any recommendations for what octane to use with an engine that has dynamic compression of 9.52. thanks craig
what car is it in? converter? Cam specs? what timing and ignition? What cylinders heads and cc's? Run the lowest oct you can run before it pings.
my car is a 3600# 71 skylark, 430, 3800 stall, hei ign, 62cc iron heads,zero decked, old version KB-107 cam, with 34* total timing , cylinder pressures are @ 210. i think i need 110 octane . any input much appreciated
I ran 93 pump gas in my Drag Week car no problem. 10.7 compression and solid cam equivalent to TA's 308. 5000 stall converter.36 degrees timing. David
I wish people would learn from people like you since you have done proven it does work, exspecially on a one week drag racing at several different tracks and traveling over a thousand miles to boot. But they will never learn nor will they listen. Are you attending this yrs drag week?
That's pretty high dynamic compression. My motor is 13:1 static with TA heads, .040 gasket, 3cc valve notches 5 in the hole. I get 8.2:1 dynamic compression with the 308S cam. I drive around on a mix and race with 110. What cam are you running?
How did you calculate 9.52 Dynamic compression? What is the static compression? The KB 107 cam had advertised specs as 320*/322* with a 107* LSA. Assuming an ICL of 103*. As near as I can figure, you would have to have 14.5:1 static compression to see 9.5 DCR. I don't see how that is possible with a 62 cc chamber and 0 deck. What pistons are you using? Dish cc's?
Pistons are 22cc dish. The static compression is at 10.6 . The KB 107 cam duration is 240 int/262 exh @ .050. Hope these numbers help. Thanks again Craig
The problem is that when trying to calculate DCR you're mistakenly using the cam's valve timing events at 0.050" valve lift usually listed on the cam card. Instead you need to use the advertised intake valve close point so you can see when the valve is truly closed. If you don't have it, the only way to find it is to put a degree wheel on it. edit: according to http://www.v8buick.com/showthread.php?t=65890 , the advertised close point is 93 degrees ABDC. If this is correct, your DCR is around 6.3:1 which should be fine with pump gasoline. It all depends on the accuracy of the info. Devon
I used the same DCR calculator I always used. http://www.empirenet.com/pkelley2/DynamicCR.html I assumed a 430 bored .030 over with the KB MarkC107 cam installed 4* advanced at a 103* ICL. With a 4.2175 bore, 62 cc chamber, 22cc dish, 0 deck, and a .040 head gasket, I get 10.55:1 SCR. My KB catalog says the KB Markc107 cam has advertised duration as 320*/322*, with a 107* LSA. Using those specs in the calculator, I get an intake closing angle of 83*, resulting in a Dynamic Stroke length of 2.477, and a DCR of 7.06. This engine should run on pump gas. I don't understand why the cylinder pressures are so high though.
I knew these guys could help :TU: "cylinder pressures" This was a compression test? I have a solid cam similar to 308, I forget what we set it at for cam timing? But after we figured out that the motor is at 10.7-1 it was going to be a pump gas motor. That was planned. Alum TA stg 2 TE's. My compression tester says 161lbs. ? Maybe try a buddy's and see what changes?
240-262 @ 50 doesn't seem right to me to be 320-322 adv.20 degree split @ 50 is only 2 degree differance @ advertised? Jamie
That's way I have Several cam companies I call to get the true DMC Dynamic compression, I have better things to do then do stuff like that, Here is a hint, Call 248-674-4967 at LSM Systems Engineering and ask for either Steve Sr or Steve Jr and tell them what you have and the info on the cam and they will spit out your actual compression and dynamic compression within a half point and they will tell you if you can run on pump gas or not, then again you can keep going on with this guy's if you like. Oh by the way Mike Moran's new Mutt of a engine is using a LSM systems engineering cam and the engine is a 550 CID that is going to be supporting over 3000 hp that's all:shock:. I learn from the best not the rest.
