2.7 Compression Ratio

Post Thu Jun 30, 2005 7:28 am

Does anyone know what the ideal compression ratio would be for my 2.7 conversion as it looks like i'm going to have to buy some new pistons and i can have anything i want, but i can also get hold of some pistons which have a ratio of 9.75-1.

Would these be any good or would i need a higher ratio?

Post Thu Jun 30, 2005 7:50 am

If you want to save money use early 325i pistons which will then give you a CR of 10:1 - 10.2:1 which is ideal.

Quaser used these pistons on his 2.7 and got 205bhp without a 6 branch, he had a cat and was running a maf conversion.

Point is that the engine was capable of getting over 200bhp with tuning and there is still more to come.

Rather than shelling out for new pistons I would say this is a very good way.

You must get the CR right otherwise eyoull be very unhappy. Also make sure that who ever is making it does the correct measruements otherwise its going to be very underpowered.

9.75:1 aint gonna produce the power unfortunatley.

Post Thu Jun 30, 2005 4:49 pm

M5pilot wrote: 9.75:1 aint gonna produce the power unfortunatley.

That's what i was thinking. The reason i ask because i've been speaking to Jeff Ireland (Ireland Engineering) and he said that the 9.75:1 ratio would be alright. I think they need it in america due to the low octane fuel (93 octane).

I might just go back to plan A) and just use all the 2.7 engine parts and just modify the head.