Is AWD mechanical socialism?

[Kenny]

Okay guys, I have been struggling with how to make AWD a viable performance/road race setup. After a long discussion with Mark Ortiz about my approach there may be some clarity. The project is a "03 Blazer.

The down sides of AWD are well documented. Sharing too much front wheel power with lateral forces cause push. Using a viscous coupling is not adjustable to drop the power percentage to the front and is not variable. Of course there is the added complexity, weight/distribution, and frictional losses. The advantages we are looking to exploit are forward bite, tail out driving without total loss of control and swapping ends, and improved brake balance (I'll explain later).

Here is the plan. Either a nv136 transfer case from a 99 up Astro/Safari with chain drive and clutches from a 246 tc or a 246 tc with the high/low range planetary removed and using a 136 input shaft. This gives a RWD drivetrain with front assist. As it comes from GM the control module allows very little wheel slip before the clutches apply to bring the front axle into play. The hard part is finding a way to adjust the computer to allow a higher percentage of slip. I'll be shooting for 10-15%. All of this can be juggled with clutch preload and programming.

One advantage of AWD is the ability to make the front wheels normally acceleration neutral by applying a small amount of front drive to keep them up to speed without being road driven, which would have the same effect as being required to pull too much. What I am saying is that on most of my vehicles, the front wheels are rolling at the same time the back wheels are while traveling down the road. Crazy! When braking there would be the advantage of stopping wheel lock-up with the tc helping keep the low traction wheel up to road speed........ Thoughts? Mechanical socialism with all that power sharing and such?

[jbake]

Well as with socialism its sounds workable on paper, but real life is not paper. Couple other problems I see is one, the front drive axles for your blazer would be IFS. Ask any off road rock crawler or mudder, these front ends are junk. They are even smaller than the 10 bolt in the rear. The cv joints are tiny as with axles. I had a 95 blazer with a 4.3 and 5 speed. I could not keep cv joints in pass side axle. Would blow about ever 500 miles and thats with factory 4.3.
Tire size also is a problem. You would need to run same size on all 4 or you will blow the TC apart. And it is not just same diameter but also same width. TC are pain in the rear. That's why I gave up 4wd n got into cheaper playtoys.
Good luck you are starting down a path the high blood pressure and balding. Eather stress will make you bald or you ripping your hair out.

[Kenny]

It seems that when something works on paper, but not in real life, there has been some pertinent information left out of the paperwork. I have been dealing with S-10s for about 20 yrs just because they are my favorite platform. I have seen 2 front diff failures out of dealing with dozens of trucks and they were due to neglect or abuse. both failures were on the same truck with 200k + drivetrain miles. It was, as you mentioned, a rock crawler guy with a V-8 and 30+" tires. He smoothed off a pinion gear and later lost the spider gears. Once he let us know the front diff would unlock under full throttle(low vacuum), and suddenly engage again with one tire off the ground, we replaced the diaphragm with a manual locking mechanism and the problem went away. I will not have the axle that is engaged part time. I have never seen the chronic CV failures that you experienced even when dealing with some real hotrod Sy/Ty clones using the aluminum case.

The tire height issue is not a problem with my tire selection, but the fact that this will be modified to allow more wheel slip % will reduce or eliminate that issue. There is also the possibility of adjusting the computer to read a front and rear speed with pulse differences as normal (not sure if that made any sense). So many of the objections in my mind have been overcome. The remaining objections that I had involved the open front diff. That is in the process...... I am working with the possibility of having a waveloc diff custom built off an existing core. This will give gear style differentiation without going completely "open" like the Truetrac or Torsen. Another fear is the smoothness of engagement. Working with careful tolerances, basket surface prep and treatments, and preload settings are things that will receive careful attention.

The main concern of this posting was how to get the dynamic handling behaviors we all like, and it looks like 10-15% wheel slip will give predictable tail out driving goodness.

[exwestracer]

I can't speak to the technical end of it, but I'm amazed at the AWD system in our new 2011 Charger. It's the earlier gen M-Benz 4matic system, and engages the front drive based on various circumstances. I've had that car in a 4 wheel drift, felt the front drive kick in, and it just tucks the nose back toward the inside of the corner. I know it apparently violates the laws of physics, but I've done it; and I'm sold on "smart" AWD as Dodge does it.

[Kenny]

That is exactly what I am looking for....... Evidently the weight/ drag issues don't even come close to negating the advantages when it is even close to right. This is considering that, in the mountains, we don't have a lot of open straight stretches where it might lose it's advantage. Even with that being said, we always have weather, dirt and debris on the road, etc..... I just don't see a down side for my personal daily driver. The settings of the GTR system is where I will baseline since it is just so good

[nine lives johnny]

well awd platforms can be used in a performance/road race application. we've built and raced/built with an sti, evo, and audi tt. can an 03 blazer be any good? well i wouldn't put the qestion to if your stock parts will hold up, but will your car be safe? generally in auto x road racing you dont need to beef up your drive train componets as much as you would when building a drag car. the blazers center of gravity is very high even when lowered (on awd platforms). i would be more worried about the thing rolling over. any precautions to stop it from rolling over, would make it lose allot of road manners and be uselless of road. blazers have a towing copacity of 6k lbs. i would take money that you where going to invest in the blazer and buy a 1980's f body or fox body. it will cost the same, and use the blazer to tow it to events. or get a 2wd truck to race. my .02

[Skip Fix]

Might look at the old Typhoon/Syclone GMC trucks that were basically a Buick GN with AWD in a truck./SUV platform. Some of them were pretty bad a$$ and dropped pretty low.

