Some extra power from modding your headers

[Dr.Ben]

For those of you who might contemplate these mods on a Hatori muffler on a YS engine, proceed with caution. Mr. Hatori VERY carefully tests the size of the exhaust header hole to ensure the motor has adequate back pressure to run correctly. You can ruin the way a YS engine runs on a particular Hatori exhaust by disrupting the ideal backpressure balance.

Ben Minor

[Shannon Davis]

I would have to believe that even though 2-strokes are a bit of a strnge animal- they like all Internal Combustion engines are just air pumps-- better flow thru the engine can only result in a more efficient pump.

I also agree that this could require a chnge in some other engine parameters-- like the ex. pipe. But I would be the first to break out the grinder on a minifold that doesnot match the port.

Thanks for the info Augusto-- goood to see you posting here.

[Augusto]

Here's a picture of both the exhaust of one of my SZs and a C-Spec. It's interesting that the SZ even being a different engine than the C-Spec or PS for which the SB-17 and 18 were designed for it works perfectly with those mufflers.



I guess there is not that much black magic on those Hatori headers since they work perfectly well for two very different engine exhausts. So after looking at this pretty clear evidence my recomendation is to just get off the high horse, get your hands dirty, mod your header and enjoy the extra power it'll give you or simply don't do anything and simply forget about this post.

Augusto.

[Shannon Davis]

well put Augusto

[Scrub]

I did this mod to my MPII header (YS) last year. I couldn't tell any difference in power. RC Cars guys have been doing this for years on their headers.

[3DME]

Ok I will add a bit of insite on why this mod can't hurt it can only help. Without going into complete two stroke theroy here it goes. When a two stoke motor fires it sends an exhaust pulse into the muffler. This pulse is bounced off of the pipe walls and this sends a pulse back to the engine. Otherwise known as exhaust scavaging The length of the header and the shape of the expantion chamber cause the pipe to resonate at a specific rpm. (also known as the powerband) Any disruption in the pulse either way (two the pipe or from the pipe) will result in a loss of torque. I have proven this on a dyno with the bigger two stokes. I am quite positive this will also work with the model engines as well.

Back pressure is not an issue with this mod. The tail-cone of the pipe is what creates back pressure. Dr Ben is correct, you need a certain amount back pressure for the motor to run properly. If there is not enough back pressure the return pulse is weak resulting in loss of scavaging. An obstuction in the exhaust port(namely the header) could cause the pulse, or the return pulse to arrive too early or too late.

I have two of the FH pipes I am going to modify one of them just to see if it makes a difference. Then I will compare them back to back on the same machine. I will have my buddy Conrad fly the machine just to get a second opinion. I just cannot see this mod hurting the performance.

I do belive Hatori tests their pipes for max HP. But I also belive the headers are made to fit a number of different 91 sized engines. If this is so it cannot fit all motors perfectly. In the stock car world you can spend 3000-5000 on a set of heads and intake, even these need to port matched for max power. I had a 6,000 set of Winston Cup J rollover heads and they needed to be port matched to the intake and the exhaust. Match porting is where you make two pieces that bolt together smooth so there are no steps or obstruction in the port. This is aslo called gasket matching. This process is almost allways left up to the end user because it is labor intensive and gains are minimal, but if you want to be competitive get to grinding.

Mike

[EricLarson]

I guess there is not that much black magic on those Hatori headers since they work perfectly well for two very different engine exhausts.

Guess I better get out of the sand box :wink:

I was just curious if you had #'s to back up any of the expected results. Nothing more or less. I still stand by my original thought that some modifications are extremely beneficial and others don't do what a person things no matter what the theory.

I know I have spent a lot of hours on test rigs checking modifications that I did to see if they really where better or not.

One other question. Since we are talking about flow rates is there a modification to the outlet on the back of the exhaust as last time I checked the outlet hole was 1/2 of the area of the hole in the exhaust header.......

[Augusto]

The reason why a smaller sized outlet hole works is because the muffler converts a discrete flow from the chamber explosions into a more continuous flow at the outlet.

The only time the gas passes through the header is when the piston opens so the volume of gass that needs to pass in a much shorter period of time requires a larger hole size. The dutty cycle is probably around 30%

That same volume of gass passes through the outlet hole in a more continuous flow and is not limited to a time window as it happens in the header so even though apparently the hole is smaller the flow is less constricted because of the duty cycle being 100%

Augusto.

[EricLarson]

So is there a good reason they may have reduced the area of the exhaust opening on the new SZ vs the SX motor. Seems that would reduce the volume of gas that will flow per your description. Should we widen the exhaust opening of the SZ to increase the area so we get better flow? That will not affect the timing but that should be doing the same type of thing that the original header mod that was described will do.

[Shannon Davis]

I can see where port size has everything to do w/ the overall flow of the engine- scavanging the cyl etc. but if the header reduces that size I can only see it as a restriction that needs to be corrected-- unles the ports were designed to be restricted by the header-- which I doubt.

[EricLarson]

You may be 100% right Shannon. That would assume the header design was a mistake, accident or a limitation of design. Since these pipes where designed and tested on the SX and the new SZ seems to have the same type of exhaust area as the header, that may not be a coincidence......

[Shannon Davis]

I would guess maybe just a limitation of "Get 'R Done". The manifold is just a generic adaptor that was not made to fit the engine as good as it could. I don't follow this stuff and don't know what was designed for what or what was "close enough".

[Augusto]

I don't think they have reduced the total area. I think they made it taller so that total are is probably the same but I could be wrong. I need to measure it to be sure.

In the case of the exhaust porting. Shifting the port like they did is sometimes needed because of the way the intake ports are located and directed to create a sort of tornado effect when the mixture gets into the cylinder. I don't know if that's the particular effect in this engine though. Opening a port like that could interfere with the desired effect that the designers had in mind but then again it could be tested and the worst that could happen is having to replace a cylinder liner.

We used to do a lot of experimenting a long time ago when I was racing formula I and Quickies. You could pickup a Clarence Lee engine and that thing had a lot of mods in porting, carbs and all around. It was an art on itself but it was worth it when you got a good mod to work right.

Augusto.

[H to the C]

3DME funny, I like the rookie comment..hahahaha rotflmao (i got your rookie, its called stratus smack)

[Rodney]

Does OMI use a dyno? If so let him test do some test work.

[BigVanVader]

Originally Posted by H to the C

( its called stratus smack)

You can smack on DEEEEEEEZ!!!!!!

[3DME]

HC I figured you would like that comment. But dont worry you will be flying like Rodney in no time. HC, what you got in more like chin smack. lol

Mike

[H to the C]

hahahhahahahaahahahah funny!!! Vance can smack his lips on deeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeez!


I could never , ever, be as good as Rodney. Those PMaxi's are off the string.
hc

[BigVanVader]

[G MAN]

The Hatori SB 17 & 18 are not tuned for maximum efficency for the engine application. They both use the same muffler assy but a different header designed to fit the engine application. How can the same muffler be tuned for 2 different engines with very different port timing. The OS has lower exhaust timing 153 degrees and the YS is 160 degrees. There is always a bit of a compromise because of need to fit and manufacturing processes. DOUG