[Healeys] Longbridge head modifications

Andy Thorp bce257 at yahoo.co.nz
Sun Sep 6 12:59:37 MDT 2015

These are air flow numbers measured on a flow bench. 

The later head looks like it should be much better than the early one but in reality the biggest issue is small valves and poor combustion chamber shape, not the actual gallery. The only place where the stock BN4 head outflows the later one is at very low lift and this is due to having 30 degree valve seats which have a larger curtain area than the later 45 degree ones. This makes no real world difference in horsepower though.


On Mon, 7/9/15, Wilko2 <e-wilkins at cox.net> wrote:

 Subject: Re: [Healeys] Longbridge head modifications
 Cc: healeys at autox.team.net
 Received: Monday, 7 September, 2015, 5:17 AM
 Are these numbers theoretical, or
 from actual dyno?
 I'm very curious about how that design could out-perform the
 later design.
 On Sep 6, 2015, at 1:05 AM, Andy Thorp wrote:
 > Since it is a bit quiet, here's something I've been
 playing with over the (southern hemisphere) winter. I was
 always interested in just how "bad" the Longbridge gallery
 head was given that it is pretty much the same layout as the
 later ones with two carbs and a log manifold channeling air
 through a series of abrupt 90 degree bends. The biggest
 improvement in the later head is the bigger valves, and when
 these are fitted to the gallery head with chambers and ports
 relieved accordingly, the air flow rises to above the stock
 3000 setup. The exhaust is a little different though- the
 3000 exhaust valve is too big and reduces flow due to
 bore/block shrouding. Hoping for 125hp from an otherwise
 stock Longbridge engine this summer once it is all back
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