I don't mean to hijack this topic, but I've been following it with
interest. I was wondering, is there any advantage in putting the later
head onto an early block? Or is it even possible?
I have a TR250 and will be looking at getting into the engine rebuild
sometime next year.
Thank you kindly, - Robert -
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Navarrette, Vance wrote:
> Ken:
>
> The later head has much better profiles on the ports, and so
> flows much better than the earlier head. Also, despite the fact that the
> earlier head has a larger exhaust valve, I believe the later head flows
> better on the exhaust port than the earlier head. The reason is valve
> shrouding. The larger exhaust valve moves the valve too close to the
> wall of the combustion chamber. If you are looking for a performance pop
> on the later head, install some nice stainless valves with waisted stems
> and swirl polished faces. Don't forget a 3 angle valve job too.
> The downside to the later head is the much lower compression
> ratio - this will cost you a lot of power unless you mill the head to
> bring the compression up to something respectable.
> The later head was used to restore some of the power lost to the
> lower compression ratio, which was necessitated by the tightening
> emission standards. The later cam was better than the earlier cam as
> well, once again to regain lost performance. HP was virtually the same
> even though torque had fallen off.
>
> Just my $0.00002
>
> Cheers,
>
> Vance
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