Big bore short stroke vs. small bore long stroke

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Re: Big bore short stroke vs. small bore long stroke

Post by 289nate »

Truckedup wrote:Honda uses a longer stroke than most the competition especially in Acura 4 cylinder engines. Some of 2-2.2 liters fours have strokes near 3.5 inches with a redline of over 8000 rpm. Now there might be emission or packaging considerations... But Honda is known for high RPM engines so they might know something...
A 4v cylinder head changes bore size limitations dramatically. You can get a whole lot of valve area for a specific bore with a 4v cylinder head. I've been told the move to smaller bores and longer strokes was to do with emissions. Not power.

Look at how much better the Chevy LS7 head is to what is on the smaller bores of the 6.0-6.2L engines.

People need to remember that when you extend the rpm range you can use a lower rear gear. RPM range and gearing is a huge factor in accelerating the vehicle. A lower rear gear will produce greater torque at the tire. So what seems like a low end torque disadvantage on the dyno can be easily overcome when the appropriate gear is used for the higher rpm engine. The kicker is the lower rear gear will produce greater torque at the tire over the entire rpm range. So you don't just make up for (to whatever degree) the low rpm range but also have the gearing advantage working with a superior upper rpm engine power output.
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Re: Big bore short stroke vs. small bore long stroke

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mustangcobra438 wrote:How much would the rpm need to increase going from a 4.100 stroke to a 4" stroke with same head and bore?
Would it be benificial to shorten the stroke with bore and valve size same between both?
58lb crank in both apps.
You'd be ahead of the game trying to increase the rpm range with a 4.1" stroke.
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Re: Big bore short stroke vs. small bore long stroke

Post by BlitzA64 »

What about in a restricted engine? Weren't the NASCAR guys running smaller cubic inch with the restrictor plate deal years ago? I thought I heard a minimum ci was mandated back then?
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Re: Big bore short stroke vs. small bore long stroke

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The largest stable bore you can use allows a larger intake valve.
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Re: Big bore short stroke vs. small bore long stroke

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BlitzA64 wrote:What about in a restricted engine? Weren't the NASCAR guys running smaller cubic inch with the restrictor plate deal years ago? I thought I heard a minimum ci was mandated back then?
Yes, Yes
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Re: Big bore short stroke vs. small bore long stroke

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289nate wrote:
Truckedup wrote:Honda uses a longer stroke than most the competition especially in Acura 4 cylinder engines. Some of 2-2.2 liters fours have strokes near 3.5 inches with a redline of over 8000 rpm. Now there might be emission or packaging considerations... But Honda is known for high RPM engines so they might know something...
A 4v cylinder head changes bore size limitations dramatically. You can get a whole lot of valve area for a specific bore with a 4v cylinder head. I've been told the move to smaller bores and longer strokes was to do with emissions. Not power.

Look at how much better the Chevy LS7 head is to what is on the smaller bores of the 6.0-6.2L engines.

People need to remember that when you extend the rpm range you can use a lower rear gear. RPM range and gearing is a huge factor in accelerating the vehicle. A lower rear gear will produce greater torque at the tire. So what seems like a low end torque disadvantage on the dyno can be easily overcome when the appropriate gear is used for the higher rpm engine. The kicker is the lower rear gear will produce greater torque at the tire over the entire rpm range. So you don't just make up for (to whatever degree) the low rpm range but also have the gearing advantage working with a superior upper rpm engine power output.
True... but why is everyone but Honda using oversquare engines with 4 valve heads in the same displacement class ?
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Re: Big bore short stroke vs. small bore long stroke

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Truckedup wrote:
289nate wrote:
Truckedup wrote:Honda uses a longer stroke than most the competition especially in Acura 4 cylinder engines. Some of 2-2.2 liters fours have strokes near 3.5 inches with a redline of over 8000 rpm. Now there might be emission or packaging considerations... But Honda is known for high RPM engines so they might know something...
A 4v cylinder head changes bore size limitations dramatically. You can get a whole lot of valve area for a specific bore with a 4v cylinder head. I've been told the move to smaller bores and longer strokes was to do with emissions. Not power.

Look at how much better the Chevy LS7 head is to what is on the smaller bores of the 6.0-6.2L engines.

