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Turbo compression newbie
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2009/11/16 1:18
From Sydney, NSW
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Hi all Ive been trying to gather information about preparing my engine for mild boost. From what ive read Nissan have done a good job of building stock strong. People mention lowering compression to prepare for boost via pistons head gasket or both..

Just wondering if someone could suggest a head gasket to use? And explain it like I'm 5 re what lowering the compression does?

Posted on: 2/13 21:04
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Re: Turbo compression newbie
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From Mordialloc
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Really i'f its a STREET car and your under 10 psi for an A12/13/15 dont bother complicating things and just use everything stock.

Just my opinion

dp

Posted on: 2/14 0:41
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Re: Turbo compression newbie
No life (a.k.a. DattoMaster)
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From Coondle, WA Australia
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there is plenty of info in the web on just this subject

http://dsportmag.com/the-tech/boost-v ... -high-compression-ratios/

this for a start might yield some info.

as zigmondo said, if your going to mild boost on the street, keep it stock, particularly if you have a good motor to start with.

If you are rebuilding from scratch, you may want to drop it a little, but even then for the effort, its prob not worth it.

You can cheat and use two head gaskets to drop the compression a little.
maybe get a steel spacer cut.
those would have to be the cheapest ways to drop the compression a little for boost. After that its pistons and machining and expensive options.

If you lower compression (ie increase the combustion chamber size) it basically means you can jam more fuel and air mix into each pot and get more bang.

it helps with a few other things like detonation and heat management, but its all about cramming in more fuel and air.

Posted on: 2/15 4:17
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Re: Turbo compression newbie
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The whole reason for lowering compression for a turbo motor is last decade stuff. The reason for it was to help avoid detonation on pump gas at higher boost levels. You sacrifice off boost torque/hp and lower spool when you lower the compression. In my area, E85 provides the ability to keep higher compression with boost and still avoid detonation. So, I have no reason to lower compression if I go turbo. However, a strong metal or multi layer steel head gasket is ideal no matter the compression, just get the thickness you need to maintain .032 to .060 inch piston to head clearance so you don't mess up the quench and induce more detonation (Err toward the smaller distance, .032" as much as possible).

Posted on: 2/19 0:33
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Re: Turbo compression newbie
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Yes, it's old thinking. The newest cars have up to 14:1 compression with turbo. Ecoboost is 10:1 since 2010

Drag racers like to lower the compression and use the turbo boost for maximum power but as noted above that lessens part-throttle power -- not great for a street car

Interestingly, one of the first turbo cars (1962 GM Cutlass) had 10.25:1 compression and used water/alcohol injection to prevent detonation. Pity it didn't catch on, people forget to check the level of the fluid

Posted on: 2/19 4:26
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