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High comp NA Zetec, how to calculate CR

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Old 06-09-2008, 11:22 PM
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JohnT
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Default High comp NA Zetec, how to calculate CR

Hi all,

Im using a 1.8 zetec head which is not skimmed, 2ltr block with standard pistons and a standard 2ltr motorcraft head gasket and weber alpha 45mm throttle bodies. the engine is built and running in the car! Problem is, its over fueling on a standard 2.0ltr map which im told is going to happen due to higher the C Ratio.

Does any one have the volumes of these to hand or know where i could get them from.

Thanks in advance.

John T
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Old 06-09-2008, 11:25 PM
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pa_sjo
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I think someone has lead you up the garden path.

What you need is it to be properly mapped for YOUR spec. Also, it'll be a pain to map as those throttle bodies are faaaaaaar too large for the spec you mention above. You'll only have to map about the first 25% of throttle opening and that'll be it!
Old 06-09-2008, 11:29 PM
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Chip
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CR has very little effect on the fuelling really.

Someone has been talking horseshit to you IMHO
Old 06-09-2008, 11:41 PM
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JohnT
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Ive got cams and ported head on it also but didn't think that would matter.

I need to get it running in a drivable manner as I live in Jersey Channel islands and need to drive it to the rollers on the mainland. I want to get a chip made up for me and sent over so I was thinking If i new the CR it would help them with creating the basic map.
Old 06-09-2008, 11:42 PM
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Chip
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Ported head, TBs and Cams, all effect the fuelling FAR more than the CR does IMHO

All 4 of those will effect timign though, and in this case the CR is the key factor
Old 06-09-2008, 11:43 PM
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Chip
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PS what management are you on?
Old 06-09-2008, 11:52 PM
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JohnT
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Originally Posted by Chip
PS what management are you on?
Im using weber alpha.

Just thought im using a map created for this set up but with 1.8 bottom end so really all ive done is increase the cc and cr
Old 06-09-2008, 11:54 PM
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Chip
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When you say for that setup, you mean designed for the headwork you have etc?
Old 06-09-2008, 11:55 PM
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Chip
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Anyway, bottom line is, take it to someone to get it mapped, dont bother guessing at more basemaps
Old 07-09-2008, 12:08 AM
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JohnT
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Originally Posted by Chip
When you say for that setup, you mean designed for the headwork you have etc?
thats correct.

oh and it will cost £700 extra sheets to get a trailor onto the boat to get it to the rollers. so a couple of base maps sent over to me seems a better option.
Old 07-09-2008, 07:49 PM
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Aside from the other excellent advice you've been given, as the 1.8 and 2.0 have the same CR when standard, at 10:1, its easy to just back calculate the combustion volume. Although there will be a slight error due to the piston dishing, to all intents and purposes, a 1.8 on a 2.0 gives a CR of 11:1.

As has been said, that won't really effect the fuelling MAP, but check for the spark being a bit too far advanced under load.
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