RX7s and Rotary Swaps

Enlighten me. Is there any reason to keep the 13b rather than swap in a 20b, except for price and effort? And I assume it moves the COG forward X amount of inches.

Which RX-7? Makes a big difference as the ancillaries on the later ones (FC and FD) seemed to expand to fill all available space.

Sticking a 20B into a 1st gen should be possible, I think there is (almost) enough space if you misplace the engine-driven fan and fan housing and replace it with an electric push fan. Obviously you'll also want to upgrade the cooling system I doubt that the standard radiator can cope with the additional heat being generated.

On top of that, you'll need to sort out the engine management and that's potentially a non-trivial (read: more expense) task. I don't think there is a dizzy available that can run a 20B although I'm happy to be correct on this, so you're looking at something like Megajolt at the very least to run the spark (if that can even do it, I'm just guessing) or a potentially an expensive standalone engine management system.

Of course, it all boils down to price and effort, with enough of each I'm sure you can make it fit .

Oh, and another point that tends to count against it - 13Bs are already not that brilliant on fuel, 20Bs are even worse.

Ah I've got an FD in mind. I see all the RX7 guys shoving those 20bs in there. Greater torque and longer life seem to be the biggest pros, but whenever I hear that someone wants greater power they go straight to a 20b (or talk about it). I'm surprised; I thought I would hear more about tuning the 13b.

The big problem with the 20B is the LS1. More power, better CoG, cheaper...

Osterkraut wrote: The big problem with the 20B is the LS1. More power, better CoG, cheaper...

Very true, but the LS1 is so common and part of the appeal of the RX7 is its rotary.

IIRC it's quite major surgery to get one into an FD as the engine is kinda to long for the bay. It's doable but you end up relocating a heck of a lot of parts.

I'm also not that big a fan of LS1s in RX7s but I guess for the money required to get a 20B into an FD, you can probably buy a Corvette C4, swap the LS1 into that one and stick a 13B into the FD.

Longevity of the 20B very much depends on how high you crank up the boost tho', much like the 13B.

BoxheadTim wrote: IIRC it's quite major surgery to get one into an FD as the engine is kinda to long for the bay. It's doable but you end up relocating a heck of a lot of parts. I'm also not that big a fan of LS1s in RX7s but I guess for the money required to get a 20B into an FD, you can probably buy a Corvette C4, swap the LS1 into that one and stick a 13B into the FD. Longevity of the 20B very much depends on how high you crank up the boost tho', much like the 13B.

Yeah, what I've head on the boards is that the 20b moves the COG forward 6 inches. Now, I did say "heard on the boards..." so heck if I know if that's accurate, but I do know that it's a fair bit longer. Lots of fabrication for the job. So much that I wouldn't even consider it if not doing it myself (but what fun would that be?)

With an equal amount of boost and all other things being the same, I would expect the 3-rotor 20b to last longer.

JeepinMatt wrote: Yeah, what I've head on the boards is that the 20b moves the COG forward 6 inches. Now, I did say "heard on the boards..." so heck if I know if that's accurate, but I do know that it's a fair bit longer. Lots of fabrication for the job. So much that I wouldn't even consider it if not doing it myself (but what fun would that be?)

From researching that swap myself, my impression was that the change in CoG is the least of the problems - you'll end up moving the radiator and ancillaries further forward due to the increased length of the engine so you're pretty much rearranging everything under the hood.

JeepinMatt wrote: With an equal amount of boost and all other things being the same, I would expect the rear tyres on a 3-rotor 20b equipped car to last about two minutes.

Fixed that for ya.

BoxheadTim wrote: From researching that swap myself, my impression was that the change in CoG is the least of the problems - you'll end up moving the radiator and ancillaries further forward due to the increased length of the engine so you're pretty much rearranging everything under the hood.

Yeah that whole swap pushes everything out so far it makes me wonder if it's worth it. I mean if I wanted a Japanese Camaro, I'd buy a Supra (don't attack, Supra-people) The RX7 is interesting because it's a well-balanced, relatively lightweight (2800 lbs minus the unnecessary stuff, like carpets, A/C, radio etc... ) Screwing with that 20b might be great for the drag strip, but I'd rather stick with the 13b and keep that weight more in the middle of the car.

