Westach Tacho Checking

[Phil Gillespie]

Recently purchased a 2.5" tacho from Westach for my 39 Coupe after engine rebuild. While I was at it I also wired up my 38 PU also +ve ground and 46 Mercury -ve ground so I could easly swap tacho between cars. Tacho mounts on steering column. Wiring slightly different for -ve ground.
Some results are : GPS used for MPH.


38 PU. 3.78 rear end 16" radials. Tyre Height: 28.7"
30mph: 1700rpm. 50mph:2500rpm. 60mph: 3100rpm.


39 coupe 3.78 rear end, 16" radials: Tyre Height: 29.3"
30 mph: 1500rpm. 50mph: 2600 rpm. 60mph: 3200rpm.


46 Mercury Coupe 3.54 rear end 15" radials. Tyre Height: 26.9"
30mph: 1800rpm. 50mph:2900rpm. 60mph:3300 rpm.


All seem similar at same mph speeds which were taken from GPS.
The 15 tyres on Mercury compensated for by the 3.54 rear end which gives just a slightly higher rpm.
As no cruise control these are the best i could record but am happy with the ability to be able to swap out the tacho between cars.
39 Coupe rear end ratio confirmed on recent dyno.
38 PU rear end ratio unchecked but it is a 3.78 as per above.
46 Mercury rear end confirmed by the engine turn calc one rear wheel jacked up.


All cars run well and travel well at the 60 mph.
Road speed limit in NZ is 100km/hr or 60mph.
Phil NZ

[Black Fifty]

Originally Posted by Phil Gillespie

Recently purchased a 2.5" tacho from Westach for my 39 Coupe after engine rebuild. While I was at it I also wired up my 38 PU also +ve ground and 46 Mercury -ve ground so I could easly swap tacho between cars. Tacho mounts on steering column. Wiring slightly different for -ve ground. Phil NZ

So you're happy with the tach, Phil?
I was going to get one after the first of the year for my shoebox.


Mike

[Phil Gillespie]

Originally Posted by Black Fifty

So you're happy with the tach, Phil?
I was going to get one after the first of the year for my shoebox.


Mike

Yes very happy with it and good easy to follow info for fitting.
Recommend these tachos.
Phil

[tubman]

You may be interested In a product I am producing. It allows you to use any commonly available 12 volt negative ground tachometer on a 6 volt, positive ground system. It is a simple "black box" that is easy to install. It will allow you to use anything from a $10 "swap meet special" to a $600 Autometer with memory and data recall. I have bunch in the field with no complaints. It is competitively priced with a Westach unit and allows you to have something other than the "agricultural look" they have.

Here is a video of one of my units : https://www.youtube.com/watch?v=TaxpuDkWAqc

[Brian]

38 PU. 3.78 rear end 16" radials. Tyre Height: 28.7"
30mph: 1700rpm. 50mph:2500rpm. 60mph: 3100rpm.


39 coupe 3.78 rear end, 16" radials: Tyre Height: 29.3"
30 mph: 1500rpm. 50mph: 2600 rpm. 60mph: 3200rpm.


Phil, not to be a smartarse...but these figures don't seem right. A tire with a dia of 29.3, has a larger circumference than a tire measuring 28.7. I know we're only talking half an inch, however, a tire with a larger circumference obviously travels further per revolution. Therefore, as indicated at 30 MPH readings, engine revs will be lower with the bigger tires, however your recorded RPM's at higher speeds don't follow; the opposite is apparent. Both vehicles equipped with 3.78 bums. Why the different readings?

[John R]

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I don't want to be a smartarse either, but if it takes 1700 rpms on the 38 PU to get 30 mph, it would need 3400 rpm to go 60 mph. However, you get 60 mph with less than double the 30 mph rpms - only 3100 rpm. For the 39 coupe, to get 60 mph, you need more than double the 30 mph revs.

[Phil Gillespie]

Originally Posted by Brian

38 PU. 3.78 rear end 16" radials. Tyre Height: 28.7"
30mph: 1700rpm. 50mph:2500rpm. 60mph: 3100rpm.


39 coupe 3.78 rear end, 16" radials: Tyre Height: 29.3"
30 mph: 1500rpm. 50mph: 2600 rpm. 60mph: 3200rpm.


Phil, not to be a smartarse...but these figures don't seem right. A tire with a dia of 29.3, has a larger circumference than a tire measuring 28.7. I know we're only talking half an inch, however, a tire with a larger circumference obviously travels further per revolution. Therefore, as indicated at 30 MPH readings, engine revs will be lower with the bigger tires, however your recorded RPM's at higher speeds don't follow; the opposite is apparent. Both vehicles equipped with 3.78 bums. Why the different readings?

