885 Head mods for Stroker.

[AntParker]

Hi guys,

As a few of you know- I am currently collecting together parts for a M20 2.9 stroker, Forged pistons, M52 Rods, Shrick 288, RHD ITB’s etc.
The engine will see mostly track use.

I seem to remember reading somewhere that the 885 head is very good in stock form, I was planning on a full de-coke, obviously lap valves etc. and was planning on having the head ported and polished (at very least port matched to the RHD intake manifold and exhaust ports opened out slightly- retaining stock valve sizes.

I was wondering if you guys have any recommendations on how far to go with this, is it worth Polishing intake and exhaust, should exhaust port just be opened out to the size of the gasket etc. are there huge gains to be had from bigger valves?

I also understand that porting & polishing intake tracts splits opinion, do we think this works well on M20’s or not?

I have been doing some reading and it seems most people either go the whole way- ported polished, roller cams etc. or leave the head stock.

Interested to hear your thoughts and opinions.

Many thanks

Ant

[ForcedFirebird]

Unless your head porter has a flow bench, leave it alone honestly, they are finicky about modifications.

I have messed around with a lot of them, posted some info a while back...

http://www.r3vlimited.com/board/showthread.php?t=261381

[digger]

the m20 heads are quite ok when compared to similar era OE castings but there is enough improvement in there when done well it is always worth it on any spec engine that you want more performance on, the hard part is finding someone who actually does a good job. if using standard size valves you can get majority of benefits from multi angle valve job, backcut valve and some light metal removal from key areas without too much outlay

i wouldn't pay money for a ported head if the person doing it hasnt used a flow bench to verify what they have done. i can sand casting marks myself for free making things smooth but cutting proper valve angles, and porting the right areas is a skill that needs experience, the right tools and equipment and then validation from how the engine performs through dyno testing. the idea isnt to just get the most CFM, though good heads do flow more CFM

as an example one member on here (morerevsm3) said he gain 20rwkw (30bhp) from a ported head on a e30 racecar which is class with m20b25 with standard b25 engine and cam but open to head porting and exhaust.

[ForcedFirebird]

Digger, you know if stock valves are required in that class?

I have found the ports are borderline too large for a stock valve as it is.

[digger]

I believe it is standard valve sizes.

[AntParker]

Sorry for the delayed response guys.

Appreciate your advice- all seems to make sense- i am not sure of anywhere locally that would be good enough to improve these heads.

I would be interested in a 'three angle valve' job though, i have looked into these in the past- i wonder though, do special 'three angle valves' need to be purchased, or can stock valves be ground/cut for the 3 angles?
also do the seats need to be replaced, or can stock seats also be re cut/ ground for the three angles?

Probably basic questions, but i cannot find too much information on this online.

Many Thanks

[jeffnhiscars]

The only cutting that's done on the valve is to clean the face and possibly a back cut to help air move. As for the seat, when you cut a new face in it the contact area gets wider. The 3 angle cut reduces the contact area and makes for better air flow.

Avoid any machine shop that hesitates when you ask