How Gearing Effects HP from 1-3rd in 727's

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70DusterBob

70DusterBob

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I recently made a mod that increased my hp at 2600 RPM by 84 hp in 3rd gear on the Dyno. I was wondering how much of an hp increase that would be in 1st and 2nd individually.

I have a 1970 Duster, 3:55 gearing with 15" rims in back I can get the tire size if you need it, but the speedometer reads 100% perfectly accurate with the set up I have now: the 3:55 gears and the large rear tires I have.

Engine is a 1975 360.

Thanks,
Bob
 
I don't think it matters. 84 HP at 2600 is just that, regardless of gear.
 
....................The same in every gear, but u can feel it better in lower gears as the HP is multiplied by the lower ratio's..........kim..........
 
Gears do not change horse power one iota.
 
Charrlie_S said:
X-2. Gears will change torque at the wheels.
Click to expand...

Sorry Guys, I should have asked the question better:

The Dyno is a Chassis Dyno, so the HP and Torque were measured at the rear wheels. The HP and Torque are more in first and second, I think anyway, at the rear wheels because the gearing is different. I understand the engine is putting out the same HP, Torque, but what is the increase in 1st as opposed to being in 2nd and 3rd?

You can pull a heavier load in first than in third. Someone in here told me before but I my forgetter kicked in.

Thanks again,
Bob
 
You make torque at the crankshaft, and this is a moment of force that is used to calculate horsepower. The more revs you have while making that torque the more horsepower you are making - you are able to do more work due to being able to exert that moment of torque more times per minute (more rpm!)

A dynamometer will calculate "tractive effort" which is the amount of torque and/or horsepower made at the wheels. The gear the transmission is in at the time will effect this - if you made 400ftlb in 3rd gear, the reading might be 600ftlb in 2nd gear and 1000ftlb in first gear. This is because the transmission is now turning a lot slower for the given engine rpm - about a 1.5 and 2.5 reduction for second and first gear, respectively.

You are able to tow better in 1st and 2nd because the engine is turning more rpm (more moments of tractive effort) over the same amount of time, assuming a fixed speed.

- boingk

EDIT: As discussed above, the gear you are in will affect the 'tractive effort' reading but it will not affect the horsepower because at any given rpm the engine will be making a set amount of torque, and thus a set amount of horsepower. The 'tractive effort' might be able to be manipulated by the transmission with gearing, but the torque and horsepower actually made at the engine remains constant.
 
boingk said:
You make torque at the crankshaft, and this is a moment of force that is used to calculate horsepower. The more revs you have while making that torque the more horsepower you are making - you are able to do more work due to being able to exert that moment of torque more times per minute (more rpm!)

A dynamometer will calculate "tractive effort" which is the amount of torque and/or horsepower made at the wheels. The gear the transmission is in at the time will effect this - if you made 400ftlb in 3rd gear, the reading might be 600ftlb in 2nd gear and 1000ftlb in first gear. This is because the transmission is now turning a lot slower for the given engine rpm - about a 1.5 and 2.5 reduction for second and first gear, respectively.

You are able to tow better in 1st and 2nd because the engine is turning more rpm (more moments of tractive effort) over the same amount of time, assuming a fixed speed.

- boingk

EDIT: As discussed above, the gear you are in will affect the 'tractive effort' reading but it will not affect the horsepower because at any given rpm the engine will be making a set amount of torque, and thus a set amount of horsepower. The 'tractive effort' might be able to be manipulated by the transmission with gearing, but the torque and horsepower actually made at the engine remains constant.
Click to expand...
--------here we go again--------------
 
So my next question is: Does a Chassis Dyno measure or read out the HP and Torque of the "Engine" or of the Tractive Effort? I assume it is the "Tractive Effort".

They Dyno Operater said that in 3rd gear the ration of engine to rear wheels is relatively 1:1. Meaning to me that it would be what the engine is producing, but then you have the size of the tires to deal with, right? I mean the crankshaft is what 2-1/2 to 3" in diameter where the rear wheels are over 2 feet in Diameter. When you pull on the far end of a Torque Wrench, you are exerting Ft Lbs on the nut, but if you were trying to pull you hand by applying Torque to the "Nut" you would be losing Torque not gaining it. Does that make sense?

