performance 904 vs. A500 (42RH)

[sledger46]

I finally got back to the track with a working shifter to get some comparative data between the A500 and the 904 that it replaced. The A500 was setup non lockup and the same Edge Racing 9.5" torque converter was used with both transmissions. The engine tune was the same (timing, carb jetting), same 3.91 gear ratio, same Riken Raptors 255x17 tires on the back.

NEW INFORMATION:
904 Dry weight 103 lbs
A500 Dry weight 147 lbs

Changes to the car included swapping in the A500 itself (+ 44 lbs) adding a sub box in the trunk (+25 lbs) removing the AC/Heater box from under the dash (- 35 lbs) and removing the console (-20 lbs) which results in a total additional weight of 14 lbs. The 14 lbs is would only result in a .014 second penalty and .14 MPH penalty. Hardly worth noting in this case.

2014 - 904..........2015 - A500
...............1st Pass
60ft 1.867.............60ft 1.887
330ft 5.390..........330ft 5.518
660ft 8.348..........660ft 8.568
MPH 82.99............MPH 80.32
1000 10.915........1000 11.228
1/4 13.093.............1/4 13.493
MPH 103.55..........MPH 99.51

...............2nd Pass
60ft 1.878.............60ft 1.861
330ft 5.368..........330ft 5.461
660ft 8.309..........660ft 8.494
MPH 83.40...........MPH 80.69
1000 10.860........1000 11.140
1/4 13.024............1/4 13.394
MPH 104.35..........MPH 99.82

................3rd Pass
60ft 1.880.............60ft 1.861
330ft 5.369..........330ft 5.466
660ft 8.306..........660ft 8.500
MPH 83.57...........MPH 80.61
1000 10.854.......1000 11.145
1/4 13.016...........1/4 13.398
MPH 104.42.........MPH 100.00


...............4th Pass
60ft 1.887**..............60ft 1.846
330ft 5.342**...........330ft 5.440
660ft 8.252**...........660ft 8.472
MPH 84.33**............MPH 80.68
1000 10.775**........1000 11.117
1/4 12.913**.............1/4 13.367
MPH 105.61**..........MPH 100.17

** in 2014 I removed 100 LBS before the last pass by emptying the trunk.

Just looking at the numbers above and focusing on the first 3 passes, it looks like the additional power to turn the A500 cost me about .40 seconds and 4.0 MPH in the 1/4 mile even after you factor out the weight change. I guess it just bugs me more because it pushed my car out of the 12s and back into the 13s.

 

[65goldcuda]

Very detailed post! Thank you, this is for your 67 dart? What engine and HP are you running? (just curious).

Thanks.

 

[sledger46]

Very detailed post! Thank you, this is for your 67 dart? What engine and HP are you running? (just curious).

Thanks.

Yes this was in my 67 Dart. The Dart has a LA 360 short block of unknown origin and unknown miles. The short block has EQ Magnum heads with 2.02 intake valves with thin head gaskets which resulted in 8.7:1 compression. The cam is a mild roller with 224/230 .050 numbers and .515" lift with the 1.6 rockers. It has the MP dual plane intake and a Holley 750 vac secondary carb. It is probably putting out around 300HP or 250 RWHP.

Full build can be found here:
http://www.forabodiesonly.com/mopar/showthread.php?t=98167&page=1

 

[65goldcuda]

Thanks, that is a great bench mark for me to compare to. I have not taken my car to the track yet, but it seems to perform at about a 12.2-12.9 second level. (I am not building a track car, I just get asked a lot what it will run in the 1/4.

Any idea what your current car weight is without you in it? Did you add any weight over the wheels to get you traction?

 

[sledger46]

Thanks, that is a great bench mark for me to compare to. I have not taken my car to the track yet, but it seems to perform at about a 12.2-12.9 second level. (I am not building a track car, I just get asked a lot what it will run in the 1/4.

Any idea what your current car weight is without you in it? Did you add any weight over the wheels to get you traction?

I added a small sub in the trunk that sits behind the back seat. I have a full spare, jack, tool bag, folding chair, helmet in a bag, and jacket in the trunk. Race weight (with fat driver) is right around 3550lbs.

 

[FredS]

You're finding the weight penalty in the rotating mass within the transmission is more than just about the amount of additional weight in the car.
What's your RPM at the end of the 1/4? I take it you still in 3rd at this point. You might bump it from 3.91s to 4.10's, to get it back, or a slightly smaller diameter tire.

 

[sledger46]

You're finding the weight penalty in the rotating mass within the transmission QUOTE]

Spot on sir! After I already pulled the trigger on the swap I ran across ads stating you could drop 1 - 1.5 seconds swapping a 904 in place of a A500. This might be true if you were replacing a bone stock A500 + converter with a race 904 and race converter. I was really worried about the power loss associated with swapping the other direction: replacing a 904 with the A500.

The .4 seconds and 4 MPH equates to a 40 HP loss just from the transmission. If I had used a stock type lockup converter in the A500, the results would have been even worse.

 

[67Dart273]

Geez. That much of a HP penalty, it almost seems like the mileage gain from the OD would be negated by the power it takes to turn it!!

 

[sledger46]

Geez. That much of a HP penalty, it almost seems like the mileage gain from the OD would be negated by the power it takes to turn it!!

The additional rotational mass has a bigger effect if you are trying to accelerate it as opposed to keep it at a steady speed. Everyone has heard if you reduce the weight of a car by 100 lbs it will be .1 sec quicker ET wise. When it comes to rotational weight the effect is 10x as much. if you put lighter wheels on a car, say 10lbs lighter then the originals (that's 10lbs total for the car) you will see the same .1 sec reduction in ET.

If you are cruising down the highway at a steady 70 MPH, the amount of power it takes to maintain that speed with the 904 in D and the A500 in D (not OD) should be very close. When you click the A500 into OD everything in front of the OD unit is turning 69% as fast. Lower rotational speeds means less friction and less power to maintain that same steady 70 MPH.

Makes you wonder if part of the reason Ma Mopar put lower gears in the A500 was to offset the power loss when accelerating. I am seeing .02-.03 sec better 60 foot times with the lower gear in the A500 on street tires. After the 60 foot the additional rotating mass really comes into play slowing the acceleration of the car down.

 

[rustytoolss]

The additional rotational mass has a bigger effect if you are trying to accelerate it as opposed to keep it at a steady speed. Everyone has heard if you reduce the weight of a car by 100 lbs it will be .1 sec quicker ET wise. When it comes to rotational weight the effect is 10x as much. if you put lighter wheels on a car, say 10lbs lighter then the originals (that's 10lbs total for the car) you will see the same .1 sec reduction in ET.

If you are cruising down the highway at a steady 70 MPH, the amount of power it takes to maintain that speed with the 904 in D and the A500 in D (not OD) should be very close. When you click the A500 into OD everything in front of the OD unit is turning 69% as fast. Lower rotational speeds means less friction and less power to maintain that same steady 70 MPH.

Makes you wonder if part of the reason Ma Mopar put lower gears in the A500 was to offset the power loss when accelerating. I am seeing .02-.03 sec better 60 foot times with the lower gear in the A500 on street tires. After the 60 foot the additional rotating mass really comes into play slowing the acceleration of the car down.

I see all of your data ET/speed for drag racing. But you did not say anything about if you felt that installing the A500 was an improvement to drive on the streets.
Even with the slower ET's. Do you feel the swap was worth doing ..overall (considiring ET's and street driving)