A500 and A518 Parasitic loss

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rustytoolss

rustytoolss

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I can find info about the 727's parasitic loss (about 45HP). I can find info about the 904's parasitic loss (about 25HP)
But I can not seem to find any info about the parasitic loss of the A500 and the A518 overdrive transmissions.
I've read that the overdrive unit is always spinning, even before it engages into overdrive. I guess that at that point it becomes a RPM benefit .
But does the power loss (if any) out weigh the lower cruising RPM.
My current 727 is in need of a rebuild. So by installing a 904. (and pickup about 20HP). But would like an overdrive really. Would installing the overdrive suck up a lot of power ?
Also whats the parasitic loss for each, A500- and A518 ?
This swap (if made) will be in a 350 HP street drive vehicle. Might see the track once a year.
 
I think that's because they are pretty much exactly the same.
The only real difference is that the 500 and 518 spin the output shaft and OD section, which has very little drag when not in OD.
Once in OD you have a planetary set to run through, but it's not running either of the other sets in the forward section of the trans.
 
TrailBeast said:
I think that's because they are pretty much exactly the same.
The only real difference is that the 500 and 518 spin the output shaft and OD section, which has very little drag when not in OD.
Once in OD you have a planetary set to run through, but it's not running either of the other sets in the forward section of the trans.
Click to expand...
Let me get this right..When the A500/A518 engages into overdrive. Everything in the front main case is no longer engaged ? WOW, did not know this!
So from what you said a 904 and a A500 should have about the same parasitic loss :)
 
rustytoolss said:
Let me get this right..When the A500/A518 engages into overdrive. Everything in the front main case is no longer engaged ? WOW, did not know this!
So from what you said a 904 and a A500 should have about the same parasitic loss :)
Click to expand...

Not quite what I meant.
I meant when in OD everything up front in the A500 trans is exactly like it is in third in the 904, but the power flow goes through another planetary set when OD is engaged.
So parasitic loss from the 904 to the A500 would really only be from spinning the OD section.
I'm thinking the difference is super minimal if any.
So yes, I think they are really close.
 
In OD the front clutch is applied, so the front part of the transmission is running in direct drive. Since the pump runs off the torque converter shell, the major parasitic loss is the same regardless of gear. I would suspect the the losses between the two transmissions would be similar. Also, iff you shift kit calls for significantly increased line pressure, expect significantly increased parasitic loss.
 
Good answers regarding parasitic loss.
But here's something else for consideration - neither the A500 nor A518 trannys are going to fit in your A-body trans tunnel without serious modification to the trans tunnel. No big expense if you can do that work yourself.
But if you have to farm out the trans tunnel mod work then you may want to consider a 200-4R OD trans that does fit in an unmodified A-body trans tunnel. Check out the various threads about this alternative.
The 200-4R has about the same parasitic loss as the 904, a better gear spread and a better 0.67 OD.
I'm putting a 200-4R behind my built 360 and going to run 4.30 rear gears. With the 0.67 OD it will be like having 2.88 gears when in OD for some freeway cruising.
 
ocdart said:
But if you have to farm out the trans tunnel mod work then you may want to consider a 200-4R OD trans that does fit in an unmodified A-body trans tunnel. Check out the various threads about this alternative.
Click to expand...


May fit the tunnel itself but ya still have to hack the torsion bar crossmember. I know someone sells a piece that goes in there but you still have to cut it up.
 
I put in an A500 in my 68 and didn’t modify the tunnel at all. The torsion bar cross member is another story, but it’s not difficult if you can use a torch and welder. You can also reuse the shift linkage and kick down linkage from your 904.
 
How much larger and heavier are the o.d. transmissions compared to the 904 and 727?
and you need a new driveshaft? new torque converter?
 
abodyjoe said:
May fit the tunnel itself but ya still have to hack the torsion bar crossmember. I know someone sells a piece that goes in there but you still have to cut it up.
Click to expand...

