Should my power fall off this soon?
11-17-2008, 10:57 PM
#1
Should my power fall off this soon? Maybe I'm just being paranoid but it seems like the power on my dyno run seems to fall off too soon...at first I was just thinking that maybe it was the ls1 intake, but have begun to second guess that.
Anyone have any ideas? Maybe its just the nature of the cam?
98 ls1
2000 ls1 heads untouched other than being surfaced
comp 230/224 111+3 lsa cam on xe lobes .572/.567
ls1 intake, stock minus plugged emissions
pac springs (comp 918 equivalents)
ported throttle body, coolant bypassed
stock maf
long tubes with open cutouts very close behind
ported ls6 oil pump
ls2 timing chain
no a/c
new plugs and wires
4l60e, stock except for transgo corrector kit, unlocked and in manual 3rd during run
12 bolt 3.42 gears
mail order tune, could it just be something in the tune? I expect more power with a good tune, but I'm not informed enough on this stuff to know if it could just be a tune issue, I'm leaning more towards it being the nature of the cam...even though I expected it to behave more similar to the tr230 on which its based
ignore the sharp decline on run #2, that was my stopping because I saw smoke (tailhousing on tranny busted all the way around)
I'm just wondering if this is an indication of a problem I should be searching for or just me worrying too much
Anyone have any ideas? Maybe its just the nature of the cam?
98 ls1
2000 ls1 heads untouched other than being surfaced
comp 230/224 111+3 lsa cam on xe lobes .572/.567
ls1 intake, stock minus plugged emissions
pac springs (comp 918 equivalents)
ported throttle body, coolant bypassed
stock maf
long tubes with open cutouts very close behind
ported ls6 oil pump
ls2 timing chain
no a/c
new plugs and wires
4l60e, stock except for transgo corrector kit, unlocked and in manual 3rd during run
12 bolt 3.42 gears
mail order tune, could it just be something in the tune? I expect more power with a good tune, but I'm not informed enough on this stuff to know if it could just be a tune issue, I'm leaning more towards it being the nature of the cam...even though I expected it to behave more similar to the tr230 on which its based
ignore the sharp decline on run #2, that was my stopping because I saw smoke (tailhousing on tranny busted all the way around)
I'm just wondering if this is an indication of a problem I should be searching for or just me worrying too much
11-18-2008, 09:59 AM
#2
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Seems very odd.
With an IVC of 43, HP should peak closer to 6000-6300 rpm's.
Thats an unusual curve. I would concur that either the LS1 intake is cutting the 'breathing' needed at higher rpms, or there is a mechanical issue.
I don't think a tune by itself would really account for that unusual peak. Is the cam overly advanced?
A lot of people have ran reverse-split cams with success, so perhaps others will chime in.
..WeathermanShawn..
With an IVC of 43, HP should peak closer to 6000-6300 rpm's.
Thats an unusual curve. I would concur that either the LS1 intake is cutting the 'breathing' needed at higher rpms, or there is a mechanical issue.
I don't think a tune by itself would really account for that unusual peak. Is the cam overly advanced?
A lot of people have ran reverse-split cams with success, so perhaps others will chime in.
..WeathermanShawn..
11-18-2008, 06:37 PM
#5
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Nice car by the way!
By no means an expert on valve float. Had it once (dyno) and it looked a lot worse than that. It fell ~200-300 rpms at 5600rpms. Was pretty obvious.
I will let someone else comment. Not sure with your trans and gear if that could account for anything peculiar on the dyno.
Still 'guessing' intake.
Good luck.
..WeathermanShawn..
By no means an expert on valve float. Had it once (dyno) and it looked a lot worse than that. It fell ~200-300 rpms at 5600rpms. Was pretty obvious.
I will let someone else comment. Not sure with your trans and gear if that could account for anything peculiar on the dyno.
Still 'guessing' intake.
Good luck.
..WeathermanShawn..
11-18-2008, 06:58 PM
#6
I do know my tranny/driveshaft combo didn't like the dyno much...makes me kinda afraid to go back on
the only other thing is it did feel like the rpms came up a lot slower on there than on the street, but that might just be the way the dyno loads to car...this was my first time around one period, not even sure if I was supposed to have it in 3rd like I did or in Drive...the guys running it were just high school kids, didn't seem to have much interest in me...just said run it up to 3rd, give a thumbs up to him then nail it and let off when I wanted, didn't want it to try to rush up in to 4th and have to kick down and look like a jackass for doing it wrong...
the only other thing is it did feel like the rpms came up a lot slower on there than on the street, but that might just be the way the dyno loads to car...this was my first time around one period, not even sure if I was supposed to have it in 3rd like I did or in Drive...the guys running it were just high school kids, didn't seem to have much interest in me...just said run it up to 3rd, give a thumbs up to him then nail it and let off when I wanted, didn't want it to try to rush up in to 4th and have to kick down and look like a jackass for doing it wrong...
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12-01-2008, 08:50 PM
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I dunno if I can be of any help to you but I'm dealing with the same problem in a built 6L. My mods are similar to yours but I'm running a truck intake manifold, a 218/224 cam and my heads are hand ported. Below you'll see a scan of my best run. I think you and I alike are dealing with a cam and or a valve timing issue. My truck is in storage for the winter but maybe have you considered putting a dial indicator on the pushrod and rotating the engine over to make sure the lift at the rocker matches the lobe lift? If not, maybe you were shipped the wrong cam? My vote goes for either you got shipped the wrong cam or it's advanced way too far. I don't think that'd be an intake restriction. Just like on my chart. Look at how much power I have then it falls off dramatically. I wish I could tell you what mine is but I think it's more a valve timing issue than it is a breathing issue. Let's see what others say:
12-02-2008, 09:56 PM
#16
It will have high vacuum if your intake or throttle body is becoming a restriction at high rpm, ie. like sucking through a small straw. I would tend to agree with the above on valve float, it should more ratty before the power drops off. I'm sure you can find a good example of valve float with a search here.
