BUILD THREAD 86 GP 2+2~Blown 6.0

[64nailhead]

Take all of this with a grain of salt please, I can't believe that you're putting this much wood (power) to break the same rear that the household Cutty (in my sig) can run mid 10's at 18 psi. It launches soft and hit's like a sledgehammer later. But gosh dangit, you've got the carnage to prove it. The Cutty has about the same rear as you have - Mosers 30 spline in a Yukon posi with 3.73's.

Damn, that (your) stick is tough on it!!

Be advised, the 14 bolt will eat 30-50hp and is stupid heavy.

 

[Northernregal]

Take all of this with a grain of salt please, I can't believe that you're putting this much wood (power) to break the same rear that the household Cutty (in my sig) can run mid 10's at 18 psi. It launches soft and hit's like a sledgehammer later. But gosh dangit, you've got the carnage to prove it. The Cutty has about the same rear as you have - Mosers 30 spline in a Yukon posi with 3.73's.

Damn, that (your) stick is tough on it!!

Be advised, the 14 bolt will eat 30-50hp and is stupid heavy.

But its the "Light" version.

I kinda wanna see how this experiment works, stop trying to talk him out of it.

 

[64nailhead]

But its the "Light" version.

I kinda wanna see how this experiment works, stop trying to talk him out of it.

okay

 

[Supercharged111]

Take all of this with a grain of salt please, I can't believe that you're putting this much wood (power) to break the same rear that the household Cutty (in my sig) can run mid 10's at 18 psi. It launches soft and hit's like a sledgehammer later. But gosh dangit, you've got the carnage to prove it. The Cutty has about the same rear as you have - Mosers 30 spline in a Yukon posi with 3.73's.

Damn, that (your) stick is tough on it!!

Be advised, the 14 bolt will eat 30-50hp and is stupid heavy.

You bring up some good points. I missed if OP broke the diff on launch, a shift, or steady state.

 

[81cutlass]

This pass it broke on seemed off from the burnout. This track has you back into the water box instead of pull through it and I wonder if the water box was too dry or I didn't get backed in far enough. Usually to do a burnout I give it about 2000 rpm of throttle with the clutch pressed in 1st gear and let out quick and move my left foot to the brake while trying to get it to 4000+ rpm. Normally it spins easy and I do a short burnout to clean the tires off and tack them up a bit.

Here, I gave it about 2000 rpm to do a burnout like normal and as soon as the clutch grabbed it wheel hopped pretty bad. Like there was no water on the tires, I gave it enough throttle input that it got itself out of the shake after about 2.5 seconds. No noise or anything so I said it's fine.

It broke at about 18mph maybe 30-50 feet off the line. You can see the 2 step launch RPM of about 3500, the rpm plateaued off, and TPS is 100%. I usually don't dump the clutch but I let it out quick (it's a stage 3 puck style and there isn't much slipping). The RPM starts at 3500 and dips slightly to a low of 3375 before I get grabbing and wheel speed. No bogging! Thats good.

You can see here it snaps at 18mph, the mph log slope increases dramatically at a slope higher than really possible.

This was my 11.97 1.76 60ft run from Friday. See how the mph gain is pretty consistent.

So to answer the question, maybe it hurt itself in the burnout? The moment it broke was mid range in 1st gear. I shift to second at 48mph or so, and it broke at 18 mph. For sure not at the shift, for sure not right at the launch.

 

[81cutlass]

I agree with the 'how am I making enough power to shred axle stuff so easily' comment.

3 years ago I broke the spider in the stock gov lock and twisted a chyna 1350 slip yoke. Totally understand. Not quality parts
2 years ago I snapped the axle at the same track. Kinda surprising since they are 30 splines but stock axles are hard and brittle. I'll bite.
This year it absolutely grenaded the yukon diff.

The back story is I damn near had it fixed and back on the road.

I had the car pushed off the track and back to the pits area. I pulled up marketplace and found someone had a Moroso (eaton) posi on marketplace 30 mins away. I messaged them, asked if it was 28 or 30 spline, he said he counted 30. Dad and I pulled the diff and a pile of posi parts fell out.

If you can tell in this picture it literally split the damn case in half axially. It cracked through the center pin and expanded the case OD radially about 1/4". It broke the lock bolt in 3 pieces and bent the center pin.

I had the diff out in 20 mins and tried getting the gear off. I didn't want to come off. Turns out when the spider blew it made the case OD larger than the gear ID and I had to grind the OD of the case down to get the gear off. Worked on that for an hour and got the gear off after using 3 batteries in the cordless grinder. Wacked on it for 20 minutes alternating between the grinder, a hammer, and a file.

You can see me totally in my element thinking I have to get the thing fixed since I am 7 hours from home and there are no trailers left. Clean room for sure! I havn't looked at the gear yet, it might be totally hooped since I had it sitting on the asfault.

