Several years ago I put my 23 Touring on the dyno at one of the tours (Kanab, I believe) and did pretty well with my Z head and 280 cam. I rechecked it again at Branson last year and even with the lower elevation and higher atmospheric pressure, had dropped several HP. I have been trying to find why the change with no changes in the engine except I put a filter on the carb. I have yet to see an air filter that is larger than one used on a lawnmower for the stock T carb and wonder if this is restricting air into the engine. Have anybody doing dynamometer testing taken a look at the difference of running with or without an air cleaner? I believe an air cleaner is essential to keeping the car running as long as possible, but wonder if I should try to fabricate a larger intake system with a larger air cleaner.
Next time you're around a dyno, how about testing it with and without the filter? That should answer the question.
The filters sold by the part vendors are too small for a T engine. I have one of the light green foam K&N filters sold by most of the vendors. Installing it gives a noticeable drop in performance. It is probably fine on a 100 CC motorcycle.
I suspect that if you wanted an air filter that did not harm performance you would need to adapt one from a car engine with similar displacement.
I would not run my T without a filter. I use a 4" x 2" filter made by Spectre pt# 4790 that I adapt to my OF carb. It fits nicely in the limited space right behind the carb.
I've talked to the tech at Spectre and he assured me that this filter although he didn't have flow test data was adequate for a model T size engine.
I had my '12 on the dyno at Kanab and if I remember was the 2 or 3 highest hp of the non O/H cars tested. The engine has a Z head, 250 Stipe cam, chevy valves, OF carb and a Bill Dubats crank. My top speed recorded with old alum Warford is 70 so I don't think I have any air restriction. If I do that's a Good Thing...
I suspect that the carburetor and intake system was made to run most efficiently without a filter. A different setup made to run with a filter, might have performed very well.
Can't say that I noticed any change in performance when I put a vendor supplied filter on.
Thanks for the responses. I will check on the Spectre filter for both my T's. I had noticed I lacked some top end on my 23 with the filter on but hadn't made the association at that time. My HP at the rear wheel also dropped by about 3 HP from Kanab to Branson with no other changes and it took me this long to make a possible association and ask the question if anybody else had noticed it. If there is a dyno in NY this summer, I'll try it with and without.
My T has made it 89 years without an air filter. It may be one of the lowest-mileage T's in existence, as it lived much of it's life on a privately-owned island with no paved roads, but when I pulled the head off for inspection purposes, I believe that I was the first one to see the valves in a very loong time. There was no significant cylinder wear. It will continue to do without an air filter.