That's... not how special valve jobs work or what they can do for your engine. I'll start by saying I've seen flow bench results that say the unspecified 5-angle valve job and back-cut valve gave a 65% increase in low lift flow (up to 2mm), with the effect diminishing at high lift, but still giving a 5% increase at 12.7mm. Given that increase was obtained *without* an increase in cross sectional area, it was accompanied by an increase in airspeed of a proprtional amount. This also means that port energy at that lift increased by v^2, or to 2.7x it's original amount. It's debatable how the math works out exactly inside a running engine, but what isn't debatable is that port energy fights flow reversion under all circumstances and as such increases volumetric efficiency when you have a piston rising and the inlet valve still open. The increase in flow also allows for better scavenging, as a properly tuned header will generate a negative pressure in the exhaust port at the tuned rpm, which can clear the combustion chamber of exhaust gases completely at tdc (valve overlap) if you get it right, increasing volumetric efficiency further. How do they do this? Go back to your seat and valve cross section. Rotate the picture until the valve becomes the floor. The seat now resembles a straight pipe with a 45 degree flare on one side at each end. This isn't as bad as a square edge, but it's nowhere near as good as if the flare was a bellmouth. If you cut a three angle seat (usually 30/45/60 for reasons like "I've never done any development work" and "those are the cutters I have") the angles start to approximate a bellmouth. If you do a 30 degree back-cut on the valves the the floor starts to resemble that same bellmouth. 5 angle seats do the job slightly-significantly better (depending on the port and combustion chamber) What have you got when you have a bellmouth in and a bellmouth out? A venturi. Just about the best way to give a given pipe more kinetic energy at a location you choose. Radius seats also have a flat valve sealing portion. They show an increase on a dry flow bench but don't work in practice when you have fuel going through them. Use them on exhaust seats all you like. What do these results add up to? I've heard of up to 0.2 seconds on a nominally 12-second pushrod v8 car going from a 3 generic 30/45/60 3-angle cut to a well chosen 3-angle cut with a back cut valve and a bowl blend (essentially a radius from the throat angle to the port done by hand). I suggest you read a lot more. Especially by David Vizard, man is s genius and is willing to share his secrets
I was going to ask about the radius valve seat with a single-seat, interesting that it does not work with a fluid flow, i guess this is like a surfboard rail where a round rail is used for grip as the fuel will wrap around it and a sharp edge is used for release. So I guess the atomized mix flows better over a multi-edge due to release. less of the Coandă effect.
Hey guys, not only that but he also said we wouldn't notice an extra inch on our shafts... we damn well know that is not a fact. In fact I'd go as far as to say we all would notice if we had an extra inch on our shafts. It would be life changing!
There's so many variables in this description you just gave. You sure the extra performance was down to the valve cut and not the fact that the cylinder head was cleaned up and skimmed in the first place? I cant imagine someone pulling a cylinder head just to ONLY do a valve seat cut. Then, the performance measurement is highly variable too, and is also subject to the previous variables on top. You said that the flow bench was 65% better on low lift, id like to see data regarding that tbh. What about other lift heights? Was the test done properly? How was the test done? How much extra air does that equate to during the entire valve cycle? Because I have to say, Im fairly skeptical. Seems like snakeoil if im being honest.
Thanks for explaining the 3 vs 5 angle cuts I did buy a set of Pontiac Kauffman Racing Equipment aluminum heads and the specs did say 5 angle cut these will be put on a 400 with a 461 stroker kit Im looking for an all out Torque monster with a relatively mild cam shaft. Im looking at 390 foot lbs at 3100 and 308 hp at 4500 at the rear wheels. thanks once again for your video ..
You pretty much answered my question with this vid, thanks. Unless you've a high revving engine even 3 angles aren't really needed. Old school porting, polishing etc. will do the job just as well. I've got a '68 Ford 302 V8 and have a pair of extra heads. I was considering getting all fancy with them, 3-angles etc but will leave as is and just do the ports and such.
