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| Supercharged 1275 https://ausmini.com/forums/viewtopic.php?f=2&t=99856 |
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| Author: | mrberry [ Sun Apr 12, 2020 11:02 am ] |
| Post subject: | Supercharged 1275 |
Hi All, I am building a Supercharged 1275 +60 and have just done the dry build. I have found the piston sits 1.52mm down the bore and has a dish of 11cc. This is giving me a compression ratio of anywhere between 7 and 9 to 1 depending on which calculator I use with most results in the 7's. I am aiming for 8.5:1 . I have tried working it out manually but maths was never a strong point so am struggling to get an accurate result. The pistons I am currently using are NOS Mahle with a compression height of 37.13mm or 1.462in. I don't want to skim the deck any further and am considering changing the pistons. Does anyone have any other options or any suggestions which pistons to go for? I don't want forged due to the cost. Thanks |
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| Author: | simon k [ Sun Apr 12, 2020 12:31 pm ] |
| Post subject: | Re: Supercharged 1275 |
I had both Russell Engineering and Hypatec when my motor had a blower, both made the required squish and bang. GR machined the dish in the RE pistons for me |
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| Author: | FNQ [ Sun Apr 12, 2020 1:13 pm ] |
| Post subject: | Re: Supercharged 1275 |
If you want someone to check your calculations, they will need the chamber cc and possibly gasket being used. |
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| Author: | mrberry [ Sun Apr 12, 2020 1:18 pm ] |
| Post subject: | Re: Supercharged 1275 |
Thanks. I will be using the BK450 gasket and a 26cc chamber. |
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| Author: | ken@miniauto [ Sun Apr 12, 2020 2:57 pm ] |
| Post subject: | Re: Supercharged 1275 |
Your published figures equate to 8.2:1 CR head 26.0cc bk450 3.0cc dish 11.0cc deck 6.0cc (1cc per .010" bore) total 46.0cc 1330 332.5cc per cyl total 378.5cc cr 8.2:1 378.5/46.0 hope this helps For 8.5:1 you could take .020" off head |
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| Author: | MINI66 [ Sun Apr 12, 2020 7:17 pm ] |
| Post subject: | Re: Supercharged 1275 |
I am using stock Mahle pistons in a 1310 (1275LS engine). They have a slight dish. I am running about 14-15psi with no worries. BK450 gasket, stock head (12g940 not shimmed). Not sure what CR but it does the trick. I wouldn't worry too much as long as it in the ballpark. Just need to adjust timing curve to suit. |
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| Author: | mrberry [ Sun Apr 12, 2020 10:28 pm ] |
| Post subject: | Re: Supercharged 1275 |
Thanks for the responses. I am thinking I might settle for the 8.2:1 and if I need to I can skim the head later. |
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| Author: | mrberry [ Sun Apr 26, 2020 7:13 pm ] |
| Post subject: | Re: Supercharged 1275 |
Another issue I have just found when putting on the timing chain. The chain appears too long. I have checked the part numbers on the box which are correct. I can think of 1 of 2 things causing it. 1- Incorrect chain in the box or 2- I have muffed something up big time. I have contacted the supplier, just awaiting a response. Can someone please tell me that it is the chain and not me... |
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| Author: | drmini in aust [ Mon Apr 27, 2020 7:35 am ] |
| Post subject: | Re: Supercharged 1275 |
Count the links, should be 52. |
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| Author: | Mr Anderson [ Mon Apr 27, 2020 9:31 am ] |
| Post subject: | Re: Supercharged 1275 |
I was interested so I counted the dots/pins from the photo and got 54 if that was what was supposed to be counted? |
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| Author: | drmini in aust [ Mon Apr 27, 2020 1:08 pm ] |
| Post subject: | Re: Supercharged 1275 |
Mr Anderson wrote: I was interested so I counted the dots/pins from the photo and got 54 if that was what was supposed to be counted? Yes. So it's 2 links (actually are half links) too long. Can cut it and fit a joining link. |
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| Author: | mrberry [ Mon Apr 27, 2020 6:53 pm ] |
| Post subject: | Re: Supercharged 1275 |
I got a call from the supplier today. They had a batch that had 54 instead of 52 links awhile back. I have now removed the 2 links and fits perfectly. Thanks for the advice |
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| Author: | mrberry [ Fri May 01, 2020 4:49 pm ] |
| Post subject: | Re: Supercharged 1275 |
I have a timing cover with an external oil seal. How well do they work or should I give it a miss? Thanks |
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| Author: | mrberry [ Tue May 05, 2020 5:31 pm ] |
| Post subject: | Re: Supercharged 1275 |
Hi I am sorting out my primary gear now. I need to get a thrust washer so how can I work out which size to get. I don’t really want to go trial and error if it can be avoided. I don’t have a 1275 one to try. I have a new minispares gear and a backing ring and C clip. Are the backing ring and C clip the same for small and large bore? Thanks |
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| Author: | Scoop [ Tue May 05, 2020 10:40 pm ] |
| Post subject: | Re: Supercharged 1275 |
Yes, the thrust washer is not though. |
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