Acceptable Compression Ratio

[dliff]

Hey,

I'm about to pick a head gasket which will determine the compression ratio for my 2.0T. The pistons/rods are forged and it was overbored 0.5mm, but the turbo and everything is stock, besides a Stage I APR tune.

Cometic offers sizes that will give me either ~9.5:1 or ~11:1 ratio, vs the stock 10.5:1 ratio. I really don't want to run over 10.5, but I haven't been able to determine how it will run at 9.5 with stock boost.

The gasket below *should* give me about 10.5:1, or close to the stock ratio, but the brand is unknown.
https://store.034motorsport.com/comp...yer-steel.html

Asking 034 about the manufacturer, I receive

It's for sure an OEM supplier, (ie. Victor Reinz, Genuine Audi/VW, et al.).
Not sure exactly, but it's quality.
Nothing Chinese Ebay or anything weird like that.

If anyone has experience running different C/R's with stock boost, I would appreciate the insight.

Thanks,
Daniel

[aluthman]

I would go with 9.5:1 personally, but 11:1 would likely be fine if you stayed otherwise stock. If you have a tune or plan on upgrading at all in the future, go 9.5:1.

[Flexcj5]

The head gasket from 034 is a multilayer victor reinz. It's been modified with an extra layer and then reassembled. I have it in my motor.

[dliff]

I would go with 9.5:1 personally, but 11:1 would likely be fine if you stayed otherwise stock. If you have a tune or plan on upgrading at all in the future, go 9.5:1.

I actually forgot to include the amount taken off when decking... looks like the 0.086 would bring me to about 10.1:1

In theory, what would a half point of lower compression feel like? As in, what would be the noticeable effects when driving? I understand the advantages of lowering CR if I later want to increase boost, but I'm curious how it will run stock when I get it back from the shop.

Thanks.

[vce1232000]

I would go with 9.5:1 personally, but 11:1 would likely be fine if you stayed otherwise stock. If you have a tune or plan on upgrading at all in the future, go 9.5:1.

x2 ^^^^ lower compression ratio are optimum for more boost. So if you have plans on going BT in the near future. Go with the 9.5:1

[vce1232000]

I actually forgot to include the amount taken off when decking... looks like the 0.086 would bring me to about 10.1:1

In theory, what would a half point of lower compression feel like? As in, what would be the noticeable effects when driving? I understand the advantages of lowering CR if I later want to increase boost, but I'm curious how it will run stock when I get it back from the shop.

Thanks.

ilty will be negligible imo.a good stage 1 ots tune would make up the

[dliff]

Thanks guys! Looking forward to getting it back on the road!

[Van Black]

Higher CR would lead to a risk of knocking hence you need to use higher octane nr. gas.
Higher CR leads to better efficiency meaning more MPG while lower CR helps performance, more HP.
Of course, it all needs to be well thought, going 11/1 doesnt mean you'll double you range and 9/1 won't
get you 100 extra ponies. It only sets the stage for a good tune

[aluthman]

Higher CR would lead to a risk of knocking hence you need to use higher octane nr. gas.
Higher CR leads to better efficiency meaning more MPG while lower CR helps performance, more HP.
Of course, it all needs to be well thought, going 11/1 doesnt mean you'll double you range and 9/1 won't
get you 100 extra ponies. It only sets the stage for a good tune

Lower compression will give you lower power with all else being equal.

[Van Black]

Lower compression will give you lower power with all else being equal.

You're right, I forgot to mention that. I meant lower CR and bigger boost

[aluthman]

Yes, but he was staying stock.

[Ali SC3]

If you are not turning up the boost a bunch then there is no reason to lower your compression ratio generally speaking, but since you had the head decked some you can go with the next size thicker and it will sort of even itself out (you wont get full 9.5:1 with the 9.5:1 gasket). If you are not raising the boost alot then more compression is better cause you will make more power at the same boost level... but 11:1 sounds high and with the head decked it will be a little higher even, which would be good for e85 but pump gas not so sure.