gracer7-rx7

iTrader: (16)

on Flickr

I bought this hooptie a few years ago. It's a shell of a an old race car. No engine or transmission but has an Autopower roll cage, Illuminas, Ground Control coilover setup, aluminum seat and other goodies, The original plan was to built it for LeMons, Chump, Lucky Dog.

I accumulated some parts along the years:

• S5 NA complete engine and wiring harness
• FB transmission
• some cheap 15" wheels off CL
• FC front subframe, LCAs, 5 lug hubs, calipers uprights, dead struts

Beyond accumulating parts I've done nothing with the car for the last few years. I've gone back and forth on whether to build or sell. I've finally decided to build. Life is still busy and very stressful but planning and wrenching on this car has been somewhat of a stress breaker.

FC Subframe Swap
I've researched this and will be installing the S5 FC subframe and front suspension in the FB. I'll be cutting up the frame rails to recess the FC subframe into the FB frame rails to avoid the roll center issuers. I'm in the process of mocking this up.

I'm hoping to find someone with a 4 lug FC to swap my 5 lug parts so that I can run 4 lug wheels front and rear.

Interior Gutting
The interior was already mostly gutted but the dash and some other unnecessary parts are being removed. The dash was pretty nasty looking and I don't need it so out it comes. Along with the HVAC system, sound deadening etc.

on Flickr

Anyone need these?

Engine Bay
Remember I said I had the S5 wiring harness? That means that I don't need the FB engine wiring harness. I removed it and just about everything else from the engine bay. I'm going to clean it up, remove some surface rust here and there and repaint it.


That's it for now. I ordered some POR15 to paint the engine bay so that'll be the next step. I'm also trying to figure out subframe positioning but it's been difficult to mock up since I don't have correct size 5 lug wheels and tires to mock this up with. Need to figure that out....

gracer7-rx7

iTrader: (16)

Work continues on this.

Found some 4 lug FC front and rear parts locally. Wound up with calipers front and rear, rotors, hubs and the rear knuckles from the FC.

I spent some time cleaning up the uprights aka spindles aka knuckles. Put them in the vice to hold them and hit them with a wire wheel on my drill then showered them in brake clean. They were pretty gross. Look much better now.


I also disassembled the hubs to check condition. The grease was nasty black. The guy I bought them from had removed the rear seal and had lost a couple of bearings so I wound up reusing the bearings from the S5 5 lug hubs. Now I need to source some seals for them.

Cleaned these up too.

I also finished cleaning up the engine bay and removed the brake booster and clutch master. Both of these look nasty. Even though the brake master was full of fluid, it only leaked from the driver side hose. They look very similar to Miata parts so I will probably try and swap them out since I have a ton of Miata parts.

Next tasks:
- continue mocking up the subframe so that I can figure out placement and where to cut
​​​​​​- quick wash of the engine bay
​​​​- list the 5 lug FC parts and FB parts for sale or toss them

mustanghammer

iTrader: (3)

Cool project, looking forward to your updates!

gracer7-rx7

iTrader: (16)

spent some time on the car yesterday. Positioned the subframe on the stock FB front stud and bolted on the strut, lca and upright to try and get an idea of how far forward / off center this will place the wheel in the wheel well. I'm going to test how things fit with the subframe mounted to the front stud then position it back ~1" to re-test fitment.

I ovaled the hole in the FC subframe a wee bit with the power drill so that I can get it through both sides of the FB studs and mount it temporarily and free up my jack.

Using the original front stud, it was obviously a little forward of center but didn't seem to have any clearance issues. Unfortunately, I need to get a tire on the wheel to truly check this. I’ll probably get a used tire mounted for temporary measurements.



The angle of the lca is ugly with the subframe bolted onto the FB frame rails. That will get fixed when I start cutting into the frame rails to recess the subframe mounting position and fix the roll center.

I really need to give this thing a wash. I hate working on dirty cars...

