Will gears change dyno #'s?
Thread Starter
Drifting
Joined: Jan 2007
Posts: 1,460
Likes: 38
From: Broken Arrow Oklahoma
Will gears change dyno #'s?
I am having 3.90 gears installed. I was wondering if my dyno #'s would change. I know it will feel like I will have more torque but would it show up on a dyno tune? I have heard that I may lose rwhp. Thx for any input.
Team Owner
Joined: Mar 2005
Posts: 20,933
Likes: 905
From: salem OR
You could easy do 4.10's. With your non z-51 tranny. I have 390's and love them. 410's cut about 5 mph @ 2k. Didn't lose any mileage shocked about that.
Burning Brakes
Joined: Apr 2008
Posts: 946
Likes: 0
From: 1BadC6 New Jersey
St. Jude Donor '08
You won't lose any power. They say they dyno less. But did they reset the dyno. The Dyno Jet has a option for different gears. The operator sets 3.42, 390 whatever gear you have, on the dyno screen.
You could easy do 4.10's. With your non z-51 tranny. I have 390's and love them. 410's cut about 5 mph @ 2k. Didn't lose any mileage shocked about that.
You could easy do 4.10's. With your non z-51 tranny. I have 390's and love them. 410's cut about 5 mph @ 2k. Didn't lose any mileage shocked about that.
I hope to hook up with Chuck Cow next week 4.10s.
Mike
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
The engine uses the same load even when you change gears. In other words the load cell when you are at a set cruise speed is higher for a lower rpm and lower for a higher rpm. It uses 11hp to maintain a 55mph cruise and the engines power output is higher at at higher rpm. So using 11 hp at 2k vs 11hp at 1600 with a taller gear wont change gas mileage since the engine isnt doing any more work. If you log the car, you can see in a scan that at 1600rpm a car may be at .32kpa load and at 2000rpm with a steeper gear its at .28kpa load. The engine is actually more stressed at the lower rpm since it is making less HP than it does at 2000rpm's.
I noted there wasnt a load difference after the cam swap because the power band moved up making the best efficiency appear at 2100rpm but at a lower load than with the old cam. gears made no difference since the power band, load, and hp were just as efficient with either gear set. 4.10's, 3.90's ect, dont make a car worse on gas unless you are making the car produce more HP by rpm increases when you floor it which translates into more load sooner in the rpm band. In other words you can see yur injector flow rate increase much faster in the rpm band as you climb in rpm. They definitely waste more gas in that context but they are making you move faster.
To illustrate, say you and I are at 100mph and side by side on the hiway. If we had the exact same engine power I at 3000rpm would be at 240hp on the curve and you at 2600 would be at 210hp at that mph. If we maintain the same mph, the engines are doing the same work. I dont have to push down on the throttle as much because my car is making more HP so I require less gas to make the car stay at that speed. Understand this doesnt mean that your cam is the same efficiency at the different rpm's; it is a characteristic of the power band and applies only to different rpms with two different cams. If we accelerate though, I am always at a higher HP position which is always using more gas....so floored my car is then less effieicent than you at a set car speed. My car would always make more HP at any given vehicle speed. Since I at any spped am at a higher rpm the car would always make more HP so it winds the gear faster. I shift and then fall to 4800rpm (now lower HP level until you shift) and then you fall to 4500 with the taller gear which is again lower HP. We both have 1 launch and 3 shifts but I wind each gear fatser because I am always at a higher HP for any given speed. When I get to the traps, I am out of rpm but I am at the full output power (HP) that my engine makes and you would cross the traps at 5900 which with an aftermarket cam is 400 short of the HP peak. Thats why its best to gear for the trap speed.
In C6DVL's experience he used SOTP to describe his car going from 140 to a higher speed as faster with 3.90's which isnt true. At 100mph both us next to each other he is at 2850 and I am at 3k. Again I have more HP if the engines were the same. Now at 126, he is still in 4th and I would be in the bottom of 5th. He would be waaaaay faster until he had to shift. I would still be 5% higher in engine rpm than him. If the race was from 126 to 138 he would win.
I like 4.10's for the street (even though my trap speed on the bottle would never stay below 4th gear) because on the street things are more like a 1/8 mile run and its over at or before 100mph (unless you do race to higher mph and dont care about accidents). Since I can hit 100 in 3rd the 4.10's make for a killer ride on the street with traction.
