tachometers

Guys, I'm in the market for a tachometer from the period (late 60's to mid 70's) for my 258/6 75 CJ5.

I've about given up on finding a column mount NOS/original Jeep tach that mounts on the steering column, so I have been looking for a Stewart/Warner or Sun tachometer from that era that is also column mount.

I have the 75 Service manual but I can't find the RPM range listed anywhere. Does anyone know what the actual red-line is for the 258/6? I'm guessing probably 5500 RPM, but just looking for some other opinions....Thanks.....

 

I think it may be 5000. I seem to remember being told that.

 

Probably closer to 3000 RPM or less for the '75. I know mine sounds pretty much wrapped out at 2500 RPM - whenever the Emissions Tech revs it up that high I cringe. When I'm driving I never run mine above about 2200 RPM. I'm certain parts would be flying apart at 5500 RPM...

 

I would not advise revving a stock 258 over 5000 RPM; I think anything above 4000 is pointless. There's no "red line" as such that I know of... If you look at the peak torque/hp ratings, that will give you an idea of the usable range:
HP 110@3500
TQ 195@2000

Basically HP is TQ x RPM. Up to the TQ peak, the HP is increasing faster than the RPM is increasing, ie you may have 4x the HP at 2000 than you have at 1000 RPM. The HP curve starts to fall off after 2000 and is flat at 3500, decreasing at higher than 3500.

Anyway, the stroke of a 258 is pretty long, so it's not a high-revving engine. For best longevity, I'd definitely keep the revs below 4000.