ESE's works engine tuner

**G Jones** · 2nd August 2013, 11:55

Originally Posted by wobbly

Honda faggots off their forum abusing me that the NSR wont rev if taken below 0.8mm

Sorry - couldn't resist that - I'll not be using any H parts now or ever if I can avoid it...
I was just trying to tease out of you what the limit might be for a TZ350 - in this case with a Hoeckle crank (pro-digital Ignition) - we're down at approx 0.75mm at the moment - and it appears to be ok - although I'm not sure if I'm brave enough to take it any further...
The "not free" lunch was pointing in the right direction though...
Thanks.

**richban** · 2nd August 2013, 14:57

Originally Posted by wobbly

You dont really need the Ex timing to establish the head geometry, and yes the 6mm number seems to work with most " usual " combustion chamber geometries.
Avgas works with anything from around 192 to 202 Ex duration at around 15.8 full stroke.
Smaller bores or lower bmep setups can go 16.2, big bore oversquare or very high bmep like slightly less at 15.5, air cooled of course needs alot less.
As long as you hit the lower mechanical squish depth limit, then adjust the width to hit 38M/Sec MSV you will have good squish turbulence that helps the flame speed - reducing any tendency to deto
the end gasses.
That MSV number is meaningless in the context of all but hitting the head when within the normal rev limits, but as a guide it works every time.
The sharp bowl edge increases the flame speed, and a very deep angle away from that edge into the bowl is synergistic by pulling the turbulence further into the combustion space, again increasing the flame propagation speed,
over a wider band.
Pushing the combustion parameters this hard means a digital ignition is mandatory to balance the timing against the high peak cylinder pressure now being generated.

More fantastic help. Thanks yet again. I have been using this ( http://www.torqsoft.net/squish-velocity.html) calculator to look at the MSV and as a design guideline.

It does want the captive compression that I will not be able to work out until I know the timing. But might just wing it. Was looking at around 15.1. static.

Looks like to get the shape I want without welding up the heads I will have to take around 1.5mm off the top if the head. It will be pushing it. If I feck them up then inserts will have to be made.

**wobbly** · 2nd August 2013, 18:42

A TZ350 will run 16.2 with a proper toroid as its bmep is pretty low, and can run at 0.85mm spinning to 11200.
Miss a gear and hit 12,000 and the pistons clip the head, this is with one of the good aftermarket cranks, I would stick with 1mm if using the soft Yamaha junk.
These piston port engines love the deto free high com of a toroid, with way better mid power, and the overev comes back with the new ignition retard available from HPI etc.

Work backwards from the trapped com cc used in the program, as you know already what 15:1 is - easy calc = engine cc/14

**Yow Ling** · 2nd August 2013, 18:53

Rich, Heres the head Wob did for my RGV100 VJ22
http://www.kiwibiker.co.nz/forums/sh...post1130150762
http://www.kiwibiker.co.nz/forums/sh...post1130149522

if he has the fixture for boring the head skull maybe it would be easier, if you cock the cc shape its only an inch of brass to fix it

**Neal** · 2nd August 2013, 19:06

Has anyone done comparison tests for different squish area ratios ? Eg 40% vs 45% vs 50% . Just curious

**wobbly** · 3rd August 2013, 09:20

Yep, I did that as a job for a cylinder manufacturer in Belgium.
All that the lower MSV does when reduced by narrowing the squish width is to reduce power and increase deto.
You can get a little of the power back by increasing the timing ( offsetting the lower amount of squish induced turbulence ) but then of course you run into even more deto issues.
Pulling the squish depth down to the mechanical limit then shooting for a good MSV number is the end of the story and works every time.
I have had serious flame wars at times with people convinced that "big" engines are completely different, but they havnt even come close to the 70RWHp we used to get from a 250MX on Avgas
in open class karts.

**F5 Dave** · 3rd August 2013, 14:15

Eek. What sort of revs does one have to spin one out to to achieve that?

**richban** · 3rd August 2013, 14:49

What a funking lemon. Just started to strip the top ends. Only got as far as removing the barrel on the bottom cyclinder to find 3/4 of a piston and a completely shaged bore. At that point I gave up and am now having a beer thinking of how I should proceed with what is now turning into a complete engine rebuild.

**husaberg** · 3rd August 2013, 15:42

Originally Posted by richban

What a funking lemon. Just started to strip the top ends. Only got as far as removing the barrel on the bottom cylinder to find 3/4 of a piston and a completely shagged bore. At that point I gave up and am now having a beer thinking of how I should proceed with what is now turning into a complete engine rebuild.

The more beer you drink the less shagged it will become. Oddly the exact reverse thing happens with ugly chicks though

Dare I say 54mm stroke crank and RG150 cylinders or maybe something a little different

**richban** · 3rd August 2013, 16:04

Originally Posted by husaberg

Dare I say 54mm stroke crank and RG150 cylinders or maybe something a little different

Tempting. But part of the reason I like these bikes is that fact they are 250cc. If I wanted to go big I would just build 690 single 4 stroke. Still will one day.

**husaberg** · 3rd August 2013, 19:47

Originally Posted by richban

Tempting. But part of the reason I like these bikes is that fact they are 250cc. If I wanted to go big I would just build 690 single 4 stroke. Still will one day.

Sorry now i am confused........Presumably the only class it will be eligible for is F3......
F3 goes up to 400cc 2 strokes........
Are you really really wanting to be the underdog that much?