Hey guys.

Set up info:

42# injectors
55-60 psi at the rail
stock intake pump
ATI FMU
ATI inline pump

Went to the dyno the other day and layed down good numbers. 505rwhp/640tq. The problem is that I can never complete the pull because every time we run around 5000-5300 rpm's the car starts go lean real fast. No matter how much fuel we throw at it about 5000 rpms it always goes lean. Its also weird because we did a pull, car was extremely rich 10:1 through the pass and we CHANGED NOTHING, waited 15 minutes did another pass and it was around 12:1. He thinks its the FMU. Now its obvious that i'm going to need a 255lph pump but heres where I need input...

The owner of the dyno shop highly recommends ditching the FMU and getting a Kirban 1:1 regulator. He says my inline should be fine but ditch the FMU and just increase the static pressure with the regulator. He says it will be alot more consistent than the FMU and should be easier to tune. Is this an ideal solution? The guy knows his crap, I just want to know if this is the way to go...

All input is appreciated

 

I have seen this same problems on the dyno with a low battery.If you have a short in the car draining the battery it can cause this same problem.

Now as far as the inline pump,Im not a fan.I know people do this but it is just a band aid.WE have had several cars in the shop that the inline pump with a stock intank pump created a cavatating problem.The stock pump is only desighned to let so much flow through it.THe inline pump can pull more fuel than the intank pump can supply causing it to cavatate.
Did you have a gauge to see if there was a fuel pressure drop creating a lean condition?
Dave

 

No battery problems or anything like that. So I dont think their is a draw on it.

We did have a gauge on it and it would increase only to maybe 58-68 psi at the rail. It only appeared to go down at the shift point. However on every single pull the car would go lean at exactly the same rpm no matter how much fuel we threw at it.

 

Any body else?? Is the regulator the way to go?

 

why not ditch the FMU altogether. Get yourself a chip burner and a tune it on the dyno. Not only will things smooth out, You'll make more power over the entire RPM range along with getting better mileage. An FMU is just a band-aid and will never make the power of a properly tuned ECM. If you need any of the equipment your more than welcome to borrow or buy my setup off me. I'm going away from the Gen I SBC and won't be needing my Chip Burner,chips, nor the software. PS there are plenty of info on how to get this done in the DIY Programming Forum.

CCB

 

We actually were doing prom tuning at the dyno. I just wasnt sure if I should lose the FMU or not. Never heard of any thirdgens using a regulator w/ 1:1 boost setting. You have a pm chris

 

you should have about 75-80 psi when you see boost with a fmu. if you get rid of the fmu, you might have drivability problems at lower speeds.