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Asphalt

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Germini, black forrest

15th Apr, 2010 at 01:35:38pm

Hi!

Is there some sort of rule of thumb for dynamic CR vs. octane rating?

Like; what dynamic CR should be aimed at to be able to still run on pump gas (resp. 98 octane (RON))? I know it's more to it than just a calculated dynamic CR - but since I have no clue - maybe there's a rule of thump? For a n/a motor, btw. :)

Cheers,
Jan

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GaryOS

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Formally spanner181187

Dublin, Ireland

15th Apr, 2010 at 01:53:56pm

Can you calculate dynamic CR? Isn't it completely dependant on cam, head, valve sizes etc?

On 12th Nov, 2009 Paul S said:
I think Gary OS has taken over my role as the forum smart arse *happy*


On 30th Apr, 2010 Rod S said:
Gary's description is best

Asphalt

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Germini, black forrest

15th Apr, 2010 at 05:38:48pm

I think the term 'effectice CR' would be more appropriate (it's still a 'static' calculation). It depends on cam inlet timing & static CR.

What I can't find is the relation between ECR (effective CR) & octane. resp. the maximum ECR I could run with 98 RON.

But: I think there's more that needs to go into the equation, like VE (volumic efficiency) resp. total cylinder pressure. To determine what ECR would be safe for 98 RON. Am I right...? (I hope not *happy*)

Hope that makes sense... My english isn't that good *oh well*

Maybe it's just not possible to relate ECR to octane requirements and I'm talking bollocks!? *happy* That's of course a possibility too *happy*

Cheers,
Jan

Edited by Asphalt on 15th Apr, 2010.

[X] nail here for new monitor

Sprocket

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Preston On The Brook

15th Apr, 2010 at 05:55:07pm

http://www.rbracing-rsr.com/comprAdvHD.htm

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 Is it A-Series only? I think it should be...
So when some joey comes on here about how his 16v turbo vauxhall is great compared to ours, he can be given the 'bird'...


On 26th Oct, 2004 Tom Fenton said:
Yep I agree with TD........

Asphalt

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Germini, black forrest

16th Apr, 2010 at 11:48:52am

Ok, but still nowt about octane... :(

Ok, let's try it the other way 'round:
If I have a ECR of about 9:1 - will it still run fine on 98 RON?

Cheers,
Jan

[X] nail here for new monitor

PaulH

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16th Apr, 2010 at 12:31:03pm

In most caces if your cam is 286 or more you will get away with 11:1 on pump gas anything over that and you will need to be adding somthing like CVL or the likes to boost octane,

For example My race engines run a 300 druation cam with a static compression ratio of 12.5:1 with 98 RON and 800ml of CVL to 25L Petrol (giving you 100RON fuel) this works fine but is hard on head gaskets.
The yellow bible has a very indept look at working out Dynamic Compression ratios

On 17th Feb, 2009 Rob H said:
I find the easiest way is to super glue the bolt to the end of one of my fingers.

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