Great vid as always Matt ! . I love the way you cut through the BS and talk about what matters. When my CB500 next needs an oil change I'm swapping the engine over with the one I rebuilt, and aside from a strip and clean, I did in fact just lap the valves back in as I understand the loss of compression and power from carbonised and warn inlet/exhaust valves etc at a basic level ( assuming I'm not misunderstanding anything ) It was working before and it will work again, and I thought what else can I do to improve it, so before I fit it I'm going to clean all the carbon out of the ports. Of course I did clean up the head around the valves and the piston crowns them selves but didn't touch the ports. As far as I was concerned a quick lap back in would suffice for a decent mate but this was an error on my part that I'll rectify before fitting. Re cutting valve seats and replacing valves to some multi faceted arrangement would seem pointless in this instance if the basics arent done. Amazing what some people will needlessly do/buy to enhance performance. What I got from this though was the benefits of a multi facet over a single face as I didn't know the actual reason for it. Good to have if it's there but no point in going after it if a good clean up will achieve more. One question though, if turbulence on inlet is good for mixing fuel/air why is porting an inlet beneficial and if you are going to how would you know that you have done it right ?. You truly are a master of your art here mate, I have learned a huge amount from you., as my three very well maintained/rebuilt motorcycles attest to without a mechanic in sight. Cheers Rich
WOW now thats a comment lol so getting straight into it - "One question though, if turbulence on inlet is good for mixing fuel/air why is porting an inlet beneficial and if you are going to how would you know that you have done it right?" Porting and port flow is something I need to cover in greater detail, as for the video above, turbulance WITHIN the cylinder is a good thing, turbulance in the port is bad. What you want is to increase the flow speed in ports. Once the charge is in the cylinder then it doesn't matter because its a dead end as far as the charge is concerned. As for is a good porting job has been done, well if they're no sticky outty bits thats a good start. As for performance and optimisation, as port need to be tested on a 'flow bench' This is something else I need to cover and demonstrate. Cheers - matt
Cylinder head flow is one of the most important aspects of engine efficiency multi angle valve seats are done for a reason they affect flow rates at different valve lifts angles seat width blending and back cutting of intake valve all can make an engine perform better most knowledgeable engine shops do this as standard practice ,in the case of 5 angles it's more detailed work that said multi faceted cutters are readily available so seats and angles are cut in one pass ,you might pay a little extra but it's worth it .
kinda pointless is taking it a bit far, getting more cfm flow with a 3 angle means more power. without actually showing head flow figures this guy is being very general/dismissive of 3 and 5 angle merits.
Interesting, regarding separation of laminar flow; texturing the surface can aid in reducing turbulence, as with glider pilots putting textured tape on the upper wing surface towards the trailing edge, as you say though: the area of turbulence at the valve seat is small and I doubt there'd be any tangible gain in performance with any sort of viable textured step/golf-ball-dimple solution.
Excellent comment - "Golf balling" as some have come to call it has also been introduced to produce force a boundary layer of turbulance in some ports, something I'm going to cover in a future video. Here's an example - i208.photobucket.com/albums/bb121/jim_ss409/dimples_3_zps8462d1dc.jpg well in the realms of OTT, but would be a good topic to cover. Funny you mension tesser tape used on trailing edges, that takes me back lol. - matt
I'll be sure to stop by and watch that. Beautiful piece of engineering there, OTT as you say, almost a shame in a way that things like that get hidden once built.
o0k cool mate, but i had a set of heads with the factory cut, i gained 32cfm flow with a 3 angle valve job, flow sheet to prove it as well, 32 cfm is a big gain mate
if you start with a shitty design, yes. Also, every tuner knows that bench cfm rate is not directly translated into performance. You can increase cfm on a bench but in a real engine it will degrade the flow.
Lol obviously. If you have a cam that's duration @050 of 230 by say 232. And 559 lift at 110 lsa, but your compression is at 9 to 1 an heads flow 250 It's gonna be trash
this is great info for me while im building my first 4 stroke engine with performance in mind. I race MX bikes and theres not alot in the way of upgrading parts so doing all of this performance tuning myself that others cant or dont have done is a really big game changer. im really interested in what you mean by "matching oil viscosity to the pump" how do you do this? maybe make a video on it if theres not one already, thanks
Hello mate, so in high end racing they firstly measure the oil pressure during running, not just on idle but mid and high revs. They then take this data and experiment with different oil viscosities. Trying to use the thinnest oil until the oil pressure starts to drop. Thinner oil requires less force to move it around the engine. This in turn means less energy extracted from the engine so more can be used to push you forward - matt
Another informative quality vid Matt. You mentioned 3 & 5 angle valve jobs & asked why not just go for a circular type cut? I believe this is offered as the ultimate vale cutting job, I've seen it referred to as a radiusing cut. I expect, as you say, if you're looking for the ultimate 0.001% in top flight racing (& money's no object) it'd be worthwhile but for those of us who are mere mortals it's just another means for tuning shops to lighten your wallet.
