Best Mods to Get a CUCV to go 75mph?

[dubiousgarage]

I’m new to CUCV’s and square body’s but just picked up a non-running 1985 m1010 ambulance. Plan is to make an overland camper. After reading forums it sounds like it’s got a pretty low top speed with stock 6.2 engine, tire size, etc.

What’s best budget way to get it to comfortably go 70-75 mph on highway?


There seem to be a number of variables
1. tire size (but lift? Need to cut body?)
2. diff gearing?
3. transmission?

 

[chevymike]

Welcome to the M1010 club!

Tire size will help. No lift you can do 33" tires without issues (that's what I am running). If you can go up to a 35" tire (about a 2.5" lift needed) that will help more but will not get you to cruise comfortably at 70-75. You will need some type of overdrive as well, either an OD trans or a Gear Vendors OD (which is what I currently have).

Even with 33" tires and the GV OD, 65 is really the comfort level. I have run at 70 for a bit but above that, it's not comfortable and gets to be a little twitchier to drive. That air drag of the box and the fairly compliant rear springs with no sway bar makes a little less stable.

I have not tried the to regear and not sure I would want to as the 4.56 will be helpful offroad, given the engine is not a powerhouse by any means. 4.10's would be as low as I would even think of going.

M1010 = The Slow Life....

 

[porkysplace]

Welcome to the M1010 club!

Tire size will help. No lift you can do 33" tires without issues (that's what I am running). If you can go up to a 35" tire (about a 2.5" lift needed) that will help more but will not get you to cruise comfortably at 70-75. You will need some type of overdrive as well, either an OD trans or a Gear Vendors OD (which is what I currently have).

Even with 33" tires and the GV OD, 65 is really the comfort level. I have run at 70 for a bit but above that, it's not comfortable and gets to be a little twitchier to drive. That air drag of the box and the fairly compliant rear springs with no sway bar makes a little less stable.

I have not tried the to regear and not sure I would want to as the 4.56 will be helpful offroad, given the engine is not a powerhouse by any means. 4.10's would be as low as I would even think of going.

M1010 = The Slow Life....

I think 4:10's are still going to be screaming at 60-65 , 3:73's might get you 70 , but the gutless 6.2 might never get you there.

 

[chevymike]

I think 4:10's are still going to be screaming at 60-65 , 3:73's might get you 70 , but the gutless 6.2 might never get you there.

4.10 WITH an overdrive of some sort and larger tires. No way just regearing is going to do enough. Biggest key is an overdrive of some sorts.

 

[Tow4]

I’m new to CUCV’s and square body’s but just picked up a non-running 1985 m1010 ambulance. Plan is to make an overland camper. After reading forums it sounds like it’s got a pretty low top speed with stock 6.2 engine, tire size, etc.

What’s best budget way to get it to comfortably go 70-75 mph on highway?


There seem to be a number of variables
1. tire size (but lift? Need to cut body?)
2. diff gearing?
3. transmission?

Find a Chevy donor pickup and put the Duramax with axles and drive train under it. No way a brick with a 150 HP is going 75 mph.

 

[98G]

Just my opinion... but if cruising at 75mph is the goal, the cucv is not the tool to get you there.

With fairly extensive mods you can make it go 75, but not well. Just not the tool for the job...

And once you mod it to go 75 (poorly), you've then taken away its ability to do what it actually does well.

If I've absolutely got to have a pickup variant cucv, then 60ish mph is something I live with. If I absolutely have to cruise at 75mph, then a pickup variant cucv isn't something I'm considering.

 

[Keith_J]

The governed maximum speed of the engine is debated often..per the calibration on a DB2829-4520, the pump delivers maximum fuel of 48-52mm^3 at 3600 but still delivers 40mm^3 at 4000 RPM. At 4400 RPM, it should be nearly nothing @ 8mm^3.

Since this is the pump in my M1031, I can attest it will do 75 MPH. Noisy for sure but it isn't going to throw a rod. The engine is not very efficient above 3200 RPM, partly due to poor breathing but mostly because of heat loss around the precombustion cups.

If 70 MPH is your goal, it will require a top notch cooling system with an overdrive transmission and locking torque converter. And you will be at high fuel rate in a 1010 with the drag so expect 12 MPG at the most. Any grade will kick it out of OD and drop speed to 60.

 

[dubiousgarage]

“overdrive transmission and locking torque converter”

I’ve been reading about overdrive transmission conversions. It looks like a 700R4 is a reasonable possibility? Not to many modifications?

or other suggestions?

 

[chevymike]

“overdrive transmission and locking torque converter”

I’ve been reading about overdrive transmission conversions. It looks like a 700R4 is a reasonable possibility? Not to many modifications?

or other suggestions?

If built correctly, they can work well BUT before you go down that road, make sure you can track down a 700R4 TB cable bracket that is used on the 6.2L diesels. Without that rare bracket, you cannot hook up the TB cable correctly (it is not a kick down cable and is essential for a 700R4 to work correctly). Other option is a 4L80E which requires a stand alone aftermarket computer but doesn't need that bracket and it much stronger. Other option (which is what I ended up doing for the time being) is a Gear Vendors OD which bolts to the rear of the transfer case. It by far is the easiest to install, taking only a few hours and nothing has to be removed from the truck (i.e. trans and/or transfer case).

 

[Keith_J]

GV OD would work on a 1008 but 1010 and any towing application would lose considerable energy in torque converter slip.

Yes, the 4L80 requires electrical logic for full automation. It can be manual shifted via simple switches. With aftermarket controller, it is quite simple to get a modern shifting system.

 

[Skinny]

Best way to cruise at 75mph

I have an M1031 which is probably 3/4 of your weight/drag. I'm able to cruise on 35s with AC on no problem but that's near sea level, not concerned about fuel economy, and certainly not passing anyone without strategic planning.

