Some extra power from modding your headers

[DavidH]

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.

From comparing the SB17 and SB18 side by side. The SB 18 is approx an inch longer than the SB 17. At least the mufflers I was comparing were labeled SB17 and the other SB18. I believe the SB18 was labeled OS 91 also.

David

[3DME]

I belive what Gman is saying is that the SB17 and SB18 are the same for the OS as the YS except for the mounting hole spacing(header)? Of course I have no clue as I have never owned an OS 91. Dave, is the muffler stamped with "OS 91 or is it the header? Or are you talking about the one piece muffler.

Mike

[3DME]

Also for some reason I belive my FH header is drilled for both the YS and the OS. When I was buying the muffler I remember thinking I could sitll use the muffler if I ever switched to OS. I think I will pull the muffler and look. I am really thinking about trying the OMI OS setup.

Mike

[DavidH]

Well I was just going by what was stated.

They both use the same muffler assy

I was refering to the two piece mufflers that have the FH designation. YS motors and OS motors have different bolt hole spacing on the exhaust manifold. Also the OS is using bolts thru the crankcase to hold on the muffler in place. YS using bolts that thread into the crankcase. The header that Augusto pictured is for an OS 91 motor. The header for OS/YS has two sets of holes.


SB17 = 275 mm long
SB 18= 310 mm long

[G MAN]

MY bad,it's the SB 16 that fits both YS and OS,the SB17 & 18 are for the OS only.

[3DME]

I must have the one with two sets of holes. If this is true how can it be tuned for the YS and OS at the same time? Has anyone tried this mod with the YS 91 and the YS/OS FH muffler?

Mike

[G MAN]

You have the SB16FH that fits both the YS and OS,and obviuosly cant be tuned properly for both. The OS is tuned for a lower RPM range and this is why it likes the higher 7.9 and 8.0 gear ratio's. The YS is ported for higher RPM and likes the lower 8.5 ratio to let the turn a little higher. DOUG

[DavidH]

You have the SB16FH that fits both the YS and OS,and obviuosly cant be tuned properly for both.

Doug,
That may or may not be the case. Using the fixed header one piece muffler as an example. Yes there is a YS version and an OS version. The only difference between the one piece mufflers is how they bolt to the engine. The header port is the same on both versions of the one piece.
Mr. Hatori is a great gentleman to sit down and have a conversation with. I have had that pleasure on a couple of occasions. He understands english fairly well, he needs a translator to translate his speech to english. He does test his exhaust systems on YS and OS engines. He has pilots that report back to him what works and what does not work. Mr. Hatori is just not welding mufflers together without a specific reason or design for there application.

David

[G MAN]

David,my point is the SB16FH fits both engines with no change at all. It cant possibly be tuned for both engines with such different porting specs. Hatori makes fine mufflers but they do have their faults. They are not perfect out of the box.
As far as the new SZ we will have to see,OS has a way of words, but i dont see much difference in the SZ and C spec other than a new carb,which might and might not help. They state more power in the specs for the SZ. but it is at a 1000 rpm increase. My suspisions are the SZ with an OMI mod will be the way to go.
OS's track record with the 91 hasn't been all that great as an out of the box engine.

[DavidH]

The SZ is ported completely different than the C spec. So there is difference. The porting is different in the crankcase and cylinder from what I can see. The SZ carb is already at 10.6 mm. I am not sure if James at OMI will spend the time for .2 mm. The BB 60K carb is only 10.8 mm. I would suspect the SZ carb will work fairly well. There is connection between OS and OMI, so OS does watch what is going on elsewhere.

David

[ChrisLaFollette]

David is right. I spoke with James on the phone and OS knows what hes up to. I think I recall him making about 5000 viperheads for the OS 91's. Or maybe it was 500. I think it was 5000. He made a TON of them for OS. James is a good man to talk with. Ah I cant wait until OS comes out with a motor that doesnt require a few hundred on top of $300 to make it run right.

