Hey, first time poster, and new to the rotary world.. I just want to apologize in advance for not being very specific.. I just picked up an 85 rx7 and I'm just curious as to whats out there to build this to run in around the mid 9s low 10s

 

You will need about 450-500rwhp and slicks. There lots of choices on how to achieve it beyond this.

A mate of mine years ago did low 10s with a 12A and T04E/66, s5 turbo transmission, Torsen LSD and stock axles but he was going through gearboxes and axles like butter. 10s is pretty much the point you will start breaking differentials, axles and Mazda manual transmissions.

In Australia, a common setup for these figures in a 1st gen is a ported 13B, T04Z running on E85, Hilux diff (or Ford 9" but more work involved) and auto transmission of some sort (often our guys use modified Jatcos or C4s). Not sure whether the parts and know-how translates to the US though. You guys have better access to more modern turbos at cheaper prices and probably wider choice of diffs and transmission too.

 

Maybe you bought the wrong car. Lots of mustangs out there! LOL!

It will take a lot of money and time to make it do that level of performance. Maybe you have
both? This car was designed to run road courses not be a drag strip queen.

That said, with just bolt-ons for a 12A you can increase the HP by almost 50%, so you can go
from 105bhp to ~155bph without opening the engine at all. My SA gets about 135hp at the rear
wheels with my mods. Factor in the loss and its at about that level of crank hp.

 

Lets forget how to get the power, and look at to put the power down..
A diff change will be likely..
any tire that will get you into the 9s or 10s will not fit the stock FB body. so over fenders, or tubs, or just look like a tool and be cheap.. you are better off with an FC. those can fit wider tires and put the power down on the stock turbo rear ed pretty well.. the rx8 would be even better for tire fitment, but you'll be changing the diff in it to

 

start reading in this forum to see what others have done: Rotary Drag Racing - RX7Club.com

 

Apart from the diff change (which is not only likely - it's imperative), I disagree with this.

I can reel off the names of plenty of 1st gens which have runs low 10s and into the 9s without any tubbing. You can fit a 245 tyre or 9.6" if you want to use slicks language in the back of a 1st gen quite comfortably. This is ample. As an example, almost 15 years ago, AJC13B (who was a member here) did a 10.32 with 26x8.5" slick, Borg Warner diff and s4 rx7 5 speed manual. Here's a 1/4 mile top 20 for untubbed Aussie street rotaries from 2002: www.mazdarotary.net - Non Race/Street Based Untubbed Top 20 Rotary Records Things have advanced massively since then with better turbos, E85 fuel and 2-step. Untubbed 9s are pretty common now - here's a more recent list (still probably 10 years old!) but only 1st gen on there: www.mazdarotary.net - Outright Untubbed Rotary Records Best 1st gen is series 1 RX-7 with 28x9 slick, 9.16 @151mph.

Actually, looking back at these lists, I've realised that the auto trans isn't really necessary - plenty have done it with fc manual boxes.

FC gives you a 200+ kg weight penalty unless you fully strip it down to race spec. Probably want to revert to a live axle diff as well. As a street car, it's not as good as a 1/4 mile weapon compared to a 1st gen.

 

with no personal experience with a 1st gen at that power level... i cant image how a 245 is ample.. i would want 285 for anything over 400. 315 for 500.