Mike Adams
Enthusiast
Will having 355 gears give a different dyno results than 307 gears
Gears and Dyno question
- Thread starter Mike Adams
- Start date
jrkermode
Enthusiast
The 3.55 will have a greater driveline loss, simply because there are more gear tooth interactions than the 3.07, but it is unlikely the dyno is accurate enough to actually measure a difference. The dyno only looks at engine RPM and torque on the drum. It completely ignores road speed, which is the only thing you are changing.
P.S. Minimizing driveline loss is why its best to put your tranny in a gear close to 1:1 during dyno pulls.
P.S. Minimizing driveline loss is why its best to put your tranny in a gear close to 1:1 during dyno pulls.
Martin D
Enthusiast
yes - from what I have been told, with your mods, you will lose about 15RWHP.
By the way, did you also Extrude your intake?
Regards,
By the way, did you also Extrude your intake?
Regards,
phiebert
Enthusiast
I had a similar question in the dyno topic section. Does that mean that those of us with 3.55s should use a gear like 5th? That seems a little extreme but would that now be closer to 1:1? I had very disappointing numbers on my dyno and I'm looking for answers because the dyno doesn't match my ETs (which I'm happy with).
varanus
Enthusiast
do a search. There was a rather lengthy thread about this a while back. The general feeling was gears didn't make a difference on the dyno although i thought my car dynoed a little low and I have 3.55.
Mike Brunton
Enthusiast
I remember having a looooong debate on this very topic with a guy I worked with who is pretty much at the top of his game. I was wrong back then (I thought you DID lose power on a dyno).
There was, someone, who posted that shorter gears would give "incorrect" readings because the dyno did not "have time" to get a reading. The debate I had with my co-worker went on a long time, and we actually did a conference call with DynoJet. Their answer was...
You may show less power on the dyno, but that's because you're putting less to the ground. They said that it was absolutely NOT true that their dyno would give a false reading with shorter gears.
When you think about it, the dyno only does two things. It measures the acceleration of a drum of a known mass (so you know the power being applied to the drum and you know the diameter of the drum so you know what torque was applied to it in order to get it to accelerate at the speed being measured). The dyno also measures the RPM at which the acceleration of the drum is taking place, so with RPM and torque, it can calculate horsepower.
The theory of "not enough time to get a reading" is pure BS. Shorter gears simply increase torque multiplication (with a bit more loss) - the dyno is no less accurate with shorter gears than it is with a 600RWHP car versus a 400RWHP car.
There was, someone, who posted that shorter gears would give "incorrect" readings because the dyno did not "have time" to get a reading. The debate I had with my co-worker went on a long time, and we actually did a conference call with DynoJet. Their answer was...
You may show less power on the dyno, but that's because you're putting less to the ground. They said that it was absolutely NOT true that their dyno would give a false reading with shorter gears.
When you think about it, the dyno only does two things. It measures the acceleration of a drum of a known mass (so you know the power being applied to the drum and you know the diameter of the drum so you know what torque was applied to it in order to get it to accelerate at the speed being measured). The dyno also measures the RPM at which the acceleration of the drum is taking place, so with RPM and torque, it can calculate horsepower.
The theory of "not enough time to get a reading" is pure BS. Shorter gears simply increase torque multiplication (with a bit more loss) - the dyno is no less accurate with shorter gears than it is with a 600RWHP car versus a 400RWHP car.
Marc Lublin
Enthusiast
I spoke to Dynojet a few weeks ago. It could account for as much as a 4% loss. There is no real calculation but the higher # gears do show up as less HP.
pauls
Enthusiast
Then what determines the base gear ratio of an accurate reading.
Are we assuming 3.07 is a standard measurement and anything different needs to be factored? Corvette or Mustang have "shorter" gears to start with?
Are we assuming 3.07 is a standard measurement and anything different needs to be factored? Corvette or Mustang have "shorter" gears to start with?
OP
OP
Mike Adams
Enthusiast
Well if guess I am the guy that is going to spend an extra 100 bucks to settle the debate then. I was hoping we would have someone who knew for sure. I will dyno with 355 then pull them and dyno with 307's then I will have one of my gear carriers for sale LOL. 355 definetly make the car much more fun. But if I don't sell the car I will have to put a blower on and don't know which gears to keep.
