Why do SV's have engine braking?

Originally Posted by a1a

All I know is I love the gobs of engine braking of the SV650. Just curious how the SV1000 engine braking compares to the SV650. Has anybody rode both bikes to compare?
Cheers!

Yes, I have. The SV650 has (rather strangely) more engine braking than it's larger capacity brother. Not a lot but the 650 deffo has the edge. Maybe related to gearing in some way?


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Originally Posted by jonboy

Maybe related to gearing in some way?

From conversations I've had on here in the past, my IL4 Hornet and the SV650S are very similarly geared in all gears.

Yes but I was referring to the difference between the 650 and 1000, suggesting that one is much higher geared than the other would make a difference to the engine braking.


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Originally Posted by RandyO

why do you think a twin has any longer stroke, sport bike 90° vees are not harleys , they have same oversquare ratios as inline 4's Sv bore & stroke is same as haybusa

I do think that the engine braking of an inline 4 at 12,000 rpm is similar to that of a twin at 6000 rpm.

You can't the compare the SV with a Hayabusa, it's twice the capacity. The stroke of the 650 Bandit is 48.7mm, the SV is 62mm. The SV pistons have to go further and faster on each revolution. On the other hand, the total piston circumference on the Bandit is 823mm and the SV is 509mm so the frictional area of the two is 40080 to 31558. I should immagine piston skirt length is similar in both so, all in all, frictional losses should be very similar.
It's got to be down to crank case pumping.

engine braking is not caused by frictional losses, it's all pulling vaccum thru the intake

[ophic]

Originally Posted by RandyO

engine braking is not caused by frictional losses, it's all pulling vaccum thru the intake

or at least this is the part that tends to vary between bikes - and we're talking about the effect of different engine configurations here - so we can ignore frictional losses, gearing etc.

Having said that, there is also perception. For eg the braking force of a hayabusa engine or an SV1000 might be greater than an SV650, its just that the bike is also heavier so the actual deceleration caused is less.

Most people notice a reduction in engine braking when the exhaust is changed for an aftermarket can. Hence the SV1000 probably has a much less restrictive exhaust as it has twin pipes, which may also be a contributory factor.

I still can't see why an IL4 should have less braking than a v-twin. The vacuum pulled against a closed throttle per revolution should be the same, even though its split into 2 cylinders instead of one, given an engine of similar bore/stroke/capacity/compression ratio etc etc. If anyone can give a definitive explanation of why this is so, i would appreciate it.

Also, how does the engine braking of a parallel twin compare to a V?

think about vacuum, and a closed throttle, but the throttle is never completly closed, there is alwasy enuf air comming in for a idle, some engines have more airflow at an idle

raise your idle speed and you will loose some engine braking

[ophic]

Originally Posted by RandyO

think about vacuum, and a closed throttle, but the throttle is never completly closed, there is alwasy enuf air comming in for a idle, some engines have more airflow at an idle

raise your idle speed and you will loose some engine braking

i thought this wasn't the case anymore since modern regulations/FI systems insist that the throttle is completely closed on overrun - ie no fuel gets into the cylinder. However I am unsure as to whether this is true or even if it is, whether it applies to bikes. Either way i can't see it making enough difference. Raising the tickover may compensate for engine braking - but not eliminate the cause.

Originally Posted by ophic

i thought this wasn't the case anymore since modern regulations/FI systems insist that the throttle is completely closed on overrun - ie no fuel gets into the cylinder. However I am unsure as to whether this is true or even if it is, whether it applies to bikes. Either way i can't see it making enough difference. Raising the tickover may compensate for engine braking - but not eliminate the cause.

if no fuel mixture got into cylinder, it would not be able to idle, the engine would die everytime you rolled completly off the throttle , and I didn't say raising idle would eliminate engine braking, just that you will loose or reduce some of the engine braking effect

[ophic]

Originally Posted by RandyO

if no fuel mixture got into cylinder, it would not be able to idle, the engine would die everytime you rolled completly off the throttle , and I didn't say raising idle would eliminate engine braking, just that you will loose or reduce some of the engine braking effect

i'm saying that is exactly what happens in some engines - the engine effectively dies until either the throttle is opened again or the ECU detects it nearing tickover - when it will supply the appropriate idle mixture to prevent it cutting out. Whether this happens in the SV or not i have no idea. However this is getting way off the point.