I would try another run with a different set of plug and gaps. experiment around some and see what you com eup with. Like mentioned, the gap isn't huge, but I would bring it a little closer to see what that nets you.
Are you heading tothe dyno again soon?

 

My car did the same thing (droped from 430hp at 4300rpm to 398hp at 4450rpm) with a 150 shot, I have no idea what it is from. I got a purge valve the bottle was just filled presure was at 1050psi. I checked the plugs and they were fine too!!!!!

Good luck and let me know what it was so i can fix my car too!!!!

Scott

 

Anybody have a good FR mounted regulator they'd like to recommend?

 

Go with a Aeromotive. We've used both 13101 & 13109 without any problems. I think Nasty Performance has a kit if you want to go that route.

 

I highly doubt its the stock regulator. The dip is too sharp. And I have made 700-720 rwhp on a completely stock fuel system (Lines and regulator, fuel rail) mare than a handful of times. And I cant count how many times I have made 550-650.

THats not to say you may have something defective in your stock setup...like the regulator. But if everything is working properly....650 rwhp+ should be a breeze. Same with a sustained TQ of 650+.

Just buy some NGK TR6 plugs...gap at .030 and redyno. Check all you plug wires for good contacts and connections as well as your coil pack harnes to be sure its seated etc. At your Tq level you should not be having that dip. I am still going with plugs.

 

oh...and the only other thing I have actually seen cause crazy dips and surging (with all else working properly) is belt slippage. Yes it sounds weird but it does something with the alternator and causes things from mild dips to wild surging. Check to see if you have excessive belt dust. If so change belts and get a Katech tensioner.

 

Attached is a dyno of a stock ci heads/cam/intake car with a Racetronix fuel system, stock regulator. After removing the stock regulator and using a rail mounted FPR the problem went away. Your large dip around 4600 RPM (on the 75 shot graph) is close to the dip on my attached graph.

 

then there was likely somthing wrong with the regulator on that car. Can you show the AF graph on that run where the regulator was causing problems. It should have been very lean to cause a sharp power loss like that....obviously lean.

If Patrick can run again with a wideband and get an AF he should be able to determine wether it is fuel or spark.

 

Nothing wrong with the stock regulator, I just think you got real lucky with yours! LOL!

The car never went lean, they go rich, from the system being a "return less" system and having the regulator located in the tank, above the pump. I'll try to dig up the graph with the A/F, but I agree 100% with ya, if Patrick can get back on the dyno with a wideband he will know if it's the fuel system causing him to go real rich for a few hundred RPMs.

 

I am still going to have to disagree. If your saying the regulator at the tank cant keep up...the car would go lean right after the juice hit. I have never seen anyone say the regulator causes rich spikes?? and loss of power??

I have personally been involved with atleast 10 cars that dynoed in the 500+ range. And 3 that went into the 700 rwhp range with stock fuel systems excpt for Walbro intank pumps with hotwire kits. This is stock regulator, stock rails, stock feed line from back to front.

I just cant see the regulator being a problem at 500 hp mark. Unless maybe you had the stock pump. But in any event it seems like it would be a lean spike.

 

Interesting thread. The last time I had a similar dip my clutch died soon after.

 

+1 on 383LQ4SS

we have seen so many 500-600 rwhp stock fuel system cars here in tampa its not funny. rich = dip in the power curve, not lean. the only issue is the lean spike from the stock fuel pump not being able to keep up, but thats on the initial hit of the nitrous.

 

Multiple people have said the location of the regulator is a big problem. Here's a quote from Jack at Ractronix that was made here on LS1tech.

"Dropping pressure is due to the lack of regulation at the fuel rail. If the return line was at the rail then pressure would be stable.

In other words the problem is with the position of the regulator in the LS1.

Q. If the pressure is stable at the back of the car under W.O.T. (58PSI) where the regulator is in an F-LS1 but the pressure drops at the fuel rail due to line drop WHERE do you suppose the problem is?

Q. Why don't '97 C5's with front-mounted FPR's experience the same level rail pressure loss as compared to later model C5's or F-LS1 cars with rear-mounted FPR's?

Q. How can the regulator adjust for line pressure drop (by backing up the feed line to the point of pressure relief at 58PSI) if it is located at the back of the car where the line drop is not occurring?

Go plumb a pressure gauge into the back of an F-LS1 car which has rail pressure drop and come back and tell us what you find!

Then relocate the regulator at the front of the car with a return line without upgrading the feedline and you will find that the pressure is stable which indicates adequate volume.

So in conclusion if you want to save a more than a few bucks relocate your regulator to the end of the fuel rail with a return line!!!"


Right, the car will go lean very quickly & shortly after the fuel solenoid is opened up when using a FPR in the stock location. With a FR mounted FPR you will not see that pressure drop, and the car won't go lean.

Now, back to my point, with the FPR being located in the rear how is it to keep a stable fuel pressure at the rail? It can't. The regulator is at the back of the car and the pressure drop is happening at the fuel rail.

I still believe Patrick G 's problem is fuel pressure based, and it is causing him to go rich and lose power. Attached is the dyno graph from above with the A/F chart.

 

Im not trying to argue with you. But I am going to stick to logic because you are seriously losing me here. You post that the regulator being in the back will cause the rail to lose pressure under big, rapid demand. So how does that make the car go rich? You are plumbing the fuel noid off the rail are you not?
If your saying it will go very lean at first...then surge back to rich....thats another story. But if thats the case that 11 to 1 your graph is showing will not cause such a SHARP loss of power without dropping a cylinder momentarily.

Your dyno graph definately shows rich...but not so rich that it should cause THAT amount of rapid power loss. As a matter of fact the AF is all over the place...but that dip in HP is really the ONLY huge spike in power loss. I mean a 75 shot is not that much power and not that huge of a shock.

Im just not seeing it.

 

What's more interesting is on your graph it dips to 11:1 prior to your dip in the power, seems funny that if the problem is as you claim you would see a dip in both places?

 

We're all flying blind here, as no one really knows what his problem is without a wideband.

My logic is this: Upon the fuel solenoid opening there is fast lean condition (lean conditions usually show a spike in power). To compensate for this lean condition the FPR over adjusts by sending too much fuel (usually causing a dip in power). This cycle continues through out the RPM range, over and over and over again which is seen in the A/F. Since there was not a wideband used no one can tell. From our experience this has been the culprit, with the solution being a FPR located on or near the fuel rails with a return. Considering the lower horsepower levels in this example it could also be ignition related and as stated earlier nobody will know until there is a dyno pull with wideband present.

 

One more thing, didn't he have this problem n/a and on the gas, so your reasoning again doesn't hold up.

 

Yeah...Im not saying a front mount FPR is a bad thing. But it just may not cure this particular problem and there are other possibilites.

Anyways...Patrick...get back on the dyno and let us know.

 

Umm, no. Where do you see that? His NA runs are fine.....

 

I apologize; the only graph I could find at the time was one using a progressive controller. The progressive controller does not turn off until around 3800 RPM. Let me go through some other dyno graphs and find one that better illustrates my point.