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Will I have enough valve to piston clearance ?
#1
I have a 72 351 CJ motor that I am assuming right now it has stock pistons in it.  Note that I am going to confirm the pistons when I pull the heads to have them machined for studs.  I will also do the clay check method for checking.  Right now I just want to get a rough idea if the cam that I have will be ok from a clearance standpoint with stock pistons if that is truly what I have.  The specs of the cam are Advertised Duration 299/319, Lift .579/.563.

https://www.summitracing.com/parts/cca-3.../make/ford

Thanks
Wade

Thanks!
Wade
1972 Mach 1 351 cj 4speed
"We confide in our strength, without boasting of it; we respect that of others, without fearing it."--Thomas Jefferson

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#2
I thought the compression ratio was dropped quite a bit in 72.

My wild guess is that clearance isn’t going to be an issue, but that unless you do something to raise your compression ratio that camshaft is going to lower your dynamic ratio down into the weeds.  You planning on new pistons?

Once you get everything apart consider measuring deck height, piston and chamber volume...
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#3
(01-13-2019, 11:31 AM)Bentworker Wrote: I thought the compression ratio was dropped quite a bit in 72.

My wild guess is that clearance isn’t going to be an issue, but that unless you do something to raise your compression ratio that camshaft is going to lower your dynamic ratio down into the weeds.  You planning on new pistons?

Once you get everything apart consider measuring deck height, piston and chamber volume...

The motor was rebuilt by the PO so not sure what is in it other than a very mild cam.  I am just guessing they are stock pistons right now.  If they are stock pistons is there a way to raise my compression ratio?  Im trying real hard to use this cam sense I got it from another forum member and it will be a good lopey sound.

Thanks!
Wade
1972 Mach 1 351 cj 4speed
"We confide in our strength, without boasting of it; we respect that of others, without fearing it."--Thomas Jefferson

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#4
The cam is way too aggressive based on what you have said about the overall build. Find a local Ford engine builder with 351C experience to help you select parts that complement each other. Chuck
[+] 1 user Likes c9zx's post
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#5
(01-13-2019, 12:53 PM)c9zx Wrote: The cam is way too aggressive based on what you have said about the overall build. Find a local Ford engine builder with 351C experience to help you select parts that complement each other. Chuck

+1

The 72 Q-code compression drop was accomplished with the open chamber heads only. The 71-72 Q-code shared the same cast flat top pistons as the 70-72 H & 70-71 M code engines. Dished pistons came in '73.


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#6
If you have stock pistons and open chamber heads your static compression ratio is 8.6:1. This is about where you want your dynamic compression ratio to be with that cam. You will need a static compression ratio of around 11:1 with that cam to be effective and have a decent dynamic compression ratio.

The cam manufacturer usually has a list of things that are needed to make the cam work, like compression ratio, transmission type and/or torque converter stall, rear end ratio, and so on.

Flat top pistons and open chamber heads will only give you around 9:1 compression ratio. You will need domed pistons to get your compression ratio up enough to use that cam.

You'll definitely have the lope with that cam, but your power will likely go down, not up. Driveability (throttle response) will also suffer.

You can use the camshaft selection spreadsheet in this thread to give you an idea of a starting point for selecting a camshaft for your engine and car, and to play around with different values to see the effects. The, carefully read the cam manufacture's recommendations.
https://www.7173mustangs.com/thread-cams...#pid278395



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#7
A cam suited for your engine is only around 200 bucks. No sense to use one just cause you have it. You will be disappointed. If possible do like Chuck suggested and find a machine shop that’s familiar with Clevelands. Good luck with your build!

run_horse Run Horse Run!
John 72 Q Code
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#8
I was afraid you guys were going to say this.  I really wanted to have a roller cam and having this one made it a little more affordable.  I may still go roller cam but it will knock the completion time back since I have to buy a cam now.  I could do a piston swap but by the time I buy pistons, rings and machining I could pay for a roller.  There is a guy on the Cleveland forum that a lot of people go to for custom ground cams.  I will get with him once I have pulled the heads and see what heads and pistons I have.  I am betting stock flat tops.

Will I be able to get a really aggressive lope profile if I do have the OC heads and flat top pistons?

Thanks!
Wade
1972 Mach 1 351 cj 4speed
"We confide in our strength, without boasting of it; we respect that of others, without fearing it."--Thomas Jefferson

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#9
(01-14-2019, 07:09 AM)scgamecock Wrote: There is a guy on the Cleveland forum that a lot of people go to for custom ground cams. 

Will I be able to get a really aggressive lope profile if I do have the OC heads and flat top pistons?

who is it?

you also need to match the cam with stall converter if it has an auto trans, and to the gear ratio and intake etc.
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#10
Yes you do want to check the clearance but stock cam or comp cam should clear. The valves are closed when the piston is up unless they are pushing the limit on cam profile someway.
My car has flat pistons with the eyebrows.
There is a gain from cam change without having pop up pistons. More fuel air means more power yes the burn might not be as good but will be more performance.
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