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Junkers
29th May 2010, 21:44
This is an idea for anyone whose game..

If you remove standard spark plug (say a BPM6A) and replace it with a BP6ES, you can use the extra thread length to 'fill' the volume of the compression dome. You won't be able to screw it in all the way as it will foul on the piston, but if you space it out with with a spark plug washer you should be able to reduce the TDC volume and thus raise your compression ratio.

I'm going to give it a go soon enough, shall post on how I go.

FJRider
29th May 2010, 21:54
I love good theory's ... :lol:

I love them even more if they can be proven to give noticeable improvement ... good luck with that ... :yes:

imdying
29th May 2010, 22:39
How about checking your squish with some solder and getting some differing thicknesses of gasket paper from Repco, and setting it with your base gasket?

imdying
29th May 2010, 22:41
I love good theory's ... :lol:

I love them even more if they can be proven to give noticeable improvement ... good luck with that ... :yes:Getting your squish from something like 2mm to 0.7mm might be noticeable :D

AllanB
29th May 2010, 22:49
I look forward to your next post.....

"Will Bondo fix my piston?"

FJRider
29th May 2010, 23:29
Getting your squish from something like 2mm to 0.7mm might be noticeable :D

sounds painful ... why not just try a higher octane fuel ... ???

imdying
29th May 2010, 23:32
sounds painful ... why not just try a higher octane fuel ... ???You'll hardly need a fuel with a higher knock resistance if you're running a squish gap waaay over 1mm! Get it down to a more acceptable value first and then you need to worry about that.

Nutter34
30th May 2010, 02:42
getting some differing thicknesses of gasket paper from Repco, and setting it with your base gasket?

Only problem there is you change the port timing in the process... Would it be better or worse? Or are they not that sensitive? We had this discussion tonight regarding another guy... We aren't sure if he may or may not have done this very thing.

imdying
30th May 2010, 13:57
Doesn't appear to hurt it, but we don't know if that's because we're still running the crappy exhausts or not.

Nutter34
30th May 2010, 14:09
Interesting. How much thinner did you go with the gasket?

neels
30th May 2010, 14:47
Watch out for carbon buildup filling in the threads on the spark plug that are in the combustion chamber stripping the threads out of the head when you unwind it out again.

imdying
30th May 2010, 16:43
Oh yeah, one other reason why the port height isn't a big problem, there are 32 and 33mm stroke cranks, either of which could end up in the cases. I suspect the ones we have with a huge squish gap are 32mm cranks. Unconfirmed though, but something else I should measure.

daz71
30th May 2010, 17:06
You could throw ya gasket away and just use some loctite copper maxx, allso change your 2stroke oil to a better grade like castrol tts , also ive seen a bike go real fast when he sanded his piston flat but it lasted about 6 or so hours .lol


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Junkers
30th May 2010, 19:45
I don't think the compression boost will be that severe, HKMOTO's offer a kit with 17:1 compression using the same grade of parts. I don't think this mod will be hitting a ratio that high.

Bought a plug home from work today, found it will allow 7 turns in before it will foul on the plug. I have a spare head here so I will cc it at some point. Had the engine ticking over briefly, seems fine.. had a different exhaust note, more 'poppy'. Haven't had a chance to take it for a spin yet.

We didn't have a B6ES in stock so I had to settle for a BP6ES, with it's protruding head. Being a longer plug compared to the BPM6A it also has a longer insulator on it which has a lot of empty area surrounding it. I might try a 'flat head' style of plug from an RX7 if we have any handy at work.

Imdying: Will give this a crack first, not so keen on stripping gaskets :)

pete376403
30th May 2010, 19:59
What is the volume of the projecting portion of the spark plug and how does that compare to the volume of the combustion chamber? Do you end up with a *measurable* increase in CR?

Did RX7s use surface gap spark plugs? My kawasaki 350 used one of those back in '72

scumdog
30th May 2010, 21:21
Take cylinder head off.

Pop-rivet some meaty galvy washers to the top of the piston.

Reinstall cylinder head.

Viola!

Comp. ratio up!

imdying
31st May 2010, 08:56
You could throw ya gasket away and just use some loctite copper maxxBelieve it or not we've considered it... on some of them, even that would leave an adequate squish.

change your 2stroke oil to a better grade like castrol ttsWouldn't run anything else anyway :yes:

I don't think the compression boost will be that severe, HKMOTO's offer a kit with 17:1 compression using the same grade of parts. I don't think this mod will be hitting a ratio that high.Remember it's a 2 stroke so the effective compression ratio will change with the porting.

IWill give this a crack first, not so keen on stripping gaskets :)It's 4 bolts and 1 gasket, believe me, it will not put you out of your comfort zone.

What is the volume of the projecting portion of the spark plug and how does that compare to the volume of the combustion chamber? Do you end up with a *measurable* increase in CR?Of course it'll be measureable?? I think you mean *worthwhile* :laugh:

Take cylinder head off.Cylinder head is attached to the barrel... think side valve V8.

Comp. ratio up!Don't you mean crank out of balance? :laugh:

888mike
31st May 2010, 09:39
Sounds like you guys need to buy some Polinis "lol"

imdying
31st May 2010, 09:59
Or some Ultimas :D

Junkers
31st May 2010, 18:44
Did RX7s use surface gap spark plugs? My kawasaki 350 used one of those back in '72

Yeah they do. Not cheap!

I cc'd the head today with both the BPM6A and the BP6ES. 0.3cc in difference.. hoorah! :S

That BP6ES consumed a noticeable amount of volume/liquid so hopefully with a surface gap plug that will change the outcome.

So that works out to be 9.7:1 with a little rounding vs 9:1... brace yourself for the G's :rolleyes:

{.bLanK}G_o_D
1st June 2010, 12:31
Watch out for carbon buildup filling in the threads on the spark plug that are in the combustion chamber stripping the threads out of the head when you unwind it out again.

Good point.

Junkers
3rd June 2010, 19:03
Had another crack at it today except this time I used a BU8H plug which is completely flat with a center electrode. After cc'ing it, this gave a compression ratio of 10.8:1.

One problem, the gap is around 1.6mm and you can't alter it. The bike will start but as soon as the plug get's contaminated the arc can't manage the jump, the bike cuts out. If I can find a more suitable plug I'll post it up here.

Chur

{.bLanK}G_o_D
3rd June 2010, 23:37
Still running that 55 idle jet?
That won't be doing your plugs any favors.

Junkers
5th June 2010, 18:18
Yeah man still running the 55, haven't managed to get around to ordering those new jets yet. Actually had it running with the BU8H plug today, might of drawn a conclusion to quickly. Was going fairly well with the new plug. Seems to have a little more pep but there's only so much you can tell from your driveway.