My Bemsee dyno results

[Luders]

Look forward to the results.

The compression testing details are in the manual, 107 - 164 psi.

[TwoStroke Institute]

Closing or opening? and which dyno curve.....

I call it 'closing' because of closing the resonator, you could say opening the sub ports.
I meant the original curve posted.

[dave32]

Im with Luders on this,if the valves are fully open and there's nothing mechanical wrong/fuel supply and jetting are good/ignition is good and the only difference between when it went well and now it doesnt is the barrels and head have been modded then Bobs cocked up,again
so what was the tune supposed to do,what did he say you would achieve with the mods he was going to do?
Did he know/ask what pipes you were using?
There really isnt a big difference in stock and the Nikons,they allowed the engine to overrev a bit further but peak hp wasnt anything in it so i cant believe its that.
So what did he offer as advice as to what could be wrong and did he advise any settings before?
I was told to slot the pick up and advance the timing as far as i could,tried it,made know noticeable difference.
Then it was a case of "your jettings out",well no after going from over rich to borderline seizure lean on the needle and main,it was still gutless.
i dont expect NOT to have to mess around with settings once an engines been modded,i know in some cases people shouldnt have tuning done as they wouldnt know if it was running right or not(this isnt aimed at anyone BTW)
If i think back to how many engines ive known that have been tune by some of the more renowned tuners in the UK and how many of them actually were better than a well setup stock motor it makes me wonder how they keep going,maybe the customer just end up assuming its something there not doing right and give up and go back to stock.
I think if you are tuning an engine like the KR where everything works together to give really good power as stock then you need to realise its not an LC350 or something that is in a low state of tune and upping the comp and raising the exhaust port wont give back good results.
you would be better off blue printing,setting the squish exactly and maybe install a good ignition,getting the jetting spot on and then leave the engine and concentrate on suspension setup and riding craft,it would make more difference to a lap time than 1 or 2hp on the dyno.
Sorry for the rant

[scooble]

when I took the engine to Bob, I said I wanted a race tune for trackdays and the occasional race. Although I may not know as much as MJ, I have conducted literally hundreds of dyno runs on various different engines in the past and set up my TZ250 to run good (with some help).
I'm pretty sure I told Bob at the time which pipes I would be using as I can't think that would be the kind of thing I would leave out. I also told him that I would be using 35mm carbs too (whether he was listening was another matter)
When I got my engine back after it had been tuned, I was told the spec was;
Head vol =10.5cc
Comp ratio = 7:1
Squish angle = 17 deg
Squish band width approx .72mm

When I collect my engine on Saturday I ask about the port heights again.

I too have heard horror stories about some of the top tuners (except Graham File), though it does seem that they can also do exceptional work for some of their 'special' customers, however, I'm pretty sure I'm not one of them!

[maccas]

Hi Tricia,

From those figures you have just given I have just done a quick back of an envelope calculation that tells me that the exhaust port height is 25.78mm from the top of the cylinder. If that is the case then that is the problem with your bike I would say. The exhaust port is too high. This is backed up by your hp figures below 8k which are about 5hp short of what they should be.

Obviously I don't know which exhaust port (kips or main) bob used to calculate the corrected compression ratio. I would assume the highest port which would be the kips if he has kept it such that the kips opened first. Which would contradict my theory on high main port which results in the crap drive below 8k. If bob tunes a cylinder in the same way Stan does you can bet that he has raised the main port above the kips as he did on my KR1 cylinders though.

Also I'm assuming that the quoted 10.5cc is the fitted clearance volume of the head with the piston at TDC. It may well be the flat plate volume of the head not taking into account the dome of the piston and head gasket etc. If it is the flat plate volume then the corrected compression ratio quoted would result in a lower exhaust port as the clearance volume would be less than 10.5cc.

Hope this helps

Dan

[scooble]

I do know though that the top of the cylinders have been skimmed so that the combustion chamber is within the head. Not sure by how much though

[maccas]

Ok my mistake i should have wrote 25.78mm from TDC not to the top of the cylinder.

Dan

[mj43]

Closing or opening? and which dyno curve.....

I call it 'closing' because of closing the resonator, you could say opening the sub ports.
I meant the original curve posted.