I understand you liking the 3.90's as a preference and your reasons. Thay are valid points but I dont see the economy trade-off myself. I never reset the lifetime fuel economy calculation the car does. I always for the life of my car saw 17+ as the average and 28-32 on the hiway. My recent trip south to help out Braciole was 280miles and I got home with 1/4+tank. I drive pretty aggressive so I of all people would see the difference. My friend ran 2 10.5x passes with 4.10's at the track so I know its not a limiting factor there. In the end if you hate seing 2100rpm, you wont get them. I think if you got a cam and saw 22mpg at 1600rpm vs. 29mpg at 2200rpm you would think differently about it. You have to do what makes you happy though.
I noted there wasnt a load difference after the cam swap because the power band moved up making the best efficiency appear at 2100rpm but at a lower load than with the old cam. gears made no difference since the power band, load, and hp were just as efficient with either gear set. 4.10's, 3.90's ect, dont make a car worse on gas unless you are making the car produce more HP by rpm increases when you floor it which translates into more load sooner in the rpm band. In other words you can see yur injector flow rate increase much faster in the rpm band as you climb in rpm. They definitely waste more gas in that context but they are making you move faster.
To illustrate, say you and I are at 100mph and side by side on the hiway. If we had the exact same engine power I at 3000rpm would be at 240hp on the curve and you at 2600 would be at 210hp at that mph. If we maintain the same mph, the engines are doing the same work. I dont have to push down on the throttle as much because my car is making more HP so I require less gas to make the car stay at that speed. Understand this doesnt mean that your cam is the same efficiency at the different rpm's; it is a characteristic of the power band and applies only to different rpms with two different cams. If we accelerate though, I am always at a higher HP position which is always using more gas....so floored my car is then less effieicent than you at a set car speed. My car would always make more HP at any given vehicle speed. Since I at any spped am at a higher rpm the car would always make more HP so it winds the gear faster. I shift and then fall to 4800rpm (now lower HP level until you shift) and then you fall to 4500 with the taller gear which is again lower HP. We both have 1 launch and 3 shifts but I wind each gear fatser because I am always at a higher HP for any given speed. When I get to the traps, I am out of rpm but I am at the full output power (HP) that my engine makes and you would cross the traps at 5900 which with an aftermarket cam is 400 short of the HP peak. Thats why its best to gear for the trap speed.
In C6DVL's experience he used SOTP to describe his car going from 140 to a higher speed as faster with 3.90's which isnt true. At 100mph both us next to each other he is at 2850 and I am at 3k. Again I have more HP if the engines were the same. Now at 126, he is still in 4th and I would be in the bottom of 5th. He would be waaaaay faster until he had to shift. I would still be 5% higher in engine rpm than him. If the race was from 126 to 138 he would win.
I like 4.10's for the street (even though my trap speed on the bottle would never stay below 4th gear) because on the street things are more like a 1/8 mile run and its over at or before 100mph (unless you do race to higher mph and dont care about accidents). Since I can hit 100 in 3rd the 4.10's make for a killer ride on the street with traction.
I understand you liking the 3.90's as a preference and your reasons. Thay are valid points but I dont see the economy trade-off myself. I never reset the lifetime fuel economy calculation the car does. I always for the life of my car saw 17+ as the average and 28-32 on the hiway. My recent trip south to help out Braciole was 280miles and I got home with 1/4+tank. I drive pretty aggressive so I of all people would see the difference. My friend ran 2 10.5x passes with 4.10's at the track so I know its not a limiting factor there. In the end if you hate seing 2100rpm, you wont get them. I think if you got a cam and saw 22mpg at 1600rpm vs. 29mpg at 2200rpm you would think differently about it. You have to do what makes you happy though.
Last edited by SpinMonster; Jun 5, 2008 at 11:16 PM.
Melting Slicks
Joined: May 2006
Posts: 2,891
Likes: 1
From: NJ..."the way I saw it, everyone takes a beating sometimes."
The engine uses the same load even when you change gears. In other words the load cell when you are at a set cruise speed is higher for a lower rpm and lower for a higher rpm. It uses 11hp to maintain a 55mph cruise and the engines power output is higher at at higher rpm. So using 11 hp at 2k vs 11hp at 1600 with a taller gear wont change gas mileage since the engine isnt doing any more work. If you log the car, you can see in a scan that at 1600rpm a car may be at .32kpa load and at 2000rpm with a steeper gear its at .28kpa load. The engine is actually more stressed at the lower rpm since it is making less HP than it does at 2000rpm's.
