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Guest gliding_serpent

1973 BMW 2002 tii compression ratio in Canada? Answer: 9.5:1

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Guest gliding_serpent

Bought in Canada new in 73. Was searching on the topic for my rebuild (I am learning) and came up with surprising variability... but thanks to the help below I have updated things.

1. Head: E12 (after Sept 72).

2. Pistons: 89mm, raised grand piano

3. Compression ratio: 9.5:1 (Euro and Canada) and 9.0:1 (US)

I do not know how much boring the block will require at this point but I am looking to keep stock compression ratio. I understand factory pistons are pretty much non-existent, so I was looking into forged options (IE), or from older BMW models including flat tops from 3.0, 528, 630i, 530i (with US 8.3:1) that are slightly taller than the grand pianos to give similar compression ratio at the end of the day. My understanding is BMW factory pistons are available a few sizes above standard spec. Am I wrong?

Does anyone know if Canadian cars used US or Euro spec compression? (Update, according to my original manual the compression ratio is 9.5:1) Any big issues going to 9.5:1 with 91 octane and appropriate timing? (currently dual webbers, but plan to eventually get thee KF injection back on)

Thanks for any help.

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Per my factory shop manual:

1. Head: E12--all 73's used an E12 head; only the early 72s used a 121 head

2. Pistons: 90mm, raised grand piano (what used the ones rotated by 45?) Standard piston size was 89mm, piano top

3. Compression ratio: 9.5:1 and 9.0:1 have both been quoted. US tii's had 9.0 compression; Euro cars were 9.5. At least the Euro spec tii's with 121 heads had 10.0 compression; manual doesn't state a different ratio for US cars.

Those original piano top pistons are still available in both standard and oversize with both US and Euro spec compression ratio; it's the pistons for the 121 heads that are NLA.

Cheers

mike

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Guest gliding_serpent
Per my factory shop manual:

1. Head: E12--all 73's used an E12 head; only the early 72s used a 121 head

2. Pistons: 90mm, raised grand piano (what used the ones rotated by 45?) Standard piston size was 89mm, piano top

3. Compression ratio: 9.5:1 and 9.0:1 have both been quoted. US tii's had 9.0 compression; Euro cars were 9.5. At least the Euro spec tii's with 121 heads had 10.0 compression; manual doesn't state a different ratio for US cars.

Those original piano top pistons are still available in both standard and oversize with both US and Euro spec compression ratio; it's the pistons for the 121 heads that are NLA.

Cheers

mike

Thanks, I was way off then. Good thing I checked.

I just spoke with my local BMW parts department and all standard and over-sized are NLA.

IE has cast 90mm for the E12. My BMW '02 restoration guide (by Mike Macartney, not you by any chance?) mentions using taller flat tops from the 3.0s, 528, 630i, 530i. Can anyone give guidance on that option.

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Guest gliding_serpent

A source told me that Canada got 9:1 compression ratio for those that may be interested.

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If you're looking for Mahle higher-compression pistons, I have some - email me (button above) for more info. -KB

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Guest gliding_serpent
If you're looking for Mahle higher-compression pistons, I have some - email me (button above) for more info. -KB

email sent. I will need 90mm pistons.

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Guest gliding_serpent

For any doing a search, I just wanted to update to stop the spread of mis-information. According to my original users manual, my Canadian bought car comes with a 9.5:1 compression ratio, just like Euro cars, as opposed to 9:1 like the US cars.

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My friends at BMW AG Mobile Tradition told me that all 2002 Tii's with a VIN that starts with either 276 or 278 are US Spec cars and thus would have 9.0:1 C/R.

mac.

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