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project "top heavy" awd
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Author:  johnnybusa [ November 28, 2013, 2:42 am ]
Post subject:  Re: project "top heavy" awd

I like the idea of the BMW but is it over computerized and can it be had with a clutch? Part of The subarus appeal is that I could put an aem unit on the engine and be done. And my love of boxers.
No I've never driven awd, I loved my mr2s but I personally never fell in love with a mid engine ride. The idea to locost a subaru came from the fact that awd is extremely apealing to me, I love turbos, I love boxer engines, and I can't stand 4 door sports cars.
Also are you guys saying that wouldn't handle at least some better than the wrx? I understand it won't be a 7, but the near unlimited launching traction and acceleration is the big appeal to me. Or am I giving this idea too much credit for its ability as a half drag half road car?

Author:  erioshi [ November 28, 2013, 5:17 am ]
Post subject:  Re: project "top heavy" awd

carguy123 wrote:
I think what he's saying is a transverse mid mounted engine will be hard to get balanced at the edge. Look how many years Porsche took to get the 911 working. And the other cars you mentioned are longitudinally mounted not transverse.

I personally think he's right. Look at how much bad press the At-om gets on handling. It's simply not stable and they've been working on it for years. Everyone talks about how hard it is to be consistent, how twitchy it is and what a handful.

Sure there will eventually be a formula that makes it work, you can make anything work such as putting the engine back behind the rear axle, but it takes much more time money, and maybe lives, than any of us have to give.

It is essentially this. With the engine more forward and the weight close to 50/50 but a longer polar moment of inertia (like weights at both ends of a weight lifting bar) the car tends to slow down how quickly it reacts to change, and it becomes much easier to drive at the limit, and more forgiving for most drivers. With a typical middy, all the weight is concentrated in the center with a very short polar moment of inertia (think two weights in the center of a weight lifting bar) which makes it harder to catch and correct the vehicle's behavior. Part of the problem with the short PMI is the car reacts more quickly, and corrections generally need to be made more quickly, and in in finer increments.

Those examples are kind of the extremes, but they illustrate the point. The Miata, Elan, Caterham, most locosts, etc. seem to sit in a sweet spot for most driver's ability to feel and react to what the car is doing.

Author:  toyotus [ November 28, 2013, 12:24 pm ]
Post subject:  Re: project "top heavy" awd

I was originally planning an awd build using an early Rover 3.9 and 5spd, using offset Rover rear and an ifs 7.5" front diff from a Toyota. After all the magic shoehorns in the world and the car building gods on my side, (and my entire life span to build it) i arrived at the conclusion that it would be exactly what i wanted, but would understeer like crazy, and i wouldnt be able to rotate it (oversteer) like im used to in my AE86. And of course the sheer size/bulk associated with the design, and the nosecone required to hide the front diff, it would end up being a +886 or something, and look like an oversized bloated seven like it was supposed to be a "put in water and watch it grow to twice its size" thing, that had been forgotten about and left submerged as long as the average Locost takes to build.

But thats my opinion.

Author:  gregk [ November 28, 2013, 12:51 pm ]
Post subject:  Re: project "top heavy" awd

johnnybusa wrote:
are you guys saying that wouldn't handle at least some better than the wrx? I understand it won't be a 7, but the near unlimited launching traction and acceleration is the big appeal to me. Or am I giving this idea too much credit for its ability as a half drag half road car?


How well it handles would depend quite a bit on you, maybe it will handle better than a WRX maybe it won't, but it almost certainly won't be as responsive as a Miata, and it definitely won't be as responsive as a Locost. It will be fantastic in a straight line though, and depending on what kind of road use you have in mind it could be a great half-drag/half-road car for you, but it's going to fall short as a sharp and nimble canyon carver.

Author:  johnnybusa [ November 28, 2013, 6:06 pm ]
Post subject:  Re: project "top heavy" awd

gregk wrote:
johnnybusa wrote:
are you guys saying that wouldn't handle at least some better than the wrx? I understand it won't be a 7, but the near unlimited launching traction and acceleration is the big appeal to me. Or am I giving this idea too much credit for its ability as a half drag half road car?


How well it handles would depend quite a bit on you, maybe it will handle better than a WRX maybe it won't, but it almost certainly won't be as responsive as a Miata, and it definitely won't be as responsive as a Locost. It will be fantastic in a straight line though, and depending on what kind of road use you have in mind it could be a great half-drag/half-road car for you, but it's going to fall short as a sharp and nimble canyon carver.


The math in my head says it would be a wrx except lighter and better, pmi wouldn't be great but it would be better than the family sedan it started with.

