would like to get anybody and everybodys opinion on this cam for 390 4v, 10.5 compression, headers, c6 with all the goodies f100 4x4

 

I hope you like buying race gas!

Read this article, and look at the chart comparing dynamic compression to octane requirement toward the bottom:

http://www.popularhotroddingweb.com/...power_squeeze/

Then, without closing that, use this calculator:

http://www.kb-silvolite.com/calc.php?action=comp

The proper number to use for "intake closing point" for that cam is 56.

I think you'll see what I mean. I think what I'm saying here is, bigger cam or lower compression. Unless of course you're building a race motor using race gas, in that case go for it!

I'd still like to know why everyone thinks their motor has 10.5:1. Just because that's what the pistons say doesn't mean that's what you'll get. Go use the calculator.

 

rusty
thanks for the input and the links makes for good brain fodder
and to just clarify the compression ratio mater i did not say that i had 10.5 pistons
i was reffering to what ford published for the engine that i have
325 hp 390 ci 10.5 ratio 1-4 Holl carb 1.73 rr H lifter 63.50 head cc 1968 ford fairlane now i haven't done the math on this engine so i can neither confirm or denie the compression ratio just going by what the guys back in 68 said it was thanks agian

 

Call up Comp and find out what the intake valve closing point is for your cam. They used to have it on their web site, but now its top secret. Be careful, even their cam cards have typos on them. Real quality control.
Using the KB DCR calculator:
Cyl head vol=63.5, piston vol=10, gasket=0.04 (felpro), gasket bore=4.2, cyl bore=4.08 (0.030 overbore), deck clearance=0.01, stroke=3.78, rod=6.488, intake closing guess=70 abc (after bottom dead center, NOT 0.05 event). RESULT is static compression = 10.56 and dynamic = 8.0:1. This will run on regular gas at elevation of Sharidan. Now the problem is the quench is not good at 0.04 for the head gasket and 0.01 for piston below deck for a total of 0.05 clearance. So deck the block 0.01 to 0.015 to drop quench clearance between piston top and cylinder head to 0.035. This would be real good quench gap. Now we need a piston volume of 14 CC to drop dynamic compression back to 8.0:1, or choose a different cam with an intake closing point that is later (hotter cam) to drop the dynamic compression back near 8:1 which in D. Vizard's book is about the max for non-premium pump gas. Compare the required 14 cc to a stock 9.5:1 piston. Silvolite offers this in a cast piston. Both pistons have a flat surface around the piston recess to act as a good quench pad. If you need to cut the piston recess deeper, make sure to leave about 0.200 minimum piston top thickness at bottom of recess. I had to increase the piston recess volume on my 416 cid to 17 cc. Just chuck the piston up in the lathe, leave as much of the outer flat portion of piston top as you can to get the cc's you need, without violating the minimum piston top thickness. On my engine, I have 9.5 static compression and 8.0:1 dynamic. Runs great on regular gas pulling trailers or hauling 1 ton loads in the box. Truck is 67 F250 4x4. Put a good ignition system on it too. I started with Ford duraspark and switched to DUI. Starts even quicker now. JMO, hope this helps.

 

The compression is lower than ford says, don't worry about that. I personaly have thought hard about the 274ex, but i feel it is big for an automatic 4x4 truck. If I were to use it i would either get 4.10's or a stall.

I wish comp had a camshaft between the 262 and the 274.

 

FEmtnmax
thanks for the input thats why i posted it here because i needed more insite than just myself and the trash that i hang with now just a little somin somin on the old 390 i have it only has 70,00 miles on it so it will stay stock bore old pistons look good mesure good but i have a set of flat top trws that are still in the box so i guess i need to get them out and do some mesuring thanks agian and keep your powder dry
fordever i agree with you comp needs a ex cam in between but i think that my slitly lose 2500 stall converter sould work if not guess i'll have to figure out how to make that transfercase up to that t10 i have laying around

 

that stall probaly lets go at 2000-2100 right? That should work, the 274 isn't a whimpy camshaft.