My Suzi T500 Project *It's Alive Video*

Re: My Suzi T500 Project (exhausting!)

Heads are a whole other situation. In a squish head we want maximum turbulence with a respectable MSV. As the squished gases pass the sharp edge into the bowl it creates turbulence that helps atomization and that's what we are after.

Knife edges are another issue again. Gas flow separates as it passes a knife edge, where it flows around a bullet nose. That's for example why people are often told not to knife edge the transfer port divider.

When I say low rev motor, were are talking GT's. A GT has a 64mm stroke so with a peak mean piston velocity of say 3500, that equates to 8500 revs max. So if we are looking for a nice meaty powerband, we want to focus on the 6-7k are rather than looking for peak power at 8500 and ignoring losses lower down.

That's what I mean by low revs. A kart motor by comparison is living between say 11,000 and 14,000 and they used to go much higher than that.

Header length is important up to a point, but what dictates tuned speed are gas temperature, exhaust duration and overall length. With the same pipe, if we want to move power up or down the rev range, the belly section is the place to do it. Bimotion calls for a header length of 7 to 9 times the exhaust port diameter. That works out to roughly 300 - 400 mm. A little less is OK but much longer and I'd expect drag to start to rise.

With section changes there are a number of factors at play. Larger angles create stronger pulses, but over a narrower rev range. Larger angles also tend to result in flow separation which in a 100-120mm pipe is really not too much of an issue, but could be a problem at the tail pipe entry where a venturi is a better way to merge. Changes in angle are usually limited to around 3-3.5 degrees in the divergent cones and 12 degrees or more in the baffle cone.

The thing I try to keep in mind is that almost any pipe will flow enough gas. What I need to focus on are the sound (pressure) waves moving up and down the pipe. Pressure waves are traveling at the speed of sound where the gas is moving at less than half that speed most of the time. Gas speed changes with engine speed but pressure waves change only with temperature. There is some reversion of the actual gas, but mainly it's about the pressure waves which often travel in the opposite direction to the gas.

Let's say we want to change our existing design to something shorter for more top end. We might use the same pipe with a smaller tailpipe to try to push temperatures up, or we could lean it out at the top end or retard the ignition to get more heat into the pipe. More advance at lower revs (if the motor can take it) and less at the top end might be enough to stretch a powerband.

Or we go with a shorter pipe. That means a shorter belly and that's not practical, so we have to increase the cone angles which makes for a larger diameter belly or a longer one of the same diameter - or some mix of both. If we keep the same belly diameter and go with larger included angles, that allows us to shorten the whole pipe.

If we got it right, power will go up at the top end and we will lose in the mid range.

You are right to focus on transfer ports. A GT has insufficient transfer area. At a target of say 8bar BMEP at say 7750 rpm, we have enough exhaust area to support 70 crank HP but only enough transfer area theoretically to support 56 crank HP. As revs go up, that situation gets worse, so we need to keep revs down and to make the exhaust work better to empty the cylinder and pull gas up through the transfers. At 7500 transfers gases flow nicely but at 8000 gas velocity drops, the temperature peak from exhaust rises by over 400 degrees in the top of the transfer port compared to the 7500 rpm effect. The same happens with transfer port gas velocity and pressure. At 7500 works like a charm, at 8000, not so much. Looking at the pressure, temperature and velocity traces at both engine speeds it's clear that the transfers are in crisis at 8000 and the exhaust is out of synch.

For a race motor with good CR 6 speed trans, the package of ports and pipe may well be very different. That's phase 2 :)

In the real world though, all we can do is to try something and see if it works. If it does, great and if not, well it's back to the drawing board.
 
Re: My Suzi T500 Project (exhausting!)

Richard, looking forward to seeing how the pipes work out. Appreciate the knowledge you are sharing here with us.
 
Re: My Suzi T500 Project (exhausting!)

You guys do realize that I make this stuff up on the fly don't you? :) That's not entirely true, but often a questions comes up that I have to go and do some more research and analysis to work out why things are the way they are.

In most old bikes there's a shortage of transfer port time area and raising the ports doesn't always work. Late model RD400Fs for example have wider transfers than early models and that's good. Any modern two stroke has transfer ports all around - check out a CPI Cheetah and compare the transfer area to say a stock RZ or and RD350 and you'll see what I mean.

On an RD350 the smaller auxiliary boost ports are 13mm wide. On a late RD400 they are 18mm wide which is close to a TZ350 dimension. It's all relative and it all changes.
 
Re: My Suzi T500 Project (exhausting!)

That's all good stuff, thanks for sharing. We're on the same page with much of what you say, I think you just do a better job of explaining yourself than I ;D

Everyone has their own way of looking at things of course. For example you mention Bimotion's multiplier for header length which is relative to exhaust port size. I may use that for a starting point but always make sure I use a header length of about 1/3 TL. Sort of a combination of Blair and some other theories or rules of thumb I've picked up over the years talking to people and reading. Different strokes as they say.