I just sold the FC 5 lug hubs but it seems like nobody wants the FB parts so I'm going to toss them soon.

mhr650

A problem you will be having with using the FC 4 lug front hubs, and standard FB axles is that you will have 2 different bolt patterns, and neither one is a pattern which have good availability of wheels. If you use GSL-SE axles you will have the same 4X114.3 bolt pattern, and wheel availability is better than the really odd 4X110 standard FB bolt pattern, but still pretty limited. What I did was to machine adapters to allow me to use 4X100 wheels, these fit Miata’s, E30’s, Honda’s, and I am sure others. No other bolt pattern has as many reasonably priced 15-inch wheel options, and you can easily get the wide 15X10 wheels you will need to run the latest 245 tires.

mhr650

An S5 13B in one of these cars can run pretty fast but do yourself a favor and before you even start throw away every bit of the electronics that came with the 13B. Get yourself an MS3Pro and start from scratch, it was the single best modification I ever made to my car. 80’s era EFI is so bad it really limits how the engines run, it they all go crazy rich at high RPM.



I would be happy to share anything you wanted to know about the combination I was running, it is pretty easy, and I made 210 at the rear wheels with it.

gracer7-rx7

iTrader: (16)

Yep. Also different offset capabilities front and rear - I think... The wheel question has been confusing me a bit since there seem to be multiple options and I'm not what is 'best'...

I'm not worried about the PCD too much as there are a decent amount of wheels that are dual PCD with 4x114.3 AND 4x100. Ex: XXR, Konig, Enkei etc.
I can also easily do adapters on either or both axles to convert to 4x100.
Or redrill the rear axles for 4x100 too.
I'm also not sure what the impact of the FC front subframe and suspension on offset fitment...

I'm also not opposed to having dedicated front and rear wheels with the appropriate offset for the tires I want to run.

I feel like I have too many options with regards to the wheels and I'm not sure which approach to go with... A few of the rear studs already backed out so I'm leaning toward redrilling the rear axles for 4x100. At that point, I think I can run my Spec Miata wheels on the rear (15x7 +25) - not sure if that will need a spacer. Then figure out what to do about the front. The used, cheapo Enkeis in the pic is 38 offset


ECU
On the topic of the ECU and wiring, yeah, I briefly thought about it but have not yet researched that. If you have a link to anything that I should read or info about how you did it, please post a link. Thanks!

mustanghammer

iTrader: (3)

On the wheel question, 15x7 wheels with 25mm offset will fit fine on the back. I run 35mm offset 15x8s on my car with a 5mm spacer on the rear - so a net of 30mm and they fit with inner fender lip flattened. Also my car is really low so not as big an issue at higher ride heights. I drilled my Moser GSL axles to 4x100 which makes the rears easy. On the front it is hard to say what you will need to do. The track using the OE style spindles is narrower on the front compared to the rear with GS/GSL axles.

As for wheels, straight 4x100mm wheels are lighter than dual pattern wheels or any wheel with a 4x114.3 pattern unless you look at custom made racing wheels (Real Wheels for example). I believe the extra weight is due to the wider pattern and the need for more material in the center of the wheel.

Since I converted to 4x100, I shop for wheels on Goodwin-Racing because they list the weights of what they sell. Also Tirerack works as long as you tell them you have a Miata or a VW Golf from the 80s.

Carl

iTrader: (2)

Pretty sure you will need a spacer with the et25 miata wheels in the rear. For reference, I run 25mm spacer/adapters (4x110 to 4x100) and in the rear can use ET30 to at least ET42. ET30 is pretty much the max without significant rubbing with 205 Toyos. Hoosiers might rub more, never ran them on the RX7 only the Spec Miata. I know you have a long way to go before that decision becomes critical, but thought I would comment while the discussion is still "hot".

