thunderstruck507

iTrader: (18)

Trying to determine why it noses over so hard after a low peak. It was even worse with the ls1 intake, before I put on a Fast 90/90. Used to peak at 5500rpm and slope down to 6000rpm then it fell hard.

Now it peaks at ~5900rpm and slopes over. Numbers also are unimpressive.

Other ideas?


SPEC CARD# 13789308 SPEC CARD INQUIRY BY SPEC CARD NO

PART # 54-000-11 LS1 CHEVY LS1/GEN III '97-UP ROLLER
CORE C99 DUMMY OVERRIDE CORE
GRIND # LS1 3718 /3715 HR111.0

DURATION @ .050 INTAKE 230

DURATION @ .050 EXHAUST 224

LOBE LIFT INTAKE .3370

VALVE LIFT INTAKE .572 LOBE LIFT EXHAUST .3340

VALVE LIFT EXHAUST .567 LOBE SEPARATION 111.0

DURATION .006 INTAKE C/L 108.0

TAPPET LIFT INTAKE 283 ADVANCE 3

TAPPET LIFT EXHAUST 277 HYDRAULIC Y

VALVE TIMING .050 OVERHEAD CAM N

VALVE OPEN INTAKE 7

VALVE OPEN EXHAUST 46

VALVE CLOSED INTAKE 43

VALVE CLOSED EXHAUST 2-


INTAKE LOBE ID 3718

EXHAUST LOBE ID 3715
DATE SETUP 03/07/2008

Fbodyjunkie06

iTrader: (10)

Could be bad coils, plug wires, plugs, it definatly looks and sounds tune related to me.

Intake centerline verified when installing the cam?

thunderstruck507

iTrader: (18)

Plugs and wires were new for the first dyno in 2008 and replaced right before the other in 2010.

Had 3 different mail order tunes and then a dyno tune. It's not on that graph but the car made right at 370rwhp/340rwtq at XP on a different day, but the driveshaft snapped and took out the trans. It was also lean. Went back months later with a new driveshaft (it was hot as ***** and the car was heat soaked) and he fixed the a/f and made that pull and we called it good.

Been that way since. Car runs 90mph in the 1/8th at 1840 DA. 110mph in the 1/4 (but this was shifting at 6500 which looks to be way too much for the powerband.

I didn't degree the cam, installed dot to dot (100% sure that was done correctly though). I am going to check pushrods but I doubt that's a problem. I have GMPP replacement lifters and 7.4 pushrods. Heads were not milled but were surface ground and reinstalled with FelPro stock like gaskets from Parts Plus so they should be stock thickness.


All dyno pulls were with the cutouts closed and converter unlocked.

Jared H

iTrader: (1)

I blame the reverse split on unported heads ... try a different cam.

thunderstruck507

iTrader: (18)

There are cams almost identical to this one making 380-400rwhp cam only. While it's not the best choice anymore, I still think it is underperforming for some other reason.

I would like to swap cams when I have it apart to install ported 799 heads, but I'm trying to work with what I have for now. I could very well be wrong, but I was under the impression this would be peaking at 6100-6200 in my combo and carry out a touch, rather than peaking before 6000 and dropping off after peak.

LilJayV10

iTrader: (39)

What valve springs are you using and what's the install height on them?

thunderstruck507

iTrader: (18)

They are the PAC 918 equivalent springs. They were installed by the machine shop that surfaced the heads so I'm not certain and there's no way he would remember since they went on in 08.

Thanks for the help so far guys

trey1010

iTrader: (3)

I vote TUNE. but it seems like your car is running pretty good.

ls1wallen

Tourque Conveter maybe? I am a member on another LS site where a guy spent tons of money on his combo and couldnt find out why it wasnt making power. His converter was fried.

NC98Z

iTrader: (1)

The fast 90/90 moves your power band peak up about 500 rpm by itself. It needs a set of heads.

