Many of you may remember my quest for help this spring, but have a little more info on my car that may change suggestions on where to go from here. Many felt that my cam was too much for what I had done and that it should be pinging like mad. After installing intake and exhaust from Gessler & adding the 2 1/2" exhaust, it still hardly pings on pump gas. uzzled: Here are engine specs. 70 Olds 455 Turned an balanced factory crank Zeroed the deck 2260+.030 forged alum flat top pistons & 3200 Zero gap rings Double roller timing chain Race cam bearings JM-3-4 cam & lifter kit / (cam specks = Intake 326 lift 230 duration / Exhaust 338 lift 240 duration @.050 / lobe centers 110 ) Installed at zero degree E heads port & polished & 2.072 x 1.680 valves installed Intake by Gessler W/Z Exhaust manifolds by Gessler 2 exhaust Hemi Walker mufflers I have run a compression test on it cold with carb cold & closed and averaged between 215-230. Second test was warmed up with carb open and averaged 228-235 lbs. I currently have a factory Rochester untouched on it. Sooooo, what do you think of the cam now, compression, & what should I do to carb.?
I think that there is some misunderstanding with respect to what causes ping. The cause of ping is heat. Whether the source of the heat is the combustion chamber is the cooling system, compression or excessive advance, the cause is heat. It appears that the shape of the combustion chambers will allow more advance, or ping would be the result. I would first be sure that the advances operate correctly, and are correctly sourced to vacuum. Normally, a rich mixture will ping before a lean one since the flame travel in a lean mixture is relatively slow. I do not know the particulars with respect to the distributor's operation, but I would leave the carb alone if it is working well. Set the advances before messing with the carb, since breathing will affect the carb's settings, and the advances will affect the breathing. Start with the advances, and be sure of the settings before we continue. I suspect that the distributor has a problem. Can you tell me what the manifold vacuum is at idle? Let me know... Ray
I took a guess at the pistons, Mondello's site shows 2060 pistons for 455 as having a 14 cc dish, and about 9.7:1 compression w/80 cc heads. So they aren't flat-tops. http://www.mondellotwister.com/PisPinRingBrng.htm With that cam, I suspect your compression tester is optimistic. Have you verified the accuracy of it's pressure readings? Middle 9's for compression and a borderline mild cam shouldn't ping. Don't know why you'd expect it to ping, except that Olds has a crappy chamber with little squish. Curve the centrifugal and vacuum advance, verify fuel mixture, and you should be OK.
I'm sorry I have not gotten back sooner. My mother, 79, had a heart attack this last week end and I have been real busy with her. She's doing alright now. Schurkey; I have not checked the accuracy of compression tester, as it is new. It may be off though. I'm not saying you are incorrect, but how did you figure the heads at 80cc? They are the E heads worked over by Mondello. Will that make a difference? Ray; You are right about distributor. I have not touched it yet. I agree on the advances. I will have to check vaccum at idle when I get a chance. Thanks for your replies! Dale
Hope your mother is doing OK. http://www.442.com/oldsfaq/ofhed.htm scroll down for guesstimate of chamber cc My limited experience is that the heads have larger chambers than listed. Which accounts for Olds' overly optimistic compression ratio advertising. In short, if you don't cc them, you have NO IDEA.
