Raising stock S52 compression

[ZEKTI]

Hi all,

Local BMW Motorsport shop is decking the head on a stock internals S52. Their engine builder who has many years of experience building these engines asked if I️ would like to take more off the head to increase compression. It would be a small amount but what are real world gains for this? 5hp? Motor has the typical bolt ons and is OBD1. Thanks


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[AWDBOB]

Hi all,

Local BMW Motorsport shop is decking the head on a stock internals S52. Their engine builder who has many years of experience building these engines asked if I️ would like to take more off the head to increase compression. It would be a small amount but what are real world gains for this? 5hp? Motor has the typical bolt ons and is OBD1. Thanks


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IMHO, you likely will not see any HP from just an increase in compression.

Are you running stock s52 cams?

[ZEKTI]

IMHO, you likely will not see any HP from just an increase in compression.



Are you running stock s52 cams?

Yes all stock internally and pink tops.


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[AWDBOB]

Yes all stock internally and pink tops.

Maybe someone else will chime in but:

IMO you won't see much from it and you'd be regretting your decision if you wanted to service the head again in the future.

I believe stock service limit for an S52 head is 139.7mm and stock is 140mm, so there's really not much to take off to notice a huge difference (0.3mm or 0.0118" serviceable material).

For reference, a typical "clean up my head deck" is 5-10 thou, 5 being a light skim and 10 being a healthy cut.

I don't know the stock S52 cylinder head volume offhand, so it's hard to calculate exactly how much compression you'd be gaining by decking the head a few extra thou.

[ZEKTI]

Thanks for the info. The Block is also at the shop. I’ll get more details of what the builder had in mind. But if I️ don’t have/plan on purchasing supporting mods this I️ don’t want it to take material off if it’s not noticeable. This is purely a street motor.


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[digger]

yeah bout 2-3 numbers depending how much the CR changes.

you can take some off the block or run a thinner gasket and get the piston and head nice and tight to help the squish/quench which will also increase CR. depends how much you want to chase the last few hp

[ZEKTI]

Going stock, makes no sense to mess with it. Especially if I️ plan on FI later on.


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