Fundemental car question

I hate Rice · 10-02-2001, 10:55 PM

Alright I know what torque is and what HP is, but what I am curious is what are the determinents of it. I've been chipping away at it and does stroke or bore play more of a role in determing torque, or does it matter. I was hoping some one would just explain a little engine theory or at least point me in the right direction. I really dont want to one of those stupid 17 year olds that doesnt have an independent thought in their head. Thanks

sedanman · 10-02-2001, 10:59 PM

Be a little more specific in your question and I think we could answer it a little more effectively. I know there are several bright guys in here and several mechanical engineers (myself included). Do you want to know how stroke and bore effect the power curve, or do you want a whole speal on torque and horsepower and how your motor makes them?

Kevin Price · 10-03-2001, 08:22 AM

Moved to Blue Oval Lounge

------------------
SVO siamesed 351 stroked to 417ci,Yates heads, solid roller,Trans King glide and a little blue bottle
of giggle gas. My Car

bigwhitecobra · 10-03-2001, 08:46 AM

Ok, I'll give it a try. Bare in mind that I'm not an engineer or some technical wizard.

Horsepower is the amount of work being done by the engine burning the fuel(gas, desiel, etc).
Wait, I'm getting ahead of myself....
Horsepower is defined as the amount of force that is required to lift 100 pounds 100 feet for 1 minute.(I think that's right, if not UNIT5302 can explain it) I'm not sure how torque is defined, but I know that it is directly related to engine size. Ok, given that, let's say you have an engine making 200HP and 250lb-ft of TQ at the wheels. And let's say that it's a 5.0L. Anything that you do to will increase the output(output being HP and TQ). Now, if you have a larger engine, and do the same type of upgrades, you will end up with a higher output figure than the original engine.
Here's why. The larger engine has the ability to move more air and fuel than the smaller one, creating more power. (Which is why I don't understand why the import guys are so cocky) By nature, a 351 will make more power than a 302, and a 302 will make more power than a 289, and so on.
I hope that I haven't confused you any. I don't know if this is as factual as I think it is, but this is what I've come up with. I think it works.
Anyway, later.

------------------
"Is that a Cobra?"
"Yeah"
"It's a V6, right?"
"Yeah"

PKRWUD · 10-03-2001, 11:47 AM

When you're riding your mountian bike uphill, and you have to stand up in your seat in order to pedal over the top... that's torque. When your flying down the other side... that's horsepower. They each play an important role. While you certainly aren't flying up the hill, you are making it. But, if you tried to use all that power to go fast, you'd hurt yourself. Imagine flying down the hill while trying to pedal faster standing up. At the same time, the horsepowere aspect, flying down the hill, you're crouched and pedaling quickly in short strokes. It works killer for going fast down hill, but try climbing the hill like that. You wouldn't get very far. Generally, stroke and compression are the biggest factors. A long stroke will generate more torque, while a short stroke allows the engine to rotate faster, creating horsepower. Bore is important, but not as big a deal as stroke. Horsepower = speed. The faster an engine can turn, the more hp it can generate, bores being equal.

Another way of looking at it is a test my college engine rebuilding class did 16 years ago. About 20 miles from where I live is the Conejo Grade. It's part of the 101 freeway, and basically goes straight up a 1800' incline in less than 2 miles. It can be brutal to small, weak vehicles. Anyway, we had received as a donation two brand new VW Rabbits. One was a diesel and the other was a GTI. The diesel redlined at 3000rpm, and the GTI went to 7000rpm.We raced them up the Conejo Grade. Obviously, the GTI kicked *** , the first time. The second time, we attached a trailer with a few engine blocks on it to both cars. The added weight was close to 1500 pounds. The diesel won the second race. In fact, the diesel finished within 20 seconds of the time it took to reach the top the first time. The GTI didn't even make it to the top. We ended up driving the diesel around again, and towed the GTI's trailer for it.

What we learned from this was that while high speed horse power is desirable, low speed torque is more practical. At least in an application with such a small engine. Most street racers think they want horse power, but what they really want is torque. To build a high horsepower engine, you are sacrificing torque, and creating an environment where you need to maintain high rpms. A 700 horsepower engine doesn't do well grocery shopping, or cruising for that matter, but a high torque engine will snap your neck and bark your tires.

