Oversize valves - Miata Turbo Forum - Boost cars, acquire cats.

General Miata Chat A place to talk about anything Miata

Oversize valves

Old 03-21-2008, 07:28 PM
Junior Member
Thread Starter
Join Date: Jun 2006
Location: scotland/Houston
Posts: 127
Total Cats: 0
Default Oversize valves

Anyone any experience of fitting 1mm oversize in/ex valves to their head?

looking for any help/advice,do,s /donts on having these fitted.

Does the head/valve seats have to be ground out also for max effect?

any info appreciated.
rockdoc is offline  
Old 03-22-2008, 01:33 AM
Senior Member
iTrader: (13)
Join Date: Sep 2006
Location: San Diego
Posts: 606
Total Cats: 0

Yes you need to match the valve seat to the valve diameter. Otherwise you aren't getting any extra flow and the oversized valves are a waste of money. Just tell your engine builder that you want oversized valves or whatever and he'll take care of the rest.
jasonrobo02 is offline  
Old 03-22-2008, 01:41 AM
Elite Member
iTrader: (15)
patsmx5's Avatar
Join Date: Aug 2007
Location: Houston, TX
Posts: 8,824
Total Cats: 268

I'd say you definitely don't need oversize exhaust valves, and really don't need oversize intakes either. They are quite shrouded stock. I would suggest unshrouding the stockers myself. Of course, most people don't unshroud valves properly either. Besides, oversize is only 40 thousandths over, not 200 like on old 302's and the like. Bigger valves will be shrouded more, so there is a point of diminishing returns. For example if a 8mm oversize fit, they would be so shrouded they would flow less than the stock size. IMO, the head has the right size valves in it stock. Bowl work and unshrouding will make it much more efficient, oversize valves won't really.
patsmx5 is offline  
Old 03-22-2008, 05:04 AM
Junior Member
Thread Starter
Join Date: Jun 2006
Location: scotland/Houston
Posts: 127
Total Cats: 0

Thanks for the reply,s- i,ll leave that to the machine/head shop.
rockdoc is offline  
Related Topics
Thread Starter
Last Post
Build Threads
08-09-2018 07:54 PM
Suspension, Brakes, Drivetrain
04-21-2016 04:00 PM
09-20-2015 11:28 PM
Bruce MacKay
General Miata Chat
09-05-2015 08:05 PM

Thread Tools
Search this Thread
Quick Reply: Oversize valves

Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2018 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.