Hello guys. I would like to ask , what are the most popular oversize valves among Mini tuners? After a search, i found oversize valves from +0.5mm up to 2mm. What are the advantages and disadvantages of oversize valves in a NA engine?
I am interested for a ported/polished head, with camshaft and oversize valves for my Cooper non S.

 

larger valves for any vehicle whether naturally aspirated or forced induction will help will air intake and scavenging exhaust gasses. there are however "too big" and the vehicle will not run properly. using a factory head is not a good idea for oversized valves. the valve guides are pressed in and have to hot oil soak in order to install new ones. machine shops will also have to drill out the hole for the valves and then you have to change springs and valve keepers and such. not really my cup of tea. could get kinda expensive. after market heads are popular because all of the technical work has been done for you. they are basically bolt ( and time) on mods. for the money your looking to put into a stock head porting and polishing, machining, replacing valves and keepers, replacing springs, changing cam, you better off just buying a head. have you seen the RMW website?......

 

Are you saying that Jan's head is not an OEM head that is machined to his liking including valves and P and P???

 

i couldnt say if it is or isnt, im saying that jan has done the research and technical stuff and all of the designing and machining so you dont have to. buy a RMW, or Thumper, or Mini mania head and save yourself the frustration of trying to build one yourself unless you dont mind spending a few buck and know what your doing. I highly doubt someone who doesnt do head work decides to build their own head laps all the valves and gets everything right. by buying an aftermarket head, its almost worry free.

 

The RMW head is a completely new head. It is custom CNC'd to Jan's specs and that is why it is by far the best head available

 

OK... Jans heads are NEW OEM heads!! Then he works them. The key to a N/A engine is the VELOCITY of the air flowing!! the boosted engine is the amount it can force thru! Thus the Bigger than stock valves on the MCS will allow more top end, and when the valve gets too larger.. the air flow will slow and the expression ".......... yeah, but after 4500 it flys!!" come into mind!! Stock...or +.5 mm are a good valve size for the mods you are looking for n/a. Bigger and you could join the "after 4500 it flys "crowd, yes? Then there are drivers, that will sacrifice the low and mid rage for that upper rpm power!!

Modifing the OEM heads are no where as intense as it has been made to seem!! Guys the MINI heads are not a new item on the market!! SOHC 4 valve per, has been around a long.. long time!! The guide replacement and oversize valve installation isnt any different than any other Alum head!! cool?? A +1mm will go quite easily, as well as the +1.5mm. It isnt the work or technique... it is that the larger valve has the tendency to flow too much and result in a lazy low end!! TUNE is the key after ANY head change!! Most heads are showing a 20-35 whp gain. Funny how in the past year all the Head debates have gone!! and the "showing of Dyno" numbers for head changes are missing also.......

Just me...............................

Thumper

 

Now that's what I'm talking about....It's not black magic, it is solid R and D work, especially if you don't have a flowbench(or even if you do)....A little common sense...come on ya know, get rid of those rough sharp edges, they have to affect the air flow! The casting on the factory head is terrible and it doesn't take much to improve it...I just got finished mine on an NA motor and got 10ftlbs of torque and 8 hp. Everything was completely stock except the porting. Next, I might do the same thing with another one and go bigger valves, what would that net me. I won't know until I do it, each time learning what does or doesn't work.

 

Another question, are the stock valve springs sufficient for 7500rpm?

 

I should say.. yes!! but not for a racing application!! If the cam is bigger ( for 7500-8000 rpm) and the engine is racing around the track for a long period of time.. I should want an upgrade on springs!! Howerver with the stock cam or the mild replacement cam.. we are seeing 7200-7500 with not power loss do to float or bounce!! But then again, in real life it isnt the max lift and rpm that is the issue...

There are a bunch of un truths out there on the MCS head.. like it has "sodium valves" the springs are no good for over 5500 rpm blah blah...
look at the valves pictured... just a solid steel unit!! as for springs.. we run stock units.

Just me...........................

Thumper