Cool mod to raise your compression ratio

[scumdog]

Take cylinder head off.

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

Reinstall cylinder head.

Viola!

Comp. ratio up!

[imdying]

You could throw ya gasket away and just use some loctite copper maxx

Believe 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 tts

Wouldn't run anything else anyway

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*

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?

[888mike]

Sounds like you guys need to buy some Polinis "lol"

[imdying]

Or some Ultimas

[Junkers]

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

[{.bLanK}G_o_D]

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]

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]

Still running that 55 idle jet?
That won't be doing your plugs any favors.

[Junkers]

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.