Tow capacity upgrade

[Road Trip]

If I “had” to replace it, today, I would be looking for a standard cab, long wheelbase dually C30 Squarebody. Buick 455 or Cadillac 472/500, Th400 or SM465, 4.56 gears, Class 5 hitch.

Man that sounds tasty. The Caddy 500 can be common sense built to generate up to ~590 ft/lbs of torque,
according to this web page. (Teaser: They tested both the Q-Jet & the Holley 850. Including rejetting.)

Well worth reading, not your typical 'high peak HP number only' clickbait: (500 built for towing greatness)

Since a SM465 can make a SBC feel like a Caddy 500, I can only imagine the sheer unstoppability
that one of those built for max torque 500 Caddy would feel like with an unbreakable Granny 4-speed
behind it.

As for the Turbo 400, the only thing I would add would be tracking down and using one of the 1st-generation
switch pitch torque converters. It was dropped after the first couple of years, judged to be needless added
cost, but I had one behind a high compression 425ci Olds, and that combo pulled like a freight train.
Basically a 2-speed torque converter that would make that 4.56 feel like a 5.13 when the go pedal is nearing
the floorboards.

HP is great for figuring out how much of a hole you can punch in the air at the salt flats or the Texas Mile.

But torque is how you figure out how much real work you are going to do from stop light to stop light.
And the more area under the torque curve = the more grinning you will do while getting the job done.

One last thing. I've talked to literally thousands of fellow enthusiasts over the decades.
The ones that could only translate what they wanted into a single HP number? Rarely if ever happy.

But the rare individual who could draw out the torque curve of their engine on the back of a napkin?
They were always the happiest dudes at the show & shine. Their eyes would light up when they
described how the engine pulled in the sweet spot of 2nd/3rd/4th.

And the dude who took it to the next level, and could draw the power at his disposal in a mph vs transmission
gear selection in a graph? Hard to convey, but these guys always had that 'all thought out' zen kind of presence: (Torque Truth)

****

Didn't mean to riff all over your powertrain choices. But I just wanted to tell you how much
I would want to drive a creation like you described. Righteous stuff. :0)

 

[CruiseLifeB]

I did the frame grafting on my project it dose not matter the wheel base or pickup or suv but I would say stick with 8 lug 4x4 if the 2wd was 8 lug if it is a C-1500 it is okay to graft on a 8 lug front but I would tink it would be harder then doing a K-1500 or a ld K-2500 both are 6 lug 2wd ld 2500 is 6 lug for a visual of what I mean by grafting the fame

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where the yellow is is where you cut more or less you remove the tbar cross member has 2 bolts on each side if I remember right the rear bolt location is actually where you cut or at least that is where we cut had to drill new holes for the rear bolts again from the tbar cross member forward to the all 4x4 frames are the same from front bumper to tbar cross member trucks and suvs

Man he already sold it so guess I’m keeping her for now. I got another offer for a 99 F-250, seems like a good hauler but idk It’s just something about that obs square body

 

[Scruffy]

Been threatening to build “this” for years. Just at a normal working ride height. I already have a lwb Sweptline, a 413/727/Spicer 70 dually rear axle and a D/M400 solid front axle.
But by the same token, have a C60 with a pto equipped SM465.

I don’t do “normal”…

 

[South VA]

One last thing. I've talked to literally thousands of fellow enthusiasts over the decades.
The ones that could only translate what they wanted into a single HP number? Rarely if ever happy.

But the rare individual who could draw out the torque curve of their engine on the back of a napkin?
They were always the happiest dudes at the show & shine. Their eyes would light up when they
described how the engine pulled in the sweet spot of 2nd/3rd/4th.

And the dude who took it to the next level, and could draw the power at his disposal in a mph vs transmission
gear selection in a graph? Hard to convey, but these guys always had that 'all thought out' zen kind of presence: (Torque Truth)

Amen. I learned this lesson the hard way on a 2014 Dodge Charger R/T AWD. That was some expensive tuition!

 

[Road Trip]

The Caddy 500 can be common sense built to generate up to 590 ft/lbs of torque,
according to this web page. (Teaser: They tested both the Q-Jet & the Holley 850. Including rejetting.)

