531 Valve Seat sizing

[Samman88]

Hello all,

Just have some questions for anyone who may have some experience in this area. Sorry for the english post, I can translate your swedish replies though

I have a 531 head I am working on building with larger valves. I have a KL racing T5 cam, stiffer springs, KL racing extreme exhaust manifold and a custom intake manifold I am welding. I currently use a Holset HE351cw turbo but would like to use the larger HX52.

What is the recommended valve size for such a set up with 600hp goal? I was considering 40mm exhaust and 46mm intake?

What size inserts diameter and inside diameter do you usually use for such valves to have good flow? I have an RVR machine to do seats and some porting/shaping chamber with.

Has anybody lifted the intake port flange on the head to a 30mm higher position to improve intake angle? I can do this on the RVR machine and sleeve the port but if there is no gain it is a waste of time .

Thankyou for your help

[Samman88]

Hej, allihop,

Har bara några frågor till alla som kan ha erfarenhet inom detta område. Ursäkta det engelska inlägget, men jag kan översätta dina svenska svar

Jag har ett 531 -huvud som jag arbetar med att bygga med större ventiler. Jag har en KL racing T5 -kam, styvare fjädrar, KL racing extremt avgasgrenrör och ett anpassat insugningsrör jag svetsar. Jag använder för närvarande en Holset HE351cw turbo men skulle vilja använda den större HX52.

Vad är den rekommenderade ventilstorleken för en sådan uppsättning med 600hk mål? Jag funderade på 40 mm avgaser och 46 mm insug?

Vilken storlek skär diameter och innerdiameter brukar du använda för att sådana ventiler ska ha bra flöde? Jag har en RVR -maskin att göra säten och en del portning/formningskammare med.

Har någon lyft inloppsflänsen på huvudet till ett 30 mm högre läge för att förbättra insugsvinkeln? Jag kan göra detta på RVR -maskinen och hylsa porten men om det inte finns någon vinst är det slöseri med tid.

Tack för din hjälp

[Erland Cox]

Use 46-38 valves. With them you can use your stock inserts.
With that mild cam you could use stock valve sizes too probably without a loss.
A turbo engine does not need a bigger exhaust valve than an N/A engine.
The camshaft sets the rpm for the engine which sets the port size which sets the valve size.
You do not need or want bigger valves than smallest port diameter / 0,88.

Erland

[Erland Cox]

I use 88-90% of valve diameter in the throat.
From 90 degrees i go to 75-60-45-35 degrees on the intake in a Volvo head. Blend from 75 degrees into port. 1,3mm seat.
On the exhaust 30 to 35 top cut, 1,3 to 1,5mm seat, 1mm 60 degrees, 75 degrees and then blending into port.
Raising the port should help but not with that cam.

Erland

[whilliam]

Use 46-38 valves. With them you can use your stock inserts.
With that mild cam you could use stock valve sizes too probably without a loss.
A turbo engine does not need a bigger exhaust valve than an N/A engine.
The camshaft sets the rpm for the engine which sets the port size which sets the valve size.
You do not need or want bigger valves than smallest port diameter / 0,88.

Erland

The highlighted red is for "maximum power" goals..... If you need the most drivable engine (good power band) the exhaust valve should be as big as possible. (the port -size and -flow does not need to "follow" the valve size - better if it is quite low to keep up the speed of exhaust gasses)

What to aim for is big flow at low valve lift (on exhaust side, intake could use normal "N/A- prescription")

[Erland Cox]

One question I missed.
If you want to put in inserts or valve guides the interference fit is the diameter through 250.
So for a 50mm valve seat 50/ 250 = 0,2mm.

Erland

[Samman88]

Thankyou for the information Erland and Whilliam!

46/38mm valves seems to be popular so I will go with that combination. Is it that there is really little gain to go to 40mm exhaust or is it that people do not like to change valve seats? It may be challenging to open up the exhaust port to 90% of 40mm I guess. But 40mm valves cost the same as 38mm valve.

Is there a benefit to go larger seats than original when doing 46/38 to increase the inside diameter of the seat or can I bore out the original seat a little bit (to 90% of valve area) without weakening the press fit?

I have been reading the Tommy Luhr thread on here and will take some inspiration from his combustion chamber design. I will forget about raising the intake ports on the head, too much effort for little gain.

Thanks again


Swedish:

Tack för informationen Erland och Whilliam!

46/38mm ventiler verkar vara populära så jag kommer att gå med den kombinationen. Är det så att det verkligen är liten vinst att gå till 40 mm avgaser eller är det så att folk inte gillar att byta ventilsäten? Det kan vara utmanande att öppna upp avgasporten till 90% av 40 mm antar jag. Men 40 mm ventiler kostar samma som 38 mm ventil.

Finns det en fördel att gå större säten än originalet när man gör 46/38 för att öka innerdiametern på sätet eller kan jag utträda det ursprungliga sätet lite (till 90% av ventilytan) utan att försämra presspassningen?

Jag har läst Tommy Luhr -tråden här och kommer att ta lite inspiration från hans förbränningskammars design. Jag kommer att glömma att höja intagsportarna på huvudet, för mycket ansträngning för liten vinst.

