3.91 Gears adds to dyno or losses? and boost loss whre to look? - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

Reelgrinder · 11-02-2015, 08:46 AM

Was wondering does 3.91 gears make your dyno read higher or lower?

Also

I have seem to have lost some HP?

I was making 615 on a mustang dyno last Nov with 10 to 11 psi on the eforce.

I since have done 3.91 gears and the tuner says I'm down to 8 psi IATs read same about 140. out side temp on last years run was 58 deg. Last week it 70 deg.

Belt isn't slipping
Compression is fine

Where could I be loosing 3 psi?

cc-rider · 11-02-2015, 10:31 AM

It's probably just the atmospheric conditions between the runs accounting for some of the boost. I wouldn't think that boost could change that much...but there was just another post here about a month back where a guy was logging the same amount of boost changes with different ambient temps. The density of the air can change, and temp is a major factor but not the only one.

I wonder if anyone has ever done a study on atmospheric conditions and how that affects boost (keeping everything with the engine/charger fixed variables). Would be really interesting to read and study. I think that all of us that have forced induction have felt the performance of our cars swing from day-to-day.

Unreal · 11-02-2015, 10:50 AM

Belt wear, air filter, weather, etc. I've seen 3-4psi just cleaning the airfilter.

Gears have no effect on dyno numbers.

JANNETTYRACING · 11-02-2015, 11:21 AM

Quote:

Originally Posted by Reelgrinder

Was wondering does 3.91 gears make your dyno read higher or lower?

Also

I have seem to have lost some HP?

I was making 615 on a mustang dyno last Nov with 10 to 11 psi on the eforce.

I since have done 3.91 gears and the tuner says I'm down to 8 psi IATs read same about 140. out side temp on last years run was 58 deg. Last week it 70 deg.

Belt isn't slipping
Compression is fine

Where could I be loosing 3 psi?

Gears should have no affect on dyno numbers unless your spinning your tires which will affect numbers for sure.

What pulley combo are you running?

Ted.

Reelgrinder · 11-02-2015, 11:57 AM

Quote:

Originally Posted by JANNETTYRACING

Gears should have no affect on dyno numbers unless your spinning your tires which will affect numbers for sure.

What pulley combo are you running?

Ted.

2.75 and stock cranks..

Unreal..

I have and the tuner has seen belt slippage in the past none is present

can't see how a worn belt would make a difference if nothing is slipping

Reelgrinder · 11-02-2015, 11:59 AM

Boost was 7 or 8 psi in lower rpm then upward rpm it was abt 11.. now down low its 6 or 7 and 8 in upper rpm coming on late.

JANNETTYRACING · 11-02-2015, 12:11 PM

Quote:

Originally Posted by Reelgrinder

Boost was 7 or 8 psi in lower rpm then upward rpm it was abt 11.. now down low its 6 or 7 and 8 in upper rpm coming on late.

Belt slip is most likely.

Ted.

AGP Turbo · 11-02-2015, 12:13 PM

Down and up and down?
Maybe your bypass is not holding shut. Something isn't right there.

cc-rider · 11-02-2015, 12:52 PM

Quote:

Originally Posted by Reelgrinder

2.75 and stock cranks..

Unreal..

I have and the tuner has seen belt slippage in the past none is present

can't see how a worn belt would make a difference if nothing is slipping

Reel-
Are you 100% sure that belt is not slipping? How have you confirmed this?

Not trying to discredit you or call you a liar. But as others have said, it is certainly the most obvious thing. Would suck to go chasing other more complicated things when the most obvious culprit has not be 100% ruled out.

Reelgrinder · 11-02-2015, 01:40 PM

Pretty sure the curve looked dam smooth.. I had matt Sorian from FSP look at it last year and it did slip with him and you could see it but once I got the upgraded tensioner and green belt Its been ok.. So ya pretty sure.. I saw nothing like before.. but the belt so cheap and my AC belt is pretty crappy down to 3 ribs lol So Ill do them both..

Unreal · 11-02-2015, 02:09 PM

When a system has a borderline belt system it won't slip at first, but after some mileage it will. Just because it wasn't slipping before doesn't mean it isn't now. With a 2.75 upper if it doesn't have at least an 8 rib I wouldn't expect belts not to slip.

