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My other options seem to be the 3.15 and the 2.73, the latter of which seems to be right between how the C5Z is geared with stock power and how Chevrolet geared the ZR1.
The ZR1 has different trans ratios. RPM can rebuild your trans with these ratios. Or run the non-Z06 trans trans which has a first ratio in between the two.
The autos had the highways gears like your looking for I think. You could just swap the whole diff. I think it would be pretty doggy imo.
The ZR1 has different trans ratios. RPM can rebuild your trans with these ratios. Or run the non-Z06 trans trans which has a first ratio in between the two.
The autos had the highways gears like your looking for I think. You could just swap the whole diff. I think it would be pretty doggy imo.
The first 3 gears look pretty good. 60/86/125 C5Z 2.73 vs. 66/93/124 ZR1.
The top 3 gears do look pretty doggy, though, you're right. 179/213/319 (!!!) C5Z 2.73 vs. 150/186/224 ZR1
Looks like the better swap would be the tranny, not the diff, yep.
So during an autocross, are you running out of rpm now?
I guess my question is what are you trying to gain with the gearing change? Do you need more mph in 1st, or are you just trying to dull down the horsepower for traction sake?
I don't have much specific advice for forced induction with a Vette, but I would suggest careful planning to get something with a nice linear power curve. I had a centrifugal supercharger on my Mustang (615rwhp), and a turbo on my Miata (um, less hp), and neither would I call linear. That was part of my motivation to buy a Corvette. I love the linear N/A power. No surprises mid-corner.
What exactly are you trying to accomplish? My car had just under 500 ft. lb., base C5 trans ratios, 3.90 in the rear, put my total gearing just barely taller than a stock C5Z... it's manageable.
I run a c6z trans with 3.42's. I shift to 2nd as soon as possible and ride it out for most the track, sometimes shifting into 3rd and back. 1st is constant peddling and 2nd after 4500rpm is too.
I'm trying to have my fun on the street but not spin the car during autocross. The issue is traction. First is usable with throttle modulation in a straight line but I suspect more power would just make the car more difficult to drive quickly.
Have you thought about heads and cam instead of forced induction. We did heads and cam on my brothers z and he is making 480ish to the wheels I think, you don't heed a ton of power for autocross, to much can cause you problems and you add a lot of heat when you go forced induction.
The problem with staying in first in an autocross is that the car slows down as soon as you lift and there is a huge amount of weight transfer due to engine braking that tends to upset the car.
Since you can only put down as much power as you generally have in second gear coming off of even slower and medium speed corners, trying to get a lot more power is generally a waste of time (literally).
Or, to put it another way, if you try to put down more power than you have in second gear you're likely going to just have a bunch of wheel spin or you're going to break the back end loose.
If the events you generally run are "point and squirt" type of events then what you are thinking about might help, but the idea in autocross is to maximize corner speed and corner exit speed because you aren't generally accelerating that much anyway.
Roger Johnson tells the story where when he was just learning the sport, at the last event of the season he got beat by like 2 seconds and he was determined that it was that his year of car was way down on power compared to the guy that beat him... Over the winter he did a bunch of engine mods and when he came back out at the first event of the year got beat by 4 seconds by the same guy....
At that point the light bulb came on and suddenly realized it wasn't power, it was the driver and grip that was the most important in autocross and the rest is history.
Since you haven't spent a bunch on a supercharger yet you could invest in handling and seat time and have more fun and spend less overall.
If you are bound and determined to go with some kind of forced induction you don't want a centrifugal supercharger, you want a positive displacement blower that will get you more power in the mid range as opposed to just high end power.
As I noted above, running in first takes a lot more finesse on the throttle not to upset the car. This is why Matthew Braun always just gets the car in second and drives it and never bothers to downshift, even in slow corners. As he always says, the gain in acceleration isn't worth the upset of the car when running in the lower gear.
First, I always try to get into 2nd as quickly as possible.
Secondly, I've never seen any benefit to a supercharger, or turbocharger, at an autocross. I've seen a lot of frustration and a lot of overheating issues though.
Back when I was running an Austin Healey Sprite I used to comment that I had never been beaten by a 930 Porsche Turbo. I think my Sprite had about 35 horsepower and it was always faster than any Porsche, especially the 930s.
When I ran nationally I had less horsepower than anyone in my class. Of course everyone in my class accused me of having a very expensive high horsepower engine. Actually, I encouraged that thought.
I always wanted to be protested for engine modifications. Just don't look under my car.
The problem with staying in first in an autocross is that the car slows down as soon as you lift and there is a huge amount of weight transfer due to engine braking that tends to upset the car.
Since you can only put down as much power as you generally have in second gear coming off of even slower and medium speed corners, trying to get a lot more power is generally a waste of time (literally).
Or, to put it another way, if you try to put down more power than you have in second gear you're likely going to just have a bunch of wheel spin or you're going to break the back end loose.
If the events you generally run are "point and squirt" type of events then what you are thinking about might help, but the idea in autocross is to maximize corner speed and corner exit speed because you aren't generally accelerating that much anyway.
Roger Johnson tells the story where when he was just learning the sport, at the last event of the season he got beat by like 2 seconds and he was determined that it was that his year of car was way down on power compared to the guy that beat him... Over the winter he did a bunch of engine mods and when he came back out at the first event of the year got beat by 4 seconds by the same guy....
At that point the light bulb came on and suddenly realized it wasn't power, it was the driver and grip that was the most important in autocross and the rest is history.
Since you haven't spent a bunch on a supercharger yet you could invest in handling and seat time and have more fun and spend less overall.
If you are bound and determined to go with some kind of forced induction you don't want a centrifugal supercharger, you want a positive displacement blower that will get you more power in the mid range as opposed to just high end power.
As I noted above, running in first takes a lot more finesse on the throttle not to upset the car. This is why Matthew Braun always just gets the car in second and drives it and never bothers to downshift, even in slow corners. As he always says, the gain in acceleration isn't worth the upset of the car when running in the lower gear.
I agree with both of these. I ran my C5Z in autocrosses for 6 years and took my fair share of FTDs.
Listen to these guys in #10/11/12. You will be shooting yourself in both feet (for autox) with a supercharger. But, I know, guys do what they're gonna do, so all the best.
What about a healthy shot of Nitrous for messing around? You can take the bottle out anytime you want. It won't add any weight to the front for autocross.
Listen to these guys in #10/11/12. You will be shooting yourself in both feet (for autox) with a supercharger. But, I know, guys do what they're gonna do, so all the best.
I agree with everything said here. The experience I got this year suggested more power would be unusable ... without taller gearing, that is.
If I can't figure out a way to not hurt drivability and traction ... I just won't do it. Right now it seems like the easiest answer is "if you want a faster Corvette, buy one that's geared to be usable at autocross." At C5Z + $5500 + install + tune + clutch ... without even considering gearing ... the C6Z starts looking like a real deal.
You should ride in a supercharged C5. The power is somewhat on/off - it would be hard to control at lower speeds unless you really underspun the centri (low boost). Roots/maggie style make power from idle up but they overheat from what I have seen.
2.73 complete diffs are cheap.. try one if that is what you want. Not a hard swap just somewhat time consuming.
10-31-2016, 10:25 AM
Gearing a supercharger for autocross
