Spent the day at Transgo and the discussion came up of what we are putting our trucks thrugh. The Ally components are rated at a max of 5K rpm. Some of you big boys are pushing much more than that internally. Watch out. Find a good blanket. The components in the Ally are much bigger and heavier than most transmissions. A blow-up could be devastating to the driver.


mike

I'll find out I'm going to be turnen my 8.1 close to 6k if I ever get done.http://www.dieselplace.com/forum/smileys/Disapprove.gif

A common diameter tire of 33 inches and the Duramax gearing of 3.73 reaches 118mph at 3200RPM in 5th, and a hypothetical 186MPH at 5,000RPM.


Someone would have to manually shift it, or lock out overdrive to overrev the Allison with a Duramax. Perhaps people are doing this, but I don't see why.

Amric,


I think mike was addressing the fellas that play at the track. There are quite a few that tip into the 4k + range. I think that most of them are only looking for an extra 500 RPM in 2nd and 3rd. However, they will go as high as possible in 4th through the trapps.





Mike, it is my understanding that the Ally is good for about 4,500 RPM of applied force and right close to 5,000 RPM of retarding force. Please correct me if I'm wrong.





Burner------------> http://www.dieselplace.com/forum/smileys/Big Smile.gif

Lock out overdrive and you can go through the traps at 110MPH at 4180RPM.


I still think any more RPM would be a waste even at the track. The extra 500RPM could help at the track, but much more than that would probably show the HP dropping off much faster than the gearing could make up for.

On a stock Duramax, it appears to make peak HP right up to redline, and when the trans shifts, you drop to a lower part of the curve. You normally shift about 500 rpm past the point where the power starts to fall to get the best ET's. I'm willing to bet that if you did NOTHING to a stock Duramax except move the limiter up, it would go quicker. This is based just off stock dyno data. 250rwhp accelerates harder in 2nd gear than 250rwhp accelerates in 3rd gear, so even if the HP curve is flat, it is better to spin it.


If you could run a 1/4mi pass without using 5th, you'd go quicker. And if you are making peak power at 5000, you'd keep spinning it for the best ET's.

I wonder what the valve train is good for?? For all we know, the valves would probably float at 5k or before.http://www.dieselplace.com/forum/smileys/Ermm.gif Since the motor was never designed to go over 3200 or so, why build a killer vavle train when you could get away with much weaker spring if you keep the revs down. Could the engine even support combustion at that rpm without some type of catalyst?http://www.dieselplace.com/forum/smileys/Ermm.gif


Things that make you go Hmmm!!!http://www.dieselplace.com/forum/smileys/Approve.gif


Jason

The factory redline appears to be 4800 going by the tach. Look where the solid red starts. GM believes that the valvetrain is good at that RPM after the valve springs have 100,000mi on them.

Forced Induction, what exactly happens to the valves when they "float" at high RPM? What would be the real dammage to the valve train or pistions? http://www.dieselplace.com/forum/smileys/Confused.gif


Burner------------> http://www.dieselplace.com/forum/smileys/Big Smile.gif

Burner,


Hopefully nothing will happen. That is of course based on the assumption that the duramax is a Non-Interference engine which I believe it is. When the valves float it simply means that the springs can no longer control valve motion and the valve will basically stay open all the time because the spring is not strong enough to close it before the lobe comes around again. Since the valve is now open throughout the compression stroke it is usually not good when the piston comes up to see him.


Jason

In a gasser valve float will keep it from spinning much higher under load, a poor mans rev limiterhttp://www.dieselplace.com/forum/smileys/Dead.gif(not really cuz its hell on the motor and the valve springs will start to float sooner next time). Lifters are flying off the cam lobes and valves are staying open longer than they need. Some times you can get the pistons to kiss the valves in a tight tolerance motor but most factory motors dont.


On a turbo diesel......I think valve float could get ugly quickhttp://www.dieselplace.com/forum/smileys/Dead.gif

Who is spinning the motor above 4500 rpm at the track? http://www.dieselplace.com/forum/smileys/Confused.gif I only go up to 3500 if the converter isn't locked on the street or strip. I've held it in 4th gear up to 4000rpm (it pulls hard up to 4K too but I let off since 100+ mph on the street attracts the blue lights) and I've seen 4000 rpm in 3rd gear low range truck pulling but that's about it.

4K rpm at the motor (same as input shaft) in 5th gear puts output shaft speed at 5440. Can you imagine rear planet letting letting loose at that rpm?


mike

4K in 5th gear 148 mph with a 33" tire. If I'm trapping at that speed I'll be more worried about stopping this beast than anything elsehttp://www.dieselplace.com/forum/smileys/Big Smile.gif Thank's for the heads up Mike

Edited by: mtomac

I wonder if they set up the Ally for "stupid mistakes".... like, trying to engauge the Tow Haul button and locking out 5th at 95 MPH? er, that is having the speed limmiter envoked.





Burner--------------> http://www.dieselplace.com/forum/smileys/Big Smile.gif

what Mike L is saying is true, and the calculation most of you are forgetting is the trans does not always spin at 1:1 ratio. The gear sets are overdriven in 5th, so 3000rpm going in is going out at more, say 4000. If you have ever held any of these internal parts in your hand, I can bet ya you wont want to see them come up through the floor...