Author:  esp42089 [ November 28, 2013, 11:56 pm ]
Post subject:  Re: project "top heavy" awd

It won't be. Despite the reduction in weight, you will be losing weight from everywhere except the front of the car, drastically increasing the front-heavy feel. It will be fast, but it will steer and handle worse than the parent sedan. If you don't mind that (it is all relative) and you find the idea attractive, go for it!

Author:  erioshi [ November 29, 2013, 1:41 am ]
Post subject:  Re: project "top heavy" awd

I agree. Essentially, you'd need to find a way to offset the all the weight in the front with a similar amount near the rear (but the driver could count towards that) to get back to having a car that turned well and felt as toss-able as your WRX does now. Without the weigh in the rear to offset all that weight in the front, the car will be very heavily prone to understeer. It might be a problem you can tune around, but the larger the weight imbalance, the harder it will be to fix with things like wider front tires, suspension geometry & parts, etc. In my opinion, I think the negatives would probably outweigh the positives unless I was looking for a drag car.

To add a little perspective, I'm an Evo guy. I loved having a heavily built, but still highly responsive engine with AWD, and really good driving dynamics. But to create a "locost Evo", I'd need to fight all of the same problems you face with your WRX. It can be done, but the plan would mean building a car that will probably weigh over 1,800 lbs and need a very strong chassis & cage structure. After looking hard at what that project would mean to me, I've decided that if I ever do an Evo again, I'll probably build an Evo 6/9 hybrid instead of a tube framed custom. But first I have to build my middy.

Author:  carguy123 [ November 29, 2013, 2:37 am ]
Post subject:  Re: project "top heavy" awd

erioshi wrote:
With a typical middy, all the weight is concentrated in the center with a very short polar moment of inertia (think two weights in the center of a weight lifting bar) which makes it harder to catch and correct the vehicle's behavior. Part of the problem with the short PMI is the car reacts more quickly, and corrections generally need to be made more quickly, and in in finer increments.

Those examples are kind of the extremes, but they illustrate the point. The Miata, Elan, Caterham, most locosts, etc. seem to sit in a sweet spot for most driver's ability to feel and react to what the car is doing.



That hasn't been my experience at all, but then again nearly all my rear, longitudinal, middie experience has been Ferrari's and Lambos. My wife buys me cool birthday & Christmas presents - driving experiences, not the cars themselves. (I don't want to spoil it for her, but indications are for this Christmas I'll be getting a school at COTA driving the McLaren.)

Every longitudinal middie, I've driven whether it was a front middie or a rear middie, has been extremely stable and required very little input to keep it going where I wanted it. More importantly it changed directions easily and with little hesitation.

I agree with the statement that the car reacts more quickly or would it be better said to react more easily. And it doesn't over react. Now should I over react, which is the most likely thing to happen, I've found them much more forgiving.

An MR2 is the only rear, transverse, middie that I can remember driving (there may have been others but they don't come to mind right now) and while I loved it and thought it handled very well it was a lot more work to get it handling like we liked it. We had to throw more time on sway bars, wheels and tires to get it so that it drove as well as we liked. We eventually made it work better than the Miata, but it took a lot more work. The Miata was much nicer out of the box and much easier to work on. Which is another problem with a transverse rear middie - access. Well actually that's a little bit of an issue on every rear engined car I've ever played with except an aircooled VW or older Porsche.

And if you are moving around one of those weight bars with the weights on it that you were talking about, you'd rather carry it around with the weights in the middle. It's much easier to move it around and it's less likely to give you a hernia as one end takes a sudden dip when you change the horizontal axis or try to swing one around a corner. Same applies to a car.

Author:  erioshi [ November 29, 2013, 3:22 am ]
Post subject:  Re: project "top heavy" awd

And this is where it get hard, lol. I actually suspect our points of view are closer than a quick glance at our posts might suggest, but this is the internet and the tiniest of apparent differences always seem to get blown all out of proportion and loose analogies tend to be misinterpreted in every way possible, cut into the tiniest of slices and then each slice debated endlessly, sometimes completely without the context of the original analogy.

Your experiences with the MR2 are exactly what my post you had quoted was about. The MR2, when stock, made it harder for you to reach your performance limit than the Miata did. The MR2 could be tailored to your driving style, but it took both parts and effort to "catch up" to the Miata. But yes, ultimately, the performance limit was higher with the MR2.

That pretty much sums up what I was trying to say, thanks Chet!

Author:  johnnybusa [ November 29, 2013, 2:18 pm ]
Post subject:  Re: project "top heavy" awd

ok I seem to get it more now, I did like my 3rd gen mr2 it didn't dance like the Miata out of the box but it was good. the first gen was a dog, understeer into snap oversteer with little warning, and it wasn't easily if at all possible to resolve most of the time. that car spent a lot of time in the grass and that's why its now my locost.

what I want is a car that doesn't fight for traction in every gear like the higher powered locost I've seen always do, im sure there are some out there but I've never gotten to see one personally. those videos of at-oms sliding around trying to drag race are very cool though my goal is still about 250hp with a boxer and that part wont change. so do you guys have any suggestions or alternatives to get 250 whp with at least some traction? would you try front engine or mid engine? the mid engine design sounds nice if done right and it wasn't far off in the 3rd gen mr2, it was just not quite as good as a Miata stock for stock. I live in Alabama so if you don't have a mustang or a big truuuuck you have to be able to beat the mustangs or you will be laughed at.

