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rx7 people - Learn me injector sizing


Alex3000
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I haven't been able to find a straight answer around the web so I thought I would consult the local champcar rotary people:

 

I have my megasquirted build up and running but no real track/hard pull testing done.  So I don't know for sure my setup won't work but I am running 4 x 450cc (rx8-yellow) injectors.  But when I read about other builds from around the internet everyone runs huge 1,000cc+ secondary injectors.  Why is this? Is it necessary?

 

In stock form my GSL-SE motor had 2x700cc injectors for a total of 1,400cc.  My new setup is 4x450cc for a total of 1,800cc.  So, I'm like 400cc more, party, bonus, excellent. What am I missing?

 

The internet would have me running 2x450cc and 2x1,000cc for a total of 2,900cc!

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From what I remember, people didn't have an injector that was just a bit bigger that fit the stock fuel rails.  The injectors available at the time jumped way up in size.

 

The reason you can get away with running such a large injector for the secondary is because you don't care about idle control or transient response on the secondary injectors.   Therefore go big and be safe. 

 

That being said, I would run the rx8 injectors if I was running a rotary still.

From what I remember, people didn't have an injector that was just a bit bigger that fit the stock fuel rails.  The injectors available at the time jumped way up in size.

 

The reason you can get away with running such a large injector for the secondary is because you don't care about idle control or transient response on the secondary injectors.   Therefore go big and be safe. 

 

That being said, I would run the rx8 injectors if I was running a rotary still.

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Stock injectors will support 220 hp ....so 450's will be all you need..we run 750's on all four , and even though the duty cycle is regulated by the ECU , we are way rich at some points,  the internet is turbo centric , so that is why the big injectors abound....we will probably switch back to turbo injectors ( 550's I think ) , and re -tune , in an effort to maximize fuel mileage

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44 minutes ago, Alex3000 said:

OK good, this confirms my thinking.  I was getting worried I might get out on track and have some crazy lean event at 7k rpm.  It's a street port gsl-se so probably max looking at 180hp.

Lean won't do too much to an na rx7.  I wouldn't necessarily run it lean all the time on purpose, but it's not nearly as bad as it is for boosted rotaries.

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On our turbo II we ran the stock injector and made nearly 300hp. Raised the fuel pressure though but can’t recall number. The monster six port motor used the same injectors and fuel pressure. The rotary can use very low octane fuel along with premix oil and can be run quite lean. The turbo car liked it on the rich side though. Naturally Aspirated rotary motor is very hard to detonate. Compression is relatively low. You can run quite a bit of spark advance as well. If you tune it on a dyno you will be able to see if the injectors reach the max duty cycle. Low octane pump gas and a quality premix oil and you should be good to go. 

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2 hours ago, ablesnead said:

You will need to shift at 8k  with a stock box to put down  180 when you need it ,  that normally means 2nd at the hairpin and  10...possibly the tower turn ( which is rear ratio dependent ).

Yeah, I set the shift light at 6,800, assuming the driver will then shift at 7k.  For champcar purposes I would rather we keep at a safe shift point rather than stress the motor to get a few more 10ths.  That being said, the last time the car was raced it was with stock ecu and the motor would start to drop off over 6,500 anyway.

 

Thanks for everyone chiming in here.  I'm feeling much more confident at the prospect of shaking the car down come spring. 

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52 minutes ago, wvumtnbkr said:

I don't think 8k is gonna hurt a rotary.  On downshifted we would see up to 9k on accident...

 

Yeah I know.  I also blip it up to 8-9 on downshifting too.  Don't forget the GSL-SE rotors and stationary gears have less teeth than the S4/5 motors as well as wider apex seals.  Not that I have ever really heard of anyone sheering stationary gear teeth.

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Short tube header with a merged collector big pipe 3" at least and muffler spintech or similair.  Might need a bit larger than a street port though.  Exhaust port opened as well.  Big turbos and poor maintenance is only real way to break a stationary gear.  Good ideas to add some extra clearance on the rotor bearings and bump the oil pressure too. It would be great to run another rotary.  Maybe an injected peripheral port 13b.  How many points would a 2nd gen with that setup be?  Is that considered "porting and polishing"?  Its done with hand tools.

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I wish I had something tested to add here but when I was planning on running MS everything I read told me RX-8 yellows on all 4 injectors.  That said, I've never actually gotten the car to run with them, the MS, the OEM ECU, stock S4/S5 injectors, in any combination...  Hopefully the engine @wvumtnbkr is bringing to Sebring for me will solve the issues, and if it does I suppose someone needs to see just how far a P&P 13B can go on fuel in this series.  Work done with hand tools is free, right? 😈

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If you have the rx8 injectors and a stand-alone ecu then you should be good to go. Are you using a FC crank angle sensor? Or a wheel?  Does MS have the correct ignition setup for the rotary?  I ran the Haltech E6K back in the Stone Age with my car. It was very easy to get started and running. Rotary can run pretty rich to start.  Tuning is the trick. I would definitely love to see it running 

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