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Hi Bob, the unit has 2 pick-ups, so with a 4/4 you need both coil pick-ups to get 2 pulses per rev, same as with the 2/2; if you had a 1 cylinder/2 stroke it would give 1 pulse per rev; therefore the number of cylinders matter. With the V6, 2 pick-ups also produce 2 pulses per rev, but since they are occurring a slightly slower rates the frequency to voltage conversion was not accurate; I changed the R/C filter on the input and adjusted the internal reference pot to increase the rpm readout ... drove around for a few weeks with it in my Sonoma to verify calibration with Sonoma Tach. The rpm max reading is 9999. Jeff -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bob White Sent: Friday, May 08, 2009 12:18 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: John Downings Tach Hi Jeff, Thanks for the tip. There is something I don't understand about the specs for this unit. It's good for 4 cylinder 4 stroke or 2 cylinder 2 stroke. If I use the spark plug wire for the pickup, a 4 stroke (piston) engine will see one spark per two rev. Why does it matter how many pistons there are? If it's a wasted spark system, then one spark per rev. just like a two stroke piston engine. There must be something basic I don't understand. What sort of mod did it need for the V6? BTW, what is the maximum rpm reading for that unit? Thanks, Bob W. On Fri, 8 May 2009 07:48:47 -0700 Jeff Whaley <jwhaley@datacast.com> wrote: I like the belt and suspenders!! I am using a UMA digital tachometer 2 1/4" from Aircraft Spruce that was originally designed for 4 cylinder engines using an electrical impulse pickup from spark plug leads. I modified it to mate with the Ford V6; I have modified it again to connect to the EC2 driving the R1 PRI injector. The rotary firing system is similar to a 4 cylinder so if this tach is still available (Part # 10-24885) it would work off spark plug impulse couplers. Jeff -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bob White Sent: Friday, May 08, 2009 12:14 AM To: Rotary motors in aircraft Subject: [FlyRotary] John Downings Tach John is using a standard tach that is normally connected to a distributor/coil ignition system. The straight 12V pulse used for the LS1 coils wouldn't activate it. I built an interface for him that involved taking that pulse as an input and generating a shorter constant pulse width output. I modified the tach to trigger on the lower voltage signal, and adjusted the scale factor to read correctly with one pulse/rev. As John reported, it worked for about 0.8 hours, then quit. He is sending everything back to me so that I can find out where the problem is. I would like to find a tach solution that John can use without modifying anything. The parameters are he has a 2 1/16 inch mounting hole, the tach needs to read correctly with 1 pulse/rev (would be the same as a two cylinder piston engine with coil and distributor), should trigger directly on a 12V pulse. I've found tachs on the web that mention working with distributorless or electronic systems, but none of them were the 2 1/16 inch type. I found a converter, the MSD 8913, but on the Summit Racing catalog it specifically says it won't work with the LS-1 system. It work by sensing the current pulses to the 12V power lead on the coil. I don't know why it wouldn't work with an LS-1 coil, but it doesn't seem like a good investment when the LS-1 is specifically mentioned as not working. Can anyone recommend a tach solution that John can use with his LS-1 Coil rotary engine combination? On another topic, John has the only system I've heard of that has the capability to run on either EFI or a carburettor. John posted a picture of his Tailwind a few days ago. It's a very good picture but considering the redundancy of the EFI/carb system, I felt that the picture was lacking. I submit this edited version as being more indicative of John's desire for uncompromised safety. Bob W. -- N93BD - Rotary Powered BD-4 - http://www.bob-white.com 3.8 Hours Total Time and holding Cables for your rotary installation - http://roblinstores.com/ -- Homepage: http://www.flyrotary.com/ Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html -- N93BD - Rotary Powered BD-4 - http://www.bob-white.com 3.8 Hours Total Time and holding Cables for your rotary installation - http://roblinstores.com/ -- Homepage: http://www.flyrotary.com/ Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html