Big bore short stroke vs. small bore long stroke

[AdioSS]

the answer is 42

[twinturbo496]

Look at an F1 engine.

[SWR]

Big bore = more valve curtain area / higher breathing capacity
Small bore = sonic choke occurs at lower rpms than for big bore

...but only if you are valve area restricted... a 4-or 5-valve head most often are not, and they're a completely different ball game.

[ibmorjamn]

Big bore = more valve curtain area / higher breathing capacity
Small bore = sonic choke occurs at lower rpms than for big bore

...but only if you are valve area restricted... a 4-or 5-valve head most often are not, and they're a completely different ball game.

Interesting and familiar topic. In the case of my single , 4 valve at 500 cc it started out with a 3.905" bore (99.2mm) and a 2.543" (64.6mm) stroke 30 ci
B/S ratio 1.535:1
R/S ratio 1.769:1
in stock form it makes about 34 hp to the rear wheels (atv)

450cc 4 valve bore 3.779 x 2.440 similar B/S , R/S and hp slightly higher
however the deck height is shorter.these engines accelerate quite fast .

[1989TransAm]

Just thinking about this thread and the EMC. If one had a particular block in mind to use for the EMC would it not be beneficial to bore it out to the safe maximum and then adjust the stroke to get the desired displacement? Is was thinking of something like the Dart SHP block.

[Stan Weiss]

Just thinking about this thread and the EMC. If one had a particular block in mind to use for the EMC would it not be beneficial to bore it out to the safe maximum and then adjust the stroke to get the desired displacement? Is was thinking of something like the Dart SHP block.

This might be the case if there was no RPM limit.

Stan

[ibmorjamn]

with 2 valve big bore drag V8's it seems most answers are written in stone (generally) however with single cylinder 4 valve engines I think the rules are still being written. slightly larger than 500cc, say 511cc bored and stroked engine making 70 hp/ 40 torque. 2.2 hp per cu. in. Bore size is limited to about 102 maybe 103 due to block/ bolt/cylinder spacing.

I don't know if it is over looked or what but a single with a real light piston can accelerate very fast more so than say a larger bore but a single piston kind of magnifies all details.of course when you bring F1 out as a trump card the rules are very different. still big bore small stroke long rod engine the pistons are small and very light. short crank throw very fast acceleration .
the drag of the piston rings and other parts become very critical when you have a single piston to depend on. IMHO.friction and reciprocating weight have got to be key factors.

[vincenelson]

I have been told that in two single cylindar engines having the same displcement as example a 1" bore by a 120'' stroke, vers a 10.96" bore with a 1" stroke, and each engine being able to achieve the same amount of cylindar fill, both engines would make the same power but the short stroke engine would produce more useable energy output because of less friction in the ring pack and internal drag of the parts. I have also been told that the only subsute for cubic inches is cubic dollars.

[agawam]

in the mid to late 60s for built the 428, long stroke smaller piston,they specifcally built it to compete with thier own 427 bigger piston shorter stroke, but this was for basic street racing, on the track the 427 beats the 428,.gear ratio type of fuel compression, carburation,all factor in, to make the engines equal they would have to be built very differently and the cars would have to be built different also(gearing tire size)

[mustangcobra438]

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.

[900HP]

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.

unless your rules favor small inches or restrict you in some way go with the cubic inches. Cubic inches wins every time, I would never intentionally make an engine smaller unless there was a weight/cubic inch rule or a cubic inch maximum.

Big cubic inches is much harder to make the hp/cubic inch target with which is why you see a lot of small engines at Engine Master's Challenge but the larger motors will make more overall power/torque and do it with less rpm which means reliability/longevity.

[quickd100]

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.

unless your rules favor small inches or restrict you in some way go with the cubic inches. Cubic inches wins every time, I would never intentionally make an engine smaller unless there was a weight/cubic inch rule or a cubic inch maximum.

Big cubic inches is much harder to make the hp/cubic inch target with which is why you see a lot of small engines at Engine Master's Challenge but the larger motors will make more overall power/torque and do it with less rpm which means reliability/longevity.

I agree,
I'm just a dumb Millwright with a dyno, but for a street/strip motor I'll take a mild large displacement engine any day. You can't argue with torque and big motors make big torque. My mild 605 truck motor makes 765ftlbs.@3500rpm (start of the dyno pull) and peaks at 818@4800rpm and holds 800+ till after 5500rpm.Dave

[mustangcobra438]

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.

unless your rules favor small inches or restrict you in some way go with the cubic inches. Cubic inches wins every time, I would never intentionally make an engine smaller unless there was a weight/cubic inch rule or a cubic inch maximum.

Big cubic inches is much harder to make the hp/cubic inch target with which is why you see a lot of small engines at Engine Master's Challenge but the larger motors will make more overall power/torque and do it with less rpm which means reliability/longevity.

What about parasitic loses form longer stroke and windage as well as longer stroke being harder in engine from weight rotating farther out?
Would longer stroke still prevail in same scenario as mentioned before?
I should mention this is a nmca na10.5 type motor but current block won't allow more than 4.125 bore without rpm causing cylinders to move around.

[Truckedup]

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...

[900HP]

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.

unless your rules favor small inches or restrict you in some way go with the cubic inches. Cubic inches wins every time, I would never intentionally make an engine smaller unless there was a weight/cubic inch rule or a cubic inch maximum.

Big cubic inches is much harder to make the hp/cubic inch target with which is why you see a lot of small engines at Engine Master's Challenge but the larger motors will make more overall power/torque and do it with less rpm which means reliability/longevity.

What about parasitic loses form longer stroke and windage as well as longer stroke being harder in engine from weight rotating farther out?
Would longer stroke still prevail in same scenario as mentioned before?
I should mention this is a nmca na10.5 type motor but current block won't allow more than 4.125 bore without rpm causing cylinders to move around.

I'm not saying a long stroke "prevails" I'm saying cubic inches prevail. If you are limited to a 4.125" bore, you WILL make more power/torque with a 4.100" stroke than with a 4.00" stroke because you have more cubic inches. You will not make the horsepower per cubic inch with the larger motor but you will make more power overall.