So running flat tops on a L20B i'd want to run the U67 head then is basically the consensus?

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the reason for this is they are all fuel injected big difference between efi and carby. If running carbs the most comp you would want would be 11:1 but just to throw something else into the ring skys the limit if you were to use E85 instead of premiun unleaded.

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Jason
1600 Historic Touring Car

Alot of those engines would have a very much more advanced head design than the old L series as well! 2 valves on one side of the head is pretty old school (I'm guessing the basic L series design probably dates from the early 60s at best!)

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Think I mentioned the combustion chamber shape.
Other than the bikes, they were/are all carburetored.

The point I was making is that there is no "fixed" maximum CR.
There are general rules of thumb & others experience, but nothing more.

Personally, for street use, using appropriately suitable camshaft I wouldn't run a L series motor over about 10.5:1 CR. Even that would be pushing the boundaries, given the poor quality fuel we get ripped off for here in Australia.

For a racing car, with a much different profile camshaft (lobe seperation/overlap), and likely more effort put in to sourcing better/fresher fuel when required (not just wheel into any servo that you happen to be nearby), I would be happy to push it up to 11:1-11.5:1CR. But at that, you would want to make sure you had your tune up spot on.

if you have both heads give them both a go then you will know for yourself.

a mate of mine that works on a drag team tested 98 fuel from a few survos and the best one was caltex that actually had a slightly higher octane than 98 but that was a few years ago.

5 years on and I'm finally actually looking at doing this. Engine is out. Better later than never!

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E85 and 12:1 now

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http://www.healingchambers.com.au

ka24de head would save you heaps of $$ and already make 150hp ate maybe a tad more with bike carbs and more with tuned header
lifting the comp and notching your block for valve clearance as the head sits on an 89mm block and your L20b will be 87.5mm for safety?
Otherwise an L18W block could probably be safe at 88mm as well and maybe lighter due to shorter deck height or not due to siamese bores.
https://www.youtube.com/watch?v=QanZ8mOiuqg

I'll stick with my A87 head and just a standard rebuild of the bottom end i think.
I got a price for getting a little headwork done and a cam from Les Collins, which seems quite reasonable (any other suggestions?) so i'll probably go with that, my SU's and that'll keep get it all going along a little nicer than before without breaking the bank (or using up mountains of time i don't have)

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You may as well throw on some flat top Pistons while it's apart. I run flat tops in my l18 with an a87 head and it runs well on 98 octane fuel

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Chris Thomas

1971 1600, mild L18, 5 speed

All I want is less to do, more time to do it and higher pay for not getting it done.

What's your compression ratio in the end? I calculated my l20b with flat tops and a87 and i think it was somewhere in the 11s which i felt was too much.

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