The Stovebolt Site Forums The Shop Area Engine Shop What is my rev/speed limit...

Have not been around here for a while but need some input on this. I have 49 half ton with '57 car motor, dual two bbl, dual exhaust and have just changed my diff to 355 with the kit from Patricks... I feel the extra speed potential but not sure just how fast I should go w/o over revving the motor. I don't have the speedo correction gear yet but I know I'm going about 6mph faster than it reads at 50 mph.

So what do you all think my max cruising speed should be kept at or below ?

What is the loaded diameter of you your tires?

2500 RPM would be a safe/quiet engine speed.

3000 RPM would be OK, but I bet your MPG would be low.

I'm at 3000 at 60mph. 3 speed no OD, 3.73 rear ratio and 25" tall tires

Tim,
Thanks, but I don't have a tach installed. I'm running 16" wheels and I'm guessing my dia. is maybe 28" I dunno what rpm I'm at when I am going, say, 50mph.

2130 RPM

50MPH
high gear 1.00
tire 28"
3.55 rear end

http://www.csgnetwork.com/multirpmcalc.html

Not sure if this is helpful, but if you are one of those newfangled smartphone users, you can set up your gps location doohickey to give you exact mph, then put a tach in your vehicle, and feel your way to a comfortable number for you. These engines are resilient and can take a lot of punishment, but if you 'feel' you are pushing its limits, you probably are.

I really like the addition of a tachometer. Cheap, easy to install.. + to positive, - to negative, and green to the minus side of the coil. You will never wonder how hard you are pushing the old girl again!

Thanks guys. I really don't want to push her but with the 355 rear I might want to go hwy speed if I need to..say 55mph...I'll get a small tach installed and go from there.

Am I to understand that 2130 is a high comfort zone for that motor ?

2130 comfortably low (fuel efficient)
2500 mid zone
3000 high zone (for cruising)

Different people have difference tolerances/preferences.

Thanks Tim: Exactly what I needed . I'll go to Reibies and get a small tach today

I would like to add a tach to my '51 so I know how hard to push it.
Can someone give me the name or a link to a tach that is cheap and easy to install?
Thanks guys.

12v or 6v

number of cylinders

Not to de-rail, a question.

I have a '71 C-10 with 250 engine, Saginaw 4 spd. and a 4.11 rear end. On the 250 what is the safe rpm limit? At 70 it's about 3650 rpm as close as I can see on the Tach. Is that safe?

Thanks.

For my 12v I used this Sunpro

OK...tach in just this AM and I'm running about 60mph at 2700rpm in 4th gear... seems to be smoothe and happy

Thanks again to all who chimed in...

Dodari: I'm betting that at 3650rpm you are over revving by about 600...at least according to the numbers posted here before but I'm certainly no pro. Put that 355 diff gear in and you will be better off.....IMO..

Dogface,

Thanks for the reply, yeah I think you're right. I'm gonna search for a 3.55 or look into a 700 R4 or 200 4R. At 3600 to 3700 or so it's screaming its' guts out. I'm cringing at that point, don't wanna grenade the mill.

There are plenty of places to get the 3.55 but it seems to all come from Patricks..some are less $$ though.. You will need the install bearing kit too...more $$ but it will pay off I think... I am a believer that if it sounds like it's about to come apart..it is and will. My 235 high pressure oiler sounds fine at about 2700 which I think is about 55 mph. Tim said 3000 m/l is cruising but I'm not happy there..or my ears aren't ... and, to date, I don't need the extra mph.

Edit: Just for the record, Tim is a master guru and really knows his stuff...nice guy too.

I disagree with if it sounds like its gonna come apart, it will. We used GMC 6 cylinders in the 50's and 60's to haul gasoline. We constantly kept them above 3k. My first semi was a 550 GMC with a 370 V8. I down shifted at 3800 and up shifted at 42 to 4400. Solid tappets and steel fans make a lot of noise, but that's just how they were. Back in those days, the people who had engine trouble were the ones who lugged their engines. Rod bearings need high rpms to oil properly and piston skirts wear in a hurry when engines are lugged. I don't try to fix or calibrate old speedos. A gps works good enough for me.

Granted i just posted this video up somewhere else but here is 70mph at 4000 rpm with fuel starve.