What my truck lacks in low end it makes up for it at the opposite end, at this speed the truck was solid, no shaking, vibrations or wandering or heating problems and the air conditioner was on.

3 speed A-727 transmission.
3.07 gears.
Michellin tires.
Ram-Air.

I was only using less than 1/2 of the throttle at this speed
I had it here for about 7 or 8 minuets until I slowed down slower than the flow of traffic.

Although it was quiet inside I am sure it wasn't outside.

Can anyone spot where I have been?

I have extra think padding in my truck, I installed an aluminum spacer under my throttle pedal to ensure full travel.



How much HP does it take to push our trucks to 90 MPH?

I would like to see our trucks in a wind tunnel.

Jim

 

I am jealous. With my 4.10 gearing, stock tires and 5 speed I would be past our engine redline at 90 mph!

 

Another thought I had was timing. Is it possible that at those RPMs he's past the timing advance capabilities?

Perhaps a timing bump would restore some top end power, though I wouldn't get into it that far until I did all throttle mods to make sure I was getting full travel.

Anything you can do that's free should be tried first, especially if it can be returned back to stock if you don't like it.

 

hey-Hey!!!,
Just to be clear, all the manuals except the G56 have the same .73:1 top gear. Next one down is also the same at 1:1( this includes the NV5600 ).

I've driven 3.54:1 manuals and still think they spin the motor too fast with 235/85 tires. My 1990 came with 4.10's in the rear axle and it was pure torture getting it home. Now sporting 3.07 axle and it eats miles comfortably. If I have to two, I still have the bottom 5 gears...
cheers,
Douglas

 

wow, 90 MpH. I'm jealous. Just checked and adjusted the throttle cable a bit, not really much play there and verified full throttle pedal travel again, the only thing i noticed is a little bit of play in the piece where the end of the throttle cable attaches, i can move the throttle cable about 1/8-1/16" inch before the actuall assembly moves, then no extra play, with the throttle pedal on the floor, the piece that the throttle cable attaches to has no play in it when i try to move it by hand.

Another thing i think i should point out, I don't have a MpH number, but when i "hit the red line" in any other gear, its very smooth.

I can go as fast as the truck will let me with the throttle floored in 2nd, 3rd, 4th gear and the truck gets loud, but sounds "right", its only in fifth gear that im having this issue.

Can i assume that this prevents the problem from being "low fuel pressure or timing related"? wouldnt either of those issues cause the same problem, at the same rpm/engine load, in the lower gears?

 

I thought a 3200 rpm spring would fix your problem because it seems like your not getting enough top end fuel, but that is really weird that it is different at WOT in different gears. I can't see how the transmission would have an effect on it at all, unless it was the wind resistance at that speed holding you back, but we all know that with these engines that's not a problem.

On a slightly related note, what are the long term effects of driving at high rpm like this? I would really like my truck to last just about forever (or until they stop selling diesel) and I feel like when I rev it past 2000 that I'm putting undue wear on the parts.

 

You are these motors are not meant to scream like a gasser. Although I can't see 2000 rpm's hurting anything to much dads 90 would only do 120/kph to the floor at 2500rpm's so it saw atleast 2000 most of the time n same with his second gen. Swap gears you wallet will thank you at the pump and your truck in the end will thank you.

 

You guys have me convinced I should go with gears either way, even if i am having a fuel issue, just to keep wear down on the engine and increase fuel mileage, I almost never tow now and I'd like to increase reliability as much as possible.


Thanks for all the advice, I'll post back with what happens after the gears are installed.

Now to tackle some interior issues I've been wanting to take care of on my truck for a while, in another thread....

 

I have 4.10's and a 47rh lock up trans. I also have about a 33 inch tire and cruising at 70 my rpms are about 2050. I just filled up today and got 18.7 mpg's. Hope it works out for you.

 

I wish you lived closer, Id trade ya a set of 3.5 for that 4.1.

My first and only truck with 4.1 wouldnt go any faster than 85 mph.....that was all there was. I believe its the gearing as well. Go with a 3.07 set if you can find one.

 

A thought on the RPMs causing wear, these engines come on gensets and pumps which spend thousands of hours on their governers. I wouldn't be too worried about a couple minutes/hours of highway driving a day.

Since you've decided to swap rears now, I think 3.54s would be a great gear. I have 3.07s, and there's a funny spot around 45-55 where 4th is too high and 5th is too low.