ESE's works engine tuner

[Kickaha]

this is budget racing!

You're a funny cunt, ever considered a career in comedy?

[speedpro]

About exhaust ports and ducts. I'm just working on a MB100 cylinder so single exhaust port. The duct still has the standard duct to pipe flange with the step at the top. I've enlarged the port by raising it to achieve the desired timing and widened it to a measured more-or-less 68% of bore width. At the moment the port width reduces to the nearly standard port duct width in about 15mm and then tapers out to the standard duct to pipe flange. My question is - Is there a benefit in keeping the reduced duct cross-section or should the duct taper smoothly from the cylinder face to the pipe flange?
Given the size of the uncovered port versus the duct cross-section at various times in the cycle there would seem to be a benefit in keeping the duct cross-section down and therefore gas velocity up.
The reduction isn't a lot, maybe 2mm per side.
This cylinder has stock untouched transfer ports which even using just the single base gasket are at the desired timing. They of course need modification in both width and port roof angle which will have to be achieved with grinding and Devcon. This cylinder also has Boyeson ports(?) or ducts cut from the reed passage to the transfer passages. Looks like a good thing for flow at BDC.

[husaberg]

Agreed.

R.E. logging etc, this is budget racing!

A guy I work with (a sparky) is mad on model aircraft has all the swish gear FPV heads up display etc his set up features an auto pilot feature that uses GPS weigh points. His set up is not that expensive.
he almost wet himself when I showed him the post Frits did on the pylon racing.

then again I am fluffing around doing f-all anyway



I think too Wob that you missed my point re the strokes I said I thought Robinson was wrong.....

[Frits Overmars]

I'm just working on a MB100 cylinder so single exhaust port....At the moment the port width reduces to the nearly standard port duct width in about 15mm and then tapers out to the standard duct to pipe flange. My question is - Is there a benefit in keeping the reduced duct cross-section or should the duct taper smoothly from the cylinder face to the pipe flange?

My answer: you've got a great opportunity to educate yourself here. Preserve the reduced cross section, measure the power, then modify the duct and measure again.

Mind, if the first measurement makes you happy, don't modify that cylinder - never modify your best cylinder; work on another cylinder until that becomes your best.

[trevor amos]

This is perhaps a question for Frits and/or Wob.

It is well known that having water flowing around the entire exhaust duct is advantageous. However, in situations where the duct has too large a volume is it on balance, better to reduce the volume with a Devcon in-fill and lose some cooling effect, or not?
Welding in-fill to the duct profile is, unfortunately, not a viable option.
Any advice will be most appreciated.

Trevor

[Frits Overmars]

It is well known that having water flowing around the entire exhaust duct is advantageous. However, in situations where the duct has too large a volume is it on balance, better to reduce the volume with a Devcon in-fill and lose some cooling effect, or not? Welding in-fill to the duct profile is, unfortunately, not a viable option.

Hard to say, Trevor. I tend to prefer the small duct volume but I can't really say because we never used Devcon there; it may crumble and enter the cylinder.
And Devcon is not famous for its lubricating qualities.

[trevor amos]

Thank you for your comments Frits.

If I fill the floor I can still get about 2/3rds of the duct cooled directly by circulating water, and have the advantage of a better flowing duct. Yes, the Devcon will be a potential hazard, but I will try it and see what happens.

Is there anyone else out there with experience of this dilemma, that can maybe offer advice?

To do, or not to do, that is the question!

Trevor

[Haufen]

Just one thought to add to the 125 stroke thing - the Aprilia made peak power at 12800 and reved to 14500, if we tune the long stroke in a similar fashion we will have peak HP at 11800 and peak revs = 13500 to give 26M/Sec.

Why not let the long stroke engine rev to 14500 also? 28m/s for a 58mm stroke engine at 14500 sounds feasible to me. I mean, there are cars being sold which reach 26m/s in a serial application. And not all of these are sports cars.

[wobbly]

Re filling the Ex with weld - I have just had a go at a cylinder I cut up, and plastered birdshit all over it with alloy stick welding rods.
The rods are available form Weldwell, but you have to buy $150 worth - they are made specifically for easy/quick repairs on your weekend tinny.
Getting inside the Ex duct of a 2T or the intake port on a 4T with a 3mm stick is easy,and i found that if you angled the part such that the liquid flux runs away from
the weld pool, the deposit looks OK and isnt porous.
Is gonna make building up oval Ex ducts easy, where even a mini tig torch is all but impossible to control.
In many many tests I have found that with a single port the best power is found with an exit area of 90% of the effective port area at the bore is best.
So in many cases leaving the duct alone and simply making the port 70% odd and lifting it to normal race timings you end up with the right size exit.
I have tried steps ( with bigger header diameters ) but never found an advantage in this concept when using a single port and 90% exit size.
Reducing the duct vol by lifting the floor a few mm above BDC and filling in the bottom corner rads is what was done progressively more and more at Aprilia
and has a proven results, by increasing average velocity thru the cycle but also reducing the direct short circuiting from the A port front corners.

