Track Tac

Bore/stroke

D

Dirtkart90

Member
Hi, I was wondering if bigger bore size or longer stroke in open modified engines actually make a difference on little bullring tracks biggest track we run is 1/10 mile?
 
It would depend to some extent somewhat how slow the corners are. If rpms drop greatly in the corners I would go bigger bore and go for quicker rpm pickup. If theyre bowl shaped, fast corner tracks I would like more stroke and torque. The obvious answer is both. Get the 58mm crank rotating assembly and the 72mm block. Now if you dont have a high flowing cylinder head I would buy one of those before changing the rest, assuming money keeps you from diving into the whole deal. You can later use the better head on later changes you make.
 
There's no replacement for displacement.
I'm with Mike though, that a big bore short stroke engine will accelerate up off the corner quicker and make more power at higher rpm, while the big stroke small bore engine will pull harder at lower rpm.


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I don't completely agree on the theory of displacement as the holy grail on any engine. I that would be true those small Jap cars would have any chance to beat cars with bigger engines or the 100cc rotary valve SA kart engines wouldn't still hold records at many tracks around Europe and other sprint tracks, for example. There are many different ways to achieve performance without using displacement. The dominating ride in UAS nowadays is a 150cc 2 stroke powered kart whenever they show at a track, and that can apply to a small block 4 cycle at many tracks too.
 
When you factor in cost and reliability .
The small engine loses . Lots of power at a high cost with lots of maintenance .
Now bang for the buck , Big bore provides that . .060" or more , .010" is just a clean up .
 
rainman said:
I don't completely agree on the theory of displacement as the holy grail on any engine. I that would be true those small Jap cars would have any chance to beat cars with bigger engines or the 100cc rotary valve SA kart engines wouldn't still hold records at many tracks around Europe and other sprint tracks, for example. There are many different ways to achieve performance without using displacement. The dominating ride in UAS nowadays is a 150cc 2 stroke powered kart whenever they show at a track, and that can apply to a small block 4 cycle at many tracks too.
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UAS has weight/CC rules not a true RWYB
 
racinnut15xm said:
UAS has weight/CC rules not a true RWYB
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OK, yes, but have you seen any RWYB class run faster at any track or beat the UAS lap records? Obviously not, so what's your point? I have raced UAS over 10 years so I know very well how it works. I'll even add something, if you run the 150 BRC with a light driver in RWYB it will be even faster because it could run lighter while the big engines won't be able to be lighter even because of the package weight.
 
rainman said:
OK, yes, but have you seen any RWYB class run faster at any track or beat the UAS lap records? Obviously not, so what's your point? I have raced UAS over 10 years so I know very well how it works. I'll even add something, if you run the 150 BRC with a light driver in RWYB it will be even faster because it could run lighter while the big engines won't be able to be lighter even because of the package weight.
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i dont have any uas stuff around here not even been to a race to watch. Just pointing out the fact that rules exist that maybe make one package better than another. Not as clear cut as you would like it to be. If you dont have displacement you better be able to spin it up high. RPM's are cubic dollars, stuff starts flinging apart alot faster the more you want to turn. Thats why you hear the no replacement for displacement. More guys have budget to build a smaller CC engine and not need to spin it up to 10-12k and it might live a little longer.
 
racinnut15xm said:
i dont have any uas stuff around here not even been to a race to watch. Just pointing out the fact that rules exist that maybe make one package better than another. Not as clear cut as you would like it to be. If you dont have displacement you better be able to spin it up high. RPM's are cubic dollars, stuff starts flinging apart alot faster the more you want to turn. Thats why you hear the no replacement for displacement. More guys have budget to build a smaller CC engine and not need to spin it up to 10-12k and it might live a little longer.
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Well you should know then than the high rpm engines in most cases have less moving parts so most times you just replace piston, pin and ring, and if run properly they don't necessarily come apart, while the big 4 strokes for example when they do break most times are completely gone, sine you have to replace the block, etc. Most top racing engines don't need huge blocks to perform, but updated technology. Again check that BRC beating big engines and in fact not braking or coming apart like other engines.
 
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