I hope that helped.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

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Capri306 · 10-03-2001, 12:44 PM

Just an FYI here:

Torque is the twisting force an engine -- or anything else for that matter -- exerts. For example, if I have a breaker bar on a fastener, and I apply 50 lbs of force (at a direction parallel to the tangent) one foot from the center of the fastener, that would be 50 foot pounds (or pound-feet if you like speaking an engineer's bass-ackwards English) of torque applied to the fastener. Just the same is happening at the flywheel, the wheels, etc. In fact I have some rather lengthy formulas to determine torque applied to the ground on a car if you know the engine's torque.

Horsepower is the ability to do work, which of course envolves time. Time is the crucial element here. One horsepower is the amount of work required to move 550 pounds one foot in one second. That is the very definition of it.

So to clarify, torque is that "push" feeling you get when accelerating, and horsepower is the ability to keep doing it over time...at least that's the way it works out mathematically.

------------------
Capri306, Moderator, The Mustang Works Online

"PROUD TO BE AN AMERICAN!!!"

73 Mustang Boy · 10-03-2001, 02:03 PM

It is also important to consider that in an internal combustion engine the HP and Torque will always be equal at 5252 RPM's since the definition of HP is Torque* times RPM/5252. When you dyno a motor it measures the torque of the motor then does the math to get HP.
*Torque measured in FtLbs

I hate Rice · 10-03-2001, 03:43 PM

I am a potential physics major so i know what HP, and torque are and how to calculate HP from torque and what not, what i am primarly concerned with is how compression effects torque and horsepower, and how stroke and bore relate to power. Lets say you have a 4.6 but the cylinders are very narrow and long and vice versa were they are very shallow. How does this effect hp and torque. Also what can you do to change compression. It just for my knowledge cuz their are plenty of mods before any deep engine work on my pony. Thank you.

73 Mustang Boy · 10-03-2001, 04:56 PM

I am an mechanical enginering major at Georgia Southern University and by no means an expert. I think that all other things beeing equal, 2 motors with the same displacement, one with long stroke and small bore the other with short stroke and large bore, should produce the same amount of torque if both motors have the same efficiency. But, the longer the stroke on a motor the faster the piston has to move up and down the cylinder (I'm sure there is a limit on how fast that can be before something breaks). The larger bore would increase friction in the bore but not piston speed. In either case the increased friction would cause more heat in the motor lowering its max RPM. I personaly think it would be better to modify the stroke on an engine. This would maintain the effiency of combustion in the combustion chamber since the cylinder heads were designed with a specific bore in mind. Someone feel free to correct me if I am wrong because like i said I have no clue, just guessing from current knowledge.

1965GTO · 10-03-2001, 11:53 PM

On two engines of the same displacement there are many variables that affect torque and horsepower besides stroke and bore. Such as rod length, compression, etc. The one thing I can say for sure is that increasing displacement will increase torque. And I would not try comparing deisels with gasoline engines.

PKRWUD · 10-04-2001, 10:03 AM

That's too bad because displacement alone has nothing to do with torque, and a gasoline/diesel comparison is actually excellent. Two engines with the same bore and stroke, one gasoline, with 9:1 compression, and the other a diesel, with 23:1 compression, have completely different horsepower and torque numbers. But I'm sure you already knew that.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

PKRWUD · 10-04-2001, 10:06 AM

65 Goat-
How does rod length affect torque and horsepower??? Unless you are referring to stroke or compression, to my knowledge, it doesn't. Please explain.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

PGkelly · 10-04-2001, 09:43 PM

rod length does affect torque output. a longer connecting rod will help generate more torque, because the longer connecting rod will let the crank reach the moment of 90* (where it produces most of it's torque) faster. intertesting, i never really thought about it. an old hot rodding trick was to bore out an engine at a slight angle to help increase torque as well. there was a little paragraph about this very subject in the magazine "motor cyclist" not long ago.

