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My turbo questions post 

 

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 Post subject: My turbo questions post
Posted: Mon Mar 13, 2006 8:33 pm 
Oompa Loompa
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Ok i have started pulling apart my ebII i6 engine and am planning to turbo it.
I figured i would ask all my questions in the one thread to make it easier for me to track.

hopefully the outcome will be a bulletproof engine pushing out 350-400rwkw running 25+psi, so i want to build it properly the first time.


1st question... i want to get the comp down to about 7.5:1.
before you all tell me to get a thicker head gasket thats not what i want to do.
i want to know how to change the comp without using a thicker gasket.
would using a 3.9 crank change it? different pistons? rod lenght?

 

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Posted: Mon Mar 13, 2006 8:34 pm 
Smokin em up
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Dish top pistons will lower the compression ratio and getting a Head reconditioner to grind out the chambers equaly will work to

 

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Posted: Mon Mar 13, 2006 8:51 pm 
Oompa Loompa
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yeah that was my next question.
what pistons come with a larger dish?
how much dish is needed?

my old man works for yella terra so all the machining and headwork will be done by him.

 

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94 ED GLi - RIP
92 180sx - Sold
93 EBII GLi - Now wreaking. email me at plappen@bigpond.net.au for parts
97 EL Fairmont Ghia - New daily
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Posted: Tue Mar 14, 2006 7:10 pm 
Smokin em up
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IMO 7.5:1 is too low for street use, and 25psi is too much for prolonged street use.

ACL sell a forged piston which is designed for forced induction. I believe it lowers the compression about a 1/4 of a point. Combine with a EA head, remove the swirl ridge in the chambers and that should lower it at least another 1/2 a point. This should get you to ~8:1. You could try an open up the chamber more but I would already question the burn quality of the chamber.

I personally would slap in the forgies, run a EF head. Clean up the ports and chambers SLIGHTLY and leave it at that. This combo would be more responsive both off and coming onto boost due to the extra torque.

Is this honestly a 25psi street engine??
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Posted: Tue Mar 14, 2006 7:20 pm 
Smokin em up
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my mates wrx is running 25psi it goes hard but the gearbox didnt like his launching. So $6000 later spending it on an import gearbox made by some freak asain overseas and it goes again. The car is dodgy though interior was done bodgy. Anywho onto the subject 8:1 is a good compression to run 14psi

 

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Posted: Tue Mar 14, 2006 11:08 pm 
Getting Side Ways
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7.5:1 isnt realy needed to make 400rwkw and 25 psi isnt needed ether. just buy some aftermarket ba xr6 cp pistons and gett the head chambers machined. 8.0: - 8.5:1 should be fine.

 

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Posted: Wed Mar 15, 2006 4:05 am 
Oompa Loompa
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ok mixed responses then..

i have heard of guys running 7.5 comp.

the engine wont be for street.. i just want to see how much power i can get out of one.

bert: first you say a ea head is the way... then ur saying slap a ef head on it.... which one?
i have seen the acl website and the pistons there for the eb have only 5cc dish... but the ea ones have 11cc.

evil au: 25psi on a wrx is hardly the same when we are talking about a 2ltr turbo.. compared to a 4ltr with a to4 bolted onto the side..
its a known fact that wrx boxes are weak... 2nd gear always seems to go.

fritzz: are the ba pistons a direct replacement?

so whats everyones opinion on comp ratio and boost to make the power i want?


i need all the research i can get before i start building it

 

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94 ED GLi - RIP
92 180sx - Sold
93 EBII GLi - Now wreaking. email me at plappen@bigpond.net.au for parts
97 EL Fairmont Ghia - New daily
01 Suzuki GSX-R750 - Weekend toy

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Posted: Wed Mar 15, 2006 4:30 pm 
Getting Side Ways
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the ba pistons do fit but require a ba rod!! i think they have a longer rod and shorter skirt on the piston.

http://www.fordmods.com/forums/viewtopic.php?t=5764

look at this el xr6 with 407rwkw he is using ba rods and pistons.

 

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Posted: Wed Mar 15, 2006 5:44 pm 
Oompa Loompa
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ok read the 14 pages... lots of questions were answered but still doesnt say anything about what comp he is running and how he lowered it

 

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94 ED GLi - RIP
92 180sx - Sold
93 EBII GLi - Now wreaking. email me at plappen@bigpond.net.au for parts
97 EL Fairmont Ghia - New daily
01 Suzuki GSX-R750 - Weekend toy

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Posted: Wed Mar 15, 2006 9:26 pm 
Getting Side Ways
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Power: 608 rwkw

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if it isnt a streeter 7.5:1 will be ok. for starters the ba pistons will lower it a bit then just get the chambers machined. u may need to machine the top of pistons to.

 

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Posted: Thu Mar 16, 2006 12:55 am 
Getting Side Ways
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fritzz wrote:
the ba pistons do fit but require a ba rod!! i think they have a longer rod and shorter skirt on the piston.

correct, the ba uses the same rod length as the au, which is bout 5mm longer than the e-series

 

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Posted: Thu Mar 16, 2006 12:57 am 
Oompa Loompa
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longer rods would actually increase compression correct?

is there a rod/piston combo that would help drop it?

standard rods shot peened with ba pistons?

 

_________________

94 ED GLi - RIP
92 180sx - Sold
93 EBII GLi - Now wreaking. email me at plappen@bigpond.net.au for parts
97 EL Fairmont Ghia - New daily
01 Suzuki GSX-R750 - Weekend toy

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Posted: Thu Mar 16, 2006 1:37 am 
Getting Side Ways
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longer rods fitted to ba pistons wont affect compression, you need them.

i wouldnt try adjusting compression by moving the piston height! especially not 5mm.

 

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Posted: Thu Mar 16, 2006 8:23 pm 
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BA pistons in an E or A series motor is a big no-no, the valve reliefs cut into the pistons are in different places. Really not a good idea, unless your going to machine the pistons (which will weaken them anyway) or shorten the rod length (not good for combustion). Either:

Fit EA Race series pistons, oring the block, and fit a copper gasket from ACL, there a thick gasket (comes in 1mm and 1.6mm) and will drop compression further.

or

Get custom forgies made up with your selected compression ratio - just fit a multilayer steel gasket (AU) if you do this, as its an easier setup to maintain. If your getting custom forgies, mirroring the combustion chamber shape will help with swirl, may as well since they have to make them custom anyway.
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Posted: Thu Mar 16, 2006 9:37 pm 
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The EF head is a better head compared to the EA head. The EA head has a giant cast in swirl ridge in the combustion chamber, remove this and the compression will drop. BUT you have now altered the flow quality characteristics, how this affects power under boost, who knows?

Dropping the compression will make the engine doughy off boost and violent coming onto boost due to the lack off NA torque. The motor would only be good IMO for drag racing or dyno queen.

You should never use thicker gaskets because for one it increases crevice volume due to 99% of the time the gasket outline not matching the bore and/or head. This is bad and I can't explain it all.

Lots of boost does not mean lots of power. An engine is just an air pump, think about it.
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