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Regarding the front hub on the GTU car, I don't know what they were running. A solution that I have seen on a couple of local cars is to machine the OE spindle pin off and replace it with a Pinto spindle pin from Speedway Engineering. Pinto spindles have huge bearings and hubs with 4 and 5 lug patterns are available. I have also seen the same thing done with a wide-five spindle pin so that wide five hubs/wheels can be used. It just depends on the class you are going to compete in.
I think is should be noted that the GTU car was on 16" slicks mounted on 10-11" wheels. Those are sticky tires and would tend to stress anything that was original equipment. That explains pretty much everything they had to do to make the car work because they clearly built the car to be able to use the tires that were allowed in the class. Which, by the way, is how it works in all forms of racing.
Regarding the front hub on the GTU car, I don't know what they were running.
i don't either, although there were a couple of choices at the time. Mazda had the competition strut/hub and brake setup, which you would have seen on the early cars, and then there is a Datsun Z car strut that was popular too. There are a few flavors of Z car struts, and hub/brake setups. they are the same design as the Rx7, just beefier, 4x114 wheels too
there is a road test of the Kent Racing GTU car in the November 1979 Road and Track. this whole mimic a GTU car is tough, as Scott says, there is a lot of rules creep, so the factory 1979 car is wildly different from say Tommy Kendall's car
Although this article is about the TCR car that didn't happen, there are some interior and close up shots of the Tommy Kendall GTU car near the bottom.
i don't either, although there were a couple of choices at the time. Mazda had the competition strut/hub and brake setup, which you would have seen on the early cars, and then there is a Datsun Z car strut that was popular too. There are a few flavors of Z car struts, and hub/brake setups. they are the same design as the Rx7, just beefier, 4x114 wheels too
I saw some pictures of an 85ish Toyota Supra - same kind of strut design as an FB. Looked beefier and very adaptable to an RX7. I wonder if the Celica of the same year was the same.
I saw some pictures of an 85ish Toyota Supra - same kind of strut design as an FB. Looked beefier and very adaptable to an RX7. I wonder if the Celica of the same year was the same.
yes those are possible too. i know there are a bunch of variations in the Toyota ones, they are all the same tube diameter, which is the same as the SA/FB, but different lengths (all of them longer) and then some have the bolt spacing at the bottom that are the same as the Rx7. kind of a rabbit hole, but there are options
To address the cooling: It's interesting that the thermostat didn't make a difference in the car's temps on track, so I'm inclined to run one just in case. I guess the cardboard shroud goes to show that a little ducting can go a long way! I'm not sure how the Honda is designed in regards to radiator and body panels up font, but the RX7 seems to have a nice big shroud or duct made by the front bodywork forward of the radiator. I bet that does something in regards to cooling efficiency, but a simple shroud around an E-fan will also likely help a lot! I think that's the route I'll end up going.
The IMSA stuff: to start off I LOVE that Racing Beat video of the 83 24HRS of Daytona! I can't tell you how many times I've watched it! Their GTO car is the car that I dream of building; the one that I wish I could build. That car, however, is a bit more removed than I was thinking of building. Mustanghammer has brought it up a few times, some racing classes out there very quickly turn the cars from modified factory production cars into bespoke, purpose made racing machines. Racing Beat's GTO car is to a stock FB RX7 what a Dekon Monza is to a production Chevy Monza! They share a roof and doors and that about it! That's why the SVRA IMSA regulations caught my eye and have been my focus: they stop at the 1983 (or somewhere around there) set of rules. That particular set doesn't allow full tube frame cars and many other things that were allowed later in the lower classes such as GTU. In my mind that allows my to keep the majority of the car Mazda based, but still allow for changes in certain parts to allow for better performance or greater availability. That mentality is why I'd be ok throwing a Ford 9" rear in the car for example. It may not have been made by Mazda, but they can be made extremely strong and parts are readily available, and they can be made bolt to the car in a similar to stock set up so as to not alter the car too drastically. The same goes for things like the hubs. Stronger components would be nice, a would a different wheel pattern for better choices and availability, but I wouldn't want to change the style of suspension. A couple of y'all have put it well: that's just the nature of racing!
