Advice for better highway travel

[planecycle]

1979 K10 SWB with 350 power through SM465 / NP205 to 3.73 gears running 235/75R15 tires.

I'm currently driving a lot of freeway with 75mph speed limits which equals ~3300rpm. During the summer I tend to pull more weight both in hauling camping gear and more people w/ an occasional trailer but I'm realistic with 1/2 ton loads and limits and don't push it too hard. During the winter I normally only haul myself.

Up for consideration is changing gears from 3.73 down to 3.08s which should get my RPM down to ~2650. OR, I consider a transmission swap to one with overdrive. I just completed a CAM swap to a CompCAMs RV model 206 http://www.summitracing.com/parts/CCA-K12-206-2 and feel pretty confident in my mechanical skills. Honestly I'm certain I could swap a transmission physically but I don't know enough yet about driveline or mount changes required. The gear swaps I know very little about at this time - just starting my research.

From forum experience, which route would you guys take with your own rides if you found yourself in this situation? From what I've researched a lot of advice tends to be to install bigger tires or do complete axle swaps to Dana 60... should I just go this route and not over-think it?

Thank you in advance!

[Irish_Alley]

i would go with lower ratio. you prob dont use the granny gear so its just sitting there. if you go to 308 you still shouldnt have to use it but you can still use it if you need.

[planecycle]

You're right about not using the granny gear. I only occasionally use it when I'm trying to finesse my way through a grass parking lot with tons of kids running around (summer concerts, yay) or when starting to pull another vehicle, etc.

[rich weyand]

That's only a 28.8" tire.  You could get another set of rims and run 33x10.5R15, which is a 32.7" tire.  28.8/32.7 is .88, so it would get your rpms at 70 down to 2900.  That's about the biggest you can go for tires on a '79 K10, but they would look good.

Tires, overdrive, axle ratio all would change feet traveled per engine rotation.  All of these methods will also make your speedometer inaccurate, so you might want to think through your speedo ratio and what adapter you need to change to (there is an adapter on your transfer case already).  Some ratios are more available than others.

BTW, are you sure that is an NP203 on the SM465, and not an NP205?  Was the truck converted from auto to stick at some point?

[planecycle]

Hey Rich, I've been cruising through a TON of your timing related posts today across all sorts of forums to help me dial in my Ford Bronco 2 that I just Durasparked.  Regarding my K10 - I'm not absolutely certain about the NP203, but I did some homework a few months back and I emailed myself links about the NP203 showing the shift pattern of [Fwd = 4L, then Neutral, 2H, and Rear = 4H]. Also I have manual spicer hubs up front.

Also, I just found a set of tires on wheels as you suggested for $250 right here in my backyard. I'll go get them tonight and put them on. I measured my bolt pattern to be 6 x 5" and I'm hoping the new wheels bolt right on as they look nicer than my stock steels with hubcaps... If not I'll just swap the tires out and sell off the 235s for some savings.

I have a camp trip tomorrow to test them for rub, etc. then a road trip to Williston, ND on Sunday with the truck. I sure look forward to better RPM range for this trip over the noise and abuse of the last two trips (Seattle to Bozeman and Bozeman to Williston and back). The difference was the last two trips had a junk cam (only 4 flat lobes AND a lifter laying under the intake for 5 total failed valves!!). This trip includes the last 400 miles of cam break in so I want to take it a little easy on the motor if possible.

[Irish_Alley]

203 shift pattern
4Low lock
4Low
N
4High
4High lock

205 shift

4Low
N
2High
4High

[rich weyand]

Yeah, that sounds like the NP205.  Not an NP203, not without 2WD LO.

33x12.5R15 on 15x10 rims will rub a bit at the steering extreme when going up a driveway or something.  33x10.5R15 on 15x8 rims shouldn't rub at all.

[planecycle]

Yep you're absolutely right about the NP205. I just looked at the back of the transfer case and I have the tell-tail "3 bolt cover" on the back that I just read about.

[planecycle]

Good advice fellas. Last night I purchased a used set of 33x10.5R15s tires already mounted on steel rims for $260 and an 18 pack of PBR. Mounted them up today and took the truck for a test run with dual GPS setup and I show 66mph indicated as 75mph even and now I'm running at only ~2950rpm on flat pavement. The perceive a faster acceleration especially when I get into peak torque range. I'm much happier now than before.

The only iffy part of the whole process was that each of these wheels has a wheel weight on the inside. The steering knuckles have about 1/8" clearance from the lead which makes me a touch nervous. My thoughts on letting it go this way were that if a weight started to come off the wheel, it would definitely get a solid whack from the knuckle on the next go-round and being lead would give way to the knuckle without permanent damage. And, well... if I'm wrong I get to change a knuckle out too.

I took before and after measurements for ride height as I was curious how much higher my dog would have to jump to get onto the tail gate. Turns out its a solid 2" at every corner. She's not old enough yet to know the difference but she'll be there before long.

Anyhow, thanks again guys!

[rich weyand]

If you look-see what ratio adapter is between the NP205 and the speedo cable on the tail of the NP205, you can calculate what ratio adapter you need to replace it with to get the speed back to reading right.  Some are cheap, some not so much.  Depends on what ratio you need.

[roundhouse]

A NV-3500 5 speed a 97-2007 Silverado should be a bolt in if your 205 has the circle 6 bolt pattern from the Trans adapter


Sent from my iPhone using Tapatalk