Carl

mustanghammer

iTrader: (3)

On my car I use 15x7 Drag brand wheels that have a 25mm offset for 205/50x15 Hoosier rain tires. On the back I have a 5mm spacer and on the front I have 25mm adapters + 10mm spacers. Those are the spaces I run to get the 15x8's to fit and conveniently the 15x7s fit with out need to remove the spacers.

The rear axle/rear tire fittment on my car should match up with car in this thread as long as GS/GSL axles are used. If GSL/SE axles are used a spacer may be needed because those axles are 10mm longer than GS/GSL axles.

All bets are off on the front because of the FC conversion.

gracer7-rx7

iTrader: (16)

I've recently read many old posts from both of you on the topic of wheel size, adapters and spacers. My brain gets confused with offset and the impact of spacers for some reason...

For the sake of this post, I'm going to focus primarily on some of Carl's numbers since he runs 7" wide wheels.

15x7 +20 is the Konig wheel size that are readily available and fit the 4x110 PCD. That's not too far off from my SM size 15x7 +25 with the exception of the PCD.

Re-drill Rear: Given the above, if I re-drill the rear axles for 4x100 PCD, they might fit OK but also might need a ~5mm spacer to get to the equivalent of the +20 wheel. Correct?

Not Re-drill
Using adapters/spacers instead of re-drilling...
If I add a 25mm / ~1" adapter/spacer and am using a 25 offset wheel, that effectively gets me to a 5 offset. This would NOT work. - Is my interpretation correct?
This seems to contract mustanghammer's numbers below where he runs a 25mm adapter and a 10mm spacer on a 25 offset wheel... I'm confused again...
From Carl's comments below, it seems like the sweet spot on offset on a 15x7 is +35 with the 25mm adapter netting what I think winds up to be a +10 offset?

Am I thinking about this correctly?

Reference:
​​​​​​​

Thanks

mustanghammer

iTrader: (3)

25mm spacer under a wheel that has 25mm offset makes it a 0 offset wheel. A 5mm spacer under the same wheel makes it a wheel with a 20mm offset.

What helped me was to draw out the actual width of the wheel on paper. A 7" wheel is actually 8" wide when measured from front outside edge to the rear outside edge. So a 0 offset wheel has 4" backspacing and there is 4" of wheel on the front side of the hub face.

mhr650

If you are going to be racing on 200TW tires you need much wider wheels. To be competitive you need 15X10 wheels with 245-40-15 tires, there are even 275-35 15 200TW tires coming. I ended up using 40mm thick adapters on the front, and 20mm adapters on the rear, the fronts need to be much thicker for the tires to clear the struts. This picture is not great, but it shows the big difference between the front and rear adapters.

This shows my car with 15X9 +35 wheels and 245 tires. That is what I could get back when I was last racing my car. As I bring my car back, I will save the 15X9 wheels for narrower rain tires, and convert over to 15X10 +25 wheels since those are what are available nowadays.
It looks like my car sits high in the picture but that is mainly because the splitter was mounted high, used mainly to improve cooling and looks at that point, and avoid damage when going off track. At full compression my front tires rubbed the inner chassis structure, I want to lower it even more so I guess I will be cutting some of that structure away and adding some bars in the engine bay to make up for it.

mustanghammer

iTrader: (3)

The thing about wheel offsets and spacers is that wheel width determines allot.

First, wheels are actually 1" wider than their advertised width because advertised width is the measurement from the outside of each bead seat. But typically a wheel will have around a 1/2" material on the outside of where the tire bead sets. So a 7" wheel is actually 8" wide when taking into consideration things like back spacing and how offset affects it. I call this measurement the "total width of the wheel" and it matters more than the advertised wheel width. This sound counter intuitive but if you measure a wheel you will see what I am talking about. Also you can confirm this by looking on sites (like Summit Racing) where wheel back spacing is reported.

