Best Mods to Get a CUCV to go 75mph?

[patracy]

I went from 31's to 35's. That helped a little on speed, but it slowed down a bit. I added a turbo. That helped put me back where I was. Then I went up to 37's. That allows me to run 60 now without too much drama. But it's still revving to high IMO. I've got a 4L80e in a donor truck I need to swap into it.

4.10's would be a compromise. But I'm not willing to give up the pulling power.

 

[Keith_J]

This is why I am doing the turbo before 4L80E transplant. It only adds 50 Hp but nearly 100 foot-pounds of torque.

Engine torque curves track volumetric efficiency curves. Adding a turbo only changes charge density, the volumetric efficiency remains the same. Power is based on mass flow rate.

 

[chevymike]

You can fit 35" tires without a lift but there is not much rear wheel travel before you hit the wheel wells. Here is 35" on Hummer H2 wheels and no lift. You can see the tire is already tucked up some.



Here is the rear with a 2.5" shackle flip, which gives you back full travel without too much extra height.



The front was still stock height and needed a 2" lift springs to get is more level but it cleared with just a minor fender trim. Never took it offroad but street driving, no issues.

Before



After



By comparison, this is 33" tires on stock suspension. No clearance issues.

 

[ssdvc]

What is antiquated in stock form? My old K5 would do 75/80 no prob.

Now lifted sure, the steering is squirrelly when you hit the brakes up or a bump but that's all fixable with money.

Both of my trucks even heavily modified will hammer down the left lane as fast as you want to burn the fuel. It's really not a problem.

There is nothing inherently wrong with a straight axle Chevy from keeping up with modern traffic. The engine and lack of gears is the only limiting factor.

RGR that Skinny. If you modify a few things, I agree you can run a higher speed with minimized concerns. I was just talking about a stock truck. I have done 75 (in short bursts) with my 09, but she is stock all the way. Precise road handling is just not there. I have to pay a lot more attention when at that speed in my truck.

 

[Skinny]

RGR that Skinny. If you modify a few things, I agree you can run a higher speed with minimized concerns. I was just talking about a stock truck. I have done 75 (in short bursts) with my 09, but she is stock all the way. Precise road handling is just not there. I have to pay a lot more attention when at that speed in my truck.

I will say two things really dial back the handling. Stock height and age springs. The clapped out reverse arch front springs at the age they are at suck.

The other huge one is stock push pull steering. I had it on my M1031 in stock form and lifted 4". It was God awful either way. If the truck bounced from a bump it would pull you in one direction.

If you hit the brakes hard it would always steer you into the ditch. Even worse with no sway bar or soft springs.

Crossover is like driving a sports car compared to push pull. Especially with a new tight steering box that gives you good assist. I can drive both trucks one finger down the highway at 80mph. It has zero bumpsteer and turns very sharp in parking lots.

I wish I did overdrive and crossover ten years ago.

If you are stock height I don't think it fits so it's a commitment for sure.

Do you get drive line vibes at that speed with the 09? I imagine the short rear driveshaft doesn't like that speed.

 

[Mainsail]

If you hit the brakes hard it would always steer you into the ditch.

Several years back I was commuting to the Bellevue area, and on my way back to the ferry terminal one evening I was in the left lane of I90 going with traffic, so about 65MPH. As I was approaching an onramp that feeds in from the left (idiot road designers) a car entering the freeway and the car on the freeway decided to play a game of You-go-no-you-go and they both pretty much stopped.

The weird part was that i was paying full attention, but the suddenness of the speed change occurred too quickly for me to react properly. So I went from humming along nicely to TOO-MUCH-SMASH! in about half a second. Like Elwood Blues; both feet on the wide pedal max effort braking.

I have to tell you, the noise and smoke the M1009 makes with all four wheels fully locked from 65MPH is as impressive as it is unforgettable.

The backs locked up first, then the left front, followed about one second later by the tardy right front. That put the truck into a leftward trajectory. I will point out that there was 100% no way the mighty CUCV Blazer was going to stop in time- even with the brakes fully locked I was still going to hit either or both of those vehicles at totaling speed. Roll the ambulances now, cause this is gonna be messy....

The leftward trajectory that resulted when the right front disk showed up late for the party, while unplanned and unanticipated, was in its own way beneficial. Even though I was sliding towards the soon-to-be piles of twisted metal, the nose of the truck was pointed towards a clear space between those cars and the left jersey barrier. All I needed to do was make the truck go in the direction it was pointed instead of the direction it seemed content to continue.

Having some experience with old fashioned do-what-you-tell-them-to-do brakes (no antiskid) I quickly released the pressure I was applying to the brake pedal, the wheels unlocked, and the truck shot through that opening still traveling about 45MPH, blowing by those two cars like they were standing still, which they pretty much were.

No worse for the wear.

 

[ssdvc]

I will say two things really dial back the handling. Stock height and age springs. The clapped out reverse arch front springs at the age they are at suck.

The other huge one is stock push pull steering. I had it on my M1031 in stock form and lifted 4". It was God awful either way. If the truck bounced from a bump it would pull you in one direction.

If you hit the brakes hard it would always steer you into the ditch. Even worse with no sway bar or soft springs.

