BUILD THREAD 86 GP 2+2~Blown 6.0

81cutlass

Comic Book Super Hero
Feb 16, 2009
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Cool info!

By that logic a 31 spline is 21% stronger than a 30 spline simply from size. Moser/strange claims the 1541H axles are something like 20% stronger than stock. I havnt seen claims for 4340 over stock. So basically good aftermarket 30 spline=stock 31 spline

Stock axles are 1050
Low grade aftermarket are 1541H
High grade aftermarket are 4340

The shear modulus for all steels is the same (80gigapascals or 120ish thousand PSI, also called KSI)

What you gain is that 1541 is more hardenable than 1050 and 4340 moreso than 1541.

Hmm, they claim 1541H is equal to 4340 in torsion, just that 1541 is induction hardened (uses an electric coil that moves over the part, think hard surface soft core) which is fast and cheap, done in an open air environment, vs 4340 which is likely carburized which is done in an oxygen depleted furnace that has "cracked" natural gas in the air so that the high amount of carbon from the gas diffuses into the outer surface
https://dutchmanaxles.com/axle-rearend-tech.html


That dutchman link claims 4340 has a higher yield strength with 4340 vs. 1541H (which is true), thus making it stronger, but my engineering degree says that doesnt matter and torsion is calculated with shear modulus (which is the same). I'd have to dust off my textbooks, it's been 4 years since i took that class. It seems like their link info is a bit inaccurate in that earlier it says 4340 is better in torsion (which formulas say no, I guess depending the effect of heat treat, but then 2 sentences later says they are the same if you do it right.


What I see is that even if I went with a 9", I better go with 35 splines since if I blew up a 30 spline, and stock 31 spines are only 20% better than stock 30, and good 31's are only 20% better than stock 31', Id be dumping 2 grand on shafts and a 9" axle that is at best 40% stronger than what I had which blew up without too much effort (assuming I didn't just have an axle that had poor material and was weaker than it should be)
 
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Streetbu

Know it all, that doesn't
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May 22, 2011
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As far as this car or that car that has X amount of hp and the rear end survived... One thing you forgot. Most people drive automatics which are MUCH more gentle on the rear end compared to a stick shift...
 
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MC96

Master Mechanic
Dec 7, 2015
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Unscientifically Im not sure you are at the 35 spline point yet, how hard can you shock the tires with a manual car? If youre at the 35 spline point with those hardened axles it might be time to run a pro gear as well, and get some more side wall into the car. Do they make 35 spline flanged axles? I was thinking they all might be floaters. I sold all this stuff for years but I am not a drag racer.

31 spline quick change axles can hold up to late models approaching 1000 HP, you might not think on dirt there is a lot of stress but most guys cant run gun drilled axles on the RR because they snap on tacky tracks.

Be careful with 35 spline stuff, 31 spline is no big deal because all the splines are cut to match how ford had them cut, but 35 is all aftermarket and certain companies use proprietary splines. They will all have the same major and minor diameter but there will be an interference between some axles and spools in the spline shape.

Isnt there 40 beyond that?
 

64nailhead

Goat Herder
Dec 1, 2014
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As far as this car or that car that has X amount of hp and the rear end survived... One thing you forgot. Most people drive automatics which are MUCH more gentle on the rear end compared to a stick shift...

This is a good point that I often overlook. I can't say it's wrong or right, but it could definitely be part of the issue though.


From looking at your axle pictures again, you can see the issue in the axle - that axle was a dud. It broke inside the side gear before the rest of it broke. For comparison only because we run an auto, we have the same 8.6 posi (Yukon) with a set of Moser 30 splines and run similar 60ft's, 1.8-1.95, and are just under 105 in the 1/8. I checked the diff 3 weeks ago - looks like I just put it together and the splines look the same as the day we installed them.

When you increased the timing what happened to the AFR or did you read the plugs? You mentioned people running 18 degrees on 18 psi with a 5.3 on E85, corn, whatever. I believe that is with a turbo, not a blower - apples and oranges IMO. I'd really like to have seen your plugs or know your AFR on that run with 13 degrees.

Keep the posts coming - love this thread :):)

ps - are you running a stock ecm?
 
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81cutlass

Comic Book Super Hero
Feb 16, 2009
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Unscientifically Im not sure you are at the 35 spline point yet, how hard can you shock the tires with a manual car? If youre at the 35 spline point with those hardened axles it might be time to run a pro gear as well, and get some more side wall into the car. Do they make 35 spline flanged axles? I was thinking they all might be floaters. I sold all this stuff for years but I am not a drag racer.

31 spline quick change axles can hold up to late models approaching 1000 HP, you might not think on dirt there is a lot of stress but most guys cant run gun drilled axles on the RR because they snap on tacky tracks.

Be careful with 35 spline stuff, 31 spline is no big deal because all the splines are cut to match how ford had them cut, but 35 is all aftermarket and certain companies use proprietary splines. They will all have the same major and minor diameter but there will be an interference between some axles and spools in the spline shape.

