3/5/7 angle valve jobs?

3/5/7 angle valve jobs?

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Discussion

Brummmie

Original Poster:

5,257 posts

166 months

Monday 12th December 2011
quotequote all
Ok, so whats the deal?
Is it more angles the better, or i suspect who is doing it that is a factor.
I am going to have my Dart LS heads done over the salted roads period, and i have been offered all of these options!!

sparkybean

193 posts

135 months

Monday 12th December 2011
quotequote all
Have always wondered this. Supposedly more angles are better, but this must mean that the best valve cut is a smooth circular seat (infinite angles etc), no?

Brummmie

Original Poster:

5,257 posts

166 months

Monday 12th December 2011
quotequote all
sparkybean said:
Have always wondered this. Supposedly more angles are better, but this must mean that the best valve cut is a smooth circular seat (infinite angles etc), no?
but then what radius!?

ringram

14,692 posts

193 months

Monday 12th December 2011
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+1 my understanding too. Air doesn't like hard turns.
Some good info from David Vizard and Darin Morgan about porting. Most gains are in the inch before and after the valve seat. (ie) chamber and pocket, plus maybe the short turn radius. speedtalk.com is good for info!

stevieturbo

14,241 posts

192 months

Tuesday 13th December 2011
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A smooth turn is best. But lets face it. You're dreaming if you think a 7 angle ( if it exists ) is actually going to yield any noticeable power over a standard 3 angle seat.

And you also need to consider that AFAIK the valve only actually seals on the middle angle. The others are just shaped for flow.
Any head Ive ever installed and ground a valve into, you can clearly see a single band on the valve and seat where contact is made.

And in order to dissipate heat, certainly on the exhaust side anyway, you want a much wider contact area than the intake. Which might mess up any fancy angle job.

Either way, I still say you'll never notice the difference

Pumaracing

2,089 posts

152 months

Tuesday 13th December 2011
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Having spent 20 years studying the effect of cylinder head modifications on my flowbench all I can tell you is it's far too complicated to summarise into simple rules like "more cut angles = better".

A completely smooth radiused seat will not necessarily flow more (usually less) than one with discrete seat angles and sharp edges between them. Sharks have rough skin (in fact most fish have scales) because the discontinuities actually reduce surface friction and drag. Golf balls have dimples because that lets them fly further than a ball with a smooth surface. "Smooth" does not always equate to friction free or higher flow.

The choice of seat width and bottom cut angle are far more important than just the number of cut angles which tell you bugger all about the knowledge of the person doing the job. Most places just have a small range of standard cutters which can't possibly be right for every valve size and nearly everyone cuts the main seat too narrow. A nice wide seat conducts heat away much better. The OE seat width is usually spot on because the person who designed the engine knew a lot more than the idiot with the Serdi who thinks 1mm wide valve seats are "race seats" or somehow better than what was there to start with.

Seat concentricity is more important than just about everything else combined and the commonly used Serdi machines are awful at achieving that unless the guides are in perfect condition. In fact most places with Serdis will try and tell you they need to either replace the guides first or at least hone them out (which of course buggers them) until they fit their next larger seat cutting pilot just to get the machine to work properly (they won't actually admit it's to get the crappy machine design to work properly of course). Far better are machines with fixed pilots which lock into the guides like the Sunnen system than rotating pilots like the Serdi where any play between guide and pilot translates straight into seats with poor concentricity.

Seats that flow well at high valve lift don't always flow well at low valve lift and vice versa. Seats that flow the absolute most might not last very long. Everything is a compromise and every seat I've ever cut has been tailored to the exact engine spec, cam lift, its intended use and the valve sizes.

If you want some simple rules for general use the 45 degree seat should be about 4.5% of the inlet valve diameter wide and use the same width on the exhaust seats which will usually translate to about 5.5% of their diameter seeing as they are smaller. So a 50mm inlet valve will want a 2.25mm wide seat and so on.

A 70 degree bottom cut always outflows the normally used 60 degree cut because it better splits the transition from 90 degree throat to 45 degree seat. A 60 degree bottom cut means a 30 degree transition from the throat and only 15 degrees from the seat angle which is a stupid way of trying to minimise the change of flow direction. Obviously the ideal would be to split the 45 degree difference and use a 67.5 degree bottom cut.

So why does everyone use cutters with 60 degree bottom angles? Because that's what the seat machine manufacturers list as stock items and hardly anyone out there is smart enough to question it. Actually OE heads usually have the correct 70 degree or similar bottom cut angle which your local engine reconditioner will happily and cluelessly bugger up when he refurbishes the head for you.

Similarly the top cut should split the difference between seat angle and chamber roof angle, i.e. with a flat chamber roof use a 22.5 degree top cut. With hemi heads or other heads with angled roofs use a bigger angle like 30 or 35 degrees.

