Hi guys, just looking for some opinions on rear end gearing, I have a 68 Goat no A/C no PB. It's a 400 #16 heads and stock cam? M20 Muncie, 323 currently, runs strong and is a older build with stock parts and does exhibit detonation.My question is would I benefit enough to justify a change in rear gears or should I wait till I rebuild the engine. In other words once I change gears would this then dictate how I would need to build the engine?Thanks in advance.
Hi Slick...It sounds to me like 3.23 is a pretty good street compromise for your car. Do you have a positraction differential? They are a must for almost any performance car, but not every GTO was delivered with them. That would literally double your traction off the line with the same tires, and contribute to a quicker launch, whether stop light to stop light, or at the track. Your description of detonation and stock parts rebuild seem to indicate you retained the over ten to one compression ratio this engine was built with, and might have even increased it if you had the heads milled for flatness, or decked the block. I had the same problem with my '68 Firebird 400 with the same engine when I first bought it. Unless you want to run race gas all the time, it WILL suffer from this problem. To run on todays 91 octane stuff, you probably need something closer to mid to low nines on compression, which might require swapping to heads with larger chambers if you want to remain with iron heads and stock appearance.I think perhaps you need to tell us a bit about what you wish to accomplish with any change. For example, if you are looking for quarter mile ET's you might wish to go to something more like the 3.90's that many of those cars were delivered with, but that will increase your cruising RPM by several hundred RPM, and impact economy, if you care about those things. If you are suffering from detonation, I think I would fix that first, which will take new heads or dished pistons or race gas. This would also be a good time to verify your posi is working properly, or install that feature on your existing gear set. Once it's running good, then you will be able to measure the performance you actually have, and decide whether or not you want to change the rear gear. You are not getting all the performance that 3.23's will deliver if you are suffering from detonation, a "one-legger", or both.At least I think that would be a logical way to approach this...
"Wherever you go, there you are."..Buckaroo Banzai, 1984
+1 PonchoIf you go with deeper gears now, you'll wear out what you have all that much faster.Personally, I think 3.23 is an excellent multipurpose ratio for a non-overdrive car.Yes, gear selection is a big factor in engine configuration of a new build.If you have an older build, too squeezy for pump gas at this point, cocktail some race gas with pump premium until you find a happy mix. Maybe score a 5 gallon pail and try it. You are guaranteed to like what it does for your power.