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Hey guys I've been a long time lurker and finally took the plunge last week. This car will be mainly for autocross for now. I plan on just making this car fun and am not worried about what class I'm in. I'm using the Chris Gibbs frame but modified to resemble the CSR SV chassis. I will also be fabricating everything myself if possible and using one donor to cut costs.

I went and bought a great condition 1988 RX7 GXL w/ only 101k miles. It was owned by an old lady for 20 years and by the second owner for less than a year before the clutch went, so I got the car for a really good deal. $700 w/ two sets of the 11.5lb BBS 15" wheels. Those wheels will be perfect with 205/50R15 and 225/45R15 tires. It also comes with a whole ton of goodies that I have parted out to earn back the cost of the donor.

I also went and bought almost all the ERW tube that I needed. Still need to find a cheap supplier for the seamless as I need a whole ton to build a full rollcage. I plan on integrating the rollcage into the frame of the car. Anyways, I got 144' of 1" square, 40' of .75" round, and 20' of .75" square all for $80. It's 1020 CRS too! I got it from a tubing manufacturer so there was no middleman.

Now for plans. I am bridgeporting and installing hayabusa ITB's before the engine goes on. Part of the reason is for a MUCH smaller and less complicated engine and less weight, and the power from ITB's doesn't hurt either. I was considering just putting on the ITB's and not touching the engine but later on when I want to bridgeport it I would need to change runner length and I decided to just get everything done with at once. The engine will be managed with Megasquirt I. Transmission and LSD will come from the donor, but I might use Miata axles since they seem to be shorter. I'll look for a manual rack from a MG or something.

For now I am still parting out the car. I should be done in less than 2 weeks. After I take the shell out of the garage I'll get the build table going. I frequently make custom exhausts and can TIG well pretty well so I don't feel like the welding will be the biggest challenge for me. The biggest challenge will be designing the proper suspension geometry using the RX7 knuckles. I plan to use all heim joints since this won't be a regularly street driven car and comfortability is not an issue. I'll definitely look into what emile did since his setup is pretty close to mine.

Steven

Shoot. That's a good looking RX-7. Fix it and sell it for four times what you paid and then buy a proper POS donor that I don't mind seeing die.

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He is a wise man who does not grieve for the things which he has not, but rejoices for those which he has.

Well I already did that when I got my last RX7. If I keep buying and selling rx7's I'll never get a donor Plus I wanted a donor with a drivetrain in good condition with low miles.

Wow, thats an amazing price for tubing. Where abouts did you go? Is there a tubing manufacturer in your town or something?

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+442E, SR20det, Thunderbird/Markviii IRS with clutch lsd, R1 suspension all around, Mustang II 2" drop spindles, Woodward steering rack

Welcome Steven and congratulations on a couple of locost purchases ( donor and steel). There are several of us who are building similar rotary cars, each with our own flavors.

What I would do over if I had the chance is to build a +4 wider chassis. It is ideal for the RX-7 rear end. I have a Champion book frame and had to shorten the halfshafts.

Keep your log going as you continue your build and keep us informed.

Chuck

I'll offer a different opinion. IMHO you only have to shorten the half shafts if you don't like the wide track and wide rear fenders. I used an 88 RX-7 LSD and housing with 99 Miata halfshafts on my book car. I'd guess the track is about the same as the stock RX-7. The pic below illustrates it pretty good. Note the extra space between the tires and the frame. It doesn't hurt the looks of it IMO and it's a small price to pay for a wider track. (it actually makes the shocks a lot easier to mount and adjust once they are on there)

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He is a wise man who does not grieve for the things which he has not, but rejoices for those which he has.

Hi Steve, glad to see another rotary build. I am useing a Chris Gibbs (+2 over book) frame with parts from a 1986 RX-7. Here are some pics from the back with stock rims and 195 65 R14's and 8x15 "0" offset rims with 225 50 15's.

well with the offset input flange on the differential and reduced passenger area I'm considering making a wider chassis. If you guys had to do it all over again, would you have gone with book, +2, or +4? I'm 6' 0" 170lbs so I'm not that big of a person. Emile seems to have widened his by 2" and Ralph started with +2 so maybe I'll go with that.

I'm happy with the book, but that's just a personal preference. The original Lotus 7 was smaller than the book, so any bigger IMO is more of a departure from the original than I want. I'm 5-10 and 185 (trust me it's solid muscle- I appear to be hewn from solid stone ) and I fit fine.

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He is a wise man who does not grieve for the things which he has not, but rejoices for those which he has.

I am 6'1" - 235bls and I have plenty of room. Leg room is not a problem in these cars IMO .

That's a nice donor .
With regards to chassis choice, for a guy your size the book should be fine.
I recommend reading this - http://www.locostusa.com/forums/viewtopic.php?t=4603

Moti

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Moti

My R1 powered Locost build log

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As I was removing the differential today I came across something. By going with a 22.9" tire I'm reducing my tire OD by 7.3%, which means I need to decrease the amount of gear reduction by a similar amount. The 3.9:1 LSD out of an automatic GXL will spin 5.1% faster than the 4.1:1 LSD that came in my manual GXL. It won't be expensive, just hard to find. I'm staying w/ a 15" wheel because a 13" wheel will not clear my 4 piston calipers. Even if I had gotten the 13" wheel (Which I can't) and gone w/ a 20.9" OD tire then I would have needed to try to find the 3.63 gear, which would have been much more difficult to find and expensive.

Did you try fitting a 13" wheel over the brakes?
I'm asking because I am going with 13" wheels and wa wondering about the RX7 4 piston calipers mainly to reduce unsprung weight.

Moti

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Moti

My R1 powered Locost build log

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I took a quick measurement with a ruler and it's 6.5" from the center of the hub to the farthest point on the caliper... So if I want to use the factory upright and 10.9" rotor then unless the 13" wheel was bigger than 13" on the inside where the caliper is, I don't think it's going to work.

All 5-lug came with the bigger bigger rotors. Because I don't want to get smaller rotors and make a custom upright, I'd rather live with 15" wheels. You probably have smaller rotors so if they're a similar thickness and you're making a custom adapter bracket or upright then it may work for you. Only issue with staying 15" is there is no tire size in between a 225/45R15 and a 275/35R15

I'm wondering if the RX7 calipers could be adapted easily to the miata upright with just a simple caliper bracket...

Moti

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Moti

My R1 powered Locost build log

Visit the Blackbird Fabworx Facebook Page!