AlwaysBroken

Several years back I overheated the engine due to a radiator hose (the bottom one) rupturing on the highway (it overheated pretty much instantly). I took the head off, had a local machinist straighten it out and reinstalled it. Compression has never quite been right on the middle two cylinders since then but the car runs ok.

Anyway, I want to get a new 99-00 head or a valve job on the current head. I'm not looking to drop 3k on a race head that flows 89035105x better than stock, I just want valves that seat properly without breaking the bank. I'm in the Tampa area.

I don't currently have the ability to control VVT (I put this car together over 10 years ago) but I'm open to the idea if it's not too much of a pain in the *** and getting a 2001-2005 head will save me a bunch of money or bring huge performance gains. I understand you control the cam angle by opening/closing solenoids that control the oil pressure that the VVT part sees. Is it just RPM dependent or are there gains from adjusting angle depending on boost level?

Jeffbucc

Boosted or not? No need to break bank on Supertech valves and springs if not, any competent machinist can put a 55-60 thousands seat that will be great for many miles.

Expect around 4-600 for the valves job.

No clue on VVT.

AlwaysBroken

Yeah, sorry, car is boosted. T3/T04E .50, 18 PSI, built bottom end, ARP studs, lots of other small engine mods.

cyotani

iTrader: (8)

<p>I have oversized supertech valves and upgraded springs&nbsp;for sell if your interested. If you just want to rebuild the oem head you can reuse and recut the stock valves as long as they are within a certain spec.</p>

AlwaysBroken

In addition to the cost of valves/springs, will it complicate a valve job to use different length/diameter valves than stock?

Also, does anyone has any recommendations for a good (ie, honest and competent) machinist in this area (Tampa, FL) who can do this sort of work? I'd be willing to drive a bit to get this done properly.

patsmx5

iTrader: (16)

With running 18 PSI, valve springs would be a good idea due to high pressure on the exhaust side pre-turbo trying to push your exhaust valves open.

If I were you, and looking to do it cheap/right, have the head inspected. Shaved if needed, new guides if stock guides show any wear, change valves as needed, get the seats cut/valves ground, clearances set to spec, and use upgraded valve springs.

If you wanted to spend anymore, I'd opt for better valves and seatwork to improve flow.

patsmx5

iTrader: (16)

Bigger valves will drive the cost up a lot. The machinist will have to cut the seats larger to realize any benefit of running a larger valve. This is time consuming, and machine shop, time = money.

Joe Perez

iTrader: (8)

Any modification which changes the way the engine breathes has the potential to affect your fuel tables, depending on what ECU you're using and how it computes fuel.

This effect is likely to be small.

If you have something like a Megasquirt and are using MAP-based fuelling, you may need to tweak the VE table a tad. You could probably get close by just adding a very small linear multiplication across the board.

If you're running a MAF sensor, its unlikely that this will even matter.



Aside from that, there shouldn't be any major issues. But as others have said, the return on investment isn't huge here, and the cost to just have a shop re-cut the seats and inspect / replace valves as necessary will be a lot lower than going all-out with aftermarket valves.

AlwaysBroken

Awesome, thanks for the informative replies.

AlwaysBroken

Oh yeah, does anyone know anyone decent in the Tampa region for this sort of work?

noname4me

If you want to use a VVT head and don't have a standalone ECU which can control the cam angle, diyautotune.com sells a device called VVTuner which will control the Miata VVT solenoid with closed loop feedback control (the Miata VVT system has a cam range of about 40 degrees and the solenoid is PWM controlled).

AlwaysBroken

I'm currently running a 99 head with the exhaust cam sensor from the 97. Doesn't the VVT require a crank sensor as well to work?