------------------
If it ain't broke, make it go faster

AOL: MCVillain45

PKRWUD · 10-05-2001, 03:20 AM

In otherwords, a shorter stroke. The rod length is an after-thought. If the actual rod length was what was doing it, all racing pistons would be 1/2" thick with longer rods. That's an interesting theory though. It goes against what I've been taught, unless you add a governor to keep the rpm in the torque range. Otherwise, a shorter stroke will actually take the engine out of the torque range faster.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

silver_pilate · 10-05-2001, 01:24 PM

The way I see it, a stroker crank, while increasing displacement by making the pistons travel further, also increases torque by creating a longer moment arm. The longer the moment arm, the greater the torque (given the same angle of force on the crank...which we all know changes due to increased rod angle). This makes sense to me why stroker engines are such torque monsters: the moment arm (distance from the axis of motion to the application of force) is greater.

As far as all of the other issues, I don't want to think about that right now. I have to study for my Patho test.

--nathan

------------------
--silver_pilate

'91 GT, Built 306, Wolverine 1087 cam, ported Windsor Jr. Irons, and all the goodies...click the link to the left to see a full list of my mods...

Tried and True 302 Being Built to Outrun You! heh heh heh...
--Texas Panhandle--
Check out my site

Unit 5302 · 10-05-2001, 06:31 PM

I'm suprised I didn't notice this topic earlier.

Here's the deal. Torque is a product of cylinder pressure and displacement. Those are the two components that go into making torque. Bore is a larger component of displacement than stroke.

The equation for determining cylinder displacement is (pi)(r^2)(h). Take a V-8 with a 3.5"x3.5" cylinder. It would displace 269ci. Now make it's bore 4", so 4"x3.5". It now displaces 352ci. Now make the stroke 4" so 3.5"x4". It now displaces 308ci.

While the long rod guys would like to argue the longer the rod, the more force exerted on the crankshaft, and thus, the more torque produced. That theory is lacking regard for the actual cylinder pressure component, and the speed at which that force is being exerted. A long rod engine will be exerting maximum force where the actual amount leverage on the crankshaft is the greatest, however the time spent in that position is greater, all the while cylinder pressure is falling. The long rod engine will also have a great deal of time spent at low force positions where it's angle of force is less, furthermore, the energy taken to move that longer rod with more weight while not on a power stroke would be detremental.

For an example of a classic low torque engine I will use the 5.0HO. With a 4.000"x3.000" cylinder configuration and modest 9.0:1 compression, on paper with stroke theory guys, it should be a kitten. It's rated at 300lb/ft at a modest 3200rpm.

Now for an example of what should be a much torqier engine. The Chevy 350 used in the early 90's Z28. 4.000"x3.480". With it's much longer stroke, and significantly higher 9.75:1 compression ratio it should blow the doors off the 5.0HO (302) Ford's torque numbers. Even if the stroke was the same, the much higher 9.75:1 compression should create more torque than the Ford.

The result is 225hp@4200rpm and 300lb/ft@3200rpm for the Ford. 240hp@4400rpm and 345lb/ft@3200rpm for the Chevy. Numbers are very similar when the 302 is pitted against the 351 in similar configurations. The 302 defies the engine builder long stroke/small bore torque theory.

Horsepower is the amount of work done by the force (torque). The equation as noted above for figuring out hp is (torque x rpm) / 5250.

As far as a diesel vs a gasoline powered car the results can be very much skewed by altered gear ratios which allow a car to increase the actual torque at the wheels by torque multiplication factors, and the pure torque available at a given rpm. Giving that GTI the gearing necessary to run at 7000rpm where the Diesel was running 3000 would have resulted in a different ending I think.

Then again, all of this is very much based in theory as well.

Unit 5302 · 10-05-2001, 06:36 PM

By the way, I've come to the conclusion that that 302 can make more power with conventional parts than a 351 ever can, simply by the amount of rpms the 302 is capable of running past the 351 in relation to critical mass and percentage of displacement.

I hate Rice · 10-06-2001, 12:40 AM

From what I have read and what not, i became curious on compression. Compression seems critical to torque and therfore ponies. I have only basic, basic knowledge of engines and I dont do much wrenching, I just wanna know to satisfy my curiousity but how do you change compression ratios and is there a formula for safe octanes to work in a given engine at a given temperature. Maybe a chart of some type. I am interested in N/A applications and since I have plenty of time to build my beast I would like to start learning. Thankyou.