Crossover is like driving a sports car compared to push pull. Especially with a new tight steering box that gives you good assist. I can drive both trucks one finger down the highway at 80mph. It has zero bumpsteer and turns very sharp in parking lots.

I wish I did overdrive and crossover ten years ago.

If you are stock height I don't think it fits so it's a commitment for sure.

Do you get drive line vibes at that speed with the 09? I imagine the short rear driveshaft doesn't like that speed.

Actually, no vibrations at all when traveling 65 to 70 and even at the occasional 75mph. When I first got the truck, she wanted to wander quite a bit when on the highway. I replaced the drag link and now she goes where pointed, for the most part. When everything is functioning correctly, I have found my truck to be very solid, tight and vibration free. I have a friend of ours coming over and doing the rear main seal and the transmission rear output seal on the 7th. Once that is done and with the newer Vacuum Regulator for the trans in place (thanks Skinny !!) I am hoping she will shifting as she should and running even better than before.

 

[Skinny]

That's pretty good. Imagining going over 55mph stock is funny because of the difference in gearing. I felt like the engine was going to explode with the 4.56s.

Not a problem! Hope it all works out. Don't push the back too far.

 

[ssdvc]

RGR. I am going to experiment with the regulator, starting in the middle of the adjustment and working from there. It will still be a few more weeks before I can get to it.

 

[dubiousgarage]

You can fit 35" tires without a lift but there is not much rear wheel travel before you hit the wheel wells. Here is 35" on Hummer H2 wheels and no lift. You can see the tire is already tucked up some.

View attachment 865833

Here is the rear with a 2.5" shackle flip, which gives you back full travel without too much extra height.

View attachment 865834

The front was still stock height and needed a 2" lift springs to get is more level but it cleared with just a minor fender trim. Never took it offroad but street driving, no issues.

Before

View attachment 865835

After

View attachment 865836

By comparison, this is 33" tires on stock suspension. No clearance issues.

View attachment 865837

Super helpful Mike. Great photos.

How wide were the 33’s? 11.5?
and the 35’s? 11.5 or 12.5?

I found some interesting new narrow tires oot
Kenda Klever
33x10.50R17LT 121R E
35x10.50R17LT 121R D

 

[chevymike]

Super helpful Mike. Great photos.

How wide were the 33’s? 11.5?
and the 35’s? 11.5 or 12.5?

I found some interesting new narrow tires oot
Kenda Klever
33x10.50R17LT 121R E
35x10.50R17LT 121R D

The 35" on the H2 wheels (17x8.5) were 12.5" (35x12.5-17)

The 33" ones are (wheels 16x7) 255/85-16. Then end up close to 10" wide. The equivalent in a 17" wheel will be 255/80-17.

 

[ballencd]

Chevymike, If I am reading this right, you have the 2.5" reverse shackle on the back of your rig or was that your old rig? How did you find the handling with it added? Also, did you put crossover steering on your M1010? How much did you have to lift the front to have it fit? How did you do that? Anyone that has an answer would be appreciated her. I am in the midst of trying to get this truck to do 70 - 75 when I need it to for getting on the highway mostly. Most of my driving will be 60 probably but I need to be able to get on the highway and possibly pass someone at some point. I am leaning toward a 4L60E transmission but if I could find a reliable builder for a 700R4 I would not be unhappy about that. I don't really want more lift but I do like what I read about the crossover steering being more precise and this brick at 60-70 needs to be a bit more precise.

 

[chevymike]

I did a 2.5" shackle flip on my old M1010 (camo colored one). I did not notice any change in handling or ride. I never got around to lifting the front, as I was going to do that after I built out the back and figure out where the end ride height was going to be. Sold the rig before I got to that point. I think to do crossover steering, you need 4" of lift. I have had mine up to 75 but really 70 is the max it really likes. Rig felt solid. If your steering, suspension and ball joints are all in good shape, I don't feel any need to go to crossover, unless you are lifting it 4"+

 

[ballencd]

I don't plan on lifting if I don't have to and crossover sounds like it requires a lift so that's probably out and my four wheeling is just access roads and some woods/fields with wet tracks. I just don't like to get stuck. Seems like somewhere I read on here that you can go to 35" tires on the front with minor fender trim. I wonder if the rear wheel wells could be expanded up a few inches and give me a bigger tire and a bit more speed without altering the suspension. I think the enlarged wheel wells could be hidden in cabinets/beds fairly easily.

 

[ballencd]

I just reviewed above and it was you who trimmed the front and fit a 35" tire. I'm running 33.5" on my suburban with just a slight alteration on the rear of the front fenders and have had no trouble. I may leave that for another day as I just put the 33" on my M1010. I probably should have researched before I put tires on it but tires I got on it were way too old to trust at more then about 10 mph. By-gones.

 

[chevymike]

Yeah, I was surprised the difference between my current 33" tires and my old M1010 with 35" tires. I never felt like I needed an OD in my old one, with the larger tires. I have wanted to stay away from lifting my current one, so 33" was my option but added the Gear Vendor to help.

 

[Bob H]

6.2 LS swap, they like RPM's
I see alot of people trying to get speed out of these CUCV's, could be worse,
My USAF Ambulance has 4.88 gears and weighs 7400 pounds with a 175hp gasser.