Friday, September 17, 2010

Porting the 45 Inch Flathead

I have to admit, its not something I'd have given much thought a few years back. What got me onto the subject, was having a customer bring in a 45" WR (racing) motor last spring. Being somewhat unfamiliar with the nuances of such an engine, I decided I would read up on 45 engines in general on the Flathead Power Bulletin Board .

Now, I have frequented the board for some time, but had always skipped the 45 section of the forum because, well, there just aren't enough hours in the day to read everything on the Internet. But now, with a new found reason, I tackled the job of reading the backlog of posts on the Flathead 45 ....well at least those with titles which indicated they were engine related. A huge task, and it has taken me some time, but I am nearly through.

I was SHOCKED. Who would have expected a forum on 45 Flatheads to be such a hotbed of performance talk? That stirred my interest.

Then, soon after the WR motor came in, another long time customer brought in a 45" trike motor. While the WR is here for a rebuild/restore, the trike is in need of a little more power. Well, 45 or not, that is still right up my alley. In the past I have had to slap myself to keep from doing performance modifications on an old cast iron Briggs and Stratton that I had apart for no other reason than to clean and paint it for display; sure markings of a gear head bordering on lunacy.

There are two ways to modify a motor. One is to do all of the things that you think should help and then test the results. On an engine type that you are not likely to get a lot of repeat business, that is the sane way to do it. The other way is to test each modification before going on to the next. That way you find out how much each step helps, or in fact if it helped at all, or even in some case if it hurt. Its a lot more work, and you are seldom paid for it, unless you consider increasing your knowledge base as "pay."

So, as if I needed to prove my insanity to anyonen else, here are the results of my first step in "porting the 45 Flathead"; a flow test of the stock ports.

Intake .100" lift - 48.2cfm
Intake .200" lift - 83.8cfm
Intake .300" lift - 98.7 cfm
Intake .350" lift - 102.6cfm
Intake .375" lift - 103.8cfm
Intake .400" lift - 104.3cfm
Intake .450"lift - 104.4cfm
Exhaust .100" lift - 41.9cfm
Exhaust .200" lift - 82.4cfm
Exhaust .300" lift - 104.4cfm
Exhaust .350" lift - 110.6cfm
Exhaust .375" lift - 113.3cfm
Exhaust .400" lift - 115.7cfm
Exhaust .450" lift - 119.3cfm

Tests were done on a Superflow SF600 @ 28 inch test pressure with a radius entry directly on the spigot (no manifold)

The next test will be with conventional porting work performed. Stay tuned.

1 comment:

Dan said...

You got my attention on this one. My 45 is my favorite bike, slow but classy.