Valve Job Information

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SRS_Chris
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Valve Job Information

Post by SRS_Chris » Mon Feb 12, 2018 12:44 pm

I was enjoying a cup of coffee when I stumbled across this (see below). Thoughts? I have been starting to play with seat widths, throat angles/widths, and so forth myself lately. Anyone else care to share any findings and/or general rules of thumb?

Found at this link... https://www.pistonheads.com/gassing/top ... 087429&i=0


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.
Chris Simpson
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Re: Valve Job Information

Post by Frankshaft » Mon Feb 12, 2018 1:00 pm

I strive for .0005.001 run-out. It really only needs to be as good as your guide clearance. I have done thousands of valve jobs and have seen many hundreds of those heads again, to see how guides wear, valves, seats etc. Most times, when I freshener a valve job, it requires a bump with a finish stone, and a bump with a stone on the top cut matching the angle obviously. If the seat is a bit wide yet, I set up a single angle blade that matches the bottom angle, and throat transition angle, and recut those on the machine. My valve jobs usually have 4 angles on the intake. A radius form under the seating angle on exhaust seat. I am not going to get to much into the angles, but, I will tell you, much of what you said above, I disagree with​. I can also tell you, I have personally seen how much changing a few angles can have on power out put. We're talking extreme case, as much as 100hp!! and that no bullshit. I also love telling this to guys, a flow bench is an intermediate learning tool. I get a kick out of that comment.

I should add, I am a big believer in using the machine and cutters to cut the seats, establish depths and widths, etc, and using stones for a finish truing cut. Much like boring and honing a block. There is nothing that matches it for finish or accuracy.

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Re: Valve Job Information

Post by Newold1 » Mon Feb 12, 2018 6:14 pm

Obviously this post is going to get a lot of discussion, disagreement, opinion, variation, digression, dissension, etc. and some possible confusion and a lot of varying understanding.

My learning, experience and formulation has taught me one important thing about cylinder head performance, air flow, port, bowl, throat and valve seat structure and their related affects on performance of any cylinder head- "IT'S A VERY DIFFICULT AREA OF ENGINE PERFORMANCE TO BOIL DOWN TO SOME SIMPLE RULES!" In my opinion and many others some of which are what I call "experts" opinions valve seats, throats, margins, angles, radius, throat size. depth of margins, seat widths and depth, valve back cuts and valve backside angles you are going to get a mountain of information, variation, testing, results, methods and preferences from a general question area such as this. It's going to get very complex, complicated, technical and opinionated beyond belief!

These kind of boil downs are not simple in the slightest. These type of questions and answers are going to be so totally dependent on the engine type, use, level of performance and power required, cylinder head type, valve type, valve quantity, N/A, charged, rpm ranges, fuel type, cylinder head size and configuration, etc., etc., etc., that to simplify these valve jobs down to simple methods is like trying to take all the animal species on the earth and put them into three simple types! Doesn't Work! and it's seems somewhat pretty futile to try.

I think if we are going to have some meaningful and "EDUCATIONAL" discussions of this subject we are going to have to narrow the subject matter and input. We just contribute to the overall novice, enthusiasts and semi-skilled misunderstanding and confusion that already exists in spades on the internet about this very subject, and don't always produce some good general knowledge on the subject of a "VALVE JOB"!

In any event you guys have at it. I am just going to get out my popcorn, sit back and enjoy the roller coaster ride! Have Fun!

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Re: Valve Job Information

Post by jcisworthy » Mon Feb 12, 2018 7:26 pm

To me this is one of those, where does it ever end subjects and does anyone really have the best answers. I don't think it really does end and it probably cant be said that anybody has the ultimate best answers because there are so many variables in the equation.

I spent the last year and a half developing 45* seat cutters. I went through a boat load of cutters with varying angles, widths, depths, top cuts, bottom cuts etc. In the end I have two 45* seat cutters that work well in conjunction with the chamber and bowl cutters I have. One cutter I have works better for 15* angles and less the other for 18* and higher. One bowl cutter for intakes and one for exhaust. In fact, I just got my two latest cutters last week.

