Porting the 45 Inch Flathead : Big Valves

So, what about those bigger intake valves? As we saw in part two, we finished with a 13% flow increase just from porting along with a backcut on the valves. Just how much more is there to be gained from bigger intake valves?

Before I go any farther, I'd like to mention that a reader left a comment stating that the legendary tuner Tom Sifton would actually reduce the valve size to reduce shrouding (close proximity of portions of the chamber to the valve which inhibits air flow). To clarify, I assume that Mr. Sifton was dealing with WR engines and their already oversize intake valves. The normal 45 has a valve size of 1.625" on both intake and exhaust. A WR had a 1.810" on the intake and 1.560" on the exhaust. Another difference on the WR, is that the valves were "tilted"such that the edge of the intake valve was much closer to the cylinder bore than the standard 45. There are reasons that this was an advantage, which I will come back to that later.

It is a valid question, though. If a bigger valve is better, then when, or does it ever, become too big. Unfortunately, due to time considerations, I will not provide a definitive answer to that question at this point. Testing multiple valve sizes was just not practical on this particular project. I chose to use a readily available oversize valve marketed expressly for 45 inch motors. This valve has a 1.875 head diameter, which is about all that will actually clear the head gasket on a 45.

Now, let's see if I can put this diplomatically. I was somewhat taken aback upon receiving these oversize "performance upgrade" valves. My first thought was "these are nothing but antique tractor valves with a hard tip installed." OK....I may be wrong on that. They may have been made for an antique auto engine, but the fact remains that they have all the modern technology of a 1920's Minneapolis Moline. Conveniently, instructions included with the valves detail how to back cut, shape and polish the valve head as per the factory KR manual. Finished valve is shown below.

Where was that promised diplomacy you ask? Let me get to that. My guess is that these valves have been available from this supplier for quite some time, and as such they have been a valuable resource for many hot rodders over the years. What I am trying to say is that, before custom made valves became affordable, these were the best way to get a big intake into your 45. And as long as you have the equipment and ability to do the mods to these valves, then they will be a cost effective alternative to their custom made modern performance counterparts. But if you have to pay someone (like me) to do the modifications to the valves, well, then not so much. Next time around, I will probably have a pair of valves custom made to spec. In fact, if I were to get some indication that there is enough demand, I would probably have multiple pairs made and offer them for sale. The price might be slightly higher for the custom valves, but they would be a high performance valve right out of the box.

But enough of that; on to the results. The oversize valve has a 30 degree face rather than the normal Harley 45 degree. This has an advantage for this application, which I will discuss later. For now, I began the seat by opening the "choke" to 85% of the valve diameter. This was an arbitrary figure I selected (very conservative) and in retrospect I wish I had opened it up more after initial testing, because it may have provided further gains. Truth be told, by the time I had all the other testing done, I had forgotten that I had started with such a small choke until I looked at my notes to write this. The next step was a 30 degree seat cut, which I narrowed on the port side with a 45 degree, and then added a 60 degree also on the port side. Had there been room, I would have added a 75 degree cut, but opted to hand radius the 60 into the choke.

On the top side of the valve, since I lacked a stand alone 15 degree cutter, I opted to use a "flat" cutter to provide a top cut and thus some unshrouding on the back side (away from the cylinder bore). I made this about .090" larger diameter than the valve, which took it just about to the gasket.

For this set of tests, I switched over to the front cylinder, so a comparison between these figures and those from part 2 will not be apples to apples.

.100" lift - ported 1.625 valve 50.3cfm / add 1.875 valve 57.0cfm
.200" lift - ported 1.625 valve 85.5cfm / add 1.875 valve 88.9cfm
.300" lift - ported 1.625 valve 104.7cfm / add 1.875 valve 105.9cfm
.350" lift - ported 1.625 valve 106.7cfm / add 1.875 valve 111.9cfm
.375" lift - ported 1.625 valve 108.1cfm / add 1.875 valve 113.1cfm
.400" lift - ported 1.625 valve 109.0cfm / add 1.875 valve 113.6cfm
.450" lift - ported 1.625 valve 109.7cfm / add 1.875 valve 112.8cfm

As you can see, it came out to a nearly 5% gain at .350" lift. Next up was to unshroud the valve on the bore side (there is no where to go on the back side since we are already to the gasket.

The results of unshrouding (as shown in above picture) are as follows:

.100" lift - previous test 57.0cfm / add unshroud 60.9cfm
.200" lift - previous test 88.9cfm / add unshroud 94.0cfm
.300" lift - previous test 105.9cfm / add unshroud 111.3cfm
.350" lift - previous test 111.9cfm / add unshroud 115.6cfm
.375" lift - previous test 113.1cfm / add unshroud 116.7cfm
.400" lift - previous test 113.6cfm / add unshroud 117.3cfm
.450" lift - previous test 112.8cfm / add unshroud 116.1cfm

About another 3% increase at .350" lift. So what about relieving? That's next. There are plenty of resources available that describe the process, so I won't attempt to describe it here. I just want to add a couple points. Since I was already satisfied with the exhaust flow, I relieved only the intake side. Also, you could think of the relieving as extending the unshrouding that I did in the previous test all the way to the cylinder bore. In other words, if you are going to relieve, then skip the unshrouding step. I did them one at a time for testing purposes. The relief is shown in the picture below.

Flow results were:

.100" lift - previous test 60.9cfm / add relieve 58.8cfm
.200" lift - previous test 94.0cfm / add relieve 94.3cfm
.300" lift - previous test 111.3cfm / add relieve 115.5cfm
.350" lift - previous test 115.6cfm / add relieve 119.6cfm
.375" lift - previous test 116.7cfm / add relieve 120.8cfm
.400" lift - previous test 117.3cfm / add relieve 120.8cfm
.450" lift - previous test 116.1cfm / add relieve 118.9cfm

That shows a 3% increase from the relieving vs. unshrouding, or a 6% increase from relieving as opposed to installing the larger valve alone. The last change was to modify the face of the valve as per the KR instruction sheet ....well almost. The sheet suggests cutting the face down to until there is only a .025" margin left. That seemed too narrow for my taste, so I cut it to .050". The results were:

.100" lift - previous test 58.8cfm / add face mod 60.5cfm
.200" lift - previous test 94.3cfm / add face mod 95.0cfm
.300" lift - previous test 115.5cfm / add face mod 113.5cfm
.350" lift - previous test 119.6cfm / add face mod 118.8cfm
.375" lift - previous test 120.8cfm / add face mod 120.3cfm
.400" lift - previous test 120.8cfm / add face mod 121.0cfm
.450" lift - previous test 118.9cfm / add face mod 120.8cfm

Somewhat inconclusive on this modification. Small gain at .100-.200 and a small loss at .300- .375, and again a small gain at .400 and above. I was happy that I didn't make the margin any smaller than .050".

In my next post on this subject I plan to go back to the rear cylinder to give a direct comparison from the stock readings to the finished product, along with some analysis of what caused what. Incidentally, I am not happy with the readability of the "charts" I put here on my blog, so if anyone is interested in having a better version emailed to them, contact me at lee@leesspeedshop.com and I will be happy to send out something.