I am trying to figure out what the HP and Torque increase is in 1st, 2nd based on 3rd. It was approximately a 50 Ft Lb increase in Torque at the same time approx an 84 HP increase at 2600 RPM. It was approximately a 35% increase in both. To me, that just means at the Engine Speed of 2600 RPM, with the Rear Wheel RPM unknown, in 1st, 2nd, or 3rd, and the Diameter of the Wheels unknown, I don't really know what the increase is in "Engine HP and Torque". I am just finding out what the difference is after it is reduced by wheel size and affected by the transmission and rear gears. Right?

The problem with this is I need to know what the engine HP and Torque increases are so I can present an "Engine HP and Torque" increase to someone who would be interested in leasing my patent rights, and/or investing in my idea to help me lease it to industry. Will I basically have to test the engine outside of the car? Also, I would still like to know what that translates to in 1st and 2nd.

I calculated 84 HP in Third to be a 126 HP in Second, according to multiplying 84 by 1.5 and 210 Hp increase in First based on multiplying 84 by 2.5. If this is right. What ball park figure would that increase have on an ET in a Quarter mile in about a 3200 lb car including driver? That 84 HP and 50 Torque increase was the max increase at 2600 RPM. But it tapered down to a 10Hp increase at 4200 RPM because of the factors such as using a performer intake, the cam I use, and the engine size. But in never went lower than without my prototype on it than it was without it.

I realize for 100% accurate figures I need expensive testing and to get the car on the track, probably do an "Engine Dyno" test. But what ball park figures can you guys give me? I need to give some kind of figures to a couple people who are interested in investing in the idea. I have applied for patent already.

Thank you so much!
Bob
 
A chassis dyno measures torque and the dyno computer does the HP math. HP is just a simple math problem "torque x RPM/5252 = HP".

Gearing provides torque multiplication, but it doesn't change the engines HP or torque output..

Telling me how much HP change per gear would cause me to laugh in your face and walk away from you shaking my head..... It would tell me to avoid investing in your product.
 
T-N-T said:
A chassis dyno measures torque and the dyno computer does the HP math. HP is just a simple math problem "torque x RPM/5252 = HP".

Gearing provides torque multiplication, but it doesn't change the engines HP or torque output..

Telling me how much HP change per gear would cause me to laugh in your face and walk away from you shaking my head..... It would tell me to avoid investing in your product.
Click to expand...


So, the Chassis Dyno is measuring Engine HP or "Rear Wheel after it goes through the Gears and Rear Wheels HP"?? That is what I am trying to figure out.

I guess I could ask the Dyno Operator, but I just got a sheet printout with an 84 HP increase and a 50 Torque increase at 2600 RPM, that is all I know. It is the weekend and I can't call him right now.

I am good at vaporizing fuel, I don't know that much about Chassis Dynos or how Engine HP/Torque is calculated from the rear wheels, if it even is, or if I really need an "Engine Dyno" test to figure that out.

Thanks,
Bob
 
If your trans gear ratio is 2:1 for a simplified example, and the engine is at a given RPM, the wheel torque would be doubled by the trans gearing but the wheel speed would be halved. Since wheel HP is the product of (wheel torque) X (wheel speed) X (a constant conversion number), the 2x torque is canceled by the wheels being at half speed, and the resulting wheel HP would stay the same. So that is why wheel HP does not change with trans gearing.

All that the chassis dyno can directly measure is how quickly the car can accelerate the rotating mass of the drum(s) and any rotational drag load placed upon them by the dyno's equipment. It then can mathematically compute wheel HP and torque from the acceleration and known rotating mass & drag load, using an accurate measure of wheel diameter as an input.

It then makes some assumptions on the power loss through the rear gears and trans to make a stab at computing flywheel HP/torque. Putting the trans in top gear at 1:1 makes the trans loss it's lowest, (since the power/torque is coupled straight through); that makes the assumptions on trans power loss as accurate as they can be.

