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Moving the Top Speed Limiter

Husker_1911

By Husker_1911
in Engines & Drivetrain

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6_2LTZ Enthusiast

6_2LTZ

Posted
Posted

Every time this question comes around pandemonium erupts. I'm amazed that we got to the second page before being told to think about the children. For once I'd like a discussion on the real mechanics of why a speed limiter is in place. It took me way too long to find solid info one day so hopefully if I summarize what I found out maybe someone with actual knowledge can clarify it further. 

 

My understanding is the driveshaft is the weak point when it comes to top speed. The critical speed of the driveshaft occurs long before the truck tops out. (It's possible in trucks with a shorter drive shaft that air resistance could the critical factor in top speed.) A crew cab RWD truck is at a disadvantage due to having a longer drive shaft than the 4WD models. 

 

Here's a video of a straight cab standard box truck doing 120mph without issue. https://youtu.be/P32WCFcIzR4?t=141

Here's the driveshaft from that truck: https://www.dormanproducts.com/p-99708-946-306.aspx

Specs: Diameter 3.5", Length 67.71", Material: Steel, Thickness: .083"

 

Put those specs into this calculator here: http://www.wallaceracing.com/driveshaftspeed.php and you get ~5500rpm as the critical speed. 

 

A 6L80 ratio in fourth gear is 1.152, 3.08 rear end, I'll guess an 32" tire, and in the video the engine is turning at ~4500 rpm. 

Plug all that info here: https://www.dennysdriveshaft.com/potential_speed_calculator.html and we get a speed of 122mph. This confirm the tranmission gear. 

 

To calculate the driveshaft rpm take the engine rpm divided by the gear ratio. In this case 4500/1.152 = 3906 rpm. Under the calculated critical speed. 

 

To calculate the theoretical limit just multiple the critical RPM by the gear ratio to get engine rpm. In this 5500rpm is critical so multiplying it by the 4th gear will put us over the engine rpm limit. We'll use fifth gear instead. 5500*.852= 4686. Pop that in the calculator and we get 166mph with a 3.08 rear end. 

 

Based on researching the dorman site, it seems that there are many driveshaft combinations based on engine size, cab size, bed length, axle ratio, and drive type. The thickness can differ, material, and diameter for each model. Each truck will then have a slightly different critical speed based its' driveshaft. 

 

 

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Husker_1911 Enthusiast

Husker_1911

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2 hours ago, Grumpy Bear said:

:lol:  SS502 is unraveling me :lol:

 

A speed limit is no different than which side of the road to drive on. Here we've all decided to do so on the right side in this country.

 

Made a social contract with each other to abide by the rule of law for the sake of safety, promote order over chaos.

 

Once a law is broken you no longer have order and more importantly you no longer live in a predictable environment. If you break one which one can I count on you to not break? The list gets shorter each year. 

 

Not talking about OOOPS I looked down and was 5 over. I'm talking about I have a RIGHT to violate this contract while holding every other breathing thing on this planet to it. Case in point? Your child is run over and killed by a speeding driver. How vigorously would you like the law to prosecute the offence? Give them a pass? They have a right to?  Is that contract only in force when damage has been done? When a cop is looking? Even that hardly matters anymore. They are usually right in the middle of the pack.....

 

Speeding with intent is for the track. The argument that because I have broken the law is your ticket to do likewise is...???????? Well that would give me allot of power wouldn't it?

 

And Stan gets to it while I type.....He's had a figure on me awhile now :thumbs:

Wow...  with as much #%&ked up stuff going on in the country and you liken the very occasional triple digit pull (plenty of open spaces to do that for whatever reason either way I go...  west to The Boss’s family, up to the Dakotas to see mine) to a cardinal sin?  I really don’t know how to respond to that.  Maybe because I’m very jaded about social contracts.  Blame my day job, where I’ve really seen the worst this world has to offer and punching my time card means violating a commandment so Joe Snuffy can go home, for that.  I just asked about raising my speed limiter, got some good recommendations about mods to support that, and you get on a moral soapbox.  Oh...  were my daughter to get hit (despite situational awareness being a big part of how she’s being brought up...  because there’s worse things out there than bad drivers), I probably wouldn’t wait for the law.  I’d more than likely take a page or two out of Frank’s book.  Whatever.  You do you Chior Boy.  White Devils, Strike Hold, AATW.

Husker_1911 Enthusiast

Husker_1911

Posted
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Posted
2 hours ago, wforrest08 said:

I think I would look into a 2 piece drive shaft conversion long before I’d ever consider putting a 308 gear into the truck. (— THATS GOING THE WRONG WAY...  Maybe that’s just me? 

If that’s really a thing, I’d love to get a link to it.

Grumpy Bear Senior Enthusiast

Grumpy Bear

Posted
Posted
5 minutes ago, Husker_1911 said:

Wow...  with as much #%&ked up stuff going on in the country and you liken the very occasional triple digit pull (plenty of open spaces to do that for whatever reason either way I go...  west to The Boss’s family, up to the Dakotas to see mine) to a cardinal sin?  I really don’t know how to respond to that.  Maybe because I’m very jaded about social contracts.  Blame my day job, where I’ve really seen the worst this world has to offer and punching my time card means violating a commandment so Joe Snuffy can go home, for that.  I just asked about raising my speed limiter, got some good recommendations about mods to support that, and you get on a moral soapbox.  Oh...  were my daughter to get hit (despite situational awareness being a big part of how she’s being brought up...  because there’s worse things out there than bad drivers), I probably wouldn’t wait for the law.  I’d more than likely take a page or two out of Frank’s book.  Whatever.  You do you Chior Boy.  White Devils, Strike Hold, AATW.

