BP4W and BP05 heads flow - Miata Turbo Forum - Boost cars, acquire cats.
Found this recently on another forum (mx5nutz), and since it contains some good info/measurements, I thought I would share here for future reference as well. All credits go to na8cgee over there!
This project is to see how much flow/power I can make with thorough testing of the cylinder heads via a flow bench (which I am currently designing/looking to build shortly).
So to start the project off, I sourced a BP05 (93-98 1.8 mk1) and BP4W cylinder head. These were stripped of their valves on two cylinders and I used a horizontal bandsaw to make cuts across the ports. The end result was good, it helps me to visualise what I want to achieve, shows me the thickness of the casting, allows me to take accurate measurements and also leaves 1 individual cylinder to perform porting/development on.
There are many differences on the inlet side of the casting between the two but the exhaust side is very similar. Everything being discussed beyond this point is a comparison between stock castings.
There are three main differences on the inlet side.
The first is the port angle to the valve: the BP05 has a port angle of 12 degrees vs the BP4W at 17 degrees. The higher the angle, the more the port ‘see’s’ the valve which as a general rule means more flow.
The second is the port floor, the BP05 head has a lower port floor and is fairly flat/un-shaped vs the BP4W which has a higher floor and is shaped to improve flow to each cylinder. This goes in the BP4W’s favour as it should help improve flow at low valve lifts/low port speed.
The third is the port shape into the bowl transition / short side radius. The BP05 head has significantly better shape in this area compared to the BP4W, which will help to evenly spread the airflow around the whole valve circumference. The short side radius on the BP4W is pretty horrible with no real radius at all.
Not too many differences between the two castings on the exhaust side. You can see the bean counters became a factor when casting the BP4W as there is significantly less material around the port (This is most evident around the port exit near the manifold flange). The castings are not great, significant restriction from the valve guide area and both SSR (Short side radius) are pretty poor.
My rough/guess ported BP4W made 217cfm at .400" (10mm) lift, I know this head has achieved good power on my current engine so as a minimum I want to at least achieve this but hopefully exceed it. I'm fairly confident I can achieve the same peak flow at the same lift regardless of the castings I use, but its the area under the curve that i believe can be improved on the most.
You'll see in the pictures some black pen marks on the inlet side of the ports, the solid lines is the safety margin (This is a 2mm line that I can port upto but still retain the 2mm material thickness I believe is required). the dotted lines is my rough guess to how I want the modified port to look although this does not include the epoxy I will be adding into the port, it just facilitates it.
1) SSR - the radius on the BP4W is bad, you can see in the pictures its almost a cliff edge rather than a radius!
Here's an interesting one though, the BP4W has significantly better port angle of entry. I don't yet understand how significant this will be but my basic understanding is a higher port angle = better flow around the whole valve diameter. BUT, is a better SSR worth more than a better port angle? I don't know but flow bench testing will tell me!
With the inlet ports of each head casting cut in half, I wanted to find how much material I could safely remove from the port roof whilst retaining enough material to be of solid construction. This meant a lot of grinding, somewhat crude but got the job done. In the end I found that the BP05 casting has less thickness about 1 inch into the port on the roof, to the point where I thought I had left 2mm of material I actually broke through (glad this happened on my test head!).
This ability to improve the port roof, I think, will allow me to build a better short side radius on the port floor by adding material whilst retaining the port cross sectional area I need to make power. This is just applying theory at this stage but hopefully in the coming months I can prove that theory with improved low lift flow.
I think the BP4W head with its potential 25 degree port angle will be the better of the two with the figures I have at this stage, but the flow bench will prove/disprove it!
This part was very easy and quite fun, the first step was to remove the valves and clean the inlet tract with brake cleaner to remove as much carbon as possible.
As you can see, the BP05 has a much better short side radius. It’s actually better to say the BP4W doesn’t really have a sort of short side radius lol. More like a cliff edge into the valve!
Finally the last job was to cut each mould into sections to compare the cross sectional area of each section against each other.
They were both cut up at the same points for comparison reasons.
I have taken measurements of the CSA of each moulding and it’s quite interesting the differences between the two. I haven’t yet quite completed my 3rd goal which was performing the calculations, I still need a good few hours to sit down and go through it all.
