...wear guides more...but you know how power is; you always want more. I will probably install the 1.70 next year. (assuming I have spring clearance and piston to valve clearance). Steve

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Mike R.
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32.97.239.33 Valve reliefs
No score for this post March 29 2001, 7:45 AM

I would plan on .100" clearance on the intake and .120" on the exhaust.

The piston tops are usually in the neighborhood of .200"-.350" thick. There is usually a relief molded into the bottom side of the piston to allow for the valve relief coutout on top. Generally the absolute minimum thickness a piston top can be at it's thinnest point is about .080", but that's only on engines that will not be at full throttle for very long. I would not want to cut one that thin though. It's probably best to talk to the piston manufacturer and find out what they recommend.

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StickBBF
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205.158.104.42 Clearances & Thickness
No score for this post March 29 2001, 8:53 AM

Mike R, Thanks for the additional info and pointers!

Since my buildup is planned to go into a stick-shifted drag car, I'll try to figure keeping the valve-to-piston clearances near the .120".

I now have obtained the compression height value for my pistons; 1.420". So, if I'm figuring it correctly - if I take half of the stroke, 4.14"/2 which is 2.07" and add it to the rod length of 6.80" and the compression height of 1.420"; I figure I'll have a stacked assembly height of around 10.290". My finished deck height is 10.315". So - I figure my slug should be about .025" below the deck at TDC. Then given a compressed gasket thickness of .041", I should have a combined .058" clearance to the head surface. Does that sound right?

Now, if I can only determine how far below the Edelbrock aluminum head surface the valve will extend, using 1.73 rockers and the fat .726" lift cam...... Hmmmmmm, any ideas, guys?
Thanks,,, Ryan


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Steve
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209.140.200.237 The facts
No score for this post April 3 2001, 11:33 AM

Got some facts. Just assembled my 466 this Saturday-Sunday and ran it. 466 SCJ block .010 deck height, SRP Sportsman FT's with valve reliefs (same as your JE's). Run 6.605 Eagles, 3.850 crank (chank). Run DO0E heads with 2.25 intakes and 1.60 Rockers on a Crane solid roller (with .720 lift with 1.70 rockers) and .672 lift with 1.60 rockers. Run .060 copper head gaskets. Cam installed straight-up. Piston to valve clearance was .170 intake and .220 exhaust(measured with clay). A mile.

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Walt Barnes
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12.36.108.21 Can you estimate...
No score for this post April 3 2001, 2:59 PM

I'm a big fan of facts! Especially on something like this. But, having said that, can you make an estimate? Does this tell us ANYTHING about what a stock 70/71 CJ short block might support?

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Steve
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209.140.200.121 No
No score for this post April 6 2001, 11:37 AM

Walt,
I dont know anything about the reliefs in a stock CJ piston. My engine is stock shortblock with the exception of the .060 gaskets, which would give .020 more clearance than the stock .040 gaskets. Besides that its simply a valve relief comparison. Mine are .250 deep.

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Bigd
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24.160.144.58 for what its worth..............
No score for this post April 7 2001, 4:59 AM

put together a longblock month or so ago........ dove-a 2 bolt block, 429 crank, 6.605 cj rod, trw L2366 single valve releif cj piston. Dove-c heads 2.19 intake,1.76 exhaust, CAM solid comp 249/264 @ .050 .588 lift both sides, installed straight up, piston to valve clearance intake .140 exhaust .120. just trying to help......... BIGD

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Mike R.
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4.54.206.203 Cam specs
No score for this post April 7 2001, 10:44 AM

Hey Big D, is that a custom ground cam? I like those specs. It's hard to find a cam with that wide of a spread between intake and exhaust duration, but I believe that will work really well with these 385 series engines with iron heads. I'm planning on getting a cutom ground roller with around 14-18 degrees spread between intake and exhaust duration.

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BIGD
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24.160.144.58 Yes it was kinda......
No score for this post April 7 2001, 11:52 PM

It was a comp cam flat tappet solid using there MA(max area lobes) out of the back of the book, it goes along with the previously mentioned shortblock, dove-c heads intake gasket matched 308cfm, exhaust heavily ported 207 cfm. The split duration was made to help the exhaust achieve approx 70% intake to exhaust. What I was told was the MAX area lobes help out when u have a smallish head flow or small carb, kinda like a restricted winston cup engine of sorts.Im not a guru at this but the person who had the cam custom ground for this seems to know whats goin on......... this combo is gonna have a edelbrock torker II(hood clearance issues) and 800 DP, and go in a 69 falcon with toploader. You met the person that the car belongs to in columbus at the swap meet........ BIGD

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Mike R.
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4.16.193.113 460
No score for this post April 8 2001, 12:26 AM

I suspected that was the 460 you were describing. David said it had a unique cam that should perform really well. Real nice guy by the way. He mentioned you were working on a much more radical engine and from the sound of those aluminum heads you have it sounds like a good one. If you don't mind me asking, what are some of the particulars of your new engine (cam, intake, cubic inches, etc.). If I remember correctly you have the 70 torino with the wide ratio toploader and the 15x8 magnums, etc. I'd be interested to hear about how things are coming along. If you'd rather e-mail me, I'm at [email protected]
or
[email protected].
 
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