Got the thing apart, hopped in a car and drove to a walmart parking lot to buy this posi carrier from marketplace. Looked at it right away and knew it was wrong. It was a small bearing (pre 88) unit and probably 28 spline. I counted it 4 times and got a different number every time, sometimes 27 and sometimes 29 but never 30. I had dad count and he counted 30.

So I threw the towel in. No yards were open and nobody had any 30 spline carriers available at the short notice. Year 2 it's ended up on a trailer behind a white ford.

However the car is back home. Dad and I bummed a ride home in a supercharged trailblazer and a guy whos car didnt get done in time dropped the car off at my house tonight. Car is in the garage. Just need to decide what to do.


Few pictures from today. Track was open at 9am and rain came at 1130 and shut the event down. Half the crew didnt get runs in which kinda sucked. Track was like 55 degrees which would have made for a great run or two.

Event promotors new N/T car.

Cutlass flywheel failed Friday night.
Nova oil pan met a bridge on the drive Friday.

I literally cannot say how much I dig Randy's fbird. 540ish pontiac on nitrous. 8500 rpm, carbureted.

Watching him back a trailer into a motel parking lot at 9 oclock at night manual steering made me laugh. What lunatics do this? Haha!

Forgot the dual setup shot from the pair of birds. Red bird ate a valve or a plug tip friday.

Ed accidentally drove his turbo pontiac powered Triumph through metro Chicago from Great Lakes to Rockford. Drove by O'hare airport and was like 2 hrs late to the track Saturday.

 

[81cutlass]

So the Nova didn't run DW-end this year. It overheated on E85 and didn't want to run on Methanol for the 750 mile trip. He just got done doing a 25.3 cage in it and big block over the last 2 years. It will probably run next year.

He did run it like

last time it did DW-end he ran in the 8's. He clicked this pass off like 3 weeks later. It had a 8.50 tech at the time, obviously it needed more safety equipment....

 

[64nailhead]

The wheel hop issue ‘adds up’ .
What a bummer

 

[81cutlass]

Take all of this with a grain of salt please, I can't believe that you're putting this much wood (power) to break the same rear that the household Cutty (in my sig) can run mid 10's at 18 psi. It launches soft and hit's like a sledgehammer later. But gosh dangit, you've got the carnage to prove it. The Cutty has about the same rear as you have - Mosers 30 spline in a Yukon posi with 3.73's.

Damn, that (your) stick is tough on it!!

Be advised, the 14 bolt will eat 30-50hp and is stupid heavy.

I have been stewing it around a bit and the wheel hop in the burnout probably explains it, but I can't have a rear that is that fragile. If it can't take 2 seconds of wheel hop is it really that strong?

I ran 8 passes at the 1/8 mile track and it didn't blow up. 2 good 1.80ish 60ft
I ran 7 passes Friday and 2 were good 1.75 60ft
Broke 1st pass on Saturday

Literally this carrier has maybe 2000 street miles and 4 semi OK launches. It's obviously not fatigue related.

I agree I am not at the power level that I am not making the power level that it should have broken. Did it break from the burnout? I don't know. Would it have broken with an auto? I don't think having the manual had any effect on the random wheel hop in the burnout.

There are 2 camps
1. Put a 9" in it!
2. That really shouldn't have broken with the parts in it

The 14 bolt I am speaking about is the semi float 9.5" version. I don't think they are that much worse than the 9" or any normal 8.5 but could be wrong. Are you thinking of the 2500/3500 HD full floater version? I am not overly familiar with the rear TBH. I'm sure it takes some more power to spin and more weight than a 8.5", but a 9" is notoriously inefficient and an iron case isn't light either. I agree a full float is a tank. Again, I've never worked with one so I could be off base.

The 9.5 semi float version I would use likely would have the axles shafts cut off (or down) and replaced in some extent with some 7.5 or 8.5 tubes.

 

[81cutlass]

Well the 14 bolt build, or something more 'HD' is actually looking likely. I need to call on some stuff and make sure a moser/dutchmen 33 spline axle for a 9" fits in a 14 bolt carrier. It should. I have an interested party in the wagon as a roller with a good rear and if I can fund the 14 bolt by selling the 8.5", I'll see what I end up with.

Edit.

The 6 lug gmt400 series 9.5SF 14 bolt seems cheap but factory posi is gov bomb.

I can get a 9.5SF 14 bolt out of a TBSS for $400 and it has good posi but its 4.10. Not sure I want 4.10's in my car, since it goes through the traps at a good RPM as is, but looing at the calculators it's not terrible.

The TBSS rear has the 'light' duty tubes so thats a bonus too. Just cut the brackets off, weld on those moser ends and LCA brackets and make a new UCA plate and hopefully i'm good to go?