1.6mm or 1.9 mm head gasket?

Im about to order a spesso uprated gasket. There are two types and im tempted to go for the 1.6mm as id like to increase compression a little. Reason is im fitting wossner pistons and although the manufacturer claims no loss in compression ive heard they do lower CR a litte.

Not sure how many skims the head has had in the past but only 4 thou was removed this time.

How much can i expect the CR to increase?

thanks
Deme

lower the compression increase the boost

Just about fits the 1.6mm gasket - which also means that just about nobody will have the 1.6 in stock!

1.9mm is the Group N fitment

Compression increase will be less than 0.2

Hi Nyssa

What do you mean by "just about fits"?

cheers

Deme...... I have 1.9mm and my head has never been skimmed so your compression will already be a tiny amount lower than mine..... Your not going need massive boost either to reach 325 ish bhp with your turbo!
Get the 1.9 one and get it built..... Aslong as you get it live mapped then I don't think you need to worry about your compression ratio's ??!!

Nick

Cheers Nick, i'll probably play it safe and go with the 1.9mm but wanted to hear a few opinions.

Typo - must learn to read before I hit submit

should say "nobody fits the 1.6..." my cursor moved without me noticing

8.0:1 CR is low enough! Why would yo want even less compression??

There's more to choosing head gasket thickness than just thick gasket = less compression = more boost

lowering the compression via thicker gaskets, shims, etc. also increases the squish area. Increasing the the squish area too much decreases resistance to detonation, which isn't a good thing.

Not to mention to mention it makes the 16VT's already not-so-great fuel economy even worse! Personally I like to use a gasket that keeps the squish area <1mm thick and keeps the CR as close as possible to 8.0:1

Having said all this, the Spesso 1.9m gasket option has been the tried and tested way for many many years. So we know it definitely works. And would work in this case too. But I just want to make the point that choosing gaskets (and other components, for that matter) isn't just a simple case of stick in something 'uprated' and go!

Nonsense! Last time I filled the car up, I managed 30mpg, which included motorway driving to Wales, getting the missus to adjust the fuelling on the motorway and a hoon around the Evo Triangle and I'm 7.2:1 CR

And I managed 32 mpg with 8:0 CR to Torbay with my Missus, luggage and the full interior! C'mon, you're not going to tell us that lower compression ratios get better fuel economy than higher one's are you?

...Oh yeah and I nearly forgot; with a cylinder heads that's been fettled to within an inch of it's life and a custom-designed, tubular exhaust manifold, of course it's going to get improved mileag. It's not even comparable to most other 16VTs around. Not even my own engine is as worked as yours. The only way you could comment on the effect of CR on fuel economy is if ran exactly the same engine spec with 7.2 CR and then again with 8.0

LOL at "and the full interior!"

B's scaffolding must weigh a fair bit though!

Anyhoo, I pussied out and ordered a 1.9mm.

Well i'm hoping to get 50 mpg on my journey home from Bristol when I collect my car..... Nice & sedate cruise back, none of this 'pedal to the metal' malarchy!!

Nick

No, but to say low compression gives worse fuel economy is a bit mis-leading

Deme, scaffolding is 30kg's


Yes, when...?

Funny funny funny!! Flea is actually fiddling with my waste gate as we speak..... Won't be long now!!
Deme you could be the proud owner of the 'fastest rebuild of a 16vt'.... You only 3-4 years to beat!! Lol!

Nick

i had a 2x lancia beta volumex's with a comp ratio of 7.5:1 opened up the combustion chambers and got it down to 7.0:1 and it never made a difference to fuel economy even when i did pack the boost valve with washers and when from 7psi to 12psi off boost .... lowering the comp ratio will bring on off boost stugish pedal feel but you can increase boost without the risk of detonation and a melted engine

I'll take that accolade! as long as "fastest engine failure after rebuild" doesnt follow it!! Gulp..

Standard build 16v engines have the pistons way down the bore,at least any I've ever stripped have been. I suspect it's Fiat/Lancia playing safe and not caring aboiut a few % of extra performance. The real way to do it is to have the piston 1mm (ish) from the cylinder head suface and then the squish will actually be doing the job it's capable of,a worthy job it is too. This means rods made to an accurate length, blocks vary if deck height, at least enough to require measurement before ordering rods. 1.6 or 1.9 gasket is a moot point when the pistons are nowhere near the deck anyway.

How far down are the pistons usually?

I've seen nearly 2 mm, mostly less than that though. It's the deck height that varies. Big reason why I like custom rods, easy to dial the squish in then.

Yes all very true!

In this particular case Deme's going to use Wossner pistons. Presumably Wossner must have thought about the squish issue because their pistons actually stick out above the deck with standard-length conrods; In my engine 0.65mm. Which is nice because it means you can choose a head gasket thickness to give you the right squish.

Yes indeed. I prefer to use standard length rods and tweak squish height with custom piston design. There's more than one way to skin a cat, as they say.

Usually the accepted method is to design the piston first with regard to ring pack and compression height, then once deck height and half stroke is established a rod can be ordered to join the two together. To compromise the piston design for the sake of a connecting rod isn't something I'd do, not while Cunninghams will make to a thou anyway.
A longer rod than standard has some small gains,such things as side loading of the piston and max and average speeds take a step towards improvement. Maybe it's just me who seeks the small %.
Interesting that wossner have the pistons out of the bore, I'd worry that a block would be used that had the piston too close to the head and some less than careful builder would not notice until it was too late, someone might fit a nice thin MLS gasket. Makes for a scary skim of the block methinks. Blocks do vary in height.

Easy there tiger!