I had my vette's computer chip reprogrammed about a year ago with a Granatelli Big 'G' Tuner. At that time I had also installed a Vortex Ram Air system with an air sensor and put in a Bassani cat back exhaust system. Life was beautiful.I used to be able to hit 165mph + (Don't worry - I've promised myself I will no longer be doing that).

However, I have noticed that ever since I installed a rear spoiler and changed my rear axle ratio to 3.90my vette has lost some top speed (my vette redlines at about 158mph now).....but it has gained a lot more power at low/mid level speeds. My mechanic told me this would happen so I was not surprised. However, I am curious to know if anyone else has had this happen to their vette. I wonder if it's the rear spoiler that's slowing down the car more than the rear axle ratio.....or is it the other way around? Unfortunately I had both these installed at about the same time so now I can't tell which is having the greater effect in reducing the top speed of the car.

 

It happens to everyone and anyone who changes their rear axle ratio from the stock 3.42 to a 3.73 or 3.90 or evenhigher.

Some months back I posted a very long discussion about this, which goes into all the ins and outs of changing rear axle ratio including this and many other changes it brings.

https://www.corvetteforums.com/m_26639/tm.htm

By changing from the stock 3.42 to a 3.90 rear axle you were changing the speed at red line in 5th from the stock 175 to 3.42/2.90 x 175 ==> 155 or so. This was inevitable, predictable in advance,and will happen on every 'vette where this change is made. Yuu also picked up 3.90/3.42 times as much torque at low speeds -- whether you can use it depends on if you have tires that can put it to the ground.

NOte: in that post I conclude that a change to a 3.73 ratio does not really hurt top speed in a 'vette because of various factors. I think a change to a 3.90 would.

 

I'm still good to about 180 - comes in handy sometimes on the way to Vegas......

 

Thanks Lee....I read the whole thing! Very informative.....I guess I'm happy with my trade-off.....I'd rather have the added torque than the higher top speed.....I have a 4-speed auto tranny so now I've been trying to figure out how to launch my car without redlining it....not easy!......But I've discovered that by using the 1,2,3 and D on the shifter I can better control the tach from red lining....my mechanic had my car adjusted on the Dyno to help match my new torque with my auto tranny but he says I still have to keep an eye on the redline.....right now I'm trying to figure out at what RPM I should shiftup while my foot is all the way down in order to get maximum acceleration without hurting my engine (any advice on that?)

Of course, I only do this when I'm feeling racy because for the most part I can leave the shifter on 'D' and give the gas pedal a good hammering and the car responds delightfully as long as I don't keep my foot to the pedal too long.....in any case, I like having the extra pep in my step ...... I know I didn't gain any real horsepower, but it sure as hell feels like it!!!! And the sound it elicits from my Bassani exhaust is even more delightful....I feel like a king when I'm out on the road!!! (Better not let me catch you on the road, Lee .....just kidding)

In any case, this added torquehelps me make up for all my other insecurities... ha ha ha ha . Besides, those high speeds weren't good for my health anyway....low/mid level speed gives me a better chance of survival in the event something were to go wrong.....of course, I pray nothing ever goes wrong! Once again, Lee, Thanks!