Isnt there 40 beyond that?

Yeah, I also doubt I am at 35 needs yet also. I agree that if I needed 35's I'd be past the point of the stock t56, past the point of being able to use anything but a 28 10.5/15 slick and pro gears. They do make 40's but they are often gun drilled and floater style. Yeah, moser/strange charges additional $$$ for 35's on flanged axles BUT I havnt seen a carrier for a 8.6 with over 30 spline.

The more I look at it the more I think good 30's should hold and that 31's aren't that much better than good 30's. Maybe I have a case of I already made my mind up and now finding data and reasons to support my position (just like everyone does with politics :p )
 
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81cutlass

Comic Book Super Hero
Feb 16, 2009
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This is a good point that I often overlook. I can't say it's wrong or right, but it could definitely be part of the issue though.


From looking at your axle pictures again, you can see the issue in the axle - that axle was a dud. It broke inside the side gear before the rest of it broke. For comparison only because we run an auto, we have the same 8.6 posi (Yukon) with a set of Moser 30 splines and run similar 60ft's, 1.8-1.95, and are just under 105 in the 1/8. I checked the diff 3 weeks ago - looks like I just put it together and the splines look the same as the day we installed them.

When you increased the timing what happened to the AFR or did you read the plugs? You mentioned people running 18 degrees on 18 psi with a 5.3 on E85, corn, whatever. I believe that is with a turbo, not a blower - apples and oranges IMO. I'd really like to have seen your plugs or know your AFR on that run with 13 degrees.

Keep the posts coming - love this thread :):)

ps - are you running a stock ecm?

I do agree with the stick vs. auto part. I just don't know how much more I need?

I don't disagree with that axle possibly being a dud. I just can't point for sure at that being the issue. It was definitely cracked inside the spider gear but I am not sure if that cracked and then caused the rest of the axle to fail or if it failed and then caused the axle to crack down that far because of internal stresses being released or stuff whacking around inside. The splines on about half of the diameter outside of the side gear were twisted so that does make sense, axle cracked, twisted axle at splines, added load and couldnt be supported. Just can't say for sure.

I didn't read the plugs or check the AFR thats why I am calling that pass a dud. My HPtuners didnt connect on that pass due to my laptop deciding to restart in the staging lanes. It could have gone way lean, way rich, I have no idea.

I am running the stock ECM. Its out of an 01ish sierra. It's segment swapped (non factory programs) to the extreme. I plugged a DBW throttle body part out of a denali in it, a camaro T56 trans section, eventually a tahoe engine side to get a flex fuel sensor, and of course the HPtuners speed density OS.

It's not perfect tuned, there are some dead rich spots when im accelerating in a goofy way or gear, but overall it's not bad. The car knocked down 17mpg on e85 which is REAL good. Thats like 24 on gas, which for a car that runs possibly deep into the 11's if I can launch the thing is great!
 
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81cutlass

Comic Book Super Hero
Feb 16, 2009
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Western MN
So I dug through my photos, you can see a hairline crack coming off the spline about 3 up facing downwards at about 5 o'clock.

The splines are visibly twisted and the crack goes all the way into the side gear area.


1538744018400.png

1538744094506.png


The case hardened material also flaked off around the area where the axle actually broke.
1538744124244.png
 

motorheadmike

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Nov 18, 2009
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Reason I was surprised it slowed down with more timing is many LS tuners say 10PSI and 10 degrees of timing is safe for boosted LS world and you wont blow up.

That has to be the worst bit of information circulating the internet today. Boost is just a measure of restriction, and other than contributing to excessive heat, it does nothing to factoring in air density/air mass; and setting arbitrary timing figures is very narrow-minded. What works for one combination will not work for another.

The same goes for equivalence ratios.
 
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TexasT

Master Mechanic
Mar 20, 2008
411
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Texas
<iframe width="320" height="30" src="https://realtuners.com/?powerpress_embed=1361-podcast&amp;powerpress_player=mediaelement-audio" frameborder="0" scrolling="no"></iframe>

Not real sure how to embed
This link and scroll down to the episode fifty. Might be old info to you vet tuners but I thought it quite interesting as a newby.
https://realtuners.com/realtuners-radio-episodes/
And down to episode 50. Tuning on idle and off idle stumble

Also is there more pix of that nifty wheel cutter you made. Was wondering how it adjusts, if the angle grinder moves around or the wheel is moved up or down. I saw where http://www.millertire.com/products/wheels/front-tractor-imp/blank/15x-6-rim/ has other hoops so maybe a 16 or 17" front skinny with a stock center might be possible.

Keep up the good work. As far as that axle it looks like it twisted before the break and no telling if it was twisted before you even put it in the car. The Bigger diameter 35 ans 40 spline axle wont fit into the housing as I understand it. That is why the gm stuff only goes to 30 spline. You need to go to something that can take the bigger diameter axle like the s60 or ford nine inch to be able to go to the bigger axles.
 
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