FormulaZR

iTrader: (7)

Ok, So here's the scenario. I have a 383 LS1 in my jet boat.

When I first completed the swap the engine ran with a Super Victor intake and 850 Demon carb. Peak rpm was 5800-5900 rpm. With a Performer RPM and the same 850 Demon carb peak rpm was 5600-5700 rpm.

After a year, I decided I wanted to convert to EFI; so I put a Fast 90/90 on it. Now the boat will only rev to 5300-5400 rpm. There were no other changes to the boat. Depending on which impeller chart you go by, I have lost somewhere between 50-80 horsepower. Timing has always been 29*, whether carb or EFI.

Now, here's the question. Did I lose that much power from just the intake/carb...or do I potentially have other issues? I know the carb created ice cold air (the intake would frost if I was in the throttle more than 30 seconds)...and the Super Vic was probably a better in the 5500+ rpm range...but I just wouldn't have expected to lose *that* much power.

Any ideas? I feel like my tuner (PatG) is VERY capable...so I don't believe I have a tune issue - but I'd really like to get my power back, if possible. But I have no O2 sensors (and can't run them because the exhaust is water injected)...so no AFR data.

Should I be looking to put a Super Vic EFI intake and Accufab TB on...or...what? I really don't want to go back to carb, because other than the peak power loss, the EFI really does run MUCH better in all rpm ranges.

Engine specs:

383 LS1
11:1 compression
MTI Heads - 310 cfm intake/225 cfm exhaust @ .600 w/ 2.055/1.6 valves
Bullet Cam - 238/244 @ .050, .603/.610 lift, 112 LSA Hyd Roller
Yella Terra Ultralight non-adj rockers
Long tube headers 1-7/8"
Fast 90/90 intake/TB
42#/hr injectors

S10xGN

iTrader: (11)

What ECM? Had it tuned?

Jay-P

iTrader: (16)

Exactly, the fast will run much better in the low and mid. That carb setup will shine at peak.

How does this thing run, full out all the time? If so, then ya, I would consider switching to some other setup.

FormulaZR

iTrader: (7)

First, I have to say...I just realized I've had a series of idiot moments. For some reason, it has never occurred to me to check fuel pressure at WOT. I will be checking fuel pressure tomorrow; and perhaps that will shed some light on the problem. This could all be as simple as a pump or regulator issue.


GM "0411" PCM. Yes, it's been tuned by PatG.


Well...it's a little different than a car. I do "cruise" at 3000-4000 rpm quite a bit...but when it's on the floor it's all about peak power. I'm sure that sound obvious...but under 5000 rpm it really doesn't matter what intake and fuel delivery system I'm using, because of the way the pump loads the motor. The engine is either at idle, 3000-4000 rpm, or WOT.

jimmyblue

iTrader: (11)

A "shade tree" measure of what the FAST front end
is costing you, for airflow, would be to put a DMM to
the MAP sensor output and its GND, read the KOEO
voltage and then the voltage at your peak RPM. You
can get from that to a rough manifold vacuum (but
then, too, you could tap off a handy vacuum port
and read it, old school, if you have that kind of gauge).

This gets you as far as the plenum pressure at least.
The Super Victor probably has less restrictive runners
than the FAST, I bet. But that you were icing the
manifold means some serious expansion after the carb,
meaning no small plenum pressure drop there.

Anyway, knowing the FAST pressure drop would let
you figure what to look at - high drop wants bigger
throttle body or maybe some improvement of the
intake lineup - descreen MAF, maybe MAFless speed
density, larger panel filter and better ducting etc. -
to lessen the losses there. If you don't have much
MAP drop at WOT, then it is either runners (not much
to do there, other than maybe sending it out for
porting) or the tune particulars - maybe you could use
more advance, maybe leaner fueling could be tolerated
with better mixture / atomization, etc.

FormulaZR

iTrader: (7)

The boat has no MAF, it's speed density right now. And I checked the fuel pressure...it's rock steady at 58 psi.

I guess I'm just wondering if anyone else has run similar setups and what their results were.

pinkston.jon

Having a jet boat w/ water injected headers also; why don't you run a wideband temp & turn the water off for tuning purposes? Just stay away from the game wardens while you're tuning.

Grr

iTrader: (2)

from experience with the super victor, you are right on the money, you know what the problem is

With your heads and cam, you are in fact loosing 50-80hp with the FAST on there. Good thing is you can sell the fast and swap to an injected super and accel TB for about the same money. I know my super makes more power at 4000 than a breadbox intake does, and from 4k and up the gap just gets bigger

FormulaZR

iTrader: (7)

Ok...so I had thought that 4500-5500 was sort of the bread-n-butter range of the Fast 90. But you're staying that a Super Vic with yours picked up power over a Fast above even 4k rpm?

Grr

iTrader: (2)

Yup, your intake valve closing point is hating that fast. If you had a different cam it might equal or make a couple horse more up to 5-5500, but as is you need a single plane, or a Holley hi ram/ edelbrock proflo.

FormulaZR

iTrader: (7)

Thanks for the info. I'm thinking about a change to forced induction, so I'm not sure what direction I'm headed yet...but if I stay N/A I'll probably be looking to swap to a Super Vic.

Any idea how the Holley Hi-Ram or Edelbrock ProFlo compare to the Super Vic?

Grr

iTrader: (2)

all 3 will make similar power, the Hiram is the best of the bunch IMO, super vic will make nearly the same power but the plenum volume on the holley is fantastic. Its better for boost too if you use a centri supercharger