People need to remember that when you extend the rpm range you can use a lower rear gear. RPM range and gearing is a huge factor in accelerating the vehicle. A lower rear gear will produce greater torque at the tire. So what seems like a low end torque disadvantage on the dyno can be easily overcome when the appropriate gear is used for the higher rpm engine. The kicker is the lower rear gear will produce greater torque at the tire over the entire rpm range. So you don't just make up for (to whatever degree) the low rpm range but also have the gearing advantage working with a superior upper rpm engine power output.
True... but why is everyone but Honda using oversquare engines with 4 valve heads in the same displacement class ?
Because the Honda block is more compact with tighter bore spacing, it doesn't allow for the larger bore so they are increasing stroke to get the displacement.
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Re: Big bore short stroke vs. small bore long stroke

Post by wyrmrider »

larger bore = wider bore centers = expensive new tooling
also chassis fitment challanges
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Re: Big bore short stroke vs. small bore long stroke

Post by Truckedup »

Interesting...so Honda who was always been at a leader in high RPM production engines would compromise the engine to fit it in the chassis? I might be wrong but I would think Honda would redesign the car to fit the engine. It's not like they don't redesign every few years....
The Honda S2000 sports car was a fresh rear wheel drive platform , but Honda chose a long strong engine...
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Re: Big bore short stroke vs. small bore long stroke

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Truckedup wrote:Interesting...so Honda who was always been at a leader in high RPM production engines would compromise the engine to fit it in the chassis? I might be wrong but I would think Honda would redesign the car to fit the engine. It's not like they don't redesign every few years....
The Honda S2000 sports car was a fresh rear wheel drive platform , but Honda chose a long strong engine...
2.0 S2000 was 3.42 bore x 3.30 stroke making it "oversquare". They upped the stroke to increase displacement to 2.2L and bring rpm down. That engine is 3.43 x 3.57 making it "undersquare". ALL Honda 4 cylinder engines have either a 90mm bore spacing or a 94mm bore spacing. This is like ALL small block Chevys have a 4.4" bore spacing. This even carried over to the LS engine even though it was a "clean sheet" design. This limits bore size.

Because of the bore spacing, Honda is unable to go much bigger with bore so the only way to increase displacement is with stroke.
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Re: Big bore short stroke vs. small bore long stroke

Post by user-612937456 »

Well My wife made it quiet simple when ask that question I think she just said Size Matters
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Re: Big bore short stroke vs. small bore long stroke

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gvx wrote:Well My wife made it quiet simple when ask that question I think she just said Size Matters
But does she prefer a small bore/long stroke at low rpm or is she more of a big bore/short stroke high rpm sort of girl? :lol:
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Post by 140Air »

beth wrote:My opinion is it depends on the rpm range. If rpm is restricted to 5000 to 6000 the longer stroke will prevail. If the range is 8000 to 10000+ then the short stroke has advantages.
beth
The largest possible valve diameters give the best breathing and power no matter what the rpms. So, the biggest possible bore always has volumetric efficiency advantages. But, there are always other design considerations such as efficiency, packaging, etc. Also, for most engine builders, they are working with existing designs that already fit a restricted range of bore/stroke ratios, restricted maximum valve diameters or other factors.

Usually, breathing trumps all other considerations, but combustion efficiency, friction and thermal efficiency can put a stop to how far you can go in the direction of bigger bore, shorter stroke. After pneumatic valve springs "solved" the valve train limit on rpm, F1 designers went for the maximum rpms they could get. But they were limited by the poor combustion chamber shapes they had from the ultra large bore/stroke ratios and they had to deal with the high friction of high rpms. The bigger bore also increased firing forces on the rods, crank and block and increased oil film loading in the bearings at the same time they were trying to reduce bearing diameters to reduce friction. Even though they always knew the advantages of higher rpm it took them on the order of 6-8 years to get from 13,000-14,000 rpm to 20,000 because of the downsides of big bores.
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Re: Big bore short stroke vs. small bore long stroke

Post by Krooser »

900HP wrote:
gvx wrote:Well My wife made it quiet simple when ask that question I think she just said Size Matters
But does she prefer a small bore/long stroke at low rpm or is she more of a big bore/short stroke high rpm sort of girl? :lol:
My wife thinks I'm a big bore with my short stroke… as if she remembers back that far.
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Re: Big bore short stroke vs. small bore long stroke

Post by 140Air »

Krooser wrote:
900HP wrote:
gvx wrote:Well My wife made it quiet simple when ask that question I think she just said Size Matters
But does she prefer a small bore/long stroke at low rpm or is she more of a big bore/short stroke high rpm sort of girl? :lol:
My wife thinks I'm a big bore with my short stroke… as if she remembers back that far.
LOL!!! ROTFL!!!
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