Hi all,
just after some advice on a turbo engine I am building. I have the choice between 4 heads, two giving a CR of around 7.5:1, the other two 8.0:1 and 8.3:1.

This is for a daily driver so the 7.5s are out, but I'm not sure which other head to use. My options are
EDIT: should be asleep, I meant to say

L16 open chambered, 38.5cc giving a cr of 8.3:1
L20b closed chambered, 41cc giving a cr of 8.0:1

I know the open chambered heads are supposed to flow better and resist detonation, but 8.0:1 sounds better from a more boost perspective (hoping for ~11/12 psi max). I want the car to be fun whilst still driveable.

Any advice/info would be appreciated.
Oh, and do we have any megasquirt masters on 1200.com?

personally i will still go for the 8.3 with 11psi it will be drivable anyway even u will have less vibration on idling.

its not a technical opinion but personal - what i will do if i was in the situation

I would also go for the 8.3 head...

Doesn't the L20B (U67 I think) have MONSTER intake ports? I'd run one of those if you have one. It mite be a tad more laggy, but the reduced flow impedance in the intake track will yeild gains when you're on boost.

Yep spot on. The U67 has quite large ports but is the L20b open chambered head and would take the cr down to about 7.6:1. This is what I had intended when I started building the engine ages ago but now I'm worried that it will be slower than my push bike off boost. The V91 L20b head would bring it up to 8 but does not flow as well.

Only one way to find out though. I can always give it a go and if it is too much of a pig just change the heads over. Trick there is that I have to grind out the intake ports to accomodate the injectors and tap extra mounting holes. Not too tricky.

You're building a street engine, but if you're anything like me it wont be long before you're cranking up the boost, and looking for bigger numbers.
If it's too lame off boost, skim .020 or more though off it.

I like your thinking!
If 7.6ish was good enough for the 280zxs then I'll give it a shot. Still a bit worried but it may have the added benefit of stopping me being a traffic light hero and snapping driveline components. Only one way to find out. I'll chuck some photos up of the engine next week.

just run a thinner headgasket. problem solved. Id go for the larger ports for sure! even if it was a pig down low.