Chester Brzostowski Posted October 21, 2012 Report Posted October 21, 2012 I install a WesTech tachometer. While doing the install my wire to the distributor broke off. I think it was hanging on by a thread. I was going to remove the distributor anyway to adjust the bracket because I couldn't set my timing dead nuts. So I guess this was the weekend to do it. I removed the distributor and moved it slightly on the bracket so I could get a little more advance. Of course I repaired the wire and reinstalled it. I retimed the engine and it is running better then ever. Very easy to start and more power off the line. So a little problem turned into a good day. The enigne is now timed perfect and the Tack is a nice addition. The Question for those with a Tack in your P15 and running a stock 218. What is your cruising RPM. I'm thinking 3,500 seems OK ? Chet... Quote
bamfordsgarage Posted October 21, 2012 Report Posted October 21, 2012 I generally run 50-55 mph in my stock-drivetrain D25 which is 2,500-2,800 rpm. 3,000-3,500 is probably fine if the engine is in good shape, but it sounds busy to me and I've gotten comfortable with life in the slow lane. Quote
Robert Horne Posted October 21, 2012 Report Posted October 21, 2012 Chet, nice tach you have. Seems most tachs we see now of day, have 10,000 or 12,000 rpms on them. I put a marine tach in my coupe. Something I can read easy. Last week I was doing a test run, since I installed a Ranger rearend. The tach was reading about 1800 rpm at 40 mph. Will do some more test runs soon with a GPS so get a better idea of speeds, and rpms............ Quote
greg g Posted October 21, 2012 Report Posted October 21, 2012 On the chasis dyno,my engine runs 3280 @ 63mph. Rule of thumb I heard years ago,is thr cruising rpm at or about 80/5% of peak hp rpm is fine. Hp rating was taken at 3600 for our engines. A little math will give you your answer. Quote
Chester Brzostowski Posted October 21, 2012 Author Report Posted October 21, 2012 RPMs OK here is what I have recorded with tires 205/70 R15 RPM's........... MPH/Car..... MPH/GPS 1800 ........... 30 ............... 30 2000 ........... 32 ............... 32 2500 ........... 39 ............... 38 3000 ........... 50 ............... 47 3500 ........... 56 ............... 51 3800 ........... 60 ............... 55 4000 ........... 65 ............... 60 Maybe 225/70 R15's might bring down the rpms a bit ??? Quote
Randy L Peterson Posted October 21, 2012 Report Posted October 21, 2012 I plan to run 215/75/15 next summer .. I had a set of 215/70/15 layin here and put them on my car.. The 75 series is much taller tire and about the same diameter as what the car originally came with.. RLP Quote
Uncle-Pekka Posted October 21, 2012 Report Posted October 21, 2012 Chet, Is that a 6V tachometer or have you converted your car to 12V? Chris; Great looking vintage tacho - I suppose that is a 6V unit, right? Robert, what brand is your tacho? Very clear readable face. 6V? Quote
Robert Horne Posted October 21, 2012 Report Posted October 21, 2012 My white tach is 12 volt. I do not remember the name. It has a "GH" on the front. It was for a boat, but works good in my Coupe. The only things 6 volt in my Coupe, are the heater blower, and the fuel gauge.... Quote
bamfordsgarage Posted October 21, 2012 Report Posted October 21, 2012 Chris; Great looking vintage tacho - I suppose that is a 6V unit, right? Six-volt yes and no. The bulb that illuminate the dial is 12 volts. The tachometer function seems to not care about the voltage — the unit is connected in series between the coil and distributor (ignition current goes through the tach) and there is no separate pickup etc. If I recall correctly, there is no selection switch for cylinder count so it must have been intended for a six-banger and I got lucky. $20 at the Hershey 2010 swap meet. Quote
Chester Brzostowski Posted October 21, 2012 Author Report Posted October 21, 2012 (edited) Chet,Is that a 6V tachometer or have you converted your car to 12V? Chris; Great looking vintage tacho - I suppose that is a 6V unit, right? Robert, what brand is your tacho? Very clear readable face. 6V? Yes 6 volt. A little pricey I believe they sell in the $120 - $145 range. 3 point breaks to one rotation. Edited October 21, 2012 by Chester Brzostowski Quote
Chester Brzostowski Posted October 21, 2012 Author Report Posted October 21, 2012 I plan to run 215/75/15 next summer .. I had a set of 215/70/15 layin here and put them on my car.. The 75 series is much taller tire and about the same diameter as what the car originally came with.. RLP Randy, I think that's the size I need. Chet... Quote
greg g Posted October 22, 2012 Report Posted October 22, 2012 mine are 225 75 15. I believe the diameter is listed as 27.8 in. which is quite close to the 600 16 that was original. Quote
Chester Brzostowski Posted October 22, 2012 Author Report Posted October 22, 2012 mine are 225 75 15. I believe the diameter is listed as 27.8 in. which is quite close to the 600 16 that was original. Greg, I calculate that if I switched to 225 75/15 form 205 70/15s. I would drop my RPM’s across the board by approximately 500 rpms lower on the higher speeds. Tire circumference difference is 6.245 inches. Tire Diameter And Circumference Calculator see link below. http://www.csgnetwork.com/tiresizescalc.html A little cheaper then the overdrive transmission as a quick fix. Tks Chet... Quote
TodFitch Posted October 22, 2012 Report Posted October 22, 2012 RPMsOK here is what I have recorded with tires 205/70 R15 RPM's........... MPH/Car..... MPH/GPS 1800 ........... 30 ............... 30 2000 ........... 32 ............... 32 2500 ........... 39 ............... 38 3000 ........... 50 ............... 47 3500 ........... 56 ............... 51 3800 ........... 60 ............... 55 4000 ........... 65 ............... 60 Maybe 225/70 R15's might bring down the rpms a bit ??? Looks like both your speedometer and your tachometer have errors that are not linear with speed. Assuming, of course, that the GPS is accurate. If the RPM/MPH ratio at 30 MPH (GPS) is correct then your RPM reading at 60 MPH (GPS) should be 3600 and not 4000. And, by the way, either 3600 or 4000 RPM at 60 MPH is a lot higher than I'd expect with the stock rear end and stock tire size. Quote
Chester Brzostowski Posted October 22, 2012 Author Report Posted October 22, 2012 Looks like both your speedometer and your tachometer have errors that are not linear with speed. Assuming, of course, that the GPS is accurate. If the RPM/MPH ratio at 30 MPH (GPS) is correct then your RPM reading at 60 MPH (GPS) should be 3600 and not 4000.And, by the way, either 3600 or 4000 RPM at 60 MPH is a lot higher than I'd expect with the stock rear end and stock tire size. Todd, I agree. if you look at the 32 mph to the 60 mph. We are looking at 2000 to 4000 rpm's +- 5% error. Seems pretty close. I think the small tires are creating a problem and yes the Tech might have an error or me reading, writing, and driving might be slightly off. It is a small faced gauge. Needless to say I agree that something isn't quite right and further investigation is warranted. But definitely my tire size needs to be addressed. Chet... Quote
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