Chevy P20 Step Van-King Project

[Psyekl]

I'm new to the forum (see my post in the "welcome" thread) and after only one day of poking about I managed to identify my step van with fair confidence: VIN # PS328F------

P - Forward Control (cab over)
S - In-Line 6 Cylinder Gasoline Engine
3 - 1-Ton
2 - Chassis/cowl/bus
8 - Model year 1968
F - Assembly plant: Flint (I assume Michigan, not Texas)

Darned handy forum! My step van has a V8 in it, obviously it isn't unrealistic to think that it had an engine swap. I was told it was a 350 though I haven't verified it yet (I am aware that the P20 came with 2 available V8s in 1968).

I'm planning a rat-rod RV project and I plan to tow a small trailer. I need to upgrade the suspension and brakes, steering, engine and transmission. I have experience in a metal fabrication shop and have assisted in building a couple of race cars among several other interesting projects. I'm lucky enough to have a friend who is a fabricator, access to a metal shop as well my own wood shop and garage.

What I do need help with is the knowledge of people with more expertise with old Chevys and Chevy step vans than I have: I do not have a lot of experience with older vehicles and I certainly do not have any experience with industrial cargo vehicles. My searches have not turned up much to tell me what I need to know about where I can find parts for upgrading or what vehicles have parts that are interchangeable to use for upgrades. I can always pull entire suspension systems off of something modern in a junkyard and fabricate it on, but I'm not looking to do that much work and would rather just try to stay as simple as possible.

[mongocanfly]

Welcome....
A whole chassis swap will probably be easier than piecing together a bunch of parts....what does the frame look like...does it resemble a truck?
There may be parts that will fit it from other trucks....what exactly are you wanting to upgrade on the suspension...just brakes? Springs? Steering?......or more......

[Psyekl]

Originally Posted by mongocanfly

Welcome....
A whole chassis swap will probably be easier than piecing together a bunch of parts....what does the frame look like...does it resemble a truck?
There may be parts that will fit it from other trucks....what exactly are you wanting to upgrade on the suspension...just brakes? Springs? Steering?......or more......

I originally was suggesting to my shop partner that we do a chassis swap. It was his idea that we just try to change out whatever few parts that require modification since he wasn't too sure there'd be too many real benefits for doing so with a truck like this.

I haven't climbed under it to look at the frame (but it does say "bus" in the VIN), and from what I see from under the hood it definitely looks like a truck chassis. The only real difference I see immediately is the forward-control orientation of the steering linkage.

I want disk brakes in the front and power steering. The suspension feels pretty good, so I don't think that will need to be upgraded other than just to have all of the worn parts replaced. I'm going to throw in a 5.3L LS1 and a newer transmission, probably a newer rear end as well since something has it geared very low (I doubt it's a transmission issue). We are going to be pulling the body off of the frame for the build in order to clean, paint and do any custom fabricating that we may require, so it will be a good time to get at everything that needs getting done.

I'm definitely open to any suggestions. I'm going for an RV that tows a small trailer (~1500-2000lb). It will see cross-country driving over mountain passes, twisting higways and I plan on more than a few dirt roads (rough, but within reason- no 4x4 stuff).

[mongocanfly]

if you go with od trans your low geared rear may be ok...afterall,you are moving a big brick

[Psyekl]

The problem I'm having is that I've been told that it won't reach freeway speeds. I haven't had the opportunity to drive it yet since it isn't legal for the street at the moment, but if it's top speed is too slow for modern freeways then I'll have to do something. Obviously, If I'm pulling a trailer I don't need to be going too fast anyhow (and I'm not looking for a hot-rod out of a step van), but I would like to be able to maintain as efficient an RPM rate at cruising speed as possible.

Despite the "rat rod" undertaking, I'm also going for whatever efficiency I can accomplish; during the build I'll be focusing on keeping the weight down, The engine will be a modern fuel-injection with some modifications and I planned to use a more modern transmission with a better gear ratio (suggestions requested). I may be a dreamer, but I'm also a realist and I'm not expecting to get any better than low teens fuel economy out of this, at best.

[grumpyolddog]

Your tire size can play into your thinking too

[Clyde65]

Idk about California but here in Texas the minimum speed on an interstate highway is 45MPH, even with the 6 in it, should go at least that.

