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Background

I'm looking at a few cars for a track day car that I can abuse.

One of the vehicles I'm considering is an older Mazda RX7. The primary reasons being that it has a rotary engine as well as the curb weight, which is very low.

I like the idea of the rotary because if I over rev it by downshifting to early that the engine doesn't have any poppet valves to destroy. The performance profile, other than weight, isn't a giant concern but I want to do something to it to get a little more umph out of it.

Questions

  • What are common modifications done to the Wankel engine to improve HP?

  • Do common engine improvements to a rotary engine such as port timing modifications provide the same benefits to a Wankel engine as a normal piston engine?

Wankel Engine Basic Operation

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Bit off-topic but I would advise against using that car for track days. They are too costly to operate. Something more conventional and newer will provide more smiles per $. – race fever Jan 16 at 23:28
    
I ran this through chat for staying within scope before I asked it. If you feel like it's out of scope please vote to close it. I don't want to push the community boundaries. Close voting creates the parameters we live by. To be clear, I say this with absolutely no malice or judyness. :-) – DucatiKiller Jan 16 at 23:35
    
I'm trying to stay as far away from product recommendations as I can too. – DucatiKiller Jan 16 at 23:35
    
Oh I didn't mean your question was off-topic. I meant it that my comment was off topic. Not trying to steer you away from the RX-7 but passing along my experiences with them. (: – race fever Jan 17 at 0:28
    
Lol. Sorry. My bad completely. :-) – DucatiKiller Jan 17 at 1:13
up vote 8 down vote accepted

The rotary engine is still a pump so opening it up helps it rev higher and make more power. Opening the inlet and exhaust ports is a big way to make more power at the engine. You still need the rest of the path to open up as well so opening the exhaust and intake path helps. Earlier Mazda RX-7s had anti pollution gear that killed power. There was a reburn chamber that spoiled the scavenging of the exhaust gases as it collected gases and burned off unburned hydrocarbons. I took that off and added straight pipe and made 5% more power.

Just be careful as you do this the engine will just make more power as the RPM increase. You have to watch out for running gear like the RPM sending gear (on the '78s anyway) was plastic and wouldn't take the extra revs. There was a brass after market replacement though. Big the key is to open up the engine to let it rev higher to make more power. There is a point where your apex seals will wear faster but for race work that's not bad. I had a '78 RX-7 that I loved and made these mods to.

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