Anyone have proof that a long stroke makes torque?
01-20-2014, 10:50 PM
#61
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Additionally, the majority of torque comes from roughly the first inch of downward motion on the power stroke. A shorter stroke engine means the piston is moving slower at the same RPM, keeping the piston in the "power zone" (for lack of a better term) longer.
IMHO there are too many variables to consider to just stand on theory. That's why I was asking if anyone has built the engines and made the comparisons with LS engines. Gen I comparisons between the 383s and 377s don't necessarily translate.
More generally, consider this... If stroke is more important than bore, why did the GM 307 (3.875×3.25) and 305 (3.73x3.48) perform so poorly compared to it's short stroke brothers, the 302 (4.00×3.00) and even the 283 (3.875×3.00)?
The 4.3L L99 (3.73x3.00) in my old 95 caprice performs surprisingly well pushing around a 4000+ lb car. This was very unexpected but it would seem that all those nifty LT1 parts on the little 265ci mouse motor made a significant difference despite the small valve, small stroke and even small bore of the engine.
The 307 was designed as a truck engine and worked great in its application. And as a matter of fact I had one that we put a duntov cam and double hump heads on and won many of street races with.
Simple thing to do would go with the 6.0 and maybe a longer rod to play with piston dwell for torque.
01-21-2014, 07:15 AM
#62
Higher knock thresholds favor small bores and large strokes.
01-21-2014, 09:24 AM
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NOT opinion...these fellas....David Reher and Buddy Morrison had a stranglehold on Pro Stock back in the 80-84 seasons before Lee Shephard unexpectedly died on a trire testing pass where he was supposed to lift early. This is truth for a competition engine. For an rpm limited street engine...meaning 2500-6500 the long stroke engine continues to show how/why simple physics can NOT be ignored. Go ahead and build your combo which will unequivacly make great power per inch....however a 5500 lb vehicle at 2200 rpms for mileage needs leverage....period !!!
01-21-2014, 01:56 PM
#68
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OK, Here's a dumb question for you folks that think I'm not too bright. GM created the 6.2L truck engine using the same stroke as the 5.3L but they increased the bore from 3.779" to 4.065"? The torque differences between the 5.3L and 6.2L engines: 340 ft/lbs @ 4000 RPM (5.3L Gen IV) vs 417 ft/lbs @ 4300 RPM (6.2L Gen IV). Why didn't those knucklehead engineers increase the stroke instead? Why would they do this to truck engines?
01-21-2014, 03:50 PM
#69
OK, Here's a dumb question for you folks that think I'm not too bright. GM created the 6.2L truck engine using the same stroke as the 5.3L but they increased the bore from 3.779" to 4.065"? The torque differences between the 5.3L and 6.2L engines: 340 ft/lbs @ 4000 RPM (5.3L Gen IV) vs 417 ft/lbs @ 4300 RPM (6.2L Gen IV). Why didn't those knucklehead engineers increase the stroke instead? Why would they do this to truck engines?
We have to remain aware that there is often a big gap between the practical, and the theoretical.
01-21-2014, 04:14 PM
#70
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A lot more going on in their minds than maximum torque production. The LS series motors were designed around the 3.62 stroke. I thas been shown numerous times on here that long stroke motors especially beyond 4 inches have higher oil consumption and piston scuffing issues. I am sure it was more economically viable to buy a bunch of 6.2 blocks to use in Corvett/Camaro/Truck applications using a common format than a one off block with longer liners for truck production. They met a torque value they wanted while maintaning economies of scale. By extension the 5.4 Mod motor is a long stroke design becasue forced packaging into front wheel drive cars forced a narrow bore spcing in the mod motors.
We have to remain aware that there is often a big gap between the practical, and the theoretical.
We have to remain aware that there is often a big gap between the practical, and the theoretical.
01-21-2014, 04:30 PM
#71
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It was an Olds from a competitor in the competition. It's not some backyard build with claimed pistons and a 3/4 race cam. The Olds was a well refined combo as well.
Who promised that? Research Sir Harry Ricardo and his fuel bomb tests. Then maybe try some Charles F. Taylor and his work on combustion while he was at MIT.