[mongocanfly]

Since your going LS I would get a complete engine/trans pullout....then everything will already be setup to work together....check and see what your rear ratio is along with your tire size.....A calculator like this will help figure out what you need...http://www.csgnetwork.com/multirpmcalc.html

[Psyekl]

Originally Posted by mongocanfly

Since your going LS I would get a complete engine/trans pullout....then everything will already be setup to work together....check and see what your rear ratio is along with your tire size.....A calculator like this will help figure out what you need...http://www.csgnetwork.com/multirpmcalc.html

Excellent! Thanks for that.
Vortec 5300 LM7
Be aware, I am not "dead set" on the "LS" swap: I had chosen the 5.3L LS (edit: recent research shows that the engine I have chosen is actually designated the Vortec 5300 LM7; the "truck engine" based on the LS I, all following info is still valid) because it is a very common swap, parts (stock and aftermarket) are readily available & relatively inexpensive, there is a LOT of support for this engine online and they can be found anywhere. Is there any reason I should consider another engine for this build? I want durability, efficiency, power, cost-effective maintenance and easily available replacement parts (and aftermarket mods won't hurt, either).

I am probably just going to purchase a whole running vehicle and do as you suggested: pull everything including the wiring harness. Unless convinced otherwise I plan on going with a modern fuel-injection. I had considered doing a nice 4-barrel carb "hot-rod" old-school setup but I'd rather have the efficiency of a more modern system. - What would be a good vehicle to get a good 5.3L engine/trans pairing from? Silverado? Suburban? Escalade? Yukon? Avalanche? Express/Savana? Sierra? Tahoe? Were some years better than others as far as the engine/transmission/electronics/ fuel delivery are concerned (design tweaks)?

I had considered the option of a diesel, but I can't justify the cost in maintenance and modern fuel inflation for my intended use. (Any objections?)

Thanks again for the info, it's gold. I'm off to measure tire size and to figure out how to calculate my rear gear ratio...

[mongocanfly]

Some of those on your donor vehicle list use the 6.0s....if you want basic 5.3s stick to the pickups and Tahoe style donors....I considered the diesel route but the extreme cost of a donor engine ran me off...it's one of those things just do your homework when you find a possible donor....the earlier engines didn't have the vvt,afm and other things....

[Psyekl]

Originally Posted by mongocanfly

Some of those on your donor vehicle list use the 6.0s....if you want basic 5.3s stick to the pickups and Tahoe style donors....I considered the diesel route but the extreme cost of a donor engine ran me off...it's one of those things just do your homework when you find a possible donor....the earlier engines didn't have the vvt,afm and other things....

I did learn during my seaches that some of these definitely had the 6.0L as an available option (or perhaps the 5.3L was the option?), but I wasn't looking for something that large since I'm going for economy (well, as much as is possible for this type of vehicle) and the 5.3L should have all the power I need.

Thanks for the heads up about vvt and afm, etc.

[Psyekl]

Originally Posted by Psyekl

I did learn during my seaches that some of these definitely had the 6.0L as an available option (or perhaps the 5.3L was the option?), but I wasn't looking for something that large since I'm going for economy (well, as much as is possible for this type of vehicle) and the 5.3L should have all the power I need.

Thanks for the heads up about vvt and afm, etc.

While doing research I discovered that the engine in the truck is a code 10243880: "96-up 350 cu-in 2 & 4-Bolt Vortec Roller" I was under the impression the engine was much older than this. As long as it's salvageable, I really don't see any real reason to swap it out with anything fancier.

Up until now I've had my leg in a cast, but now I've been able to get to work crawling around and working on it. The frame underneath is simplicity itself: just two straight c-channels, and after pulling out the old interior I discovered that someone used 2x2s to space the roof to increase the headroom.

I'm still open to suggestions for this engine (keep it/swap it out/mods?) at the moment it is equipped with a 4-barrel carb, but I still prefer the idea of fuel injection. Thanks again for any info.

[Psyekl]

Well, dang: there is no ID tag on the rear differential so now I have to calculate the gear ratio the "hard" way. Unfortunately my driveway has a severe slope (and I have no jack big enough here at the house) so it'll have to wait until I move it to my shop. Does anyone have any suggestions for what would be a good ratio for pushing a heavy truck/RV with the aerodynamics of a sheet of plywood down the freeway most efficiently?

I know how to calculate the ratios, but I have no clue what ratios to look for in rear ends or transmissions (I'm fairly competent with engines, but the toothy-wheeled spinny bits confuse me).

