Honda Spree and Elite 50 Forums

Greetings:

I agree with The Bear on the importance of Dynamic compression. Current Hi-Po SuperSports streetbikes feature "Compression Ratios" approaching a Diesel-like 14:1, but that doesn't factor in the substantial valve overlap that drops the actual cylinder pressures back down to Pump-Gas-Sustainable levels. At very high RPM, the 4-strokes use the same pressure-wave supercharging effects from their airboxes and exhausts as 2-strokes (scroll to the bottom of the page...) do with the expansion chambers. At that very high (over 13,000) RPM, those static compression numbers actually occur. How they make it happen without detonation and top-end destruction is the slowly-advancing Black Art of Internal Combustion Engineering. Kawasaki's upcoming 2011 ZX 1000 boasts a Specific Output of well over 200HP/liter. No supercharger, just decades of careful attention to the impossibly fast combustion chamber events.

One thing we Amateur 'Smoker Fans don't seem to address as seriously as the Expansion Chamber wave is the importance of the pressure waves from the Intake side. Late racing Factory 2-Strokes all used them - no Pod filters on the track. An airbox carefully volume- and shape-matched to the cylinder has the potential to do from the incoming side what a well-tuned pipe does from the output side. I'm still wating on my BGM Pro airbox from Der Faderland - evidently back-ordered and on a slow boat from China - to experiment with this issue.

Kerry wrote:actually...i'll stick around and pin point everything that upsets you and concentrate on it

Wow you really need to get a life.

Wheelman-111 wrote:Greetings:

I agree with The Bear on the importance of Dynamic compression. Current Hi-Po SuperSports streetbikes feature "Compression Ratios" approaching a Diesel-like 14:1, but that doesn't factor in the substantial valve overlap that drops the actual cylinder pressures back down to Pump-Gas-Sustainable levels. At very high RPM, the 4-strokes use the same pressure-wave supercharging effects from their airboxes and exhausts as 2-strokes (scroll to the bottom of the page...) do with the expansion chambers. At that very high (over 13,000) RPM, those static compression numbers actually occur. How they make it happen without detonation and top-end destruction is the slowly-advancing Black Art of Internal Combustion Engineering. Kawasaki's upcoming 2011 ZX 1000 boasts a Specific Output of well over 200HP/liter. No supercharger, just decades of careful attention to the impossibly fast combustion chamber events.

One thing we Amateur 'Smoker Fans don't seem to address as seriously as the Expansion Chamber wave is the importance of the pressure waves from the Intake side. Late racing Factory 2-Strokes all used them - no Pod filters on the track. An airbox carefully volume- and shape-matched to the cylinder has the potential to do from the incoming side what a well-tuned pipe does from the output side. I'm still wating on my BGM Pro airbox from Der Faderland - evidently back-ordered and on a slow boat from China - to experiment with this issue.

Honda has known about intake tuning for at least 40 years. Proof, look at the Spree intake system, no air box cover and it runs like *. Most people are 4 stroke educated and 4 strokes are not anywhere near as sensitive as 2 strokes in either intake or exhaust tuning.

This could go on forever but I'm not here for that. I'm here to learn without being talked to like a child, please move on.

toad772 wrote:

Kerry wrote:actually...i'll stick around and pin point everything that upsets you and concentrate on it

Wow you really need to get a life.

I took Wheelman's suggestion and purchased a Harbor Freight tester. 135#'s...tested it a few times to make sure and it was quite the relief.

Kerry wrote:I took Wheelman's suggestion and purchased a Harbor Freight tester. 135#'s...tested it a few times to make sure and it was quite the relief.

That is just about perfect.

Thanks TJ

I did go and read the manual and for the motor 114-170 psi...so I'm thrilled

thanks crew!

Greetings:

I am pleased your compression is OK. Gauge error that significant is unacceptable.

I agree with The Bear that 2-strokes aren't as sensitive to intake side issues as 4-strokes, but not with his example. Sprees
Run lousy without the airbox because the size of the inlet pipe is smaller than the draw demand, which produces a negative airbox pressure that is necessary to make the tiny Pilot circuit pull fuel. It is NOT the pressure wave timing issue that high performance sportbikes utilize to ram in extra mixture just before the intake closes.

I would also submit that 2-strokes are Supremely sensitive to the exhaust characteristics, the Black Art of expansion chamber design underscores this. Pipes don't seem to do as much to 4-strokes' top end, as long as they don't restrict flow. They do
affect the midrange on less than full-on racing engines.

The point of the boost bottle is to control such waves on the intake side.