Thread: Cam Choices

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Originally Posted by techinspector1

dcurtis, here's your homework assignment. Call the cam grinders of the cams you have chosen and get me the intake closing point @ 0.050" tappet lift. Let's try to get this right the first time so you're happy with the outcome.

The xtreme energy 274 has intake open @9, intake close @41, and the exhaust open @52, and close @4.
will get the other cam in a minute.

Just tried to call the lunati phone numbers on holley's website and none of the numbers will work. So I will have to find them some other way.

Just found a 350 build that used the voodoo cam and it made 437 ft.lbs tq at4200rpm's and made 411 hp at 5800 rpm's, they had 9.6 to 1 compression, a crosswind intake and a 750 holley, also ran a 2400 stall.

I think since I have lots of time to finish the engine I will just save my money for a while and get some world products or some dart iron eagle heads, or whatever manufacture has a descent set of heads at a descent price, don't want to go over $800.00 for a set, and will probably get some with between 170cc and 180cc runners, still need cam help but another question is, if I run a set of 4 valve relief flat tops, what chamber size would I need to get around 10 to 1 compression, because thats about where I want to be compression wise, where would 64cc or 67cc chambers get me with a standard deck 350 and a .040 thick gasket?

Originally Posted by techinspector1

Erik, coming from you, I'll take that as a compliment
You may have noticed that I don't respond to every thread, because my area of expertise is limited to certain areas of car building, but I'm pretty sure that engine combinations is one of those areas.
You know that I value your knowledge and opinion, do you agree that I'm giving the correct advice in this instance, or is there something different that you would advise?

We where only five degree's different on our cam recommendations.
I would recommend that he favors the exhaust by 6-8 degree's.

Here's the calculator for KB pistons that I have used many times to get close on a combination.....
http://kb-silvolite.com/calc.php?action=comp

Use the following values:
Cylinder head volume 67
Piston head volume 5
Gasket thickness 0.039
Gasket bore 4.100
Cylinder bore diameter 4.03
Deck clearance 0
Stroke 3.48
Rod length 5.7
Intake closing point 56 (the calculator uses the actual intake closing point @0.050" tappet lift plus 15 degrees, so add 15 to 41 on the Comp 274 cam and you enter 56 into the calculator. When I first began using this calculator, we settled on 8.00 to 8.25 to 1 DYNAMIC compression ratio as a figure to attain for pump gas. Since then, I have been advised that these figures are valid, but that the KB calculator is a little on the conservative side. So, I think if we shoot for 8.4 to 8.5, we'd be a little closer to reality with this particular calculator.

Plugging in the values, we get 10.046 static compression ratio and 8.536 dynamic compression ratio. This is using 67 cc heads, flat-top pistons with 5 cc's of valve relief, zero deck (piston crown even with the deck at TDC) and a Fel-Pro 1074 or similar gasket that compresses to 0.039".

You can play with the calculator and enter different values to find the results, but I would shoot for somewhere between 8.4 and 8.5 dynamic compression ratio no matter what combination you use.

The other thing I would advise is to shoot for 0.035" to 0.040" squish. I have shown this build with zero deck and a 0.039" gasket for a squish of 0.039". You can achieve the same results by juggling the deck and gasket thickness. For instance, you could have a deck height of 0.024" and a gasket of 0.016" for a squish of 0.040". Or you could have a deck height of 0.012" and a gasket thickness of 0.028" for a squish of 0.040" It doesn't matter how you get there, as long as you get there. Without this tight squish, you'll never get the motor to operate properly on pump gas.