Sunday, September 26, 2010

Porting the 45 Inch Flathead, part 2

In part one of this series, I published the results of a flow test on a stock cylinder from a '48 WL. In order to get an idea of what effect different modifications had on the process, I resigned myself to spending a lot of extra time with multiple flow tests. My first step in the process was to do a basic porting job. The cylinders were in need of new valve guides anyway, so I removed the old ones before working on the ports. In almost all cases, more flow can be obtained by doing the port work with the guides removed. Much of the "work" involved opening the intake port to a nominal I.D. of 1.250 inches. This is a modest increase in size, and I would consider it to be the minimum that one would want to invest effort into.

Once the ports were cleaned up and shaped, new guides were installed and sized. Next the seats were cut for new stock size Rowe valves. The exhaust seats received a radius seat, which in actual practice on a motor such as this, does very little. The "choke" or "venturi" just below the 45 degree seat is too large relative to the valve size for the radius to enhance the flow much more than a conventional three angle valve job would. If you lack the equipment to do a radius seat, just do a 3 angle and blend it into the port. The intake seat (only one since I would be installing larger valves next) got a multi angle seat, although this too suffered from similar size issues as the exhaust.

The results of a flow test in this state are as follows:

Intake .100" lift - stock 48.2cfm / ported 42.5cfm
Intake .200" lift - stock 83.8cfm / ported 81.7cfm
Intake .300" lift - stock 98.7 cfm / ported 107.1cfm
Intake .350" lift - stock 102.6cfm / ported 114.2cfm
Intake .375" lift - stock 103.8cfm / ported 117.3cfm
Intake .400" lift - stock 104.3cfm / ported 118.6cfm
Intake .450" lift - stock 104.4cfm / ported 121.0cfm
***
Exhaust .100" lift - stock 41.9cfm / ported 52.0cfm
Exhaust .200" lift - stock 82.4cfm / ported 92.8cfm
Exhaust .300" lift - stock 104.4cfm / ported 112.4cfm
Exhaust .350" lift - stock 110.6cfm / ported 117.2cfm
Exhaust .375" lift - stock 113.3cfm / ported 120.8cfm
Exhaust .400" lift - stock 115.7cfm / ported 121.2cfm
Exhaust .450" lift - stock 119.3cfm / ported 124.6cfm


You will note that there was actually a loss of flow under .300" lift on the intake side. This is due to the shape of the Rowe valves. Basically what they do is manufacture an exhaust valve and offer it for use in both intake and exhaust. Nothing wrong or deceitful about that. It is not sold as a performance valve, and in the long run, by reducing their manufacturing costs, Rowe is saving the owner of a stock motor money at rebuild time.

But back to the valve in question; on the back side, just below the 45 degree face, is a lip (shown in picture above) which inhibits flow. Which leads to the next logical modification: a 30 degree back cut on the valves. It is well established that air will "follow" a 15 degree change in direction with minimal flow loss (if you have never heard that before, then just now a light bulb should have come on in your head explaining why a three angle valve job consists of angles of 30, 45, and 60 degrees). With a 30 degree back cut on both valves, the next flow test looks like this:

Intake .100" lift - ported 42.5cfm / add back cut 48.7cfm
Intake .200" lift - ported 81.7cfm / add back cut 88.4cfm
Intake .300" lift - ported 107.1 cfm / add back cut 109.5cfm
Intake .350" lift - ported 114.2cfm / add back cut 115.7cfm
Intake .375" lift - ported 117.3cfm / add back cut 118.1cfm
Intake .400" lift - ported 118.6cfm / add back cut 119.2cfm
Intake .450" lift - ported 121.04cfm / add cut 121.8cfm
***
Exhaust .100" lift - ported 52.0cfm / add backcut 58.1cfm
Exhaust .200" lift - ported 92.8cfm / add backcut 99.2cfm
Exhaust .300" lift - ported 112.4cfm / add backcut 114.0cfm
Exhaust .350" lift - ported 117.2cfm / add backcut 118.4cfm
Exhaust .375" lift - ported 120.8cfm / add backcut 121.3cfm
Exhaust .400" lift - ported 121.2cfm / add backcut 122.5cfm
Exhaust .450" lift - ported 124.6cfm / add backcut 126.2cfm


As can be seen above, adding the 30 degree back cut on the valves adds flow at all lifts, and more than makes up for the loss of flow in the previous test. At this point, for this application, the exhaust ports are done. They still outflow the intake by a substantial amount, just as they did when stock.


Before moving on to installation of a larger intake valve, there is one more modification that I felt was worth a try. Due to the long length of the valve guides in a Flathead 45, I felt that it would not significantly shorten longevity to remove the short portion that protrudes into the intake port. I have never been a fan of this modification, and though I have seen it done before (I believe it is more prevalent with auto engines) I have never done it myself. The 45 however, seemed a promising candidate. The results are thus:

Intake .100" lift - prev. test 48.7cfm / add guide mod 48.5cfm
Intake .200" lift - prev. test 88.4cfm / add guide mod 87.3cfm
Intake .300" lift - prev. test 109.5cfm / add guide mod 109.7cfm
Intake .350" lift - prev. test 115.7cfm / add guide mod 116.4cfm
Intake .375" lift - prev. test 118.1cfm / add guide mod 118.9cfm
Intake .400" lift - prev. test 119.2cfm / add guide mod 121.8cfm
Intake .450" lift - prev. test 121.8cfm / add guide mod 124.9cfm


This would seem to be the first modification that did not really pan out. The flow differences at .375 lift and below are inconsequential and would rule out shortening the guide at this level of modification. Better flow at .450 lift does nothing if your cam only lifts the valve .360" (as the regrind that this motor is getting does). I have to admit that I kind of dropped the ball on this one though, in that I did not test the other cylinder with the bigger valve before and after modifying the guide. That would have told us whether it was more viable at the higher level of modification. The increased flow at higher lifts would seem to suggest that this mod could be more beneficial with say, for instance, a larger port diameter.


So, what have we learned so far? Porting work; Do it! With the little done so far we show a 13% increase on the intake at .350" lift. Just be sure that you put a back cut on those Rowe valves. As to the shortening of the valve guide. At this point I would say no. Definitely not if you are not going beyond stock valve size. Further testing using a larger valve is in order though.

Up next: a larger intake valve with step by step testing. Stay tuned.

2 comments:

Anonymous said...

i read some where that tom sifton would put smaller valves in his 45 race bikes because the cylinder head shape would shroud the valve

St.Lee said...

I don't think I have heard that before, but valve size is something I did give some thought to before I started. Keep in mind, though, that the race motors (WR) had a larger intake valve to begin with (1.810 vs 1.625)

A bigger valve is definitely in order, the real question is, how much bigger? The ideal size could be determined with enough R&D; the problem being that each scenario costs someone time and parts. If you know someone willing to donate a half dozen cylinders, heads, and valves along with paying for my time, I will be happy to come up with a definitive answer. In the mean time I will just have to continue doing the mods in a (hopefully) logical order, testing as much as is practical along the way.