miatauser884

iTrader: (11)

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.

gospeed81

iTrader: (51)

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.

gospeed81

iTrader: (51)

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.

sn95

iTrader: (2)

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.

JasonC SBB

Ah yes, this fits in after supertech valves and is part of "some mad skillz".

cueball1

iTrader: (13)

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.

JasonC SBB

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".

neogenesis2004

iTrader: (12)

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.

sn95

iTrader: (2)

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).

JasonC SBB

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.

ZX-Tex

iTrader: (15)

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.

inferno94

iTrader: (2)

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.

webby459

iTrader: (8)

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.

webby459

iTrader: (8)

Bumping this, because I want one of the smart guys to read it and fill me in.

sn95

iTrader: (2)

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.

webby459

iTrader: (8)

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.

neogenesis2004

iTrader: (12)

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.

webby459

iTrader: (8)

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.

sn95

iTrader: (2)

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.

mrtbon

iTrader: (1)

its another one of those pressure differential things, more boost always = more power. almost always..