If you wanted really close numbers on the engine, then by all means an engine dyno is best. But once you have a chassis run, and if you keep the same wheels/tires and driveline numbers, relative changes in the engine will be reasonably accurate. How good do your numbers need to be? Unless you are running an engine program, or building engines for a living, pulling an engine for an engine dyno run seems like quite a waste.
 
Let me just say that I never said the Engine HP increases with the Gearing. I asked what the SAME engine HP Increase would result in 1st Gear and 2nd Gear at the rear wheels. I don't know who assumed I thought the engine HP would increase...

I guess I will have to get an Engine Dyno test done to test for the EXACT Engine HP/Torque Increase...

Thanks,
Bob
 
Last edited:
nm9stheham said:
If your trans gear ratio is 2:1 for a simplified example, and the engine is at a given RPM, the wheel torque would be doubled by the trans gearing but the wheel speed would be halved. Since wheel HP is the product of (wheel torque) X (wheel speed) X (a constant conversion number), the 2x torque is canceled by the wheels being at half speed, and the resulting wheel HP would stay the same. So that is why wheel HP does not change with trans gearing.

All that the chassis dyno can directly measure is how quickly the car can accelerate the rotating mass of the drum(s) and any rotational drag load placed upon them by the dyno's equipment. It then can mathematically compute wheel HP and torque from the acceleration and known rotating mass & drag load, using an accurate measure of wheel diameter as an input.

It then makes some assumptions on the power loss through the rear gears and trans to make a stab at computing flywheel HP/torque. Putting the trans in top gear at 1:1 makes the trans loss it's lowest, (since the power/torque is coupled straight through); that makes the assumptions on trans power loss as accurate as they can be.

If you wanted really close numbers on the engine, then by all means an engine dyno is best. But once you have a chassis run, and if you keep the same wheels/tires and driveline numbers, relative changes in the engine will be reasonably accurate. How good do your numbers need to be? Unless you are running an engine program, or building engines for a living, pulling an engine for an engine dyno run seems like quite a waste.
Click to expand...

Thank you for this rather accurate and "What I was Looking For" reply. The HP and Torque increased approximately 35%, so based on what you just said, is it safe to assume that there is a 35% increase in Engine HP and Torque as well at whatever the gear is. Right?

I think a 35% increase for a non-moving part, that bolts under the carb is pretty much good enough for me to find someone interested in it. I am making tweaks to the designs, but like you said, I'm not looking for a 1hp increase, I am jumping 10% 20% and 35% with my design variations. I think this chassis dyno should suffice. Thanks a million!

Bob
 
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70DusterBob said:
The HP and Torque increased approximately 35%, so based on what you just said, is it safe to assume that there is a 35% increase in Engine HP and Torque as well at whatever the gear is. Right?
Click to expand...
Correct.. the computed % changes in engine number will be approximations but they will certainly be well in the ballpark.

Now, that does not mean that some accurate 'guarantee of performance' numbers would not eventually be needed for some reason. But if this 'thing' is so good, then you will be swimming in $$ and you can then buy your own engine dyno and pay some people to run it for you LOL

Do I believe that this 'thing' will give 35% HP and torque increase? No, but that is another matter.
 
nm9stheham said:
Correct.. the computed % changes in engine number will be approximations but they will certainly be well in the ballpark.

Now, that does not mean that some accurate 'guarantee of performance' numbers would not eventually be needed for some reason. But if this 'thing' is so good, then you will be swimming in $$ and you can then buy your own engine dyno and pay some people to run it for you LOL

Do I believe that this 'thing' will give 35% HP and torque increase? No, but that is another matter.
Click to expand...

I do fully understand there are a lot of "performance" issues that go into any given engine's performance. I do not believe it will give a 35% increase across every engine, on every car it is put on, but it did produce a 35% increase "at 2600RPM" on my engine. The percentage of increase declined as RPM's increased, but that was the max increase for the device. It never lowered the HP or Torque even to top end. My 360 has a 750 Holley DP, Edlebrock Performer Intake, mild cam, Long Headers, and 9.5:1 Forged Pistons. Running Pump Super Unleaded, that is the Number I got off the Chassis Dyno Test. I am going to run it again, next week hopefully, to see if it is that significant again. But I did make other protos that only boosted the HP by 10% and 20%. I learned and re-configured it and got 85 hp or a 35% increase.