I noted there wasnt a load difference after the cam swap because the power band moved up making the best efficiency appear at 2100rpm but at a lower load than with the old cam. gears made no difference since the power band, load, and hp were just as efficient with either gear set. 4.10's, 3.90's ect, dont make a car worse on gas unless you are making the car produce more HP by rpm increases when you floor it which translates into more load sooner in the rpm band. In other words you can see yur injector flow rate increase much faster in the rpm band as you climb in rpm. They definitely waste more gas in that context but they are making you move faster.
To illustrate, say you and I are at 100mph and side by side on the hiway. If we had the exact same engine power I at 3000rpm would be at 240hp on the curve and you at 2600 would be at 210hp at that mph. If we maintain the same mph, the engines are doing the same work. I dont have to push down on the throttle as much because my car is making more HP so I require less gas to make the car stay at that speed. Understand this doesnt mean that your cam is the same efficiency at the different rpm's; it is a characteristic of the power band and applies only to different rpms with two different cams. If we accelerate though, I am always at a higher HP position which is always using more gas....so floored my car is then less effieicent than you at a set car speed. My car would always make more HP at any given vehicle speed. Since I at any spped am at a higher rpm the car would always make more HP so it winds the gear faster. I shift and then fall to 4800rpm (now lower HP level until you shift) and then you fall to 4500 with the taller gear which is again lower HP. We both have 1 launch and 3 shifts but I wind each gear fatser because I am always at a higher HP for any given speed. When I get to the traps, I am out of rpm but I am at the full output power (HP) that my engine makes and you would cross the traps at 5900 which with an aftermarket cam is 400 short of the HP peak. Thats why its best to gear for the trap speed.
I like 4.10's for the street even though my trap speed on the bottle would never stay below 4th gear because on the street things are more like a 1/8 mile run and its over at or before 100mph (unless you do race to higher mph and dont care about accidents). Since I can hit 100 in 3rd the 4.10's make for a killer ride on the street with traction.
I understand your liking the 3.90's as a preference and your reasons. Thay are valid points but I dont see the economy trade-off myself. I never reset the lifetime fuel economy calculation the car does. I always for the life of my car saw 17+ as the average and 28-32 on the hiway. My recent trip south to hep out Braciole was 280miles and I got home with 1/4+tank. I drive pretty aggressive so I of all people would see the difference. My friend ran 2 10.5x passes with 4.10's at the track so I know its not a limiting factor there. In the end if you hate seing 2100rpm, you wont get them. I think if you got a cam and saw 22mpg at 1600rpm vs. 29mpg at 2200rpm you would think differently about it. You have to do what makes you happy though.
I noted there wasnt a load difference after the cam swap because the power band moved up making the best efficiency appear at 2100rpm but at a lower load than with the old cam. gears made no difference since the power band, load, and hp were just as efficient with either gear set. 4.10's, 3.90's ect, dont make a car worse on gas unless you are making the car produce more HP by rpm increases when you floor it which translates into more load sooner in the rpm band. In other words you can see yur injector flow rate increase much faster in the rpm band as you climb in rpm. They definitely waste more gas in that context but they are making you move faster.
To illustrate, say you and I are at 100mph and side by side on the hiway. If we had the exact same engine power I at 3000rpm would be at 240hp on the curve and you at 2600 would be at 210hp at that mph. If we maintain the same mph, the engines are doing the same work. I dont have to push down on the throttle as much because my car is making more HP so I require less gas to make the car stay at that speed. Understand this doesnt mean that your cam is the same efficiency at the different rpm's; it is a characteristic of the power band and applies only to different rpms with two different cams. If we accelerate though, I am always at a higher HP position which is always using more gas....so floored my car is then less effieicent than you at a set car speed. My car would always make more HP at any given vehicle speed. Since I at any spped am at a higher rpm the car would always make more HP so it winds the gear faster. I shift and then fall to 4800rpm (now lower HP level until you shift) and then you fall to 4500 with the taller gear which is again lower HP. We both have 1 launch and 3 shifts but I wind each gear fatser because I am always at a higher HP for any given speed. When I get to the traps, I am out of rpm but I am at the full output power (HP) that my engine makes and you would cross the traps at 5900 which with an aftermarket cam is 400 short of the HP peak. Thats why its best to gear for the trap speed.
I like 4.10's for the street even though my trap speed on the bottle would never stay below 4th gear because on the street things are more like a 1/8 mile run and its over at or before 100mph (unless you do race to higher mph and dont care about accidents). Since I can hit 100 in 3rd the 4.10's make for a killer ride on the street with traction.
