Hypothetical questions, 500 in a work truck?

[Big-Daddy]

We have a truck up at work called a Isuzu NPR. It's a cab-over job, quite popular. It's factory equiped with a Chevy Vortec 350. Optional on this model truck was a 4 cylinder diesel making about 80 hp.

The truck has a 16 foot box, and a max weight capacity of 12,000 lbs. Every time we use it, it's right up there close to the max. We use the crud out of it. The 350 is seriously starting to show signs of it's impending doom. The boss is unhappy with his options when the truck dies. Either replace the 350, which is underpowered to start with, or buy a bigger truck to the tune of $20,000+ [for a good used one]. Our truck only has 60,000 miles on it.

Fortunately, the boss is a hot-rodder at heart, and he has taken a ride or two in my caddy powered machine. When I said it looks to have pleanty of room for a big-block swap, it peaked his interest.

The truck is already equiped with the Allison tranny with a chevy pattern.

It spends 98% of it's run time in stop and go traffic.

What I'm thinking is a basically stock low compression 472-500, with fresh rings, bearings, gaskets, and a valve job. Top it off with a tweaked HEI, good carb rebuild, and a set of headers with big dual exhaust.

Since the truck is set up for a diesel application, the gearing in the tranny and rear mean the 350 rarely revs above 3500 rpm, so I feel a cad swap is perfect.

My questions are about cam selection. Everyone wants bigger cams, but little attention is paid to stock type applications, or less than stock profiles that are designed to build huge torque numbers just off idle.

What do you fellers think?

[DaveM]

The truck would be great with a caddy motor... But a 350 with only 60K..and it's bad.. I guess it can happen.. at where I work we have a 92 chevy pick-up , the motor has never been taken apart, and has 420K miles the last time I looked...and still goes down the highway at 80 mph..maybe another 350 would be a whole lot eazier...maybe one with a little higher compression...

[Big-Daddy]

80,000 miles is actually the normal life expectancy for a gas 350 in this size truck, and we really are hard on it :lol:

A couple months ago it was taken on a trip to New Orleans loaded to the max, and towing a 6000lb trailer. When it got back, it smoked at startup, and has developed a ticking from the valvetrain.

A new GM crate 350 will be $2000, a 454 will be more like $3000+.

I'm thinking we can do a 472-500 for about $1500

[DOC]

Hey Big Daddy,

I think that is a perfect swap. The Caddy will out work that SBC at part throttle. If you have a complete donor engine, it will be the least expensive. Two things to think about: emission laws in your area, and be sure the trans is not a 4L80E (it requires a stand alone computer). All that being said, with just a mild cam upgrade (MT10?), minor bowl work in the heads, and Performer manifold, you would have a heavy duty, long lasting, work truck that would be a blast to drive.

DOC

[Terrible One]

Man I sure would like to see that swap go through! Go for it! No question the Caddy engine will be plenty of power, long lasting, etc etc. But will it fit? Have you taken measurements? Do you see anything that may get in the way?

[Big-Daddy]

There looks to be PLEANTY of room. A good 6 inches on each side of the motor, tons of pan clearance, and about 8 inches above the intake. No steering linkage or anything to get in the way.

The tranny is indeed an Allison. It's a "series 4" or something like that rated to over 500 ft/lbs.

The only thing I have concern with is cooling capacity with the existing radiator. I know isuzu makes bigger trucks with diesel engines over 500 cid. Locating one should not be a problem, I am just unsure if it will fit in the frame.

I'm still looking for advice on a low rpm high torque cam.

[Terrible One]

Alright, well that sounds good. I was mostly thinking of the steering linkage, so glad you don't have a problem there. The current radiator might work, and might not. Slap a temp guage on there (unless it already has one) and see. If it's just running a bit too hot, get it flushed and rodded, or re-cored. If it still doesn't work, you'll have to find a way to make a bigger one fit.

Glad to hear about the Allison. So far this sounds like a reasonable swap that won't be such a pain that it isn't worth it.

I think a #3 or #5 series MTS cam should do you right (depends on how much you want it geared towards bottom end power/torque) but you ought to get a suggestion from Al

[moturbopar]

I know this might be against the cad code but something like this why not just swap in a 383 shortblock or even a 400? you could reuse the vortec heads with a fresh valve job. I think this could be done cheaply and easy.

[Vern]

Moturbopar,

Just some thoughts. Its a HEAVY truck low rpm torque is far more valueable than higher rpm HP/TQ both for being useable and for reliability. You can easily build a 500+ cube Cad motor to make 550 foot pounds of torque. Building a sbc to do that would be entirely different. The big Cad leaves the 383/400 far behind in this area. Also ever price doing a 383 its generally a lot more expensive than doing a regular rebuild. Even fuel consumption might be less with the Cad. Going down the road with the big Cad does not require keeping your foot heavy on the pedal. Trying to leave a light with traffic puts your foot heavy on the gas and straining the sb where as the Cad would leave a lot more effortlessly without smashing the gas pedal.

[moturbopar]

Yea this is all true, but if its an NPR wont it be fuel injected? Doesnt it need to stay fuel injected?I guess if there are no emissions on the vehicle it wouldnt be a problem to do the swap. Locally you can get a 383 shortblock for $899 outright same for 400. The 500 would for sure be the best swap if no emissions are required and down time isnt super important. just thinking best for a business.

[SMITH29]

Use a r/v type cam from MTS.
Install valve seats in the intakes and stainless valves all around.
Balance it too.

[curtis73]

wait, wait, wait. Didn't he say that it was an allison transmission with a chevy bolt pattern? That won't work with the Caddy.

First of all, I don't know of any Allison tranny before 2003 that has a Chevy bolt pattern, and if this one is bolted to a 350, it certainly is not one of those. If its an Allison in an NPR it has an SAE 3 or 4 pattern. The back of the Chevy has an SAE transfer housing, and the Allison has the SAE pattern.

So, if it truly has a chevy pattern, it won't bolt up to the caddy block. If it has a two-piece SAE bellhousing, you need to locate a BOPC to SAE adapter. They exist, but I couldn't tell you where to find one.

[Illraceya]

Definitely do the cad swap and then post some burn out pics!

[Big-Daddy]

Well, after carefull consideration, the boss has decided to go with another small block chevy :roll:

So much for geand ideas of a truck with enough power to get the job done.

[Terrible One]

Awww. :cry: That would have been a really cool swap.

[mepr]

Im a big time Isuzu guy so my first thought is run the deisel that belongs in it!(they perform alot better than they look like on paper) :lol:
But past that a 500 would rock i think. I four wheel a guy who has a 500 in 72 K-5 blazer and he swears he will never look back. He tows a camp trailer whith it for hunting, mud boggs it and does trail rides whith us. Only thing i would worry about is getting an Isuzu smogged whith it.