Anyone ever put one on a flow bench? Curious about what the flow rate is compared to a stock BP05 head. Everyone says the flow much better but I want to see the numbers.

 

Its not just the head, but the angle at which the air flows through the manifold and through the head. an 05 head is damn near a 90* corner into the valve, where the 4w is more like 78. Or something similar. I seem to remember the port being raised 22 degrees on the 4w. Anyone else, am I way off here?

 

<p>I have flow bench data of a stock bp4w head and will post it up when I get home today.&nbsp;</p>

 

sounds good, thanks

 

Cutaway views of two 1.8 Miata heads:



Top is BP (94-97), bottom is BP-4W (99-00). I assume (but have no proof) that the ports looks pretty much the same on the BP-Z3 ('01-'05) and MSM heads as the BP-4W.

 

both are incredibly crappy. BP4w, just lest crappy

 

Agreed.

That said, I have noticed the casting quality between the '99 head and a 2003 and 2004 VVT head, both VVT heads had a higher quality casting, mainly the core-shift was almost nothing compared to the '99 head. So even if the port designs are the same between them (I have no idea), the two VVT heads I have would flow more at a given lift just from the improvement in casting quality.

But still I agree, these heads don't flow well stock. The good news is that means there is room for improvement!

 

I have some flow data in my build thread.
My engine builder have also commented about the difference in casting between the BP4W and BP6D, especially behind the valve.

There are improvments to be made, but it's no Honda or MZR.

 

Given that casting quality as a function of core shift is something that's going to vary greatly across the lifespan of a given mold set, I'm not sure I'd accept a blanket generalization that the casting on the VVT heads is inherently superior to that of the earlier NB heads, especially with a small sample size.

The number of heads which would have to be dismantled and analyzed in order to make such a determination, across a number of engines made during different production runs, is quite large.

 

Top one doesnt have the fuel injector port on the intake side, so I'm thinking the top one is a 1.6

 

Sure.

Still my sample size I posted happened. I only posted my experience, I'm not writing miata laws for people to abide by!

If anyone cares, I've had 2 99' heads, and 2 VVT heads and both 99' heads had random ports with bad core shift, where both VVT heads were much better in this regard.

The reason I posted that is if you're gonna flow a 99 head, they may very well flow different between the ports due to the random core shift. Also it makes porting the head a huge pain. Doing a VVT head is much easier. Also, funny enough, the combustion chamber design on the VVT head is a lot better regarding shrouding compared to the 99 heads. (again, in my experience with my small sample size don't attack me ignore if you have a problem with my post just posting what I've seen) Maybe I need that disclaimer for all my post.

 

So I keep reading about core shift -- presumably that's where the chunks of sand on the interior of the casting mold don't stay in the place they're supposed to? How does that manifest? What should I be looking for to try to see it?

--Ian

 

When you take the valves out, and look in through the seat, you'll be looking into the port. The area immediately behind the seat is called the throat. That's where the air has to turn from the port to the seat. The spot where the seat meets the throat is where I've seen the core shift. They should hit each other perfectly lined up. But instead, one or 2 will be shifted about .10" to .15". So this leaves a wall for air to hit on one side, and a dip on the other side. Both are bad of course.

Easy to see if you pull the valves out of the head.

 

My BP4W had some of this, resulting in casting flash so bad I cut my finger on it. It also had what looked like ***** of motlen metal on the port floors that fell off the roofs during casting. Its probably why my NA build made 127ft/lb but only 130 HP before porting.

 

The cross sectional cut through those heads are a good guide but I think it's a bit mis-represented... The top picture which might be a 1.6 head doesn't have the cut down the center of the runner of the exhaust port. It looks very narrow but you can see it expands wider if the cut was further back.

It might also be that the BP-4W head's intake cut wasn't on the centerline too as that looks a like it would be wider too if cut further back. I wouldn't have thought it would narrow down like that.

My understanding is that the 1.8 heads are very similar in terms of cross sectional area of the intake and exhaust ports with the BP-4W having more height and so less curvature in the airway around the valve. I know my BP head which is heavily ported has very large intake paths into the valves, with the curvature smoothed out a lot around the valves. It would be interesting to flow test the head as I'd be curious what a full developed BP head is capable of.

 

Local experience gives that a unmodified BP4W flows about the same as many many hours fiddling on a BP (with stock valve sizes).
The work done on the BP was for a National Rally 323 (stock valve size, no material added , ...).

 

I'm not exactly sure what has been done to my head as I purchased it as a long engine already built. At the end of the season I plan on pulling it down to have a look. I know the intake and exhaust valves are oversized (+2mm I believe) and that the port work lines up with the stock gaskets and looks smooth and equal all the way down to the valve tops. I would expect some material was added as the curvature looks way less than the cross section shown in the posts above.

I know it has custom valves and that the lengths are different? Not sure why that would be done unless they have been re-positioned in the head or are seated differently.

What would you say would be the HP limit of a BP head? I'm getting a bit over 200wHP with mine. What sort of power with the 323 rally head?

 

Comparing whp for boosted engines (especially optimized against different rules) is quite useless.

 

Oh the 323 is boosted... for some reason I thought it was a N/A build and if it was, would have been highly developed. I used to rally a turbo Familia with my brother. No idea on the power but it was an awsome car to drive. It kept blowing center diffs and started getting expensive to maintain.

 

That image was taken from SoloMiata, which I generally trust as a reliable source of information.

I'm not 100% certain that the upper image is a BP head vs. a B6 head. I do know that the two cross-sections were clearly not made at precisely the same location, so it's entirely possible that the injector port was simply not bisected by the cut of the earlier head.

At any rate, here's a Honda B16 head:



Pretty dramatic and obvious differences.