Re the long stroke rev thing - we were looking at apples Vs apples, and the same scenario could then be applied to the 54.5 engine - rev that to 28M/Sec and it becomes superior again.
But that exercise would then need someone to re employ Mr Thiel and his 100 minions at Aprilia to do the R&D needed to re optimise every single element of the design.

In reality it isnt " well known " that having a cool Ex duct is advantageous - its only lucky people like us that have been exposed to the thinking of people like Frits and Jan Thiel that this concept
sees the light of day.Their Noddy boss at Aprilia didnt agree, and most all of the current manufacturers of 2Ts dont have a clue.I have taken to boring holes and slots in the castings to get water right
up to the flange face like we see in Jetskis ,to try and get some of the benefits available.

[Haufen]

Re the long stroke rev thing - we were looking at apples Vs apples, and the same scenario could then be applied to the 54.5 engine - rev that to 28M/Sec and it becomes superior again.
But that exercise would then need someone to re employ Mr Thiel and his 100 minions at Aprilia to do the R&D needed to re optimise every single element of the design.

I understand your point in comparing apples with apples, but I don't think the square engine would come out on top in such a scenario. Because trying to let the square engine rev to even higher piston speeds, it would run out of time-area, whereas the long-stroke engine would not (yet). I believe there is a chance that, had Jan Thiel started with a long-stroke engine instead of the square engine layout, and put the same effort into it as he did with the RSA, that engine might have even more horsepower. That concept worked by going from short stroke engines to square engines, so why should it not work again by consequently optimizing a long-stroke engine? Maybe you can find out if that path would be worth trying in converting your RSA simulation model into a, say, 52 x 58,8 engine? What do you think?

[peewee]

seems like i asked onetime what the results would be with a undersqaure RSA. from what i recall it was never tried so it would be difficult to answer the question.

[TZ350]

For those interested in such things.



Does more oil make more power? well I think so.

Chambers finally got on top of the gearbox oil being sucked into the motor problem on Av's bike. We dynoed it plenty of times over the weeks to see if we had stopped the leak passed the rotary valve. Each dyno session it smoked real bad and drank about 200ml of gear box oil.

The night the smoke stopped we lost 4% of the hp we were making when it smoked.



As all the work was being done on the rotary valve and cover, the piston and cylinder were not disturbed.

So I guess its fair to say that the difference in power is oil related and not the result of any inadvertent change to the piston and cylinder during re assembly.



Playing with Chambers RG50 on the dyno getting the ignition and jetting right..

For those interested in what the Air Correction Jet can do.



Purple Line is the original 170 main jet, Blue line is a 220 main jet and it improved the lower and mid range part of the torque curve. The Red line is the Air Correction Jet opened up to 1mm, clearly more to go, tomorrow hopefully we will get a chance to open the Air Correction Jet up some more.

In the end, with a bit more work on the Air Correction Jet I expect to be able to keep the better lower and mid range pickup of the 220 and have the top of the curve extending out as far as the original 170 main jet did.

The 170 main jet was chosen for peak power, I must be like 100's of other people who do plug chops and all sorts of tricks to find the best main jet for peak power.

But now, in setting up an engine I would be more inclined to choose a main jet that worked well as the engined climbed the torque curve and then bend the top of the fuel curve to get peak power by adjusting the air correction jet.

[trevor amos]

Wob, thank you for that reply and for sharing your experiences.

I wonder if I may pose another question to you and Frits? As I`m sure you know, over at Pit Lane Jan Thiel has been explaining the problems he encountered with the bridges on the auxiliary ex ports of the Aprilia cylinder. Could there be any flow advantage in shortening the centre bridge on, say Honda RS cylinders, and indeed any 2t ex duct with a similar arrangement? I was particularly thinking of the effects during the critical blowdown period, where area, time and flow capacity are all in short supply!

Trevor

[Frits Overmars]

Does more oil make more power? well I think so.

So do I. There is a slogan "where there's oil, there can't be petrol". But hey, oil will burn too.
Ever tried CH3NO2? Granted, there are better lubricants, but horsepower won't be a problem.

Playing with Chambers RG50...

So Chambers is using an RG50 frame? From the stories on this forum I get the impression that Av knows her racing, so I wonder: did she ever ride that 50?
And what did she comment? An RG50 frame is almost as stiff as a wet newspaper...

Purple Line is the original 170 main jet, Blue line is a 220 main jet and it improved the lower and mid range part of the torque curve. In the end, with a bit more work on the Air Correction Jet I expect to be able to keep the better lower and mid range pickup of the 220 and have the top of the curve extending out as far as the original 170 main jet did.

You seem obsessed with that Air Correction Jet. This screams for an of-off powerjet!

[TZ350]

Attachment 303210Attachment 303211

Chambers had me order one of these today for his RG50.

Pretty cheap of Ebay, it may be a good, inexpensive ignition (hopefully), anyway when it turns up I will let you know how it goes.