#21  
Old 10-14-2021, 12:40 AM
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Originally Posted by i82much View Post
maybe the blue one, since it probably makes more average power over the range of rpms that it will see in street use ...
For sure.

  #22  
Old 10-14-2021, 07:40 AM
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Originally Posted by slowbird View Post
Guys this is the street section not the race section. Racing rpm and hp are king but for a street car (one that actually gets driven a lot with good drive ability) not sure rpm/hp is king. Say you have 4000lb car with 3.42 gears and 3000-3500 stall, which one you taking?
If that's the case I'd move the cam timing around and take the blue one.

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  #23  
Old 10-14-2021, 08:50 AM
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next up would be a 2800lb street car.....
Now you kinda need to go RED as the BLUE would blow the tires off trying to get it rolling....
It's always "the combination" that makes things work out well. The engine is merely a single PART of that combo. We have all seen awesome XXXX that absolutely runs terrible because the OTHER 25 "parts of the combination were NOT matched up with XXX. Some parts can HIDE a mismatch like..great power...wrong GEAR = still runs pretty good. So i will stick with the "application specific" required before buying either of those engines....

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Old 10-14-2021, 09:48 AM
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As long as it actually still drives well, I think Ill take the extra HP every time.

Ive slowly began to feel that the "torque for the street" theory is antiquated mostly from looking at single plane vs duel plane stuff.

When I am street driving, I am mostly just cruising. Its under 3500 RPM, I am not trying to scare old ladies. Its more important to me that when I do want to put my foot through the floor that ALL of the beans are there.

Now no rules are hard and fast. As mentioned if the math were done and the blue line actually makes more average HP, then thats different. Generally speaking however, give me the power up top for the track. I wont miss 20-30 foot pounds at 2500 RPM. I WILL miss the tenths on the ET if I lose them.

It comes down to tangible vs theoretical for me. The butt dyno is inaccurate at best. Even with spirited street driving, as long as you have enough torque to break the tires loose its kinda all the same. But those ETs on the other hand, they are tangible and accurate. I would rather have that top end to make sure I get those hard numbers. Burnouts all look the same. ET Slips do not.

The other asterisk would be drive quality. Nobody wants a hard starting, snotty cam that wont idle below 1200 RPM and doesnt have enough vacuum for accessories. There is a point of diminishing returns.

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  #25  
Old 10-14-2021, 10:00 AM
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Originally Posted by RocktimusPryme View Post
As long as it actually still drives well, I think Ill take the extra HP every time.
I love this video.
The original tractor engine made more torque / low RPM power but the new Volvo engine makes more horsepower across RPM range that can be used.
https://www.youtube.com/watch?v=9yHl24QynOM

Maybe he should race his neighbors tractors.


Last edited by pastry_chef; 10-14-2021 at 10:43 AM.
  #26  
Old 10-14-2021, 11:03 AM
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Simple answer, where does the engine spend most of its time on the street.
Are you a aggressive driver who cares little about F.E. vs a smooth driver
like Jackie Stewart on the street.

Build and Cam the engine for those modes of operation. Drives well is a subjective thing.
Tom V.

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  #27  
Old 10-14-2021, 11:24 AM
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The original question is to choose for street application. As mentioned, HP and torque on these engines is interrelated, and as Tom mentioned, choice is determined by application.

Here's a question: you need to choose an engine to power a 18 wheeler weighing 80,000 pounds. Your choices are 1. CAT 900 cu.in diesel, say 900 ft-lb of torque from idle to 2500 RPM, 450HP, or a GM LS, say 450 ft-lb @5000RPM, 450 HP @ 6500 RPM? (Just shotgunning the numbers but probably close....)

State the reasons for the choice.

George

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Old 10-14-2021, 12:00 PM
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Quote:
Originally Posted by george kujanski View Post
The original question is to choose for street application. As mentioned, HP and torque on these engines is interrelated, and as Tom mentioned, choice is determined by application.

Here's a question: you need to choose an engine to power a 18 wheeler weighing 80,000 pounds. Your choices are 1. CAT 900 cu.in diesel, say 900 ft-lb of torque from idle to 2500 RPM, 450HP, or a GM LS, say 450 ft-lb @5000RPM, 450 HP @ 6500 RPM? (Just shotgunning the numbers but probably close....)

State the reasons for the choice.

George
of course you would choose the diesel. two engines with equal peak power.

that said, a 700 HP LS engine with enough mechanical advantage will accelerate any load, including an 18 wheeler, faster than a 450 HP engine with far more torque. there are many reasons why it is not practical to do so, but power, not torque, is what determines how *quickly* you can do work. and accelerating a vehicle - be it a crotch rocket or a space shuttle - is work.

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  #29  
Old 10-14-2021, 12:11 PM
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If you are not changing rear axle ratios, trans ratios (except by manually locking a trans in a given automatic gear), then engine rpm and if the engine is happy at those rpm points, gives you the answer WITHOUT a lot of math or opinions.

Choosing a dyno curve without real world vehicle information (engine installed) in that vehicle and road tested is purely bench racing and a waste of time.

Tom V.

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  #30  
Old 10-14-2021, 01:59 PM
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Quote:
Originally Posted by i82much View Post
power, not torque, is what determines how *quickly* you can do work. and accelerating a vehicle - be it a crotch rocket or a space shuttle - is work.
Yes.
formula is.
pounds of force to the tire now = (horsepower now x 375) / MPH now.

Not factoring for aero or rolling resistance.

----

900 ft-lbs of torque sounds like a big number to some, in context it is not. I can do that with my hands and a sturdy length of pipe.
I doubt any human could generate even just 5 HP, most not even 2 HP.

Horsepower is what puts thousands of pounds of force to the tires. High horsepower launches 10,000 pound monster trucks over many cars.

  #31  
Old 10-14-2021, 02:54 PM
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I think one way to look at it is this. The peak HP rating doesn't tell you the full story of how much work you can accomplish in a given amount of time with a given engine in a given car, because the engine doesn't spend the whole time at the HP peak. The peak torque number is just another data point that gives you some idea of what the power curve looks like, and thus provides some insight into the "area under the curve" that a given engine will provide in a given car.

in a heavy car with highway gears and a tight converter, the engine will tend to operate at lower RPMs. as a consequence, the data point for the peak torque number is more important than for a lighter car with gear and looser converter that spends less time at lower RPMs.

in either case you are trying to optimize average power.

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  #32  
Old 10-14-2021, 07:00 PM
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Quote:
Originally Posted by Tom Vaught View Post
Simple answer, where does the engine spend most of its time on the street.
Are you a aggressive driver who cares little about F.E. vs a smooth driver
like Jackie Stewart on the street.

Build and Cam the engine for those modes of operation. Drives well is a subjective thing.
Tom V.
This is what Iíd do too.
Usually I go for a long broad torque curve but thatís because it usually suits the engines power band with a Pontiac even in drag racing.

But occasionally a perky HP engine is whatís needed for certain applications say a light weight speed boat that spends a lot of its time at max rpm and HP

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