Tom. M

You can't look at his numbers and compare directly to Scott's or yours..... You have to look at the before/after to see the gain from baseline. If he ran on a dynojet you might have a better comparison..but not many folks use the dynapac (on here anyway).. ...so it sounds like he gained 15hp and 25 ft-lbs for just some fuel tweaking.. I think that sounds about right...(I gained 30hp and 50 ft-lbs just by changing the fuel/ign management)..so his results aren't out of the ordinary. I think Louie gained about the same by tweaking his GT way back in the day..

Good results

mark kibort

I spent a good deal of time on the dyno with my 84 and changing fuel. I went down to 12.1 :1 and started a high as 13:1. i ended up with 12.6:1 and the change of the 3 ratios fell with in a 6hp range.

Ive run dyno jet vs dyno pack and had only about a 5 hp difference between runs Ive normally seen on the dynojet vs the dynopack. on the holbert car, it was 318 dynopac vs 322 on the dyno jet.

these are big gains. 15hp just for 12.1 vs 13.1 is pretty unusual.

123quattro

I didn't need the fuel system stuff really. What I needed to be able to do was vary pressure reliably and adding the Aeromotive regulator made it easier (for me). That, and I had it sitting on the shelf so I figured I may as well use it. Mainly I puts those parts on for down the road when I swap over to the Haltech.

mark kibort

sure, the gains started with a pretty strong 84 to begin with . 220rwhp out of of a US Ljet is on the high side. But , why the 20hp above what scot got, and HE had the devek B1 cams AND the euro intake.
All I can think of now, is what you might make if you put the euro intake on! 280 or 290rwhp?
out of a 4.7! with the US Ljet intake, you basically have a 50% restrictor plate running on it right now. you are dynoing at near 3/4 throttle on a euro set up.

dr bob

Mark, the change in fuel pressure vs fuel flow through the injector doesn't change depending on the injection controller you use. Physics stays exactly how John decribes it- actual flow changes at the difference in the square root of the pressure drop, until you get to a choked condition (not really possible the way the system is working). On the original regulators, the control piston sizes are the same for both fuel and manifold sides, so the bypass pressure moves wth manifold pressure at 1:1. A 1psi increase on the manifold side changes the fuel side up 1psi, assuming the pump can maintain that pressure with the increase in flow. This is stuff you already know, I'm sure.

mark kibort

I get what you are saying, but my only thought was that the spring pressure of the regulator might effect the differential pressure differently than the ability of the RRFR to change that spring tension or valve position. Its an easy test. all I need to do is put some pressure at the fuel regulator and see what 5psi or 10psi does to the fuel pressure when added to the back side of the diaphram.

again, since we see and only, 5psi drop in pressure for a 17psi vacuum (oops I mean, 17"Hg or really 8.3 negative PSI ) applied to the fuel regulator, tells me there are other things going on related to the spring pressure. the majority of the control lies in the size of the return hole.
adding pressure to the back side of the diaphram, I dont think, has a 1 to 1 effect on fuel pressure rising.

mk

123quattro

Mark,

I think the confusion is coming from the vacuum side of things. Intake vacuum is rated in inHg, not psi. I've never seen a vacuum gauge in psi either. 18 inches of vacuum against Mercury is 8.8 psi, which is pretty much in line with the fuel pressure change you noticed as measured in psi.

My next plan for the car is to make a new intake and adapt a GM LSx throttle on. It will be a short runner, twin plenum design in aluminum. I'd like to do ITBs, but don't want to deal with Alpha-N control.

I actually like the fabrication end of things better than the driving bit, but I'm decent at that too.

SharkSkin

Nice result! Gotta love it when a plan comes together.

mark kibort

You are right, i was thinking of my old school gauage with the needle showing 17"Hg. I usually use the Sunx sensor, which has positive or negative PSI. I think I even posted some pics of it. If I recall, vacuum was around 8-9psi negative. Still, the fuel pressure only changes less than 5psi for that vacuum attached to the fuel regulator. Again, unless you put a guage on the fuel line, we wont know for sure. Next time I mount the fuel guage on the engine, Ill put some pressure on the regulator and see what i get.

dprantl

Funny, I ran into this exact problem when I was programming one of my techedge gauge views for boost. It kept reading -9 when it was supposed to be -17 and I was scratching my head. Then I looked closely at the analog gauge units for vacuum, duh! Of course it could never read less than -14.7 in that config, which would be a perfect vacuum!

Dan
'91 928GT S/C 475hp/460lb.ft

123quattro

I have a mechanical gauge on it now. Disconnecting the vacuum reference to the regulator changes rail pressure about 7 psi on my car.

mark kibort

Ill check and see what mind does when I get some free time to mess around with it. Negative 17psi! Ha ha. What was I thinking