I thought the Allison RPM limit was rated at the input shaft not the output shaft. And the weight should not matter if the balancing is correct. Just look at a 500 big block crankshaft that is spinning at 9000RPM+ in Top Fuel, or even 8000RPM for a few old 427 street cars I used to play with. I have the Allison manuals at home, but I'm at work now. Can someone confirm or deny that the RPM rating is for the input shaft? Edited by: Amric

The Ally is rated at the ouput shaft. They say 5K, it might be a little conservative but a big block reving 6K or better could be in trouble.


mike

4600 rpm is Max input speed ..... Final gear Ratio is 0.71:1 ....


While I'm looking thru the specs ...


If you've ever seen the Parking Paw in a Allison you'd eye pop ....


It will withstand a 2.5 MPH Impact .... Engagement speed 1-3 MPH during deceleration ... Vehicle will roll a Max 5.91 inches on a 10 Percent grade ...





Mac





Edited by: Mackin

Yall wanna know what over reving the engine will do to valve train, Ask peenut he's been therehttp://www.dieselplace.com/forum/smileys/Cry.gif


Geno

4600 rpm is Max input speed ..... Final gear Ratio is 0.71:1 ....





I also found this in the specs. 4600 input is equal to 6500 rpm on the output shaft. It also fits more in line with the RPM limit of the 8100.

I was trying to change the subject to parking paw ... Wasn't looking to mix it up .... http://www.dieselplace.com/forum/smileys/HiHi.gif


Mac

Amric


Allison puts a limit on their transmission. They do not specify what engine goes in front of it. 6500 rpm out put shaft speed would worry me. I posted this info to try and help the guys here. Take it for what it's worth. Believe it, or don't.

Not trying to cause any trouble. Personally, my Allison has never seen more than 3200rpm, as I'm not that concerned with squeeking out that last 1/10 sec. I have great respect for your knowledge of the Allison, and I also know you are looking out for all of us.

So max imput speed is 3550 in OD? According to a .71 OD and a max 5k input???


A smaller trany or clutch set up coming apart will take off limbs or kill ya depending on were it hits, an Allison blowing up would probably resemeble a bomb going off under the truck.http://www.dieselplace.com/forum/smileys/Dead.gif

Max Full Load Gov Input speed is 4600 RPM





***Edit- Armic I read your post wrong. According to my calculations based on the ratio mike was using your max input to keep the max output under 5k would be 3675Edited by: Max Power

Max Full Load Gov Input speed is 4600 RPM


Tony


Figure out what that output speed would be with 245 tires in 5th.http://www.dieselplace.com/forum/smileys/Ermm.gif


mike

Well the output speed of the trans would be the same no matter what size your tires are.http://www.dieselplace.com/forum/smileys/Embarrased.gif


Edited by: Max Power

I get under 3550http://www.dieselplace.com/forum/smileys/Confused.gif Am i needing some help with my math? http://www.dieselplace.com/forum/smileys/Embarrased.gif

dmaxalliTech explains why here:


what Mike L is saying is true, and the calculation most of you are forgetting is the trans does not always spin at 1:1 ratio. The gear sets are overdriven in 5th, so 3000rpm going in is going out at more, say 4000. If you have ever held any of these internal parts in your hand, I can bet ya you wont want to see them come up through the floor...


I used the same ratio as Mike L. which I rounded off to .735

I used .71, that would be the reason.

You guys are starting to scare me I just got my new cam specs its going to pull to 6200rpm. Most of you are talking about OD and I plan on still being in drive at the end of the 1/4 mile.

You guys are starting to scare me I just got my new cam specs its going to pull to 6200rpm. Most of you are talking about OD and I plan on still being in drive at the end of the 1/4 mile.


Don't see how that is possible. Duramax will be in 5th gear converter locked at eigth mile. It will pull last half in fifth with converter locked.


mike

he probably has the gas motor with allison trans.

I think you must be mistaken Mike, Steve Cole told me if the input speed went over 4100 rpm the transmission would immediately come apart.

4K in 5th gear 148 mph with a 33" tire. If I'm trapping at that speed I'll be more worried about stopping this beast than anything elsehttp://www.dieselplace.com/forum/smileys/Big Smile.gif Thank's for the heads up Mike




Hey Mike, I've had a lot of practice packing chutes from my altered days, so I could help u out packing your chute or chutes http://www.dieselplace.com/forum/smileys/HiHi.gif


Too bad I don't have any of mine left or I could rig u one up for the reese tube, that would be a sight at the end of the track http://www.dieselplace.com/forum/smileys/Cool.gif

Yep I've got an 8.1l and I will be raising some eyebrows with my new engine. With the cam I have now I'd shift at 5000rpm and still be in drive win crossing the finish line at 105mph. I think staying out of 5th was one of the reasons that my Alli gave me a very few problems that and my lack of TQ compared to a D-MAX.

Tierod, are u going to spray the same amount of NOS?


A new engine to pick up 4 mph doesn't sound to good.

Tierod, are u going to spray the same amount of NOS?


A new engine to pick up 4 mph doesn't sound to good.





No I am going to put more to it 250hp. On the 12.95 pass my bottle ran out on top end it was the first time in about 10 passes the truck hooked up. It cut a 1.70 60ft instead of 2.00 that it had been getting. Thus my lower MPH. Never thought I'd have problems getting off of the line in a 4x4.LOL


New engine is going to be pushing 600hp all motorhttp://www.dieselplace.com/forum/smileys/Evil Smile.gif