16v or 8v heads to 89mm bore - Alfa Romeo Forum
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Warning 16v or 8v heads to 89mm bore

Hi dear friends,

I have a freshly bored 1.7 boxer block, 89mm wich I want to link to a 1.5 crackshaft. I have forged aluminium dished (8v) venolia 343 pistons. This will create a very nice oversquare engine with a bore/stroke ratio (>1.30) that puts it in the region of lambo countach en hayabusha engines.
I have 1.5 105HP mech. lifter heads and fast road C&Bs and can choose from 36's and 40's cams. The aim is obviously being able to reach viciously high rpms occasionally. I like treating people with the unexpected

I am currently wondering wether to go with these 8v heads or take a pair from a freshly revised 16v block(will need fast cams and mech.tappet conversion$$). I think with the shorter stroke the dished pistons wil not be a problem for the 16v heads but I haven't measured(dont want to take the 16v apart if not needed).

Megasquirt is possible for both options if I would choose to go with injection instead of carbs.
The question remains; go with the 8v heads or with the 16v heads for this application.
Any thoughts?


Currently driving a type 1 33, 1.3
Past alfa's 1998 3.0 GTV, several 33's

Last edited by ItsBrown; 23-06-10 at 19:31.
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Consider that going 16v will require double the cams which are already expensive for 8v plus they are not mechanical. Going 8v might be cheaper , simpler and easier for you.
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Hi !

And also consider the difference between the combustion chamber volume of the 8 and 16V heads,
which affects the compression ratio (this is now slightly raised by the increased the bore
from 87 to 89mm: more air into the same chamber)
According the workshop manual the combustion chamber volume in the 16V cyl. head is 47,5cc,
while the 8V head has 49,5cc. But the 8V and 16V pistons are different also...

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8V is definately simplest
8V is probably cheapest

If you want revs though 16V is the way to go.

Your engine capacity will be about 1672cc

Unless your pistions are flat top I dont think they would be any use for the 16V.

You could initially try the engine with std 16V cams to reduce cost

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Hi all, thanx for the replies,

A tad more info.
The initial idea was indeed to go the 8v road(hence I have the heads, cams etc..), but I started pondering reading about the lighter 16v valves. So going 16v from now will definitely be more expensive

The 105HP 8v heads are flatheads, so minimal cc's (just 1mm above intake valve + the spark plug gap) I reckon between 5 and 15cc. So 16v heads will definitely set compression back in comparison to 8v heads when using the same dished pistons.

The 89mm venolia 343 pistons are dished, not flat. I measured the cc's of the dish, its about 21.5 cc. I guess the 65mm stroke and the dish dept (5mm)leaves enough space between 16v valves and this piston.

So still some more pondering and calculations to do here ;-)

Any tips on the oil pump? Will the standard pump be strong enough or is an external electrical pump the better choice?
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The standard pump would be fine, but I would recommend baffling the sump to stop high cornering forces starving a bank of cylinders and crank.
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16v , 89mm , bore , heads

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