[Kenny]

well awd platforms can be used in a performance/road race application. we've built and raced/built with an sti, evo, and audi tt. can an 03 blazer be any good? well i wouldn't put the qestion to if your stock parts will hold up, but will your car be safe? generally in auto x road racing you dont need to beef up your drive train componets as much as you would when building a drag car. the blazers center of gravity is very high even when lowered (on awd platforms). i would be more worried about the thing rolling over. any precautions to stop it from rolling over, would make it lose allot of road manners and be uselless of road. blazers have a towing copacity of 6k lbs. i would take money that you where going to invest in the blazer and buy a 1980's f body or fox body. it will cost the same, and use the blazer to tow it to events. or get a 2wd truck to race. my .02

Nice...... tip over much do ya? This is an exercise in handling and will never see off road (intentionally). While the the truck will be a bit lower and many low mounted components. The CG may not be that out of line, and if we were to check closely, it may have a better CG height to track width ratio than what you have worked with. I'm guessing that getting the roll center correct for balance is gonna be most important followed closely by really good shock valving. I like that you chimed in because the topic always brings about the dominance factor of AWD in the cars you just mentioned, even though in theory they are the worst platforms you could start with being front drive with rear assist (too much front power to be ideal) and associated balance issues. Maybe you could give me some insight as to drive and wheelslip percentages that you used to stop push or even do some tail out dirt track style driving. Just in case the point hasn't come across, wheel slip percentage manipulation will be used for four wheel drifts rather than just wagging the rear out with weight.

[nine lives johnny]

kenny,
i must admit that i'm not the guy that sets up the diffs on the awd cars, and as far as distribution percentages down i don't know what's the perfict % is. generally we try to get as much power to the rear as we can. audi tt's are built with 75% of the power headed to the front tires. that's why we leave that chassi behind. it's too hard to get it to stop under-steering (pushing) when you get on the power. first things first when your looking into setting up your chassis forget about power and where it goes. you have a blazer, i assume your cross weight is 60-70% over your front tires. this means your blazer will generally push threw turns without any power being added. your fount tires are being put to the limit, now add in the fact that power is going to go to those wheels, and kiss going around a tun good buy. i know you want to have your car act similar to a gt-r but it won't. i think if you invest 20grand into your car it will handle similar to an wrx (not a wrx sti). expect lots and lots of understeer. seriously the blazer is a good tow rig, pick up a sti or some other sports car. you'll be much more happy.


if your dead set on a suv racer (and it sounds like you are) look into this http://www.jeepsunlimited.com/forums...d.php?t=531598

[Kenny]

I'm not sure what the cross is but it scaled out at 3860 with some fuel. It was right at 2000 lbs up front and 1860 rear which figures around 52%/48%. No lightening has been done yet. The L92 weighs about 30-35 lbs less than the V-6, the battery will be 35 to the rear (effectively 70), and my torque converter is supposed to be 20 or so lbs lighter than stock. It will get near 50/50 but I wouldn't sweat it at 52% front. I have already gotten rid of most push with the 245/60-15's I have now by doing nothing more than using ZR2 torsion bars cranked all the way down, alignment work, and fresh Bilsteins. This setup will give way to a junkyard transverse leaf from a '06 vette, which should be a little stiffer if I need it and knocks off a couple more lbs........ I'm giving it the ol' hillbilly try.

[Kenny]

kenny, this means your blazer will generally push threw turns without any power being added. your fount tires are being put to the limit, now add in the fact that power is going to go to those wheels, and kiss going around a tun good buy.

This is a very important part of the conversation that only got glossed over in the first post. Power is always applied to drive the front wheels even in a RWD only vehicle. The front tires in a RWD are road driven rather than axle driven, but they are still receiving forces other than lateral to keep them up to speed. This has the same effect as applying a little too much power. Part of the "system tuning" is applying a very small amount of drive to make them "drive neutral". I know this seems insignificant, but I have been assured that there is substantial benefit in lateral traction and predictability. The Nissan system is defaulted to a 98/2 split. It seems that the 2% front assist has a measurable effect and is beneficial for reducing "push". This can also have deceleration implications as well. Think of a lightly loaded inside wheel that locks up, using (sharing) the same energy through the AWD system. This will keep the wheel up to road speed that would normally lock, while transferring the braking power from that rotor, that would normally be wasted, to the other wheels.

[nine lives johnny]

well the cross weight is not to bad. what is your power distribution for your center diff? your planning on doing a l92 swap too? you gotta hack the crap out of the oil pan to fit one into a awd platform. be well aware of the oil starvation with lsx type blocks, get your self an accusump before you hit the track. sounds like your ol' hillybilly try is going to some uncharted watter. keep records and do a build thread. i would love to see something different.