Author:  carguy123 [ November 29, 2013, 4:11 pm ]
Post subject:  Re: project "top heavy" awd

At 250 hp, a Mustang will be beneath you and not worthy of your time.

At 200 hp it will probably take a breathed on Mustang to give you much grief. Most people just don't understand the impact of a good power to weight ratio.

All of that presumes that you will be smart and cut your runs off at 90-100 mph (don't worry you'll be far in the lead at that time) because the 7ish body shape really will have major impact on higher speeds.

Running 240 hp (S2000 motor) and running in the Detroit Iron class of NASA, we just walked all over the "Iron" until we hit the straights. They'd pass us and we'd pass them back at the end of the straight since we could brake about 3 cones later and get on the gas much quicker.

If you're using the Subie motor then it follows you'd have a longitudinal middie which I believe would be much easier to make handle well than another more traditional transverse FWD engine.

But if you're using the Subie motor I believe the placement of the weight of the engine so far in front of the front wheels, vs a more traditional transverse engine, would make it hard to get the handling down right. When you're talking a car this light the mass and placement of the engine has a much greater impact than when you're talking a full bodied car.

Author:  gregk [ November 29, 2013, 5:35 pm ]
Post subject:  Re: project "top heavy" awd

johnnybusa wrote:
so do you guys have any suggestions or alternatives to get 250 whp with at least some traction? would you try front engine or mid engine?


Mid engined with ~40F:60R to ~35F:65R (with driver) is the way to go. A rearward weight bias means you need wide rear tires to keep the car neutral in corners, and when you combine the two you get lots of traction. It's the same formula that drag racers have been using for decades. And as a nice benefit, you end up with better braking performance as well. It makes even more sense if you're set on using a Suby motor, as you can just use the stock transaxle and not have to fool around with adapter plates.

Author:  johnnybusa [ November 29, 2013, 6:41 pm ]
Post subject:  Re: project "top heavy" awd

gregk wrote:
johnnybusa wrote:
so do you guys have any suggestions or alternatives to get 250 whp with at least some traction? would you try front engine or mid engine?


Mid engined with ~40F:60R to ~35F:65R (with driver) is the way to go. A rearward weight bias means you need wide rear tires to keep the car neutral in corners, and when you combine the two you get lots of traction. It's the same formula that drag racers have been using for decades. And as a nice benefit, you end up with better braking performance as well. It makes even more sense if you're set on using a Suby motor, as you can just use the stock transaxle and not have to fool around with adapter plates.

I've seen some transaxle conversion threads but I don't think im typing in the right words becasuse im not finding the threads. so if there were skinny tires up front and big ones in the back it would be more controllable?

Author:  erioshi [ November 29, 2013, 6:44 pm ]
Post subject:  Re: project "top heavy" awd

Based on what you've said are your goals, and the constraints you've given (fairly easy to drive, keeping the boxer engine, and especially not wanting a car that swaps ends too quickly and ends up in the grass...) I'd probably recommend a more conventional front-engine, rear-drive locost. You could widen the front chassis a bit to fit the subie, and then cover the whole thing with a body similar to Jack's Lalo .. or whatever else you wanted to try. You would give up a bit of rear weight bias (and thus some traction), but you'd gain very predictable handling and a chassis that was fairly easy to tune to your driving style.

Some additional thoughts: You could probably gain back a bit of that traction by using a De Dion tube in the back if you wanted to. That would eliminate camber gain and loss in the rear suspension with bump and droop. The penalty would be higher unsprung weight, which very light cars can be quite sensitive to. That said, there are quite a few sevens out there with live rear axles so that weight may be a non-issue. More possible alternatives for adding traction might be long, forward reaching rear links (think pre-downforce 60's F1 cars) or possibly traction bars. A fair warning though, I'm not familiar enough with traction bars to offer an informed opinion on how they would impact cornering.

That said, a subie based middy would probably offer more overall potential performance. It may well just take more time, work, and parts to achieve that potential.

Author:  johnnybusa [ November 29, 2013, 10:25 pm ]
Post subject:  Re: project "top heavy" awd

it seems like if the boxer engine was behind the driver with it still being far in front of the back axle it would be a good mix of part Miata drivability with part mr2 handling and nimbleness right? it sounds like the further back you put the weight the better off you are if you're a good enough driver, is that about it?

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