Yes, very nice kit manufactured and sold by US Car Tool. The kit is designed specifically to install the 200-4R in a Mopar A-Body. Take a look at the pics on the link:

67-75 A-Body GM2004R Cross-Member Kit
 
jas0162 said:
I put in an A500 in my 68 and didn’t modify the tunnel at all. The torsion bar cross member is another story, but it’s not difficult if you can use a torch and welder. You can also reuse the shift linkage and kick down linkage from your 904.
Click to expand...
Did you replace a 904 or a 727 when you installed your A500 ?
When you did this swap. Did you notice any lose of power (like being lower on power/Parasitic loss) while daily driving ?
Also after doing the swap. Did you notice a free wheeling effect (overdrive) at cruising speeds ? Any MPG change. What rear gear are you using. How much power are pushing through that A500 ? Sorry for all the questions. Just want to make an educated plan.
 
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ocdart said:
Good answers regarding parasitic loss.
But here's something else for consideration - neither the A500 nor A518 trannys are going to fit in your A-body trans tunnel without serious modification to the trans tunnel. No big expense if you can do that work yourself.
But if you have to farm out the trans tunnel mod work then you may want to consider a 200-4R OD trans that does fit in an unmodified A-body trans tunnel. Check out the various threads about this alternative.
The 200-4R has about the same parasitic loss as the 904, a better gear spread and a better 0.67 OD.
I'm putting a 200-4R behind my built 360 and going to run 4.30 rear gears. With the 0.67 OD it will be like having 2.88 gears when in OD for some freeway cruising.
Click to expand...
Thanks for the info about trans tunnel mods. But if you look at my avatar . I will have no problems with fitting the A500 trans in my A100. :) Well except a very short driveshaft.
But I might opt for an A999 with lockup (easier install/ almost like OD..kind of). Think I can get on cheap !, from a 1986 Ramcharger.
Does anyone know what kind of RPM drop the lockup converter makes ?
 
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ocdart said:
Yes, very nice kit manufactured and sold by US Car Tool. The kit is designed specifically to install the 200-4R in a Mopar A-Body. Take a look at the pics on the link:

67-75 A-Body GM2004R Cross-Member Kit
Click to expand...


yup made for a 200 trans. and i've seen it before and you still have to hack the stock torsion bar cross member out and a bunch of guys don't want to do that....
 
rustytoolss said:
Did you replace a 904 or a 727 when you installed your A500 ?
When you did this swap. Did you notice any lose of power (like being lower on power/Parasitic loss) while daily driving ?
Also after doing the swap. Did you notice a free wheeling effect (overdrive) at cruising speeds ? Any MPG change. What rear gear are you using. How much power are pushing through that A500 ? Sorry for all the questions. Just want to make an educated plan.
Click to expand...

I went from the 904 to the A500 and had to cut out some of the top of the loop over the trans and mod the trans mount cross member. (NO floor mods)
Didn't notice any difference in power overall, but the A500 has a lower first gear and I noticed that big time, as it gets the car off the line a lot quicker.

No freewheeling in od or lockup either one, and went from 18mpg on the hiway with the 318/904 to 25mpg with my 350hp Magnum and A500.
Driveline had to be shortened almost 4 inches IIRC.

273 rear gears give me 2,100 RPM's at 80mph and 25mpg out on the open road on 87 fuel.
It does better with 91, but I never actually noted how much and only noticed the same amount of dollars got about the same distances.
15 inch 60 series tires on it.
When out on the interstates I normally do 80-85 for hundreds of miles at a time.

Just a fun fact, (or not):D
I can't get anywhere near lockup in CA since it comes on at 70, so doing the 55 speed limit there in OD the engine runs at about 1,500 RPM's.
I really don't like running it that low in R's, so I usually turn OD and lockup off.

