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60 Mph

twospeed

Donation Time
60 mph at 4200 rpm's,does this sound right?
My APP on my Iphone and also the cars speedo says so.I thought this car would go faster that this.I dont want to rev it too high. Wish I had a overdrive in it.
 

RootesRacer

Donation Time
60 mph at 4200 rpm's,does this sound right?
My APP on my Iphone and also the cars speedo says so.I thought this car would go faster that this.I dont want to rev it too high. Wish I had a overdrive in it.

4200 would be about right if you have a 4.22 (OD final drive ratio).

60 occurs at 3800 or so with the 3.89 and direct trans drive.


Your engine should run safely to 5500rpm. This would be about 78mph based on the 4.22 final drive.
 

twospeed

Donation Time
4200 would be about right if you have a 4.22 (OD final drive ratio).

60 occurs at 3800 or so with the 3.89 and direct trans drive.


Your engine should run safely to 5500rpm. This would be about 78mph based on the 4.22 final drive.
1592 motor with stock rods? I would like to take this on a little trip on the highway, just alittle scared.
This has a non overdrive trans with a set of 373 gears with 14in tires.But as i said before my app and stock speedo are in sync with each other so I must be close.60 occurs at 3800 or so with the 3.89 and direct trans drive, I wish.
 
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alpine_64

Donation Time
Tach could be out.. but also while you have a 3.73 (rootes post vintage sourced?) what size tyres are you running? you need to have at least 195/60 to be close to stock rolling radius (still slightly under). The stock tyres had a dia of 23.28in
 

RootesRacer

Donation Time
1592 motor with stock rods? I would like to take this on a little trip on the highway, just alittle scared.
This has a non overdrive trans with a set of 373 gears with 14in tires.But as i said before my app and stock speedo are in sync with each other so I must be close.60 occurs at 3800 or so with the 3.89 and direct trans drive, I wish.

If you are running the 3.70 gearset, you are NOT running 4200 RPM at 60.

So if your GPS said 60, your tach is not right.

I assumed by your post you had verified your tacho.
 

Ron67Alpine

Silver Level Sponsor
I've had no problems doing 70+ in my SV. I have no idea of what rear end I have, never checked it, nor rpm at speed, but it seems happy.
Ron
 

Tom H

Platinum Level Sponsor
Virtually every tach that has not been recallibrated since it was made nearly 50 years ago will be off by a lot. Of the 2 dozen that I have worked on, I think every one of them read high by somewhere between 20% and 70 % high.

Very easy to check, using your GPS to gauge speed. In your driveway use chalk to mark the ground and the tire where it touches the ground. Push the car exactly 2 tire rotations and mark the second spot on the ground. Measure the distance between the two marks on the ground and divide that distance by 2, That tells you distance per tire rotation. Divide 63360 inches ( 5280 ft *12 = 63360) by that distance. That tells you how many TIRE rotations in 1 mile. Multpily that by 3.73 (or whatever your axle ratio is) and that will tell you how many ENGINE rotations per mile. That number is exactly the number of Engine rotations per minute (RPM) if the car is moving 60 MPH - I mile per minute . If your calculations say, for example, 3750 at 60 RPM and your road test shows the tach indicates 4200 at 60, you now know the tach reads 12 % high.

Tom
 

George Coleman

Gold Level Sponsor
All sounds good, 40 years ago I noticed this with 4.22 gear my alpine5 was doing 4000rpm at 60 mph. It seems that that motors magic number was to keep it under 4000rpm it was happy. I went to the 3.70 gear and that helped greatly, and then added a toyota 5 speed with a .84 fith and the rpm dropped to 3500 rpm at 72 mph. I have run this for almost 10 years and am very happy. With use of the 3.70 gear it would be a very good use of you money to use it if you did not want to go the 5speed route. I get 33 mpg with my car now running the 2bbd weber down draft.:cool:
 

Alpine 1789

SAOCA President
Diamond Level Sponsor
Very easy to check, using your GPS to gauge speed. In your driveway use chalk to mark the ground and the tire where it touches the ground...

Alternatively, you can just do what I did. Attach a dwell tach to the engine, carefully shut the hood and put it inside the passenger compartment. (As I recall, I had to fabricate an extension cord for part of this, but that wasn't a big deal.) Then go for a drive. :)

Like all of them, mine read high; I think I was at around 20%. I just elected to drill a hole in the back and adjust the potentiometer. With my wife's help, I got it to where the car's tach was accurate at 3500 RPMs and didn't worry about the best. I figured that range was the most important one to be sure about.
 
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alpine_64

Donation Time
With my wife's help, I got it to where the car's tach was accurate at 35000 RPMs and didn't worry about the best. I figured that range was the most important one to be sure about.

Jim 35K rpm! wow you are spinning it! :D

The electronic tachs are not a bad design.. but age doesn't do them favors.. I still have the early series cable driven setup.. I had mine rebuilt in 2000 and a new cable a few years back.. still works pretty well.. slight needle wobble now and then.
 

twospeed

Donation Time
Tach could be out.. but also while you have a 3.73 (rootes post vintage sourced?) what size tyres are you running? you need to have at least 195/60 to be close to stock rolling radius (still slightly under). The stock tyres had a dia of 23.28in
I am using 185-65 r14 tires the rear end is a ford mustang with 3:73 gears.
 

agmason54

Donation Time
Beamers
Not beleving my tach or speedo l just put two thousand miles on aSV with a4:22 rear e.d with strombergs.with nothin better to do than eyeball mile markers l determined my odometer added ten percent.l got 30+mpg and believe l was cruisin at55 ataround4200...
I will say the carbs and ass end are a total blast for tearing around winding roads so fear not
RedCartheWhiteGuy
in blue Sv
 

alpine_64

Donation Time
I am using 185-65 r14 tires the rear end is a ford mustang with 3:73 gears.

with those tyres you have a dia of 23.47 inches with a 3.73 i think that leaves you at 18.72 mph per 1000 rpm so 60mph would be 3205 rpm
 
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Eleven

Platinum Level Sponsor
60 mph at 4200 rpm's,does this sound right?
My APP on my Iphone and also the cars speedo says so.I thought this car would go faster that this.I dont want to rev it too high. Wish I had a overdrive in it.

Me too, I am at 3500 at 60. with a 46 yr old engine, I have not the nerve to stay there long...
 
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