Comfortable RPM's

[Hodee]

I have a stock Ser V Alpine and I'm sure the Tach is not "perfect" but out of curiosity, What would you believe to be a comfortable cruising rpm? Yes, it's a422 rearend but with large diameter 225/60/15 rears slightly over 25 inch dia. so I know the speedo is off too. I'm not trying to do 80 mph just a comfy rpm range. Thanks.

 

[alpine_64]

In theory 3800 rpm at 60mph was a stock 3.89 non o/d so the cars can sit at 3800 comfortably.. maybe your ears cant though... the cars feel relaxed at about 3200rpm i find.

 

[Hodee]

Wonder how that would translate for a 4.22? I guess 4800-5000 is out of the question for a well running 1725? I typically use that as a shift point but not too sure about cruising. the motor sure sounds good there though.

 

[alpineracer]

I have a stock Ser V Alpine and I'm sure the Tach is not "perfect" but out of curiosity, What would you believe to be a comfortable cruising rpm? Yes, it's a422 rearend but with large diameter 225/60/15 rears slightly over 25 inch dia. so I know the speedo is off too. I'm not trying to do 80 mph just a comfy rpm range. Thanks.

Hi! I was wondering if you had run the math....

 

[Bill Blue]

Wonder how that would translate for a 4.22? I guess 4800-5000 is out of the question for a well running 1725? I typically use that as a shift point but not too sure about cruising. the motor sure sounds good there though.

If it does, I'd suggest you take a look at your tach. You say your tach is not "perfect", do you have any idea how "imperfect" it might be? If you've never checked it against a good tach, I'm betting you will be surprised.

Bill

 

[Hodee]

getting the tach checked is on my to do list. I am hoping it is way off as many of them are, so I could feel more comfortable about the engine while doing 65 mph or so. Have not done the math yet but printed out the post that explains engine rpm and distance by marking on the driveway.

 

[alpineracer]

Math with that tire size:

rpms mph
1000 18
2000 36
3000 54
3500 63
4000 72
5000 90
6000 108

Can send the .xls

 

[Bikesandfires]

4.22 rear, 25' tire, 65MPH= 3688RPM by my calculation...3546RPM if the tire was 26"

 

[alpineracer]

Math with that tire size:

rpms mph
1000 18
2000 36
3000 54
3500 63
4000 72
5000 90
6000 108

Can send the .xls

mph=a/b*c"/12*60min

whereas- a=rpm; b=rear end ratio; c"=tire cir inches

 

[gordonra]

A few years ago I created a spreadsheet to calculate the engine RPM vs. Tire size. It includes rear member ratio and transmission ratios.

Kevin McLemore added quite a bit to it along with some graphics.

If anyone would like a copy of it you can access it here:
https://dl.dropboxusercontent.com/u/39675377/Tire-speed calculator V2.xls

If that fails:
https://www.dropbox.com/sh/abm8vdasdav1g7p/ruGoty5lYH

Regards to all,

Rich

 

[Hillman]

I have a 1725 in my SII. The engine feels 'comfortable' to about 4200 rpm, although I might not want to do that all day. Somehow it feels better if the OD is driving the 3.89 rear end with stock wheels, otherwise too noisy.

 

[Hodee]

I love this forum. Thanks to all. Now I feel better about 65 on the highway,especially with the bigger wheel/tire selection. Besides, I like the look better too. Just my opinion. See attached photo if I can get it to work.

 

[Eleven]

I have a dead stock SV. I have no idea if the motor bottom end has ever seen daylight, I did the valves a couple of years ago. I have a Tom H tach that I trust and hit the numbers quoted below. It scares me to death to run that old engine at 3500-3800 on the highway for any length of time; afraid I will throw a rod. Should I worry about that? Does't appear you folks are.

 

[George Coleman]

I have noticed that any RPM under 4000 seems to be ok for the 1725 motors. My Alpine V had a 4.22 rear end and at 4000 rpm I was doing 60mph, our cars in stock condition are not made for todays highway speeds, that's why I installed a 5 speed box. Now at 3500 rpm I am doing 72mph that keeps me in line with highway traffic. Just sayin!

An OD would give you about the same results.

 

[RootesRooter]

cars stock are not made for todays highway speeds,

I don't think Series V's with 4.22's were made for 1966 U.S. freeways, where 70mph speed limits were the norm.

 

[alpineracer]

Found this data:
Power & Torque
The Alpine has a peak horsepower output of 81 HP @ 5,200 RPM. Maximum torque available is 93 ft-lbs @ 3,600 RPM.

If true, IMHO, cruising at peak torque is efficient and reliable.

Eric

 

[SRQJeff]

Tach rebuild

My tach was horribly off. Had it rebuilt by Tom Hayden, and he did an excellent job. Right on target now. If you're interested, you can contact him at thayden@keithley.com. Or if you want to do it yourself, Tom has provided us with instructions:

http://www.sunbeamalpine.org/downloads/alpine_tach_repair_rev5.pdf

 

[Jay Laifman]

RPM is relative and subjective. I remember having no problem "cruising" on the freeway in the early 80s at 4200 rpm. Now a days with cars so quiet and smooth, it seems a bit more busy than it used to. But I also notice that when I'm driving on the freeway, when 65 seems high in the rpm range, as time goes on, I'm well over 70 and not even noticing the rpm.

But I have to add that in the 80s, I couldn't wait to give it more power. All the while, my dad kept saying to get an OD. Then around 90 I rebuilt it with Holbay head, cam and Webers. It was a great change. But then I finally got an OD. It was so much more of a change than the whole Holbay set up. Truly reformed the car. Even then, when I was fine with running higher rpm all day, I appreciated how much nicer it was.

 

[Hodee]

I'm contemplating an OD but also struggle with changing the originality of the car. Currently all numbers match, original paint with only a few mods such as wheels and aftermarket steering wheel for more leg room. Just trying to decide if I need to go 80 on the freeway.

 

[Jay Laifman]

Originality? Are you saying because you won't put a 5 speed in? You could put in a stock Alpine tranny and OD.

Or are you concerned because your car didn't come that way from the factory? I've had my Alpine for 35 years. I'd love to think Alpines have finally gotten their due, and are worth lots of money. But, at least from my viewpoint, they have never really been discovered, and it's now after that 30 year window when cars are supposed to be worth their most. I'm not seeing people pu pu Alpines because they are not exactly as they came from the factory.

So for goodness sakes, add the OD if you want. If anything, I think it will increase its value.

My $.02.