Not saying they are the best or better than what anyone else has, but they work very well for all makes I have tried them on so far. I am sure each make and head casting can be tuned in better with something different but like I said, where does it all end.

My final cutters start with the chamber cutter having a radius into a single angle, the seat cutters have five angles on them, .040 wide seat, and a three angle bowl cutter for the intakes and a single radius for the exhaust. Nine angles and a radius all together for the intakes and my final designs have reasons for each.

I feel that the more I can direct the air with cutters to and past the valve while keeping each chamber cut, seat cut and bowl cut as close to the same depth one from the other the better the valve job is and the more power the heads will make.

Like it has been said, there are so many variables involved with valve jobs, locking it down to a limited criteria, I'm not so sure.

So if someone hangs the phone up on me when I say I am not using an .089" wide seat, well, ok have a nice day.
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Re: Valve Job Information

Post by modok » Mon Feb 12, 2018 9:17 pm

Good discussion.
LIFT gets left out too often. Like above the 60 VS 70 bottom angle, it's seems pretty clear the 60 will flow better at lower lifts while at higher lifts the 70 will be better, so.... what lift?
If the engine has a big valve and VERY low lift, it might even like a 52 degree lower angle and a 37 degree seat!

And then there is the "ignore low lift flow" camp, and that's possibly the way to go IF you have plenty of lift, might end up with a 50 degree seat, 75 lower angle right up to it, and that might work or it might not.

In the middle, .25-.3 lift/valve size, where most run, the valve angles approximate a radius. it does not have to be a perfect raduis but you go too far away from a radius and rarely is it better. So looking at it that way, sure, 70 is better than 60 of you have only one lower angle, because it's closer to a radius.
75 and 60, and 45 all the same width, even better.
Now you want to narrow the 45? then tilt the upper and lower angles towards it to make up for it being narrow. now maybe 72, 55. 45, 37.... or something like that. You can re-arrange it but still close to a radius.

Now what I think might be controversial today, is....it does not have to be the same all around. One side....maybe toward the center of the cylinder could have a 70 degree right up to the 45....(like the FK low lift theory0, and the other side, maybe the shrouded side, or short side? could have three wide angles under it.
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Re: Valve Job Information

Post by SRS_Chris » Mon Feb 12, 2018 10:44 pm

modok wrote:
Mon Feb 12, 2018 9:17 pm
Now what I think might be controversial today, is....it does not have to be the same all around. One side....maybe toward the center of the cylinder could have a 70 degree right up to the 45....(like the FK low lift theory0, and the other side, maybe the shrouded side, or short side? could have three wide angles under it.
This is interesting! I have seen (and experimented with) non-symmetrical throat diameters, but only below the 'cuts'. I would love to see what the pro stock and comp eliminator crowds are doing these days.
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Re: Valve Job Information

Post by ProPower engines » Tue Feb 13, 2018 12:24 am

Well hey Chris were almost neighbours. Been racing in your neck of the woods before many times in our winged sprint cars.Too bad about the sun valley track. That was a nice place to run. Old Bob started a great thing but like the same old story some one whines about about the noise.

I do some work on a regular basis for a few customers that have that high end quality of head and I can tell you that they like playing with angles, And lots of them.
The NHRA super stock engines are about the most time consuming yet restricted engines you can work on. The head rules while they seem straight forward are tedious and finicky to get perfect.
I do some iron hemi head work for a few guys here and while they can be time consuming its more fun then other basic HP head work.
And while I always hone fit every valve and try to stay under .0005 run out in all cases. Both stem and valve seat. There is the argument that the clearance will determine if its worth the time to get them perfect but IMO I believe that the extra time will just make the end result last longer as long as the rocker geometry is right.

