The technical adventures of Dr_C

jon andersson said:

I wanted to understand exhausts as I plan to build my own. Came to the conclusion that I need to build myself a dyno first. ..

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Basically...
When the intake valve opens, the downward moving piston creates a "suction" of intake air/fuel gas mixture. That creates a negative pressure wave ("vacuum") which moves upstream towards the intake opening orifice. When this happens, the surrounding air pressure, which has a higher pressure than the negative wave, gets "sucked" into the intake. This causes a positive wave to travel downstream through the intake. This wave bounces between a closed intake valve and the intake opening before it reaches the inlet valve, just when it opens. The ambition is to adjust the intake length in order for the intake positive wave to reach the open intake valve at the 3rd wave (for better overall power, 2nd for best top end) at a certain rpm. In my case this is appr. 8750rpm. The flip side of this coin is that these dynamics causes a negative wave to reach the intake valve in another part of the power band. In my case I get a dip* in around 7200rpm, which is really annoying and messes up the exits out of the corners. This is where the exhaust design is supposed to help out!

When the exhaust valve opens, a positive pressure wave enters the exhaust system and travels downstream towards the final exit to open air. When the positive wave enters a lower surrounding pressure (fx a sudden increase of area in the system, like the chamber in my first muffler), a negative pressure is created behind it. This negative wave travels upstream the system, and reaches the exhaust valve next time it opens. That helps to scavenge the combustion chamber from exhaust gasses. The length from exhaust valve to a sudden increment of area, determines (together with a bunch of other parameters) where in the power band you will get this positive effect. I would like this to happen at 7200rpm... I manufactured the system with an adjustable joint at where the primaries go down in front of the engine. This makes it possible to adjust the length +/-15mm, or so. Dyno will tell what it should be adjusted to.

On one of my systems, the correct tuned exhaust length increased power in the dip* by no less than 11 RWHP!

Thank you for that, interesting for sure and I hope you will continue sharing your knowledge and experience!

My plan (dream/idea) is to have 3 different dimensions of pipe and slide them into each other at different lengths until desired curve/effect is achieved. Then later it has to be taken into account that a 90 bend equals friction of roughly 2m straight pipe when it is time to weld it.

But I will not highjack this excellent thread with my dreams!!
Thank you for some good input Following this thread since a long time.

Efficient (read: boring) exhaust system! Mechanical and intake noise, seems louder than what comes out of the muffler...

https://vimeo.com/163159692

Hi Dr C,

I have a quick question about the liner orings

do you find the 1.1mm deep x 2mm wide groove and 1.5x100mm orings to be ok ?

have you tried anything different ? im wondering if 0.7 to 0.8mm deep could work for 104.775mm bore


regards
Bushie

Dr_C said:

I machined 1,1mm deep grooves according to the spec for 100x1,5mm viton o-rings. That leaves 1,4mm in my 104mm sleeve. As the mtrl has a tensile strength of 500MPa, I would say that: If your design works, so will mine! [emoji1]

View attachment 3963

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bushmechanic said:

Hi Dr C,

I have a quick question about the liner orings

do you find the 1.1mm deep x 2mm wide groove and 1.5x100mm orings to be ok ?

have you tried anything different ? im wondering if 0.7 to 0.8mm deep could work for 104.775mm bore

Click to expand...

Hi Bushie!
Those grooves and o-rings worked OK. They may not always survive to be reused, but there have not been any problems (leakages) with that configuration. Thus I have not tried any other alternatives...



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Sounds great,

Where can these o-ring be found?
I had to reuse these ones a few times already.

Have you guys just been machining your own liners?

I'm worried about future repairs on my 550.

If you know a car engine or something that we can buy a pre-made liner for and just modify it, that would be awesome.

Surely an Iron liner would stay round better? It would just add a little bit of weight?

Also wondering when/who is going to make new rods for the 550 motor.

Borgschulze said:

Also wondering when/who is going to make new rods for the 550 motor.

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We may have to arrange that ourselves too - We might want to take the opportunity to figure out improvements to the crank while we're at it? I.e. a bigger crank pin. Ideally, if the 550 crank can be machined to take a bigger crank pin which then again allows the use of a stock rod from something, then ... that's ideal I guess?


Re. liners - Bushmechanic for one has posted some links / info on liners and liner mfr's

I'm fairly certain there is room to enlarge the crank pin.

Although it might have to get a tiny bit more stroke at the same time, it's fairly close to the main bearing races as it is.

Borgschulze said:

I'm fairly certain there is room to enlarge the crank pin.

Although it might have to get a tiny bit more stroke at the same time, it's fairly close to the main bearing races as it is.

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1. What do you hope to accomplish with a larger dia crank pin?
2. Bare in mind that the crank webs are hardened (yes, particularly the surface of the crank pin holes) and the strength of the assembly depends on it.

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Dr_C said:

1. What do you hope to accomplish with a larger dia crank pin?
2. Bare in mind that the crank webs are hardened (yes, particularly the surface of the crank pin holes) and the strength of the assembly depends on it.

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Click to expand...

Thanks for the good points! - The idea is that the 550 crank pin is overly narrow, weak, and allows too much flex. I'm only parroting it from Bushmechanic

Some deliveries. Bearings and steel sleeves.



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spanner said:

Sounds great,

Where can these o-ring be found?
I had to reuse these ones a few times already.

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My local sealing/bearing shop provided them! Remember to ask for viton! I believe these dimensions (100x1,5) are not obtainable in any other rubber quality than viton.

Or would you like me to get some for you?

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I will keep an eye open for 100x1.5 viton on my job. If I see a pack I will forget it by mistake in my bag.

what would be really good for 104.8mm bore would be 0.039 x 4 " or 1.0 x 100mm

Thomas of engine hardware used them

the only way i find those is in a roll of 39 thou and then join together

bushmechanic said:

what would be really good for 104.8mm bore would be 0.039 x 4 " or 1.0 x 100mm

Thomas of engine hardware used them

the only way i find those is in a roll of 39 thou and then join together

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Yup. I was also doing that consideration when designing the steel sleeve. I didn't want to add more possible failure sources... i have enough of them already!

Tempted to try sealing it just with good quality silicon gasket, no o-rings, anyone
tried doing that?

spanner said:

Tempted to try sealing it just with good quality silicon gasket, no o-rings, anyone
tried doing that?

Click to expand...

You have, Bushie, haven't you?

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yes DrC threebond 1207 B 360 hrs or so, no grooves and no leaks

and lots of 1207B , contiman tried with standard silcone and just a smear it didnt work for him, IMHO the sealing is helped by a big bead at the bottom of the water jacket

my thoughts are that 3 small grooves filled with good silicone would be very very good, perhaps a lip inside the water jacket too

however such simple things sometimes make people afraid

The steel sleeves are now in place! The race preparation of a "new" set of cases continues! Finally the weather allowed me to paint the fairings this weekend.







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