Fueling a low boost supercharger
 

I was looking at a Jeg's catalog a while ago (or something similar), and they had some low boost superchargers available for the Mustang that didn't require any changes to the fuel system or computer since the boost levels were low enough for the PCM to deal with.

My question is, since we've got such a friggin' rich car anyway, would it be possible to install a 4 psi or 6 psi supercharger and not need to add a piggyback fuel control? At cruise, the car is closed loop, so the PCM should adapt, right? Does anyone know how to determine how much boost would turn the WOT AFR from 11:1 to 13:1?

Is there domething drastically wrong with what I'm thinking? :Freak_ani

~ Matt

its quite possible. there was one shown here a short while ago that had no piggy back or alteration of the stock maps in any way.

here https://www.rx8club.com/showthread.p...8&page=1&pp=15

Cool. So it can be done. Who knows how to calculate the maximum boost with the stock fueling maps?

~ Matt

the folks doing the sc in the link;)

Don't know about SC, but my piggyback was screwed up when I first got it from Greddy, so I was running the stock fuel map with FI. I was running 5.5 lbs. of boost and I was detonating like crazy at high rpms.

That's a little scary!

So, I'm guessing something like 4 or 4.5 psi is probably safe. I don't have the funds/balls to do a homebrew kit, but it sounds feasible.

~ Matt

The problem isn't the fuel.....its the crazy high compression ratio and associated ignition advance. You need to be able to back the ignition down from 25-30 degrees at WOT to keep it from detonating. If you could control the ignition advance, its possible that a low boost system could be made to work (me thinks)

agreed. my car runs ~9.8AFR over 5kRPM under no boost. This makes me think there is plenty of fuel being delivered by the stock ECU for at least some boost. Of course, that's my 8, not necessarily (or even likely) any one else's.

-MD

Are you serious? 9.8? holy crap man, that is so rich you should be smoking.....how are you testing that? what are you tuning with?

well if thats the case a canzoomer/greddy piggyback would do the job easily and with zero grief

No way I'd run boost without fuel control. Closed loop will create conditions far too lean for boost and I believe the MAF bottoms out at around 2psi of boost.

You could probably get away with running less than 2psi, I wouldn't try it, but anything more and I'd start a pool for #of feet till you got an apex seal rattling around.

The RX8 PCM runs a MAF based strategy. So, it won't be in closed loop under boost, as LOAD would be > 1 !!!

I think that is part of the difficulty with the 8's computer as opposed to other ecu's is that is does remain in closed loop under load. For us, closed loop operation is not only load dependent, but also rpm dependent. That is why Greddy had to use the cold water temp dongle to force it into open loop when under boost.

No shit. That's why I dyno'd 169HP stock. Rediculous, no? That's measuring with an innovate LC-1. I am running the emanage, but I'm talking about cruising, not under boost over 5kRPM. It is in open-loop at these RPM, though. The stock ECU is tageting that AFR all by itself.

BTW: I dynoed +15HP with the canzoomer.

Like all / most engine management systems...

No I think it does it in order to disabled the adaptive fuel learn (LTFT) in areas where the kit will cause troubles by going over the expected (inferred) load.

Fabrice