The radius isn't the seat it is a blend into or out of port adjacent to the valve seat ,the contact area that actually touches the face of the valve is the seat or sealing surface.
The reason why a radius isn't used is because the valve guide isn't perfectly in the centre and there's clearance between it and the valve. This means the valve won't sit perfectly in the centre and cause the valve to tip slightly
Very interesting, thank you. Is there an established order of actions that engineers take to improve a bikes performance? Like a flow-chart of diminishing returns?
Forgive my ignorance. I don't know how to concisely phrase the question. I wonder if you might consider a video explaining what limits a small bikes top speed. Are there any simple strategies to increase it slightly? Would spending £300 on a performance exhaust offering an increase of 2 HP over stock be madness? It's hard for a dumbass like me to evaluate what changes, if any, are going to have any worthwhile effect. You explain things so clearly on your channel, I'm in awe :0)
Thanks for the compliment dude, and to answer your question I'll be doing a video titled "How to make your 125 faster?" As you've probably noticed there's a ? mark in the title. I'd tell you here but its better in video format - cheers again - matt
It'd be an interesting video, I'd certainly watch it. A cheap accessible way of altering the performance of a motorcycle is gearing; changing the size of the sprockets, larger sprockets at the rear roughly equate to a trade off in top-speed in favour of swifter acceleration, the reverse is true of the front sprocket - but beware; you will be altering the clearance betwixt chain and swing-arm. Generally there won't be much of a gain in top-speed by altering stock gearing alone.
Sorry for the harrasemnt but dont know who to ask The Manual says: Do not lap the valve to the valve seat, using the grinding compound. It will come off oxide film treated surface of the valve. The Service manual only shows how to grind valve seat whit proper tools but nothing about lapping valves but if i dont lapping how can i be sure of perfect fit? Or is lapping not a must ?
I have to disagree about it not making any noticeable difference as I've had the valve seats cut on a bandit motor which made a measurable difference on the dyno 5-6 bhp however I'm told these heads are particularly restrictive here so I suppose it depends on the head. I suppose the low valve lift period of the cycle is always the bit you want to improve upon - in an ideal world we would have valves that open instantly, flow fully, then close instantly
Bollocks - 5-6 bhp on a bandit is like 5 to 6% increase. There is no fucking way on earth that just having a valve re-cut increased your output by that much.
The Workshop : What I meant was that the advice might be a bit rubbish, not the work, as it isn't the best bang for the buck in my opinion. Also it is a hell of a lot of labour for marginal results. I suppose someone with deep pockets that didn't mind having the bike off the road for a while wouldn't mind so much. I agree with your assessment.
I always laugh at this subject. A perfectly smooth curve causes turbulence and to get around the head of the valve the air basically has to make a 90°turn. Then you take into account the speed the air is traveling. You could put a million cuts on your valve seat and still be left with a shit load of turbulence.
That's... not how special valve jobs work or what they can do for your engine.
I'll start by saying I've seen flow bench results that say the unspecified 5-angle valve job and back-cut valve gave a 65% increase in low lift flow (up to 2mm), with the effect diminishing at high lift, but still giving a 5% increase at 12.7mm.
Given that increase was obtained *without* an increase in cross sectional area, it was accompanied by an increase in airspeed of a proprtional amount. This also means that port energy at that lift increased by v^2, or to 2.7x it's original amount.
It's debatable how the math works out exactly inside a running engine, but what isn't debatable is that port energy fights flow reversion under all circumstances and as such increases volumetric efficiency when you have a piston rising and the inlet valve still open.
The increase in flow also allows for better scavenging, as a properly tuned header will generate a negative pressure in the exhaust port at the tuned rpm, which can clear the combustion chamber of exhaust gases completely at tdc (valve overlap) if you get it right, increasing volumetric efficiency further.
How do they do this? Go back to your seat and valve cross section. Rotate the picture until the valve becomes the floor. The seat now resembles a straight pipe with a 45 degree flare on one side at each end. This isn't as bad as a square edge, but it's nowhere near as good as if the flare was a bellmouth. If you cut a three angle seat (usually 30/45/60 for reasons like "I've never done any development work" and "those are the cutters I have") the angles start to approximate a bellmouth. If you do a 30 degree back-cut on the valves the the floor starts to resemble that same bellmouth. 5 angle seats do the job slightly-significantly better (depending on the port and combustion chamber) What have you got when you have a bellmouth in and a bellmouth out? A venturi. Just about the best way to give a given pipe more kinetic energy at a location you choose.
