Jump to content
kronus

M30 valves easy way to get +1 in M10?

9 posts / 3336 viewsLast Reply

Recommended Posts

Has anyone heard of this working? I have some M30 valves and an M10 head, and they seem to fit fine when mocked up, but I'm not sure if the shaft lengths are the same.

Dimensions on M10 valves: 46x8 intake, 38x8 exhaust

Dimensions on M30 valves: 47x8 intake, 38x8 exhaust

So if I'm reading this right and the valve lengths work out, M30 valves are an easy way to get +1 valve size in M10s.

Share this post


Link to post
Share on other sites

Funny that I was saying the same thing last night.

When Eric Kerman was building my head, I asked for larger valves. He said they weren't needed and would add nothing to the performance until you used a 328 cam or worse.

John

Share this post


Link to post
Share on other sites

Exactly Toby! Unless you are trying to get over 230 hp the bigger valves are not going to help you and will actually hurt low end torque. You need to make sure the valve reliefs in your pistons will clear, you will need new seats in the head etc.

BTW they are the same length and you can use them in a M10.

2 identical Race Engines (13:1, 336 cam etc,etc) one with 46mm intake, the other with 47mm intake valves both with 38mm exhaust valves. Big Valve engine lost 3lb/ft of torque @ 4000 rpm and gained 5hp @ 8000 rpm, torque peak moved from 5900 to 6100 rpm. This is with 42 mm chokes in 50 DCO SP carbs and a 1 3/4" primary tube header. I really do not recommend this for a street car!

Share this post


Link to post
Share on other sites

Thanks for the info! Interestingly, you guys say that it works and folks on another forum say that they're different lengths. I'll measure my m30 valves when I get down there and see what's up.

I've also figured out that I don't need oversize valves because I'm building a turbo engine, not a high-RPM NA one.

Share this post


Link to post
Share on other sites

OOPS, I screwed up, it has been a long time since I did a M30 head. The valves are different lengths.

Share this post


Link to post
Share on other sites

In my humble opinion with proper attention to the short side and lesser valve face angle the low lift numbers for the larger valve are notably better on the flow bench. How that relates to real life dyno numbers will be directly related to cam profiles effective area. In theory the better flow will require a reduced area cam to generate the same bmp. It's all about the air flow and how you apply it.

Share this post


Link to post
Share on other sites

sure, but the short side on an M10's already pretty good,

and increasing valve size by .5mm radius isn't going to make

more than a couple of gnats's asses of difference...

In a 'no effort spared' motor, sure, but anything less, it's....

t

Share this post


Link to post
Share on other sites
Exactly Toby! Unless you are trying to get over 230 hp the bigger valves are not going to help you and will actually hurt low end torque. You need to make sure the valve reliefs in your pistons will clear, you will need new seats in the head etc.

BTW they are the same length and you can use them in a M10.

2 identical Race Engines (13:1, 336 cam etc,etc) one with 46mm intake, the other with 47mm intake valves both with 38mm exhaust valves. Big Valve engine lost 3lb/ft of torque @ 4000 rpm and gained 5hp @ 8000 rpm, torque peak moved from 5900 to 6100 rpm. This is with 42 mm chokes in 50 DCO SP carbs and a 1 3/4" primary tube header. I really do not recommend this for a street car!

I had heard pretty much the same thing from a German friend of mine that did lots of tuning/building of M10's. He did recommend using a slightly larger exhaust valve though - 39mm as opposed to 38mm. Honestly though, the 1mm larger valve in a street motor wouldn't seem to make a whole lot of difference....

www.alpinabmw2002.com

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.




×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.