This is a bit of a bench racing question from an idea that just popped into my head but could a transverse engine, with its transaxle be set up mid engine and longitudinally and use the two transaxle outputs to go to front and rear diffs for a simpler and lighter alternative to a lot of current mid engine awd systems? What would make this infeasible or stupid if you simply offset either the diffs or the engine?
Yes. IIRC this was done on one of the 4x4 shows
Gearing will be your main problem. Say your transaxle has 4.10 final then you're going to the diffs at say 3.27 at best. That gives you great acceleration but horrible top end speed.
In reply to Stampie :
I didn't even think of that. Makes sense.
In reply to Evanuel9 :
Keep coming up with crazy ideas. You're in the right place for them.
In reply to Stampie :
Correct. It was for a rock crawler. IIRC hey used a GM supercharged Ecotech from a cobalt SS.
Didn't Dirt Every Day do that as well with a rav4 and it's stock engine? Really cool concept but final drive would kill ya.
In reply to Stampie :
I think the 4x4 show, on spike? Has a final drive of 64:1. They were using it as a rock crawler id I recall correctly.
Stampie said:Gearing will be your main problem. Say your transaxle has 4.10 final then you're going to the diffs at say 3.27 at best. That gives you great acceleration but horrible top end speed.
The sort-of exceptions are the GM 4Txx automatics (4T40, 4T60 or 4T65, 4T80 or 4T80E, whatever), only b/c the final drive is a planetary attached to the differential which (in theory) should be easier/ cheaper to remove or weld solid.
There is an aftermarket numerically-low gearset available for Tesla drive units intended to solve the problem if you want an EV.
Otherwise, I have not found any transaxles which would NOT require a whole lot of work and/or $$$$ special gears.
In reply to Stampie :
And it wouldn't be feasible to say rebuild the diff with a larger pinion gear? Either way I'll pursue this idea when I'm older and can afford it for a $20xx car because acceleration beats top end on the autocross, and it seems just the right amount of jank for that event.
In reply to Oapfu :
I bought my GTI with the express intention of turning the planetary final drive of a 4T60 to 1:1 with some grinding and welding, and mounting it in the back with a supercharged 3800. With a turbo off each side too.
Getting a rear differential short enough was one of the issues. The GTI is a lot smaller than it looks.
In reply to Evanuel9 :
Gearset would cost a pretty penny and even then you won't get it to where you want. The planetary gear talk above sounds cool. Wonder if the transverse auto version of the 4L80e can do the light switch mod. Maybe a PI to control it. could be done cheap and cool.
I’ve seen that before, kinda.
It was a 1994ish former VA tram. The kind that was used to move people from the parking lot to the front door. It seated 13 and had a wagon style trailer that seated another 15 if I recall. The thing had a 3.0 Mitsubishi motor and transmission out of a Chrysler minivan. It had a full van wire harness complete with headlight and taillight connectors that weren’t used.
It had a stub bolted into the front facing trans output, so all power went to the rear facing output. This fed what I assumed was a traditional bus rear end. Top speed was around 25mph.
One other impact is that FWD transaxles generally have the motor sitting in front of them. So if you turn it sideways you're either you're going to have to offset the front/rear driveshafts (along with differentials and different length axles) to one side of the car, or you're going to get some odd left/right weight distribution because the motor won't be centered.
Pete. (l33t FS) said:In reply to Oapfu :
I bought my GTI with the express intention of turning the planetary final drive of a 4T60 to 1:1 with some grinding and welding, and mounting it in the back with a supercharged 3800. With a turbo off each side too.
Getting a rear differential short enough was one of the issues. The GTI is a lot smaller than it looks.
Awesome!!! Did you have ideas for anything other than leaving the open "center" diff?
