Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
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theres quite a few flat tops with valve reliefs for 5 cc which makes 11 to 1 compression on 64cc heads. Which is fine for aluminum heads and pump gas with 230 degree cam or so... recipe for 450-500hp there.
Further dish would be in the 12-16cc range i think.
The only 7cc flattop i've seen is by Keith Black, 7cc 383 piston for 6" rods.
KB122 thats the part number
I will use the XFI280 cam and the DCR will be appr. 8.5 . From a lot of reading that I´ve made it seems lika this is really borderline for pinging on non race gas.
Maybe you have hands on experience from this cam?
I´ve read plenty of your posts and you have built some real good motors.
I ran 11 to 1 compression on my 383 with AFR heads and a cam that made DCR around 8.3 to 1 and had no problems. I think if you run a good aftermarket head that has a good combustion chamber you will be ok with that cam and 93 oct gas. You wont need much timing anyway with a good head. I ran 34 degrees total all the way up to 39 and didnt see any gains above 34. So i ran 34. On the dyno I started high and worked my way down to 34 and it seemed to make more torque the lower i went
If in doubt, go lower on the compression. Flattops are usually around 5-6cc total dish. Next step down is usually about a 12cc total dish volume.
You can tune anything to work, but you'll make more power with slightly lower compression and optimized timing than you will with too-high compression and timing dialed back to keep it out of detonation.
Do you think it would be better to go with a 12cc dish and end up with SCR 10.2 / DCR 7.9?
My setup is/will be: Shortblock with 3.75" stroke, 6" rods, pistons?, Brodix IK180 heads, XFI280 cam, HSR intake, 58mm TB, Hooker 2055 headers, dual 2.5" exhaust.
I will also run up to 150 hp N2O.
My previous setup 350 with flat tops and XFI268 did 12.06s / 119mph (100hp N2O)
Next seasong I would like to be well into 11s
Do you think it would be better to go with a 12cc dish and end up with SCR 10.2 / DCR 7.9?
I calc your combo with 12cc pistons; DCR of 9.3 (w/.040 quench )
What quench are you looking at ?
It plays a major factor in likelyhood of detonation. A higher CR engine with good quench is less likely to detonate than a lower CR one with bad quench; all else being equal
In the process of building your engine you can make adjustments to get the quench in the "sweet" spot. Zero deck the block and run a 0.041 composite gasket to get desireible 0.041 quench
"I calc your combo with 12cc pistons; DCR of 9.3 (w/.040 quench )"
When I use the Keith Black calculator http://www.kb-silvolite.com/calc.php?action=comp and a intake closing point of 69° I actually ends up with DCR 7.9 for 12cc dish pistons??
Heads are 64cc.
Which calculator are you using? Or am I doing something wrong in my calc?
Which calculator are you using? Or am I doing something wrong in my calc?
I don't like that one; it seem to give unrealistic high DCR numbers using the .050 + 15 seat settings.I personally don't believe 15 degrees past the .050 value has the valve close enough to the seat for compression to begin.
You put your engine specs in the CR Calculator
cam specs in cam timing /overlap calculator ,
then go to the dynamic stroke calculator to calc effective stroke.
Go back to CR Calculator , tick the stroke box and it calculates the DCR
Do you think it would be better to go with a 12cc dish and end up with SCR 10.2 / DCR 7.9?
My setup is/will be: Shortblock with 3.75" stroke, 6" rods, pistons?, Brodix IK180 heads, XFI280 cam, HSR intake, 58mm TB, Hooker 2055 headers, dual 2.5" exhaust.
I will also run up to 150 hp N2O.
My previous setup 350 with flat tops and XFI268 did 12.06s / 119mph (100hp N2O)
Next seasong I would like to be well into 11s
BR
No, i think just do a flat top, zero deck block with standard .040-.041 MLS gasket and IK200's with that cam. Make sure you get better springs for the heads tho, that cam needs good stiff springs to work properly. 11 to 1 compression and that cam should work out well. If your nervous about it, get comp to grind it on a 111 lsa to help get DCR down a touch. DCR is just a guideline, not a true indicator of what will run on pump gas.
That above setup should be a mid high 11 second car. 150 shot will be in the mid high 10s
14psi, pump gas street tune 