Radius seats also have a flat valve sealing portion. They show an increase on a dry flow bench but don't work in practice when you have fuel going through them. Use them on exhaust seats all you like.
What do these results add up to? I've heard of up to 0.2 seconds on a nominally 12-second pushrod v8 car going from a 3 generic 30/45/60 3-angle cut to a well chosen 3-angle cut with a back cut valve and a bowl blend (essentially a radius from the throat angle to the port done by hand).
I suggest you read a lot more. Especially by David Vizard, man is s genius and is willing to share his secrets
I was going to ask about the radius valve seat with a single-seat, interesting that it does not work with a fluid flow, i guess this is like a surfboard rail where a round rail is used for grip as the fuel will wrap around it and a sharp edge is used for release. So I guess the atomized mix flows better over a multi-edge due to release. less of the Coandă effect.
thanks for the info skippy!
Hey guys, not only that but he also said we wouldn't notice an extra inch on our shafts... we damn well know that is not a fact. In fact I'd go as far as to say we all would notice if we had an extra inch on our shafts. It would be life changing!
exactly, its just another design with other target, and other disadvantages, but the guy only took one point of view.
There's so many variables in this description you just gave. You sure the extra performance was down to the valve cut and not the fact that the cylinder head was cleaned up and skimmed in the first place?
I cant imagine someone pulling a cylinder head just to ONLY do a valve seat cut.
Then, the performance measurement is highly variable too, and is also subject to the previous variables on top.
You said that the flow bench was 65% better on low lift, id like to see data regarding that tbh. What about other lift heights? Was the test done properly? How was the test done?
How much extra air does that equate to during the entire valve cycle?
Because I have to say, Im fairly skeptical. Seems like snakeoil if im being honest.
Hi Matt. I love your explanations. You cut into the BS like a hot knife through butter. Thank you so much for sharing this!
lol thanks for the comment dude - matt
Thanks for explaining the 3 vs 5 angle cuts I did buy a set of Pontiac Kauffman Racing Equipment aluminum heads and the specs did say 5 angle cut these will be put on a 400 with a 461 stroker kit Im looking for an all out Torque monster with a relatively mild cam shaft. Im looking at 390 foot lbs at 3100 and 308 hp at 4500 at the rear wheels. thanks once again for your video ..
You pretty much answered my question with this vid, thanks. Unless you've a high revving engine even 3 angles aren't really needed. Old school porting, polishing etc. will do the job just as well. I've got a '68 Ford 302 V8 and have a pair of extra heads. I was considering getting all fancy with them, 3-angles etc but will leave as is and just do the ports and such.
Great vid as always Matt ! . I love the way you cut through the BS and talk about what matters. When my CB500 next needs an oil change I'm swapping the engine over with the one I rebuilt, and aside from a strip and clean, I did in fact just lap the valves back in as I understand the loss of compression and power from carbonised and warn inlet/exhaust valves etc at a basic level ( assuming I'm not misunderstanding anything ) It was working before and it will work again, and I thought what else can I do to improve it, so before I fit it I'm going to clean all the carbon out of the ports. Of course I did clean up the head around the valves and the piston crowns them selves but didn't touch the ports. As far as I was concerned a quick lap back in would suffice for a decent mate but this was an error on my part that I'll rectify before fitting. Re cutting valve seats and replacing valves to some multi faceted arrangement would seem pointless in this instance if the basics arent done. Amazing what some people will needlessly do/buy to enhance performance. What I got from this though was the benefits of a multi facet over a single face as I didn't know the actual reason for it. Good to have if it's there but no point in going after it if a good clean up will achieve more. One question though, if turbulence on inlet is good for mixing fuel/air why is porting an inlet beneficial and if you are going to how would you know that you have done it right ?. You truly are a master of your art here mate, I have learned a huge amount from you., as my three very well maintained/rebuilt motorcycles attest to without a mechanic in sight.
Cheers
Rich
WOW now thats a comment lol so getting straight into it -
"One question though, if turbulence on inlet is good for mixing fuel/air
why is porting an inlet beneficial and if you are going to how would you
know that you have done it right?"
