Icedawg

I have a JDM 1999 1.6 L Miata engine, an NB6. I bought it to put it into an Ice Racer, running the old 323 GT B6T turbo setup.
I have put 1990 Miata engines in the car previously and they worked out well.

But this newer engine has solid lifters and a different intake cam, marked B6KA, where all the older HLA 1.6 L cars had a cam marked B660, with slightly different grinds depending on the car (Miata, vs Protege,vs Capri turbo, vs 323 GT turbo)

So I am running a distributor. But the new intake cam no longer has the extended shaft to connect to the distributor. The race season starts in two weeks and I am not going to try to swap over to crank angle sensors and aftermarket ECU's and all that entails in the time frame.

I am looking at swapping a 1990 Miata intake cam in to replace the B6KA cam. The base circle dimensions are the same, but the lift is 9 thou higher on the older cam. (I note the valve stems were 10 thou shorter on the 90 head than the 99 head). The duration may be the same or different, it is hard to tell by eyeball.

I see advice on this forum that the HLA vs solid lifter cams in the 1.8 L are not a good swap. But I also see that the base circles are different for these two cams, as is the duration, and the timing. So I can see where a lot is changing in making that swap possibly difficult for the 1.8 L.

I have spoken to a friend who is Mazda mechanic, and he thinks the swap should work; that any profile differences for the 1.6 L will be done to give a bit more gentle attack on the rising and falling rates for the solid lifters, so at worst it will create a bit more valve train noise. There is enough clearance for the 9 thou greater lift. And I was able to adjust the lash to 8 thou with the older cam, which is the solid lifter spec for the 1.6 L intake.

Does anyone know enough about the grinds on the solid vs HLA cams in the 1.6 L to know if this swap might be a disaster?

HarryB

Difference on lift on itself is negligible, given that you can set the lash right. If timing is OK, I would run it.

sixshooter

iTrader: (12)

Send it.

Icedawg

So I installed the 1990-91 1.6 L intake camshaft in the 99 1.6 L JDM head. Kept the solid lifters, and 99 valves.
Mounted the distributor, and ran the engine at idle for 40 minutes.
It worked!
Rough at first but as it warmed up it settled into a nice steady idle. A little bit of valve train noise, but not much different than any other B series I have used.
Responded OK to a few throttle blips. Easy to set the advance on the timing.

Seems good so far. But since it is not a street legal car I will have to wait for a track to truly test it out.

sixshooter

iTrader: (12)

Did you set your valve lash?

Icedawg

Yeah, set to 8 thou, either a tight fit of the gauge, or a looser fit, but bigger than 7 and smaller than 9.

All of the intake shims had to go up by a few thou, but I think that was specific to this cam. Mazda specs the 90-93 cams at 1.300" on the base circle, but this one was 2-3 thou smaller for some reason. No obvious wear on it, though. The lift was also about 2 thou smaller than Mazda specs for the NA 1.6 L.

Oh, and just for the record, there was plenty of clearance for the cam lobes over the "valve bucket region", for lack of the right name in my head at the moment.

Icedawg

The engine survived it's first race weekend!
Pleased with that.
Weekend two is coming up right now.
It pulled nicely, but still had some blow by, like the last 3 engines, which I was hoping this one might not show.
The engine has good compression, and ~ 2% leakdown.

The reflashed stock 323 GT turbo ECU goes to an AFR of ~ 10 at WOT and 10 psi of boost (full boost is 10 psi on this set up). Is there any chance being so rich could contribute to the blow by, and the nasty foam I collect from the head?
For instance, could it lead to a bit of cylinder washing that gives lower quality ring seal? Is that thing?
Or could the excess fuel be why the foam is so nasty, when collected?
Or is it just inherent when spending so much time at WOT?

sixshooter

iTrader: (12)

Shoot for 11 or 11.5. Cylinder washing is real. And your power will be down from being too rich.

Icedawg

Thanks for the info.
I have no option to change the ecu, without it being a big job. The re-chipped original stock ecu is pretty much unadjustable at this point in history. And switching over to a mega squirt or something would be a fairly involved job, given how the old stock system was put together. Not to mention costing money. For an ice racer.

As far as power goes, I can advance the timing from stock 10°, or turn up the boost from 10 psi, butI can already spin the wheels in any gear!

But if the AFR of 10 is part of the blow by problem, through cylinder wash down, that might make the rest of the effort worthwhile.
Do you know of any way to tell?