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BN4 Longbridge Oversized Valves?

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Csarneson

Csarneson

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I am just starting an engine rebuild on my gallery head bn4 engine. I have a couple engine experts telling me that I should have enlarged valve seats and valves put in. Has anybody done this? Theoretically there are performance gains to be made but I have no idea. I've read that performance on this head is primarily limited by the carbs but again I don't have a good grasp. Thoughts?

Chris
 
Your performance is NOT limited by the carbs....it is limited by the head design. Get a 6 port head and don't waste your money on a galley head. There is a good reason why they changed to a 6 port head.
 
Thanks Richard. I don't plan to swap out the head anytime soon. I will probably just do a basic rebuild then. I appreciate your help.
 
The 2-port head has a very dismal inlet tract, and I agree with Richard that there's nothing to be gained by fitting larger valves__certainly nothing you'd feel in the seat of your pants! If you're planning to keep the car/car's engine in original appearance, then you're just going to have to suck it up and take what you can get.

When I built the Longbridge engine for the car that Jim, aka healeyblue, restored, I fitted it with a BJ8 camshaft (and also a raft of polymer coatings, but more in the name of efficiency & longevity, than performance gains); you might ask him for his opinion on how it runs today, but I am not sure if they ever got the chance to drive it before the engine was removed and sent to me.

I did manage to get a few pics of the galley head before I put the core-plugs back in, to give you some idea of what the intake charge__air/fuel mixture__has to thread its way around to reach the cylinders. It's not pretty! If you're not concerned for originality, don't miss the last pic...

IMG_1173.jpg


IMG_1180.jpg


And for the kill shot! Looking forward from the rear:

IMG_1182.jpg


Down the galley itself, and you see the row of head-studs that bisect the corridor.

IMG_1188.jpg


Same shot, but from the front of the engine.

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From the induction standpoint of a Healey, this is everything that the 2-port head is not ;)

ct3.jpg
 
Randy if I were to swap in a 6 port head does it have to be from a 100-6 or will a later 3000 work as well?
 
Except for a skight detail difference near the water temperature port, there is little difference, so yes, you can use either one. I'm 99.99% certain the valves/ports are the same size, but look the valves up in a parts catalog, and you can verify for yourself.
 
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