On another front, my flow bench design is coming together, follows a few guides including Dtec (Google it there’s an online PDF you can view/print - it’s very good) and I’m following David Vizard’s books as well which are also good.
So with the Christmas period been and gone, I’ve made some good progress with my flow bench build.
The flow bench itself contains four 2 stage vacuum motors (the type from a Henry wet/dry vac), using 2 digital Manometers and calibrated orifice holes. It also uses 3 different size valves to bleed off air to achieve the correct test pressure as required.
The build itself follows the same principle of the DTEC bench but I’m using digital manometers rather than an actual water manometer. I’ve done this mainly for easy of install and improved accuracy.
I’ve tested it to in excess of 50 inches of water (digital manometers ran out of range!) and it the box didn’t collapse which was good. The bore adapter was fun to make, it’s just MDF and a 83mm ID aluminium bore pipe which is the same stroke height as the actual engine. It also used the head bolt holes to align the bore as per the head gasket would do.
Everything works but I need to make a valve opener so I can test at various lifts, I’ll use a manual height adjuster and a dial gauge to measure the distance - shouldn’t be too long till I can start messing around and making some gains!
I've performed in excess of 30 tests on the BP4W test head, ranging from the standard setup to the outright bonkers ram it full of putty and see what happens!
I'll share with you some of the interesting comparisons that I found when messing with these heads.
These were relatively low numbers but remember flow benches are like dyno's to some degree, its the Delta between two tests which is the most important here. or in other terms my flow bench seems to be a bit of a heart breaker!
So this basically killed the low lift flow of the head but assisted at the top end (Although only above 0.4 lift which is my max cam lift at 10mm). So without replacing the 3-4mm of material on the port floor I was at a loss with this move, although it did show that raising the roof of the port was improving the flow at the high lift areas.
This setup seems to be a good balance between increased port size but retaining low lift flow. this is also without any additional putty in the port to recover the 3-4mm port entry so I knew I could find some additional low lift flow by filling that area in/shaping it accordingly., maybe even more additional flow across the test sweep? who knows!
I'm really happy with these results, mainly because this is using the stock valve seat angles and stock valves, just shows how much of a good increase can be achieved, but I reckon there is a lot more available - I just need to find it!
So I approached a local engineering/engine shop near to me, Lockside Engineering and started to talk about my goals/what I wanted to achieve. They came on board with me and we began the process of choosing the valve seat width & 3 angles for the inlet side and backcutting the inlet valves for testing on my flow bench!
Without going into too much detail, I chose very similar angles because I wanted to see how much gain would be seen by going to a thinner valve seat (But still within OEM Manual limits). I could have gone thinner than 1mm but then reliability/valve sealing comes into question which is something I wasn't interested in answering!
The inlet valves were back cut at 30 degrees on both tests.
Well hello low lift flow gains! As expected the 1mm valve seat width has allowed for a large increase in low lift flow compared to the 1.1mm valve seat. More so than I expected if I'm honest, but I wanted to see how much of a trade off would be to have the extra re-assurance/durability of the additional seat width vs more performance with the smallest width seat.
The angles I chose were based on a lot of research, they were the most 'accepted' standard for improving low lift flow with heads with a poor short side radius. If I'm honest, there will be additional gains by using different angles I'm sure of it, but at a cost of £40 to test each 3 angle combination, I had to take a calculated best guess before choosing them! I wish I had the money/time to test out some other theories I have from my research but I don't!
Studying the above graph, it shows that the port itself is the limitation beyond 0.35 lift (above 8.9mm lift) which makes a lot of sense considering the max OEM cam valve lift is around 9mm lift for the BP4W head if my memory serves me correctly.
The BP's low rod ratio rears it's head again as a constraint in that the BP is very sensitive to port velocity. Hog the ports out so it makes magic numbers on the flow bench, lose velocity at mid lift and you are guaranteed to make less power than a stock head.
Makes me wonder if all this effort was worth it.
AFAIK no, but if an update pops up, I will repost it here. I know that as-is it is only half the picture, but it was an interesting read for me nonetheless.