This car is really starting to tee me off. I recently installed Stage 1 heads on my 455 and it's been all down hill since then. Before this transformation I used to use regular 87 octane all the time now I have what I think is spark knock on 92 octane, it's kind of a low toned hollow sounding rattle at part throttle. Now these heads were cut 020 thousandths which should raise the compression about 1/2 a point, she's already got 9.3 hyper eutetic pistons but the blocks never been cut so the compression should be lower than 9.3 to start. Its also got a Poston GS116 cam in it which with its overlap numbers should raise cylinder pressure at low engine speeds. Did I mention that this engine is running very poorly at idle and cruise but seems to pull hard at full throttle? I finally put a vaccum guage on it tonight and it's almost a blur ranging from 16 to 18 psi, my books with pictures and detailed explainations do not describe my exact situation and I am at a loss here. I really want this car running right but am running out of patience here! Please help!!! Dave Berryou: ou: ou: :rant:
sounds like you know your way around a buick much better than me, but here are a few questions I would want to answer before I poured the sugar in the tank.
Hit the wrong key, permit me to continue Did you radius combustion chamber surfaces after head milling? Have you checked distributor for proper advance? Is carb. leaning out. ( this is the only thing that made my buick ping) 71 and newer Qjets were calibrated pretty skinny, especially @ idle and part throttle. Isn't negative atmospheric measured in HGs? 7 of which, I have heard, are ideal for a streetable motor
Dave, First thing I would check is spark advance curve. How much total advance do you have, and are you running vacuum advance? I've heard of guys running on 87 octane. I don't know how they do it, I can't, no way, my engine would do a cheap immitation of a diesel. With a low overlap cam, you do indeed build more cylinder pressure. This would make an engine more likely to detonate. Any hot spots in the cylinder will make it ping. Polishing the combustion chamber and piston tops, and 0 decking the block all help an engine run on lower octane. Too hot a plug will also contribute to detonation. Whenever you change something in your combo, you will have some tuning to do to optimize things. I would start with the obvious thing the timing. My engine likes 30* total. That's all it wants and needs. Some other guys run 34, 36, or even 38. See what your engine needs now that you have changed things.
I believe you are correct that vaccum is measured in inches of mercury. No I didn't radius the combustion chamber edges after milling and the carb is a John Osborne Q-Jet set up for my cam and other engine specs. By the way tommyodo I'm from southern Illinois also just a ways north of Saint Louis. Larry I normaly run 12 degrees inital with 16 mechanical in the distributor thats all in at 2000 RPM, no vaccum advance. I tried to power time it like some people do, adjust ignition to the highest vaccum reading which did take the flutter out of the vaccum guage and it went to 19 HG but the starter wouldn't turn it over it was so far advanced. Does anyone know a site that really explains how vaccumcan be used to diagnose a tunning problem? Something like Vaccum for Dummys!! Dave Berry o No:
Dave, I'm surprised you stuck with that cam, after the crappy dyno pulls I got with it I jerked mine,(went to TA290-94) made a monsterous difference in the engine, with just the cam change and going to a small body hei conversion I picked up 50hp and instead of nose diving after 4400rpm I continued to make power all the way 5000. I took some measurments off that cam when I pulled it, it was the most inconsistent POS I've ever seen, base circle measurements were as much as .050" different from eack other, and no two lobe hieghts were the same. Not that the cam is your problem, kinda sounds like a bad plug wire.
Hey Dave, Good to know you are nearby. I have a bunch of extra pieces I need to get rid of Cheap. I am presently putting a 72 stock 455 back together to go into an 84 LeSabre Ltd. I am putting a newly turned 10-10 75 crank w/ 75 rods and pistions. For some reason these pistons came with dishes that measure, in dish depth, the same as early high compression pistons. Go figure. I run Holley 650 DP Spread bore, 75 hei w/ autozone $5.00 curve kit (brass springs), stock exhaust w/ 2 1/4 turbos dropped infront of axles The car i am putting the motor in came with a 8.5" rearend and 4 3/4 on 5 axles. I put a 3.23 posi out of an old cop car w/ 5 on 5 bolt spread. Will be changin out axles tomorrow. I use a T400 w/ TransGo stage II shift kit. This combo w/deeper dished pistons in the car pictured to the left handled Mustang GTs and SS Impalas like they were tied to trees. Gonna be selling all this stuff plus extras for under $2500. Let me know if anyone in the neighborhood is looking. tom