I understand your liking the 3.90's as a preference and your reasons. Thay are valid points but I dont see the economy trade-off myself. I never reset the lifetime fuel economy calculation the car does. I always for the life of my car saw 17+ as the average and 28-32 on the hiway. My recent trip south to hep out Braciole was 280miles and I got home with 1/4+tank. I drive pretty aggressive so I of all people would see the difference. My friend ran 2 10.5x passes with 4.10's at the track so I know its not a limiting factor there. In the end if you hate seing 2100rpm, you wont get them. I think if you got a cam and saw 22mpg at 1600rpm vs. 29mpg at 2200rpm you would think differently about it. You have to do what makes you happy though.
Going soft on us Spin?
Sik Six, this is an informative thread.
http://forums.corvetteforum.com/show...ght=gears+dyno
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Going soft on us Spin?
Sik Six, this is an informative thread.
http://forums.corvetteforum.com/show...ght=gears+dyno
Sik Six, this is an informative thread.
http://forums.corvetteforum.com/show...ght=gears+dyno
Wow, I forgot I made that thread....here is the core of it quoted:
Did anyone do a before and after dyno to see what the driveline loss is when you add 4.10's?
I hear varying amounts and was wondering if there was a person in the know.
From this thread on LS1tech.com:
http://www.ls1tech.com/forums/showthread.php?t=4552
He listed this as his differences at each rpm. There could be other varyance accounting for some of the change but I wanted to know what other people experienced.
These are the values measured (and I said values "measured" so please spare me the "it isnt actually lost power from the motor"......I know, Capt. Obvious...the engine is still producing the same HP) that he saw lower at each rpm:
rpm HP
2500 2.9
2600 2.5
2700 3.1
2800 2.1
2900 2.8
3000 1.1
3100 3.0
3200 3.0
3300 3.8
3400 2.6
3500 2.0
3600 2.1
3700 4.9
3800 2.9
3900 2.2
4000 1.5
4100 2.3
4200 2.4
4300 4.1
4400 2.5
4500 3.4
4600 5.3
4700 6.3
4800 6.4
4900 6.5
5000 6.7
5100 7.8
5200 8.9
5300 9.1
5400 11.3
5500 12.6
5600 12.8
5700 11.9
5800 12.1
5900 13.5
6000 16.0
6100 16.3
6200 17.7
And please dont post about how dyno's read the power and inertia loss, yada yada. I am asking for people's observed lower readings not a lesson on how dyno's work. Please excuse the abruptness, I dont want this thread deteriorating into a 'how a dyno works' thread. Just looking for some comparative data.
I hear varying amounts and was wondering if there was a person in the know.
From this thread on LS1tech.com:
http://www.ls1tech.com/forums/showthread.php?t=4552
He listed this as his differences at each rpm. There could be other varyance accounting for some of the change but I wanted to know what other people experienced.
These are the values measured (and I said values "measured" so please spare me the "it isnt actually lost power from the motor"......I know, Capt. Obvious...the engine is still producing the same HP) that he saw lower at each rpm:
rpm HP
2500 2.9
2600 2.5
2700 3.1
2800 2.1
2900 2.8
3000 1.1
3100 3.0
3200 3.0
3300 3.8
3400 2.6
3500 2.0
3600 2.1
3700 4.9
3800 2.9
3900 2.2
4000 1.5
4100 2.3
4200 2.4
4300 4.1
4400 2.5
4500 3.4
4600 5.3
4700 6.3
4800 6.4
4900 6.5
5000 6.7
5100 7.8
5200 8.9
5300 9.1
5400 11.3
5500 12.6
5600 12.8
5700 11.9
5800 12.1
5900 13.5
6000 16.0
6100 16.3
6200 17.7
And please dont post about how dyno's read the power and inertia loss, yada yada. I am asking for people's observed lower readings not a lesson on how dyno's work. Please excuse the abruptness, I dont want this thread deteriorating into a 'how a dyno works' thread. Just looking for some comparative data.
A head cam car at 480rwhp would show a 14-15hp loss and at 430rwhp its about 10-12rwhp.
Last edited by SpinMonster; Jun 5, 2008 at 11:25 PM.
Pro
Joined: Oct 2007
Posts: 708
Likes: 0
From: Mandeville LA
There are enough people acting like jercofffs today. Craig's day got ruined and some other non-sense going on. I figured I give it a rest myself.
