8 replies to this topic

[gerryk]

Hi,
Being collecting parts for a 1380 rebuild over the past year.I'm just wondering what the correct C.R should be for this spec:
MG Metro Block offset bored 73.5,
Omega Pistons 11cc dish 73.5mm dia,
Metro Turbo conrods,
swifttune SW5 Cam,
Lightend flywheel,
MED Phase 3 Head 35.7 inlet 29.6 exhaust.I have no idea what the cc in the chambers.
1.5 rolling rockers
Running unleaded 95 ron
Any idea as to what the CR should be for this setup?


Thanks

[Southy]

Are you asking what CR should be used for this setup or are you asking for a guess as to what CR it is going to be?


If your planning on running 95 you wont want a too high compression ratio. If you used 97 then you could run a higher one.

[gerryk]

Hi Southy, I'm looking for the correct CR that should be used for this set up and I suppose a guess as to what the cr is going to be before I start fitting the crank and pistons.

[Tomf]

You will need to know the size of the chamers in the head to work out the CR...

[gerryk]

I'll measure the cc in the chambers at the weekend.Anyone know if there any benefits of having 11cc dished pistons over 7cc?

[gerryk]

OK fitted the crank and pistons today.Also with head levelled,filled up the chamber with parafin oil.The chambers hold 20ml of liquid.
Pistons:
Using omega 73.5mm dia with 11cc dish.

Deck Height:
At TDC the deck height to the top of block surface is 0.036"

Head Gasket:
Im will be using Payen BK450 gasket.Its 1mm thick but dont know what the compressed thickness is.

Cyclinder Head:
Chambers hold 20ml of liquid each.Would this be classes as 20cc chambers?

Stroke lenght:
Using a standard MG 1275cc crank.Again I'm Not sure what the stroke lenght is.

Are there any example's of CR calutaions on this fourm?
Thanks a lot

Gerry.

Edited by gerryk, 19 October 2008 - 08:58 PM.

[Bungle]

i think theres a bit in visards yellow bible if no one can help

[ian2000t]

Hi mate,


Just been through all this myself. Was given a spreadsheet which should help you with this.

Std 1275 crank is 81.28mm,
I'm pretty sure BK450 is 2.8cc compressed volume,

Have a play with the spreadsheet. I put your figures through quickly and I think it was 9.96:1 but just double check everything in there.



PS. Can't actually upload spreadsheet, says I'm not allowed to........

Edited by ian2000t, 20 October 2008 - 01:05 PM.

[gerryk]

Thanks Ian2000t.

It would be handy to have access to the spreadsheet your using.
9.96:1 sound's reasonable for the set up.

Thanks again,

gerry.

Edited by gerryk, 20 October 2008 - 05:35 PM.