A LOT of raw fuel is shot into the intake when depressing the accelerator, this proto is vaporizing the crapoloa out of that fuel, thus the huge increase.

Thanks,
Bob
 
Not to worry or to take my comments to heart. I recall all of the devices that came out with the 70's Arab oil embargo.... and toilet paper cartridge oil filters LOL

I am sure your tests and work will guide you better than any off-hand comment anyone can make sight-unseen. Modern electronic production FI sure made some pretty fantastic advances in engine performance.

BTW, you are right that a lot of fuel is shot into the intake when the throttle is pressed. But that accelerator pump shot is not happening when the throttle is held wide open for a dyno pass. So that theory of operation does not quite hang together. And any such results may be highly dependent on the state of tuning on the carburetor. So your 'thing' might be compensating for a very badly tuned carb, and the same results may not be there for a well tuned one.
 
Last edited:
nm9stheham said:
Not to worry or to take my comments to heart. I recall all of the devices that came out with the 70's Arab oil embargo.... and toilet paper cartridge oil filters LOL

I am sure your tests and work will guide you better than any off-hand comment anyone can make sight-unseen. Modern electronic production FI sure made some pretty fantastic advances in engine performance.

BTW, you are right that a lot of fuel is shot into the intake when the throttle is pressed. But that accelerator pump shot is not happening when the throttle is held wide open for a dyno pass. So that theory of operation does not quite hang together. And any such results may be highly dependent on the state of tuning on the carburetor. So your 'thing' might be compensating for a very badly tuned carb, and the same results may not be there for a well tuned one.
Click to expand...

For this "Chassis" Dyno test, he is bringing it up to 2000 rpm in 3rd Gear, he then starts the Dyno "Testing Mode" in operation. Then he fully depresses the accelerator. Granted, some of it may not be 100% accurate, but he does make 3 runs looking for similar results. With an increase so significant, 20% would be good, 35% is out of this world good. I know there are many factors to consider and evaluate. Considering this is a test from sustaining 2000 RPM then floored WOT to 4500 RPM, do you still feel the same that the acc. pumps don't make sense?

I know my carb is not "tuned", so to speak, "Perfectly". But the test is to see if it vaporizes large amounts of fuel without restricting airflow. Which the Chassis Dyno 2000 to 4500 RPM would indicate is the case. The HP was higher all the way to the point at which it starts to drop off, and even then it was higher during the drop-off.

I am planned for another test to verify these results since they are so significant. I don't have enough $$ to perform more of a test or more types of tests than this. Like you mentioned, it is hard to believe. I was shocked myself to see the HP go from 156 to 241 as well when I first saw the test results. I just hope having the data sheets printed out by a reliable Chassis Dyno Test Shop will be sufficient for a couple people I have in mind as investors to take me seriously.

I need R&D out the Wazoooooo!!! I'm not disputing that at all, rather quite agree with it.

Thanks,
Bob
 
Gearing just trades you hp for acceleration (deeper gears) or top end (higher gears).

If you made an improvement of 84 hp at 2600 rpm it will be the same in each gear the only difference will be the mph at which 2600 rpm will happen.
 
273 said:
Gearing just trades you hp for acceleration (deeper gears) or top end (higher gears).

If you made an improvement of 84 hp at 2600 rpm it will be the same in each gear the only difference will be the mph at which 2600 rpm will happen.
Click to expand...

But isn't that what gear ratios are for? To increase the Torque by changing the "ratio" of the sizes of the Drive and Slave gears? I thought that if I was in first and I'm getting a 2.5:1 ratio, and in third I'm using a 1:1 ratio, that the hp and torque are increased proportionately by the ratio used...

Are you sure about this, that it is only 84 HP across all three gears at the rear wheels? I understand the Engine will be putting out the same "X" number of HP at 2600 RPM, but I think gears are to increase HP and Torque because the engine is spinning faster in the lower gears per Revolution of the Rear Wheels.

I need to know for sure here because I am getting different answers...

