3 Angle Seats

[24seven 104]

How easy is it to do this? does it require any special tools or any other work done apart from carefully wielding a dremel? Or is it a take-care-or-screw-up type thing? if the latter, then where can I get it done and how much for? Finally what performance gain comes from it?

[Man3 0]

Its not a diy job at all. Matt at QEP can do it for you at a reasonable price, can't remember how much it cost me now, maybe £54 +vat for my mi-16. By shaping the valve seat into 3 seperate angles, you get a similar effect to a small radius which improves flow. Not sure on the gains though.

Edited May 22, 2006 by Man3

[boldy205 74]

i was under the impression it didnt add to the flow rate, just provided a nice tight seal for the valve? am i right?

[24seven 104]

If there's no real gain then I might not bother. Maybe if I had a more powerful base engine, but not on the 1.6

[TEKNOPUG 3]

If there's no real gain then I might not bother. Maybe if I had a more powerful base engine, but not on the 1.6

 

 

It's not worth doing in isolation alone, only as part of a comprehensive head job.

[24seven 104]

think I'll leave it then, thanks.

[petert 554]

Do some research lads! Getting the seat profile correct is by far the greatest percentage increase in flow!

[Dom9 2]

As Peter says, it is absolutely worth doing, although usually a little more expensive than is being quoted!

 

You will get the biggest gains in cylinder head flow, especially at low lift, from 3 angle valve seats... And, for the money, it is probably the cheapest mod per bhp you can do!

[Man3 0]

I was on a bit of a budget when doing my re-build, i wouldn't have had it done if it was expensive, this was 2 years ago though and matt may have revised his prices, but then it took him no more than 20 mins to do the job from what i remember. I seem to remember having a similar quote at the head re-conners down the road from me who also use a serdi so its definately worth giving a couple of places a call.

[24seven 104]

might reconsider if £54 + VAT is about right.

[PumaRacing 1]

As Peter says, it is absolutely worth doing, although usually a little more expensive than is being quoted!

 

You will get the biggest gains in cylinder head flow, especially at low lift, from 3 angle valve seats... And, for the money, it is probably the cheapest mod per bhp you can do!

 

I'd say the exact opposite. Because the valve seat geometry is so critical your chances of someone getting it right is minimal and in fact the likely outcome is it will cost you more bhp per pound than anything else you can do. Look at the big valve thread pinned above. Three people tried 36.5mm valves in the Mi16, posted their results and all got less low lift flow than standard. That's with a valve over 10% bigger than standard too so in effect a more than 10% flow loss. Low lift flow, as you say, is almost entirely dependant on seat geometry so clearly none of those seats were correct for the type of head and valve size. Matt persevered and started using the seat widths and angles I suggested and ended up finding 10% more flow. How many people are going to find, or know, those correct widths and angles by chance? They aren't even standard cutters in most seat cutting systems. I had to design and make my own valve seat cutting system to achieve the results I wanted.

 

After nearly 20 years of studying seat geometry and looking at other people's work I'd say the following.

 

Your average local engine reconditioner without a flow bench is going to have an almost zero chance of knowing the best seat geometry to use and in fact will probably cut the same seats whether it's a 5 litre Chevy V8 engine or an 850cc Mini. In many cases those seats won't even be concentric and seal properly because the equipment is too old and shagged out to work properly.

 

Even specialist race engine builders are only going to have a 1 in 10 chance of having the right cutters and the right knowledge to get anywhere close to optimum.

 

A 'three angle seat' has at least 7 variables. The width and angle of each of the three cuts (top cut, seat cut and bottom cut) plus the diameter of the valve throat. In effect there are an infinite number of ways of recutting any valve seat and most of those will be wrong. Add in to that the geometry of the valve itself and the problem escalates further. To find out what is right takes years of study and if your seat cutting equipment supplier doesn't carry cutters with the correct widths and angles you'll still never find the optimum geometry. Even a flow bench won't give you all the answers because gas speed is a vital factor and that doesn't show up in steady state flow testing.

