What happens when you completely bulletproof your drivetrain? (Solution found)

Oct 24, 2016
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Welp, you win some, you lose some, and others are just good learnin'. Tony wanted to have some fun over the past weekend with the shop 1/2 mile car (white one), so he took it to the strip with some upgrades and new 2-step settings designed to leave the line around 23 psi.

First launch it rips the diff cover (which also serves as the diff mount) in half and slams the diff into the ground on the launch. This extreme angle also pulled the CV out of its housing destroying it in the process and tore both subframe mounts at the weld. Zero damage to the differential itself or axles, it just tried to twist it so hard the actual cast mount was not up to the task. Take a look at the carnage!

VAC is already at work machining us a couple of Billet Diff covers that will solve the problem. We're actually (sort of) happy with this result as it put to rest how tough the M3 set up is -nothing said uncle until it got to the cover. This is promising for future launches with the drag car (blue one) which will be much easier on parts being an AT instead of the manual.

We are proud to again demonstrate failures no one has seen on the platform to date. No, we are still not going with an 8.8, simply a stronger diff mount, and were good to go.

Enjoy the pictures and remember: don't try this on yours. :grin:

Chris


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MoreBoost

Sergeant
Jul 27, 2017
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Is it a stock diff?
What about the drive shaft and axles?
That's some amazing carnage.

They do say rotate the earth with the wheels. You gave it your best shot.
 

Snertz

Specialist
Nov 7, 2016
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lol wow that's impressive. How'd the cover bolt on the right side get bent like that, bolted to a diff lockdown arm?
 
Oct 24, 2016
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M3 differential. A stock one would have given up immediately (input shaft). M3 is stout, great upgrade for these cars.

As to the “how” part of damages, any question related can be answered with “torque”.

Chris
 

Bnks334

Lieutenant
Dec 1, 2016
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And people say the M3 diff doesn't lock up hard and slips lol... I had to drill out and upsize the front diff bolts from 12mm to 14mm because I kept snapping them.

There is a bit of diverging theory on this... would there be less torque shock on the mounts/cover if the bushings had a bit of compliance? Poly instead of solid? When I was snapping the front mount bolt I tried moving the diff mounts from M3 bushings --> poly street --> poly race and it did nothing. If anything it made the bolt snap faster. I know you're trying to prevent movement/wheelhop, and get as much torque to the wheels as possible, but is the diff movement really causing wheel hop or is it stock control arm bushings that are designed to bind and thus cause a fore/aft movement?
 
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fmorelli

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Aug 11, 2017
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I know you're trying to prevent movement/wheelhop, and get as much torque to the wheels as possible, but is the diff movement really causing wheel hop or is it stock control arm bushings that are designed to bind and thus cause a fore/aft movement?
I suspect there is some suspension design work that is generally missing on this platform, which would benefit the guys trying to put significant power down.

@Chris@VargasTurboTech kudos to you guys, both for continuing to relentlessly push forward, and for sharing.

Filippo
 

rev210

Corporal
Feb 24, 2019
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Nasty. Were you running a diff lockdown kit? Ive got a defiv on mine. But, to your point I dont know that its going to overcome what is a weak mounting in the diff cover itself. Shouldnt be hard to make something out of steel though
 

martymil

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Sep 6, 2017
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I use to break diff bolts all the time, like every 800 miles at one stage.

Since upgrading the factory diff bushes to bimmerworld solids and 12.9 grade high tensile bolts I stopped breaking them.

But this is on another level LOL
 

langsbr

Captain
Apr 5, 2017
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Recently I saw some super slow motion videos of the rear diffs blowing out on hellcats launching. It looks like a similar issue where the diff stays in tact and just rips right out of is mounts. Hella torque, hella grip! Interesting that even at what I would consider a reasonable vehicle weight that this happens. I thought it would be relegated to the 4500lb boat dodges lol.
 
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Oct 24, 2016
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23psi off the line very nice! Not so much for the diff. Was it a dead hook when he launched?
Sent from Tony to answer

"They had the track prepped very well for a big event the next day. This was test, and tune. My first hit. This car has a pretty complicated launch routine that has to be followed in sequence to get it right. I was a bit rusty, and didn't really load the drivetrain up like I usually do/need to. Dumped the clutch about 23psi, and it dead hooked. I didn't know what happened, car just wouldn't move after a loud crunch. Starter came over, and said might as well shut it off. You got parts all over the track. I got out, and my shoes stuck to the track, and almost pulled them off. They had it sticky that night. So this is part driver error, part lots of power, part lots of traction..."

Side note car weighs 3500lbs, it's not light by any means...
 

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Panzerfaust

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Very impressive even if the car didnt run what you wanted - or anything at all - that day lol. I love that the one long bolt survived and was just given a good kink meanwhile your diff cover looks like it got some good ol' 92 Civic neutral drop burnout levels of damage done to it. On a more serious note, it's very impressive to see that the M3 diff itself held up to what I can only imagine was a shitload more torque than anyone has come close to putting down on *any* diff for this platform.

Iirc you guys use completely stock M3 parts right? No special LSD upgrade, regular M3 axles etc, correct? I remember talking to either you or Tony a few months back and was told a write-up of your shop car builds would be posted but I dont recall seeing a full write up yet, though I do remember you guys both vouching for how capable the stock M3 rear end is. What kind of tires was he running? I'm not terribly familiar with what a 1/2 mile build looks like vs a 1/4 mile drag build other than needing extra aero, but was he on bias ply's or a regular set of radials? If radials, do you guys think bias plys might have helped the situation by absorbing more of that shock from the manual trans?
 
Oct 24, 2016
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Very impressive even if the car didnt run what you wanted - or anything at all - that day lol. I love that the one long bolt survived and was just given a good kink meanwhile your diff cover looks like it got some good ol' 92 Civic neutral drop burnout levels of damage done to it. On a more serious note, it's very impressive to see that the M3 diff itself held up to what I can only imagine was a shitload more torque than anyone has come close to putting down on *any* diff for this platform.

Iirc you guys use completely stock M3 parts right? No special LSD upgrade, regular M3 axles etc, correct? I remember talking to either you or Tony a few months back and was told a write-up of your shop car builds would be posted but I dont recall seeing a full write up yet, though I do remember you guys both vouching for how capable the stock M3 rear end is. What kind of tires was he running? I'm not terribly familiar with what a 1/2 mile build looks like vs a 1/4 mile drag build other than needing extra aero, but was he on bias ply's or a regular set of radials? If radials, do you guys think bias plys might have helped the situation by absorbing more of that shock from the manual trans?
We have found the stock M3 LSD is great for lower power builds up to around 700WHP. At that point, a Wavetrac needs to be installed to hold the power (which this car has) all other internal parts are stock. We have used stock M3 Axles up to over 800WHP, with clutch drops no issues. they are STRONG. For posterity sake. This car has DSS M3 axles good for 1200 ft/lbs we are told. This car should only be doing 1/2 mile duties as that is what its specialty is, but Tony is determined to get the manual car in the 9's so he keeps taking it back to the track. He has 2 sets of 15" welds one with Large drag radials for 1/2 mile duties, and one set for drag duties with 28" Hoosier Bias Ply slicks, with 17" skinnies up front. Once the drag car is done these will find a more permanent home on that car. Currently, the subframe is out of the car for repairs, and some beefing up. Should be back to the track soon.
 
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