Rereading this, that number doesn't mean much all by itself. So I decided to list the
GMT400 torque numbers that we're familiar with (from driving them around) as a reference:

TBI era

Engine -- max torque
4.3 ....... 235 ft/lbs @ 2000 rpm
5.0 ....... 270 ft/lbs @ 2400 rpm
5.7 ....... 300 ft/lbs @ 2800 rpm
7.4 ....... 405 ft/lbs @ 2400 rpm

Vortec era

Engine -- max torque
4.3 ....... 255 ft/lbs @ 2800 rpm
5.0 ....... 285 ft/lbs @ 2400 rpm
5.7 ....... 330 ft/lbs @ 2800 rpm
7.4 ....... 410 ft/lbs @ 2400 rpm

590 ft/lbs of torque out of a gas engine? If you were to install 2 stock L05 5.7s into a single truck,
you would only have a 10 ft/lb advantage over the deep breathing Caddy 500. Plus the non-advantage
of the extra weight & complexity?

And according to the article the Caddy motor is only 60 lbs heavier than the SBC?

This kind of twist seems to be in the light truck diesel league?
So staying with the GMT400 engine bay theme,
here's a couple of turbo-diesels from the '98 FSM:

L56 Turbo 6.5 360 ft/lbs @ 1800 rpm (Under 8500 lbs GVWR)
L65 Turbo 6.5 430 ft/lbs @ 1800 rpm (Over 8500 lbs GVWR)

Obviously GM was crowding the emissions limits of the time
with their diesels, costing the lighter trucks ~70 ft/lbs worth of twist.

****

Mulling over what it would be like to drive something like this
(think 454SS torque plus an additional 185 ft/lbs or so) I think
for tire life alone you would want to have a fibonacci spiral on your
throttle body. (So as to have a variable ratio between the speed of the
gas pedal being depressed and the throttle plate being opened. (Fibonacci spiral)

Potentially too much of a good thing?

What a great problem to have.
:0)

 

[Sean Buick 76]

My 99 K3500 c&c. Set up for bumper pull and gooseneck use. Vortec 350 (weak), NV4500 (tolerable), Borg Warner 4470 transfer case (tolerable), 14 bolt full float with 4.10s+GovLoc+huge drums. Front is still IFS (sketchy at best) with huge discs, and an appetite for balljoints that surpasses a toddler’s appetite for cookies. The cab and chassis (c&c) frame makes it a parking lot friendly dually, fits in a regular parking spot. The 350 limits it to a 10,000# tow rating. I run LT265/75r16s on the rear axle, load range E, with a 2” steel spacer between the wheels. It has mismatched LT235/85r16s up front, load range E, for a bit less strain on the barely adequate front suspension. Truck shipped new with LT215/85r16 load range D tires, no dually spacers

If I “had” to replace it, today, I would be looking for a standard cab, long wheelbase dually C30 Squarebody. Buick 455 or Cadillac 472/500, Th400 or SM465, 4.56 gears, Class 5 hitch. Same garbage fuel economy, but torque to spare. If the roads are bad enough to actually need 4wd, I’m not going to be pulling a trailer by choice. Dually + snow = bad idea.

A friend of mine built a similar truck to what your describing. It was a tow truck for personal use. square body 4x4, with a built up 500 caddy dyno tested, NV-4500, sturdy front and rear 4.56 diffs. Sadly the owner passed on and the truck is rotting away now.

The build used 9:1 compression, aftermarket con rods, a decent sized cam, pro ported cylinder heads, edelbrock intake, headers and a Q jet. I don’t have the dyno sheets handy but it was a torque monster and it still made power to 6000 RPM vs the stock 4500 or less. Easy modifications that really unlocked the potential of the 500. He did spend some $ on it, but he was making big money as a Millright and had no bills. RIP buddy.

 

[Sean Buick 76]

Rereading this, that number doesn't mean much all by itself. So I decided to list the
GMT400 torque numbers that we're familiar with (from driving them around) as a reference:

TBI era

Engine -- max torque
4.3 ....... 235 ft/lbs @ 2000 rpm
5.0 ....... 270 ft/lbs @ 2400 rpm
5.7 ....... 300 ft/lbs @ 2800 rpm
7.4 ....... 405 ft/lbs @ 2400 rpm

Vortec era

Engine -- max torque
4.3 ....... 255 ft/lbs @ 2800 rpm
5.0 ....... 285 ft/lbs @ 2400 rpm
5.7 ....... 330 ft/lbs @ 2800 rpm
7.4 ....... 410 ft/lbs @ 2400 rpm

590 ft/lbs of torque out of a gas engine? If you were install 2 stock L05 5.7s into a single truck,
you would only have a 10 ft/lb advantage of the deep breathing Caddy 500. Plus the non-advantage
of the extra weight & complexity?