Offset vs backspacing on a 15x7 wheel:
0mm offset = 4" backspacing
25mm offset = 4.98" backspacing

But the back spacing changes as wheel gets wider, For example an 15x8 wheel:
0mm offset = 4.5" backspacing
25mm offset = 5.48" backspacing

Note that a wider wheel with the same offset as a narrower wheel has more actual backspacing.

Backspace is part of the equation but you also have to consider how much wheel is on the outside of the hub face. For a 0 offset wheel that is easy to determine, it is half of the total width of the wheel. With a positive offset wheel this number is total wheel width less the amount of back space.

Using the back of my race car, I am running 15x8" wheels with 30mm offset. Back spacing is 5.68" and the amount of wheel on the outside of the hub face is 3.32." This wheel combination fits my car without rubbing even with a Hoosier 225/45 mounted. To get a tire on 15x7" wheel to be in the same position relative to the inner fender lip I would need one with an 8-10mm offset.

I agonized over this stuff for quite awhile because my class, at the time, required stock fender openings but allows an 8" wide wheel. Which frankly I wasn't sure would fit under an RX7 that was lowered allot, but it does. In the end, I got out graph paper and ruler and drew out the different wheel combinations.

The final consideration are the tires themselves. So once you pick a size, study the tires you want to use and pay close attention to actual section width and actual tread width when the tire is mounted. You would be surprised how much variance their is for the same size tire across tire brands.

Hope this is useful info.....sorry if it too much of a high jack.

gracer7-rx7

iTrader: (16)

It is all useful. Thanks fellas.
Learning about a lot of new things with this car - which is fun

Carl

iTrader: (2)

Mike and Scott have both provided excellent info and have gone way farther than I was intending in my original follow-up post. I will add that I should not have said "need" when describing the spacer for a 15x7 et25 wheel on the rear. It will actually fit fine, as there is plenty of room on the inside. "No spacer" will end up leaving about 3/4" of space on the outside of the wheel that you could use to widen the track a bit. It is probably questionable whether that extra 1.5" (2 x 3/4") rear track width would be noticeable.

I am continuing to use 15x7 wheels because: they are the max width allowed in STL/ITA with SCCA (which is where I race the car when not doing enduros with LDRL and ChampCar), I have lots left over from my Spec Miata days, and I am a budget racer.

Maybe I will see you at Laguna the weekend before Thanksgiving.

Carl

gracer7-rx7

iTrader: (16)

Made good progress cleaning up and painting the engine bay.

The astute among you reading this may wonder why this idiot is painting the engine bay since he plans on cutting and welding the frame rails… I wondered that too as it was messy, dirty work.

I think it was because I wanted to make sure that the ugly rusty areas were just surface rust. They were and cleaned up nice.

Before:



I was able to get the rust off using cheapo harbor freight wire wheels on my power drill. Then I washed everything using POR15 degreaser. Then rubbed it all down with red scotch bright pads and occasionally some sand paper or a paint stripping wheel. Then sprayed it down with POR15 metal ready to convert any remaining rust.

During:




Next, I brushed on the POR15 paint


I’m done for now. The bay is clean. The rust is gone and the areas that I took to bare metal are sealed and everything has an initial coat of paint. Once I’m done with cutting and welding, I’ll give this a final coat of gray.

Time to break out the angle grinder and measuring tools!

Happy to be working on a clean car too.

Carl

iTrader: (2)

I got a chance to see it in real life last weekend, when I broke an axle at Laguna and for the first time in years did not have a spare axle at the track. Alberto graciously offered to loan me one from his car. After a 90 minute drive each way everything got reinstalled and we finished up the last 20 minutes of the race. Sunday the axle worked great, although the carb flooded at the end of the second stint resulting in flames coming out the tailpipe and a melted exhaust hanger. 45 minutes, some bailing wire and some carb disassembly later we were back on track.

His car looks as good in real life as in the pictures. Seems like a good base for further mods.

Thanks again Alberto.

Carl