As mentioned before, the chassis is simplicity itself. When I pull off the body the work should progress very quickly as long as I plan properly. My desire to swap the front to disk brakes and power steering hasn't changed, and I'm also going to delete the fan and replace it with an electric. Since my shop partner builds hot rods and race cars It'll probably end up with headers/custom exhaust as well with whatever other custom doo-dads and bits/bobs we fabricate while it progresses. I'm not looking to build a hot-rod show-car monster, but it would be nice to have something unique to show off.

[mongocanfly]

i wouldn't worry about gear ratios until you get your trans and tire size figured out....then do the calculator thing and thatll tell you what ratio to look for

[Psyekl]

Originally Posted by mongocanfly

i wouldn't worry about gear ratios until you get your trans and tire size figured out....then do the calculator thing and thatll tell you what ratio to look for

The transmission turns out to be a THM400 or a Turbo 400 TH400 manufactured between 1964-1990. The ratios are: (1st) 2.48 (2nd) 1.48 (3rd) 1.0

The tires are 235/85R16 so they are 31.72" tall

From what I've read, I like the fact that this transmission is heavy duty but I want to see if there is something comparable with O/D. I actually prefer a 5-speed but I'm not fond of the more frequent clutch replacements.

I am going to be towing a small trailer (~1500lb) and the truck will be carrying a load so something heavy duty is definitely preferred.

EDIT: Searching about I have discovered that the 4L85e (4-speed automatic) sounds like a good choice without going crazy with electronics and adapters to try to fit a 6L90 on there. Am I correct?

[mongocanfly]

4l80 is same as t400 with od....very good trans.....I don't know about the elec controls

[Psyekl]

So I'm looking through Mill Supply Company ( https://www.millsupply.com/stepvan-p...h-drum-brakes/ ) and I see the available ring and pinion sets available for step vans: 373, 410, 456 & 513.

Granted, these are for modern designs but I don't imagine the ratios have changed too much since mine has been manufactured in '68.

I've already mentioned that I don't know much about transmissions and rear ends, but I'm guessing that I'm going to want the 373 for my build. I imagine these ratios are chosen for a reason and I shouldn't go messing with anything higher since the engineers probably know what they're doing. Thoughts?

Using the calculator ( http://www.csgnetwork.com/multirpmcalc.html ) with a 373 rear end and the Turbo 400 transmission, 55mph gets me 2173 RPM. If I can get a 4L85e working, 55mph would be 1630 RPM in overdrive.

I still haven't had the opportunity to check what is currently installed in mine, but since it was used as an ice-cream truck and I've been told it was geared low, I won't doubt I might find the low end of the spectrum.

[franken]

I think I'd spend a few bucks getting the current combo running and leagal, then drive it around for a while. They're meant as slow around town work vehicles, and a bit funny to drive. You may hate it.

[Psyekl]

Originally Posted by franken

I think I'd spend a few bucks getting the current combo running and leagal, then drive it around for a while. They're meant as slow around town work vehicles, and a bit funny to drive. You may hate it.

That's the plan. Doing this in August, but I still need to develop a game plan for the build so I'm not coming at it blindly. When I decide to start the build I need it to go quickly with as few delays as possible since shop time is at a premium.

I'm one of those people that enjoy gathering information, and lots of it. The sooner I get the info, the more I'll know and the better I'll be prepared when the time comes to get to work.

I'm not expecting it to be a 70mph freeway cruiser. 55mph-65mph to keep pace with the big-rigs will be fine with me. I've driven everything from motorcycles to tractors to delivery trucks to tanks, and having a delivery truck of my own shouldn't be too much of a problem. If I do decide I hate it I've already had offers to sell it at a profit, so there's always that option.

[richard2717]

That looks like an Eaton HO52 or HO72 rear end. From what i have found most had 4:56 and steeper gear sets in them and I don't think new sets are available for them anymore. There are usually ads running in the WTB for people looking for even 4:11 sets. Even the brake parts are hard to source (so i am told) but I think i saw where there is a conversion for the GM 14 bolt brake stuff to swap over.


here is a link to read on it http://www.67-72chevytrucks.com/vboa...gears+for+sale

The last post pretty much says it all

[Psyekl]

Originally Posted by richard2717

That looks like an Eaton HO52 or HO72 rear end. From what i have found most had 4:56 and steeper gear sets in them and I don't think new sets are available for them anymore. There are usually ads running in the WTB for people looking for even 4:11 sets. Even the brake parts are hard to source (so i am told) but I think i saw where there is a conversion for the GM 14 bolt brake stuff to swap over.


here is a link to read on it http://www.67-72chevytrucks.com/vboa...gears+for+sale

The last post pretty much says it all

Great info! Thanks for this.