HP and Torque

[Carl Stouffer]

So here's a kind of random question:

My 455 is bored .030, has about 8.5:1 compression pistons, and a Jim Bounds "Kryptonite" cam, a stock Q-jet, and MSD ignition. I'm wondering what kind of horsepower and torque it might be putting out. It certainly seems adequate for most situations, it will accelerate from 62 or 63 up to over 70 easily, for passing etc, on a fairly level road, but usually I have to downshift to pull much more than a 3-4% grade of over a mile or two. WE always are towing our four door Chevy Tracker, weighing somewhat in excess of 3000#, total weight of over 15,000#.

I'm just curious about the power output compared to a modern big displacement engine such as the Ford 7.3 "Godzilla". Any idea of an approximate range?

 

[LQQKatJon]

Here is a dyno readout from an engine build like mine. “Rv cam”. Whatever that means…



All engines are a little different.

But this is the ball park.

Peak torque was around 431lbs and peak HP was 300. With that engine’s dyno run.

Now you cant compare anything. Modern engines and the tranny’s behind them make drivability so different.

 

[Christo]

So here's a kind of random question:

My 455 is bored .030, has about 8.5:1 compression pistons, and a Jim Bounds "Kryptonite" cam, a stock Q-jet, and MSD ignition. I'm wondering what kind of horsepower and torque it might be putting out. It certainly seems adequate for most situations, it will accelerate from 62 or 63 up to over 70 easily, for passing etc, on a fairly level road, but usually I have to downshift to pull much more than a 3-4% grade of over a mile or two. WE always are towing our four door Chevy Tracker, weighing somewhat in excess of 3000#, total weight of over 15,000#.

I'm just curious about the power output compared to a modern big displacement engine such as the Ford 7.3 "Godzilla". Any idea of an approximate range?

What's your final drive gear ratio? Stock 3.07?

 

[Carl Stouffer]

What's your final drive gear ratio? Stock 3.07?

No, I'm running a 3.70.

 

[Christo]

No, I'm running a 3.70.

With that final drive and load I wouldn't expect you to have to downshift until you got to more than a 6% grade, although altitude will make a significant difference. I'd be curious to hear other opinions. How confident are you that you have the correct MH carb number and jetting, that your timing is set properly, and that your vacuum and centrifugal advance mechanisms are working?

 

[Carl Stouffer]

It's all up to spec. The carb is the original MH Q-jet (rebuilt), the timing is variable (MSD-6 with dash adjustment), Vacuum and centrifugal timing was all working properly the last time I checked. I don't have to downshift until I get to a long grade over about 4%, closer to 5-6.

 

[Carl Stouffer]

Here is a dyno readout from an engine build like mine. “Rv cam”. Whatever that means…

View attachment 16681

All engines are a little different.

But this is the ball park.

Peak torque was around 431lbs and peak HP was 300. With that engine’s dyno run.

Now you cant compare anything. Modern engines and the tranny’s behind them make drivability so different.

Thanks Jon,

That's the kind of info I'm looking for, and about what I figured it was. I tried to get a hold of Jim Bounds to see what his experience with this cam was, but both his old emails are disabled.

Yeah, I'm sure driveability is seriously affected by having multiple speeds in the transmission, not to mention all the electronic engine management.

I guess I should have paid the extra money to have mine run in on a dyno when I had all the other work done on it, then I'd know for sure.

 

[tmsnyder]

Thanks Jon,

That's the kind of info I'm looking for, and about what I figured it was. I tried to get a hold of Jim Bounds to see what his experience with this cam was, but both his old emails are disabled.

Yeah, I'm sure driveability is seriously affected by having multiple speeds in the transmission, not to mention all the electronic engine management.

I guess I should have paid the extra money to have mine run in on a dyno when I had all the other work done on it, then I'd know for sure.

It would be nice to run it on a chassis dyno.

 

[Keith V]

Thanks Jon,

...

I guess I should have paid the extra money to have mine run in on a dyno when I had all the other work done on it, then I'd know for sure.

What difference does it make? Bragging rights?
If you're not tuning it for racing there is no reason to dyno an engine, and barely a reason if you're tunning for MPG.

 

[Christo]

It's all up to spec. The carb is the original MH Q-jet (rebuilt), the timing is variable (MSD-6 with dash adjustment), Vacuum and centrifugal timing was all working properly the last time I checked. I don't have to downshift until I get to a long grade over about 4%, closer to 5-6.

There are some discussions on the forum that talk about tuning the carb for altitude and/or today's gas -- did you go through all that already or do a simple rebuild?

 

[Carl Stouffer]

What difference does it make? Bragging rights?
If you're not tuning it for racing there is no reason to dyno an engine, and barely a reason if you're tunning for MPG.

No reason, really, Just curiosity. Mostly I'm wondering what kind of difference the Kryptonite cam makes over the stock cam.

 

[Carl Stouffer]

There are some discussions on the forum that talk about tuning the carb for altitude and/or today's gas -- did you go through all that already or do a simple rebuild?

Pretty much a simple rebuild with a step or two up on the main jetting to make up for the ethanol gas. I have driven my coach anywhere from below sea level in Death Valley, to well over 10,000' in the mountains of Northern New Mexico. While I DO notice some additional power at lower elevations, I don't really notice too much of a drop at higher ones.

 

[Hal]

Pretty much a simple rebuild with a step or two up on the main jetting to make up for the ethanol gas. I have driven my coach anywhere from below sea level in Death Valley, to well over 10,000' in the mountains of Northern New Mexico. While I DO notice some additional power at lower elevations, I don't really notice too much of a drop at higher ones.

You'll have about a 3% drop for every 1000' of elevation with the carb under ideal conditions. Turbo's or any forced induction will almost negate the elevation losses. The torque is really what keeps you going. Thats why the diesel swaps work so well with low HP but high torque. Adding another gear really helps, ask me how I know .

 

[Robert S.]

Hi Carl,
I can give you Jim Bounds # however I doubt he would be of much help. But I could be wrong.

 

[sailor man]

The best source that I have found that deals with a comparison of various motor, loads, gear ratio and speeds is in a GMCWS technical seminar on 10/10/2006. I think that it was mostly written by Chuck Botts with some commentary by Jim Kanomate and Grandpa Billy.
http://www.gmcws.org/Tech/Final_Drive_Ratios.pdf
SO far it is the only comparison that includes a GMC COOP 455 motor. It is limited somewhat because it does not include any data from fuel injection or switch pitch torque converters. I think that it is a vary interesting read even though it is 17 years old.
I am interested in your opinions after you read it.

Rad Post #370, 3/12/24 on pg #19 on

Converting to LiFePO4 batteries and Sailor Man's LiFePO4 Build​