Hey guys, I know i asked about this on the end of another thread but i dont know how many people are even goingto reply to it there so here i go...

I'm wondering what the difference in the compression ratios is betwen a stock engine and a streetported engine. Or even a bridge or peripherial ported engine are? I have a streetported engine and am hoping that it has a lower compression ratio than stock. I would assume it would if the port is longer or larger because therefore the combustion chamber has less distance or amount of degrees to compress the fuel and air mixture? any thoughts? Or does anyone know for sure? I am just wondering so i can figure out if i want to supercharge my engine or if it will not be worth it if i can only run a low amount of boost due to to high of compression ratio?


Thanks
Josh

 

Porting has nothing to do with compression ratios. The rotors you are using do. The turbo RX-7's had an 8.5:1 compression ratio from 87-88, while 89-on turbo RX-7's had a 9.0:1 compression ratio. The 84'-88' non turbo 13B's had 9.4:1 compression while 89-91 nonturbos had 9.7:1 compression. The Renesis has 10.0:1 compression rotors. The 12A engines were typically 9.4:1 although there was a couple of years in there with 9.2:1 and Japan even had 8.5:1 in some Turbo 1st gens. It's all based on the rotors themselves.

 

thanks alot man! I guess i will have to retard mi timing if i want to run alot of boost on my new engine? Im not the most knowledgeable on any mechanical stuff but im learning and doing so by trial and error and your guys' help really appreciate it! how do these throw like 10-12 lbs of boost in their rotaries? or do they have other modifications?

thanks man

 

You can run boost with high compression. You just need to be able to tune it well as the higher the compression ratio, the less room for tuning errors you have as the boost rises. WIth proper tuning even a stock engine with a turbo added to it can make fantastic horsepower. I'd do some homework to decide how much power you want, what turbo you need, and how you want to control fuel and ignition control. What are your thoughts right now? Maybe some here can help guide you with your way of thinking.

 

Wouldn't suggest supercharging.

But even a stock TII turbo running 12psi on a 9.4:1 streetported 12a will get you into the 12.99-13.99 sorta bracket

 

There's nothing wrong with supercharging if it's done properly. The problem is that we have yet to see anyone do one properly on a rotary. Price is another issue altogether.

 

Hey Jobro why do you say no supercharger? just wondering?

rotarygod im just thinking rb holley/ intake and header exhaust? Then later maybe a camden 7" supercharger? What do you think? any guesses on hp after the supercharger? Someone ssaid 9" is that overdoing it? and also how many psi fuel pump will i need?


thanks guys

 

The reason people here are against supercharging is because the available kit such as the Camden really doesn't give a whole lot of performance for the amount of money you spent. A turbo is much cheaper in this regards and capable of so much more than that kit. There are different types of superchargers out there but none of them come in kit form for a rotary engine. It would take considerable money and custom work to get one to give a large power increase. Do you have any custom building skills? Not everyone does so it's important to know how much you can and would be willing to do yourself.

A RB Holley intake system with a header and exhaust is a nice performance upgrade over what you have now. That's a good place to start.