head porting bang for the bux trix
 

What I learned, in rough order of bang for the buck/time

1) Of all the head porting trix the most bang for the buck is indeed to backcut the intake valves.
2) Next is to just pay extra for Supertech intake valves if the intake valves need replacing.
3) Next is a 3 angle job, esp. if you're doing a valve job already
4) Next is if the exh valves need replacing AND a 3 angle job is planned, pay extra and get +1mm Supertech exh valves.
(Rebello tells me that +1mm intake valves need to have extra bowl work to make em flow better than standard.)

After that some mad skillz are necessary to do it right:
5) Blending back of seat into throat
6) Other Bowl work
7) That ridge in the short side when the air makes a turn.
8) Then teardropping the guides.
9) After that is their top secret labor intensive stuff

The most common problem in medium and hi miles heads is leaky exhaust valves.
I've seen this on 4 miatas now.

how to test

Lay the head on its side and point the exhaust ports up. Pick the 2 or 3 cylinders whose valves are closed and the lobes are pointing away from the valves. Pour some kerosene or thin oil or spirits into the ports. Watch for weeping into the combustion chamber. I'll bet you a donut some or most of the exh valves will weep, and the intake valves are fine.

Turn cams to close other valves. Repeat test on them.

With leaky valves turn cam to max lift and look at valve seating mating surfaces. Mating surfaces should be a shiny unbroken ring. Look for telltalle little burn marks in this ring, especially on the exhaust valve. There's your leaks. If none, look for dirt that prevents seating, clean it out, repeat leak test.


If you get some weeping (but not dripping lol), the cheapass way to fix it is to lap the exhaust valves by hand yourself. This will improve your leakdown and increase the life of the valves. While your at it, check the guides by checking how much side to side play the exh valve heads have.

I like this post, especially the leak test. If upgrading to a 1.8 didn't yield such better results, I'd be doing this.

They completely left out blending the back of the seat into the port. Thats like the #1 cheap and "easy*" flow increase.


*easy assumes you have a steady hand and experience porting heads.

EDIT: To add more, it almost doesn't matter a whole lot for uber porting anyway. The stock lift on miata heads is so low that you will never see the flow ranges that you can achieve with anything really beyond a vj and some mild porting.

Does anyone have pictures to illustrate these concepts (bowl blending, blend the seat into the port, etc.)?

/n00b

What a timely article...I've been out in the garage with a Dremel every night this week.

+1 on what neo said about blending the valve seat with the bowl. I was very surprised to see how big that lip can be...it's almost as bad as a 2.5" gasket in a 3" exhaust pipe...

For bowl blending check Hakuna's page koto.

Other than that I'm just taking casting roughness out, and doing a little deshrouding in the combustion chamber.

I don't disagree with the generalizations listed above, but it would be helpful if there were some flow bench numbers for a 1.8L head that detailed the gains associated with the various steps. Does anyone have flow bench numbers (@ 28" water) showing the intake and exhaust flow of a stock 1.8 head at .100, .200, .300, .400 & .500 lift that they can post up??

.400 and def .500 are basically useless to the majority of miata owners for the pure fact that they will never invest the money to ever realize those flow ranges.

True dat on the absolute lift with standard valve train. For trending and seeing where the port stalls, it would be nice to see .350 and then .400. Numbers anyone???

You will find this community is to...frugal... with their money to get results like that. I've ported heads and seen gains, but even I didn't want to pay for flow benching. It's highly overpriced. The vast majority of users, even here where performance is king, have 0 headwork on their cars.

I like #1 since I just payed to have my valves back cut, and #3 since that was done as well.

How much did your machine shop charge to back the 8 intake valves?? Do you have before and after pictures???

Head diassemble, reassemble, 3 angle valve job and back cut valves both intake and exhaust $320 I do not have before and after pics of the valve work. I will have after pics later.

I would pay for pictures since I could do the job at work with a little guidance and measurements.

Too much to ask that you remove one valve and attack it with some calipers for me?

Here's a start:

This site is focused on SBF Ford wedge heads but provides an overview of the tools required for porting, shows how to make port molds, how to blend the valve seat to throat transition, how to streamline the valve guide etc.

diyPorting.com

Standard Abrasives DIY head porting guide (Very basic porting, mostly smoothing and gasket matching)...
http://www.pirate4x4.com/tech/billav...0Abrasives.pdf


Engine Blueprinting book by Rick Voeglin has a decent chapter on cylinder head prep which includes some porting basics.

Not to contradict the postings about head work.

What I ask myself when I read all the above is if this car will be running the quarter mile in 9 seconds or is it been prepped to be a dyno bitch to see if it reaches 600 hp etc or whatever.

What I am trying to say is I have seen plenty of cars with UNTOUCHED cylinder heads doing 10 and 11 seconds, of course the engine has forged rods and pistons. I sometimes think porting is over-rated and unless every last drop of HP is the goal there really is no need to even touch those cylinder heads.

Do not misinterpret what I am saying, hey if you got the money go ahead and get yourself a badass port work. I think much more can be attained with a custom made intake manifold, bigger throttle body, cam (integralcams.com) etc. IMO, I would not touch at all the cylinder head... just my two cents.

+1 I think most of us can just turn up the boost if we want a little more, instead of spending $$$$ on max efficiency

but you guys miss the point.

it's right there in the thread title.

"bang for the bux"

in other words, do them in the order posted if you're doing it on the cheap.

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.

Burp
 

Tell that to all the people on the racetrack who are doing 10s and 11s on stock cylinder heads...

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 shit 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.

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.

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.

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.

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

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.

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".

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.

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).

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.

:werd: 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.

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.

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.

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.

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.

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.

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 shit. 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.

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