Crazy Horse GT · 10-06-2001, 01:09 AM

hey unit 5302 in about 2 year's , how much would you charge me to help me build my 4.6 i'm kidding , but not really you seem to know , i'm just learning these new mod engine's, i am mainly a diesel mech, i am old school on gas burner's, point's , dwell , etc all my ride's were mainly early 70's & 60's model's i can tune the he-- out of them but am just getting into the new stuff , just a thought . later

------------------

Unit 5302 · 10-06-2001, 01:10 AM

Compression definately effects torque production. Everywhere. Hence, it effects horsepower as well.

To increase the compression you can do several things. Buy domed pistons, shave/mill the head to bring the combustion chamber closer to the piston, or purchase new heads that have smaller combustion chambers ex. GT-40p's.

The actual octane required to run on a higher compression engine is related to more than just compression alone. Timing, combustion efficiency, spark quality, and several other combustion qualities go into it. That along with the kind of material the head is built out of.

On an iron headed car like the stock 5.0HO setup, you could probably get by close to 9.5:1 on 87oct. Again, it all depends on other factors. Anything above 9.5:1 will certainly require higher octane fuel to keep timing at 10* or higher. Going anything beyond say 10.5:1 or so on iron heads is pretty risky IMHO. The older cars did it, but they also required things like leaded gas with much better octane qualities than what we run today. Plus the heat generated by combustion of that type is hard to dissapate with iron heads.

There are a lot of guys on the works that can help you with the performance experiance aspect more than I can, I'm only offering the technical theory and general idea behind how it works.

You'll find a lot of what gets into that area can be disputed one way or another based on opinions.

10-02-2001, 10:55 PM	#1
I hate Rice Registered Member Join Date: Aug 2001 Posts: 81	Fundemental car question Alright I know what torque is and what HP is, but what I am curious is what are the determinents of it. I've been chipping away at it and does stroke or bore play more of a role in determing torque, or does it matter. I was hoping some one would just explain a little engine theory or at least point me in the right direction. I really dont want to one of those stupid 17 year olds that doesnt have an independent thought in their head. Thanks

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10-02-2001, 10:59 PM	#2
sedanman Registered Member Join Date: Feb 1999 Location: Indianapolis, IN Posts: 963	Be a little more specific in your question and I think we could answer it a little more effectively. I know there are several bright guys in here and several mechanical engineers (myself included). Do you want to know how stroke and bore effect the power curve, or do you want a whole speal on torque and horsepower and how your motor makes them?

10-03-2001, 08:22 AM	#3
Kevin Price Registered Member Join Date: Jan 1999 Location: Oxford, KS Posts: 935	Moved to Blue Oval Lounge ------------------ SVO siamesed 351 stroked to 417ci,Yates heads, solid roller,Trans King glide and a little blue bottle of giggle gas. My Car

10-03-2001, 08:46 AM	#4
bigwhitecobra Huh? Whatcha said? Join Date: Oct 2000 Location: Fayetteville, NC Posts: 1,073	Ok, I'll give it a try. Bare in mind that I'm not an engineer or some technical wizard. Horsepower is the amount of work being done by the engine burning the fuel(gas, desiel, etc). Wait, I'm getting ahead of myself.... Horsepower is defined as the amount of force that is required to lift 100 pounds 100 feet for 1 minute.(I think that's right, if not UNIT5302 can explain it) I'm not sure how torque is defined, but I know that it is directly related to engine size. Ok, given that, let's say you have an engine making 200HP and 250lb-ft of TQ at the wheels. And let's say that it's a 5.0L. Anything that you do to will increase the output(output being HP and TQ). Now, if you have a larger engine, and do the same type of upgrades, you will end up with a higher output figure than the original engine. Here's why. The larger engine has the ability to move more air and fuel than the smaller one, creating more power. (Which is why I don't understand why the import guys are so cocky) By nature, a 351 will make more power than a 302, and a 302 will make more power than a 289, and so on. I hope that I haven't confused you any. I don't know if this is as factual as I think it is, but this is what I've come up with. I think it works. Anyway, later. ------------------ "Is that a Cobra?" "Yeah" "It's a V6, right?" "Yeah"