You guys have added some awesome footage to this thread! Thanks!! Y'all are really helping me get my research into what they did in period to race this cars completed. The full-IMSA transition is a ways off, but its good to have this info to start thinking about how I'll be able to do it. The Tommy Kendall car is an awesome machine! It's actually built to the later set of regulations, though and it has a full tube frame and is quite removed from the production car. As much as I'd love to build something like that, I'll stick closer to the Racing Beat GTU or the Kent Racing GTU entries
Those of you who race there first-gens, are there any parts that are prone to failure that are recommended to be changed or upgraded ASAP? For example when one vintage races a 1964 Ford Falcon, one is advised to change out the spindles for later model falcon or cougar spindles because the stock 1964 style ones sheer often under racing conditions! I'm pretty sure my car may have had any simple tweaks like that done already considering it's already been raced, but I'd like to know if I need to inspect anything in particular on these cars before I hit the track as that day is fast approaching!!
Those of you who race there first-gens, are there any parts that are prone to failure that are recommended to be changed or upgraded ASAP? For example when one vintage races a 1964 Ford Falcon, one is advised to change out the spindles for later model falcon or cougar spindles because the stock 1964 style ones sheer often under racing conditions! I'm pretty sure my car may have had any simple tweaks like that done already considering it's already been raced, but I'd like to know if I need to inspect anything in particular on these cars before I hit the track as that day is fast approaching!!
the only thing i can think of are the front brake rotors, they tend to crack, and if its not replaced, they can explode which is bad. other than that its just old car stuff
84-85 Spindles have a bigger outer bearing - those are favored over the earlier years. If possible the spindles you use should be checked for cracks before use. These cars were driven on the street and could have been curbed in their life time. Even bigger ones fail and I have seen this first hand.
I never had any issues with front rotors on 12A cars. Brembo brand rotors were available but they wore out just as fast as the Chinese stuff from Autozone or Rockauto. I replaced rotors and bearings after the second set of brake pads.
GSL/SE front rotors have been know to fracture around the lug stud holes. This happened to several E Production Rx7s. So KCRaceware.com has a hub and rotor kit that solves this.
Ditto on the front rotors. Ducting air really helps. The hawk blues that I run on the ITA car really eats up the rotors. Before I added the duct, I would go thru rotor/hubs faster than pads, usually due to cracking. I learned not to buy the knock-off Brembos as I had one completely shear off in the narrow part of the casting behind the brake rotor...right front wheel beat me to turn two at Laguna. That was with the 84 big bearing fronts(GSL). If you rules allow and you can afford it, I would convert to the hubs that Charlie Clark sells. They work quite well. Not sure if they can fit under 13" rims tho...if that is what you are running.
I also seemed to have issues with third gears when I ran the Pro7 series. For whatever reason, that became less of a problem when I converted the car to ITA spec's. Maybe I just started being nicer on the trannies.
That's why the SVRA IMSA regulations caught my eye and have been my focus: they stop at the 1983 (or somewhere around there) set of rules. That particular set doesn't allow full tube frame cars and many other things that were allowed later in the lower classes such as GTU. In my mind that allows my to keep the majority of the car Mazda based, but still allow for changes in certain parts to allow for better performance or greater availability.
From a for sale ad from a while back, in case you were curious about what in-period cars of that era consisted of: https://imgur.com/a/pjz7LWk
Well I'm glad I asked about which parts tend to fail. On that list hubs and brake components are never a good thing to hear!! In regards to the hubs I'd love to be able to afford to upgrade them, either to 84-85 or to those sweet ones KC Raceware has. I need to make a choice about how I'll run the car sometime soon so I can spec it out for that class. I want to het on that ASAP but I haven't been able to so much as track it yet! Le Mans was right, racing is life everything else is just waiting!
In regards to the brake pads, the car came specced out with the Hawk Blue stuff pads. If those just eat rotors does anyone have any suggestions for other ones to try? Or are those really the only options?