Porting and port flow is something I need to cover in greater detail, as for the video above, turbulance WITHIN the cylinder is a good thing, turbulance in the port is bad. What you want is to increase the flow speed in ports. Once the charge is in the cylinder then it doesn't matter because its a dead end as far as the charge is concerned.
As for is a good porting job has been done, well if they're no sticky outty bits thats a good start. As for performance and optimisation, as port need to be tested on a 'flow bench' This is something else I need to cover and demonstrate.
Cheers - matt
Definately answers that question. Cheers
Cylinder head flow is one of the most important aspects of engine efficiency multi angle valve seats are done for a reason they affect flow rates at different valve lifts angles seat width blending and back cutting of intake valve all can make an engine perform better most knowledgeable engine shops do this as standard practice ,in the case of 5 angles it's more detailed work that said multi faceted cutters are readily available so seats and angles are cut in one pass ,you might pay a little extra but it's worth it .
That's why motogp and f1 have 5 angled seats... oh no, they don't... I wonder why that is?
@@dirtygarageguy Because they run 7 angles and more FFS!!
Who does GP teams? You sure about that?
Right on. Thanks for the great info on a nebulous subject.
Love your illustration buddy. Nice and clear.
Great video. Now I’m learning! Thank you Sir!
Really good explanation. Good to know that the angled valve is kinda pointless for most situations. Won't be worried about doing that now lol.
kinda pointless is taking it a bit far, getting more cfm flow with a 3 angle means more power. without actually showing head flow figures this guy is being very general/dismissive of 3 and 5 angle merits.
Informative as always, thanks Matt. :)
Cheers dude!
Thanks for the vid I always wanted to know this but never looked it up till now. Regards Rik
So basically the recirculation bubble is creating a streamlined, but restricted path for the air.
This guy is really clear, love the videos!
Cheers mate thanks for the comment - matt
I love this video👍🏻🤣......
He said,...."it's like,...them trying to sell you, an extra inch, on your dick!!!"☝️😅😂😆🤣
I'm done....👊🤣
Interesting, regarding separation of laminar flow; texturing the surface can aid in reducing turbulence, as with glider pilots putting textured tape on the upper wing surface towards the trailing edge, as you say though: the area of turbulence at the valve seat is small and I doubt there'd be any tangible gain in performance with any sort of viable textured step/golf-ball-dimple solution.
Excellent comment - "Golf balling" as some have come to call it has also been introduced to produce force a boundary layer of turbulance in some ports, something I'm going to cover in a future video. Here's an example - i208.photobucket.com/albums/bb121/jim_ss409/dimples_3_zps8462d1dc.jpg well in the realms of OTT, but would be a good topic to cover. Funny you mension tesser tape used on trailing edges, that takes me back lol. - matt
I'll be sure to stop by and watch that. Beautiful piece of engineering there, OTT as you say, almost a shame in a way that things like that get hidden once built.
This Guy.. Boss
Good vid Matt. On the bit about circular cuts, and angled cuts, for the seats: If a bit of shite gets into either, the valve won`t close?
Yes.
ace video Matt !!!
I always look forward to the first comment lol cheers mate - matt
o0k cool mate, but i had a set of heads with the factory cut, i gained 32cfm flow with a 3 angle valve job, flow sheet to prove it as well, 32 cfm is a big gain mate
if you start with a shitty design, yes. Also, every tuner knows that bench cfm rate is not directly translated into performance. You can increase cfm on a bench but in a real engine it will degrade the flow.
Lol obviously. If you have a cam that's duration @050 of 230 by say 232. And 559 lift at 110 lsa, but your compression is at 9 to 1 an heads flow 250
It's gonna be trash
this is great info for me while im building my first 4 stroke engine with performance in mind. I race MX bikes and theres not alot in the way of upgrading parts so doing all of this performance tuning myself that others cant or dont have done is a really big game changer. im really interested in what you mean by "matching oil viscosity to the pump" how do you do this? maybe make a video on it if theres not one already, thanks
Hello mate, so in high end racing they firstly measure the oil pressure during running, not just on idle but mid and high revs. They then take this data and experiment with different oil viscosities. Trying to use the thinnest oil until the oil pressure starts to drop. Thinner oil requires less force to move it around the engine. This in turn means less energy extracted from the engine so more can be used to push you forward - matt
Very well explained thank you sir
Another informative quality vid Matt.