10-03-2001, 11:47 AM	#5
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	When you're riding your mountian bike uphill, and you have to stand up in your seat in order to pedal over the top... that's torque. When your flying down the other side... that's horsepower. They each play an important role. While you certainly aren't flying up the hill, you are making it. But, if you tried to use all that power to go fast, you'd hurt yourself. Imagine flying down the hill while trying to pedal faster standing up. At the same time, the horsepowere aspect, flying down the hill, you're crouched and pedaling quickly in short strokes. It works killer for going fast down hill, but try climbing the hill like that. You wouldn't get very far. Generally, stroke and compression are the biggest factors. A long stroke will generate more torque, while a short stroke allows the engine to rotate faster, creating horsepower. Bore is important, but not as big a deal as stroke. Horsepower = speed. The faster an engine can turn, the more hp it can generate, bores being equal. Another way of looking at it is a test my college engine rebuilding class did 16 years ago. About 20 miles from where I live is the Conejo Grade. It's part of the 101 freeway, and basically goes straight up a 1800' incline in less than 2 miles. It can be brutal to small, weak vehicles. Anyway, we had received as a donation two brand new VW Rabbits. One was a diesel and the other was a GTI. The diesel redlined at 3000rpm, and the GTI went to 7000rpm.We raced them up the Conejo Grade. Obviously, the GTI kicked *** , the first time. The second time, we attached a trailer with a few engine blocks on it to both cars. The added weight was close to 1500 pounds. The diesel won the second race. In fact, the diesel finished within 20 seconds of the time it took to reach the top the first time. The GTI didn't even make it to the top. We ended up driving the diesel around again, and towed the GTI's trailer for it. What we learned from this was that while high speed horse power is desirable, low speed torque is more practical. At least in an application with such a small engine. Most street racers think they want horse power, but what they really want is torque. To build a high horsepower engine, you are sacrificing torque, and creating an environment where you need to maintain high rpms. A 700 horsepower engine doesn't do well grocery shopping, or cruising for that matter, but a high torque engine will snap your neck and bark your tires. I hope that helped. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

10-03-2001, 12:44 PM	#6
Capri306 Moderator Join Date: Sep 1998 Location: Grand Rapids, Michigan, USA Posts: 1,001	Just an FYI here: Torque is the twisting force an engine -- or anything else for that matter -- exerts. For example, if I have a breaker bar on a fastener, and I apply 50 lbs of force (at a direction parallel to the tangent) one foot from the center of the fastener, that would be 50 foot pounds (or pound-feet if you like speaking an engineer's bass-ackwards English) of torque applied to the fastener. Just the same is happening at the flywheel, the wheels, etc. In fact I have some rather lengthy formulas to determine torque applied to the ground on a car if you know the engine's torque. Horsepower is the ability to do work, which of course envolves time. Time is the crucial element here. One horsepower is the amount of work required to move 550 pounds one foot in one second. That is the very definition of it. So to clarify, torque is that "push" feeling you get when accelerating, and horsepower is the ability to keep doing it over time...at least that's the way it works out mathematically. ------------------ Capri306, Moderator, The Mustang Works Online *"PROUD TO BE AN AMERICAN!!!"*

10-03-2001, 02:03 PM	#7
73 Mustang Boy Registered Member Join Date: Aug 2001 Location: Georgia Posts: 84	It is also important to consider that in an internal combustion engine the HP and Torque will always be equal at 5252 RPM's since the definition of HP is Torque* times RPM/5252. When you dyno a motor it measures the torque of the motor then does the math to get HP. *Torque measured in FtLbs

10-03-2001, 03:43 PM	#8
I hate Rice Registered Member Join Date: Aug 2001 Posts: 81	I am a potential physics major so i know what HP, and torque are and how to calculate HP from torque and what not, what i am primarly concerned with is how compression effects torque and horsepower, and how stroke and bore relate to power. Lets say you have a 4.6 but the cylinders are very narrow and long and vice versa were they are very shallow. How does this effect hp and torque. Also what can you do to change compression. It just for my knowledge cuz their are plenty of mods before any deep engine work on my pony. Thank you.

