Best gear for 9.90

[rob7181]

What is the ideal gear for a 2600 lb tube chassis car with a 582 BBC and glide? Been running 4.10 with a 33" tall rear tire and it seems as it is hard to recover off stop and it wants more gear, say 4.56?

Thoughts?

[pmrphil]

Finish line RPM kinda puts you in the ballpark

[rob7181]

Would the 4.56 help coming off the stop to recover?

[Lenny5160]

Originally Posted by pmrphil

Finish line RPM kinda puts you in the ballpark

I agree that I'd base the rear gear choice on finish line RPM. As for recovery coming off the stop, you can try a higher cruise RPM, coming off the stop in low gear, going on the stop later to get the car moving, etc.

[Charlie Yannetti]

While it is true that finish line RPM plays a part, I was convinced a few years back by Eddie Jr, at Select Performance, to go to a 4.56 gear.. not only to enhance his converter set-up, but that I would be surprised by the charge coming off the stop.. I now have 2% to 3% slip in the converter at the top end, and that charge coming off the stop is awesome, and I go out the back door at approximately 7600 RPM with my 565.. I am only 2150 pounds also..

While I was a nay-sayer, until I switched from the 4.30, I doubt I'll go back.. while it slightly increased the RPM, I didn't seem to affect the MPH at all...

[Lenny5160]

Originally Posted by Charlie Yannetti

While it is true that finish line RPM plays a part, I was convinced a few years back by Eddie Jr, at Select Performance, to go to a 4.56 gear.. not only to enhance his converter set-up, but that I would be surprised by the charge coming off the stop.. I now have 2% to 3% slip in the converter at the top end, and that charge coming off the stop is awesome, and I go out the back door at approximately 7600 RPM with my 565.. I am only 2150 pounds also..

While I was a nay-sayer, until I switched from the 4.30, I doubt I'll go back.. while it slightly increased the RPM, I didn't seem to affect the MPH at all...

Are you saying that the car comes off the stop much harder, your converter got more efficient, but you didn't gain any MPH?

Was there a measurable gain anywhere? Could you stay on the stop longer?

[Charlie Yannetti]

Originally Posted by Lenny5160

Are you saying that the car comes off the stop much harder, your converter got more efficient, but you didn't gain any MPH?

Was there a measurable gain anywhere? Could you stay on the stop longer?

Although I didn't mention MPH, I'm up between one and two.. also, I usually do stuff to try and take time out of the box.. not put more time in.. and I really don't like carrying 3.00 in the box either...

[Shake & Bake]

rob7181,
Going from the 4.10 your running to say a 4.33 would only be a 5% increase, but going to a 4.56 is going to be a 9% overall increase in performance. Plus you should pick up around 3mph.

[Tom Goldman]

Like Charlie ,I run Select converters . I went to 4.56 gears from 4.29 in my Vette which weighs in at 2400# .
I picked up 2 mph with an increase of 250 trap rpm .
converter efficiency went from 10% slip to 5-6%. AND very importantly , the converter temperature dropped way down when coming off the stop.
Since Charlie's car is a '27 Roadster, one of the hardest cars to get MPH out of I'm not surprised by the lack of improvement in speed.
I would defiantly recommend 4.56 gears in your car.
Racers get too hung up on trap rpm's , if your engine is still pulling at the stripe ,let it eat !

[Keith 944]

^^^^^^this