Your thinking I didn't expect this? :lol:

 

 

Husker_1911 Enthusiast

Husker_1911

Posted
  • Author
Posted
12 minutes ago, 6_2LTZ said:

Every time this question comes around pandemonium erupts. I'm amazed that we got to the second page before being told to think about the children. For once I'd like a discussion on the real mechanics of why a speed limiter is in place. It took me way too long to find solid info one day so hopefully if I summarize what I found out maybe someone with actual knowledge can clarify it further. 

 

My understanding is the driveshaft is the weak point when it comes to top speed. The critical speed of the driveshaft occurs long before the truck tops out. (It's possible in trucks with a shorter drive shaft that air resistance could the critical factor in top speed.) A crew cab RWD truck is at a disadvantage due to having a longer drive shaft than the 4WD models. 

 

Here's a video of a straight cab standard box truck doing 120mph without issue. https://youtu.be/P32WCFcIzR4?t=141

Here's the driveshaft from that truck: https://www.dormanproducts.com/p-99708-946-306.aspx

Specs: Diameter 3.5", Length 67.71", Material: Steel, Thickness: .083"

 

Put those specs into this calculator here: http://www.wallaceracing.com/driveshaftspeed.php and you get ~5500rpm as the critical speed. 

 

A 6L80 ratio in fourth gear is 1.152, 3.08 rear end, I'll guess an 32" tire, and in the video the engine is turning at ~4500 rpm. 

Plug all that info here: https://www.dennysdriveshaft.com/potential_speed_calculator.html and we get a speed of 122mph. This confirm the tranmission gear. 

 

To calculate the driveshaft rpm take the engine rpm divided by the gear ratio. In this case 4500/1.152 = 3906 rpm. Under the calculated critical speed. 

 

Based on researching the dorman site, it seems that there are many driveshaft combinations based on engine size, cab size, bed length, axle ratio, and drive type. The thickness can differ, material, and diameter for each model. Each truck will then have a slightly different critical speed based its' driveshaft. 

 

 

Love it!  Just to be safe, I’m going to ask my local parts guy about the PPV drive shaft.  I don’t plan on going triple digits all that often, but I’d like to know I can just in case.

Husker_1911 Enthusiast

Husker_1911

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Posted
2 hours ago, SS502 said:

See! I told ya ?

So far...  not a fan...  in the community of Pew...  it wouldn’t take long for someone who really, really knows what their doing to swoop in and push a blow hard’s $@it in for brow beating a cherry over a question.  I get it.  Wanton speeding and reckless driving are bad.  Hell, it probably is known by the state of California to give you cancer.  With that...  assuming it doesn’t offend anyone’s sensibilities in here...  it’s time for a splash of Jack Daniel’s No. 7.

Husker_1911 Enthusiast

Husker_1911

Posted
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Posted
1 minute ago, 6_2LTZ said:

Unfortunately it seems like you have one of the longest possible driveshaft combinations with 2wd crew cab. Based on the critical speed calculations, it has a top speed of ~108mph. Which is the point where everyone fears their driveshaft will blow up.

 

Here's a video of a two piece drive shaft: https://www.youtube.com/watch?v=4k8Qa474I1U 

 

143.5” WB...  Crew Cab, 5’8” bed.  I think it’s number two in OAL behind the 6.5’ Bed Crew and 8’ Bed Double Cab.  Without a different driveshaft, I’d have Lew bump it up to 105 to be safe.  The two piece looks neat...  prior to this, I’d only thought it handy for big lifts.

Husker_1911 Enthusiast

Husker_1911

Posted
  • Author
Posted
23 minutes ago, Grumpy Bear said:

Your thinking I didn't expect this? :lol:

 

 

I’m sorry.  Who are you again?

Grumpy Bear Senior Enthusiast

Grumpy Bear

Posted
Posted
11 minutes ago, Husker_1911 said:

I’m sorry.  Who are you again?

Who am I? One of the 325,700,000  people you entered into this contract with when the state issued you a drivers license. You can leave this contract anytime you like by turning in your drivers license. Please feel free to do so. 

 

 

SS502 Senior Enthusiast

SS502

Posted
Posted

Well cheers and I just had a tad too...again for me 110 but I’d probably still look at upgrading my driveshaft ? and then bump it to 120...not saying ya gotta get there but it’s there.

JimCost2014 Senior Enthusiast

JimCost2014

Posted
Posted
4 hours ago, SS502 said:

Don’t be too confused although I still am...Grumpy is a unique individual and sometimes it takes reading a few of his replies to get where he is coming from lol. He has a lot to offer, just takes a decoder at times. I respect his inputs and have learned along the way...still I am officially CONFUSED LOL

I kind of wish we had thumbs up, or thumbs down for some of the statements on here, like Facebook does...

SS502 Senior Enthusiast

SS502

Posted
Posted
2 minutes ago, JimCost2014 said:

I kind of wish we had thumbs up, or thumbs down for some of the statements on here, like Facebook does...

I guess that’s a ? for me...but I did order the chrome hooks Jim ?

Husker_1911 Enthusiast

Husker_1911

Posted
  • Author
Posted
4 minutes ago, SS502 said:

Well cheers and I just had a tad too...again for me 110 but I’d probably still look at upgrading my driveshaft ? and then bump it to 120...not saying ya gotta get there but it’s there.

My gut is telling me to look into the Tahoe PPV shaft...  and thank you for understanding that I want the capability even if I don’t execute to it...  kinda like training with Wally World ball but carrying LE Grade JHP’s you pray never get used.

JimCost2014 Senior Enthusiast

JimCost2014

Posted
Posted
2 minutes ago, SS502 said:

I guess that’s a ? for me...but I did order the chrome hooks Jim ?

Good call, I will post picture of my tail gate handle when I get it washed again, but you have confused me with your thumbs down???? (Not too hard to do)

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