5.3LJimmy

iTrader: (10)

That camshaft is almost identical to a TR230(I believe it has 0 advance) and will likely be rather exhaust sensitive. I don't think advancing or retarding the cam is going to make a big difference, though I can see it being down 10-15 horsepower when compared to an f-body with a good catback and longtubes. Tell us your exhaust specs.

I also agree with the post above that the track mph numbers look pretty good. Especially given the 3.42 gears and probably a 3600+lb raceweight.

thunderstruck507

iTrader: (18)

Track weight is 3700+lbs with me in it for sure.

1 3/4" Doug's headers with 3" collectors
3" duals to flowtech terminator chambered mufflers
no tails, at the time of this dyno it had 2 1/4" over the axle

it has dual cutouts about 12" behind the collectors, back when the car had tails they showed signs of working for about .1 and 1.5 mph at the track but now that it has no tails they show no gains in back to back runs



I have a set of heads to be ported/milled and installed but it will be a while. Right now I'm just curious about whether or not there are issues with the engine or if retarding the cam to counter the 3* advance would help make more power or extend the power band.

I would expect it to choke less up top seeing as how the biggest restriction is the MAF and the stock heads...both of which routinely allow ls1 combos to continue to make power to 7k rpm (in combos with cams meant to make power that high of course). It's the early peak, low peak, and rapid decline that have my attention.

87silverbullet

iTrader: (11)

If the tune is right all I can see is either valvesprings or there is a restriction

Maybe like mentioned earlier the converter might be letting go. I have seen that happen many times before.

99Bluz28

iTrader: (35)

If you plan to hang-on to you currect cam for a while I'd verify Intake centerline, and check the valve spring install height(1.800" for 1518s). If you do retard the cam 3* it'll only move the power up around 100RPM, but it also's going to have a little less Low-End Torque. I do think your exhaust duration(224*) is holding you back some.
IMO, a single pattern like a 228/228 or better yet a tradition split like a 228/232 would be better.

BTW, you'll want those cut-outs at least 10x the exhaust tube dia, away from your O2 sensors, otherwise you O2s could think you're running a little lean with the cut-outs open.

thunderstruck507

iTrader: (18)

I was planning on taking a valve cover off to check pushrod length and preload just to be sure, so I can have a look at the springs. Do I just measure one from the head for height?

I could just be getting worked up over nothing I suppose, kinda gets old having people tell me I should be running faster though, especially when I see some of the numbers on here.

gtotoocool1

iTrader: (6)

it could be a number of things,but here's my best internet guess:
i don't think the drop off in power is tune related..if it was me i would degree the cam to see what the actual ICL is.the cam could be father advanced than you think.i've seen a couple of cams that,once installed,were advanced about 4 degrees more than the ICL on the cam card.if it was tune related i think that would show up earlier in the powerband.
your numbers don't look that bad for your combo,other than peaking too early.A4s and dynos don't mix well,especially with unlocked converters. 3700lbs with a 110mph trap speed isn't terrible for the mild combo you have.

99Bluz28

iTrader: (35)

You"ll need a Valve Spring Height Micrometer installed in place of one of the valve springs to verify the install height (CompCams #4929, 1.600'' to 2.200'' Range Height Micrometer).

LilJayV10

iTrader: (39)

Proform sells one too. It's about 50 bucks. I ordered one and it should be here today. I've gotta my spring height too.

99Bluz28

iTrader: (35)

Yeah, the CompCams is about $70

thunderstruck507

iTrader: (18)

Ah well I won't be able to do that then. The guy who installed them should have set them up, I know when I took him the heads the first time he checked out the springs we had put on which were sold to me as comp 918s. He said something was right when I told him the specs and it turned out some jackass sold me new stock springs in a comp box.

So I just let him install the PACs when they came in since it was clear he knew what he was doing.

If nothing else I can see how the car does at the track on the 30th. Maybe shifting the 2-3 a little closer to peak instead of 6500-6600 will bring some mph back to the top end.