10-03-2001, 04:56 PM	#9
73 Mustang Boy Registered Member Join Date: Aug 2001 Location: Georgia Posts: 84	I am an mechanical enginering major at Georgia Southern University and by no means an expert. I think that all other things beeing equal, 2 motors with the same displacement, one with long stroke and small bore the other with short stroke and large bore, should produce the same amount of torque if both motors have the same efficiency. But, the longer the stroke on a motor the faster the piston has to move up and down the cylinder (I'm sure there is a limit on how fast that can be before something breaks). The larger bore would increase friction in the bore but not piston speed. In either case the increased friction would cause more heat in the motor lowering its max RPM. I personaly think it would be better to modify the stroke on an engine. This would maintain the effiency of combustion in the combustion chamber since the cylinder heads were designed with a specific bore in mind. Someone feel free to correct me if I am wrong because like i said I have no clue, just guessing from current knowledge.

10-03-2001, 11:53 PM	#10
1965GTO Registered Member Join Date: Jul 2001 Location: Dupo,ill Posts: 219	On two engines of the same displacement there are many variables that affect torque and horsepower besides stroke and bore. Such as rod length, compression, etc. The one thing I can say for sure is that increasing displacement will increase torque. And I would not try comparing deisels with gasoline engines.

10-04-2001, 10:03 AM	#11
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	That's too bad because displacement alone has nothing to do with torque, and a gasoline/diesel comparison is actually excellent. Two engines with the same bore and stroke, one gasoline, with 9:1 compression, and the other a diesel, with 23:1 compression, have completely different horsepower and torque numbers. But I'm sure you already knew that. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

10-04-2001, 10:06 AM	#12
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	65 Goat- How does rod length affect torque and horsepower??? Unless you are referring to stroke or compression, to my knowledge, it doesn't. Please explain. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

10-04-2001, 09:43 PM	#13
PGkelly Registered Member Join Date: Feb 2001 Posts: 274	rod length does affect torque output. a longer connecting rod will help generate more torque, because the longer connecting rod will let the crank reach the moment of 90* (where it produces most of it's torque) faster. intertesting, i never really thought about it. an old hot rodding trick was to bore out an engine at a slight angle to help increase torque as well. there was a little paragraph about this very subject in the magazine "motor cyclist" not long ago. ------------------ If it ain't broke, make it go faster AOL: MCVillain45

10-05-2001, 03:20 AM	#14
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	In otherwords, a shorter stroke. The rod length is an after-thought. If the actual rod length was what was doing it, all racing pistons would be 1/2" thick with longer rods. That's an interesting theory though. It goes against what I've been taught, unless you add a governor to keep the rpm in the torque range. Otherwise, a shorter stroke will actually take the engine out of the torque range faster. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

10-05-2001, 01:24 PM	#15
silver_pilate DURKA DURKA!! Join Date: Sep 1997 Location: Lubbock, TX...(TX panhandle) Posts: 1,418	The way I see it, a stroker crank, while increasing displacement by making the pistons travel further, also increases torque by creating a longer moment arm. The longer the moment arm, the greater the torque (given the same angle of force on the crank...which we all know changes due to increased rod angle). This makes sense to me why stroker engines are such torque monsters: the moment arm (distance from the axis of motion to the application of force) is greater. As far as all of the other issues, I don't want to think about that right now. I have to study for my Patho test. --nathan ------------------ --silver_pilate '91 GT, Built 306, Wolverine 1087 cam, ported Windsor Jr. Irons, and all the goodies...click the link to the left to see a full list of my mods... Tried and True 302 Being Built to Outrun You! heh heh heh... --Texas Panhandle-- Check out my site

