KR-1S.co.uk Forum

maccas wrote: Lozza,

I have tried to improve blowdown area by widening and raising the kips ports. By lowering the barrel I have gained 0.3 degrees of blowdown angle. I now have the kips ports and main opening at the same time, so I have effectively one very large port that will open simultaneously. The actually blowdown area is large but the blowdown angle may well be lacking yes. Only one way to find out really......

Dan

Isn't blowdown the time between opening the exhaust and opening the transfers ?
so you can only change it by raising the exhaust or lowering the transfers ?

JanBros wrote:
Isn't blowdown the time between opening the exhaust and opening the transfers ?
so you can only change it by raising the exhaust or lowering the transfers ?

You win the prize Jan

TwoStroke Institute wrote: The main and subs opening at the same time is the worst option. Track, dyno and simulator tells us main open first followed by the subs 2-3deg later is the only way to go.

But Frit's says '....Then raise the main exhaust port to the same height as the aux's....'

JanBros wrote:

maccas wrote: Lozza,

I have tried to improve blowdown area by widening and raising the kips ports. By lowering the barrel I have gained 0.3 degrees of blowdown angle. I now have the kips ports and main opening at the same time, so I have effectively one very large port that will open simultaneously. The actually blowdown area is large but the blowdown angle may well be lacking yes. Only one way to find out really......

Dan

Isn't blowdown the time between opening the exhaust and opening the transfers ?
so you can only change it by raising the exhaust or lowering the transfers ?

As I understand it, it is time/area so making the ports wider as well as taller, and in the case of the KIPS (lower) helps.

mj43 wrote:

TwoStroke Institute wrote: The main and subs opening at the same time is the worst option. Track, dyno and simulator tells us main open first followed by the subs 2-3deg later is the only way to go.

But Frit's says '....Then raise the main exhaust port to the same height as the aux's....'

Jan Thiel will tell you it was tried and lost torque. Also pin plugs only work at high rpm.

Jan,

Yes changing the transfer heights and exhaust heights alters the blowdown angle. So it wouldn't seem that lowering or raising the cylinder would change anything blowdown angle wise........ However when you do the maths:



Transfers at 38.5mm from TDC gives port opening at 115 degrees after TDC.

Exhaust at 26.5mm from TDC gives port opening at 85.8 degrees after TDC.

115- 85.8 gives 29.2 degrees of blowdown angle.

Lowering the cylinder 0.5mm (due to higher piston compression height and adjusting base gasket thickness accordingly) gives:

Transfers at 39mm from TDC gives port opening at 116.4 degrees after TDC.

Exhaust at 27mm from TDC gives port opening at 86.9 degrees after TDC.

116.4-86.9 gives 29.5 degrees of blowdown angle.

Therefore 0.3 degrees improvement. Yes Lozza I know this is a very low figure before you say

But without getting another set of cylinders I am stuck with what I have for now.

Lowering the cylinder by another 0.5mm would give a further 0.3 degrees of blowdown angle. Then raising the KIPS 1mm would get me to Marks tried and tested figures of 27.5mm main port and 26.5mm KIPS. Giving a total of 32 degrees of blowdown angle with 39.5mm transfers (probably not enough transfer area)

OR I would be in a position to try the main port higher than KIPS.

Anyway we will see.

Dan

thought of that to Maccas, but didn't bother to do the math as I didn't thinck the changes would make lot's off difference .

but in your case any gain is positive

Interesting to read Jan's thoughts on leaded and Unleaded fuels,but is it applicable to the Club racer on a budget?
Engines that are stressed such as road engines that are tuned for racing always seem to be more reliable and have longer service life of parts using AV,also if you have a early race bike (pre unleaded) like an RG500/TZ/RS its been designed to work with Leaded fuel,i dont believe you can just chuck unleaded in and gain anything but i do believe you can lose alot,financially.
When i purchased the TZ 250 (93 leaded) off Dennis Trollope,someone who has been running them since they were invented at top level,i mentioned how easy were they to setup,leaded versions are fairly easy,it wont matter if your a jet size out or 2 from optimum,unleaded you wont get away with it so you need "Det counters" and more frequent overhauls.
I was told the same thing with my h***a RS.
Personally im sticking to "evil and polluting" AVGAS for the above bikes and my KR1 and any other bike i take on the track.
You only have to strip your carbs down to see the residue unleaded leaves nowadays,you can leave mixed AV for weeks and it causes no problems,also the engine when stripped is very "dry" with uneaded and not with AVgas using the same oil and mix ratio.
when the unleaded ruling came out in GP's in 96/97 it had a big impact on how well the Vtwin h***a 500's perfomed,it didnt matter so much with the V4's as they had "too much" power anyway so losing a bit off peak didnt matter but wasnt good for the V Twins who needed all they could get to compete.
whats everyone elses thoughts on the topic?(if you got that far that is


)

The GP bikes only lost HP for a few months, at the finish they had WAY more HP with ULP than with leaded. I swapped to ULP ages ago and never looked back.
Leaded and unleaded require different set ups, ULP is completely relaiable and your jetted richer than avgas.

I don't belive this "designed" to work with leaded fuel, components are the same, compression, jetting and ignition changes that's all

ULP = UnLeaded Petrol ?

Cheers for the info Lozza
Isnt the exhaust design required different between the 2 fuels?
ULP,yep unleaded Jan
Yep i noticed i needed Richer jetting when swapping between AV and ULP,i guess the timing could be more advanced when running AV as its slower burning (if you wanted to get the best out of it)?
Maybe its the pump fuel we get in the UK now,but ive noticed it causing problems on seals (drying out),maybe this doesnt apply to specific race ULP?
Cheers
Dave

In general, ULP will be richer with more advance less comp, Avgas leaner less advance more comp.
Which is why I can never understand people blending 50/50 avgas/PULP

Ahh interesting,so lESS overall Advance for Slower burning AV,i was wrong in my assumption.

i cant get my head round that still,
If the fuel is "slower" burning like Avgas then wouldnt it make sense to start the the "burn" off "earlier" so "more advance" needed?
On the Exhaust ports and sub ports timing,
Does it matter which opens first as long as the timing and area are what are required for HP when combined?
Looking at it it seems on the KR1 the Main port is set to give good power below 8000rpm (when the subs are not connected to the main duct),
Above 8000rpm the subs are open and there timing is Advanced over the main so giving good Top end.
I dont see how it can be compared to a TZ or similar that uses a Guillotine PV setup which controls the MAIN port timing,the subs are OPEN all the time unlike the KR's.
if we just raise the main ABOVE the subs we lose low and mid,if we raise the SUBS we gain Duration for Top end HP but still retain the low and mid.
So from my take it matters what PV setup the engine is running as to what opens first.
Just thinking out loud

I totally agree with you Dave. I also think the type of PV matters too. It's all a compromise and working with what you have isn't it.

Dan