1989 kr1 with kr1s bits and bobs

JanBros · Post by **JanBros** » Wed May 09, 2012 10:49 pm

just to give you an idea of what I have done to my engine (it's in my inserts-topic) :

cylindres : timing is a bit raised because of the lower piston's (28.50mm comp. height):
KIPS timing : 196.4°
main exh timing : 190.4°
transfer : 136.2°

head :
RPM max 10.750
squish 0.7mm
squish width : 7mm
volume : 10cc
comp. ratio : 13.5

Lozza gave me 9/10 (but not 18/20 , probably because I still haven't got programable ignition

) for my figures, so maybe you could try to get yours in the same ballpark ?

now it was almost 3 years that I didn't ride my stroker (was going to say KR but that would only be partially true

), so I can't really compare. Before, my engine was tuned by a dutchman. It was strong (all his engines on dyno made between 70-73 BHP) and I loved it, but I was fed up with having to ad octane booster all the time.

Anyway, it feels like before and 'm sure it is stronger than standard. It still has the same caracter as before : comes on strong at +/-7.5k (rev counter not working good) and gives another great boost at 10k. haven't played with the carbs yet, as everything feels spot on.

TwoStroke Institute · Wed May 09, 2012 11:08 pm

Blowdown is from ex open to transfer open. EVERY degree is a MASSIVE improvement. You only have that period to go from high cyl pressure to less than 5 psi to get the transfers working. The less time and area you have the less chance there is for the engine to work properly.
You will have to much advance after peak you have to drop it quickly, for instance a RS125 will run 3 deg after peak and will rev on for another 1200rpm

maccas · Post by **maccas** » Thu May 10, 2012 8:58 am

Cheers guys,

I understand what the term blowdowm means but just didnt really grasp the term blowdown area. Is this the area of the exhaust port that is open just before the transfers open? i.e. the area of port available for the high cylinder pressure to escape into the exhaust through? By widening the kips ports i have gained more area but just not any more duration as yet.

Dan

TwoStroke Institute · Thu May 10, 2012 10:18 pm

Yes the area of the exhaust port above the top of the transfer is the blowdown TA.

maccas · Post by **maccas** » Mon May 21, 2012 10:12 pm

Bit of progress

Going to mod the head this week to improve the squish angle.

Dan

maccas · Post by **maccas** » Wed May 23, 2012 9:54 am

Head work beginning:

Dan

JanBros · Post by **JanBros** » Wed May 23, 2012 7:51 pm

maccas wrote:Head work beginning:

and what are the plans

maccas · Post by **maccas** » Thu May 24, 2012 9:48 am

Hi Janbros,

Well there are a couple of things that want doing to the head, the squish angle is wrong and the volume is too small for starters but I noticed this the other day:

When the head has been worked in the past the edge of the squish band has been widened to 57.8mm where a stock head is ~ 56mm.

So first I am going to skim the head until the outer diameter of the squish is nearer 56mm. This won't remove alot of material from the head as the squish angle is only shallow. Skimming a tiny amount off the face of the head will reduce that diameter by quite a lot.

Next I will measure the dome radius of the vertex pistons that I am going to use and get the squish angle cut to suit them. I will them assemble the engine and fiddle around until I've got a 0.8mm squish then measure the fitted clearance volume of the head. Once I have that figure I will remove material from the combustion bowl until I have the required clearance volume (10cc).

Just drilled the lubrication holes in the vertex's this morning and balanced the pistons within 0.1g:

Been fiddling around with base gaskets to get the pistons to sit flush with the top of the cylinder. With the extra compression height of the vertex pistons its looking like I will need a 1.2mm thick base gasket.

Dan

maccas · Post by **maccas** » Fri May 25, 2012 9:21 pm

Settled on standard base gasket plus a 0.8mm gasket to get the piston to sit flush with the barrel at TDC:

Been playing with MJ's spreadsheet on cylinder head calculations and the squish velocity comes out at 33.14m/s for how the engine was set up before.

That sounds high to me so again may have been contributing to the low peak rpm.

Dan

TwoStroke Institute · Sun May 27, 2012 11:04 am

Why do you think 33m/s is to high for msv? A parralel squish is not good for msv

maccas · Post by **maccas** » Sun May 27, 2012 12:55 pm

It just seemed high really, would you say otherwise?

Dan

TwoStroke Institute · Mon May 28, 2012 12:36 am

30m/s is the minimum you need.

maccas · Post by **maccas** » Wed Sep 12, 2012 11:48 am

Finally had the head skimmed by the uni workshop technicians so the next job is getting the squish cut to better suit the pistons. (took them 12 weeks grrrrrrrrrrrrrrr, they wouldn't let me borrow a fly cutter)

Bolted it all together the other day and measured the squish and it was 0.6mm at the cylinder wall and 1mm nearest the plug hole. Head volume still too tight at just under 9cc too

Dan

dave32 · Post by **dave32** » Wed Sep 12, 2012 2:58 pm

Have you calculated the compression ratio with that head volume?
Having a similar occurance with my RG5,get the squish clearance where i want it then the compression is too high and the CC volume is on the small side at 8.5 to 9CC.
Really i would aim for a 10CC volume to the bottom of the plug hole when installed (not just measured on its own),but ive seen quite a few RG5's (sorry off topic

) that have put decent power curves running small CC volumes (8 to 8.5CC).
Maybe the squish angle,width and clearance is more important than the head volume?
Im aiming for no more than 8.1 compression ratio and plan to run super unleaded with octane boost when it has a road outing and straight AVgas on the odd trackday.
Sorry to go off topic but thought it may be of interest

ATB
Dave

maccas · Post by **maccas** » Tue Oct 23, 2012 9:28 am

Hi Dave,

Yep calculated the compression ratio and it comes in at a whopping 8.4:1 which is too tight really as we all know for a KR1/S.

Thanks to hipringle on here I now have a standard unmolestered KR head to start a fresh with

thanks again mate!

I measured the flat plate volume of the stock head last night and it came in at 14.4cc. The modified head that I have is more like 12.5cc flat plate volume and about 8.7cc fitted clearance volume. So hopefully just bolting the new head on will get me close to ~10.5cc ish. I can then measure the squish and see how much it needs adjusting by. I'm going to leave the head as it is and adjust the squish using different base gasket thicknesses this way I can lower all the ports too as they are too high really, especially the transfers at 38.5mm from the top of the cylinder.

Comments welcome as always!

Dan