I will be unable to check this forum for new messages until Monday Evening when I get back...

Thanks though. That is a different concept than what others are explaining...

Bob
 
70DusterBob said:
Thank you for this rather accurate and "What I was Looking For" reply. The HP and Torque increased approximately 35%, so based on what you just said, is it safe to assume that there is a 35% increase in Engine HP and Torque as well at whatever the gear is. Right?

I think a 35% increase for a non-moving part, that bolts under the carb is pretty much good enough for me to find someone interested in it. I am making tweaks to the designs, but like you said, I'm not looking for a 1hp increase, I am jumping 10% 20% and 35% with my design variations. I think this chassis dyno should suffice. Thanks a million!

Bob
Click to expand...


No way on this flat earth do you eat up 35% of your power through the drive train. No borking way. I can tell you most sticks eat 17-18%, while some if using a OD will be about 20%. An automatic, starts at about 20-21% and goes up from there.

If you actually want to know exact engine HP from a chassis dyno, you need an operator who knows how to use his dyno. Then make your test pulls in your 1:1 gear. Then do a coast down to calculate drive train losses. It damn sure won't be 35%.
 
Hp at the wheels will be the same.

Torque doesn't move your car it's hp.

Say you make 300 lbs-ft at 2600 rpm which is 149.5 hp.

So say you got a 1st gear of 2.45 and 4.10 in the back with a 24 inch tires (24 inch tire gives you a 1 foot radius so it don't increase or decrease torque to the ground).

So 1st gear with 4.10 at about 18 mph would rev about 2600 rpm and 4.10 in 3rd will rev 2600 rpm at about 45 mph.

Now let's see how much hp at the tire both situation give.

4.10 in 1st give you about 10.05 overall gear ratio. So 10.05 x 300 lbs-ft = 3015 lbs-ft to the tires and 1507.5 lbs-ft to each.
2600 rpm at the engine will be 259 rpm at the wheel so let's put it in the hp formula 259 x 1507.5 = 390572
390572 ÷ 5252 = 74.25 hp per tire or 149.5 hp overall.

4.10 in 3rd will be 4.10 x 300 lbs-ft will give you 1230 lbs-ft to the tires or 615 lbs-ft per tire. And 2600 rpm at the engine will be 635 rpm at the tires. And let calculate the hp at the tires. 635 x 615 = 390572
390572 ÷ 5252 = 74.25 per tire or again 149.5 hp overall.
 
273 said:
Hp at the wheels will be the same.

Torque doesn't move your car it's hp.

Say you make 300 lbs-ft at 2600 rpm which is 149.5 hp.

So say you got a 1st gear of 2.45 and 4.10 in the back with a 24 inch tires (24 inch tire gives you a 1 foot radius so it don't increase or decrease torque to the ground).

So 1st gear with 4.10 at about 18 mph would rev about 2600 rpm and 4.10 in 3rd will rev 2600 rpm at about 45 mph.

Now let's see how much hp at the tire both situation give.

4.10 in 1st give you about 10.05 overall gear ratio. So 10.05 x 300 lbs-ft = 3015 lbs-ft to the tires and 1507.5 lbs-ft to each.
2600 rpm at the engine will be 259 rpm at the wheel so let's put it in the hp formula 259 x 1507.5 = 390572
390572 ÷ 5252 = 74.25 hp per tire or 149.5 hp overall.

4.10 in 3rd will be 4.10 x 300 lbs-ft will give you 1230 lbs-ft to the tires or 615 lbs-ft per tire. And 2600 rpm at the engine will be 635 rpm at the tires. And let calculate the hp at the tires. 635 x 615 = 390572
390572 ÷ 5252 = 74.25 per tire or again 149.5 hp overall.
Click to expand...


I will have to research this deeper because it is critical to have realistic numbers. The Dyno says it was an increase of 35% after putting my proto on than before with nothing else changing. I am not sure of the tire size, I need to measure them. I have the gear ratios and know it is a 727 trans. Other than that, I don't see why anything would change if I used the exact same set up in both tests... But I will try to get more answers on my next run sometime hopefully next week and post the data sheet in a pic.

Thanks,
Bob
 
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