In regards to that Imgur link to that ad... GOD I WANT THAT!! But come to think of it you may be right, a tube frame car may be easier, but that doesn't have enough RX7 in it for me. That unibody GTU build has just enough it seems. I'm not complaining about having to build one myself, working on cars is one of mot favorite passions, but damn... what I wouldn't have done to have gotten my hands on that thing!
One thing stood out to me in the pictures of that car, and I'd like you opinions on it. The hubs seem to have been drilled for 2 separate bolt patterns. I've thought about doing this to my hubs to be able to run some other 4-bolt pattern such as 4x100 or 4x114.3 to increase my wheel size and selection. Does it greatly compromise the strength of the hub? Is drilling the extra holes a safe practice? Are hubs drilled like that something that's safe to drive, let alone race with?
In regards to the brake pads, the car came specced out with the Hawk Blue stuff pads. If those just eat rotors does anyone have any suggestions for other ones to try? Or are those really the only options?
we used Hawk Blues on the Lemons are, and i was impressed, we could out brake everyone, but pad and rotor wear were alarming. i think i want to try the black next, hoping to get 2 events out of a set of brakes instead of one.
the PFC pads we used to use on the Hondas were much better, the pads lasted longer, and rotor wear was basically zero (they would eventually start to crack from the heat, but no wear)
Mr Battleversion, Alex used to buy Porsche pads and trim them down for his AE86's, so even though there are no pads for an Rx7, you can still do it
Porterfield does that too. Primary Raybestos race compounds but those work pretty well too.
In 2021 if I were to do a new build SVRA pre-tube IMSA GTU build, I'd use S197 spindles or something where there's millions of them and they're never going to go unavailable. Toyota 8" or Ford 8.8 both have enough final drive ratios and good LSDs - good LSDs are harder on the 9". And then carefully study what of the unibody doesn't need to be there. Figure out wheels and tires and build from there somewhat.
For brake pads I strongly recommend Raybestos ST43 front and rear. We have been using them on our endurance car for over 6 years and the pad and rotor wear is fantastic. I think my current pads will be going on their third endurance weekend . If I were going some place like Auto Club, I might change them, but Willow Springs doesn't really need brakes. The ST-43's are not as torquey as Hawk blues, but I appreciate that for endurance racing. It is a lot harder to flat spot tires if you don't have the most sensitive "braker" in the car. In any case, in my opinion, extreme threshold braking is not that important for endurance racing. You want everything to last for at least 7-8 hours if not 14-24 hrs. We do have the original design Mazda Motorsports brake ducts which help things cool. I currently use ST-43 for sprint racing too, but will probably go to something a little torquier in the future.
Somewhere I have in-car video of my car losing a front rotor (thankfully not a hub) in the braking zone of T3 at Auto Club Speedway. A gaggle of spec miatas had just passed me and I ended up repassing them on the inside as I went straight past them down the back straight of the oval :-0 That was with Hawk Blues and the damage they do to rotors. The rotor split into two pieces and went flying out the wheel well.
I am still running stock GSL brakes and have been happy with them. I think that unless you are driving a really fast car (and driving it really fast) you will be fine with what you have. As others said, check what you have now before hitting the track, but then get out there. Until you have gotten a bunch of track time, I think you will not really have a good basis for deciding what you want to do. Just my old guy thoughts. Maybe worth $0.005. Except for the ST-43 recommendation that has to be worth at least $0.02
Ran Hawk Blues on my GSL Rotors. For SCCA Regional racing I could get two sets of pads to work on a pair of rotors. I never had a rotor crack or fail but that was Regional club racing which were usually 30-40 miles long tops. Running Hawk Blues made you want to keep your helmet visor closed......otherwise you'd have metallic taste in your mouth that really screwed up the post race beers.
Regarding the hubs in the image, they appear to have two sets of patterns. Not sure why the patterns are drilled so close together. If it were me, I would do 4x100 because there are so many more wheel choices. Also affordable 4x100 wheels are lighter than 4x114.3 wheels.
