race2win

Hello everyone, I'm a Noob here so sorry for the questions if they are redundant (did a search but really didn't find what I need). I just bought a 1990 GTUs a couple days ago that I plan to autocross in SCCA's E Stock class. I have won National Tour events with a Miata in the past & was a favorite to win in Topeka a couple years ago but was unable to attend. I have always thought a GTUs could be a contender against the MR2s, & now we'll get to find out

My 1st question is about the GTUs models, specifically the 90 model. I know that they are basically left over 89s & from what I have read there are only 100 or so reported to have been sold. What I am curious about is the VIN # breakdown. The last 8 numbers of the VIN on this car are L0800001. Most manufacturers that I know of use the last 5-7 digits as the order in which they were produced (at least that is what I have heard). If that is the case with Mazda, could this be serial #1 1990 RX7?? Once again, mainly curious, would be kinda cool though.

My next questions are in regards to stock class autocross set up. I of course am going to go with a custom valved Koni shock set up, has anybody had a set custom valved for the stock GTUs spring rates? I am also able to change the front sway bar, what would be the best bet? Racing beat? What are you autocrossers using for brake pads? Hawk HP Plus? Finally, has anyone tried the 245/45/16 Hoosier A6 on the stock 16x7 rim? According to Hoosier it will fit a 7" rim, just curious about rub problems. I think the key to this car's success is getting those tires to fit, all the other ES cars have to make due with 225s (MR2, Porsche 924/944).

Thanks in advance everyone, again sorry for the newbie post. I look forward to being involved w/this site in the future, & hopefully putting an RX7 on the podium in stock class autocrossing for the 1st time in many, many years!

Mark

TehMonkay

iTrader: (-1)

people using 225s are running between 30 and 35 offsets.

Most people run konis or kyb agx.

I think a big problem you will have is the lack of the ability to adjust the alignment stock. Expecially since the rear springs always sag and will end up giving you negative camber in the rear, and well, you can figure the result of that pretty easily.

There are 3 camber adjustment points, the 2 smaller rear links and the longer center link, Smaller ones adjust each wheel long one adjusts both at the same time.
For the front you'll need camber bolts at least.

Most people opt fr the racing beat spring/sway bar package, However i'd look into eibach, however it seems as though the springs are discontinued.

As far as power is concerned, definately get a new catback, and replace the catalytic converters, more than likely, you will be able to remove the two pre catalysts sine they usually blow out anyway. Just get a replacement type main cat of the same dimensions and have it fit in just like stock and have a straight pipe run from the manifold to that.

Then also, if you can do it, i think you can, is add a front strut tower brace.

Good luck

t24todd

iTrader: (7)

dont go eibach..i had front/rear sways from them and supposably "they had some difficulties with these". the front went right on but the rear didnt stand a chance. i sent it back and they said they corrected the problem but this time it fit worse. they dont test fit there products like rb does...i went with them and they fit great first time. just trying to save you some trouble. this was about a year ago so i hope they fixed the fitment "problem" by now

RockLobster

iTrader: (7)

Most makes of 225 tires will fit the car in the front but nothing beyond that without custom offset rims or coilovers.

I ran 225s with stock type suspension in the front for a long time. Racing beat is your best bet for front sway bar.

HP+ would be an excellent pad for autoX.

Koni and KYB AGX are good options for what you are limited to. Personally i never found a good combination of springs and dampers in the front in the stock config. I had to swtich to coilovers to get things rated and valved right.

Be aware, with no way to dial camber into the front. (stock style front suspension) You have to run very high front tire pressures to get the car to handle well.

race2win

Thanks guys for the ideas. I should have mentioned in my initial thread what all I was able to do in the stock class & I didn't, sorry about that. Basically all we are able to change in stock class is shocks, front sway bar, exhaust from the cat back, a drop in air filter, & any tire that fits on a stock sized wheel. So, things like springs, rear bar, strut bars, CAI, etc are all not allowed. You can run lighter race wheels as long as they are the same size & within 1/4" of the stock offset as what originally came on the car. This is where the GTUs seems to shine with a 7" wide wheel (compared to all other NA RX7s with 6" wide wheels). Hoosier's 245/45/16 A6 tire is .4" wider than the 225/50/16, but is actually .2" shorter. So I was just wondering if anyone had tried that set up before to see if there was any rub problems.