[G MAN]

I guess we'll have to wait and see how the SZ works,OS has a way of sugar coating their specs to make an engine seem better than it realy is. I'm not anti OS,i own some myself. It took some American hacking to get the OS to perform like it's is capable of. I have delt with OS racing engines quite a bit and havn't seen one that couldn't be improved dramically with a dremel tool and some crafty american machine work. Did you realize that all the OS engines 30,50.61 91 all use the same exhaust port timing,OS is very conservative with their porting EVEN in their race engines. I raise the ex timing and modify the head on my OS50 and use 60 size exhaust sytems on them and they run considerably better.

[DavidH]

Yeah I have done all those tricks also. I used SFN's for a few years. There is an art to making it just right. Not many want to trial and error on a cylinder liner port to see what works best. The 91 motors are producing about as much power as the airframes can withstand now. So basically all I want is the motor to run consistent and be reliable.

David

[Pete Niotis]

Let's not forget that the SZ crank case is much beefier and there is good reason why they made it like that, I think this motor will rock whether you decide to run it stock pumped/regulated or slap an OMI mod on it. The results with stock pump and regulator were fantastic and I'm sure some guys are testing OMI mods by now on the SZ motor.

[G MAN]

Which we are back to the original post,taking something close and making it better.
In this case being a muffler.

[EricLarson]

Something got missed here:

The YS uses the SB16

The SB16 is a muffler as the YS motor does not like pipes very much. The reason is due to the engine timing and porting.

The SB18 is a muffled tuned pipe for the OS91. It was designed for the os91sx-cspec motor and is much different than teh SB16. The tune of the pipe was set for the 91SX. The 18 gives a deeper sound tone and is a bit quieter than the 17.

The SB17 is a muffled tuned pipe for the OS91. It has the same front "tune" section of the SB18 but the muffler section is shorter. The reason for shortening the pipe was to reduce weight and also reduce stress on the header / dampeners. The 17 is a bit different sound tone than the 18 but is tuned the same. The SB17 has my name on the box

Because these are muffled tuned pipes they are a bit less temper-mental about the exact tune than a standard tuned pipe would be. OS motors like pipes due to the timing and porting.


I personally have a lot of headers here that I also played with modifying when we where first testing the 16,17,& 18 as well as other variations of the Hatori's for the OS. For what it is worth, the headers on my engines that I ran this season are stock......

[evil]

Just my 2 bobs worth id say the mod has a lot to do with velocity :ie:The speed of which the gases can exit the exhaust port in the given cycle time. u could have a smaller volume traveling faster or a larger volume travelling slower and still move the same amount of gas.i would assume this mod increases velocity by removing restrection to flow there for an increase in torqe would be the result..

[G MAN]

Quote:
The YS uses the SB16

The SB16 is a muffler as the YS motor does not like pipes very much. The reason is due to the engine timing and porting.
---------------------------------------------
The SB 16FH fits the YS and OS,its listed that way on ricks. The question was about the tuning being spot on for a certian engine. Since the SB16FH fits both the YS and OS it couldn't be maximized for both engines,it is a compromise or fit all. The SB 17 and 18 are a different story.
He is a new 50 muffler that is tuned and fits 2 different helis but for the same engine. With the exception of the SB 50 and SB 17&18 the mufflers are a compromise in tuning,allowing for fit to different models. http://www.hatori-models.co.jp/top-sita-e.html

[WayneBrown]

To say the YS motors don't like pipes is disturbing.
The YS 61LS loved a pipe, as did the 45. I would be interested in further testing with a 'true' tuned pipe system on a YS heli engine.
The sole purpose of a tuned pipe is to increase scavenging while at the same time creating a vaccum to draw a larger air/fuel charge into the combustion chamber.
I had a small Dyno from power testing built in the early 80's for tuning and porting pattern engines, it was later used for boat engines.
I'll look and see if I can find the manufacturer or plans to build or purchase another.
Comparing the HP/RPM ratings between simple muffler, muffled pipe, and nitro pipe in various configurations would likely prove enlightening.

[3DME]

I would be interested in a small (model)engine dyno. Please post your findings wayne.

Mike