See here.


Note-this is a 90 RX7.

This is on Mickey Thompson 275/40/17 Drag Radials-a very sticky tire at 20psi of air. I just dont think I should be spinning this bad at 750ish WHP.

Few questions to other RX guys making big power.

1) Gear. I know getting the 4.10 rear out will help- for those that have made the switch how much did a 3.27/3.55 help with traction?

2) Sidewall. In my experience more sidewall helps, but I want to keep high speed stability in check. I cant go wider without modifying the fenders, so a 28 tall on a 15 inch tire is best case.
1) who has made the switch, and what was the gain in traction?
2) How does the car feel at 180mph? Anyone doing mile races running that much sidewall on a 200+ mph car?

3) More tire. Right now, I can only go taller. If there is no hope, I am not opposed to pulling out the sidewall and going to town, but its not my preference. Has anyone gone wider (and how wide please) and seen a big improvement?

Thanks! all opinions welcome.

 

I didn't have near the HP as you in my FC, but I had a lot better traction on my 255/55-16 MT ET streets at 12psi than their recommended 20psi- the FC is pretty light.

On 275s don't be surprised if you end up ~ 10psi.

As far as the higher speeds with such low tire pressures, IDK I only used the ET streets for 1/4 mile and switched to Maxxis RC-1 for the street.

You will probably die.

Also, try 6th gear for more traction... or get some traction control.

 

You have a lot more sidewall, with helps tremendously, but thanks for the review. Was that on stock wheels?

I may try to go lower-but at 16psi it was not much better, and the car was feeling sketchy above 140mph.

And 6th!? Its an overdrive gear and not made to handle the abuse. I would likely strip it at this power level.

 

Was that on stock wheels?

Close to stock FD wheels- they were 14lb 16x8 +30 TE37s.

I may try to go lower-but at 16psi it was not much better, and the car was feeling sketchy above 140mph.

Yeah, don't die.

And 6th!? Its an overdrive gear and not made to handle the abuse. I would likely strip it at this power level.

I don't know the T56, is overdrive any harder on it than 3rd gear? If its an overdrive behind the main case wouldn't it have better bearing support not worse? I do know slipping and then hooking up really kills a trans- that is how I took 3rd out.

When I was on 225 Hankook R-S3 (wheels & tires I dynoed on) I would spin 4th on a roll on if I didn't partial throttle it, so I would just stick it in 5th for roll ons.

Its nice how the V8 revs up so slow when spinning tires from all the rotating mass. My 2 rotor had 75ftlbs less torque 3-4,000rpm but it would rev up instantly and kick you into the next lane if you didn't back-throttle it when it started to spin 4th.

 

Yeah its controlable-but gets out of control over 800whp. Spinning ain't winning! 6ith is weak as its just a physically small gear. Less surface to handle the load.

 

Ever thought about a wing? You have more than enough hp to make up for the added drag, especially if you're spinning and it might just keep you, and others, alive.

I very vaguely recall something about the tii spoiler reducing rear end lift and it might be neutral. If you really don't like a wing look into a legitimate under tray.

 

I tuned a 730whp Buick that would do that. There's just no grip on asphalt. Car hooked up great at the dragstrip.

In an IRS car, rearend gear doesn't make a difference since what you don't have at the rear, you need in the trans, to go the same speed. Once you are at speed, all changing the rearend gear does is change how fast the driveshaft is turning. (In a solid axle, shorter gears make MORE traction, since there's less driveshaft torque lifting the right wheel up for a given axle torque. This is why I am taking out the 4.78s and putting in 5.43s!)

Edit - I thought that highway looked familiar

 

Fix the camber if you have not already, that is a start and will probably help.

You'll need like a 3.08 rear gear when you swap rear ends.

 

Thats a backwards way of looking at it. I can tell you from personal experience that more gear will help it hook up, and will also make it faster (if your makign enough HP). The torque is applied over a wider RPM and MPH range, so it simply becomes more difficult for the motor to over come the load. Think of it this way-lets say I had a geat that could take me from 0-150. with a 6500rpm redline, vs. one that goes 0-30 int he same RPM sweep Do you thing I would still spin the tires like I do now? Its a fine line-you want the gear that will provide the best acceleration for a given load and range of speed.


I did not mention it, but I know thats an issue. With the car lowered, I am at -2.5, and worse when the car squats down. The single link does not do much, and I dont know if I trust the adjustable links people sell. I am looking into the issue and may make my own adustable contol arm mounts.

 

What I am getting at is, if you have a gear that does 150mph at 6500, it is going to result in the same amount of torque at the tire, no matter if you have a 3.08 or a 4.11 or whatever. What you don't have in the rearend, you will have in the transmission.


That's going to be a big part of it. Lowering an FC gives you a lot of pro squat, sucks the tires up off the ground when you're on the power because of where the control arm pivot is. This is even before you figure camber into it.

 

First, get rid of the camber in the back, these are not adjustable and are stronger than the stock links:
FC Camber Links - Complete Pair

second, throw some stiffer springs on the back. This is counter intuative, but you don't have a live rear axle... any suspension compression just adds more negative camber. throw stiffs springs on the back to keep the camber where it needs to be.

third, don't die.

and yeah, some downforce definitely wouldn't hurt.