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Login to post Forums » Grassroots Motorsports » Sec Gen RX-7 Q&A

Oct. 2, 2008 4:49 p.m. Goldmember None

So, I know there are a few of you out there that own or have built SBC powered RX's. I just came across an extremely clean chassis (GTU even) with an ailing motor for $1200 asking price.

Q's: - How much fabrication to get the engine in and happy? - How bad is it to get a late model 5 spd to fit and function, how bad do you need to cut up the tunnel? - How is the handling with the newly found lump of torque inducing iron up front? - do you feel it is a worth while swap with a total target of about 275-325HP & 300-350 lb/ft for a total investment of under 5 Gs(hopefully closer to 3500-4grand)

This is a fun car, not intended to do anything but make me smile on the street and at an occasional auto-X.

As: ????
Oct. 2, 2008 4:57 p.m. Sofa King New Reader

It is a pretty easy swap. I used a paired down version of the grannys kit and there was virtually no cutting or welding. Easily had mine under budget for the 2004 Challenge even with buying the kit instead of fabricating. I went with a 350 w/ 700r4 auto because the car was originally and automatic. The tunnel didnt need any modification. (might have BFHed a little, but it has been so long ago I don't remember.) Car handles well, mid pack at the Challenge autocross, and could have been better but we drove it rather than using a ringer.

The manual shouldn't be too much of a problem. I did a monster Miata with a 1" Wilwood master and a pull slave. Depending upon your trans flavor it should be relatively simple,
Oct. 2, 2008 5:30 p.m. Goldmember New Reader

That sounds encouraging. I am not afraid of fab work, in fact I love it, but I was hoping this project would be fairly straight forward. I really don't need it, but the price/condition of the RX makes it just soooo tempting. I figure it would take a lot more coin to buy a factory high horsepower RWD in a good looking body than it would to build this project.

I'm also disgusted at the price of decent muscle car projects, so while this wouldn't quite have the character, it sounds like it would handle a heck of a lot better than most vintage Iron
Oct. 2, 2008 5:40 p.m. P71 Reader

Well Josh built an LS1/T56 FC (2nd Gen RX-7). The motor is all stock and the car has mainly suspension mods (Tein Flex's, swaybars, etc). He's consistently in the Top 5-10 overall (out of 50-60) with the PCA up here, and that's on street tires. I drag raced it to the tune of a 12.45@114. Needless to say, it's a very quick car no matter the form of motorsports.

I'm seriously considering doing a similar one, only using a SBF and an FB.

Josh used the Hinson kit, though I've heard great things about Granny's as well. Damn near a bolt-in swap.
Oct. 2, 2008 10:31 p.m. YaNi New Reader

The official V8 RX-7 Forum

If your car is an S5(89-90) GTU, it is the base model with a 4.10 open differential, single piston front calipers, and solid rear disks. If it is the 88 GTU it is a rare sports model with a clutch type limited slip diff and the turbo brakes and suspension. The n/a clutch type limited slip diffs will work with v8 power if you aren't a drag racer, as launches on sticky tires will kill it in a hurry. The 8" turbo differentials are a worthwhile upgrade and can handle big turbo power. The LS1's add <100lbs to the car, and don't noticeably upset the balance.

Personally I prefer a rotary in an RX-7, but a near bolt in 350hp and 350 torques is hard to overlook.
Oct. 3, 2008 6:44 a.m. Jensenman SuperDork

I have a buddy finishing up an LS1/T56 in a 1990 'vert, it was an easy swap. It's going to be his wife's car so it has to have A/C, etc. The only screwball part was the speedo; the tranny has an electronic sender and the RX7 has a cable. He got one of those conversion boxes which has an electronic input and then uses an electric motor to spin the speedometer. It appears there are only seven wires which need to be spliced into the RX7 harness.

If you are in the Columbia SC area and get behind a white 'vert driven by a lil' brunette that has 'THINK2X' on the tag, yeah you better think twice.
Oct. 3, 2008 6:53 a.m. Chris_V SuperDork

it's incredibly easy to make a V8 RX7 handle just fine. In fact, if you use or make the right mounts, the weight is carried evenly f/r so the weight BALANCE is not upset. My 5.0 powered RX7, with $20 homemade mounts, had a 49/51 f/r balance and weighed a mere 2720lbs overall (with a full interior and Autopower 6 pt cage). And it was a major blast...

http://home.comcast.net/~adesso/rex3.wmv

http://www.freewebs.com/adesso/mounts.htm
Oct. 3, 2008 7:44 a.m. YaNi New Reader

One problem with the carbed SBC is that you usually need to cut a hole in the hood, or get very creative with your intake setup. Thats why the LS1 is recommended over the 350.
Oct. 3, 2008 8:14 a.m. Chris_V SuperDork

With my Ford engine, I called that the "$3000 hole" as putting the hole in the hood saved me $3k over getting an LSx setup.
Oct. 3, 2008 9:36 a.m. P71 Reader

The hole in the hood for my future FB/AMC 401 project is going to be a LOT bigger!
Oct. 3, 2008 2:56 p.m. Rangeball New Reader

I always wanted to know if a swapped second gen would make a decent track car. Say over a turbo Miata? I am sure that can't be though, especially on this board.
Oct. 3, 2008 5:33 p.m. P71 Reader

Well Josh's LS1 FC beats two turbo Miata's and loses to one. Depends on the course and/or driver.

Out on the actual road course though it's no contest. V8 RX7 FTW!
Oct. 4, 2008 8:25 a.m. Goldmember New Reader

This is great feedback, thank you all a thousand times.

now:

This is horrible news, now I will have to go look at this chassis and if it is in at least 75% of the described condition I will most certainly buy it. I will have one more project that I don't really need, and I owe it all to GRM and its loyal fan-base

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