10-05-2001, 06:31 PM	#16
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	I'm suprised I didn't notice this topic earlier. Here's the deal. Torque is a product of cylinder pressure and displacement. Those are the two components that go into making torque. Bore is a larger component of displacement than stroke. The equation for determining cylinder displacement is (pi)(r^2)(h). Take a V-8 with a 3.5"x3.5" cylinder. It would displace 269ci. Now make it's bore 4", so 4"x3.5". It now displaces 352ci. Now make the stroke 4" so 3.5"x4". It now displaces 308ci. While the long rod guys would like to argue the longer the rod, the more force exerted on the crankshaft, and thus, the more torque produced. That theory is lacking regard for the actual cylinder pressure component, and the speed at which that force is being exerted. A long rod engine will be exerting maximum force where the actual amount leverage on the crankshaft is the greatest, however the time spent in that position is greater, all the while cylinder pressure is falling. The long rod engine will also have a great deal of time spent at low force positions where it's angle of force is less, furthermore, the energy taken to move that longer rod with more weight while not on a power stroke would be detremental. For an example of a classic low torque engine I will use the 5.0HO. With a 4.000"x3.000" cylinder configuration and modest 9.0:1 compression, on paper with stroke theory guys, it should be a kitten. It's rated at 300lb/ft at a modest 3200rpm. Now for an example of what should be a much torqier engine. The Chevy 350 used in the early 90's Z28. 4.000"x3.480". With it's much longer stroke, and significantly higher 9.75:1 compression ratio it should blow the doors off the 5.0HO (302) Ford's torque numbers. Even if the stroke was the same, the much higher 9.75:1 compression should create more torque than the Ford. The result is 225hp@4200rpm and 300lb/ft@3200rpm for the Ford. 240hp@4400rpm and 345lb/ft@3200rpm for the Chevy. Numbers are very similar when the 302 is pitted against the 351 in similar configurations. The 302 defies the engine builder long stroke/small bore torque theory. Horsepower is the amount of work done by the force (torque). The equation as noted above for figuring out hp is (torque x rpm) / 5250. As far as a diesel vs a gasoline powered car the results can be very much skewed by altered gear ratios which allow a car to increase the actual torque at the wheels by torque multiplication factors, and the pure torque available at a given rpm. Giving that GTI the gearing necessary to run at 7000rpm where the Diesel was running 3000 would have resulted in a different ending I think. Then again, all of this is very much based in theory as well.

10-05-2001, 06:36 PM	#17
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	By the way, I've come to the conclusion that that 302 can make more power with conventional parts than a 351 ever can, simply by the amount of rpms the 302 is capable of running past the 351 in relation to critical mass and percentage of displacement.

10-06-2001, 12:40 AM	#18
I hate Rice Registered Member Join Date: Aug 2001 Posts: 81	From what I have read and what not, i became curious on compression. Compression seems critical to torque and therfore ponies. I have only basic, basic knowledge of engines and I dont do much wrenching, I just wanna know to satisfy my curiousity but how do you change compression ratios and is there a formula for safe octanes to work in a given engine at a given temperature. Maybe a chart of some type. I am interested in N/A applications and since I have plenty of time to build my beast I would like to start learning. Thankyou.

10-06-2001, 01:09 AM	#19
Crazy Horse GT Registered Member Join Date: Aug 2001 Location: Sale Creek, TN. C. S. A. Posts: 4,652	hey unit 5302 in about 2 year's , how much would you charge me to help me build my 4.6 i'm kidding , but not really you seem to know , i'm just learning these new mod engine's, i am mainly a diesel mech, i am old school on gas burner's, point's , dwell , etc all my ride's were mainly early 70's & 60's model's i can tune the he-- out of them but am just getting into the new stuff , just a thought . later ------------------

10-06-2001, 01:10 AM	#20
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	Compression definately effects torque production. Everywhere. Hence, it effects horsepower as well. To increase the compression you can do several things. Buy domed pistons, shave/mill the head to bring the combustion chamber closer to the piston, or purchase new heads that have smaller combustion chambers ex. GT-40p's. The actual octane required to run on a higher compression engine is related to more than just compression alone. Timing, combustion efficiency, spark quality, and several other combustion qualities go into it. That along with the kind of material the head is built out of. On an iron headed car like the stock 5.0HO setup, you could probably get by close to 9.5:1 on 87oct. Again, it all depends on other factors. Anything above 9.5:1 will certainly require higher octane fuel to keep timing at 10* or higher. Going anything beyond say 10.5:1 or so on iron heads is pretty risky IMHO. The older cars did it, but they also required things like leaded gas with much better octane qualities than what we run today. Plus the heat generated by combustion of that type is hard to dissapate with iron heads. There are a lot of guys on the works that can help you with the performance experiance aspect more than I can, I'm only offering the technical theory and general idea behind how it works. You'll find a lot of what gets into that area can be disputed one way or another based on opinions.