13

Moar Horsepower?

The 1979 Mazda RX7 - Desireable Track Car

It seems this platform is very popular in club racing today. You see them as prized possessions at SCCA gatherings to simple track days. The Wankel engine can be punished time and time again and doesn't suffer from the same weaknesses as the standard reciprocating internal combustion engine.

As well, this car is light compared to it's brethren and when given upgrades it's power to weight ratio is hard to beat.

My Questions:

How can I make the internal combustion engine better?

*What are some of the performance upgrades that really bring everything together?

OR, simply put

How do I get more overall horsepower out of this fantastic platform?

  • 3
    Put an LSx engine in it. – Pᴀᴜʟsᴛᴇʀ2 Apr 22 '16 at 20:50
  • 1
    Of course, because that's the only engine on the planet. lol – DucatiKiller Apr 22 '16 at 20:55
  • Putting a reciprocating engine in that body is heresy.. – cdunn Apr 22 '16 at 20:59
  • 1
    @cdunn - Only if you hate making reliable power ;-) – Pᴀᴜʟsᴛᴇʀ2 Apr 22 '16 at 21:02
  • 1
    The rpm governor on most rotary engines is the size of the carburetor or fuel injection system, they have almost no rpm limit, so increasing the fuel delivery will allow more rpm's and horsepower. – Moab Apr 26 '16 at 23:40
19

I agree with your praise for this car, I had one back in the day and I have never loved a car as much since.

To get more from this Wankel powered beauty, it's all about two things:

  • Getting it to breath better
  • Replacing parts that won't take the higher RPM

The good news is that the only part that needs to be replaced, is the RPM gauge sender on the face plate of one of the rotors. It's plastic and won't take the additional rev's well. But, at the time anyway, there was a brass one available.

So, getting it to breath better, there are a couple things here:

  1. Starting at the intake track, the stock air cleaner and carb need to go. there were downdraft kits available from Weber that really opened up the first part of the intake. There are also air cleaner kits available that have 360 degree openings that allow lots of air to get in.
  2. In order to get the air into the engine, you have to open up both the intake and exhaust ports. I'm not 100% on what the shape needed to be, I think it was just the same shape just make wider, but I don't remember at that level of detail. I do know that you needed to open up both the intake and exhaust ports.
  3. Speaking of the exhaust ports, the first thing the exhaust runs into here is a reburn chamber. The Wankel does not burn fuel terribly efficiently and this big bag filled with hot platinum was there to convert the raw unburnt hydrocarbons into something more emissions friendly. Unbolt it from the engine, and throw it away.
  4. Replace that burn chamber with straight pipe. There were several kits available from Rotary Engineering, but that was decades ago, and I don't know if they are even still in business. But what you need is an exhaust header that collects from the two rotors and brings hem to a collector, just as they would for a reciprocating engine.
  5. Put a more open exhaust on it next. From the collector to the tailpipe it was pretty easy to go straight from the collector to the muffler. There was not a lot under the car that got in your way. Because you will be running with a lot more unburned fuel coming out your tailpipe, you need to put tips on the muffler that extend it beyond the end of the car. Otherwise you build up a black coating on the bumper and back corner. This can also mean it's running to rich and may need to readjust the carb to lean it out some. There's no ECU in this car to do that for you.
  6. Once you had added the horsepower, you can now use the over rev buzzer as a shift light.
  7. On the '79 in particular, watch for rust on the rocker panels. Having added that horsepower, you don't want the body rotting out from under you. They were known for that. It was the one big issue with them.

I hope that helps!

  • Porting is a huge part of performance RX7 builds. The effects of different styles of porting are very pronounced and are essentially the same as changing the camshaft timing & valves on a traditional engine, at the same time. Add a peripheral port and you'll have an ENTIRELY different beast, that's for sure! – Stephen Arsenault Apr 22 '16 at 22:08
  • Thankfully in Arizona we don't have that thing you talked about...rust? yeah, we don't have that problem. – DucatiKiller Apr 22 '16 at 23:26
9

Just like with any other internal combustion engine, there are two ways to increase power output: add more cubic inches of displacement; make the motor think it has a larger displacement.

More Displacement

The rotary engine (Wankel) is a different breed. You cannot just bore/stroke the engine like with other piston based engines, so you have to go a different route. The easiest way with these is to add more rotor lobes. There are kits you can purchase which will allow you to easily do this, though it does take some expertise. Each rotor of a Wankel engine should roughly be considered a 3-cylinder engine if it had pistons. By adding another rotor, you are making a 6-cylinder engine into a 9-cylinder engine (going from two to three rotors). This should have an effect of adding upwards of 50% more power to the engine combination.

Pseudo Larger Displacement

What I mean by this is to turbocharge your engine. When you turbocharge an engine, you are pushing more air/fuel into the engine, which can allow it to create more power. Due to the way the Wankel engine is designed, there are diminishing returns for this, though. Since there aren't any valves or camshafts, there is no way to control timing events to optimize how the engine will run with the turbo installed. Some of the air/fuel mixture ends up being burnt in the exhaust manifolds. This is a loss of power.

Other items in this same vane would be to look at other power adders, such as nitrous oxide, which throws a denser air/fuel mixture into the engine, causing more power to be created.

Mind you, this list is not all inclusive. As evidenced from the @cdunn and @racefever answers, there are other ways to increase power, just not as drastically as what I've talked about here.

7

Mow much money do you have? :D

In all seriousness:

  • Swap in a later 13B engine and give it a fresh rebuild.
  • Install a Racing Beat header and exhaust system.
  • The Racing Beat intake is also pretty good. Mind you, this is setup for the upper rev range.
  • Put a good carburetor on it, like a Holley 600 (mechanical secondaries).
  • Do not remove the belt driven fan!
  • Put some gear in it, I don't know if the R200 gear and pinion will fit that year. Look into those. When I say put some gear, I really mean it.
  • Tune it like you hate it.

Get a really big radiator and a set of twin electric fans. You'll need it.

Do you have a lot of money and enjoy blowing seals with boost?

Buy a later 13B-REW and swap it in. Remove the crappy twin setup and put a single turbo with a smallish head unit (like a GT28 sized with ball bearings). Get the 6 speed transmission too while you are at it.

Honestly, learn how to drive it first. Rotaries are hard to drive at speed because everything you know about keeping the engine on its sweet spot is different. Rev the hell out of it.

Buy some AAA roadside support.

PS. You can do like us knuckleheads and swap in a 3T Toyota engine and tranny and feed it nitrous. It was a fun car while it lasted. D:

  • So, your answer is to essentially buy the frame, body, and interior and then completely rebuild the rest of the car? – Ellesedil Apr 22 '16 at 22:59
  • hell yeah. Love your fervency! this would never be on the road. Track car. It WOULD GET DESTROYED at some point. so, there's that. – DucatiKiller Apr 22 '16 at 23:04
  • In terms of keeping the rev's in the sweet spot. I club raced 2 stroke MC's for awhile so it's the same deal. – DucatiKiller Apr 22 '16 at 23:05
  • I hope your heel-toe game is up to spec. You can always tie a wood block under your shoe. :P – race fever Apr 22 '16 at 23:35

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