Wasted power!

[Rctintin]

I have just had the pleasure of buying off 2 guys on this forum (J-S-Q & Sesame) a YS 91 ST and a Hattori SB16 pipe.

Now i am not an engine tuner, but have years of RC Cars and Motorbikes behind me, and have learnt how to get more power out of your engine. My GSXR 750 as seen in my Avatar produces 140 BHP at the wheel from having the engine gas flowed and fuelled correctly. The essence here is to get fuel and air mixed, and into the engine as quickly as poss, and to get the burnt gasses out as quickly as pos as well.

When I looked at the manifold on the pipe, you can see where the exhaust gasses are hitting the Alloy because the opening in the manifold is smaller than the exhaust port on the engine.

The YS exhaust port measures 10x20mm which is 200sq mm in area.
The Hattori opening measures 9x18mm which is 162sq mm in area.

That means there is a 19% smaller hole for the gasses to pass through!
With the carefull use of a dremel or file, if you open up that opening so they are both the same size, you have just given your engine more power for free! As a bi-product of this, your engine will run a tad cooler, as there is less friction from the exhaust gasses being squeezed through a smaller hole than necessary.

[Tim Procter]

Excellent advise.

In reply to your post here Rob I can confirm that when I bought a brand new GSXR750 some time back they came fitted with "exhaust restrictors" in the manifold for running-in purposes.

Took them out after a thousand miles and it was a bullet.

You are 100% correct with your post here mate so very good advise..

[Richard H]

I guess we are all drilling holes in our exhausts on Saturday then Tim!!

[Tim Procter]

I guess we are all drilling holes in our exhausts on Saturday then Tim!!

Its a fact that if the exhaust port inlet is less diameter than the manifold port then power is being wasted Richard.


Anyone got a dremel.

[Richard H]

Very very tempting!!! Surely one of the lads must have a dremel?

[trillian]

This was always my understanding with engines. The common logic was to match and polish the ports so that there is as little turbulance in the flow as possible.

But apparently some of these heli mufflers have mis-matched openings on purpose. They have run various setups on a dyno and arrived at that shape and size.

Personally I also feel that the design of nitro engine pipes is wrong in general. It should be a hollow series of cones and the silencer should be at the exit.

Baffles inside a pipe (in motorcycle tuning terms) is a no no.

But yet the designs we see from Hatori, Youngblood etc. etc prevail.

[Tim Procter]

Very very tempting!!! Surely one of the lads must have a dremel?

Before you start rasping hell out of your muffler I believe in your case the Align 50 pipe fits the hyper 50 engine perfect.

Without looking I can't say.

[Richard H]

I wonder how many posts we get soon about how many people have tried this lol. I am up for giving it a go.

[Richard H]

Before you start rasping hell out of your muffler I believe in your case the Align 50 pipe fits the hyper 50 engine perfect.

Without looking I can't say.

I would leave the rasping to you mate. You know how much of a disaster it would be if I did it

[Tim Procter]

Its a great thread started by Rob.

Don't see many tuning threads which is sad.

[Rctintin]

This was always my understanding with engines. The common logic was to match and polish the ports so that there is as little turbulance in the flow as possible.

Not to contradict your statment, but flowing is much more important than polishing.

On an inlet, you need a smooth flow, but with roughish finnish. This improves fuel and air mixture as turbalence (eddies) are created along the path of the flow helping to mix the fuel and air up.

I have not seen what is inside a Hattori pipe, but in my car days, there was a cone inside the pipe that acted as the expansion chamber that a 2 stroke requires for the correct back pressure.

[Bruinbear]

I recently contacted Hatori USA regarding just this on my OS91/SB18 and was told that the exhaust port on the manifold is deliberately smaller the the engine exhaust port for the purposes of creating the correct back pressure. I must be honest, I was about to get the Dremel out too !
Mike.

[rambo0293]

i would be very careful about doing this as it was said above that company's have put alot of time and money in to the final product trying to drain every last bit of power out of the engine. A 2 stroke engine tunes very different to a 4. May be they have done this as it then help to get the right back pressure which they coiuld mot do just in the pipe. you may open up the hole and the engine cut once up and down comes the heli in a shower of bits.

[rambo0293]

scrub my post someone beat me to it

[Rctintin]

I recently contacted Hatori USA regarding just this on my OS91/SB18 and was told that the exhaust port on the manifold is deliberately smaller the the engine exhaust port for the purposes of creating the correct back pressure. I must be honest, I was about to get the Dremel out too !
Mike.

IMO I cant see that they are correct. Far be in for me to contradict what Hatori said, but a 2 stroke engine gets its back pressure from much further down the exhaust than 7-10 (not measured) from the exhaust exit of the engine. You do not impair flow to get back pressure, you use a 'tuned' length of expansion chamber to do it for you.