I've posted this around a bit already, but it is useful information for the oft-asked questions like "will these injectors support the HP I intend to run", etc. It will also help you choose a fuel pump.

Check it out:
http://www.maxcooper.com/rx7/how-to/...tem/calcs.html

Let me know if it doesn't work as expected, or you think of something you would like to see added.

Thanks,
-Max

 

Thanks, Max

It would appear I need bigger injectors. Running the stockers at 95% yields ~330rwhp and that's what I just dynoed at. I do have a Walbro high-pressure 255l/hr pump.

On my Power FC I'm consistently seeing 85 to 91% and have seen 95% once. Running 12#, btw. How dangerous is this? Perhaps I should turn down the boost. Whaddaya think?

 

Hey Rich,

That sounds like support for the notion that anything >85% means the injectors go full open. As long as your A/F ratio was good, you are probably not in much danger of killing your motor. I have not heard of anyone "overheating" an FD injector by running it like that, and many people do, so it probably isn't a big reliability threat. The advatage of doing something to lower the duty cycle might be smoothness, and the ability to tune more precisely. Full open injectors should be able to support 345-360 RWHP.

Another option besides bigger injectors would be raising the fuel pressure.

-Max

P.S. We met at MADS in April '99, remember?

 

Max, according to this calculator, If I had 4 1600cc injectors I would not be able to make 500 rwhp without passing the factory fuel pressure and duty cycle limits. However if I "Hold'em Open (95%)" it jumps up to 751 rwhp. I love it. How bout a boost caculator??

 

Waynespeed,

Yes, the capacity increases with duty cycle linearly:

62% 490
--- = ---
95% 751

However, the calculator loses accuracy and you lose tuning control when you push the injector duty cycle over 85%. I should probably indicate that more clearly as many people are running their injectors at duty cycles in this zone (which basically means the injectors are out of control, and just stay open).

What would you like to see in a boost calculator? Input boost and output RWHP? That can be difficult to do, but I might take a swing at it. You would have to have some dyno results to extrapolate from, or perhaps I could provide some standard "mod level" choices. The components you choose and the details about how your car is running (how rich? clean plugs?) can make a big difference in how much power the car makes.

Thanks for the feedback!

-Max

 

Actually the boost calc was just a joke but now that I'm thinking about it it could be useful. For example:
street port@15psi T78 ~410rwhp. Just to give an Idea of what to expect when upgrading to single turbo's and increased boost pressures.
I'm sure you have enough data to form a valid database of approx hp expectations. Thanks for all you input in the rx7 world, keep up the good work!!!

 

Thanks for the kind words, Wayne.

I updated the calculator with some usability enhancements, some new options on the drop-downs, and support for multiple units for injectors and fuel pump requirements.

-Max