[Poopy]

Instead of messing around with GM truck stuff, why not get your hands on a wrecked Subaru and build a new frame with a proper AWD system??

[Kenny]

Instead of messing around with GM truck stuff, why not get your hands on a wrecked Subaru and build a new frame with a proper AWD system??

With the discussions I've been having with some serious suspension engineers, and the way it is being implemented, it appears that GM truck stuff is likely a more "proper" system than the scooby doo stuff. Even though the Subaru stuff has been made to work well, it is almost the exact opposite of proper. The best part is I'll be able to toss a few bags of pavement patch, some Quikrete, and my freon tanks and gauges up in that pig and make some money........

well the cross weight is not to bad. what is your power distribution for your center diff? your planning on doing a l92 swap too? you gotta hack the crap out of the oil pan to fit one into a awd platform. be well aware of the oil starvation with lsx type blocks, get your self an accusump before you hit the track. sounds like your ol' hillybilly try is going to some uncharted watter. keep records and do a build thread. i would love to see something different.

Man you gotta ease up on the negative vibes...... The H3 pan fits with no mods if you space the front diff 3/8-1/2" or you can do a mild scallop. For power split we are looking to get down to a 98/2-95/5 split. It will start with about 50lbs of clutch preload (stock is 200lbs). There is still a lot of information gathering and math going on......

There will be those warning of CV joint problems with diff spacing and a spindle drop but they just aren't that sensitive to mild changes. If they were, the factory wouldn't put them on the wheels you steer with. The problems come in when a kid rolls in with a 200K mi Honda that has established a very distinct wear pattern and they drop the thing 3"

[Kenny]

Sorry, double post

[exwestracer]

This is a very important part of the conversation that only got glossed over in the first post. Power is always applied to drive the front wheels even in a RWD only vehicle. The front tires in a RWD are road driven rather than axle driven, but they are still receiving forces other than lateral to keep them up to speed. This has the same effect as applying a little too much power. Part of the "system tuning" is applying a very small amount of drive to make them "drive neutral". I know this seems insignificant, but I have been assured that there is substantial benefit in lateral traction and predictability.

THAT is a VERY interesting concept, and perfectly explains my experience with the Charger. Thanks.

[nine lives johnny]

Man you gotta ease up on the negative vibes......

sorry man.. The inner racing purest in me is screaming you can't race a blazer, but the artist in me is saying why not.
I mean this seriously and with out sarcasm.
go for it! shut up my inner racing purest.
good luck hope to see you at LS Fest. I'll have the miata. :thumbsup:

[Kenny]

THAT is a VERY interesting concept, and perfectly explains my experience with the Charger. Thanks.

You handled that just like I did when the theory was presented. It was like turning a light on.

sorry man.. The inner racing purest in me is screaming you can't race a blazer, but the artist in me is saying why not.
I mean this seriously and with out sarcasm.
go for it! shut up my inner racing purest.
good luck hope to see you at LS Fest. I'll have the miata. :thumbsup:

I know what you are saying, and I must admit that naysayers are the fuel for my fire. The objection of others always brings about considerations that MUST be overcome to make a successful project, so I really need the negative vibes.... I am going more for the definition of "pro-touring" that fits my needs than a racer. The roads in my neck of the woods are really bad for a race RWD set-up compared to AWD when there is serious power. The tight turns, stutter bumps, and banked switchbacks are horrible for traction, nevermind the occasional bump that will almost pitch the rear off the ground. A true road race RWD would not fare well against AWD.
Just like the old saying, I know I can't turn that pig into a racecar, but I can make a damn fast pig! I'll go WEEE,WEEE,WEEE all the way home

[exwestracer]

You handled that just like I did when the theory was presented. It was like turning a light on.

While I definitely will NOT be tweaking the AWD system in the new Charger, your point did bring up a whole new line of thinking regarding instantaneous variations in F/R torque split. This kind of goes along with another idea I've had kicking around for awhile: using hyd. displacement directly from suspension travel to mechanically adjust torque split.

Hmmm, I wonder how light I could make a solid front drive axle.....

[Kenny]

On a side note I have been looking at your 2011 system and it was changed on '09-up to on demand like the system we are talking about for the Blazer. Nice.

The hydraulic method you mention was looked into as well as weight jacking for the low traction wheel, then I ate lunch and forgot what I was thinkin'.....

One of the things that is most interesting is the control boxes are often programmed to "anticipate" need by comparing yaw, acceleration rate, throttle position etc. If you are going at a low road speed and it senses a rapid rate of throttle opening by the TPS and it will just assume you are gonna have a traction problem and deal with it accordingly. That is my favorite part of EFI, it is actually pro-active instead of reactive like a carb.

Aside from the "neutral front wheels", the prospect of using this to control braking is very exciting as well. The prospect of taking out rear bias because of inside wheel lock-up always seemed like a waste because it only helps in that instance, meanwhile you are just giving up braking power in every other situation, and ABS is just too heavy handed.

I don't know what project you have in mind w/ a straight front axle, but I'd be more than happy to help research/find the right parts for it.