Dwight Romberger Posted August 25, 2014 Share Posted August 25, 2014 I am looking at a vintage tach that goes up to 2400 RPM. Would that be high enough for my '22 Buick 4 cylinder?Thanks,Dwight Link to comment Share on other sites More sharing options...
Terry Wiegand Posted August 27, 2014 Share Posted August 27, 2014 Dwight, I would think that 2400 RPM's on a little Buick 4-cylinder engine of your vintage would be heart-pounding high. Remember, we are dealing with low speed, low compression engines with flywheels the size and mass of a John Deere tractor. The six cylinder engines in my Buicks, and I'm guessing here, will more than likely be turning 1,000 to 1,250 RPM's at 25 - 30 MPH the way they are geared and with the 25-inch wheels. That really is an interesting question - how many rpm's these engines are turning at say 25 mph. The dynamics of these long stroke engines simply do not support high rpm's. It is very easy to see that they got their power from a large rotating mass (as in a 40 - 50 pound flywheel in some cases).Terry WiegandSouth Hutchinson, Kansas Doo Dah America Link to comment Share on other sites More sharing options...
Mark Shaw Posted August 27, 2014 Share Posted August 27, 2014 Terry is right on the RPMs..... Link to comment Share on other sites More sharing options...
Dwight Romberger Posted August 27, 2014 Author Share Posted August 27, 2014 Thanks Terry and Mark for the info. I have become enamored with the idea of having a vintage tach on my speedster. I understand the period mechanical ones can be converted to electronic. Link to comment Share on other sites More sharing options...
JV Puleo Posted August 27, 2014 Share Posted August 27, 2014 Presumably the high gear in the Buick is direct drive, in which case you need to know the rear axle ratio and the outside diameter of the wheels... using this, you can calculate how fast the car would be going at 2400 RPM... my guess is its a lot faster than you'd ordinarily think. Link to comment Share on other sites More sharing options...
Mark Shaw Posted August 28, 2014 Share Posted August 28, 2014 Yes, and faster than you can expect two wheel brakes to stop in time... Link to comment Share on other sites More sharing options...
C Carl Posted August 31, 2014 Share Posted August 31, 2014 Presumably the high gear in the Buick is direct drive, in which case you need to know the rear axle ratio and the outside diameter of the wheels... using this, you can calculate how fast the car would be going at 2400 RPM... my guess is its a lot faster than you'd ordinarily think.Dwight and all : The useful range of your tach will be determined in part by the simple arithmetic JV recommends. I say in part , because one of the most useful revs in any engine is torque peak. Look up the specs for your mill , throw in a couple of hundred and you've got it ! ( for my mid '20s Cadillacs , TP @ 2000 rpm ) . In general , you will be cruising and shifting at below torque peak , but that is particularly good to know and monitor when pulling a steep grade. Do you know of an off the shelf conversion kit for mechanical to electronic tach drive ? That is one great looking tach ! I hope it works for you. - Carl Link to comment Share on other sites More sharing options...
Dwight Romberger Posted September 1, 2014 Author Share Posted September 1, 2014 (edited) Thank you gentlemen for your input. If my arithmetic is correct (rear ratio is 4.60 and circumference of the tire is 100 inches), 2400 rpm would equal approximately 55 mph.Carl, I searched my 1922 Buick manuals and the internet. I could not find a TP nor even a "maximum hp at ________ rpm" I have not studied the process to convert a mechanical tach to an electronic one. I assumed the person offering the service was just fitting an electronic tach in the old case, with the old dial and pointer. He does mention he "calibrates it."The first tach sold for $400. I bought this nearly identical "bottom sweep" one for $69The glass is 3 1/2". The brass ring is 5" Edited September 2, 2014 by Dwight Romberger (see edit history) Link to comment Share on other sites More sharing options...
JV Puleo Posted September 6, 2014 Share Posted September 6, 2014 (edited) Miss-read your post... Edited September 6, 2014 by JV Puleo (see edit history) Link to comment Share on other sites More sharing options...
Dwight Romberger Posted September 7, 2014 Author Share Posted September 7, 2014 No problem JV. I don't think I will have too much trouble keeping it under 55 mph!The tach arrived today. It looks even better in person. I have assembled a pretty cool assortment of brass era gauges to use in the speedster. Only one is a real Buick gauge, and it is the wrong year, but my goal for this one is not a restoration. I will get them all together and take a picture. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now