UnbelievabLS1

iTrader: (5)

I've dynoed my car several times since I've owned it, and every time, the first 2-3 runs have huge dips in them. I'm talking like a 75 rwhp drop between 52-5700 rpms! But, just like every other time, by the 3rd or 4th pull, the dip is almost completely gone, keyword being almost as I still have a 10-15 rwhp drop between the aforementioned rpms. The first dip is the largest, then it gets smaller on each pull til it almost goes away. My air/fuel ratio is fine, as confirmed by the Wideband readings on the dyno.

That's another thing, although my air/fuel is fine, I can still hear audible detonation. What's up with that?

It seems as the car gets warmer on the dyno, the dip starts to go away the warmer it gets.

All my mods are in my sig.

I have absolutely no idea as to what's happening. What do you guys think???

TheDogofWar

iTrader: (2)

You may be getting KR in that area. Are you monitoring it during the dyno?

UnbelievabLS1

iTrader: (5)

Yep, no knock whatsoever!

Mekkadon

iTrader: (3)

I don't know if that audible detonation you were hearing is the valves slightly touching the pistons when you experience valvefloat (???). Does valvefloat cause this type of noise???

CRASH 02

iTrader: (3)

Edited because I had a momentary shutdown of the brain.

Damian

iTrader: (89)

Uhh, what? That is incorrect. Even BONE stock LS1's need to spin out to 6100 or so for best results. I spun my stock internal motor to 6200, and trapped 115 with stock internals. He should NOT be losing power until around 6K or so, then it should start dropping.

Brian, it could be a couple of things. My car used to do this back in the day, when I made the first pull. After that, it would go away. Can't remember exactly why, but something to do with the PCM learning. But, 75 rwhp is a LOT to lose. Ever had a bad missed shift? Bent valves can cause upper RPM loss as well(not to scare you). Maybe some shitty gas? What do the plugs look like?

Josh

UnbelievabLS1

iTrader: (5)

Ummmm.....yeah......OK!

But anyway, yeah Josh, I have had a couple of bad misshifts, like 3-4 to be exact. We've pulled all the pushrods, and they're all straight as can be. Would bent valves act like this on the dyno? Start off with a huge dip, and gradually clear itself up after a few pulls? I'll be installing new NGK's this weekend. The ones I pulled before looked fine, except some on the back few cylinders had little silver speckles on them. That scared the crap outta me.

Man, I just hope it's nothing serious.

CRASH 02

iTrader: (3)

Sorry about that 5200-5700 power drop thing guys. I was thinking 6200-6700. My mistake.

As far as the problem I would start with the plugs since you said the pushrods were fine. What wires are you running? I would check and see what the wires ohm out at. When you installed your old plugs did you get any anti seize on the plugs other than the treads? If you did that could be some of the silver speckles on the plugs. How long has it been since you changed your fuel filter? I would try those things first and go from there.

UnbelievabLS1

iTrader: (5)

Honest mistake.

Let's see, fuel filter is brand new, like only 1500 miles on it. Plug wires are stock, but I should probably check them now that you mention it. It's a very good possibility that I may have gotten some antiseize on there, explaiing the silver specks.

All good ideas.

Tin Indian

That anti-sieze will burn off in a couple of miles, if not less. I think it's just wishfull thinking that a little grease on the plugs (of an otherwise good running engine) will cause a permanent loss of performance.

You need to look elsewhere...

BTW, specs on the plugs can be an indication of detonation

Nine Ball

iTrader: (38)

Psssst.... Its a pretty common occurence on LS1s, we used to call it "the dip" back in 1999. If you want to magically cure it, replace your valvesprings with some Comp 918s. Its most likely caused by valvefloat harmonics. My car used to have the EXACT same issue until I swapped out the springs. That was when my engine was still stock.

Tony

StrongWS6

I agree I witnessed that same thing happen on the dyno on a 2002 LS1. He had valve float. So I believe he replaced the springs and took care of that. What caused it was all the drag strip burnouts, and burnout contests.

Damian

iTrader: (89)

THAT'S what I was lookin for. Couldn't remember exactly what is was. I remember "The Dip" days. People used to BLOW UP ls1.com with threads about their car being messed up, only cause they saw this dip on the dyno lol....

Tony brings up a good point. I remember reading something about you putting 50K+ on that Ram clutch of yours Brian. So I'm assuming you have upwards of 70K or so? If thats the case, you could definately have weak springs and be seeing some float at high RPM's. No biggie, just a better excuse to slide a cam in there . If this is the problem(which it probably is judging from the mileage) just go the cheap route. Throw yourself a Hotcam kit in the car, and roll. For less than 400 bucks the car will be faster and fixed


josh

UnbelievabLS1

iTrader: (5)

Lol.....more like 80K miles on the car now Josh! Me and a few other buddies had suspected it was the stock springs also, and that they were probably weak. Guess it's cam time!! :shift: