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Calculate compression ratio 250 crossflow 

 

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 Post subject: Calculate compression ratio 250 crossflow
Posted: Thu Oct 02, 2014 5:24 pm 
Stock as a Rock
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Hi,
Can some clever person work me out an estimated compression ratio for a 250 crossflow I have built to go in a Cortina.

250 crossflow

.40 thou pistons with 20.5cc dish

C2 alloy Head ( I read that these have a 42 cc combustion chamber maybe someone knows if this is correct)

deck on block has only been slightly shaved to clean up, nothing at all really

 

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 Post subject: Re: Calculate compression ratio 250 crossflow
Posted: Thu Oct 02, 2014 5:51 pm 
Oompa Loompa
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Do you know the head gasket thickness and piston to deck height? There are comp ratio calculators online just google it.
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 Post subject: Re: Calculate compression ratio 250 crossflow
Posted: Thu Oct 02, 2014 7:07 pm 
Stock as a Rock
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1.4 mm head gasket thickness measured new still in packet. .7 mm piston to deck measured with steel rule across top of cylinder with feeler gauges underneath (piston at top dead obviously) bore 99mm from deck to piston top at bdc 94.4 mm bore diameter all measured with with verniers best tool I have sorry.

 

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 Post subject: Re: Calculate compression ratio 250 crossflow
Posted: Thu Oct 02, 2014 7:26 pm 
Oompa Loompa
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Just put all that into the calculator and you will be sweet.
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 Post subject: Re: Calculate compression ratio 250 crossflow
Posted: Thu Oct 02, 2014 7:39 pm 
Oompa Loompa
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I get bang on 10:1
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 Post subject: Re: Calculate compression ratio 250 crossflow
Posted: Fri Oct 03, 2014 6:29 am 
Stock as a Rock
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That sounds good. the only real unknown at the moment is the C2 head I don't know for sure what the combustion chamber cc are. chambers are stock C2 . I would like to find out for sure what they are meant to be. I have had no luck on the net so far. Does anyone know for sure.

 

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 Post subject: Re: Calculate compression ratio 250 crossflow
Posted: Fri Oct 03, 2014 6:53 pm 
Oompa Loompa
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You can get rough idea by using a seringe to fill the chamber up with water. Just put a smear of grease around the valves to seal them.
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 Post subject: Re: Calculate compression ratio 250 crossflow
Posted: Fri Oct 03, 2014 9:53 pm 
Technical Contributor
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And get some clear plastic and cut some holes in it to put across the combustion chamber, put a bit of grease around the chamber to hold/seal it down.
With a graduated syringe, you can get a reasonably accurate volume. Not sure whether the spark plug electrode area cavity counts as part of the volume.

Either way though too, shows if the chambers are similar capacity as well.

 

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 Post subject: Re: Calculate compression ratio 250 crossflow
Posted: Sat Oct 04, 2014 11:54 pm 
Getting Side Ways
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I built an Xflow years ago, it had flat top pistons, an H7 (?) XF head, and was .040" over, and I CC'd it, and did the calculation, and, it was bang on 10:1 CR.

 

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 Post subject: Re: Calculate compression ratio 250 crossflow
Posted: Sun Oct 05, 2014 3:44 pm 
Stock as a Rock
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Hey thanks, I never thought of the syringe. Just so happens I have a large new one in packet somewhere. I will have a go and see what I get.

 

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