Higher knock thresholds favor small bores and large strokes.
Who promised that? Research Sir Harry Ricardo and his fuel bomb tests. Then maybe try some Charles F. Taylor and his work on combustion while he was at MIT.
Higher knock thresholds favor small bores and large strokes.
http://www.purplesagetradingpost.com...%20engine.html
Did they lie? Was it some sort of fluke?
01-21-2014, 04:38 PM
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OK, Here's a dumb question for you folks that think I'm not too bright. GM created the 6.2L truck engine using the same stroke as the 5.3L but they increased the bore from 3.779" to 4.065"? The torque differences between the 5.3L and 6.2L engines: 340 ft/lbs @ 4000 RPM (5.3L Gen IV) vs 417 ft/lbs @ 4300 RPM (6.2L Gen IV). Why didn't those knucklehead engineers increase the stroke instead? Why would they do this to truck engines?
You also have to look at the consistent increase in compression over the years, with the introduction of aluminum heads being standard on engines. Computer modeling and CNC machines, EFI...everything has evolved to the point that we're benefiting from it. Years ago, 10.5:1 was almost unheard of on pump gas, a gross cam lift over .500 was a "performance cam", and 1 hp/c.i. was the goal. All of these those now are done by pretty much any OEM. To that end, they could essentially increase the surface area without changing much else and easily attain their goals, all the while still keeping the platform modular with all the interchanging parts. Just think of what going from a 23 to 15 degree and then an 11 degree valve angle has done.
In conclusion, I think most of us can agree that displacement is displacement no matter how achieved. The longer stroke lends itself more to lower RPM based use by decreasing dwell time at TDC, allowing for increased timing and compression by reduction of inherent detonation. Many of those hurdles can be overcome with today's parts and technology so in the end, it really comes down more to how much you want to spend on such a generic build when in reality, you could make essentially the same output (regardless of which way you go about it) with a junkyard engine and off the shelf parts.
01-21-2014, 04:51 PM
#73
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My mention of science when I started this thread was meant to allude to the scientific method:
I see a lot of hypotheses and conclusions but where are the CONTROLLED tests? So far as I can tell thus far, the bore vs stroke debate is about as settled as Anthropomorphic Global Warming (I don't believe in AGW either).
- Ask a Question
- Do Background Research
- Construct a Hypothesis
- Test Your Hypothesis Through Experimentation
- Analyze Your Data and Draw a Conclusion
- Communicate Your Results
I see a lot of hypotheses and conclusions but where are the CONTROLLED tests? So far as I can tell thus far, the bore vs stroke debate is about as settled as Anthropomorphic Global Warming (I don't believe in AGW either).
01-21-2014, 05:42 PM
#74
OK, Here's a dumb question for you folks that think I'm not too bright. GM created the 6.2L truck engine using the same stroke as the 5.3L but they increased the bore from 3.779" to 4.065"? The torque differences between the 5.3L and 6.2L engines: 340 ft/lbs @ 4000 RPM (5.3L Gen IV) vs 417 ft/lbs @ 4300 RPM (6.2L Gen IV). Why didn't those knucklehead engineers increase the stroke instead? Why would they do this to truck engines?
So a 17% increase in displacement and a 7.5% increase in peak torque rpm for a 23% torque increase using completely different heads and intake and cam and VVT and a full friggin point of compression, and all you can see is more bore=more torque.
The cam besides being VVT is 8 degrees more duration and 7.5% more lift.
Once you look at all that your example is pretty poor with all the extra compression, cam, VVT etc. I would have hoped for a bigger difference AND it raised the rpm which is not what you want on this build.
You are only interested in cherry picking info to support your hypothesis details be damned. I am not saying you are wrong, I am saying look at the whole picture rather than just the part you want to see.
If you wanted a valid comparison you would look at the 4.8l vs the 5.3l since they are very much the same engines just shortening stroke, in a given year I believe they have the same specs heads/intake/cam, compression very very close. In that case the percentage torque change vs. the percentage displacement change is very very close about 9% which actually is a reasonable support to your argument that displacement is the big factor moreso than stroke except that the peak torque rpm was raised. Not the direction you want the torque curve to go for this build.