Yeah, Konis are the way to go for shocks, no problem there (I have TONS of race experience w/those shocks) just was curious if anyone had had a set custom valved for an E Stock 2nd Gen, & if so what the specs were so I can order my set. Does anyone know what the stock spring rate is for the GTUs? I could give that info to the shock builder as well. AGXs IMO are junk, have them on my Galant & don't like them (OK street shock though). I ran RB bars on my Miata & was very happy, so that is most likely the way I will go here, just making sure there wasn't some hot bar out there for these cars I didn't know about. For exhaust I already have a Corksport single exit cat back that came with the car. Any thoughts on that set up? My main concern with exhaust is light weight & flow, don't really care how flashy it looks or the sound (although I don't want something that drones at highway speeds).

Anyone have any thoughts on my 1st question about the production numbers & VIN breakdown? Thanks again for your help guys!!

Mark

Roen

iTrader: (2)

I'm planning on campaigining an STS2 GTUs as well, running similar parts as you, so here's some opinions from me:

Koni's are the way to go, however, no RX-7 race company has really valved them for stock class auto'x. You'll mostly find the valving for ITS and E-Prod racecars. I don't really see much Solo support for shocks.

Front Sway Bar: If adjustable sway-bars are allowed, look for Speedway, Tri-point or AWR style sway-bars. Always nice to adjust roll resistance based on the surface.

Catback Exhaust: Look up Speedsource Engineering in Florida and contact them to see if they make a catback for the FC. They're full exhaust system apparently makes the most power out of any exhaust manufacturer as proven on the dyno by a felllow forum member. (C. Ludwig) ISC Racing may be another option as well. Both companies are in Florida, I believe.

Drop-In Air filter: I've always liked the K&N drop-in.

Tire: Our wheels are 16x7 as claimed by Mazda, but looking at the some of the aftermarket wheels around, our 7" is thinner than a lot of the aftermarket 7". That being said, the 245 A6 may be able to fit on. My 225 Bridgestone already seems bubbly on the stock 7"; the contact patch definitely seems round.

What are the camber adjust and bushing rules in Stock class?

Fault Bucket

First off, welcome to RX-7 world...

I can't help you with the VIN questions, but can offer info on the other stuff. If you aren't already, you should become a member of Mazda Motorsports. Definitely worth it in terms of good prices on parts. You may want to pick up a fresh set of GTUs springs.

It sounds like you already know the drill on Koni revalving, so I'll not talk about that.

As for the front sway bar, there are lots of choices that are very close to the same - Eibach, RB, Tanabe, ST. The RB is a 28.5mm bar, the Eibach 28mm and the Tanabe 27.5mm. I have the Tanabe and would note that it is actually *lighter* than the stock bar. I'm not sure that you can get the Eibach front bar individually.

Brake pads - You can go with HP+, or even the stock pads. I think you can get the Hawks cheaper than the stockers though.

Air filter - Drop-in K&N. Done.

Exhaust - Stick with your Corksport if you can stand the sound level. You won't find lighter or higher flow without going fully custom.

Tires - You'll likely have rub issues with the 245/45-16. You may squeak by with some 5mm spacers in the front, but then you may hit the fender lip under compression. Your best bet is to find someone to sell/give you a used one to test fitment. You might actually look to the 215/40-16 V710 or the upcoming 215/45-16 V710. These are actually pretty wide tires (despite their marketing dimensions) and would give an excellent gearing bump.

Good luck!

jdmsuper7

iTrader: (1)

1st off, props for taking up the torch.

I doubt you are gonna find anyone with custom valving for the shocks on here, 95% of FC owners are too poor lol. Lots of people have chimed in on the swaybars and such already, listen to them.