Perhaps a slight difference and thats provided my tyre diameters are correct. The tyres on PU are 205 R16 C Dueller.
Also looking down from driving position to tacho mounted at steering column can be a couple hundred rpm out between GPS mounted on sunvisor. Still have tacho in PU and continue to check.
While driving home from town noted the revs have climbed up from above readings as much as 600 rpm. Got home and found one plug wire had dismounted from distributor, hence extra rpm.
Phil NZ

[40cpe]

I've been reluctant to comment for the above reasons, but all the reading are high when using the formula for calculating RPMs AND from my own experience. Plug Phil's numbers into this calculator and see the difference.
https://spicerparts.com/calculators/...rpm-calculator

[Phil Gillespie]

Originally Posted by 40cpe

I've been reluctant to comment for the above reasons, but all the reading are high when using the formula for calculating RPMs AND from my own experience. Plug Phil's numbers into this calculator and see the difference.
https://spicerparts.com/calculators/...rpm-calculator

Yes am aware of the calculator and the variance.
But these are actual numbers as taken by myself and the ones are per 39 coupe were verified as per revs and rear end on a dyno machine.
The fact that these are verified allowed me to cross check.
The only error could be in my calc of tyre height for those fitted on 38 PU.
These are a Bridgestone Dueller HT only markings are 205 R16C.
Phil NZ

[whizzernick]

I just installed a westach on a 34 ford . My rpm readings are high . Is that because of dual points or is the wireing (factory ) wrong ? I need help

[40cpe]

Dual points won't do it. Is the tach switchable between 4, 6, and 8 cyl?

[Phil Gillespie]

Originally Posted by whizzernick

I just installed a westach on a 34 ford . My rpm readings are high . Is that because of dual points or is the wireing (factory ) wrong ? I need help

When you ordered it as I did you would have supplied your details of engine.
The tacho will come ready for your flathead engine. There is abilty to wire up for +ve earth or -ve earth. My tacho was fitted when car was on a dyno for checking and revs were correct.
The revs will be higher should a plug lead come off as i found out. This increased revs 500 to 600. Found this out and when refittedclead all good.
Are you able to confirm the rear end ratio perhaps its a 4.11. Whats high revs say at 50 mph or 60 mph?
Phil NZ

[whizzernick]

was not ordered from westach the car is running but not on the road yet.

[tubman]

Keep fightin' the good fight, guys.

[whizzernick]

well : here is a tip when you have a problem (READ THE INSTRUCTIONS )
I did and found if you cut a wire on back of tach . RPM goes to 1/2 I was showing double so all is good now

[JM 35 Sedan]

Originally Posted by whizzernick

well : here is a tip when you have a problem (READ THE INSTRUCTIONS )
I did and found if you cut a wire on back of tach . RPM goes to 1/2 I was showing double so all is good now

That's good news. I ordered and received mine months ago, but have not installed it in my Avatar '35 Fordor. Hopefully, I'll get this done soon, as I would like to have it for some planned road trips in 2019. Will add my test results to this thread when it's installed.

[Phil Gillespie]

Just refitted tacho to 39 PU. For another check yesterday.
Speed quoted is GPS not speedo. 8 BA. 3.78 rear end. Tyres; 16" radials Height: 29.3.

20mph: 1100 rpm. 30mph: 1700rpm. 40mph:2100rpm. 50mph:2500rpm.
55mph:2800rpm. 60mph:3050rpm. 65mph:3300rpm. 70mph:3600rpm.


These figures are as accurate as can read whil driving watching road, gps and tacho.
The cruise speed at 60mph at 3050 rpm PU is running good with good rpm and good engine temp. I am pleased with this tacho for sure. Nice to be able to see actual rpm instead of by sound of engine.
Phil NZ

[Ross F-1]

Originally Posted by Phil Gillespie

Just refitted tacho to 39 PU. For another check yesterday.
Speed quoted is GPS not speedo. 8 BA. 3.78 rear end. Tyres; 16" radials Height: 29.3.

20mph: 1100 rpm. 30mph: 1700rpm. 40mph:2100rpm. 50mph:2500rpm.
55mph:2800rpm. 60mph:3050rpm. 65mph:3300rpm. 70mph:3600rpm.


These figures are as accurate as can read whil driving watching road, gps and tacho.
The cruise speed at 60mph at 3050 rpm PU is running good with good rpm and good engine temp. I am pleased with this tacho for sure. Nice to be able to see actual rpm instead of by sound of engine.
Phil NZ

How did you measure tire diameter? All your values vary by (almost exactly) 400 from calculated RPM.

The only accurate way I've found to measure tire diameter is to make a mark at the bottom of the tire, and one on the ground adjacent to that mark. Roll the truck until the tire mark has made exactly one revolution, then make a mark on the ground adjacent to that. Measure the distance between marks on the ground, and divide by 3.14159. That is rolling diameter.

[Phil Gillespie]

Originally Posted by Ross F-1

How did you measure tire diameter? All your values vary by (almost exactly) 400 from calculated RPM.

The only accurate way I've found to measure tire diameter is to make a mark at the bottom of the tire, and one on the ground adjacent to that mark. Roll the truck until the tire mark has made exactly one revolution, then make a mark on the ground adjacent to that. Measure the distance between marks on the ground, and divide by 3.14159. That is rolling diameter.

I just went on a tyre site and put in the numbers of my tyres and used the diameter as given.A check using a straight edge on top of tyre and measuring to ground contact was very close.
Phil NZ