Aw, crap, so the Atlas engines (specifically, 6-cyl "Vortec 4200" from GMT360) will NOT directly bolt up to any 4Txx? https://sites.google.com/view/vortec4200wiki/manual-trans-overview
As I understand it, there are people on GRM who have some experience with the 4T80E https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/paccwards-the-2020-pacc-racing-challenge-car/166683/page1/
codrus (Forum Supporter) said:One other impact is that FWD transaxles generally have the motor sitting in front of them. So if you turn it sideways you're either you're going to have to offset the front/rear driveshafts (along with differentials and different length axles) to one side of the car, or you're going to get some odd left/right weight distribution because the motor won't be centered.
If the front and rear driveshafts need to turn clockwise when viewed from the front (so that RWD and 4WD diffs will work like normal): you could make the vehicle right-hand drive, and then the driveshafts can be more or less on vehicle centerline while the weight of the driver helps offset the weight of the engine. Granted, cross-corner weights are still not going to be perfect. I'm always assuming there will be no room for a passenger seat.
If you want LHD: run the motor/trans the other way so the front/rear drive shafts are still close to vehicle CL but turn CCW when viewed from the front. In front you run a REAR diff which is flipped over; in back you run a FRONT diff which is flipped over (and then do whatever is needed for lube inside the diffs; at least you are not driving on the coast side of the ring+pinion).
Still SOL for a manual trans. The HMMWV diffs have 2.56 or 2.73 gears, torsen LSD, and used take-outs are ~$500 each. Maybe a good deal (depending on exactly how used), but 1) that'd be half of a Challenge budget just for diffs, and 2) even if you find a VW 02M/02Q 6-speed from a TDI (there is an awesome .xls file w/ all the ratios) you still need an engine with >10k rpm redline and absurdly tall tires to get more than 100mph top speed.
I'm kind of surprised nobody has mentioned the little utility vehicle built by a Youtuber called Donn DIY. I really enjoy his stuff. He builds a lot of really interesting things, always well thought out, and his videos are eminently watchable.
https://youtube.com/playlist?list=PLkmF7FAZBzkUZ3GjEo97GkWajmj9bCxzE
Sorry it's just a link. Not sure how to embed videos and am posting from my phone right now so my options are limited.
I think it could be done even with the gear reduction depending on which final drives you have. Something like a malaise-era US car could come with ratios in the mid- 2s. Pair that with a transaxle in the mid 2s and you're likely golden.
However... good luck finding a modern transaxle in the 3s, let alone 2s.
Aren't there a bunch of small CUV's with an almost 1:1 rear diff? They could be used for this idea.
In reply to fanfoy :
They also have extremely low torque capacity.
The other thing about parts from newer/smaller AWD systems is that b/c you would have only rear diffs to work with, the one used in front will have to be driven backwards, making the torque capacity issue even worse.
One more not-ideal work around idea: you could make simple gear boxes to hold sets of circletrack quick-change gears (or maybe gears from a medium- or heavy-duty truck transmission, or Hummer portal axle?), and put one of those between each front or rear driveshaft and diff, basically making DIY quick-change diffs. Typical off-the-shelf QC gears go up to about 0.6:1 (or 1.7:1) before they start saying "for low power applications only". That'd be one way to improve the overall gearing ratio, and/or change rotation direction, but at the penalty of say a couple hundred pounds of weight, extra driveline length, and extra $ cost. If you can do all the machining yourself, it might not be completely cost prohibitive (although NOT bloody likely under a $2k Challenge budget).
Crappy explanation of the problem with driving a ring&pinion backwards (e.g. the pinion has to rotate CCW to make the vehicle go forward, rather than CW) is not so much the strength of the gear teeth but rather the strength of the case or housing for the differential. The gear teeth are not symmetric, with a saw-tooth or buttressed shape. When rotating in the designed direction, the mostly-vertical faces of the teeth ("drive side") transmit the torque with minimal force trying to spread the gears apart and make the teeth jump past each other. In the reverse direction, the sloped backs of the teeth ("coast side") are trying to transmit the torque which results in significantly higher forces trying to spread the gears apart, and this can end up breaking the diff housing. There's a lot more going on as well, take a look at better explanation such as this one.
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