Reommendations for Mazda RX7 Front End Alignment

[knottsre]

My name is Russ Knotts and I have been the USFRA World of Speed 130 Club starter since 2006.  2011 was the second year that I ran my 1984 Mazda RX7 in the 130 Club.  In 2010, my top speed was 118.2 mph, and in 2011, my top speed was 122 mph.  I would like to change the front end alignment on the car for straight line running.  I currently run 22.5" M&H front tires on the front and 27" Mickey Thompson front runners on the rear of the car.  I would appreciate some recommendation as to setting the toe-in, caster and chamber on the car.  I have no handling issues with the car, however, I understand that aligning the front end geometry for straight line running could affect top speed somewhat. 

Thanks in advance for responding to my question.
 

[Stainless1]

Russ, I don't think anything outside of stock settings will make the speed better.  If you car is handling good on the salt don't screw with that part.  Help your rotary breathe better, not sure if any other power options are available

[johnneilson]

Russ,

the alignment would be affected if the car has been lowered, other than adding castor to help with stability you could verify the toe-in is minimal. That said, the rear end could be looked at. The gen II cars are IRS rear and have some "rear steer" built into the geometry. You should have the rear toe verified, straight is probably ok, too much in and you scrub, toe-out and you wander or hunt.

Look into the road racing sites for some ideas, if I remember correctly there is a rubber bushing to replace and possibly a link to adjust toe.

There are many options for the 13B motor, the only limit is your wallet or wifes credit card.

John

[knottsre]

Stainless and John, thanks for your responses/recommendations to my question.  I might try verifying that the toe-in is minimal on the RX7.  A note to John, my car is a first generation RX7 and doesn't have the IRS rear. 

In 2010 I ran a closed Racing Beat racing exhaust system and stock fuel injection with an aftermarket cone air filter and reached 118 mph as a top speed.  In 2011, I incorporated better breathing for the 13B, including the Racing Beat header in an open exhaust configuration, with a collector and 3" exhaust tubing out the rear of the vehicle.  As you are aware, the exhaust note on an open RX7 exhaust is loud and obnoxious.  I also ran the Racing Beat Holley 600 CFM 4 barrel carb/intake manifold kit and reached 122 mph as a top speed.  In addition, I fabricated an aluminum air dam for the front of the car and installed aluminum skirting between the front and rear fender wells. 

For 2012, I will be installing an aluminum flywheel which weighs about 13lbs. and is 12lbs. lighter than the stock flywheel.  I will also remove the front air dam and block off the grill to try and clean up the front aerodynamics a little.  The goal is to make the 130 Club in 2012.  If I don't, I've got a 1990 Camaro that I will try in 2013.

If you have any other recommendations, they would be greatly appreciated.

Stainless and John, thanks again for your insights.

Russ

 

[johnneilson]

Russ,

Bloody Hell, I was just this morning talking to a guy about a '91 and was thinking you had one also. My bad.

Yes, 1st gen is a truck axle. Do measure the toe on it. I have bent a few housings and "tuned" some for up to 3/16" toe in. Check camber as well, they can be bent up on one side and cause issue.
Also, check the watts link support on the housing, have broken a few of those also.

Your next speed step is to port the housings.
Oh,one last thing. You can fit a Miata gearbox into the Rx housing with minimal trimming. This gives a taller 1st and shorter gaps between the rest.

John

[knottsre]

John,

I am trying to implement bolt on items to improve my chances in making the 130 Club.  The 13B engine in my RX7 is a 6-port and is very limited to porting as I understand it.  I do have access to some 4 port outer housings that I may use later on if the bolt-on effort  gets me close, but not quite to 130 mph. 

I have entertained a transmission gear change but wasn't sure how to accomplish the task.  Regarding using a Miata gearbox in the RX7 housing, this really interest me.  Which year Miata transmission (I assume a 5 speed transmission) do you recommend I use?  Is the swap out limited to the Miata 5 speed transmission, or would a 6 speed also work?

I look forward to your input.

Russ

[johnneilson]

Russ,

the Miata 5 speed internals will fit into the '81-92 Rx7 cases with one modification.
The input shaft needs to be shortened. Not as hard as it sounds. I can send you the mod specs.

I would recommend a 1.8 ltr Miata donor '94-97.
The 1.6 '90-93 will work, the later has better synchros beefier gears.
I am not sure about using the '99-up trans (5 spd). Check with MazdaTrix in Signal Hill Ca.

John

[knottsre]

John,

Thanks for the information regarding the Miata transmission gear change out into the RX7 transmission. 

I am looking at lowering the rear of my RX7.  Currently, I am running 27" Mickey Thompson front runner tires on the rear.  The stock tire is about 25" tall.  I think the 27" tire height will not hinder lowering the rear of the car 2" or so.  Do you have any recommendations of how to do this?

Regards,
Russ

[johnneilson]

Russ,

not easy without doing some fab work.
Probably the easiest is to find a set of "street lowering" springs.
The alternative is to remove the stock spring buckets and use coil over shocks. This is not easy, will require structure changes.

As a side note, Mazda used to have stiffer bushings available for the lower trailing links. Do not use the stiff ones on the upper arms as it creates too much bind.

John

[knottsre]

John,

Do you know of any tall gear change outs that can be accomplished on the first generation 1984 GSL SE differential using ring and pinion gears sets from other rear wheel drive Mazdas?

Russ

[johnneilson]

Russ,

try this link and go from there.  http://www.solomiata.com/Drivetrain.html

I do know that there are taller gears available, you probably have 3.9 or 3.93?

Good luck with the Austrian turbine.

John