1/8th Mile Gear

I'm challenged when it comes to computations. I need to figure out what the best gear is I need for a 1/8th mile race. In the 1/4 mile for my application, a 4.10 is the best. I run 34.5" Hoosiers and I shift 8600 RPM and come through the light about the same. Any formulas that I can use? Thanks.

Tom

 

Thanks Mike. I have an extra 4.57 and a 4.86. Looks like I'll use the 4.86.

Tom

 

We run 1/8 mi. most of the time. We run the 34.5 Hoosiers and shift about the same spot and run a 4.56 gear. Depends on what you plan on running E/T wise. We run 3.90's in the low to mid 180's in the 1/8th. If you are a 4.20 or slower I would go with the 4.86.

Keep in mind, the taller gear is going to change the way the car acts when launching. You might want to try leaving at a little lower RPM until you figure out what it's going to do.

Good luck!

Troy.

 

Guys

When you change froma 4.10 to a 4.71 or 5 flat , do you also change your first gear to compensate and have the same numerical leave gear?

Also are you most running only running two speeds to the 1/8 ie shifting one time and them running right by the 1/8 in second gear maybe shift to third to coast??

Thinkimng of running a couple of 1/8 races so this are my concerns

thanks

JP

 

I assume all you guys are running a clutch where you have a lot more control over the launch with a lower gear. Most of my experience has been on 10.5 cars with converters and nitrous, on these cars even when running in the eigth you don't want to go too a low on the gear because of the problems launching and loading the converter.

I am curious on a Pro-Mod type car with a converter do you still try to go with as low a gear as you can spin RPM wise through the traps or do you reach a point where the gear multiplication is no longer and advantage?

I did not know what Tony from "Animal Crew" was speaking of when he mentioned ET and MPH, were you speaking about running out of gear through the traps or were you talking about violence on the launch when you cross the line from 4.20s to sub 4s?

Thanks in advance for any replies, and sorry if this is a stupid question.

 

Thanks Mike

 

Mike are we talking roots blower gear or a screw blower type??

 

we run a screw on a outlaw pm 1/8 mile we run 34.5 tires and 4.86 rear 1.63 1st gear 3 spd lenco with clutch mike must be refering to a roots set up

 

Well, at least in my case I have a 1.86 1st gear in a Turbo 400 and I can't swap it around easily. (Have a couple of Lenco's and a Bruno but that may be for next year) I was running high 4.20's with a 4.11 and just hitting 3rd at the 1/8th if I remember correctly. I want to have it shift twice in the 1/8th and come through the traps at the quickest possible in 3rd at 8600. I'm about ready to run this up to 9k as this engine has been there on the dyno and makes the most power there but I have been running trying to run it conservatively. Was thinking the gear change and the extra RPM will get me in the 4 teen or 4-0 range. Still wish there was a formula to predict this.

 

Guaranteed its roots he is talking about.

 

Sorry - I just got back to this. Yes I was talking about running out of gear. I assume you have some sort of target for max trap RPM. If we ran a 4.86 it would likely put us near 9K and we try to keep the RPMS down to mid 8's to be easier on parts. We don't have the budget to run 10K RPM.

Troy.