Added intake and return style fuel, lost power???

LS2 KLR · Dec 28, 2004

I recently added an extrude honed bullit intake and a return style fuel system. I went for a retune and walked away making 25rwhp less? On the first pass it made 296 and I thought, cool a little tuning and I'll hit the 310 I was shooting for. At 296 is was running lean and by taking out timing to prevent pinging I am at 273. My tuner even asked diablo to make and send him a file for my car and again the same problems. My tuner said he thought with so much air coming in and having stock heads was hurting me. I think there is something in my computer not meshing with the return style fuel system. Any suggestions??? I made this much power on my stock shortblock with bolt-ons

RedGTvert · Dec 28, 2004

What size injectors are you running? What is the rest of the fuel setup.

Darkhorse845 · Dec 29, 2004

What is the rest of the fuel set up?

LS2 KLR · Dec 29, 2004

I am running 24lb injectors with an Aeromotive fuel system good for 1000hp, more than I'll ever need. I also had problems of a lean spike around 31-3400 rpms the first time I had it tuned. I wasn't looking this last time to see if it was still there. Last time the car was making in the 290s but due to a lean spike I ended up with 282. I'm just pretty pissed that I spent all this money only to be slower.

Darkhorse845 · Dec 29, 2004

LS2 KLR said:
I am running 24lb injectors with an Aeromotive fuel system good for 1000hp, more than I'll ever need. I also had problems of a lean spike around 31-3400 rpms the first time I had it tuned. I wasn't looking this last time to see if it was still there. Last time the car was making in the 290s but due to a lean spike I ended up with 282. I'm just pretty pissed that I spent all this money only to be slower.

Awesome!

UVBNHAD · Dec 29, 2004

get a SCT chip and adjust your MAF curve and be done with it. I gained 37 rwtq by having a chip on my car. I was able to go from running a high 13 - low 14 ratio to a perfect 13 throughout the band.

What's you fuel pressure throughout the band and did you change out your computer when you went to a return style fuel system? The computer may still be controlling the fuel system like it was from the factory.

jstreet0204 · Dec 29, 2004

Make sure the tuner set both the fuel_pump_system_type and fuel_pump_type to 0 also check for any vacuum leaks to make sure there isn't any un-metered air getting by. I'm sure you will make more power you've just got to find the problem. Good luck.

MustangLife · Dec 29, 2004

I was always told you don't want to go past 275 rwhp on 24lb injectors. The goal is not to exceed 80% duty cycle on the injectors. Have you dynoed the car on the spray after the intake. And diablo is not a great tuning source. SCT is the dominating tuning company for 4.6's now. And theres a reason for it.

nickthegenius · Dec 29, 2004

MustangLife said:
I was always told you don't want to go past 275 rwhp on 24lb injectors. The goal is not to exceed 80% duty cycle on the injectors. Have you dynoed the car on the spray after the intake. And diablo is not a great tuning source. SCT is the dominating tuning company for 4.6's now. And theres a reason for it.

I've got 290 on 19s and no problems. Most people on Modular Depot agree that 19's are OK up to around 310hp or so and then its time for 24s or larger and a lot of them have faster N/A cars than a lot of the forced-induction cars on Stangnet.

Gearbanger 101 · Dec 29, 2004

Sounds like a bigger fuel pump may be in order too. What's the difference in stock pump size between the pumps for the return and non-return systems?

tomustang · Dec 29, 2004

go back to your stock maf. any different curve will throw off an aftermkt one

nickthegenius · Dec 29, 2004

tomustang said:
go back to your stock maf. any different curve will throw off an aftermkt one

Thats a good point too. There is a write up by Ed Clark that states that he has never seen a naturally aspirated 4.6L peg the MAF and going to a aftermarket unit is useless.

http://forums.modulardepot.com/showthread.php?s=&threadid=25092&highlight=maf

Added intake and return style fuel, lost power???

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