Cool mod to raise your compression ratio

[Junkers]

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]

I love good theory's ...

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

[imdying]

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]

I love good theory's ...

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

Getting your squish from something like 2mm to 0.7mm might be noticeable

[AllanB]

I look forward to your next post.....

"Will Bondo fix my piston?"

[FJRider]

Getting your squish from something like 2mm to 0.7mm might be noticeable

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

[imdying]

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]

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]

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]

Interesting. How much thinner did you go with the gasket?

[neels]

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]

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]

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


Hey found some old footage check it out great video great music
http://www.youtube.com/watch?v=dVm59...eature=related

[Junkers]

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]

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