My "new" tach.

[moose]

[55 Fargo]

Very Nice Moose, 4000 rpm revs or so not bad, like to get one for mine someday. Got any pics of this car, or video of the engine while it's running.....Fred

[moose]

No videos of the engine running, but here are a couple of the 55. When I first ran it and the tach was reading 250-300, I checked it with a tach/dwell meter. It idles about 600, and as soon as it starts to rev, the tach is dead on up to 2500(as high as my meter goes). So it'd have to be about right up high too.? It revs to 45-4600 easily, then my foot gets scared:eek:

[greg g]

Like the heater conrol valve, had on just like it on an old Volvo.

[Cpt.Fred]

very cool, moose!

it's always a surprise to see how quickly these engines can rev up.

i just won an auction for a radson tach, hope it gets here the next few days and i hope i can make it work!

nice, weired looking intake and header setup, by the way:)

[JBNeal]

Nice touch...I've planned on putting a tach in my '52 B-3-108, just to have another needle bouncing around to verify what my ears are telling me.

[1950dodge]

Nice tach, what brand or make is it, or where did you find it? I need one of those.

[moose]

It's a Smiths from a Jaguar 6, 12 volt neg ground. I've got it isolated and I'm using a battery pack wired in on the ground side.

Fred- In the next couple of days I'll try to draw up a wiring diagram if you want. It's a little convoluted and backwards, but do-able.

I also just wired my SW tach in the Model A. Reads low, must be for an 8 cylinder:confused:

[1937 Dodge]

Great tach and great sound. Anyone know how to modify an old mechanical tach to a modern 12 volt neg ground HEI unit by replacing the old guts with a modern sending unit while keeping the old face housing and pointer?

I have called several places but the price is way to high for my budget. Would try it myself if someone would post photos and instructions on how they did their conversion.

[Cpt.Fred]

hey moose,

that would be great!

i already opened up mine and looked in there,

when i have the engine back together i will give it a try...

you say you have an extra 12V battery pack on board for the tach?

can't it be done with a voltage converter or something like that?

fred

[moose]

I have a battery pack with 4 AA batteries(6 volts) that is wired negative to the ground, positive to the power wire on the tach. The ground wire of the tach is wired to a keyed power source. Then the sensing wire goes to the distributor side of the coil(guess it doesn't care which way is grounded). The tach is mounted insulated from the ground.

Does that make sense?

I don't know about your Radson. Is it supposed to use a sending unit? How many wires on the back?

[Niel Hoback]

It does matter which side of the coil that the tach wire is connected to. It must be connected to the positive side, the wire going to the distributor.

[moose]

It does matter which side of the coil that the tach wire is connected to. It must be connected to the positive side, the wire going to the distributor.

Yeah the distributor side of the coil. I meant it doesn't matter about polarity at that point.

[Cpt.Fred]

three wires on the radson, so i guess it won't need a sending unit. i hope:rolleyes:

thanks for the tips, i'll figure it out somehow!

[moose]

With the TomTom hooked up now and the tach too, I went on a little "proving run." It did fine. This is a 55 Plymouth, with 3.73 gears, radial 225/75/15 tires, two singles and a dual exhaust on a 51 218.

All numbers in high gear

mph RPM

30 1250

40 1700

45 2000

50 2200

55 2400

60 2600

65 2800<--and very comfortable

70 3000

75 3200

80 3400

85 3600

I didn't feel like going too fast today, but a few days ago it went right up to 4100 in high! so that'd be almost 100:eek:

[moose]

Hey TodFitch, where'd your post go? Whatever. The differences in the low RPM numbers could have to do with the tach being off, but I think it has to do with operator error:rolleyes: Also the TomTom didn't really give steady numbers too often... Maybe too much metal around for proper reception:D

[TodFitch]

Hey TodFitch, where'd your post go? Whatever. The differences in the low RPM numbers could have to do with the tach being off, but I think it has to do with operator error:rolleyes: Also the TomTom didn't really give steady numbers too often... Maybe too much metal around for proper reception:D

I pulled it within seconds of posting because I realized that I was considering the numbers incorrectly. Here is a plot of your RPM versus your MPH. It forms a pretty straight line which is what one would expect.