BTW -- with the blower I will update my plate maybe from VETEATER to ? F15 EATER
BTW -- with the blower I will update my plate maybe from VETEATER to ? F15 EATER
jrkermode
Enthusiast
You want the tranny in a 1:1 gear, NOT the overall (tranny + rear) ratio to be 1:1.
The difference between flywheel HP and rear wheel HP is simply all the energy lost spinning the driveline. The loss occurs due to friction at all the rubbing surfaces, mostly where gears mesh, especially where the meshing gears are higly loaded. Whenever you step up or step down the driveline speed, which can occur in the tranny and does occur in rear end, you get more gear meshes, more gear loading, more losses.
So, there is an actual difference in RWHP in each of the 6 gears. Choose one gear for your pulls, and stick with it so you'll be able to compare differences run to run.
The difference between flywheel HP and rear wheel HP is simply all the energy lost spinning the driveline. The loss occurs due to friction at all the rubbing surfaces, mostly where gears mesh, especially where the meshing gears are higly loaded. Whenever you step up or step down the driveline speed, which can occur in the tranny and does occur in rear end, you get more gear meshes, more gear loading, more losses.
So, there is an actual difference in RWHP in each of the 6 gears. Choose one gear for your pulls, and stick with it so you'll be able to compare differences run to run.
pauls
Enthusiast
You have 1 to 1 through the trans in some gear no matter what rear you run. It's the final drive ratio that is affected by the rear. Much different with a 3.07 vs 3.73
99 R/T 10
Enthusiast
I am hoping to get my car dynoed Saturday and I've got the 3.73's. I wish I would have dynoed before. If I get a low reading, I will take into account the 30% loss due to the gear change
.
Mike
Mike
Miles B
Enthusiast
jrkermode:
most of the loss between the flywheel and the rear wheels is in fact lost spinning up all of the shafts, gears, wheels etc. This loss is mostly inertial, not frictional... gears are a lot better than 85% efficient. The same way the engine has to spin up the dyno drum, it has to spin up the wheels, shafts etc.
Think about it this way.. if a driveline in a 500hp car "steals" 75hp all due to friction, that's 75hp of heat generated - about 56kW. That would have your car on fire in seconds.
most of the loss between the flywheel and the rear wheels is in fact lost spinning up all of the shafts, gears, wheels etc. This loss is mostly inertial, not frictional... gears are a lot better than 85% efficient. The same way the engine has to spin up the dyno drum, it has to spin up the wheels, shafts etc.
Think about it this way.. if a driveline in a 500hp car "steals" 75hp all due to friction, that's 75hp of heat generated - about 56kW. That would have your car on fire in seconds.
phiebert
Enthusiast
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Miles B:
jrkermode:
Think about it this way.. if a driveline in a 500hp car "steals" 75hp all due to friction, that's 75hp of heat generated - about 56kW. That would have your car on fire in seconds.
<HR></BLOCKQUOTE>
I thought it was getting pretty warm in the cockpit!
jrkermode:
Think about it this way.. if a driveline in a 500hp car "steals" 75hp all due to friction, that's 75hp of heat generated - about 56kW. That would have your car on fire in seconds.
<HR></BLOCKQUOTE>
I thought it was getting pretty warm in the cockpit!
jrkermode
Enthusiast
Thanks Miles B.
I was trying to make the point that gears matter, but clearly overemphasized that in re-reading my post.
There is an old rule of thumb racers use to describe the intertial effects you allude to; 1 lb of rotating weight = 10 lbs of static weight. Of course that's an oversimplification, but it gets the point across that spinning stuff, especially accelerating it, is a lot of work.
I was trying to make the point that gears matter, but clearly overemphasized that in re-reading my post.
There is an old rule of thumb racers use to describe the intertial effects you allude to; 1 lb of rotating weight = 10 lbs of static weight. Of course that's an oversimplification, but it gets the point across that spinning stuff, especially accelerating it, is a lot of work.
