How big of a difference acceleration wise is the transition to 3:73's? The bird is a 6 speed and just had the motor freshened up this last spring. Pro's and con's? Help me decide.

 

IMO you will gain more doing other mods I dont know what all you have done. So give us a list and with say $400 will buy some nice parts.

 

There won't be that much of a difference, but some. 4.10s would be a noticeable difference, but traction will become more of a problem if you race a lot. Just for "feel", they would be fine, plus with the 6 speed, you have 2 overdrive gears to tame the 4.10s on the highway.

 

If you wanted to put a number on it, it would be ~10% (3.73/3.42), which is how much faster you'll go up the rpm band. 4.10 comes to about 20%.

By the way, it's 3.73:1, not 3:73 (which would be really, really high! ), from a terminology perspective.

Dave

 

Thanks for the input. It was late last night and I didn't want to list the mods. Basically the cam is a crane powermax similar in numbers to the cc306 with LT4 heads. It has ceramic coated BBK headers ( I know should've went with long tubes but I had a misperception about ground clearance with Mac springs). It has a CSI waterpump conversion, pcm4less tuning, cloyes double roller, MSD ignition, and about any other bolt on you can think of. Right now the rolling stock is 17x9.5 borbets with BFG KDW tires. From a 20 mph roll with stepping down on it, it hazes the back tires thru first and half way into second. I would like to go with the deeper gear because I do alot of highway traveling and the RPM range on the cam is a little low in sixth gear. I could just leave it in fifth I suppose. Thought about spraying it in the near future or maybe even a mild supercharger set up. Funding is extremely limited right now (building a new house) and my wife is on me about doing some work to her GTP. I never thought she would get bitten by the speed bug but I guess I was wrong. And by the way, the car is a 95 T/A I purchased new right off the lot. Hard to think I've had this thing almost 10 years.

 

It is a noticable difference..........obviously 4.10s are more noticeable.

Pro's:
-A lil easier to keep your rpms below 2k on the highway which is right were many peoples cars start to get significantly louder.
-Your street tires won't go up in smoke quite as badly as the would with 4.10s.
-If your using a low peaking motor with enough power they could be perfect for the 1/4 mi, with a stock motor 4.10s would be more optimized for the 1/4


Cons
-Stock bolton motor with a full weight car and stock tires won't be making full use of 4th gear in the 1/4 like 4.10s would.
-You won't be following the mobs blanket recomendation of 3.73s for a4 and 4.10s for m6 cars.


Really it depends what kind of future mods your going to do. Gears should really be the last thing you do once the rest of your combination is together, but if you look ahead you can forcast well enough.

I picked a lower peaking cam for my motor. Right now 4.10s would still be slightly better than my 3.73s, but as soon as i lose some weight and find some more power i would be past my redline in 4th gear at the end of the quarter causing an extra shift to 5th. 3.90s would actually be perfect for me. I'm not a hardcore drag racer anyways so the noise, traction issues, and a killer deal on 3.73s caused me to end up with them.

 

Didn't see your simultaneous post before my last response

It doesn't sound like your overly concerned with the 1/4 mi. If you were though 4.10s would probably be ok since a 306sized cam should spin well into the mid-upper 6k rpms and at those rpms 4.10s/stocktire size are still good for a ~124 mph trap speed. I definitly don't think your trapping anywhere close to that but with spray you'd be a lot closer. You'd also need some sticky tires.

Try this (or the cz28 calculators) to get a feel for what kind of rpms you'd be turning at your highway cruise speed after the gears. Also consider the highway noise like i mentioned above.

Or you could just save your money for the house and use 5th gear.

-Brent