question about dyno #'s and gears
4/28/05, 10:51 PM
#1
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I am curious as to how much HP you lose when you get away from stock gears. For example...I'm making 313.2 rwhp and 327.3 rwtq (as if I haven't plastered it enough around here and you guys don't already know this). I have 4.30 gears installed. How much does 4.10's and 4.30's take away? I saw Sixty Six and Blazing Saddles (great movie by the way) mention something about this in Blazing Saddles thread for his CAI. Is there a break down or formula to figure this?
I just want to thank you, in advance, those that have had the patience for those of us that just don't know this kind of stuff. I have always considered myself mechanically inclined, due to being able to perform almost any mechanical task. I have personally lacked all the side-line knowledge like these questions I bring before you and little things that I have recently learned like dyno graphs-SAE hp, STD hp, or suspension differences between road racing and drag racing. I have just learned so much from you guys on this forum! Cudo's to you all as almost everyone contributes in some form or another with their knowledge or experiences.
Thank you!
I just want to thank you, in advance, those that have had the patience for those of us that just don't know this kind of stuff. I have always considered myself mechanically inclined, due to being able to perform almost any mechanical task. I have personally lacked all the side-line knowledge like these questions I bring before you and little things that I have recently learned like dyno graphs-SAE hp, STD hp, or suspension differences between road racing and drag racing. I have just learned so much from you guys on this forum! Cudo's to you all as almost everyone contributes in some form or another with their knowledge or experiences.
Thank you!
4/28/05, 11:15 PM
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Well, I know that Blazing Saddles was reiterating what he was told by his dyno guy, about the 4:10's, I was hooking him up with the info that 2005RedGT (Bryan) had learned about setting up the auto correctly on the Dyno.
It's not the first time I've heard the h.p. argument, but I haven't seen any formula's, and I'm a little skeptical myself.
What I do beleive is that by using a taller gear your getting out of the powerband too quick and that it could result in higher E.T's than expected, and maybe that relates to lower h.p. numbers by not going a little higher on the rev-limiter. If you were to take it to 6,500-7,000 rpm's you'll probably regain any lost "power".
On the other hand.....you have people like yourself, who are getting into the 12's with your 4:10's and JMS racing running 4:30's and well into the 12's.
Sounds like the beggining of an age old debate
It's not the first time I've heard the h.p. argument, but I haven't seen any formula's, and I'm a little skeptical myself.
What I do beleive is that by using a taller gear your getting out of the powerband too quick and that it could result in higher E.T's than expected, and maybe that relates to lower h.p. numbers by not going a little higher on the rev-limiter. If you were to take it to 6,500-7,000 rpm's you'll probably regain any lost "power".
On the other hand.....you have people like yourself, who are getting into the 12's with your 4:10's and JMS racing running 4:30's and well into the 12's.
Sounds like the beggining of an age old debate
4/28/05, 11:34 PM
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I believe there is a frictional lost that increases as the gears increase speed, but I have never known a specific measurement for it. I have always been told that there will be "some", "a small", a "little" loss due to the change, but no one has ever given me anything specific to work with.
4/29/05, 07:43 AM
#4
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OK, you asked for it . . . . .
Check out this website and read Section 4. Gear Train Efficiency. Be sure to have a few cold beers available.
For those that want the Readers Digest version, I'll provide the following quotes:
"Power losses in gear trains are associated principally with two factors: tooth friction and churning losses. ... The frictional losses, which are strongly dependent on the arrangement of the gear train and the reduction ratios, have been the subject of considerable investigation. Tables are available for calculating the energy lost by friction during tooth engagement for a single mesh as a function of pressure angle, gear ratio, gear size, and an assumed average value of the coefficient of friction. ...."
"It is worth noting that the largest power loss occurs at the high-reduction mesh."
As for the actual loss, they talk about an average of 1% of the "potential power" of the mesh and "potential power" is directly proportional to the gear ratio. In other words, if your 3.55 gear loses 20 hp then a 4.10 would lose ( 4.10/3.55 X 20) 23 hp and your dyno would decrease 3 hp. This calculation does not account for differences in how the mechanic setup the gears or how well the manufacturer of the gears did his job.
We have seen a lot of stock '05's dyno in the 260 hp range and have been told they actually dyno about 305 to 310 at the fly wheel meaning they lose maybe 50 hp across the entire driveline. Therefore the trick becomes in determining how much of that 50 hp is consumed by the mesh of the ring and pinion gear. I assumed 20 but it could be a lot more
This is just the way I interpreted the article. You will have to read it to see if you come to the same conclusion.
The Boss Hog
Check out this website and read Section 4. Gear Train Efficiency. Be sure to have a few cold beers available.
For those that want the Readers Digest version, I'll provide the following quotes:
"Power losses in gear trains are associated principally with two factors: tooth friction and churning losses. ... The frictional losses, which are strongly dependent on the arrangement of the gear train and the reduction ratios, have been the subject of considerable investigation. Tables are available for calculating the energy lost by friction during tooth engagement for a single mesh as a function of pressure angle, gear ratio, gear size, and an assumed average value of the coefficient of friction. ...."
"It is worth noting that the largest power loss occurs at the high-reduction mesh."
As for the actual loss, they talk about an average of 1% of the "potential power" of the mesh and "potential power" is directly proportional to the gear ratio. In other words, if your 3.55 gear loses 20 hp then a 4.10 would lose ( 4.10/3.55 X 20) 23 hp and your dyno would decrease 3 hp. This calculation does not account for differences in how the mechanic setup the gears or how well the manufacturer of the gears did his job.
We have seen a lot of stock '05's dyno in the 260 hp range and have been told they actually dyno about 305 to 310 at the fly wheel meaning they lose maybe 50 hp across the entire driveline. Therefore the trick becomes in determining how much of that 50 hp is consumed by the mesh of the ring and pinion gear. I assumed 20 but it could be a lot more
This is just the way I interpreted the article. You will have to read it to see if you come to the same conclusion.
The Boss Hog
4/29/05, 08:02 AM
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Okay, I was really looking for the short and skinny answer Boss. 
Let's see, okay, I lost 35 rwhp with the change from 3.55's to 4.30's. I'm dreaming. So, it really chaulks up to interpretation? That's been part of the problem with my learning of the side-line mechanical knowledge. I like to know the nitty gritty information. I just need to read your reader's digest version and figure it out. I appreciate it guys!
I'll be going to the track tonight to see what she'll do! I'm anxious.
Let's see, okay, I lost 35 rwhp with the change from 3.55's to 4.30's. I'm dreaming. So, it really chaulks up to interpretation? That's been part of the problem with my learning of the side-line mechanical knowledge. I like to know the nitty gritty information. I just need to read your reader's digest version and figure it out. I appreciate it guys! I'll be going to the track tonight to see what she'll do! I'm anxious.
4/29/05, 09:26 AM
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I was told that we loose between 6-10 rwhp (depending on the dyno) which is about 2% or so for our basic engines / gears. However, I have no facts to back it up, just the experice of the Dyno operator.
However, remember, it really does not matter what it 'could be' but what it is. You should be very happy with your numbers, they are very impressive
-Bryan
However, remember, it really does not matter what it 'could be' but what it is. You should be very happy with your numbers, they are very impressive
-Bryan
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