The key is a 4L80...first step in the right direction.

It sounds like you probably won't be happy with a freighted M1010 trying to keep up with traffic. Duramax is a great option if you have the money and want to stay diesel. LS is probably the cheapest way to solve your problems. 8.1 will be slightly more than an LS and will do everything without breaking a sweat.

You need more power and more gears whether that is a newer truck or a newer drive line swapped into your CUCV.

 

[ssdvc]

I have taken some pretty long excursions with my M1009. 65mph seems like a sweet spot for the truck for the best mpg and I can do short sprints to 70/75 to pass slower traffic (which is on very rare occasions) easily enough. But I aways keep in mind that she is a heavy truck, with a short wheelbase and no ABS (or airbags for that matter). All that combined makes for not the best situation at higher speeds in a panic stop, or emergency maneuvers around or to avoid stupid people on the road. Just sayin.

 

[chevymike]

I have taken some pretty long excursions with my M1009. 65mph seems like a sweet spot for the truck for the best mpg and I can do short sprints to 70/75 to pass slower traffic (which is on very rare occasions) easily enough. But I aways keep in mind that she is a heavy truck, with a short wheelbase and no ABS (or airbags for that matter). All that combined makes for not the best situation at higher speeds in a panic stop, or emergency maneuvers around or to avoid stupid people on the road. Just sayin.

Keep in mind the M1009 is NOT using 4.56 gears like the M1008/M1010. M1009 use 3.08 gears and do not suffer the same limited top speed that the others do. In stock form, the 1008/1010 at red line will hit 65mph. 55mph is about 2700 rpms. Red line is 3400.

 

[dubiousgarage]

If built correctly, they can work well BUT before you go down that road, make sure you can track down a 700R4 TB cable bracket that is used on the 6.2L diesels. Without that rare bracket, you cannot hook up the TB cable correctly (it is not a kick down cable and is essential for a 700R4 to work correctly). Other option is a 4L80E which requires a stand alone aftermarket computer but doesn't need that bracket and it much stronger. Other option (which is what I ended up doing for the time being) is a Gear Vendors OD which bolts to the rear of the transfer case. It by far is the easiest to install, taking only a few hours and nothing has to be removed from the truck (i.e. trans and/or transfer case).

Ah thanks, I now see the benefits of gear vendor overdrive — installation time. I was confused because for cost it seems you could get a transmission with overdrive.

Im leaning in direction of a transmission. 700R4 needs bracket— got it— but with the advanced adapter it then needs no mods to transfer case or driveshafts. Is the 4L80 longer? Does it need spline adapter as well for np208? And then does it need shortened rear + lengthened front drive shafts?
(Thanks for all youre comments on this).

 

[Mainsail]

I think we're all forgetting something here....

Making the brick GO 75MPH is one part of the complete puzzle- it also needs to be stable and needs to be able to STOP from 75MPH without becoming a pile of smoke and grease. Any upgrades you do to the go-faster side of the coin need their equivalent on the freakin'-semi-truck-just-pulled-onto-the-highway-in-front-of-me-and-I-don't-have-anti-skid-brakes-we're-all-gonna-die! side as well.

 

[dubiousgarage]

Best way to cruise at 75mph

I have an M1031 which is probably 3/4 of your weight/drag. I'm able to cruise on 35s with AC on no problem but that's near sea level, not concerned about fuel economy, and certainly not passing anyone without strategic planning.

The key is a 4L80...first step in the right direction.
……

(I’m currently looking into transmission options 700r4 or 4l80 and required parts.)

Whats the lift to get 35’s on your M1010? X11.5? Did you need to cut the body? Or is there a corresponding required wheel (width and offset)?

It sounds like with 33’s no lift is required on a m1010 and no body cutting?

(Asking all this since my m1010 looks to be sitting low already with 235/85/R16’s that came in it and trying to reduce the number of mods here).

 

[Skinny]

You can fit 35s stock if you don't mind trimming the fender. The greatest gain is bumping the front axle forward but that will need crossover steering and maybe a new front driveshaft.

I wouldn't sweat the suspension and brakes. The brakes will send you through the front windshield at any speed. Have you seen the size of them?

Suspension may be stiff unladen but no worse then a new IFS truck with 2.75" of wheel travel. I have driven too many new trucks from Tacoma to one tons and they suck no less then an older rig. I'd venture to say that my lifted K30 rides better then a Taco. My GFs F150 rides silky smooth but the frame shudders just like everything else. So don't get caught up in new vs. old tech. It's all relative.

 

[ssdvc]

Keep in mind the M1009 is NOT using 4.56 gears like the M1008/M1010. M1009 use 3.08 gears and do not suffer the same limited top speed that the others do. In stock form, the 1008/1010 at red line will hit 65mph. 55mph is about 2700 rpms. Red line is 3400.

I understand the differences in the models. However, my point was how safe will the vehicle be ,traveling at over 75mph? With antiquated brakes, steering and suspension, I am guessing, IMHO, not very safe at all. But hey, the OP can do whatever he wants.

 

[Skinny]

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.

 

[Keith_J]

The injection pump in my 1031 is the DB2829-4520, calibrated for 48-52 mm^3 (microliters) per stroke up to 3600 RPM. It still delivers 40 mm^3 @ 4000 RPM.
The problem is the engine breathing above 3600 RPM. Which means higher EGT and decreased thermal efficiency.

Earlier pumps have similar delivery curves, the internal parts slightly differ like flex ring drive on weight basket, inlet strainer and delivery valve.
Yes, economy drops greatly above 2800 RPM without forced induction. Which is why OD transmission is key to going 70 MPH.