Net HP ratings: 727 VS manual transmissions....

[Kern Dog]

I know that this may fall under the heading of "it depends" but isn't it usually the case that the at tire HP ratings differ a bit between using a 727 and a manual trans? Isn't the manual usually the least parasitic, resulting in a higher net HP number?

 

[F4R/T]

KD I was always told that a slush box would cost about 18-20% driveline loss as your using the engine to pump oil . The converter would consume some as well as some inefficient slippage . Manual is all gears no slip,less power to rotate everything. New transmissions use lock up converters helping to limit the loss but there still is some I just don’t know how much on like TF8 or Nag1. Manual will put more down with out a doubt but the new autos might surprise us all... but they are very unforgiving unlike an old 727 or 904.

 

[BDF6]

http://www.superstreetonline.com/how-to/engine/modp-1005-drivetrain-power-loss

 

[Kern Dog]

That article seems to have been written by a lawyer or politician. Good luck pinning the guy down on anything!

 

[Kern Dog]

I am not looking to race the car on the dragstrip. Drag racing is not my thing even though I have enjoyed it the few times that I have raced. I am just curious about how well the car will accelerate with the better gear ratios.

 

[Slap Stick]

The Ramchargers used automatics because they had better times due to quicker shifting.

 

[66Satellite47]

That article seems to have been written by a lawyer or politician. Good luck pinning the guy down on anything!

Actually written by a a guy that understands engineering, something that few lawyers or politicians understand. LOL

 

[66Satellite47]

Kern, you hit the nail on the head in post#1. "It all depends".

 

[747mopar]

I am not looking to race the car on the dragstrip. Drag racing is not my thing even though I have enjoyed it the few times that I have raced. I am just curious about how well the car will accelerate with the better gear ratios.

Although an automatic will robb additional horsepower I found gearing to be the biggest thing. With an automatic your at 1:1 ratio in 3 gears so your pulling long through each gear to have a decent cruising rpm. With your new trans you'll do the same but take 1 extra shift (I assume 4th is 1:1). I originally tried 4:30 gears as mine has a .5 6th and 4:30's put the car at the right rpm and mph at 6,000 rpm going through the traps for a 12 second car.. what I didn't realize is how slow it would make the car shifting constantly and not taking advantage of the torque. I'm back with my 3:55's where it pulls long and hard, way better! Know your motor and gear it accordingly.
Although the auto is more parasitic the added gear in the standard is where you'll feel the most difference splitting the gearing by 4 times vs 3.

 

[moparedtn]

It does all depend...however, if we're talking typical here to what we play with here,
we're probably talking 727 vs. A833, right?

Ok, making some huge assumptions here (and having just spent way too much time
reading articles on the web on the subject, which are plentiful):
Both transmissions being fairly stock, both having a final drive of 1:1 and running off
the *** end of the same engine, the automatic is behind the manual about 5% at the wheels.
That said...
There's articles all over indicating results of dyno pulls, track times, top speed runs, all
sorts of stuff out there though - and as always, I stress that people do their due diligence
on this subject, for there isn't a pat answer (too many variables).
(Insert your favorite search engine here) is really your friend on this one.
Homework time!

 

[alfaitalia]

In an article I was reading recently, in tests, the 727 and axles robbed about 25 or 26% of the power at the crank under full load....and about 15 to 18% in a standard manual box. You could not fail to notice that power advantage on the road.....but as said above on the track the time taken to change cogs in a manual box will eat into your power advantage. As of course just cruising around the street when there is little loading on the boxes bearing and shafts the loses get less. That said.....Ive always preferred manuals....only ever owned two autos in over 30 cars (Audi A8 V8 4.2 and WJ Grande Cherokee)....but they never built manuals of those!! Good luck with your Tremec KD....look forward to the thread.

 

[YY1]

Trade off.

Fun to drive and more efficient vs no shift lag (operator plus accelerator let up).

 

[RemCharger]

I know that this may fall under the heading of "it depends" but isn't it usually the case that the at tire HP ratings differ a bit between using a 727 and a manual trans? Isn't the manual usually the least parasitic, resulting in a higher net HP number?

I am not looking to race the car on the dragstrip. Drag racing is not my thing even though I have enjoyed it the few times that I have raced. I am just curious about how well the car will accelerate with the better gear ratios.

Thats 2 different questions; yes to the first, and the car will accelerate better with more gear ratios. Go for a test drive in a hellcat!

 

[Dipstick]

The Ramchargers used automatics because they had better times due to quicker shifting.

And torque multiplication.

 

[Badvert65]

From Car Craft Mag, to be taken with a grain of salt.

Just in case you're curious, power loss for various auto transmissions:
Powerglide_____18 hp
TH-350________36 hp
TH-400________44 hp
Ford_C-6______55-60 hp
Ford_C-4______28 hp
Ford_FMX______25 hp
Chrysler_A904__25 hp
Chrysler_727___45 hp
Please remember these are approximate values, and were provided by Car Craft Magazine.

My thinking is that the higher the torque a motor has, the less HP losses it would see from the transmission.
But, I don't really know (either).
jus' sayin'......

 

[myk r sanchez]

Man that's A LOT of parasitic loss..

 

[Slap Stick]

And torque multiplication.

Now, that's thinkin with yer dipstick, Dipstick!
Very good point!

 

[66 Sat]

I've never understood these power robbing figures that are produced. They just don't make sense to me. Examples:
I've owned a 1.1 litre four cylinder car that only put out 55 hp. Small car, manual box, could still get to about 95 mph top speed. If I installed a C6 auto according to the data the car couldn't even run due to the parasitic loss, yet normally has enough power to carry 4 adults and the weight of the car along at a fair lick.

I currently own a Walker ride on mower. Complicated machine, gearbox, hydraulic controls etc, has a 16 hp engine. When I engage the cutting blades it saps some power but it will still run fine, cut the grass, get up hills etc. Can't be sucking more than 4 or 5 hp under full load, yet couldn't turn the most efficient auto box from the 60's?

It just doesn't add up somehow.

I'm thinking the peak losses must be at a certain (high) RPM and are just another loss in the same way rolling resistance, wind resistance etc are "losses" that increase with speed, and stop you accelerating forever. I also suspect the losses are not linear in relation to the rpm, and they ramp up as the revs rise e.g. 5hp loss at 2000 rpm and 20hp loss at 4000 rpm, and different gearboxes would have different levels of efficiency depending on how they were operating.

Someone who has worked in this area would know the answer to all this - any Engineers out there who can answer this definitively?