01-21-2014, 05:47 PM
#75
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Probably quite a few things in all honesty. It's much like how they came to decide upon a stroke of 3.62"...it's what they found best for fuel economy, longevity, and power output. The factory stroke is not really short when you think about it, being the 350 used a 3.48" stroke for half a century. You also have to look at the cylinder length of the LS platform, it was several years before the aftermarket came up with solid piston skirt/ring pack profiles that made 4"+ stroke motors reliable enough to become DD. It was a lot of trial and error to get to that point. In the end, I think much had to do with tooling...they could easily increase bore and still attain the results they wanted with the platform they already had. Ford's modular platform was just the opposite. Since they handicapped themselves with such stupidly small bore spacing, they increased the stroke dramatically to get the 5.4. Yes, the deck height increased and I think that's what GM's engineers wanted to avoid.
You also have to look at the consistent increase in compression over the years, with the introduction of aluminum heads being standard on engines. Computer modeling and CNC machines, EFI...everything has evolved to the point that we're benefiting from it. Years ago, 10.5:1 was almost unheard of on pump gas, a gross cam lift over .500 was a "performance cam", and 1 hp/c.i. was the goal. All of these those now are done by pretty much any OEM. To that end, they could essentially increase the surface area without changing much else and easily attain their goals, all the while still keeping the platform modular with all the interchanging parts. Just think of what going from a 23 to 15 degree and then an 11 degree valve angle has done.
In conclusion, I think most of us can agree that displacement is displacement no matter how achieved. The longer stroke lends itself more to lower RPM based use by decreasing dwell time at TDC, allowing for increased timing and compression by reduction of inherent detonation. Many of those hurdles can be overcome with today's parts and technology so in the end, it really comes down more to how much you want to spend on such a generic build when in reality, you could make essentially the same output (regardless of which way you go about it) with a junkyard engine and off the shelf parts.
You also have to look at the consistent increase in compression over the years, with the introduction of aluminum heads being standard on engines. Computer modeling and CNC machines, EFI...everything has evolved to the point that we're benefiting from it. Years ago, 10.5:1 was almost unheard of on pump gas, a gross cam lift over .500 was a "performance cam", and 1 hp/c.i. was the goal. All of these those now are done by pretty much any OEM. To that end, they could essentially increase the surface area without changing much else and easily attain their goals, all the while still keeping the platform modular with all the interchanging parts. Just think of what going from a 23 to 15 degree and then an 11 degree valve angle has done.
In conclusion, I think most of us can agree that displacement is displacement no matter how achieved. The longer stroke lends itself more to lower RPM based use by decreasing dwell time at TDC, allowing for increased timing and compression by reduction of inherent detonation. Many of those hurdles can be overcome with today's parts and technology so in the end, it really comes down more to how much you want to spend on such a generic build when in reality, you could make essentially the same output (regardless of which way you go about it) with a junkyard engine and off the shelf parts.
- I'm 50 yrs old, this may be the last engine I ever design. I don't even plan to build it myself!.
- I find the results of the article that I linked to with 11:1 compression on trash gas "seductive".
- My last engine (still not finished) is an LT4 with 11.2:1 compression. Don't want to retreat to 10.x:1.
- Never owned a long rod engine. The guys I knew that had them liked them.
- I've never seen an unhappy owner of a 327 in a truck or car. Most "feel" stronger than 350s.
- I've owned Olds 305, Chevy 305, Chevy 307, and a Chevy 454 didn't like any of them.
- I've owned the Ford 302 in a towncar and a 460 in a truck. Hated the 460.
- The 350 I built for my father's 1 ton truck was an amazing success (4.045x3.49).
- Father's truck could out-pull the stock TBI 454 and all the other trucks in the family going up a 7% grade (hunting, 7-10 trucks depending upon the year).
- My Firebird with a Chevy 350 I built in the 80s was really too fast for my needs then and now.