Wow, I forgot I made that thread....here is the core of it quoted:
He had a 530ish rwhp car if I recall and the loss at the dyno peak number was about 17hp for 4.10's and I can assume 3.90's would show a dyno loss of 5% less.
A head cam car at 480rwhp would show a 14-15hp loss and at 430rwhp its about 10-12rwhp.
Wow, I forgot I made that thread....here is the core of it quoted:
He had a 530ish rwhp car if I recall and the loss at the dyno peak number was about 17hp for 4.10's and I can assume 3.90's would show a dyno loss of 5% less.
A head cam car at 480rwhp would show a 14-15hp loss and at 430rwhp its about 10-12rwhp.
Slicks can kill a few horses too !
Safety Car
Joined: Nov 2007
Posts: 4,537
Likes: 1,403
From: Bethesda MD
To illustrate, say you and I are at 100mph and side by side on the hiway. If we had the exact same engine power I at 3000rpm would be at 240hp on the curve and you at 2600 would be at 210hp at that mph. If we maintain the same mph, the engines are doing the same work.
I have noticed that in 6th at very low rpms (e.g. 1200) there is no improvement in mileage compared to a bit higher rpm (e.g. 1400) despite the higher engine rpms and added areodynamic drag of going faster. I'd guess that is a function of the cam being out of an efficent range. With a bigger aftermarket cam, I would assume that would shift further up the rpm range, working well with more gear when driving at near legal speeds.
If you log the car, you can see in a scan that at 1600rpm a car may be at .32kpa load and at 2000rpm with a steeper gear its at .28kpa load. The engine is actually more stressed at the lower rpm since it is making less HP than it does at 2000rpm's.
1) Does the kpa measure load or the pressure drop in the intake manifold? I'd be curious to see the MAF readings and see how much air is being injested. I would think that would be proportional to fuel consumed.
2) Why does making less HP cause more stress (outside of lugging an engine which I don't think your talking about for normal street driving)? For a given HP being made, the engine at 1600 rpm makes more torque than the engine at 2000 rpm. Is the extra torque the stress?
Last edited by Ragtop 99; Jun 6, 2008 at 10:44 AM.
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Melting Slicks
Joined: May 2006
Posts: 2,891
Likes: 1
From: NJ..."the way I saw it, everyone takes a beating sometimes."
Burning Brakes
Joined: Jan 2007
Posts: 1,098
Likes: 0
From: Dallas TX
It will pull like a monster. I would suggest 4.10s though, unless you are completely sold on the 3.90s.
Burning Brakes
Joined: Jul 1999
Posts: 1,141
Likes: 0
From: Mobile AL
To answer the original question:
Gear changes do affect rwhp readings. As the rate of acceleration increases, so do inertial losses. The lower the gear or higher the numerical gear ratio, the higher the acceleration, and hence, the higher the inertial loss in the driveline will be.
There was a good write-up on this on MF (ModularFords.com) back in Oct. of '04:
http://www.modularfords.com/forums/s...ad.php?t=17507
DynoDan (VP of Dynojet) and black2003cobra (brilliant individual) summed it all up (post #27 is an excellent read, FYI).
Last edited by RWTD; Jun 30, 2008 at 02:30 PM.
Pro
Joined: Oct 2007
Posts: 708
Likes: 0
From: Mandeville LA
Dynojet does not have this option.
To answer the original question:
Gear changes do affect rwhp readings. As the rate of acceleration increases, so do inertial losses. The lower the gear or higher the numerical gear ratio, the higher the acceleration, and hence, the higher the inertial loss in the driveline will be.
There was a good write-up on this on MF (ModularFords.com) back in Oct. of '04:
http://www.modularfords.com/forums/s...ad.php?t=17507
DynoDan (VP of Dynojet) and black2003cobra (brilliant individual) summed it all up (post #27 is an excellent read, FYI).
To answer the original question:
Gear changes do affect rwhp readings. As the rate of acceleration increases, so do inertial losses. The lower the gear or higher the numerical gear ratio, the higher the acceleration, and hence, the higher the inertial loss in the driveline will be.
There was a good write-up on this on MF (ModularFords.com) back in Oct. of '04:
http://www.modularfords.com/forums/s...ad.php?t=17507
DynoDan (VP of Dynojet) and black2003cobra (brilliant individual) summed it all up (post #27 is an excellent read, FYI).
Thanks for the proof James. My friend will be calling you in the next day or so to tune his turbo cobra.
LAter