 

At the back end of last year I was contacted by some people in Belgium who race an FF2000 single seater. Slicks, wings and a fairly standard 2 litre Ford Pinto engine except that the head can be ported and the valve seats are free. Initially they'd been to a German guy who, according to them, was generally rated as the best Pinto head specialist on the continent. I didn't ask a name and wouldn't have recognised it anyway. On their local rollers they had 130 bhp at the flywheel but that was well short of being competitive and they just couldn't keep up with the top cars. In limited modification race series every couple of bhp will move you several places up the grid. It's likely that the whole field will only be separated by 10 bhp or so.

 

They drove over and brought their head to me to see if anything more could be done with it. If I agreed to modify it they were going to do a back to back test on the same rollers and the end results would of course be determined by how competitive they became on track so there was, to say the least, a certain amount of pressure on me to know what I was doing. If the head had looked close to optimum I'd probably have declined the work. The head had certainly been heavily reworked, and was very shiny!, but there were obvious things that could be improved, particularly in the valve seat area. They'd been cut much as you expect to find most 'racing' valve seats. Too thin and the wrong angles. I recut the seats and made some small alterations to the port shapes in the valve throat. Total time was about three hours work and I charged them £300 for the privilege. A couple of weeks later I got an email with the results. Just under 138 bhp on the same rollers and they got their first podium position in the next race. £100 per hour but still the cheapest horsepower they were ever going to find. They now want two more heads done from scratch to keep them running for the next couple of seasons.

 

Valve seats certainly are critical but you have only a small chance of finding an improvement from the average engine builder's work. You have a larger chance of going backwards both in flow and mechanical reliability.

[Rippthrough 98]

Loads of interesting stuff.

 

 

Nice read, but surely the real questions is will the 3 angle seat cut by a local monkey be better than the stock single angle seat recut by a local monkey?

[petert 554]

Nice read, but surely the real questions is will the 3 angle seat cut by a local monkey be better than the stock single angle seat recut by a local monkey?

 

And to this I say absolutely yes. Take a DFZ head for example. The flow improvement on a wide, but reliable, factory single 45 deg. cut is more than just impressive. Whether or not you can achieve the same % improvement on a 16V head is another matter.

[Dom9 2]

So, Dave, you actually agree with me 100%... If it's done properly?!

 

Which means you are assuming it's not going to be done properly?

 

when Matt does my next head, maybe we can put a stock head on the flow bench, then a QEP 3 angle seated head on the bench and see if we can get some qualitative results...?!

[PumaRacing 1]

Nice read, but surely the real questions is will the 3 angle seat cut by a local monkey be better than the stock single angle seat recut by a local monkey?

 

There's no guarantee of that at all. Most stock heads already have three angle seats and in many cases they are quite nicely done. They'll certainly be properly concentric, seal well and usually the seat width is very close to optimum. Anyone who just follows the factory seat when they recondition a head isn't going to make things worse at least. Where everyone goes wrong is in thinking narrow seats are good for flow and that's nearly always what you'll get from so called 'performance' work and usually those are worse than standard for flow, heat transfer and also reliability.

 

Picking up extra power just from seat work on standard heads is often very hard and takes a lot of flow bench time trying tiny changes in width and angle. What I find easiest is picking up power from 'race' heads that other people have already done and cocked up.

[petert 554]

Before you worry about the seats you should make sure the guides are OK. Anyone who offers seat work without verifying guide condition should be avoided. If the guides are stuffed there's no way the seats can be cut concentric and they'll never seal properly.

[Edd-XS 0]

So does a QEP 3 angle seat'ed head flow well?

Not that im getting one....

Edd

[Rippthrough 98]

Where everyone goes wrong is in thinking narrow seats are good for flow and that's nearly always what you'll get from so called 'performance' work and usually those are worse than standard for flow, heat transfer and also reliability.

 

You know, I've never really understood why people do that, it's obvious if the seats are much too close the flow isn't going to be able to reattach, may as well just have a single angle.

 

Why do they do it?!