Building a Rotary for Towing
 

Lately I've been thinking about building a rotary pickup. I need a tow vehicle, and I like rotaries, so, two questions:

What is the best parts combo for a rotary engine used for towing? I'm thinking 6port motor into slushbox into 4.60 gears. Is there a 5speed tranny that has a really low 1-2, and an overdrive?

What's the best mini truck, in terms of style, features, strength and parts availability? The B2XXX series would be the obvious choice, but I don't need to stick to Mazda. Maybe a RX-10 (rotary S-10) or a Ro-Ranger.

In terms of capacity, figure 4-5000 lbs max towing, not very often, and flat ontario landscape, so no mountains or anything.

So that's it... Discuss...

get a repu?

don't use torqueless rotary engines for towing?

I'd have to say REPU, too. My freind and I have a few and they're great for towing things large and small.

A supercharger is always going to be better than a turbo for a rotary that's going to tow. It's kinda funny that fellow forum user banzaitoyota was trying to compare a turbo diesel to a rotary recently and didn't seem to understand why a turbo on a diesel is great while a turbo on a rotary that's going to be used for towing, wouldn't be as useable. At low RPM, what's going to spool the turbo? At least with a super, we've got instant boost at anything above idle.

Didn't mean to get sidetracked. I doubt you'd want to get that involved with your project. Anyway, an NA 6 port engine should provide nice useable torque, and a 4.626 rearend, such as found in the '74 manual REPU is a good one. As for the tranny, the stock REPU and other early ribcase trannies have very low geared 1st and 2nd, while 3rd is really tall comparebly, and 4th is of course 1:1 as it is on all Mazda trannies as far as I know. 5th is optional, although it's nice to have when your diff is geared 4.626. The '74s came stock with a 4 speed or an auto.

'74 manual 4.626
'74 auto 430 (I don't know the actual numbers, but 4.30 is close enough)
'75 manual 430
'75 auto 411
'76 manual 411
'76 auto 390
'77 manual 390
'77 auto ???

As you can see, Mazda attempted to improve the gas mileage over the REPU's production run by giving it progressively taller rear gearing. I very much enjoy the 460 diff gearing of both my '74s, but my top speed is around 110MPH or so. That's ok as these trucks have the aerodynamics of a brick anyway.

The payload capacity is really great for such a small truck. It's 1400LBs which is just a little under 3/4 ton. Not bad for a 1/4 ton style truck. They also have dual wheel cylinder in the rear and were the first minitrucks to have disc brakes up front. Compared to the B series pickups, the REPUs are more solidly built and can take plenty of abuse.

REPUs are really rare. You;d probably be better throwing a rotary into a B series and a B2600i rearend so you can swap in the REPU 4.626 uh, pumpkin. The B series pickup's tranny can be combined with a rotary tranny, but I'm not exactly sure which years of parts interchange. Anyway, you're left with the correct bellhousing for a rotary and the shifter will come up in the stock position.

I recommend getting the Racing Beat oil pressure and temperature adaptor and a set of aftermarket guages so you can keep an eye on oil temps while low speed towing when very little ram air is flowing through the radiator. Hint, hint. ;)

If you wanted to have a lot of low end torque, I'd consider one of these electric superchargers. In the low rpm range they beat any other supercharging option.
http://www.boosthead.com/home.php

Of course you'd need some extra batteries and a larger alternator, but weight doesn't really matter in your case. Also this supercharger is relatively inexpensive and you have more flexibility where to mount it. Since it's a centrifugal superchargers it's also more efficient than most other superchargers besides it doesn't really generate any parasitic loss (if you neglect the power that you need to drive a larger alternator).

If you just need it to accelerate, it'll be good enough for this job. (Keep in mind once you reach a certain speed you don't need any boost anymore.) If you try to pass some 14'000ft mountains and constantly require boost it won't work.

Torqueless? That depends on which rotary your talking about.

Look here:

https://www.rx7club.com/attachment.p...chmentid=84975


This is a freshly rebuilt 20b w/non seq twins from pettit racing. This was the initial tuning. This was done at only 6psi. With the torque available at 3.5k rpms, he wouldn't have any problem towing anything with a rotary.

What...Do you get a cut from every one of these sold?

Good info so far. The reason I didn't consider a Repu first is because of the rarity factor. Plus, this is going to be a shop truck, so building a frankenstein that works is good advertizing.

Supercharger is a great idea. Anyone ever graft a 6-71 on a rotary? I'm really thinking about an 80's ranger now. RangeRotor is kind of a cool name. Box the frame for strenght, 9" rear will have any ratio I want, could be a neat little truck...

ive seen a 3-71 on a rotary. as far as gearing you might want to look into a gearvendors unit http://www.gearvendors.com/

I'm currently doing a frame-up restoration on a '53 chevy truck, I thought about doing a n/a 20b. It would have been neat, but in the end it wasn't worth it; I blueprinted and pimped out the inline 6 for way less money.

Since I wanted it to be n/a it pretty much would have had to be a 20b to get decent torque at reasonable rpm's.

I wish they'd give me some sort of kickback for all the free advertising I do for them at times like this. Actually, I find it comical that I have one of those temp/pressure adaptors just sitting around, never used. It's still worth more to me just sitting there than to sell it for anything less than the cost of a new one. Oh well, I'll find a use for it someday. Perhaps on a supercharger project?

A Ford 9" is a good idea. The REPU rear is similar to the Ford, but just different enough to not let people like me swap parts around for LSD etc.

Speaking of the torque of an NA 20B, check this out. Stock internals, stock injectors etc, and it's nice and flat. http://fc3spro.com/PROJECTS/SKY/20B/20bna01.jpg