99_ws6

went to a local dyno day and got the following dyno graph. about 5000 RPM the TQ and HP seem to nose dive. Anyone have any thoughts?
shop suggested:
- changing plugs out (running stock platinums about 2 yrs/30,000 miles old)
- looking at knock sensor settings in tune vs stock as they seem to think it is knocking and not getting picked up by pcm (spitting smoke out tailpipe?)

car is 1999 WS6 with untouched stock motor, TSP headers and ORY with Magnaflow "catback," cat delete, SLP lid, K&N filter (cleaned about 1500 miles ago), 6 speed, 3.42 gears, 93 octane, this is the first car i've tried tuning.

video shows smoke at higher RPM:

included dyno graph and hp tuners scan log of last/best run

scotty2000ss

iTrader: (2)

Take the plugs out. See what they look like...

Fat Jesus 808

iTrader: (5)

My stock Ls1 graph looks like that

99_ws6

Pulled driver side plugs today and cleaned them for now.
cyl 1: looks normal/clean had some black deposits on end of threads
cyl 3: same as 1
cyl 5: not so good looking, oil on threads and lots of deposits. no damage though
cyl 7: same as 1 if not better.
all plugs were at factory gap .039 (acdelco platinums)

pictures included

I have a pcv catch can on already. guess rings are worse than I though at least on cyl 5. I'll be putting new plugs in and looking at them often. if I get back on the dyno in the spring I'll post if this fixed it or not.

soundengineer

iTrader: (16)

When it noses off like that...it can only be a few things...

Lifters are collapsing...possibly too much preload from too long of pushrods or they are just old and worn out
Springs are failing or binding
Valves are floating....(caused by spring issues usually)


Usually ls1 lifters don't have an issue until about 6400...above that they usually start to have issues...
Ls7 lifters are similar...but only in an engine with ls7 valves(lighter than ls1 valves)
If your valvetrain is too heavy.. ls7 lifter will do that pretty early in the rpm.

If your springs can't keep up....or are worn out...it falls off like that, you need to pull some valvesprings off and test the open and closed pressures.(this would be my guess as everything is "stock")

when you have aaftermarket cam and pushrods, You can check your preload by getting on the cam base circle...removing the rockers and reinstalling them and counting turns from zero lash to 22ft-lbs
One full turn of the stock bolt is .078 preload
Ls1 lifters hava a Max range of .160
Ls7 lifters have a Max range of .130
You should never be more than half of the Max lifter preload range..
And an aftermatket cam is usually spec'd to be at .020-.060 preload(higher and more aggressive ramp rates require less preload than stock cams)

CAMSTER

iTrader: (10)

Hard to believe went to dino day with those plugs like that, but hey now you know.
Can't blame anything else till you do a "clean" pull really.

Exhaust and or intake limitations too will manifest in similar fashion, as well as tuning call.

soundengineer

iTrader: (16)

thats not a Tuning issue.....
thats a mechanical issue showing its face on the dyno graph...





I've tuned Hundreds and Hundreds of LS1's......
theres not enough timing to be knocking on that stock LS1 motor....
its plenty safe...they usually like 26~27 up top and 24 around 4000 rpm(peak torque area)
though I would ditch those platinum plugs and go to an NGK TR55

and....
DATA LOG LESS GARBAGE ON THE DYNO!!!

you need to keep it under 24 PID's to get any kind of good data...
if you can dumb it down to 12pids or less for the dyno you will have a lot better data
theres a whole lot of stuff in your table that is just not necessary all at once....especially on the dyno

you really only need RPM, TPS, MAP, MAF Hz, Cylinder airmass, Ignition Timing, Timing Retard, A/F Commanded, and Maybe....LTFT/STFT...but you should be doing open loop pulls on the dyno unless you are doing part throttle tuning.

99_ws6

Scott, thank you for the information. It is very helpful.
that just happened to be the config I had up at the time from tuning my truck (lq4 swap 78 chevy). was a last minute thing to decide to dyno it - just grabbed the computer and went. obviously the transmission stuff was unneeded being a manual. will slim it down for next time.

given what you said, being completely stock its probably worn out springs. I will pull a few over winter and test them. and plan on the TR55's.

I have never been able to run that much timing due to random knock issues that I assumed was false knock from my awful ORY hitting everything. A new better fitting one is being made over winter. Then I will try increasing the timing again.

Again, thank you for all the helpful info esp in testing the preload and the logging on the dyno.

DANOZ28

iTrader: (1)

when mine was stock i would get valve float / flutter around 5700 rpm and my milage was 48k. now with ls6 springs (you should get even better) zero float. cheers!