Last week I posted a topic about helping a friend of a friend get his big cammed 350cu engine timed and tuned properly.Thanks to everyone's input we were able to get the total timing down to 36 deg and get the carb almost spot on.......

While I was helping him figure out his problems, I was asking him all the specs on the motor and what he was trying to get out of it and this is what he said....

He told his "engine builder" that he wanted a high Hp, big cam, radical street motor that would handle an occasional 100 shot of NOS and he didn't care if it had a rough idle cause it wasn't his daily driver. And this is what he got...

SB 350 bored 30 over
Edelbrock Victor Jr Intake
Comp Cam Magnum 292h cam, .501 lift p/n 12-213-3
World Products Sportsman 11 iron heads w/ 72cc straight plug bare heads p/n 955-012250
Valves (according to Dyno 2000 spec sheet are 2.02 int 1.60 exh,even though cam specs listed on same sheet are wrong)
Roller rockers are Comp 1.6
Carb is a Holley 600cfm factory replacement w/vaccuum secondary p/n 510-0-80450k
Pistons---???????
Compression ???
4:11 rear end gears
1972 GMC longwheelbase Truck

All Sp IIs have 2.02/1.60' valves. If the pistons are flat tops, the CR is around 9.38 with 72cc chambers and a .040" quench. A 292 cam is really too big for this CR. A cam of that size needs around 11:1 to work properly. For the CR he has, a much smaller cam will make a much better combo. Something around 260-262º would work great. However, it wouldn't have the rough idle.

If he wants to run that cam, he should trade the heads for something around 62-64cc then mill them to 58-60cc. That would give him about 10.7 SCR with a 8.04 DCR. The gears would be fine but the converter should be around a 3000 rpm stall.

What he has now is way overcammed.

protopline has a very nice 200cc head that has an advertised 50cc chamber(actually 54cc) which would work great with his combo

I think he will actually want to keep the heads and order another cam and a dual plane intake instead of the single plane one he has.Long wheelbase Chevy truck= need for torque I would think..

Last night I dug out a CHP Special Edition on SBC head comparison and they were saying that this head had a low exhaust/intake relationship and a dual pattern cam would better suit this head.

If we aren't sure what type of pistons he has, what's the best way to calculate what compression this engine has??

get a compression gauge. Or is it not in a car running?

The average compression of all the cylinders was about 140-150psi.I just don't know what I need to do with this number now... graemlins/clonk.gif

I agree that the cam is to much for the compression. The carb is also to small, something like a 750dp would work better. Then add a 3500 stall plus 10:1 compression this would clean up the combo. The other thing I would consider is adding a little port work to the head. I would think those changes would put him in the 425-450 hp range. My guess he is in the 350-375hp now