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Old 01-27-2010, 06:00 PM   #21
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Realistically, if you get new valves then don't you have to get a valve job anyway? Not that I really kmow what I'm talking about, but it seems like anytime you can use your old **** the better. 3 angle and valve cut on current valves. Then again, everyone seems to think the 120 premium I paid over a straight stock rebuild and clean for the back cut and 3 angle is a really good deal. I might cost others a lot more. Then new valves could be better cheaper option.
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Old 01-27-2010, 06:02 PM   #22
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Originally Posted by psiturbo View Post
Tell that to all the people on the racetrack who are doing 10s and 11s on stock cylinder heads...
I think you're also missing the point in that we are traditionally a DIY bunch, and a few of the items on the list can be done in your garage with a dremel.

Granted those items are relegated to the end of the list...but they're free. That's bang for your buck right there.
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Old 01-27-2010, 06:06 PM   #23
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Realistically, if you get new valves then don't you have to get a valve job anyway? Not that I really kmow what I'm talking about, but it seems like anytime you can use your old **** the better. 3 angle and valve cut on current valves. Then again, everyone seems to think the 120 premium I paid over a straight stock rebuild and clean for the back cut and 3 angle is a really good deal. I might cost others a lot more. Then new valves could be better cheaper option.

Even if all that work only netted you 6 ponies...that's the cheapest horsepower you will ever find at $20/hp.


That's on par (or better) than the dollar/whp ratio most of us get out of turbocharging...might as well keep going at that rate.

I've seen free P&P work net 15-20whp, and I'm sure the work you paid for is in that neighborhood.

To me the point of diminishing returns is a little higher cost than what we're talking about here, and this is for street usage and seat of the pants gratification...not dyno bragging rights or quarter mile times.
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Old 01-27-2010, 06:14 PM   #24
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Originally Posted by djp0623 View Post
Realistically, if you get new valves then don't you have to get a valve job anyway? Not that I really kmow what I'm talking about, but it seems like anytime you can use your old **** the better. 3 angle and valve cut on current valves. Then again, everyone seems to think the 120 premium I paid over a straight stock rebuild and clean for the back cut and 3 angle is a really good deal. I might cost others a lot more. Then new valves could be better cheaper option.
The 3 angle valve job is done to the valve seats in the head; you still need to resurface the valve seats (either single angle, 3 angle, 5 angle or radiused angle) even if you put in new valves or they won't seat properly. With new hi-po valves, you won't need the back cut operation but the machinist will probably make a light truing cut on the new valve face to ensure a perfect match with the seat. I think you got a good price on your work; don't forget that the machinist had to disassemble all 16 valves out the head and reassemble everything again after the valve and seat machining.
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Old 01-27-2010, 06:29 PM   #25
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They completely left out blending the back of the seat into the port. Thats like the #1 cheap and "easy*" flow increase.
Ah yes, this fits in after supertech valves and is part of "some mad skillz".
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Old 01-27-2010, 06:52 PM   #26
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If Pat were here he would argue about the 3 angle job being worthwhile. He and a lot of others, in the research I've been doing for my build I'm starting, say the 3 angle jobs don't do much for FI motors flow. Cleaning up the combustion chamber, deshrouding, cleaning up casting flaws, rounding the sharp turn to the intake valves are all good DIY projects that should see some returns. Polishing the combustion chamber helps keep carbon down and eliminating casting flaws and reducing sharp edges in the combustion chamber help eliminate hot spots that can lead to detonation. Instructions for that are all in that DIY head work link.

Note I'm not speaking from experience but regurgitating the knowledge shared by others.
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Old 01-27-2010, 06:54 PM   #27
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Just to kill this dead in case it comes out.

It is BS to say that "air is pushed in by the compressor so headwork doesn't help".
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Old 01-27-2010, 06:59 PM   #28
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If pat claimed that I would say he is retarded. VJ is one of the single most important parts of a head. Probably 70-80% of the gains are right there.
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Old 01-27-2010, 07:24 PM   #29
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Agreed. The best measurement of a head/port flow is total area under the flow curve NOT peak flow. Low lift flow (which is what the valve backcut and multi-angle valve job really enhance) is important because the cylinder "sees it" twice (valve opening and closing).
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Old 01-27-2010, 07:54 PM   #30
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An internal combustion engine is just a glorified air pumping system. Total system throughput is only as good as the weakest link. What good is 250CFM of custom intake runner going to do on a cylinder head that only flows 180CFM on the intake port? Cam lift beyond where the port stalls is useless and a long duration cam on a doggy port yields a peaky power curve with no low end and mid range torque.
What he said. To be nitpicky, it's not " throughput is only as good as the weakest link", it's, total flow resistance is the sum of the individual resistances.

Porting acts a bit like extra displacement, or like having extra cam duration without the low-end penalty.
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Old 01-27-2010, 08:04 PM   #31
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What he said. To be nitpicky, it's not " throughput is only as good as the weakest link", it's, total flow resistance is the sum of the individual resistances.
Unless one of the restrictions in the flow is a relatively huge restriction that dominates the others, then anyone that has taken a fluids class understands this to be true.
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Old 01-30-2010, 02:29 PM   #32
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I've had a 3 angle cut (the angles make a difference), back cut, deshrouded, mildly bowl blended, gasket matched head on a turbo bp before and it made 8psi feel like what 12psi felt like before the work. No dyno graphs but the time to cover a specific distance (a certain on ramp) was about equal to ~.1 of a sec.