I cruise at about 3200 RPM which on your car would be moving right along at 75. For me it is just a bit above 60.

I believe your engine is up to having you cruise at 75, just not sure about the suspension and brakes... Perhaps the 15 or 20 years of automotive engineering went into the suspension between your late 1940s Plymouths and my early 1930s beast make a difference. Mine is really quite a handful above 60 MPH and with the tiny drums I really have to anticipate things.

[Cpt.Fred]

i believe i want a 3.something rearend, too... i don't have a tach yet,

but i don't feel like going more than 70miles cruise speed with my 201 /4.2 rear.

it's ok, handles great for a car of that time and i'm sure there's a little more to come,

but on a german autobahn you're sitting ducks for busses and overland trucks,

and that's really uncomfortable with my 6V tail lights the size of a match book cover...

makes it saver to go on fast lane to avoid being crushed between two of these juggernauts.

[james curl]

I installed a 90 Dakota rear end with 3.55:1 rear gears and that is about as high as I feel comfortable with starting from a stop. I do not like having to rev the engine up over 1500 rpm to un-track the car. I have a 218 with dual exhaust and intake, .040 overbore, a mild cam and .100" off of the head, the engine has enough torque to pull the 3.55:1 gears with 205 75 15 tires but much more would be a strain from a standing start.

[Cpt.Fred]

true. rumbling away from traffic lights at idle is a very satisfying thing as well:cool:you can't beat the sound of that.

so the perfect engine/gears combo has to be able to do both...

[moose]

I pulled it within seconds of posting because I realized that I was considering the numbers incorrectly. Here is a plot of your RPM versus your MPH. It forms a pretty straight line which is what one would expect.

I cruise at about 3200 RPM which on your car would be moving right along at 75. For me it is just a bit above 60.

I believe your engine is up to having you cruise at 75, just not sure about the suspension and brakes... Perhaps the 15 or 20 years of automotive engineering went into the suspension between your late 1940s Plymouths and my early 1930s beast make a difference. Mine is really quite a handful above 60 MPH and with the tiny drums I really have to anticipate things.

Thanks Tod, nice graph, I did mine on a regular sheet of paper:eek: Just like I was in 5th grade! There were a lot of problems with the way I got and recorded my values. I was looking at the GPS trying to get it to stay steady, and then a quick glance back to the tach.

I really needed to have my wife in the car writing. The next time I will hold the RPM at a certain level then wait for the speed to level out.

After the graph I tried to check the accuracy of the tach using the calculator on your site. Kinda backwards guessing my way into the right speed, and my tach seems to read slow. At 30MPH your calc says my engine should be turning 1350, where my tach showed just over 1200. Through the mid range 1700-2900 it was fairly close (0-50 off). Then the high range was off again. 85 on the GPS said 35-3600 on my tach(its hard to look quick when you are going that fast) and your calc says it should be turning 3750. Overall its not off by too much.

Last week the car went up to 4100 on the tach. By correlation, if it was really turning 4300-4350, it ran 97-98mph!!

[Don Coatney]

I installed a 90 Dakota rear end with 3.55:1 rear gears and that is about as high as I feel comfortable with starting from a stop. I do not like having to rev the engine up over 1500 rpm to un-track the car. I have a 218 with dual exhaust and intake, .040 overbore, a mild cam and .100" off of the head, the engine has enough torque to pull the 3.55:1 gears with 205 75 15 tires but much more would be a strain from a standing start.

James;

Having put a few miles behind the wheel of your car I think your gearing is very good. No problem from a dead stop. I also have 3.55/1 gearing in my car but first gear in my T-5 transmission is slightly lower than first gear in a factory transmission.