redbaron442455

What are people seeing in low end torque on the 4.5" stroke 495/488 crank vs the stock 4.25" 455?
I'm building a gmc motorhome so low end is whats important.
thanks,

Rocket Launcher

Don't have an answer on the torque comparison, but I would like to see some pics of your GMC Motorhome when finished.
Been looking at the '73 to '78 GMC Motorhomes for the past few years, would love to buy one and use for travel to an OCA National Meet

Rallye469

That might be a hard to find #’s for comparison. Most folks who go 496 are going all out or all out on pump gas(myself). I doubt you’d want my engine in your motor home.

VC455

Looking at basics, the 495 has about 9% more displacement than the 455. All else being equal, the torque would be 9% greater. But as you imply, all else is not equal--the stroke is longer, which increases torque and moves the maximum torque range lower on the rpm scale.

If the longer stroke added 4% more torque, the total torque increase would be about 13%.

Parts selection can make an additional torque improvement (shorter-duration cam, longer intake passages, smaller ports, optimum compression ratio, etc.). Starting with an L-31 455, you might add ~7% more torque with parts selection.

Selecting those ideal parts on a 495 would give you the best torque output overall.

If the later (overdrive) 4-speed TH400 could be adapted to the GMC Motorhome, the wheel torque would be higher and available over a wider range if a higher-numerical-ratio final drive were available.

Koda

GMC motorhomes were TH425 oriented, I believe.

redbaron442455

their a cool rig, they have quite a following, but not many know about the engines, they just "call up joe mondello" we all know the story on that...
if you have Facebook look up the gmc motorhome groups, there's several.

redbaron442455

Haha yea im looking to make a 9.0 compression pump gas motor. My main focus is moving 10 000 lbs and trying to get the best mpg I can.
most people who want this go for the cadillac 500 out of a eldorado, id like to stick with the olds.

redbaron442455

Thanks that sounds like it be worth it, especially if I'm going to start from scratch.
it has the th425, toronado drive train, 3.08 differential, 30" tires, about 7500 lbs empty, 10,000lbs normally.

cutlassefi

I’m doing an Olds Stroker small block for a guy with a ‘76 GMC. It’s 422ci and will be over a hundred pounds lighter than his stock iron headed big block. Plus it’ll have 500+ tq in as little as 3000rpm.
Just another option.

redbaron442455

is that a 403 block? I have tossed around the idea of building my 72 350 I have sitting in my garage. Any idea how the small block would compare to the 455?

cutlassefi

Nope 350 based. 4.00” stroke, 4.090 bore. Aluminum heads, EFI, the works.
i did a 420 a couple of years ago, made 408/510 with stock irons.
Block, crank, and heads will all weigh less and be more efficient than any 455.

redbaron442455

Can I ask what makes it more efficient then a 455?

VORTECPRO

Based on the dyno data above I'd have to agree its not efficient. And heres my thoughts, you have a dyno sheet that says 626 corrected HP, you have 601 HP observed or in the room in a 29.4 baro, but you have a 124 MPH car down in Florida, guessing @ 3600 pounds which shows 528 observed FWHP, so at best case scenario your missing 70 HP, so wheres 70 HP, probably getting eaten up in windage loses or other places as well. At 2500 RPM windage might not be as much a issue for you, but I'd run the best oil pan money could buy on that combination.


So to answer your question: its easier to feed 420 cubic inches than 496 cubic inches with a inferior set of heads, VE goes down. Considering where you live, you should work closely with Bernard Mondello on your build.

cutlassefi

Much lighter internals, smaller diameter journals, a knife edged and profiled crank for less windage, and an overall lighter build.

redbaron442455

I see, a big plus for me would be i wouldn't have to use the toronado intake manifold on a 350, do you know of a good intake that would be at or lower then the toronado intake on a big block? Also do you have pistons that can make around 9:1 compression?

cutlassefi

Correct, being that a small block is a fair amount shorter than a big block, another plus when doing a small block is the fact you don't have to use that god awful Toro style intake. As far as an intake for a big block goes, there isn’t any alternative to the Toro intake for this application.

Rallye469

Your guess is way off chevy boy.

Redbarron...no matter what you do, listen to folks like Mark(Cutlassfi) and people who actually champion the Olds brand. If keeping your camper Olds powered is your goal, I’m sure you will find a combo that will suit your needs. It might be very interesting to call a good builder and run through some scenarios. Good luck!

VORTECPRO

Actually your right, my mistake, I meant 528 fly wheel HP. 626 STP corrected HP, 601 measured HP, 528 track HP @ the flywheel.