ETZ 250 - 251 diffrences

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[dave47]

The correct squish for the ETZ250 is 0.9-1.2mm, and I daresay it is similar for the 251.
My own (251) squish is 1.1mm with 0.6 mm of head gasket, so if I used a 0.2mm gasket it would be safe to add an extra 0.5mm at the base, ie same as you have done. I will certainly try this out next time I have the barrel off. Unless of course you report in the meantime that it made no difference!

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[dave47]

I will definitely do that then, it is worth it even if it increases low end a little bit.

Regarding your 1.3mm squish:
It seems to me that because you have had a rebore, even if it is just 1st o/s, it will increase the cylinder volume by enough to keep the compression ratio right, even though the squish is 0.1mm above tolerance. I am no technical expert, however!

[parrbd]

Too large a squish clearance can encourage detonation. Best to keep within specification.

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[parrbd]

Too small a squish clearance may cause clearance problems but it will reduce detonation. Too large a clearance will make detonation more likely. Refer to page 37 in the Jennings bible. http://www.amrca.com/tech/tuners.pdf

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[parrbd]

I think my reading of this research is that the squish area stops ignition of the enclosed mixture because too much heat is lost to the surrounding metal. This only works within a small range and the ideal was tested as .015". What I am inferring is that as the clearance increases it stops acting as a squish area and ignition can occur at the outer reaches of the combustion chamber, so bringing back the possibility of detonation. BTW, from experience I have had results that diverged from Jennings advice, particularly with inlet timing. (On a TZ350A I got a much more tractable engine after taking 5mm off the rear skirt and a better top end of 154mph at Bathurst, back in 1975)

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[Puffs]

Following a biased and flawed moderator choice (someone posting aggressive personal attacks is rewarded, while my technical posts are removed - behind my back & without any justification!), I have withdrawn from this forum.

[dave47]

Thats a very professional looking job.

[JawasandMZs]

I remember when the 251 was introduced and the bike press evaluation was that the 250 etz had hotted up the porting from the Supa 5 making it a (relatively) peaky, fast stroker at the expense of sub 50mpg economy. The 251 reversed this design by making the motor much more flexible sub 3,500 rpm, the point below which the etz 250 is pretty hopeless in 5th gear, resulting in better economy but probably less fun to ride.