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HARTGE 323IRS HEAD ONTO M20B25

Discussion in 'Pacific Region' started by apexalpine, Nov 14, 2016.

    • Member

    apexalpine

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    Hi, If I wanted to make this work does anyone know what would be involved ? replace with eta crank & pistons, or could you bolt it straight onto 325I M20 block? Thank you
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    MGarrison

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    Don't know the specifics, sorry can't be of help there - what's the "RS" imply? Something engine-related or abbreviation for something more generic, like 'RennSport'? My question would be wondering whether a modded or substantially modded head for a smaller displacement engine actually move more air or be appropriate for the stock/o.e. larger-displacement engine? Far from an engine expert here, but thinking that it might be a step backwards unless the valves in the 323 head are same-size or larger as the stock M20B25 head? Or, in the M20 evolution, what made up the displacement difference between M20B23 and M20B25? Were the heads the same and it was just piston bore &/or stroke increase? Folks have been ploppingM20B25 "i" heads on "eta" blocks to take advantage of the displacement difference for ages, presuming the Hartge head was for an "i", I wouldn't guess it would require doing anything with 'eta' parts. Probably would be helpful to know the camshaft specs to know what that means for swapping to a different block. Knowing specifics of the Hartge motor it came from might also be useful - I would guess, for instance, the Hartge motor wouldn't have had pistons with valve cutouts for clearance - but, if it did, stock pistons don't, and if the cam lift/duration profile opened the valves far enough to need such clearance, there would be an interference from the stock pistons. Dimensionally, I suspect the M20 block was externally the same through it's production history, my guess would be various M20 version heads would be interchangeable in that regard, but performance implications and results would vary substantially - note, that's just what I would guess.
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    • Technical Service Advisor

    charlson89

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    Short answer is no you can bolt this head straight on. So in the e30 M20 engine family there were 3 different heads the 731 used on the 320i and 323i. The 200 was used on the eta motors, the 885 was on the 325i. The M20b25 engine uses a different piston thus creating a different combustion chamber. If you were to take the that has which is basically a 731 just bored out with a different cam and but it on the M20B25 your piston would hit the valves. Yes you could swap the pistons and everything over but then you changing compression ratios and thus horse power that may not be the best bang for your buck in the performance area. Also you may need to update the motronic system to a later one for help with running fuel management for these upgrades which gets expensive as well. Just my 2 cents on the situation.
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    apexalpine

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    Thanks for the info

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