And according to the article the Caddy motor is only 60 lbs heavier than the SBC?

This kind of twist seems to be in the light truck diesel league?
So staying with the GMT400 engine bay theme,
here's a couple of turbo-diesels from the '98 FSM:

L56 Turbo 6.5 360 ft/lbs @ 1800 rpm (Under 8500 lbs GVWR)
L65 Turbo 6.5 430 ft/lbs @ 1800 rpm (Over 8500 lbs GVWR)

Obviously GM was crowding the emissions limits of the time
with their diesels, costing the lighter trucks 70 ft/lbs worth of twist.

****

Mulling over what it would be like to drive something like this
(think 454SS torque plus an additional 185 ft/lbs or so) I think
you would want to have a fibonacci spiral on your throttle body
so as to have a variable ratio between the speed of the gas pedal
being depressed and the throttle plate being opened. (Fibonacci spiral)

Potentially too much of a good thing?

What a great problem to have.
:0)

Part of the reason the 500 was rated so high was because of the testing differences between 1970 and modern ratings. The old ones were gross ratings and in 1972 the rating system was changed to be more accurate. Plus at the same time the compression ratios were lowered plus other emissions stuff added each year after.

For example just because I’m familiar with this engine specifically here’s an example using rough numbers off the top of my head. I could be off a few HP.

The 1970 Buick 350 was rated at 315 HP in its performance version Buick GS). In 1971 the same engine with a few changes such as lower compression was rated at 260 HP. In 72 the same engine was rated at only 180 HP. By 76 it was 160 HP.

We’ve dyno tested these various engines and the early ratings weren’t very accurate. The same goes for most of the old school muscle car engines, pre 72 HP and TQ numbers aren’t very accurate.

That being said we dyno tested a 500 Caddy and it didn’t take much work to reach or exceed the factory ratings but without a cam and head work it wasn’t making the advertised HP or TQ on a modern dyno. Same experiences with Buick 350s and 455.

 

[Road Trip]

The same goes for most of the old school muscle car engines, pre 72 HP and TQ numbers aren’t very accurate.

The late '60s were a different time to be sure. In addition to the gross > net ratings change in the
early '70s, back then due to competitive pressures between the Big 3 the Underachievers would sometimes
benefit from the optimistic dyno numbers that you referenced, while at the same time the Overachievers
would get under-reported just so that insurance could still be bought before the newly purchased car was
put on the road.

Here's an example of what I'm thinking of - the aluminum headed '68 Tri-power 427:

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(credit: HERE Bonus -- check out the dude in reply #7. Time & again I find his breadcrumbs in all of
the most interesting threads. Good thing his last name wasn't Smith. :0)

So, yeah, I'm with you. The '70 370hp (gross) 350ci LT-1 motor is a great motorhead benchmark, but it's
not nearly as close to the performance of the '90 32-valve 375hp (net) LT5 (designed by Lotus & built by
Mercury Marine) ...as the raw numbers alone would convince a casual observer. (LT5 'Wette Vette article)

Not to mention the fact that the modern engines can run on today's low octane juice, while the prima donna
glory engines of yesteryear required the best stuff you could feed them. (I just smelled Avgas while typing
in that last sentence, thanks mostly to my misspent youth. :0)

The point is we should thank our lucky stars that Knock Sensors & constantly fine tuning feedback loops
are included with the majority of the GMT400s still out there, for I remember what it was like to have one ear
constantly tuned for the sound of detonation when the pretty girl in the passenger seat deserved my
undivided attention. :0)

****

For what it's worth, all the GMT400 torque numbers I quoted above were net. And obviously a dyno run is
anything but. Even so, I'd like to find a Caddy convertible like this, pull the stock 500, make it as right as
rain...and put it back in & enjoy. Suits my auto hobby sense of humor perfectly. (See attached.)

Enjoyed the virtual bench racing session. Thanks --

 

[L31MaxExpress]

8.1L makes 455 net tq stock. The PSI 8.8L based off the 8.1L makes like 575 @ 1,800 rpm.

 

[L31MaxExpress]

This is the 10:1 school bus engine. 565 @ 1,500 is a strong engine on propane. They only run the 2,600 rpm for longevity and to keep them quieter. I have seen the dyno sheet and the HP is a linear climb to that 2,600 rpm. Even with the modest bus cam they make a lot more power if you raise that revlimit.

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