Contemplating a 3.8 SC swap into a 1979 Mazda RX-7

C

cook11

Registered User
I currently have a 89 Supercoupe with a badly rusted body with a good engine and 5spd and a 1979 RX7 with a good body and a shot 12A Wankel. Has anyone seen or heard of a SC powered RX7? I tried doing a forum search but came up empty handed. I would really like to know how much the SC engine weighs fully dressed compared to a fully dressed 302 or 351W.

Another question I have is how difficult is it to convert the supercharger setup for a turbo? How much turbo boost can the stock 3.8L Supercoupe block and internals safely handle? Just curious.....

Thanks in advance!
 
I had thought about putting one into a gen2 RX7 awhile back. There have been plenty of people put 302's in them - which shares the bellhousing bolt pattern with the 3.8's.

Not sure how the weights compare.

I put about 20psi on my stock shortblock.
 
You could make 400 Hp on the stock block with some turbos. I say go for it!

I've been beatin the poo out of my stock block recently with a bent rod:D and a twin screw blower somewhere in the area of 20 psi.
 
I have been contemplating a carbureted 351W swap which might be easier hell I have even thought about stuffing a 460 with aluminum heads in place. I own a F150 ecoboost and I really enjoy how quiet and powerful the V6 twin turbo is. My biggest set back from performing the 3.8 SC swap is the electrical work required to make it run. I am really having a hard time deciding on which swap I should do.
 
Would be an interesting swap but don't know if I personally could get behind it. RX-7 IMO should keep the Wankel just like a SC should stay supercharged.

Better than LS or Windsor swap though.
 
I haven't come across that swap before, but I see no reason why it couldn't be done, and I say do it! An SC engine, complete with supercharger, intercooler, and all piping, does weigh in a bit more than a 302, but not enough to worry about, and certainly way less than a 460. My advice would be to keep the supercharged setup rather than converting to turbo, at least until you get the car up and running. You will need to do a custom FMIC setup, but that shouldn't be too hard. Also you will have to check where the shifter location is relative to the engine, but I suspect you will need to run a T5 instead of the stock M5R2 that came in the SC, if for nothing else than for shifter location. This isn't a big problem though because the ECM won't care which transmission you have behind the engine, T5s are cheap, and with the much lighter weight RX7, it will probably hold up, at least to a mostly stock SC engine. If it doesn't, then at that point the TR3550 will be a direct bolt-in swap. As far as wiring goes, my advice to everyone first swapping an EFI motor into a carb'd platform is to pull everything without cutting any wires, then look at the ECM connector pinout, and just take it one wire at a time. Most wires will be going from the ECM to a sensor, so you won't need to touch them, and most of it is going to be routing what wires need battery power, what wires need key on power, and what wires need ground.
 
That would be awesome if you would put the SC engine into the RX-7! There's a guy who had put a Chevy small block into an RX-7 here, along with some modifications to the body (rear fenders extremely louvered) that makes it look like a one of a kind car. It kind of looks like a really small Mako Shark Corvette in some ways.
 
A lot. Many guys are running over 400ft-lbs through them, and that is in a car that weighs close to 4000lbs. In a lighter car, it would hold up to even more.
 
20psi with a turbocharger on a cammed 3.8l with splitport heads is going to make a whole lot of power. If you figure a 3.8l with healthy cam and good heads typical power output is in the 250hp range. At 14.7 psi the engine hp will double making it a 500hp engine. Add another 5psi for a total of 20psi and at roughly 17hp per psi this gives you 585hp engine. Given 15% drivetrain loss the will put you roughly at the 500rwhp mark at the tire. Not sure how blowers efficiency work but should be similar if running a screw style blower but account for higher parasitic loss to drive the blower.

I think putting this engine into a light chassis of an rx-7 is a good idea. Although it would not be my first choice of engine. I would run the entire engine harness out of the sc and spend the cash on a good maf off top. The ford ecu's can support a lot of power before upgrade is needed. Good luck.
 
id love to feel how this 3.8sc would feel in a light smaller car..i alwyas thought the 90+ tbird and cats should have had a 351 option or 5.0 standerd and then 94+ should have had the 5.0 gt40 motor or a lincoln 32v...they alwys under powered our cars. couldnt have a entry level car be faster than the mustang..pft.
 
Oh dear... Another Rx7 engine swap. Pretty soon there will only be like 14 Rx7s in the world that STILL have rotarys - Aside from that, with a really short wheelbase of an FB, and 300 ft lbs of torque at ~ 2,000 RPM I will be happy to see what the oversteer would be like --- I can barely keep my '94 out of the ditch now :)

That being said, that kind of oversteer is what makes drifting an FB, FC, of FD worthwhile, so I say go for it!
 
i say go for it, i had an 82 with a blown motor and the only thing keeping me from dropping my spare supercoupe engine in was the fact i didnt have any money, if i still had that rx7 it would be ford powered right now.

please do it, i wanna see.
 
You must log in or register to reply here.
Back
Top