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FMU advice needed

dweinhart

Member
How much horsepower will 250cc injectors support with 10:1 FMU. Online calculators say approx 400 crank if my math is correct but some members have talked about leaning out much earlier...any ideas?
Which FMU ratio should be adequate with 300cc injectors?
 

gloverman

Well-Known Member
Are you comfortable running those sorts of fuel pressures? Ive never bothered with FMU. If fitting a turbo I much prefer the ability to tune it properly. Some of the mapping of stock ecu is pretty unrefined to begin with.
 

dweinhart

Member
I understand it is less than ideal but I know of more than a few members who run an FMU. I am in a country with no dynos and no tuners and I do not want to deal with fighting the ecu when it keeps relearning the tune from a piggyback so I have decided to stick with manual tuning via FMU (and possibly meth injection to control detonation if needed). Not only that but I know that 8psi (72trim) should be okay with an FMU although it may (or may not be) be rich. I do plan on purchasing a Vortech recalibation kit to raise or lower FMU ratio depending on AFR wideband numbers. I will also run 300cc injectors to reduce the pressure. 6:1 on 300cc provides better flow than 10:1 on 250cc with 30% less pressure..However I am trying to get an idea where the stock 250cc max out to give me a starting point....
 

gloverman

Well-Known Member
I've seen plenty of guys running stock ecu and boost, Ive also seen more failures than I can remember. The main reason most get away with it is the stock ecu goes extremely rich up top anyway and have relative conservative timing for a naturally aspirated engine. In NA engines the top end power is improved greatly with a few degrees more timing and lots less fuel. Years ago I swapped out a set of stock 215cc to 250cc on a supercharged jetboat running 8psi. It had an intercooler with low intake temps. I was just able to supply enough fuel however I was over what I consider an acceptable duty cycle. Anything with slightly higher air temps they wouldn't have done the job. Running stock na engines on the road I'm getting reasonably high duty cycles at higher rpm however not too bothered due to the infrequent times they go there, on track engine I prefer larger injectors to keep duty cycles down as they spend lots of time at higher rpm. Theres more to consider than just the air flow ratio.
 

dweinhart

Member
I know that AFRs are just 1 key to the puzzle. I blew up a 600hp 2jz with perfect A/R due to lack of timing retard.
May I ask what horspower numbers you were running at 8psi?
Also, in your experience, what caused the grenaded motors in the examples you mentioned? Lean condition? timing? Detonation? Or rod/piston failure?
At what horsepower level?
As I mentioned, I am going to use slightly larger injectors at 80% duty cycle to decrease fuel pressure and keep that margin of safety and meth injection to control detonation....and a larger turbo to decrease air temperatures at that flow. Obviously 8psi on a t72 generates less heat than 15psi on a td04. Hence my question, at what point did 250cc injectors hit 100% duty cycle. With that info, I can reverse calculate fuel requirements with FMU and larger injectors (theoretically...). thanks for you help
 
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gloverman

Well-Known Member
Sorry that job was years ago and I can't remember that much. Every now and again I come across photos of it when I'm looking for other stuff. Ive done so many different setups I can't remember lots of details these days. Maybe 25-30 boosted 1uz's. Every other one I have done I've used larger injectors.

All the failures have been other guys setups. Just had a guy that blew two motors before he decided aftermarket ECU was the answer then went cheap and the trans is now having issues as it wasn't setup correctly. Head gaskets is common with 100000km old gaskets,, pistons is common too either burnt away or smashed to bits. Too high intake temps is common with DET and mixture issues.
 

gloverman

Well-Known Member
On 250cc injectors I normally call it quits at around 95% (fuel map + corrections + all accel fuel) on 300rwhp NA at stock pressure. Thats still supplying satisfactory afms.

What vehicle are you looking at doing? Manual or auto? This thing about stock ecu fighting aftermarket is strange to me. Maybe I do things differently.
 

dweinhart

Member
Perfect.Thats what I needed to know.Thank you

This is a 93 sc400 auto.

From reading, everyone was saying the ecu relearns original fuel trims when using a SAFC but I have no first hand knowledge of this. Can you recommend a user friendly piggyback that will "stay" tuned?
 

gloverman

Well-Known Member
I don't do piggybacks very often. Instead opting to take fuel and timing control away from stock ecu and leave stock ecu doing trans. Easy and works well. Early ECU are pretty dumb. Fuel trim is primitive
 

dweinhart

Member
I understand standalones are optimal and a must for high HP but since this is a budget build I will push the envelope with what I have. thanks for your help.....

My goal is not to squeeze the most out of this motor, but rather to squeeze the most I can for "cheap".
 

gloverman

Well-Known Member
Depending on which stock ECU you have unplugging the oxygen sensors may help overcome any chance of the ECU changing your fueling. Then set the cruise trim with the secondary device.
 

stevechumo

Active Member
I had run FMU 12:1 with turbo on my SC400 with boost at 6 psi for a long time without issue. My friend is running supercharger at 6 psi on his LS400 without issue. I'm an old time member here, got busy, so I didn't log on here for a long time. :)
 

cribbj

"Supra" Moderator
Staff member
Hey Steve - good to see you back! Sometimes I think it's just Rod & me who are still around :)
 

cribbj

"Supra" Moderator
Staff member
How do you like your AEM, and which generation is it? Is the around town driveability OK?
 

stevechumo

Active Member
The AEM from the Supra works perfectly. The only thing that I am not 100% satisfied is that after I insert the key in the ignition, I have to wait for about 10 seconds for the AEM to initialize, then I can start it.
 

stevechumo

Active Member
I actually still have the whole car and setup. But after I swapped to a new SC shell and got 95% done, I got busy and didn't have time to finish it.
 
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