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Discussion Starter #1
Tell me what you guys think, and if some1 can desktop dyno this for me...that would be great.
383
forged 4340 3.750 crank.
forged 5.7 h beam rods.
11.1 flat top forged pistons.
comp cam 292h cam.
Aluminum heads, 64 cc 2.05 and 1.60 vavles 210cc intake runners.
weiand team g intake manifold.
70 cfm carb, should i go double pumper or vac sec? manual trans.
4 speed manual trans.
4.10 gears.
hei dist.
6al ignition.
Going into a 1973 camaro.
Do you guys think 11.1 would be too much compression with pump gas, i dont think so because of the cam im running and the heads, but i may be wrong so let me know.
Thats alot guys, I relly appreciate all the help that im receving, Im a 20 year old kid just trying to fit into the hotrod sceen instead of the imports like all the other young guys.
let me know if i left anything else out.
 

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I had a very similar motor and it ran pretty well. The car was a 1989 firebird. It was right at 11:1 and ran fine on premium with less cam than you are looking at, but I would look at ~10.5:1 just to be safe. Below is my motor and what it ran.

383
11:1
xr288hr hyd roller cam (236 242 @.050 .520 lift)
victor jr intake
AFR street ported 210cc heads

it ran a 7.85 in the 1/8th mile (around a 12.3 in the 1/4) at ~3600 lbs

That was also through a really restrictive exhaust system. (1 5/8th inch shorty headers into a single pipe with 2 mufflers.

That was a mismatched combination and the motor has been rebuilt as a 406 (248 254 @.050 .600 lift solid roller cam). It will soon be back in the car, and I will post its new times.

Last thing, with the cam you are using, you could go with a set of 195cc heads instead. They will pick up some low end power and should not give much up on the top end.

Adam
 

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Well, runnin' it through the KB Dynamic Compression Ratio Calculator shows a DCR of 8.937:1

That's figurin' an intake closing point of 48 degrees ABDC. I figured that backwards from Comp's info, but I could be off a little. Call Comp and ask if the intake closing point is actually 48 degrees after bottom dead center @ 0.050" tappet lift. If it is, I think you're a little too high on the static compression ratio or a little light on the cam for pump gas. Either way, set the motor up for a squish of 0.035" to 0.040" to make it more octane tolerant.

If Comp gives you a different closing point for the cam, please post it on here and we'll re-figure the DCR.
 

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Discussion Starter #4
What if i went with a 10.30:1 piston instead, or even a 9.70:1? I think the 292 cam would do really well with my setup because of the 4.10 gears and the 4 speed rock crusher. but ill call comp cams, thanks guys
 

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It's not a matter of the rear gears or the transmission, it's a matter of the static compression ratio and where the intake valve closes to begin compression. It's a balancing act when you are planning to build a motor. If you close the valve too early for the available static compression ratio, the motor will detonate on pump gas. If you close the valve too late for the available static compression ratio, the motor will be down on power.
 

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techinspector1 said:
Well, runnin' it through the KB Dynamic Compression Ratio Calculator shows a DCR of 8.937:1

That's figurin' an intake closing point of 48 degrees ABDC. I figured that backwards from Comp's info, but I could be off a little. Call Comp and ask if the intake closing point is actually 48 degrees after bottom dead center @ 0.050" tappet lift. If it is, I think you're a little too high on the static compression ratio or a little light on the cam for pump gas. Either way, set the motor up for a squish of 0.035" to 0.040" to make it more octane tolerant.

If Comp gives you a different closing point for the cam, please post it on here and we'll re-figure the DCR.
The advertised or "seat-to-seat" valve timing events for the standard 292H are:
IVO IVC EVO EVC
40 72 80 32
LSA 110
Intake centerline 106

Use the actual IVC of 72 degrees ABDC in KB's calculator for better results.

If you use KB's suggestion... "Intake Closing Point (degrees) ABDC @ 0.050 lift plus 15 degrees" you get 63 degrees ABDC which is short and gives the impression of too much compression or too little cam for the combination.

I prefer the DCR calulator at the bottom of this page http://members.uia.net/pkelley2/DynamicCR.html
 

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Discussion Starter #7
71C10 said:
The advertised or "seat-to-seat" valve timing events for the standard 292H are:
IVO IVC EVO EVC
40 72 80 32
LSA 110
Intake centerline 106

Use the actual IVC of 72 degrees ABDC in KB's calculator for better results.

If you use KB's suggestion... "Intake Closing Point (degrees) ABDC @ 0.050 lift plus 15 degrees" you get 63 degrees ABDC which is short and gives the impression of too much compression or too little cam for the combination.

I prefer the DCR calulator at the bottom of this page http://members.uia.net/pkelley2/DynamicCR.html
Thanks guys for helping me unerstand this, can someone try to point me towards a better cam if i were to use the 10.30:1 pistons?
 

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I am interested in what the other guys say, but it seems to me that 10.3:1 with the 292H should be not problem at all. Also, what heads, exactly, are you looking at. The flow pattern of the head can also help with camshaft selection.

Adam
 

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73camaro said:
Thanks guys for helping me unerstand this, can someone try to point me towards a better cam if i were to use the 10.30:1 pistons?
If you're committed to using a hydraulic cam I'd look seriously at the Voodoo LUN-60105LK.
https://www.holley.com/data/Products/Technical/60105.pdf

If it was my engine I'd use a solid lifter cam of similar duration at .05".

I'd also use a mechanical secondary carb.

What heads are you using?

You've completely neglected the third leg of Smokey Yunicks power triangle.
 

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"I prefer the DCR calulator at the bottom of this page http://members.uia.net/pkelley2/DynamicCR.html"


Thanks for the link.

Adam
 

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Discussion Starter #12
the heads are procomps 64cc,210 cc intake runners. IM sending them out to the machine shop to double check everything, he said i mine as well go with higher cr and run higher octane gas.
 
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