No paper gasket between case and barrels + RTV Silicone sealant...?

Yo!

So currently my deck height is a little large (1.91mm) which is giving me a compression ratio of 6.7 with my measured heads cc of 59. This is on a type 1, 1600 with standard 69mm crank.

Do you think I can take off the paper gasket that sits between the barrel and case to give a little higher compression ratio?

I was also given by Stateside some elring Dirko HT grey RTV Silicone gasket maker, and advised to use this on the cam plug and barrel to case mating face. I realise this is silicone, which is known to break off and block oil passages in VW's, so wanna check if it's worth the risk using!? I have some permatex I will be using on all other areas btw.

Thanks!

 

The paper gaskets make no appreciable difference.
Even if you went 1776 with a 1.2mm deck you would only have 7.7:1 - still too low for your w100 cam.
You need to do something drastic.

 

Yeah, just measured now and without the paper gasket my deck height is 1.7mm. Which gives me a total 6.8. 0.1 difference lol!

Head work...?

 

You could machine the step in the heads to decrease the combustion chamber volume but it sounds like you need to shorten the cylinder length to reduce the deck.

I wouldn’t use silicone sealant, Permatex is fine.

 

Even

Or have the case decked. You can see where I'm going with this Joe.
If you were having both the case and the heads machined, get some 90.5 P&Cs and make it a 1776

In the meantime, can you cc your heads with something inside the lip/step... assuming you have a step?
so, if the step is 1mm and you had it machined off you're still at 7.4:1
if you also reduce the deck to 1.3mm you're at 7.7:1
still a bit low for your cam.

 

I like your thinking there, especially now Joe has ‘accidentally’ dropped a cylinder and broken it. A W100 will need much more than 7.7:1 CR to work well.

 

1776 (90.5) with those heads and 1.2mm deck is still only 7.7:1.
1835 (92) is 7.8:1
We need step depth or cc discounting the step.

 

So the step depth on the heads measure 1.3mm. Here's a photo of what I've measured to just clarify I've measured the right bit!

 

I’d machine that step completely off but where are you measuring the combustion chamber volume from – inside or on the step?

 

One alternative would be to call the step your deck height and get 1.9mm turned off the bottom step on the barrels if you can find someone to do it.
That would give you 7.7:1 and you might decide to call that good enough... with a stock cam. oh dear.

 

So I measured the heads CC volume using a flat disk of perspex sat ON TOP of that step.

I think if I'm going to have to pay for more machining, I'd rather get it right and take your advice of upgrading to a 1776. Don't really fancy bodging a 1600 together just for it to be kinda okay haha. Seems like you understand this isn't ideal too.

Out of interest, is it common for deck height to be way off with new P's&C's? I'm not being an idiot somewhere am I. I've got the crank installed all correctly, centred on bearings, case together (No sealant as I'm mocking it up) but just got the 6 M12 case stud nuts on at the mo, with no rubber sealing rings installed on these studs inside the case. None of this would make much difference to the deck height right?

Honestly, can't thank you all enough for the advice

 

That^ would work but I’d lose the step and make deck and CR adjustments with cylinder base shims. To get the CR higher also machine a bit off the squish area to reduce the combustion chamber volume. No head gaskets or spacers, or whatever snotty wants to call them of course.

Why do Type 1 have huge combustion chambers?

 

Thanks for the thoughts!
Which part is the squish area you're referencing? The cylinder head end of the cylinder? The part of the cylinder head the cylinder contacts?

 

The flat bit of the head between the step and the combustion chamber.

 

Something does seem a bit off. These AA big valve machined for 90.5-94 with valves unshrouded were 60.5cc - perfect for tight deck 2020cc engine. No step of course.

That 1.3 step though is good for 7.5cc if I calculated that correctly, so the actual combustion chamber is more like 51.5cc.

 

Yes?

 

Yes.

 

Ah, so should I be going off of calculating compression ratio from 51.5cc, rather than my measured 59cc? Or that would only apply if I had that step machined off...? Apologies if that's a dumb question aha.

 

Thanks for clarifying! Really appreciate it