ohiomoto wrote on 04/05/19 at 07:50:11:


Ohio,  I think any back pressure effect that early in the exhaust path would have only a negative effect . Scavenging occurs when the pressure wave (moving at a speed of nearly Mach 1) returns from the end of the header pipe where it has expanded,  to find the exhaust valve before it closes and the intake valve slightly open , the DD's are much to close . The stock cam (and any derived from it -stage 3)   has negative overlap which means there's no chance of scavenging in any case, which keeps emissions low on a bike equipped with a carb rather than FI. The bad exhaust channel in the head keeps hp down a  factor that seemed right for an entry level bike.

Thanks for all your hard work and incredible documentation!
-Armen

The kudos need to go to Fast650.  Filling the Dipsy-Doodle on the exhaust and raising the intake floor with epoxy were Fast650's ideas.  He sent me links on the intake epoxy trick and directly suggested the DD fill.  Plus, he donated the HammerHead.  F-65-0 should get the credit here.

Regarding the additional work on the exhaust port, it's already around 83% flow bias.  It was way easier souping up the exhaust than souping up the intake.  My limited understanding is that we really want around 70 to 80% flow bias for a naturally aspirated engine.  If we were running boost, then we might want more than 80%.

When I get setup for exhaust testing again, I will try to do a proper test on DD-2 using clay, just to see what happens.  But I am also a bit skeptical about coming up with a filler that can hold up.  The first Dipsey-Doodle is in a fairly tight notch.  We have a much better chance of anchoring the filler in that notch.  The second Dipsey-Doodle looks a lot more challenging in terms of anchoring the filler material..

My filler material test specimens are all cured and ready to be tortured. Let's see how that shakes out.

Regarding Suzuki engineers incorporating the DD for backpressure: the incredibly small 1.27" ID head pipe gives this system all the backpressure any engineer could ever dream of.  If you fiddle around with any of the readilay available formulas for header pipe ID, you will find that this particular setup is most likely intentionally designed for a tractor-pull engine.  The teeny-weeny head pipe, zero-overlap cam, undersize carburetor, single-cylinder large-displacement engine, 5+ pound flywheel, all combine for the perfect entry-level motorcycle.  Light-weight, loads of low end torque, exilerating (at-first) but not very intimidating acceleration.  I think they got exactly what they were looking for.  

Our job is to make it intimidating.  

DragBikeMike wrote on 04/06/19 at 22:28:10:


Now we just need a cam with a bit of overlap and a piston that is tall enough to correct the deck height but with enough of a dish to keep the compression ratio reasonable.

You are close to what I was thinking. What I meant would require a new casting to be custom made. Easiest way to visualize it would be to imagine a stock LS piston, then imagine a 1/8" thick ring about 1/2" wide that sits on top of the piston. That would remedy the deck height problem, give it a quench area, and the dish would be enough to keep the CR down enough to not be detonation prone..

As for the valve overlap, a little more overlap would allow for better scavenging from pipe tuning. The current overlap isn't enough for it to have much of an effect.

ohiomoto wrote on 04/05/19 at 07:50:11:


No pipe at all means 14.7 PSIA acting directly on the exhaust valve.  Not good...  At low engine speeds the ambient pressure would push spent exhaust gas right back into the combustion chamber.  This not only dilutes the fresh incoming intake charge but also kills VE by reducing cylinder pressure.  The result is a big lack of power due to crappy efficiency.

A properly-tuned exhaust system can actually create positive pressure (a sort of super-charging) and increase VE and cylinder pressure over small operating ranges.  A good reverse-cone megaphone system can achieve such an effect, as can a properly-tuned intake runner.  ALL modern auto and boat engines have tuned intakes today...

Good read here:  http://victorylibrary.com/brit/mega-c.htm

And here:  https://www.allpar.com/racing/ramchargers.html

Use a scribe and trace an outline of the enlarged opening onto the head, then carefully grind and blend until you reach the scribe line, except for the bottom of the port, that should be flat.  It should look like this when you are finished.  Note the arced scribe line along the bottom of the port.  I didn't grind along the bottom so you can still see the scribe line.

DragBikeMike wrote on 05/06/19 at 23:30:36:


I ah see it now. I am trying to decide between a 95 or a 96mm wiseco piston right now and I am assuming opening up the exhaust a bit to allow for better flow for larger displacement would be good. Any ideas on teh 95 vs the 96?