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Increasing compression in a N/A motor

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Increasing compression in a N/A motor

Post by mrbeige on Tue Oct 20, 2009 7:03 am

Just been thinking about something Tom said to me the other day about one guy fitting a mk4 head gasket to a VR. He said that it increased compression ratio by 0.5, and that led to an improvement in torque. I been thinking about why that was, and determined that all it does is improve thermal efficiency, and thus make more from the existing fuel air mixture. I did wonder what would happen if you were to increase the compression ratio a further 0.5. Do you think that would improve things still, or do you think that would just result in some blow by on the top ring due to the increased pressure? Perhaps different rings to provide a higher sealing pressure would help? Or would you end up increasing the friction losses, and thus result in lower power?

[/rambling]

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Re: Increasing compression in a N/A motor

Post by dirtytorque on Tue Oct 20, 2009 9:46 am

for a given amount of fuel/advance you will create more cylinder pressure due to the gasses expanding into a smaller space surely ?

More pressure means more shove on the top of the piston..
So I have over simplified then ?
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Re: Increasing compression in a N/A motor

Post by kevhaywire on Wed Oct 21, 2009 1:53 am

Yep, that's it /\

That's why Diesels have so much torque.... lots of compression Very Happy

You can only go so far with the VR6 though as it has no combustion chamber in the head. And if you use flat top pistons, you'll have nothing to control the squish area which'll bugger up the flamefront.

It's the old saying.... "One mod necessitates another...."

That's why the 24V VR6 does went over to combustion chambers in the head instead and 12:1 flat top pistons in the case of the R32.

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Re: Increasing compression in a N/A motor

Post by mrbeige on Wed Oct 21, 2009 2:48 am

dirtytorque wrote:for a given amount of fuel/advance you will create more cylinder pressure due to the gasses expanding into a smaller space surely ?

More pressure means more shove on the top of the piston..
So I have over simplified then ?
Nope, that's essentially what I meant. Just wasn't sure if you could go further or not. Fairly unfamiliar with the VR of 6.

Kev, so the R32 has reverted to the design of the VR6 or the same as the 24v?

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Re: Increasing compression in a N/A motor

Post by kevhaywire on Thu Oct 22, 2009 4:45 am

Sorry Stu, I meant the R32 (all 24Vs actually) now have a combustion dish in the head like a 16V, and flat pistons (with valve cut outs).

The 12V has dished pistons and a flat head.

You can get wossner pistons less of a bowl in them to get a 12V up to around 12:1 with that -0.5mm gasket too. But a certain Mr Munyard has proven that's a waste of time and money for what you get in return.

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Re: Increasing compression in a N/A motor

Post by mrbeige on Thu Oct 22, 2009 2:50 pm

I'd imagine you end up with blow by, due to the compression overcoming the top ring sealing pressure

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Re: Increasing compression in a N/A motor

Post by dirtytorque on Thu Oct 22, 2009 3:08 pm

Alot would come down to engine management with this sort of thing too.
You chewing that fat or seriously considering?
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Re: Increasing compression in a N/A motor

Post by mrbeige on Thu Oct 22, 2009 3:31 pm

Well, using a mk4 head gasket would be a first port of call to increase compression, but mostly chewing fat after that...

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Re: Increasing compression in a N/A motor

Post by kevhaywire on Fri Oct 23, 2009 1:33 am

You'll always get blow-by, but not much from a naturally aspirated motor and even less if you use "total-seal" rings. They're a ball ache to install though.

To be honest, the throttle response is only very slightly improved with the thin gasket. It's not worth it mate. If you want high compression, just get an R32 motor and it's management, it's far better and far cheaper than any high compression 12V can be Very Happy

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