mx5cartalk.com

Hi guys,

My car is back on the road driving again, I’m just not sure it is 100% right yet.
I recently had the head machined and its bolted back to the block with a stock MLS head gasket. The engine starts well, sounds good and all seems quite good.

I made sure all the timing is correct but with the head now slightly closer to the crank I assume the cam timing is slightly mechanically advanced.
Has anyone else got experience with this? Will this advance be beneficial or degrade performance? I am running a small GT2560R turbo and up to 1 bar of boost.
When I first drove the car after the head rebuild I thought the car was a bit sluggish compared to before. I had BP 98 fuel in it that was now over a month old so thought this might be an issue, I drained the tank and refilled with some fresh 98 which I think helped but didn’t totally fix it. I also noticed the A/F gauge is going very rich higher in the rev range when on boost with no change to my fuel maps (that were fine before the head work).

I am thinking about getting a set of adjustable cam gears to bring the cams back to TDC when the crank is TDC.
Has anyone used the China spec ones for cheap cheap?
http://www.ebay.com.au/itm/for-MAZDA-Mi ... 1c30ceb2db
http://www.ebay.com.au/itm/ADJUSTABLE-C ... 3a8bcd3c94

Or is it worth the extra cash and pay twice as much for some Toda gears?
http://949racing.com/toda-cam-gear-miata.aspx

Any thoughts?

Zoom zoom tried cheap ones and didn't have much luck.

Being a nb head I assume your still running the cam sensor at the front of the intake cam so make sure you get a wheel with the sensor triggers in it.

I wouldn't have thought the shave would have been to cause major changes though? How much came off?


Sent from my iPhone using Tapatalk

Thanks, I am still using the cam sensor and the gear variants I found all had the triggers on them.
What didn’t you have much luck with? The cheap gears specifically or changing the cam timing?

I didn’t think the head work would have made toooo much of a difference but you can see some material has been removed so assume there will be some (very small) cam timing change. That and a slight compression increase which didn’t think would make too much of a difference.
I’m not 100% how much they removed, they said somewhere between 5-10 thou. When I spoke to the head machinist he said the timing won’t have changed by enough to affect anything.

I can't remember exactly what Zoom zoom said he had problems with on the cheap gears but ended up replacing them with quality units.

Adjustable can gears certainly can work.

Absolutely nothing else has changed?


Sent from my iPhone using Tapatalk

read point 6 on this link. http://www.solomiata.com/CheapHP.html update 6/23/98
and also the bottom of this page http://www.solomiata.com/cams.html
cam pulleys are around 360mm circumference (roughly measured with a tape measure)
removal of 010" material from head will create .020" (.5mm) more slack in belt.
which will be taken up by the tensioner retarding the timing
by ~.5 camshaft or 1 crankshaft degrees

Removing .010" will bring the exhaust cam pulley .010" closer to the crank pulley. It's this distance alone that sets the cam timing. About .050' shaved will retard the timing by 1 degree - i.e. trivial. .005 to .010 is way less than trivial.

Thanks for the responses and info guys.

I have bought a set of adjustable cam gears and a new Gates "racing" timeing belt so am going to redo all the timing and just check everything again. (I'm getting quick at it now...)

Has anyone played around with cam timing on a FI engine? They say you get better top end power with the cams 6-8˚ retarded and better low end torque with them slightly advanced but what about on a FI car?

At this stage I was just going to get everything as close to TDC as possibe and leave it at that.

Just to close this off,
I installed the new belt and cam gears, dialed them in and got it all bolted back together.

It has never run so well, the power feels great and it's running smoother than ever. Job done!