JeepinMatt wrote: Yeah that whole swap pushes everything out so far it makes me wonder if it's worth it. I mean if I wanted a Japanese Camaro, I'd buy a Supra (don't attack, Supra-people) The RX7 is interesting because it's a well-balanced, relatively lightweight (2800 lbs minus the unnecessary stuff, like carpets, A/C, radio etc... ) Screwing with that 20b might be great for the drag strip, but I'd rather stick with the 13b and keep that weight more in the middle of the car.

Strangely enough, that was also the conclusion I arrived at. I figured that if I wanted a 20B I could always try to hunt down a Eunos Cosmo but I guess that option isn't open for you if you want something street legal.

JeepinMatt wrote:

Osterkraut wrote: The big problem with the 20B is the LS1. More power, better CoG, cheaper...

Very true, but the LS1 is so common and part of the appeal of the RX7 is its rotary.

Amen brother. IMO the appeal of the RX7 "IS" the rotary. They are like peanut butter and jelly. Or maybe I am just a little hungry now.

i have tinkered with the idea of 20b n/a for the rally/hill climb car, but the cost and weight is still a hesitant in my mind. Then again im a poor ass.

Cost is a major factor with a 20B. I've yet to see one from a JDM wrecker that costs less than $3900.

Feedyurhed wrote:

JeepinMatt wrote:

Osterkraut wrote: The big problem with the 20B is the LS1. More power, better CoG, cheaper...

Very true, but the LS1 is so common and part of the appeal of the RX7 is its rotary.

Amen brother. IMO the appeal of the RX7 "IS" the rotary. They are like peanut butter and jelly. Or maybe I am just a little hungry now.

Here here. I can't tell you how many people told me to put a 302/350/LS1 in my FB when I bought it. That girl's getting a 13B-RE and it's going to be AWESOME. How many other cars do you get to play with a rotary? They're just so interesting.

I'm holding out for the 16X. I really hope it's everything Mazda cracks it up be.

RexSeven wrote: I'm holding out for the 16X. I really hope it's everything Mazda cracks it up be.

Hmm, someone will inevitably shove one into an FB, FC or FD. From what I understand it's still a two-rotor design, although the rotors are a little bit bigger, so I don't see any/much of an increase in weight/length.

rx7club has info about 20b swaps. or google around.

This place does a nice conversion kit into the FD chassis that retains the stock engine subframe and steering angles: http://definedautoworks.com/

Other places make replacement engine subframes that position the engine slightly lower and bumpsteer kits. I think Pettit has one.

Price and effort is the issue. Most people just add boost.

This is a 1st gen, but the same method could be used for installing a 3 or 4 rotor in a FD...i could fit a V10 if i wanted too... http://members.tripod.com/~grannys/GSSshopmule2010.html

I'd love to find a straight FB, put it on a diet, & drop in a Renesis.

Bone stock, you've got 232 hp & 159 lbs of torque to play with so it's just a matter of finding a light host that can handle the power. All the better if said host is pre smog inspection though...Opel GT...X-19...914.

I built this 4 rotor and car about 15 years ago... http://grannys.tripod.com/4rotor.html , wish i would have stuck one in an FB before i was cured of rotary fever

The best rotary swap only involves one rotary.

JeepinMatt wrote: With an equal amount of boost and all other things being the same, I would expect the 3-rotor 20b to last longer.

Why's that?

ReverendDexter wrote:

JeepinMatt wrote: With an equal amount of boost and all other things being the same, I would expect the 3-rotor 20b to last longer.

Why's that?

Seems more robust, not so high-strung (not that they can't be made to be) I don't know much about rotaries, but the 20b being longer-lived than the 13b seems to be the consensus as well.

Welcome aboard, Granny! I've been lusting over your kits for quite a while. I don't care if evrybody and his brother has done it before, a 5.0 in an FB just calls to me!!

You guys are making big assumptions on longevity. Its completely a matter of setup, tuning, maintenance and usage.