Regarding the KC Raceware hubs, I believe Charlie sold some to a vintage guy that had to run 13" wheels and the GSL/SE size rotors fit. It all depends on the way that back bell of the wheel is made and the calipers that are used. When I was determining the wheels to use for my car I looked into 13x8's and determined that I could get a 10" rotor inside the back of them if I used a low profile caliper. The "not-quite" 11" Turbo II rotors fit in the back of my 15" Kosei wheels with room to spare. Keep in mind the NASCAR Cup Cars have 12" rotors inside of a 15" wheel. It is all about the parts being used.
Running Hawk Blues made you want to keep your helmet visor closed......otherwise you'd have metallic taste in your mouth that really screwed up the post race beers.
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lol! you're not wrong, since its mostly iron from the rotor, its also really corrosive. if its not cleaned off it will ruin the finish of everything
Thanks again for all the guidance! It seems like the Hawk pads are quite high performance, but quite high wear as well. I may try those Raybestos pads to see how they compare, but as Carl put it I don't have a seriously fast car and I really don't have the skills to drive it seriously fast, so sacrificing some potential performance to minimize wear may be the right call. Also It seems the Hawk pads fight back pretty viciously XD I'm not sure I want to deal with that for a several hour race! For the shower duration races it may be fine, however.
If you have pad depth, just use the blues for your first track days. They are already bedded to the disc's use have so one less thing to worry about on your first day.
Also important is the bias adjustment front to back. Later, as you play with compounds, you will need to adjust that. I saw from the photo's that your bias bar is in the engine bay. Eventually you may want to relocate to where you can reach it while driving. Mine are located where the parking brake lever used to be.
The pads are brand new in the rear and pretty new in the front so I will likely keep them until the rotors need replacing. As you said they're already bedded and I'm not wanting to just go replacing parts *****-nilly. I have seen some cars with the bias adjuster where yours is located and though about doing the same. If I do that I think I want to change to **** type as opposed to the lever type I currently have so as to not accidentally bump it. That may not be to big a concern, but it's on the list of wants!
Some Hawk Blue love. They get to temp fast. Like I have autocrossed with them and they are ready to go right away as long as you drag the brakes a little on the way to the start line. They don't fade. You may boil the fluid you are using but these pads won't be the reason you can't stop your car later in a race. They last forrrrrrrrrrrrrrever on the back of an RX7.
As far as a brake bias adjuster, I never ran on my car when it had stock brakes. In my experience, rear brake issues were always related to not enough rebound dampening in the back of the car. That plus not enough compression dampening on the front of the car. None of guys I raced with in the Midwest ever paid enough attention to rear shocks and I could eat their lunch under braking. But you might play around with what you have and see if it makes a difference.
I am everyone else above. If you have Blues already run with them. You will feel like a god when you hit the pedal. They were pretty much the standard for Pro7 and Spec7 racing. I just don't recommend them for endurance racing, because you may not make it through a single 7-8 hour day.
Good news everyone! I've finally been able to herd all the cats together and plan a trip to the track! I'll be heading to the test & tune at Willow Springs on May 21st to get my first experience on track in a car, as well as to shake down my hoopty and see what it can really do! In between now and then I'm going to replace my rear wheel bearings (the right was making noise so I'll replace them both), maybe my front wheel bearings, idler arm bushings and suspension bushings and get the thing ready to race for the first time in a couple of years. Anyone have any advice or words of warning for me as I get started and get on the track for the first time? This will be the first time getting to be behind the wheel of a car on track, but I have had go-karts on track for a number of years now, so the idea of how to conduct oneself and handle a vehicle aren't completely foreign to me. The jump to a car will be interesting though...
Advice? Wisdom? Warnings? Anyone gonna be there that day?
04-06-21, 09:45 AM
But come to think of it you may be right, a tube frame car may be easier, but that doesn't have enough RX7 in it for me. That unibody GTU build has just enough it seems. I'm not complaining about having to build one myself, working on cars is one of mot favorite passions, but damn... what I wouldn't have done to have gotten my hands on that thing!