Gas flow is funny. Should be simple but it's the opposite. I know that when I'm working on porting or a head I try to think like the gas LOL, and whatever the theories say if it doesn't look right to me I can't make my grinder do it so it looks wrong. Of course there's a difference between flow in a head and in a transfer or intake, I just try to think how the gas will react. In the head the gas being squished and pushed very fast toward the transition and the flow seems to work better with no radius while in an intake where the flow in parallel to the divider a rounded edge (radius) is superior. Obvious I suppose, it's just the kind of thing I think about,

I've never simulated a parallel wall header. Reading and talking to people I've never seen the need to go down that road, and manufacturers stopped selling them stock a long time ago. Maybe I'll design and sim a set for fun. It would make pipe building easier :eek:
 
Re: My Suzi T500 Project (exhausting!)

teazer said:
You guys do realize that I make this stuff up on the fly don't you? :) That's not entirely true, but often a questions comes up that I have to go and do some more research and analysis to work out why things are the way they are.

In most old bikes there's a shortage of transfer port time area and raising the ports doesn't always work. Late model RD400Fs for example have wider transfers than early models and that's good. Any modern two stroke has transfer ports all around - check out a CPI Cheetah and compare the transfer area to say a stock RZ or and RD350 and you'll see what I mean.

On an RD350 the smaller auxiliary boost ports are 13mm wide. On a late RD400 they are 18mm wide which is close to a TZ350 dimension. It's all relative and it all changes.

We know your making it up as you go along:) Just kidding.

I used to race Rotax engines and I remember the porting is crazy compared to my GT500. Eventually I'll get some spare barrels for the Suzi then do some experimenting with porting, maybe I'll just get a complete motor and see how far we can take it but.... I'm getting ahead of myself here!
 
Re: My Suzi T500 Project (exhausting!)

These are all 125cc per cylinder

250twins_sml.jpg


They have more port area than a GT500/750 and all make more power. An RS125 makes around 48, the TZ250 is over 80 and that RS250 Aprilia made 65 and it's a street bike slightly modified. If we had the same technology in say a 500 4 cylinder we'd have a 190HP street bike. But we don't :-(

How about a 440 Polaris which makes about 120 hp from 440cc? We can learn a lot from those motors and can see what the limits are in our oldies.
 
Re: My Suzi T500 Project (exhausting!)

Here's NASA's explanation

wdgflow.jpg


In simple terms, air striking a rounded object flows around it , but when it encounters a sharp edge it breaks into a wedge with little flow inside the pressure wave so it's flows less than around a blunted face.
 
Re: My Suzi T500 Project (exhausting!)

The NASA picture was a joke. It's real and it came from their web site but seriously....... It did happen to be the best picture I could find in 30 seconds or less, that illustrates why a knife edge is not good in an inlet port and yet people still do it.

The other stuff has taken me a while to process and I'm nowhere close to some of the guys that really understand the finer points. There are lots of smart people around and I like to try to learn. If I sat in the same room, they would be bored and my brain would likely explode. We all learn at our own pace.

When I tuned my first two stroke Villiers motor, Jennings hadn't written his book, Yamaha were making pianos and . well you get the picture. We had "Tuning for speed" and "Speed and How to Obtain it" or whatever the actual tiles were and that was it. Porting was done with a file. Things have come a long way and I'm just trying to catch up.
 
Re: My Suzi T500 Project (exhausting!)

Richard, I used to race Villiers 9e engines (highly modified) in karts they were 210cc. We did a reverse barrel on those engines.
 
Re: My Suzi T500 Project (exhausting!)

I once drove a kart with a 9E motor and it was insane (or I was !). That was so long ago I'd forgotten about it. I'm not sure I remember the whole story but it was nuts. Alpha crank and rod and all that stuff that I barely remember. My brain has worked hard to bury that memory and there it is back on the surface again.....
 
Re: My Suzi T500 Project (exhausting!)

teazer said:
I once drove a kart with a 9E motor and it was insane (or I was !). That was so long ago I'd forgotten about it. I'm not sure I remember the whole story but it was nuts. Alpha crank and rod and all that stuff that I barely remember. My brain has worked hard to bury that memory and there it is back on the surface again.....

Haha, yes karts are insane. Yes, alpha crank and motoplat ignition. If you think the villiers kart is insane try a 250 inline twin Rotax!!! I remember lapping Silverstone quicker than the GP bikes due to the high corner speed.
 
Re: My Suzi T500 Project (exhausting!)

Well I got the pipe mocked up with cardboard finally. Here are the results. Very tricky fitting the pipe in due to the tuned length but I think it looks pretty good as it is. I don't want the silencer to protrude to much so I might have to go with some shorty's.

Any input on the routing or just the orientation of any parts of the pipe welcomed.
 

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Re: My Suzi T500 Project (exhausting!)

You might try kicking out the header out to bring the dwell section under the bike more.

581_2007.JPG
 
Re: My Suzi T500 Project (exhausting!)

Are you doing a 2 into 1 pipe. or are my eyes messing with me
 
Re: My Suzi T500 Project (exhausting!)

Eric, nice bike I assume that's you? here's a pic from the front, my headers do kick in a little.

Brad, not 2 into 1, look at the front pic.
 

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Re: My Suzi T500 Project (exhausting!)

Kicking in will have them closer to the front tire and not allow to much forward movement to get the dwell section under the frame. Kicking them slightly out will help bring that section forward and under the bike and allowing the front tire more clearance.
 
Re: My Suzi T500 Project (exhausting!)

Oh yes, that is me on my bike at Mid-Ohio. Those are Jemco, (Jerry Klawitter) style racing pipes.
 
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