You mentioned 3 & 5 angle valve jobs & asked why not just go for a circular type cut?
I believe this is offered as the ultimate vale cutting job, I've seen it referred to as a radiusing cut.
I expect, as you say, if you're looking for the ultimate 0.001% in top flight racing (& money's no object) it'd be worthwhile
but for those of us who are mere mortals it's just another means for tuning shops to lighten your wallet.
The radius isn't the seat it is a blend into or out of port adjacent to the valve seat ,the contact area that actually touches the face of the valve is the seat or sealing surface.
The reason why a radius isn't used is because the valve guide isn't perfectly in the centre and there's clearance between it and the valve. This means the valve won't sit perfectly in the centre and cause the valve to tip slightly
Very interesting, thank you. Is there an established order of actions that engineers take to improve a bikes performance? Like a flow-chart of diminishing returns?
Do you mean in cost or performance?
Forgive my ignorance. I don't know how to concisely phrase the question. I wonder if you might consider a video explaining what limits a small bikes top speed. Are there any simple strategies to increase it slightly? Would spending £300 on a performance exhaust offering an increase of 2 HP over stock be madness? It's hard for a dumbass like me to evaluate what changes, if any, are going to have any worthwhile effect. You explain things so clearly on your channel, I'm in awe :0)
Thanks for the compliment dude, and to answer your question I'll be doing a video titled "How to make your 125 faster?" As you've probably noticed there's a ? mark in the title. I'd tell you here but its better in video format - cheers again - matt
Brilliant, thank you very much. Looking forward to that :)
It'd be an interesting video, I'd certainly watch it. A cheap accessible way of altering the performance of a motorcycle is gearing; changing the size of the sprockets, larger sprockets at the rear roughly equate to a trade off in top-speed in favour of swifter acceleration, the reverse is true of the front sprocket - but beware; you will be altering the clearance betwixt chain and swing-arm. Generally there won't be much of a gain in top-speed by altering stock gearing alone.
thanks
An extra inch on I would definitely notice that😂😂😂😂
yeah, mrs with be stoked with twice the length.
I don't know what crappy ass engines you're running, but a 3 and 5 angle valve job done properly absolutely will produce more horsepower!!
Provide proof
@@dirtygarageguy There's all kinds of proof out there, and has been for 50 years now. Try harder.
@@Anarchy-Is-Liberty proof on farting tractor v8s?
Donkey power. Lol🤣
thanks for making this :}
Great video.
But should i lap my ti valves with coating or is it just steel valves that can be lapped to the head?
Its for a KX450f
look in the manual, I don't know what alloy it is
Sorry for the harrasemnt but dont know who to ask
The Manual says:
Do not lap the valve to the valve seat, using the
grinding compound. It will come off oxide film
treated surface of the valve.
The Service manual only shows how to grind valve seat whit proper tools but nothing about lapping valves but if i dont lapping how can i be sure of perfect fit?
Or is lapping not a must ?
Lapping isn't a must, try doing a leak down test
Ok ill start with that, and i bought the paper service manual its fuking amazing to have! thanks
Use some dye and find out if the valve is seating completely. That’s the only way to see besides the leak down.
I have to disagree about it not making any noticeable difference as I've had the valve seats cut on a bandit motor which made a measurable difference on the dyno 5-6 bhp however I'm told these heads are particularly restrictive here so I suppose it depends on the head. I suppose the low valve lift period of the cycle is always the bit you want to improve upon - in an ideal world we would have valves that open instantly, flow fully, then close instantly
Bollocks - 5-6 bhp on a bandit is like 5 to 6% increase. There is no fucking way on earth that just having a valve re-cut increased your output by that much.
no moter
big white board no stinger lol
If someone tried to sell someone on such rubbish I would say it is important to find a new shop. 😂
Its not rubbish, it does make a difference, its just how much of a difference. Fuck all. And the price paid is OTT!
The Workshop : What I meant was that the advice might be a bit rubbish, not the work, as it isn't the best bang for the buck in my opinion. Also it is a hell of a lot of labour for marginal results. I suppose someone with deep pockets that didn't mind having the bike off the road for a while wouldn't mind so much. I agree with your assessment.
same don't fuck over people
I always laugh at this subject. A perfectly smooth curve causes turbulence and to get around the head of the valve the air basically has to make a 90°turn. Then you take into account the speed the air is traveling. You could put a million cuts on your valve seat and still be left with a shit load of turbulence.