That work cost $400 with me removing the cams (to save assembly time) and doing the gasket matching myself. I did this as I burned 6 exh valves and was rebuilding anyways.

It really helped spool and made the car very rev happy.
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Old 01-30-2010, 09:32 PM   #33
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Guys, an old friend used to cut valve seats at his home shop. Anyone here do it? Use stones or bladed cutters? Hand or machine? Got a link to a supplier? What about the valves themselves? I find myself in possession of a few too many heads/engines, and would like to tinker. I don't mind the thought of an investment in some tools if I got a chance to use them.
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Old 02-01-2010, 11:16 AM   #34
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Originally Posted by webby459 View Post
Guys, an old friend used to cut valve seats at his home shop. Anyone here do it? Use stones or bladed cutters? Hand or machine? Got a link to a supplier? What about the valves themselves? I find myself in possession of a few too many heads/engines, and would like to tinker. I don't mind the thought of an investment in some tools if I got a chance to use them.
Bumping this, because I want one of the smart guys to read it and fill me in.
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Old 02-01-2010, 11:49 AM   #35
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Default Sioux Valve Grinders

Do a goggle search on Sioux Valve Grinders or refacers. You can find used Sioux equipment on both Craigslist & Ebay and new stones are still available. My high school auto shop had a Sioux setup that we used for valve jobs. The Sioux uses a piloted stone to grind the seats in the head (pilot was inserted in the valve guide to center the stone on the seat). Quality is somewhat dependent on operator skill in using the device and selecting the proper stone. Valve faces can be cut on a specialized Sioux tool or else in a lathe (either using a turning tool or a toolpost grinder).

A lot of better shops and racing engine builders now use Serdi valve seat refacing machines which do a better job of centering on the valve seat and can also to be used open the throat right below the valve seat.
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Old 02-01-2010, 12:09 PM   #36
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sn95, thanks. So, you used the stone cutters yourself? How often do they need to be redressed? I would be concerned of them losing accuracy over time. Come to think of it, and poking around on the internet, I think my friend and I used the Neway style, with the cutter blades, manually driven with a pilot down the guide. Were the Sioux cutters you used manually driven? They are a lot cheaper than the Neway blade style.

Looking at it, it appears that the Sioux stones are power driven, can you confirm? So, the best option may be to get a kit from ebay with the driver, then pick up the stones you need new.
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Old 02-01-2010, 12:09 PM   #37
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Also the new serdi machines dont use grinding stones. They cut the valve with carbide tools similar to what you would find on a high quality lathe. This allows them to get a MUCH better surface finish which seals 100%. Also it allows them to get seat angle exact. Not a machine that people typically have in their garage.
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Old 02-01-2010, 12:37 PM   #38
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Anyone know what one of those Serdi Micro machines cost? It's like the Neway cutter with a fixture, instead of being handheld. Put another way, it's like a big Serdi machine without the big, and without the drive. Looks like the benefit of something like the Serdi is that you can control cut depth. With a Neway, you either need to keep measuring or hope for the best!

It seems like a manual Neway cutter would be a decent way to go for small volume. As long as you have good guides and lap the valve well afterwards, you should be able to ensure concentricity reasonably well. One diameter, three cutters (one for each angle) would do it for any Miata engine.
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Old 02-01-2010, 05:01 PM   #39
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Originally Posted by webby459 View Post
Anyone know what one of those Serdi Micro machines cost? It's like the Neway cutter with a fixture, instead of being handheld. Put another way, it's like a big Serdi machine without the big, and without the drive. Looks like the benefit of something like the Serdi is that you can control cut depth. With a Neway, you either need to keep measuring or hope for the best!

It seems like a manual Neway cutter would be a decent way to go for small volume. As long as you have good guides and lap the valve well afterwards, you should be able to ensure concentricity reasonably well. One diameter, three cutters (one for each angle) would do it for any Miata engine.
Do some more google searches and you'll see that a lot of people still doing old style valve grinding think the Neway stuff is ****. AFAIK, the Serdi micro is about $3k and that is lot of money to pay for a very small lightweight fixture that doesn't seem to have much rigidity or mass (very important for even and concentric seat angles, especially when cutting hardened seats). The "real" Serdi valve machines are substantial machine tools and have Serdi's floating air cushion system which helps keep the seats even and concentric even if the guide isn't perfectly centered within the seat.

A used Sioux is still probably the cheapest way to try DIY valve grinding; you just need to be patient and keep watching Craigslist and Ebay. You are going to have to educate yourself on how the Sioux style grinder works, how to measure valve seat widths/angles, how to check pilots (used pilots may be worn & sloppy HSS, carbide pilots last much longer), which stones to use and how to dress stones. Probably easier than the learning curve on a engine lathe and dressing grinding stones is a lot easier than grinding your own HSS lathe toolbits!

FWIW, unless I stumble across one of these at an absolute giveaway price, I'm not in the market.

Edit,

The Sioux power units are either electric or air powered and look a bit like a big angle grinder without the wheel. The stones are chucked up with a pilot, the pilot goes in the valve guide and ya start grinding.

Last edited by sn95; 02-01-2010 at 05:04 PM. Reason: Clarification
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Old 02-05-2010, 09:36 AM   #40
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its another one of those pressure differential things, more boost always = more power. almost always..
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