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Valves for 531.. Bigger is always better ?

SkeTchy-MechAniC

SkeTchy-MechAniC

New member
Joined
Jun 16, 2020
With some spare parts came a 531 head.. Since i've just finished a 530 with 46/38mm valves i was wondering if it would be worth it going even bigger+531. Biggest valves KL sells are 50/40, they'd also need new seats.

Any idea what kind of gains could be expected, Is there anything like to-big with valves on this head?
-NA use
-ITB's
-4-2-1 Header
-Programmable ecu
-12.2:1
-forged rods
-2300
 
here's my head with 48/40 valves from Ferrea as a reference, head is heavily ported and shaped.

59IeIByh.jpg
 
I was wondering, if the valves get bigger, doesn't the powerband move to high rpm ?

Anyone who knows how the "bigger" cams performance compares to stock cam with big valves ?

Or any related info on this subject ..
 
I did notice on mine, going from stock to big valves, spool was a touch slower, down low, mid-range it's faster, and it doesn't hit the wall up top like it does with stock valves.
 
SkeTchy-MechAniC said:
Awsome, tight fit!



What do you mean with 3mm backwards ? Have it milled 3mm?
Click to expand...

I mean that you literally move cylinder head little backwards, of course you have to drill cylinder head bolt holes to oval shape, then its possible.

My enghlish is not very good, so i can't explain that very well.

google translate:

when you move the head then more space is left between the intake valve and the cylinder wall.
 
Jussi Alanko said:
I mean that you literally move cylinder head little backwards, of course you have to drill cylinder head bolt holes to oval shape, then its possible.

My enghlish is not very good, so i can't explain that very well.

google translate:

when you move the head then more space is left between the intake valve and the cylinder wall.
Click to expand...

WTF?
 
LOL at people not comprehending shifting heads. Let’s explain angle milling next.
 
SkeTchy-MechAniC said:
With some spare parts came a 531 head.. Since i've just finished a 530 with 46/38mm valves i was wondering if it would be worth it going even bigger+531.
Click to expand...
No. Not unless you send the head out to someone in Sweden to have it ported to match, the lifters changed out for the 37mm ones and a 14+mm lift camshaft to match it all. The stock sized valves are actually ok to over 200hp with proper port work and associated complimentary mods(intake manifold, exhaust downpipe at a minimum, if not also the manifold and tuning).

gsellstr said:
I did notice on mine, going from stock to big valves, spool was a touch slower, down low, mid-range it's faster, and it doesn't hit the wall up top like it does with stock valves.
Click to expand...
One is a 530 head with stock valves and the other is a 531 head with larger valves, correct? If so, you aren't comparing apples to apples as the 531's intake port has lower velocity through it because of its larger diameter/shape and also contributes to worse performance down low. The larger intake ports also contribute to better performance up top, so you can't really say how much is due to the larger valves.
 
klr142 said:
One is a 530 head with stock valves and the other is a 531 head with larger valves, correct? If so, you aren't comparing apples to apples as the 531's intake port has lower velocity through it because of its larger diameter/shape and also contributes to worse performance down low. The larger intake ports also contribute to better performance up top, so you can't really say how much is due to the larger valves.
Click to expand...

Nevermind the combustion chambers on a 531 being larger and effectively lowering the static CR.
 
VB242 said:
That is some next level shizz, sounds like a recipe for head gasket failure. But I bet it's o- ringed too
Click to expand...

Just wait till you see how ITB guys get more valve lift/rocker ratio on B20's. I'll try and get a picture.

They drill/oversize the rocker bolts out on the head from 5/16 to 3/8" or 7/16" bolts to slightly shift the rocker shaft away from the valves to marginally increase the effective rocker ratio.
 
I think that David Vizard says that a valve needs clear space around it somewhere in the order of 67% greater than the diameter of the valve to be completely unshrouded. Don't quote me on that figure, maybe Cam will correct me on this as we were just looking at it. Point is, one hand giveth, the other hand taketh away. Also, the larger the diameter the valve, the higher you need to lift it to get it out of the curtain area. Like almost everything, the smallest you can get away with for a given power output is the best choice. Problem with that is that we're not usually looking for a given power output, we're looking for "how much can I make".
 
shoestring said:
Problem with that is that we're not usually looking for a given power output, we're looking for "how much can I make".
Click to expand...
Ha! :)

Also, the amount of flow that is coming out of the valve opening is not evenly distributed all the way around the circle opening. There is some port bias and more flow going through some spots than others.
 
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