I do dial indicate every valve stem and face every time and even the big name valve makers have something to be desired in there product quality they leave something to be desired in the amount of stem taper and runout you find at times.
Check every valve every time.
Personally I use a VGS-20. I had a serdi for a few years but sold it cause the service rep was a jack ass and I could never get it to work the way I wanted it do and found it hard to work with for HP head work but there are guys here that swear by them and have got their machines tuned in to do the higher quality work then the average job shop that don't know to cut all the seats in the head parallel to each other end to end of the head or why you would even want to do that.
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Re: Valve Job Information

Post by bentvalves » Tue Feb 13, 2018 6:46 pm

Frankshaft wrote:
Mon Feb 12, 2018 1:00 pm
I have personally seen how much changing a few angles can have on power out put. We're talking extreme case, as much as 100hp!! and that no bullshit. I also love telling this to guys, a flow bench is an intermediate learning tool. I get a kick out of that comment.

has anybody else ever seen +100hp with the "right" valve job with no bowl area blending/smoothing/radiusing?

strictly choosing the right angles and widths.

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Re: Valve Job Information

Post by cgarb » Tue Feb 13, 2018 7:04 pm

I have seen +100 HP on a set of heads with a terrible valve job being fixed. Local machinist to me, his son for whatever reason bought a set of Power Heads SBC cnc ported stock castings. You could see their ads in the 90's and early 2000's in car craft and other magazines. On an 11-1 LT1 shortblock in a chevelle they ran 14.40's. Knowing something wasn't right after a compression test, he took them off and had his father check them out. You could see daylight around most all of the valves. He threw them in the scrap dumpster and did up a bone stock set of double hump heads with small valves, 1.94/1.50 vs the 2.02/1.60 of the power heads. No porting just a good performance valve job. Car went 12.90's.

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Re: Valve Job Information

Post by user-17438 » Tue Feb 13, 2018 9:25 pm

bentvalves wrote:
Tue Feb 13, 2018 6:46 pm
Frankshaft wrote:
Mon Feb 12, 2018 1:00 pm
I have personally seen how much changing a few angles can have on power out put. We're talking extreme case, as much as 100hp!! and that no bullshit. I also love telling this to guys, a flow bench is an intermediate learning tool. I get a kick out of that comment.

has anybody else ever seen +100hp with the "right" valve job with no bowl area blending/smoothing/radiusing?

strictly choosing the right angles and widths.
Take an IHRA prostock head, and plow a 3 angle 45 degree seat valve job into it. Go to the dyno. And see what happens.. lol

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Re: Valve Job Information

Post by PackardV8 » Tue Feb 13, 2018 9:41 pm

Personally I use a VGS-20.
We've got two VGS20s in the shop at present, mostly for seats and a Kwik-Way 049 for guides.
I had a serdi for a few years but sold it cause the service rep was a jack ass and I could never get it to work the way I wanted it do and found it hard to work with for HP head work
Serdi for speed/volume production, VGS20 for precision.
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Re: Valve Job Information

Post by fdicrasto » Tue Feb 13, 2018 11:12 pm

Anybody here ever heard the term "Kenyonizing"? Goes back to the early to mid 60's and generally associated with mopar wedge drag race head prep.

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Re: Valve Job Information

Post by JoePorting » Wed Feb 14, 2018 12:30 am

I've found the Sunnen #17258 cutter to be the best 45 degree cutter. It's a 30/45/60/75/82 cutter. If you use there 82 degree bowl hog you can extend the lower angle for a few more intake CFM. All the angles are important, but I found the 30 degree top cut to be the most important cut. If it's only half in your intake flow numbers can be down by 15 CFM across the board.
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Re: Valve Job Information

Post by modok » Wed Feb 14, 2018 1:29 am

#17258 cutter, catalog says top angle is 35, not 30
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Re: Valve Job Information

Post by JoePorting » Wed Feb 14, 2018 1:38 am

Thanks. Missed that.
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