theory discussion: tracking down the root cause of poor performance
theory discussion: tracking down the root cause of poor performance let's say a person puts together a turbo project that's fairly mild and budget conscious, with mods along the lines of this:
a cam with moderate duration and lift, 114 LSA
heads with a valve job and light porting
1.7 rockers and dual valve springs
stock intake manifold
and a small-ish but proven turbo
now this person gets the tune squared away and throws the car on a dyno but it's way down on power and torque compared to what it "should" be making compared to similar examples out there, to the tune of 100 hp down or more. despite a moderately aggressive cam the power peaks WAY lower than it should (let's say 5200 rpm instead of over 6000.) the curves otherwise look "fine" with no sudden dips or other abnormalities such as what you might expect to see with valve float.
the person then goes on to check compression in the 150s, and checks cylinder leakage to be in the 7-9% range.
the car runs and drives just fine with no obvious issues, a quiet valvetrain, good oil pressure, etc.
in such a scenario, what are some of the things that might possibly create this scenario?
a cam with moderate duration and lift, 114 LSA
heads with a valve job and light porting
1.7 rockers and dual valve springs
stock intake manifold
and a small-ish but proven turbo
now this person gets the tune squared away and throws the car on a dyno but it's way down on power and torque compared to what it "should" be making compared to similar examples out there, to the tune of 100 hp down or more. despite a moderately aggressive cam the power peaks WAY lower than it should (let's say 5200 rpm instead of over 6000.) the curves otherwise look "fine" with no sudden dips or other abnormalities such as what you might expect to see with valve float.
the person then goes on to check compression in the 150s, and checks cylinder leakage to be in the 7-9% range.
the car runs and drives just fine with no obvious issues, a quiet valvetrain, good oil pressure, etc.
in such a scenario, what are some of the things that might possibly create this scenario?
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What makes you think the tune is squared away?
How many times has someone gotten a "Pro Tune" only to find out that the tuner doesn't really know what they're doing and left power on the table or worst case caused engine damage.
Provide a detailed post, car details, dyno graph or snapshot of the tune and there's lot's of guys on here who can help.
How many times has someone gotten a "Pro Tune" only to find out that the tuner doesn't really know what they're doing and left power on the table or worst case caused engine damage.
Provide a detailed post, car details, dyno graph or snapshot of the tune and there's lot's of guys on here who can help.
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TECH Fanatic
Joined: Dec 2019
Posts: 1,129
Likes: 478
Dyno is a pretty poor indicator.
A guy I know on here made 320whp with an LS1 on a chassis dyno and ran like 11.0 his first time out.
Dynos handle things like torque converters very poorly as well. You can swap from a stock converter to a 4000 stall converter and lose power on the dyno, but go half a second or more faster at the track.
A guy I know on here made 320whp with an LS1 on a chassis dyno and ran like 11.0 his first time out.
Dynos handle things like torque converters very poorly as well. You can swap from a stock converter to a 4000 stall converter and lose power on the dyno, but go half a second or more faster at the track.
TECH Enthusiast
Joined: Dec 2017
Posts: 676
Likes: 72
I would agree with converter. I had a 6l80 in a car built by patc with there bullet 10 inch quad disc torque converter and it wouldn't make but 545rwhp no matter what I did. People said take it to the drag strip. So I did it was a flat dog but fuel consumption and boost figured for way more power being made. Changed to a ptc and a 4l80 and 770hp to the rear wheels on lower boost