30 degree valve seat angle

[Enuo]

Has anyone tried using a 30 degree valve seat angle instead of 45? Been done loads in A series mini heads, any problems doing on CG13 head?

 

[frank]

gains in headwork tend to be very small enuo, use of CAD etc mean modern 16v designs are more efficient eh

 

[Enuo]

well from what I have come to understand an 8 valve engine with 30 degree valve seats runs almsot as well as a 16 valve engine with 45 degree valve seats, so a 16 valve engine with 30 degree valve seats might run as well as a 20 valve engine. More efficient as they are, they are still designed for ease of manufacture as much as for performance, 45 degrees is just easier and cheaper to manufacture... just like a cast iron manifold from 2000 era cars is better than 1950's cars, is still got nothing on a tubular manifold.

 

[frank]

45 degrees is just easier and cheaper to manufacture....

in what way ?

 

[Low Rider]

I doubt there's much in the way of gains to be had tbh, particularly with the cams used in most CG engines.

 

[Enuo]

will link a video by tony vizard explaining how gains work later, seal is harder to create with 30 degree so is more laborious to get right which is where extra cost comes from

 

[Low Rider]

will link a video by tony vizard explaining how gains work later, seal is harder to create with 30 degree so is more laborious to get right which is where extra cost comes from

I'm assuming you mean David Vizard...

 

[Enuo]

yes sorry i was rushing when i posted that!

 

[Low Rider]

I know the vids you mean, a lot of very good information kicking about from DV. I could happily listen to him for hours. Not sure how it will fair on the CG engine in reality though.

DV did a lot of work on 30deg seats, and found two problems.
1. They don't flow as well as 45 deg seats at higher lifts. I think he worked around that with some very specific cuts and blends. Unsure how sensitive this is on other engines...
2. Leakage past the valve due to thermal distortion can negate all the low-lift gains. I don't believe this was ever solved, perhaps minimized?

We were happy to stick with a 45deg seat, utilize a full 30mm solid follower and cam to enable us to lift the valve much faster and thus improve flow that way, (works well on a 16v). One could perhaps argue that this could provide adequate flow improvements without the potential downsides...

It may also be worth noting that we got pretty close to 100bhp/liter on a standard head on a less than optimal 8.2:1 compression IVC with a very good spread of torque. Had we optimized compression for the cam we could have probably got to 3 figures, while picking up torque throughout the rev range. I personally think this shows the K11 head to flow pretty well already out of the factory.

 

[Enuo]

Ok fair enough, just looking to try something a little different to the standard GA airbox and tubular manifold. I agree, I sat through the whole 2 hours of David on youtube without a break! It's pretty heavy stuff if you've not got a pretty solid grasp of how engines work and perform already, but its all genius.
What size followers does the CG use as standard then, and what work is required? I'm great with pushrod engines, overhead cam engines i'm still learning.

 

[Low Rider]

Ok fair enough, just looking to try something a little different to the standard GA airbox and tubular manifold. I agree, I sat through the whole 2 hours of David on youtube without a break! It's pretty heavy stuff if you've not got a pretty solid grasp of how engines work and perform already, but its all genius.
What size followers does the CG use as standard then, and what work is required? I'm great with pushrod engines, overhead cam engines i'm still learning.

Well the CG engines use a 30mm follower body but because it uses a top biscuit shim, you're limited by the diameter of the shim. I 'think' they are 28mm, but I don't have one to hand to verify, (just a guess).

It really depends on camshaft profile and what the overall objective is, most do just fine with the stock valvetrain. Frank found that a 260deg 10mm lift grind he had done by Autosprint was ok until around 7300rpm when valve bounce set in coupled with the risk of spitting a shim out due to the high opening rates. He however has a workaround for this, so it's not an issue any longer in terms of shims coming out and it's a cost effective method. My only concern is followers that are deemed to be flat actually have a large radius on them, so I am not sure what happens to that once the follower lip has been ground away. None the less it seems to work...