Gear change?

[Wes Harden]

Thinking online here, and putting the numbers in one place.

So truck finally drove to Apple Valley over Cajon pass w/o stumbling, hesitation, or sputters.
I didn't like was the lack of power. 50 to 55 mph on the steeper sections, in 3rd floored. Not towing.
Motor .030 flat top balanced 350. Mild cam good vacuum. 260* 4.7" lift at valve. Qjet single 3" exhuast flowmaster series 80. 700r4 trans np205.
Current 285 75r 16 on 6.5" wide steel wheels, maybe 8" in near future.
The bottom of the torque curve seems to be 2250 rpm.
4.10 ring and pinion.
Currently
65 mph 4th @1900 rpm
3rd @2900 locked up, @3150
75 mph 4th @2200
3th @3130 locked up,
4.56
65 mph 4th @2100
3th @ locked up 3000
75 mph 4th @2440
3th @ locked up 3480
4.88
65 mph 4th @2260
3rd @ locked up 3230
75 mph 4th @2600
3rd @ locked up 3730

 

[fordsucks!]

I haven't taken my blazer up Cajon pass yet, but I hope I would be doing 50 - 55 in the steep sections. Our transmissions were geared for a federal speed limit of 55, and you're pushing a carbureted full size chevy up cajon pass. Hell, I have a 2000 Pathfinder that barely does 65 up Cajon Pass.

That's just my two cents, I could be wrong. but I think you would need a motor swap to speed up Cajon Pass in any 1980s truck

 

[Wes Harden]

Don't think motor swap is not on my list. An 8.1l keeps coming to mind.
Gotta save some and look for the right donor.

 

[Jimmy85]

4.10 gears with 285/75/16 should be a deep enough ratio. I run 4.10s with 35s and am generally happy. But I also don't know anything about cajon pass.

 

[Wes Harden]

Thanks @Jimmy85 this setup is growing on me. Made a couple fine tune adjustments. Seems I had to much timing. Timing marks must be off. May adust timing down one more time before heading home. I heard it ping alitte while pulling the boat trailer up launch ramp, this morning.

 

[Wes Harden]

I decided to swap to 4.88. I think I got the correct ring gear for my 14 bolt. I have 4.10 now. The split chart says 4.10 and down, which I take to mean lower number ie 3.73. So I think to use my 4.10 and down carrier I need thick 4.88 ring gear, which I purchased.
So am I correct or do I need to reg ring gear?

 

[sweetk30]

4.10-3.73 = thin gear .

your 4.88 thick cut = fit just fine .

 

[yblow]

Not sure how your carb is tuned but do you think the elevation had anything to do with it?

 

[Wes Harden]

not saying elevation doesn't effect power, but the drive ability issue I'm chasing seems to be power band related to low of rpm to accelerate under light load or grade in 4th.

Since 1st post I towed my Manx buggy on single axle trailer from Apple Valley, 2900 elev, to Big bear 7000+ elev. I was in 2nd and 3rd for the climb prob @7 miles for elevation gain. Power was good in those gears, 25 to 40 mph. Trans temp was high need to figure that out, gear change may help with temp a little.

 

[imiceman44]

4.10 gears with 285/75/16 should be a deep enough ratio. I run 4.10s with 35s and am generally happy. But I also don't know anything about cajon pass.

4.10 is adequate for 285/75/16 with a 350, but to go up Cajon pass towing it will struggle.
It's what I have in my suburban and I am ok with it because I rarely tow, and I even more rarely tow up big hills like that.
If I was I definitely would regear.

 

[sweetk30]

i have been doing a lot of intown hauling the last few weeks with a dump insert in my k30 and a small single axle dump trailer behind me . i have a good amount of weight on and the 4.10 gears and 255/85/16 tires skinny 33" do o.k.

but i wish my one truck was done with the 5.13 gears so i could try it out with these loads . i know it would be a trailer pulling monster .

 

[Wes Harden]

Around town towing in 2nd and 3rd is acceptable, pulling boat out easy with 3.0 1st. I want to be able to maintain 55 60 on minor grade in 4th. My motor just doesn't have the HP at 1500 rpms. 700r4

 

[imiceman44]

Around town towing in 2nd and 3rd is acceptable, pulling boat out easy with 3.0 1st. I want to be able to maintain 55 60 on minor grade in 4th. My motor just doesn't have the HP at 1500 rpms. 700r4

Exactly, it's the highway grades that are the problem so around town and on flat people feel it's ok.
I even have no problem with it because I tow mostly 10-25 miles, a few times a year and maybe once every 3 years go out of state or to socal.
I would be more concerned if the long trips were more often.