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what compression ratio to what boost??? 

 

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 Post subject: what compression ratio to what boost???
Posted: Sat Nov 13, 2010 3:35 pm 
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is the there any fomula that you use to work out what compression ratio for what boost you want to run?
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 Post subject: Re: what compression ratio to what boost???
Posted: Sat Nov 13, 2010 11:07 pm 
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Now really as there is way too many variables that come onto play that stop it from being a basic calculation. Lets look at a basic rundown of the variables:
intake temp
turbo efficiency
intercooling
combustion chamber design
cam specs
cylinder head flow
cyl head and block material (alloy or iron, to determine thermal conductivity)
ignition timing and duration
fuel mixture
fuel quality (ron)
There are things like cyl pressure and cyl fill but they are all derived from the above. If you want I can whip up a spreadsheet within the next week or so that you can have a play with to give you a fair idea of what's involved.

Having said all of that there are some basic rules of thumb which are based on conservative and reliable results, but if you are pushing the boundaries then you have to factor in all of the above.
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 Post subject: Re: what compression ratio to what boost???
Posted: Sun Nov 14, 2010 1:17 am 
Getting Side Ways
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What ever std comp is on AUlll can handle 15Lb ..
Over 15 requires stronger valve springs..
To a point there's too many variables ..
8.5 would be as low you would want to go..
With 8.5 IMO 400 RWKW can easy be made...
But the lower compression means softer throttle response at lower rpm..
Especially till turbo spools or load comes on....

 

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 Post subject: Re: what compression ratio to what boost???
Posted: Sun Nov 14, 2010 2:33 pm 
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Std comp in the I6 is somewhere in the 9.something range, varying a little with each model isn't it? Then you have to factor in that almost every EA to AU would have had a few thou taken off the head during it's life, bumping up the comp, how much depends on how much has been shaved off the head to make it flat again.

Sure, 9.something to 1 comp might limit your total boost a little, but it will make the car nicer to drive "off boost". Something else to consider is fuel quality as xcabbi has stated. What fuel do you plan to run? What's the worst fuel you can run if you really need to? IE, can't get premium and your desperate for fuel, can you get away with regular or E10 & p***y foot the car around until you get some good premium fuel?

Cheers

ToranaGuy

 

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 Post subject: Re: what compression ratio to what boost???
Posted: Sun Nov 14, 2010 4:31 pm 
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AU comp is 9.6:1, EF/EL 9.3:1, ED (and earlier I believe) 8.8:1.

 

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 Post subject: Re: what compression ratio to what boost???
Posted: Sun Nov 14, 2010 8:53 pm 
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thanks for the reply's guy's and to answer what type of fuel i will be running , the only petrol the servo at home sells is premium, so if i back the compression down to 8.8 it will be safe to run say 15 pound ?
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 Post subject: Re: what compression ratio to what boost???
Posted: Sun Nov 14, 2010 9:17 pm 
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xpnutter wrote:
thanks for the reply's guy's and to answer what type of fuel i will be running , the only petrol the servo at home sells is premium, so if i back the compression down to 8.8 it will be safe to run say 15 pound ?


With correct ignition timing & enough fuel being squirted in it should be safe from pinging, but how long the pistons & rods will hold up, is anyone's guess.

Cheers

ToranaGuy

 

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 Post subject: Re: what compression ratio to what boost???
Posted: Mon Nov 15, 2010 11:06 pm 
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Don't be too afraid of E10 on forced induction...
If it hasn't been tuned I wouldn't get on it tho ...

 

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331 Dart block,3.25/ 4340 steel crank, Oliver rods,TFS ported track heat heads, TFS track heat inlet Twin SC61 turbo's
Project 1UZ-EF has started.. S475 Turbo 4.0 V8 Mustang Celica.....

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 Post subject: Re: what compression ratio to what boost???
Posted: Mon Nov 15, 2010 11:08 pm 
Getting Side Ways
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http://www.blowerdriveservice.com/techcharts.php

Calculator..
http://www.rbracing-rsr.com/compression.htm

 

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As in ZOOM 126 edition
331 Dart block,3.25/ 4340 steel crank, Oliver rods,TFS ported track heat heads, TFS track heat inlet Twin SC61 turbo's
Project 1UZ-EF has started.. S475 Turbo 4.0 V8 Mustang Celica.....

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