The curves exhibit the characteristic flattening in the power curve around 8K that happens when the power valve opens the sub port (KIPS). It might be only one cylinder is opening? I did have a KIPS linkage come off once in a race and there was a noticeable drop in power - pulled in as not worth carrying on.

[scooble]

do you mean opening the resonator chamber Mark?

[scooble]

I found out that the cylinders probably have .040thou taken off the top, port heights though are still unknown.

[maccas]

Taking material off the top of cylinder doesn't affect the port timing providing that a piston with the same compression height is used, the base gasket is the same thickness and that no material has been removed from the base of the cylinder.

Its moving the cylinder relative to the timing edge of the piston that changes the timing.

I'll be interested to see what he has done to the cylinders and I hope its fixable if it is the port work that's causing the problem.

Dan

[Luders]

I think you could get some power back, but they are probably too far gone, like your Stan Stevens ones Dan.

[dave32]

I think your probably right Scoobie in what you say,some of the stan engines like the ones he tuned for John Reynolds and Max vincent back in the supercup days gave really good power over a fairly wide range,(special customers),then there's me who gave him an RG500 top end to take out to 570 and i get it back the head has NOT been opened up to match along with the gasket (im talking 3mm here so 1.5mm over lap all the way round ).
When i queried him on this he said they have never had a prob with it
Now even a School kid would look at that and say "why is the combustion chamber SMALLER than the bore,seems odd",you dont need to be a engine guru to know that somethings not right.
In the end i got the guy who rectified the Bob 5speed farnham KR to machine it out to match,no big deal but i shouldnt have to when ive trusted a known person to do a GOOD job.
Im assuming you probably have the same tune that i had,i mentioned it would be used on the track with the occasional road use thrown in and i said i wasnt even worried if it lost a bit of midrange as long as once "on the pipe" it stayed there.
If this is the case then im sure you could get the transfer ports modded by Graham File to get the power back or to suit the exhast timing along with a well flowed Bottom end.
Thats what the guy did for me and like is said it absoulutely flies,compared to my fairly stock KR its night and day,whereas there isnt much of a "top end rush" as stock this thing feels more akin to a TZ250 even running 28mm carbs (obviuosly not as powerful,i think 80hp is too much to ask ),it just makes me wonder what he could have done if it hadnt already been messed with?never mind you live and learn
Really it shouldnt matter if your running 35's or 28's as such,it shouldnt effect what port timing you end up with,and werent all the supercup bikes retsricted to stock carbs yet they still managed a gain of over 10hp up stock
Hope you get it sorted,and BTW what TZ have you got?
Mines a ex Dennis Trollope 93,kinda makes the KR seem relaxed
ATB
Dave

[TwoStroke Institute]

Closing or opening? and which dyno curve.....

I call it 'closing' because of closing the resonator, you could say opening the sub ports.
I meant the original curve posted.

The curves exhibit the characteristic flattening in the power curve around 8K that happens when the power valve opens the sub port (KIPS). It might be only one cylinder is opening? I did have a KIPS linkage come off once in a race and there was a noticeable drop in power - pulled in as not worth carrying on.

Same thing happens with Aprilia 125's with a solenoid PV, it's the on/off, yes/no, open/close nature of this type of PV. The Aprilia is sensitive down to 100 rpm , the further you get away from optimum the bigger the dip.
Varying the resonator volume might ameliorate the effect. I have a plan to make a 2 stage or a variable volume resonator(but a variable length pipe works the best)

I don't see the sense in machining of the top of a cylinder , looses the power stroke and worse it's irreversable.

[dave32]

Ive had a measure up of a couple of barrels,regarding exhaust port distance to top of cylinder
stock B2
main port 28.5mm
subs 27.5mm
width of main 36.8mm

Terry sheppard modded S
Main and sub opening together
27mm
width of main 38.8mm

I havent got a stock S barrel to measure.
The sheppard barrels worked well on track,they had lots of overrev and a very smooth power delivery.
Strange about the subs opening first,i know its a different engine but on my 93 TZ the main opens first,sure there must be a reason though.
I have made spacers for my B2 barrels that space the chamber out by half the width again of the cover,this seemed to help drive out of low speed corners (mallory hairpin and the like).