Compression ratio....amazing what you learn

I'm not surprised, by your figures I knew you must be introducing errors somewhere.

 

It's magic ...

It doesn't know about small differences in combustion chamber volumes or deck height, but it can keep an eye on triggering of the ignition as the crank goes round. If a cylinder has slightly more compression/power, the next "ignition request" will come slightly sooner as that cylinder shoves the crank around a bit faster. Likewise for cylinders down on power: the gap will be longer. By manipulating the timing advance slightly on a per-cylinder basis, it can try and even things out. You wouldn't think something electronic could compensate for mechanical differences, but it can.

 

Any thoughts on what I should do then? I'm guessing my options are limited to either different Pistons or different heads?

Or just accept a low ratio?

 

Has @MorkC68 CC'd his 1800 heads? You can bet he has, I wonder what CC's he found.
You could have the heads flycut to reduce the CR if you know what CC's you want them.
I'm guessing you've found that there are engine calculators on the internet. I use this one. An interesting though somewhat abandoned site while you're there.
http://johnmaherracing.com/calculators/engine-calculator/

 

I was hoping @MorkC68 would be along soon because if he hasn't already, I bet he will soon.

I used the calculator on CB Perfomance site, which looks exactly the same. But I also did the calls by hand and calculator too.

 

Wouldn't I need to reduce the chamber size to get a better ratio? Or do you mean cut the lip the barrel sits on effectively moving the valves nearer?

 

Exactly that, If you imagine your round disc being lower = less volume. Material can also be taken from the flat area to retain the lip as it will still reduce the volume as the kidney shaped combustion chamber gets smaller. If I did it, it would be trial and error, but for someone who has done perhaps thousands, they would know how to approach it.

 

Make sure you have 1mm of deck height and just stick it together and run it ...it will run great ..otherwise you will have to change to flat top pistons or domed pistons ....you have low comp pistons

 

My heads are AMC ones too from my 2ltr CU. they've got the 39mm and 33mm valves. They're all measuring 56cc's and I've just checked the original VW ones the AP had and they're measuring 57cc

 

It'll be the same then assuming you had low compression pistons when you dismantled?

 

I suppose there is the fact that I'm working with a 40 yr old engine that will have about 70bhp at the most....so is this all really worth it?

I could just throw it all together, but since it stands me at about a grand, I wanted to try and make it the best I could, making sure I didn't wreck the thing

 

The old b&p's were dished too, so I suppose so yeah. I've no idea what it ran like before though

 

I'm trying to figure out the ideal shim thicknesses. What stroke have you got and are your pistons dished like mine?

I'm almost decided I'm going to do what @lhu1281 suggested and make sure I have valve clearance and just go with it. I need to get this bus running again so we can get away at weekends asap

 

That's the difference then. Flat top pistons and 3 mm bigger bore ups your compression compared to mine. I have to put shims under mine as the pistons go too close to the top of the barrels without. 2 actually go past the end slightly!