Tack igen

[whilliam]

I tried to explain NOT to aim for good flow in exhaust port, the best result will occur if the 1-5mm lift has maximized flow and the max lift flow remains the same as 36mm valve.

This is for best power band in turbo engines.

An example of engine builder that also likes this prescription (besides me and my friends) is the one that built the Pikes Peak SAAB.

[Erland Cox]

There is absolutely no reason for a bigger valve than 38mm and not more than 33mm under the valve.
The valve lift sets the need for port size as I wrote.
Actually I do think that a 44-35 valve head should work even better.
A turbo engine is pressurized between the compressor and the turbine and even if power is greater flow velocity is not.
Mass flow is greater, the air and exhaust gases are more densely packed.
People do the mistake of thinking that big valves make a 2 valve engine more like a 4 valve engine.
But the valve window is as big as the valve at a lift of 25% of the valve diameter.
So for a 44mm valve 11mm lift means that the valve window has the same area as the valve head.
By making the 44mm valve 46mm the area gain in the first mm of lift is 4,5%.
The gain all the way to 11mm is only 4,5%.
By lifting the cam 12mm:s instead of 11mm the maximum valve window area will be 9% bigger.
You want to gain area when piston motion is high, not when the piston is standing still.
If you need more low lift area you do that with duration instead.
A 4 valve engine like B234 has 2 34,5mm valves instead of 1 44mm valve.
That means that they only have to be lifted to 8,6mm:s instead of 11mm to get the same valve window as valve head area.
Which means that they need less duration and lift for the same power.
When you put a bigger valve in a 2 valve head you need to lift it higher to make use of it.
But people are obsessed about big valves.
The biggest flow loss is in the stock intake, what intake will you be running?
I can get 670 hp at 2 bars of boost with a 46-38 head and the torque has to be managed to not go over 800Nm:s.
With stock inserts and 40,5 and 33mm under the valves if not overheated or over revved these heads will live very long.

Erland

[Erland Cox]

Another question is what fuel are you running?
With E 85 parallel squish will work but I go to slanted squish in either the piston or the cylinder head.

Erland

[whilliam]

Erland wrote:
"You want to gain area when piston motion is high, not when the piston is standing still."

This is true at intake, at exhaust i do not agree. Reason for this is that when flow starts, at the first part of exhaust opening, the pressure in cylinder is high and you can benefit from a stronger pulse to the turbo.

Erland wrote:
"By making the 44mm valve 46mm the area gain in the first mm of lift is 4,5%."

True! But remember the pressure is high at first part of the lift - meaning more massflow at this point than later on.
Also, should we tell somebody that wants the best engine to "sacrifice" 4.5% ?

[Samman88]

Thankyou both for your detailed replies. I have read carefully your response and agree.
The cam I am using has 300degrees of duration and 12.9mm lift, so not much above the 11mm lift you are explaining.
I am using E85 fuel. The motor is running currently but I have this head as a spare one so I am happy to spend some time porting it. I will bore the valve seats to 40.5mm and 33mm and replicate your formula for the 670hp engine if that is ok with you

Here is some pictures if they work for you?

Swedish:

Tack båda för era detaljerade svar. Jag har läst ditt svar noggrant och håller med.
Kameran jag använder har 300 grader varaktighet och 12,9 mm lyft, så inte mycket över 11 mm lyften du förklarar.
Jag använder bränsle E85. Motorn går för närvarande men jag har det här huvudet som ett extra så jag lägger gärna ner lite tid på att porta det. Jag kommer att borra ventilsätena till 40,5 mm och 33 mm och replikera din formel för 670 hk -motorn om det är ok med dig

Här är några bilder om de fungerar för dig?

Screenshot_20210906-084838_Gallery.jpg (65.32 KiB) Visad 2049 gånger

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YL3iJo4h.jpg (130.11 KiB) Visad 2049 gånger

[Samman88]

20210906_121848.jpg (334.9 KiB) Visad 2048 gånger

Here I tried to deshroud the valve to the gasket line with a radius cutter

[Kadett4wd]

True! But remember the pressure is high at first part of the lift - meaning more massflow at this point than later on.
Also, should we tell somebody that wants the best engine to "sacrifice" 4.5% ?

Too much massflow early in blowdown can have their downsides also.

To Erland, I dynoed 619whp at 1.9bar with 36.5mm exhaustvalves.
I feel like the 38mm exhaust is a little too big for the rings in the head, thereby i grinded down the exhaustvalves to 36.5 and also gained some flow at the area nearest to the chamberwall.

[Erland Cox]

When porting the 531 head do not lay the combustion chamber wall down more on the exhaust port side.
Just port the corner where the machine work starts out to the scribed line.
On the squish side you can lay the wall down more.
I usually get 225CFM in and 165CFM out at 14 mm:s with those throat sizes.
In the 670 hp engine I left the squish flat for 3mm:s and then slanted it 7 degrees and rounded all the corners.
There is a thread about power adder combustion chambers here in the advanced section.
Never use a radius seat on the intake, use sharp ridges between the angles.

Erland