1000, unleaded conversion advice please

Post by **neiltomlinson** » Tue Apr 22, 2008 2:31 pm

hi all just looked on ebay tem number: 250238411935
can not do much else neil

Post by **bmcecosse** » Tue Apr 22, 2008 10:23 pm

P-up - my 940 head 1098 engine (standard cam + 1.5" carb on alloy inlet) pulls really well in all gears - it's NOT a high revving peaky race engine. It replaced a pretty good 295 head, and the improvement was quite susbstantial - I'ts a great improvement at very little cost.

Post by **Packedup** » Wed Apr 23, 2008 12:07 am

Aside from CR is there really any gain to be had from going big(ger) valves and ports on an otherwise mild 1098 by using a 940?

I'm not saying they're a bad choice, but I do wonder if the improvements people see come from a substantially improved CR rather than anything to do with the design of the head itself. If you assume 5cc of the compression space is head gasket, area above the pistons in the block etc then the 8.8CR becomes nearer 10.5 with the 940 head on - That's a serious increase and is going to create a lot more oomph throughout the range!

Has anyone ever done a like for like, taking a standard engine and using a 202, 295 and 940 head, all machined to give equal chamber size (so standard 940, skimmed 202 and 295) done back to back tests? Only I'm getting the distinct impression gains are coming from a better squash rather than a better head (for the application) overall...

Post by **bmcecosse** » Wed Apr 23, 2008 3:30 pm

I'm sure the Cr increase is part of the improvement P-up, but the larger valves and much better shaped ports and throats must help too. My 295 head had been 'worked over' and skimmed - so my CR then was ~ 10:1. I fitted the 940 after only lightly smoothing the throats and opening up the tight corner in the exhaust throat (and of course sinking the ex valves 40 thou) - with the same carb and manifold as before - and the improvement was very noticeable - all through the rev range. Quite a bit more noise from the standard (stainless) exhaust ! Without doubt it is strangling the engine -and that will be my next priority once I get the TR 7 back on the road.

Post by **neiltomlinson** » Sun May 04, 2008 4:59 pm

hi i dont now if you are still looking i have just spotede this on ebay
Item number: 320247895620 neil

Post by **bmcecosse** » Sun May 04, 2008 6:00 pm

That would be this one http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... :IT&ih=011

Dunno why they say too heavy to post - certainly without the inlet manifold it is well within Royal Mail Standard Parcel limits. I would want to see some 'evidence' that it is for unleaded fuel.
Edit - I don't see 12G202 on it - so I would wonder if it is for a 1098 engine anyway.