Below is an email correspondence I had with Jimmy:
Hi Bob, I talked to you last week through email about doing a MFI Enderle Birdcatcher on gas on the street … I will use your book to set up and tune my system. But i have a question that may not be covered in your book. I hate the way the air filters look for the hats, it hides the butterflies and i want mine to be seen. I talked to a guy that designed an inside air filter and he said it worked good for short while until the cotton between the wire mesh got soaked with fuel then it cut air flow way down. He said even though the blower is sucking air and fuel down you still get fuel bouncing around in the hat. My question is this: they sell all steel air filters for cars now, what if I designed an all steel (stainless) air filter to be mounted right behind the butterflies would you think that might work? That way if fuel did get on it the air flow would keep it blown through. This is a prostreet car I will drive only about twice a month to the local car shows we are talking about only driving in pretty weather and I would take the filter out for the race track. I was just trying to figure a way to run a filter on it without running one of those front mount filters. I also see people running those BDS efi bugcatchers with no air filters, there is a guy running a blown coupe like that and he said he is not worried about running with no air filter no more than he drives it. I’m running a blown BBC with a Littlefied 871, the blower is set up for gas on the street with no teflon strips so its not real tight. I just don’t want to score the inside of my blower and cylinders all up. No more than I drive it on the street it may not be a big concern. Thanks for any advice you can spare…J
Hi Jimmy, We run a coarse mesh screen between our hat and blower. Ever since I pulled a few stones out of there, I run it all the time. For the street, I would run a fine mesh screen and leave it at that. I agree with you about the filter look and the stuff. The problem is pressure drop across a paper or composite mesh. You need quite a bit of area to flow enough air. It is a problem.
I like the idea of no filter to avoid the air pressure drop issue. That air pressure drop will change the tune-up at higher RPM. That could cause a few backfires when you remove the filter and be a worse problem than dirty air. If you run a stainless top ring, it may be fairly durable with dirty air. I think you will find you will be tearing the engine down from time to time for other reasons. A quick hand hone may not be that much of an issue during these tear-downs. We have run engines with scuffed cylinder walls and they still ran great with that blower. Oil consumption was up, but an occasional plug change fixed that.
One issue is intake guide seals. Most Roots blown engines do not run them. Boost blows them off. Unfortunately oil consumption is high at idle vacuum. You may want to look into some kind of snap on seal so that you can run a seal. Ask around to see what others are doing. I have seen seals with an external snap ring around them. Slip on seals will not work very well.