You are most likely gonna rub with a 245 up front, badly. My 225/50/16 Azenis on an 8" +30 rim BARELY clear the front on the inside (oddly they clear the outside quite well, but I dunno how well a 245 will). It will probably clear the rear, but in my limited experience (only been doin this a year, but in SM2) the chassis HATES a stagger and pushes like whoa.

Please please keep us updated!

YaNi

iTrader: (2)

FYI
Stock Rules:
Tires are a free for all
Wheels are limited to stock size with +/- 1/4" offset (15x6, 15x6.5, 16x7)

STS2 Rules:
Tires are limited to 225mm street tires (no R-compounds)
Wheels are limited to 7.5"

I can't see any performance advantage by running 245's over 225's on a 7" wheel.

race2win

Thanks everyone for the great welcome & I appreciate all the advice. I know I have my work cut out for me in regards to beating the mighty MR2s, but I love the challenge!

My main thought on this subject is not just about width, but also diameter. The 245 is actually a shorter tire than the 225 (at least with the Hoosiers). Plus, I know the RX8 guys in B Stock are getting better results with 285s vs 245s on the same rim, so I think the extra width will come in handy even if its a small amount. It may prove to be a course dependant thing, as most likely the 225s will work better in transitions, where as the 245s would be better in sweepers. I like the idea of test fitting a set of 245s, now I just need to find someone in NorCal that has a used set I can try.

Are the springs notorious for softening over time/miles? This car has 180K on it, is this really something I should do?

This is interesting, does anyone know what the actual width is? I would like to compare it with 16x7" SSR, Enkei RPF1, or maybe even Koseis. I was planning to just use the stock wheels as I know they are fairly light for OEM, but if they are narrower than that it would be a good excuse to endure the cost for lighter wheels.

Yeah, I looked at these sizes, & I'm interested in seeing what the specs end up being on the 215/45. The 215/40 is too narrow, a full 1/2 inch narrower than the 225s & .7 under the 245 Hoosiers. They are short, but I am actually a little concerned over gearing since the GTUs has the 4.30 set up. A lot of auto-x courses run in the 60-65 MPH range & I don't want to be on the limiter too much. Anyone know what top speed in 2nd gear is with these cars (when the limiter hits)?

Once again, thanks guys for all the info, this seems to be a great forum & I'm enjoying the process of figuring out this car.

Mark

Roen

iTrader: (2)

2nd is 70-80 mph

RETed

Mazda has never released a breakdown of the VIN #'s to sub-models.
Technically, you have the FIRST 1990 Mazda RX-7 for North America...

As for the other comments...

I've never really like the HP+ - see other thread.
You should be fine with the HPS, unless you're seeing consistent track speeds over 60mph?
If the course is relatively slow, you should be fine with the HPS.

Fitting 245's up front is tricky.
The offset has to be dead on.
I dunno if you can get those 245's hot enough - you might not have enough speed and / or the chassis might be too light.
I've always thought 225's in all 4 corners is a good set-up for most non-turbos...


-Ted

Black91n/a

You'll need to take full advantage of the 1/4" allowance to space the wheels out to get 245's under, as many people get rubbing when running 225's on the street, and Hoosiers tend to be wide for the size. Then if you want to run crash bolts that'll cut into the clearance.

Didn't see that GRM tire test did you? They got the fastest times with a 245/38/18 A6, but that's shorter than the 285/30/18's (that size A6 wouldn't fit).

I'd look into new springs, IIRC DamonB tested his stock FD springs and they were shorter and softer than new ones, and with the camber gain in the back, getting it back up to stock ride height will help you get it to be more lively, as these cars do understeer.

You may want to look into the Suspension Techniques swaybar for the S4's, it's adjustable, but I'm not really sure if it can be run on the S5.

The FC has good brakes, probably no need to go with HP+'s.

Corksport has a single exit catback that's quite cheap and is claimed to save 36lbs over stock, and they've got a more expensive titanium one that claims 40lbs.

Not many people get really serious about autocrossing FC's, so there's limited information out there. Good luck.