Reelgrinder · 11-03-2015, 01:31 PM

I was wrong its a 3" pulley, I haven't put the 2.75 on yet.

Here are the 2 graphs to compare last Nov and 4 days ago.. You would see belt slippage wouldn't' you?

Unreal · 11-03-2015, 01:52 PM

No you don't see belt slip.

11-02-2015, 08:46 AM	#1
Reelgrinder Drives: 2016 SS Join Date: Oct 2014 Location: DFW Posts: 228	3.91 Gears adds to dyno or losses? and boost loss whre to look? Was wondering does 3.91 gears make your dyno read higher or lower? Also I have seem to have lost some HP? I was making 615 on a mustang dyno last Nov with 10 to 11 psi on the eforce. I since have done 3.91 gears and the tuner says I'm down to 8 psi IATs read same about 140. out side temp on last years run was 58 deg. Last week it 70 deg. Belt isn't slipping Compression is fine Where could I be loosing 3 psi? __________________ 2016 SS with Eforce 2300 Borla Headers Borla Atak

11-02-2015, 10:50 AM	#3
Unreal Drives: 2006 Z06 Join Date: Oct 2010 Location: Gilbert, AZ Posts: 5,712	Belt wear, air filter, weather, etc. I've seen 3-4psi just cleaning the airfilter. Gears have no effect on dyno numbers. __________________ Nick Corvette Z06 -1200ish rwhp

11-02-2015, 11:59 AM	#6
Reelgrinder Drives: 2016 SS Join Date: Oct 2014 Location: DFW Posts: 228	Boost was 7 or 8 psi in lower rpm then upward rpm it was abt 11.. now down low its 6 or 7 and 8 in upper rpm coming on late. __________________ 2016 SS with Eforce 2300 Borla Headers Borla Atak

11-02-2015, 01:40 PM	#10
Reelgrinder Drives: 2016 SS Join Date: Oct 2014 Location: DFW Posts: 228	Pretty sure the curve looked dam smooth.. I had matt Sorian from FSP look at it last year and it did slip with him and you could see it but once I got the upgraded tensioner and green belt Its been ok.. So ya pretty sure.. I saw nothing like before.. but the belt so cheap and my AC belt is pretty crappy down to 3 ribs lol So Ill do them both.. __________________ 2016 SS with Eforce 2300 Borla Headers Borla Atak

11-02-2015, 02:09 PM	#11
Unreal Drives: 2006 Z06 Join Date: Oct 2010 Location: Gilbert, AZ Posts: 5,712	When a system has a borderline belt system it won't slip at first, but after some mileage it will. Just because it wasn't slipping before doesn't mean it isn't now. With a 2.75 upper if it doesn't have at least an 8 rib I wouldn't expect belts not to slip. __________________ Nick Corvette Z06 -1200ish rwhp

11-02-2015, 10:31 AM	#2
cc-rider Drives: 2010 Camaro SS Join Date: Dec 2006 Location: MN Posts: 1,179	It's probably just the atmospheric conditions between the runs accounting for some of the boost. I wouldn't think that boost could change that much...but there was just another post here about a month back where a guy was logging the same amount of boost changes with different ambient temps. The density of the air can change, and temp is a major factor but not the only one. I wonder if anyone has ever done a study on atmospheric conditions and how that affects boost (keeping everything with the engine/charger fixed variables). Would be really interesting to read and study. I think that all of us that have forced induction have felt the performance of our cars swing from day-to-day.

11-02-2015, 12:13 PM	#8
AGP Turbo Drives: All things Turbocharged Join Date: Dec 2010 Location: AZ Posts: 1,199	Down and up and down? Maybe your bypass is not holding shut. Something isn't right there.

11-03-2015, 01:31 PM	#12
Reelgrinder Drives: 2016 SS Join Date: Oct 2014 Location: DFW Posts: 228	I was wrong its a 3" pulley, I haven't put the 2.75 on yet. Here are the 2 graphs to compare last Nov and 4 days ago.. You would see belt slippage wouldn't' you? Attached Images __________________ 2016 SS with Eforce 2300 Borla Headers Borla Atak

11-03-2015, 01:52 PM	#13
Unreal Drives: 2006 Z06 Join Date: Oct 2010 Location: Gilbert, AZ Posts: 5,712	No you don't see belt slip. __________________ Nick Corvette Z06 -1200ish rwhp