RW99

I'll try a new approach... I have this problem (red traces):



ASSUMING that the 4500 rpm+ power fluctuations at higher boost are caused by insufficient spring operation, which springs should I go with to solve the problem?

Cam is 224/224/114 0.588/0.588, heads are AFR 225's unmilled 72 cc. LS6 stock cubes.

Thanks for any recommendations.

NassyVette

iTrader: (22)

Comp 918's should do it. What spring are you using now? I've always had good luck with patriot duals, and the price can't be beat.

Ryan K

iTrader: (11)

918's will not do it at higher boost levels... I am running the upgraded AFR springs right now and have had the best luck with them.

Ryan

99Z28LS1

iTrader: (4)

im on patriot duals and have no real problem, but im not a high boost car, only 7.5psi at the max

SSilverSSurfer

iTrader: (8)

**** i broke a set of patriot duals when i was cam only, current set has been fine though

cablebandit

iTrader: (37)

i would say the patriot duals and like Ryan said...not the 918s

Pro Stock John

iTrader: (34)

The first thing is what springs do you have now, and what are they installed at?

I've run three different springs on my car from when it was supercharged to the current turbo setup.

qqwqeqwrqwqtq

If you have AFR springs and their causing you problems at 10psi boost, you have an enormous amount of backpressure.

RW99

These are the AFR springs that came with the heads; while I THOUGHT I ordered the upgraded set I can't find my invoice anywhere. So I can't be sure.
Could you speculate on the likely causes for high backpressure on my setup?

Thanks,

Rich

*edit* Guess some more details might help: this is an A&A forged LS6 with a PTK front mount T67 0.96 A/R. Griffin FMIC. SD tuning. Twin external fuel pumps through CPR rails and 60 lb injectors; fueling isn't the problem. Alkycontrol 100% methanol (but the power fluctuation happens with or without methanol).

NassyVette

iTrader: (22)

Are you sure the dip in the dyno graph is from valve float? Have you or can you log a run with hptuners or some other program?

RooRnZ28

iTrader: (14)

i went with patriot duals as well, low cost and effective...

94 slow

What's wrong with the 918's?

RW99

No, I'm not sure that this is a valvetrain problem. I'm just looking at it that way because of the specific behavior at higher rpms. It could also be a spark delivery issue that doesn't become a problem until the boost gets cranked a little more. I also wonder if I might be falling off the island on the compressor map and running into a surge problem... but the boost trace looks fairly consistent... not sure how to diagnose that one without putting on a bigger turbo, retuning, etc.

Pro Stock John

iTrader: (34)

Valve float or lack of spark would be my guess.

918's aren't enough for setups like that.

DeltaT

iTrader: (5)

Or something weird with the 2nd run or the dyno itself. A third run would at least tell if it was a consistent problem, or it might look better than the other two.

Jim

99Z28LS1

iTrader: (4)

yeah, i would imagine you need stronger springs or do 2 runs and if the problem continues then time for better springs i guess. if it broke then it was meant to be replaced with better aftermarket stuff. just my $.02

JPH

iTrader: (2)

crane #144833-16=NO WORRYS ANYMORE!

NA$TY-TA

iTrader: (21)

I agree........

Im running Patriot springs myself and ill stay with them......
We thought i had valve float with them on my kit when we 1st got it to the track. T6 flanged GT42-76 76mm turbo..... 14 psiwas all she would do.....
Thought it was valve float so we ordered a set of Comp 921's...
had two different shops test each brand spring without knowing what one had a better closed and open seat pressure.......
Patriots were better both times....
Ended up being Extreme back pressure with the turbo....
Less boost with the current turbo (S88) made a HUGE gain in HP and at the track...

Ohand on the 918's...... id never run a single spring again......
im not letting the fate of my motor ride on one spring.....
with a double you have a back up.... that alot saving your motor is worth every $$$

Kyle

RW99

Thanks to all for the advice.

DeltaT, those two runs were done at different boost setpoints on the Eboost; reducing the boost generated the smooth blue curve. The red curve was slightly higher boost setpoint and reproducibly generated the fluctuations in power. I just posted a sample of each behavior to illustrate the problem.

So would running off the compressor map (with the sudden heat increase) generate the backpressure that's been mentioned? Wouldn't I see something on the boost trace?

I think I will replace all of the wires and ensure that spark is abso-frickin-lutely well-supplied to happy plugs, and also go with the Patriot duals (anyone happen to have the right part # for my application?). If I still have the same problem, maybe it's just time to decide if I'm happy with these numbers or if I need more turbo. And I think we can all predict where I'll end up on that decision