This engine has the stock cast 76cc heads with the ports lightly smoothed out and your basic felpro head gaskets. I am running the flat top cast pistons. This engine has just under 20K miles on it. I think it is detonation I'm hearing. I seem to be able to hear it now with my flowmaster exhaust. (It seems I can kinda hear it through the exhaust). I am planning for and trying to save up for some s/r torquers and a bigger cam for hopefully next spring. I'm planning on the comp cams xe262. The cam I have now is the crane energizer cam w/ .440 lift and I think its 260 duration I'm not sure of the @ .050 dur. When I built the engine, I didn't measure how far down the bore the pistons are. At that time, I didn't know anything about the DCR and I asked for 9:1 pistons and don't know if these pistons were manufactured a little further down than desirable or not. I can only guess at my measurements. Right now, What I can figure from my guesses is my DCR is around 7.4:1 to 7.5:1. When I was considering heads for the future, it was either the vortecs or the world s/r torquers, but, I think the vortecs would make me have to run a lot more expensive fuel because of going to a DCR of around 8.5:1. The total advance of 26 you have doesn't include how much advandce the weights and springs add. I'll have to check how much those add, but from memory, I think total was around 48 degrees.
Brian Zack '70 Chevelle Malibu mailto:[EMAIL PROTECTED] -----Original Message----- From: Capt Crunch [mailto:[EMAIL PROTECTED] Sent: Wednesday, November 26, 2003 9:02 AM To: [EMAIL PROTECTED] Subject: Re: [Chevelle-list] Detonation question Brian, Did this dentination just start? I assume you hear it? First off, when we talk detination, static compression means very little. You need your cam specs and then you can detirmine your dynamic compression ratio, which is what ultimately detirmines what fuel and timing you can run. The second thing I ask is if this is a newer combo what heads do you have? How far in the hole is you piston at TDC (some call this deck heighth) and what head gasket are you using? This will detirmine your quench distance which is crucial in avoiding detination. Head design makes a big difference. A newer heart shaped chamber can run a bit more compression with out detintation. Also are you running a cast or alum head? Again alum can take much more. If you have this info and send it my way I can do some calculations and get a better feel for what your combo should need. What engine temp does your engine run at when it detinates? For working with what you got... more fuel will help with detination so I would fatten it up. I would also highly recomend running the premium grade and seeing ifthat helps. Your timing isn't much if you are running 10 and 16 for a total of 26 degrees so I doubt that is your problem. I'm not real experienced at running at the altitude you are. I'm sure this plays a role in things as well. Send out a bit more info of when this all started and your specs and I will see what I can do. Mikey >From: "Brian Zack" <[EMAIL PROTECTED]> >Reply-To: The Chevelle Mailing List <[EMAIL PROTECTED]> >To: <[EMAIL PROTECTED]> >Subject: [Chevelle-list] Detonation question >Date: Wed, 26 Nov 2003 08:28:16 -0700 > >What are the things to look at to avoid detonation? I have a 350 w/ 9:1 >compression and a pretty mild cam. I run the med grade fuel. If I am >getting some detonation under load, Do I need to look at timing, fuel >mixture, jetting? I am at around 5000 to 5500 ft in altitude. I have a hei >dist. w/ the pertronix kit and am running 10 degrees initial timing the >factory setting on the adjustable vac. advance (I think its 16 degrees) and >the lightest springs on the weights (The weights and springs came with the >kit). At the strip trying to tune it, I had to use the lighter springs >otherwise, my times were around a � sec. slower with the heavier springs. >The carb is the edlebrock 600 cfm elec. choke and I put the 1 step leaner >primary rods in. No actual jet changes. As far as going to the strip, I >don't think I can make it out again til next year, (I think it already >closed) so tuning there won't be an option. Right now, I do only have the >2.73 gears and 28" tall tires, which is probably contributing to the extra >load condition. Any opinions? > > >Brian Zack >'70 Chevelle Malibu >mailto:[EMAIL PROTECTED] > > _________________________________________________________________ Set yourself up for fun at home! Get tips on home entertainment equipment, video game reviews, and more here. http://special.msn.com/home/homeent.armx
