Gonna Give it a Shot. 3.8L Sudden Drop

[steddy]

Well, I'm just putting my dyno sheet out there to any that would be able to help figure out this mystery. Car runs good and strong on the streets, with a bit a hesitation, but relatively smooth. Could probably be leaned out a little more, but, in the graph, at around 4750, the power band drops dramatically. I'm stumped. Valve springs? Timing's off? Just a typical 3.8? Not sure.

I originally thought maybe tweaking the computer while it's in the car may help, but I'm not completely sure if it's meachnical or some sensors are getting false readings. Any insight would be welcomed.

I'm well aware this car is not a huge torque monster or racecar by any means, so, please, I don't mean to show this as showing off. I'm just kind of stumped by the results. 97rs4life, if you're out there, I know you've done A LOT of research. I could use the input.

[1BADAIR]

man . it doesnt even make it to 5250 for the lines to cross
must list your mods

[steddy]

Ok, here we go:

Block:
Balance shaft deleted
Double roller timing chain
Machined oil pump for chain clearance
Bored .030" over
Speed Pro Hyper Pistons with plasma moly rings
MI 77 bearings
Crank turned .010" under and polished
Rods stress relieved.

Valvetrain:
Stock heads with clean-up port job
stock valves
Viton seals
Yellow LS1(?) Springs
Manley retainers (gives extra .050" of clearance)
Harland Sharp roller rockers (1.6 ratio)
Comp Cams hardened push rods (at slock length, due to no deck work on heads)
Comp Cams Xtreme Energy 264 HR15 Blower Camshaft (Specs: Valve lift [installed] I: .531 E: .531, Duration @ .050" I: 210 E: 220)
MI 77 Cam Bearings
LS1 27# fuel injectors (flow matched)

Exhaust:
Pacesetter ceramic shortys
3" pipe, narrowing to 2 1/2 to magnaflow muffler, dual outlet (EGR, CAT, rear O2 delete)

Trans was also rebuilt with the Corvette servo mod. All clutches and the band are kevlar w/shift upgrade and a Beast sunshell. I believe (but right now, can't remember) the converter is roughly 1k over stock with a 3.08 posi.

That's about all that I could get off the top of my head. I hope it helps. I know it sounds pretty lame, but I honestly can't recall about the lifter preload. I do know that when it runs, there's almost no valvetrain noise, except for maybe the closing of the valves, since I think the springs are rated to 120#. It was a year ago last May when this was going on and kind of spotty, since I was using a shop and had to do it during closing hours. Honestly, yeah, she's got small hesitations and seems to run a little on the rich side, but generally, I didn't think there was a major concern (little bit of PCM tuning could be a good thing) till I saw that graph. I am currently running full synthetic in it since break-in.

[Fbomb]

Too much lift for even LS6 springs?

[1BADAIR]

yellows are good to 570. more is set perfect.


how did you adjust the rockers?

[04DetroitLS]

are the rockers even adjustable? most of the 3800 ones Ive seen arent... it almost looks like it went into a limp mode (pcm abuse mode)
when you deleted the BS did tyou use a 440 cam bearing or did you tap the oil feed on the rear of the block for it?
Most guys use the yellow LS6 springs for the smaller cams, ie VS/GT1 or 1.9 rockers, Intense recommends 105s + even for the s1x... I have a little more lift than you (~.6xx), but went w/ 130s, just to be safe
blower cam, but no blower??

wish i could help out more

I know this sounds stupid.. but any codes show up when it dropped off?

[steddy]

None are stored in the SES, but I haven't hit it with a scanner since then. I may drop by the shop and see if any can be pulled. The reason I went with a "blower" style cam was because of the machining done to the block (more area, bigger injectors by roughly 5#, more capacity, etc). I also have a CAI on it, so there's plenty of breathing that can be done. I actually tapped the oil feed. Without it, there wouldn't be any oil pressure. Limp mode almost sounds about right to me, but it didn't set the SES light. While I did have the mail order tune and advised on everything going in, still, the car isn't running right in front of them. She runs fairly well. No big complaints, but I'm almost positive there are some tweaks to be made. Best case: a dyno tune and it'll be done and over. Worst case: I'll have to crack her back open and switch out some stuff. The earlier would be a good thing. The latter, as we all know, would suck, but be done. As I start remembering, the rockers actually had a torque value directly from Harland Sharp. Now that I think of it, I believe I called for just that and they assured me that it was a torque value, not the old V8 way of adjusting.

I know a lot of people were recommending the 105s for quieter operation, but at the time I had to start getting it together, they just weren't available, which is why the Yellows were, what seemed like, a good second choice. The springs, as I could see are WAY away from bind, so I don't quite understand the noise issue myself. Even set the valve covers on the motor without gaskets and turned and no clearance issues. Hell, I thought I had it licked.

Apologies 1BADAIR for the misinfo. It was real early when I saw it and, well, I wasn't too sharp after the specs.

[1BADAIR]

yeah. the rockers should be torqued not adjusted. BUT you have to check for proper lenght pushrods to set the lifter preload
if the valvetrain is noisey then the pushrods are probably to short

[steddy]

Hmmm. I'll have to set up a video, if I can capture the sound, but understand, I really don't hear much of anything, other than what sounds like motor buzz when I'm under the car (welded the exhaust last night and was checking for leaks). Really, it doesn't sound unusual. Perhaps I can have Steve maybe run a scan on the KR function through some RPMs and see if maybe we could pull the reigns in a little more. I just threw him a message and will be off, so I may run up there, should he have the time.

[jakes_GSXR]

whoa thats weirds.

maybe its fuel or spark delivery.

[steddy]

whoa thats weirds.

maybe its fuel or spark delivery.

Hmmm. The FP, wires and Plugs (iridium) are new. The only thing with mileage are the MSD coils and everything seems to handle the load, just not in the upper R's. Although, I have been toying with the idea of getting an MSD DIS-4 ignition.

[steddy]

yeah. the rockers should be torqued not adjusted. BUT you have to check for proper lenght pushrods to set the lifter preload
if the valvetrain is noisey then the pushrods are probably to short

Hey, I just checked some notes when I got home and found that we pumped up the lifters in an oil bath, then torqued to the suggested 11 lb-ft, then a 1/4 turn more. Afterward, I checked each pushrod for any kind of play beyond a reasonable amount (meaning not too tight). As I remember, everything went ok there. Again, if it is the springs, it would just be stupid enough to be correct. Always the small crap.

[1BADAIR]

11+90 is correct BUT
that does not affect lifter preload.
what lifters do you have?
put the cam on the base circle then loosen that rocker. slowly tighten while rocking the rocker. once the lash is gone turn the wrench until it stops counting the turns.
most cams have a smaller base circle and require longer pushrods to set preload

[steddy]

11+90 is correct BUT
that does not affect lifter preload.
what lifters do you have?
put the cam on the base circle then loosen that rocker. slowly tighten while rocking the rocker. once the lash is gone turn the wrench until it stops counting the turns.
most cams have a smaller base circle and require longer pushrods to set preload

Hmm. Yeah, I'm gonna break out the wrenches and check that out, 'course, I don't know if it would do that much from the dyno run, but then again, it could be.

[farmington]

I am an old school car guy and don't know much about newer ones, but if it was mine, I'd be looking at fuel or ignition problem. Your curves are too nice up till 4800, its like something just shuts off or goes into limp mode.