I guess you could say those are my life's observations. In the past, I could never afford exactly what I wanted to build. I'm still making trade-offs on this engine, just not as many. The 4.00x3.62 would just be a repeat of what I've done in the past.
01-21-2014, 06:05 PM
#77
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So a 17% increase in displacement and a 7.5% increase in peak torque rpm for a 23% torque increase using completely different heads and intake and cam and VVT and a full friggin point of compression, and all you can see is more bore=more torque.
The cam besides being VVT is 8 degrees more duration and 7.5% more lift.
Once you look at all that your example is pretty poor with all the extra compression, cam, VVT etc. I would have hoped for a bigger difference AND it raised the rpm which is not what you want on this build.
You are only interested in cherry picking info to support your hypothesis details be damned. I am not saying you are wrong, I am saying look at the whole picture rather than just the part you want to see.
If you wanted a valid comparison you would look at the 4.8l vs the 5.3l since they are very much the same engines just shortening stroke, in a given year I believe they have the same specs heads/intake/cam, compression very very close. In that case the percentage torque change vs. the percentage displacement change is very very close about 9% which actually is a reasonable support to your argument that displacement is the big factor moreso than stroke except that the peak torque rpm was raised. Not the direction you want the torque curve to go for this build.
The cam besides being VVT is 8 degrees more duration and 7.5% more lift.
Once you look at all that your example is pretty poor with all the extra compression, cam, VVT etc. I would have hoped for a bigger difference AND it raised the rpm which is not what you want on this build.
You are only interested in cherry picking info to support your hypothesis details be damned. I am not saying you are wrong, I am saying look at the whole picture rather than just the part you want to see.
If you wanted a valid comparison you would look at the 4.8l vs the 5.3l since they are very much the same engines just shortening stroke, in a given year I believe they have the same specs heads/intake/cam, compression very very close. In that case the percentage torque change vs. the percentage displacement change is very very close about 9% which actually is a reasonable support to your argument that displacement is the big factor moreso than stroke except that the peak torque rpm was raised. Not the direction you want the torque curve to go for this build.
http://media.gm.com/content/media/us...2013.tab1.html
01-21-2014, 06:12 PM
#78
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Thread Starter
No argument there but the "Tonawanda 454" was supposed to be a desirable engine! My old 350s made me happy. I just want to be happy again :/
01-21-2014, 06:35 PM
#79
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Super Chevy 4.8 vs 5.3
http://www.superchevy.com/technical/.../photo_16.html
This would be great if they had also tested a 4.00x3.26 5.3L too.
http://www.superchevy.com/technical/.../photo_16.html
This would be great if they had also tested a 4.00x3.26 5.3L too.
01-21-2014, 07:21 PM
#80
Reggogled to make sure I used pre-VVT numbers which I am finding for 2005 330tq for the 5.3 and 285 for the 4.8l making the torque number fall by a greater percentage than displacement.
On the 5.3l L92 comparison even taking the VVT out of the equation still looking at a point of compression a lot of displacement, more cam and a LOT more head/intake flow.
On the superchevy link you posted I think it reasonable that when engine dyno tested without all the OEM hangups the engines make similar peak horse power, given the same heads and cam. GM might be fudging the 4.8l HP numbers or tune to restrict the HP to upsell the 5.3l.
The thing I still see you not paying attention to though is rpm, looks like a 4-500rpm difference in peak point, how much of that is stroke or displacement I couldn't say but it is part of the total package to be considered. The peak torque rpm is up on the L92 as well
On the 5.3l L92 comparison even taking the VVT out of the equation still looking at a point of compression a lot of displacement, more cam and a LOT more head/intake flow.
On the superchevy link you posted I think it reasonable that when engine dyno tested without all the OEM hangups the engines make similar peak horse power, given the same heads and cam. GM might be fudging the 4.8l HP numbers or tune to restrict the HP to upsell the 5.3l.
The thing I still see you not paying attention to though is rpm, looks like a 4-500rpm difference in peak point, how much of that is stroke or displacement I couldn't say but it is part of the total package to be considered. The peak torque rpm is up on the L92 as well