I get that some would, or have to go the 200R4 route so they can just buy everything, but in my specific case I did all the work myself and had about $250 into the entire swap and that included the trans, converter, 7290 yoke, shift kit, and 80"speedo cable.
 
abodyjoe said:
yup made for a 200 trans. and i've seen it before and you still have to hack the stock torsion bar cross member out and a bunch of guys don't want to do that....
Click to expand...

This is exactly right. To install an A500/A518 it is the exact same process, except US car Tool doesn't give you the loop up above. They say it isn't needed. So to install either trans the "cross member" work has to be done and is close to the same.

Now the cost of an A500 vs an 200-r4 is a different story. I was gonna go with the 200 until I couldn't find a reusable core for under $500 add on the bell housing adapter, etc. I found an a500 for $200 supposed to be rebuilt, so I am going with that.
 
Replaced a 904, didn't notice any performance loss- quite the opposite actually due to the lower gear ratio im assuming, definite mileage gain and rpm reduction, the 318 probably has 200 horse power. 3.23 gears, runs about 2200 rpm at 75
 
jas0162 said:
Replaced a 904, didn't notice any performance loss- quite the opposite actually due to the lower gear ratio im assuming, definite mileage gain and rpm reduction, the 318 probably has 200 horse power. 3.23 gears, runs about 2200 rpm at 75
Click to expand...
Sounds a lot like my future combo LA318. I'm guessing that you used a stock converter ? Do you recall if it was the stock High stall/ or the stock Low stall ?
Another question. Is that 2200@75mph with the converter in lockup ?
 
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I wasn’t aware of the different stock stalls, not sure what I have. It’s just a stock replacement for the 318 engine, yes that’s all in and locked up at 75 mph.
 
jas0162 said:
I wasn’t aware of the different stock stalls, not sure what I have. It’s just a stock replacement for the 318 engine, yes that’s all in and locked up at 75 mph.
Click to expand...
Here's my dilemma. I would like to install the A500 overdrive. Or even the A999 with lockup. I have 2 sets of gears (2.76 &3.23) tire dia 27.4". I rarely drive over 60MPH. So I'm afraid that my RPM's would be to low (even with 3.23's), if I install the A500, I'm not sure the overdrive would come into effect. And very unsure if the lockup would ever engage.
On the other hand. If I were to install the 999 lockup. I'm more sure things should work properly. maybe even with the 2.76 gears.
Any thoughts ? I just don't want to go through the trouble of installing the A500. And not be able to use it for all that it is worth.
I'm sure that the A500 , would work correctly (even with the 2.76's) if I drove at higher speeds. But at 60 MPH, just not sure.
 
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ir3333 said:
is your engine already built...what are the specs?
Click to expand...
Soon to be 1986 318 truck engine. Stock rebuild. With 302 heads (stock). Summit 204/214 cam .421/.444 lift. Edelbrock performer intake. Edelbrock 650 AVS 4brl. GM style HEI ignition (with adjustable vacuum advance). Stock exhaust manifolds, dual exhaust. Nothing special, Just a driver/cruiser.
 
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3.23 X .69 = 2.22 final drive ratio.
A bit lower than the 2.76’s.
You could reduce tire size to a 26 inch as the 27.4’s are pretty tall. You would take off faster and have a more useable use for each gear with exceptable drive rpm in OD on the Hwy.
 
rumblefish360 said:
3.23 X .69 = 2.22 final drive ratio.
A bit lower than the 2.76’s.
You could reduce tire size to a 26 inch as the 27.4’s are pretty tall. You would take off faster and have a more useable use for each gear with exceptable drive rpm in OD on the Hwy.
Click to expand...
I would hate to replace the tires. Just bought the set of four new. Less than 500 miles ago.
So you can see my dilemma. In the long run the 999 lockup may end up being the better choice.
 
Tires wear out long before transmissions do. It would be just a mater of time....
Your call...
 
With 27 inch tires and 3.23 or 2.76 you will probably get very good mileage with your nicely warmed 318!
I might just try a 904 first?
 
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