'94-'95 blocks have this passage drilled from the factory as well. They stopped doing it midway through 1995.

next lets discuss how to convert a bp4w to 1.6
allz you gotta do is weld up the cylinders, then hone em out, and voila, supercar revs

If you get it right, you gain some perceived benefit from pulling the oil from that location vs. from the other side of the motor. More oil pressure to the crank mains, but how much oil pressure are you actually losing off a 40" -4AN line pushing against an .030" restrictor?

If you get it wrong, you scrap a fairly substantial amount of money in engine seals/gaskets, plus a set of bearings and probably a set of rod bolts, plus the cost of the block itself, plus the cost of re-doing all the bore/hone machine work. If you value your time at anything more than minimum wage, you're looking at $1k+ to replace the block if your hand drill deviates substantially.

How do you plan to clean the passage out afterwards? Run the engine with the port unplugged? Use air pressure with the oil filter unplugged and then re-prime the motor afterwards?

All this for what? Have you actually measured the benefit of not pulling from the passenger side?

Who are we even talking to? I was drinking beer, watching supercross, and posting in a three year old thread. I forgot what the question was now. Pass me the chicharrones.

If you were doing this you'd do it on the block before rebuilding it when the block was bare. You do gain the nice benefit of not having an oil line cross the back of the engine and avoid all the oil pressure sender T breaking off issues or the leaky cheap sandwich plate issues.

oil supply
 

I have a 96 na8 block converted to turbo, using the oil sensor port for oil supply - Eng no BP22..... in a Clubbie. As a backup for a rebuild I have just bought off fleabay whats described as a JDM engine, no BP88.... and on inspection it has at the left rear of the block a bolt plugging the outlet described as an oil supply used by the 323GTX etc. Despite the engine no being higher than the 96 it looks like it might be a 94 or 95 block?

jp

If by "higher" you mean the distance from the bottom of the oil pan to the top of the valve cover, all 1.8L BP engines, including all Miata engines from 1994 - 2005, are identical in this measurement (excepting the protrusion of the oil control solenoid on the top of the VVT engines.)

They all had the same bore and stroke, the same rod length, and the same basic head-casting dimensions (although the '99 and later heads had a much superior internal port shape.)

The block casting of all 1.8L BP engines is identical. The only differences are in the machining; the early blocks (as well as the '04-'05 MSM blocks) had the holes cut for oil and coolant on the exhaust side, and the very late engines had a little extra machine work done at the bottom to accommodate the main bearing support plate.

oil thread
 

By 'higher' I meant the number of the engine . The block I am sure is 96 is stamped BP22xxxx, while the unknown one is BP88xxxx, but this one looks like a 95 because it has the turbo feed gallery drilled.
Was NOT talking of block height!

jp

Interesting.

Very little data exists (on English-speaking forums, at least) concerning JDM Miata engines, mostly because apart from the intake manifold on the NB models, they are wholly unremarkable. This isn't Hondaland, where the North American market got watered-down weaksauce while the JDM cars were fitted with monster powerplants.

I can't see any reason why Mazda would have continued machining the turbo oil passage on blocks destined for RHD cars, but I can''t find any data to prove otherwise. By the same token, there is no universal registry of engine numbers that I'm aware of...

I'll see if I can sneak a peak at a JDM NB 1.8 motor to verify some what but I doubt it has the oil passage tapped on the exhaust side.

My NB B6 doesn't have it tapped.

No clear answer? In 10 years???
 

I had just read through all of these posts and there was still no clear answer on if teeing off the back of the head on a BP4W would starve the valve train of oil other than a maybe lol. I personally wouldn’t see a problem with doing so since the valve train wouldn’t necessarily need as much pressure as the bottom end does for it to keep the clearances on the rods and crank. I know the cams have floating bearings and need the pressure, but do they need as much as the bottom end since Mazda had put in that restriction.

Also would there be any benefits on running a vvt oil pump then opening up the restrictions a tiny bit to allow more oil up top to possibly counter act the loss of pressure when teeing off the head to a turbo.

With that being said I’m just going to full send and tap off the head with no changes at all and see what happens, I’ve got a jank BP4W with Eagle rods, that had surface rust and slight pitting, and CP pistons that came with the rods from a $250 motor. I took those rods and pistons and slapped it in a running 96 1.8 block I got for $180 and put in some new bearings but no machining so I wouldn’t be losing too much for science if anything goes wrong. Although I did get the head machined and the whole point of this test is to see if the head is starved of oil…

Anyway it’s been running strong with a 52mm eBay turbo until today when the turbo gave out, so I just ordered a new slightly less cheap eBay turbo and wanted to change the oil feed location cause I hate how the line goes around the motor, so wish me luck if anyone ever comes across this dead thread

I just tried to measure oil pressure from an oil galley on the head on a recent build. The sensor only saw 10-20psi at that location. Move it to the stock OP site, and it’s seeing typical 30-80psi. Use that info however you’d like.

Appreciate curly, that seems to be a massive difference, I may stay with the tee at the OPS but what motor was this test on? Did you have hydraulic lifters or solid lifters? I wonder if they’d be any different even though the block restrictions are the same. I wish the BP4W blocks had that passage on the driver side, it would be so much easier to make it look good.

Although with less pressure in the head the turbo shouldn’t rob so so much especially with a restriction plate, would it even matter? I’m still very torn between this, I guess when I get everything installed I can do my own testing and report back.

I have 43K miles on my turboed BP4W with oil drawn from the driver's side port on the rear of the head (the subject of this thread, and I'm the OP).

Engine is stock and the head has never been off.

I moved the oil pressure switch from the block to the passenger side port on the rear of the head. This switch purportedly activates at 7psi. It goes off within a second of engine start-up and stays off as long as the engine is running.

The turbo is a TD04 (Subie) with a 1mm restricter.

Make a decision and go with it. Squirrels die from indecision.

DNM

Alright sounds good enough to me, I’ll go ahead and use the port from the head