So phone up a few people and ask them some searching questions because you now already know more than they do. Ask them what seat width they suggest and why. When they say they use 1.5mm on everything because that's the cutter they bought with the machine or that wide seats are good for road heads and narrow seats are good for race heads you can put the phone down. Ask them what bottom cut angle they use and why. When they say they've never given it much thought or they use 60 degrees because that's how the cutters are made you can put the phone down. Same for top cut angle.

Ask them how much time they've spent testing different seat widths and angles for flow on a flowbench. When they say "what's a flowbench?" you can put the phone down.

Ask them what concentricity level they strive for. They'll probably say their seat machine has a vacuum tester built in and they test every seat for leakage - at which point you can put the phone down. The trouble is a 45 degree valve and a 47 degree (or any other angle) seat will still touch at one point all the way round so it'll seal against vacuum but be worse than useless and burn straight out in service. I've watched a Serdi machine test every seat as perfect for leakage but then none of them would actually lap in and it all had to be redone. Only the fact that I was standing there glowering at people meant it got redone properly! I glower very well when the occasion requires it.

You have about as much chance of getting a set of valve seats cut perfectly (well what in my view is perfect) as of winning the lottery. In fact it is a lottery. If you can find someone who can answer all the above questions without you having to put the phone down first please let us know.

Brummmie

Original Poster:

5,257 posts

166 months

Tuesday 13th December 2011
quotequote all
Crikey! Remembering and rehearsing that lot, will be more prep than I did for me Cse's! hehe

Thanks for the comprehensive reply.

MattYorke

959 posts

198 months

Tuesday 13th December 2011
quotequote all
Another excellent and very educational post. Thanks Dave.

Pumaracing said:
Having spent 20 years studying the effect of cylinder head modifications....

Brummmie

Original Poster:

5,257 posts

166 months

Tuesday 13th December 2011
quotequote all
I'm off to knight engine services nr silverstone with the heads today, while I'm there I will have the ITB's port matched. But I will go armed with a few questions now.
I'll Dyno it once the work is done anyway.

dbv8

8,434 posts

165 months

Tuesday 13th December 2011
quotequote all
Brummmie said:
I'm off to knight engine services nr silverstone with the heads today, while I'm there I will have the ITB's port matched. But I will go armed with a few questions now.
I'll Dyno it once the work is done anyway.
Just stop please.
Why are you not even letting me get close? frownlaugh

Good luck finding more ponies Paul. I am a fan really.

The Black Flash

9,449 posts

143 months

Tuesday 13th December 2011
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MattYorke said:
Another excellent and very educational post. Thanks Dave.

Pumaracing said:
Having spent 20 years studying the effect of cylinder head modifications....
+1 clap

gsd2000

11,515 posts

128 months

Tuesday 13th December 2011
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Paul your not making all that power with pretty much standard as cast dart 205 heads?

gsd2000

11,515 posts

128 months

Tuesday 13th December 2011
quotequote all
great post puma racing

tinker-27

834 posts

169 months

Tuesday 13th December 2011
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Yes they are lightly ported dart heads ,

one eyed mick

1,189 posts

106 months

Tuesday 13th December 2011
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3angle seats are good enough for any normal or moderatly hi power engine, the only thing in 35 + years of building engines I have wittnessed with thin seats is poor valve life caused by overheating. Ok if you are into pulling the thing down every week use what ever system you want even radiused seats work for so long but if you want sensible life out of a multi K£engine be sensible 3 angles and proper old fashioned lapping!!

Brummmie

Original Poster:

5,257 posts

166 months

Tuesday 13th December 2011
quotequote all
gsd2000 said:
Paul your not making all that power with pretty much standard as cast dart 205 heads?
They are 225 Dart heads, i took the combustion chambers out to match the larger bore, unshrouding the valves in the process and cc'd the chambers to get the comp ratio i wanted.
I also blended the bowls in and took the casting flashes out of the runners.
There lots more to have a go at though i think..

This is what i did last time, just a light clean up.



sparkybean

193 posts

135 months

Thursday 15th December 2011
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More thanks towards pumaracing, very informative stuff.

DaveL485

2,730 posts

142 months

Thursday 15th December 2011
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Pumaracing said:
Useful stuff
Thankyou! (even though it wasnt me asking in the first place!) smile

Brummmie

Original Poster:

5,257 posts

166 months

Thursday 15th December 2011
quotequote all
Hey, he uses a Sunnen one tick in the box! and he said without any prompting they are much betterer! smile

Edited by Brummmie on Thursday 15th December 22:25

Nick3point2

3,858 posts

125 months

Friday 16th December 2011
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Pumaracing, I tip my metaphorical cap to you.