What is the usual redline on a stock 258?

Just about a month ago I put an hei in and also timed it to 9 degrees but I set the idle a little low at about 550 rpms. So I put a Sunpro tach from autozone in the jeep today and it said the idle was at about 400 rpms so I turned it up to almost 700 with the brights and the heater on. I took it out to test drive it and see how high the rpms go and in first gear when I got it to around 3500 it was really screaming so I shifted. What is the usual redline for a 258 with a 1 barrel carb on it?? Also would raising the idle from about400 to 700 change my timing to where I would need to time it again?

Thanks

 

Red line doesn't really fit with what you are asking. On an engine built for racing, the higher the RPMs go, the more power you have. Torque peaks at a high RPM, and power is basically torque times RPM. For a flat torque curve, the power increases linearly with RPM.

In such a situation (ie a race car), the revs have to stop because the engine can't survive. With a production engine, such as the 258, you will run out of power way sooner than you run out of revs. You could run a stock 258 to 5000 rpm with no damage to the engine, but it would be pointless. The torque peaks at about 2000 rpm, and by 5000 the power is actually decreasing with increasing rpm. So, the "red line" may be 5500 or 6000 rpm, but why would you ever run the engine that fast?

Also, the sound is pretty much irrelevant. Jeeps are noisy. Likely most of the "engine noise" you hear is actually fan noise - the fan blades thrashing the air. There's also a lot of gear noise. Plus, there's no insulation between the engine and passenger compartment, so you're going to hear the engine. BTW, driving around town, I'd shift at about 1500-2000 rpm. Why bother winding it out? You'll get from point A to point B just as fast. The torque peaks at about 2000, so the rate of acceleration starts to fall off after that.

What does the manual say about the idle? Are you asking about how to set the timing? Set the advance at the idle specified by the factory. Remove the vacuum advance hose.

 

Thanks for the reply tim. I understand now. The motor is actually strong enough to handle 5000 rpms but that is way beyond the stock cam's powerband. I usually shift at around 1500 but I was just curious as to how high it winded when I got on the skinny pedal. Also I took the jeep up to 55 today and I beleive the rpms were at 2400. Thats lower than it always sounded to me. After my 31" bfg mts wear out I plan on throwing a lift on and some 33's maybe. That will bring my rpms down a little too.

 

It will self regulate when the valves start floating

I highway commuted in my 84CJ for a couple of years with 4.11 gears and 35" wheels. 3300-3400RPMs got me around 65MPH IIRC. It sure sounded like the thing was revving like hell.

 

Torque and HP curves cross at 3500 rpm for a 1 bbl 258. Not much reason to go beyond that. That being said, my heap will easily rev to 4500-5000, the headers might have something to do with that. Set my redline at 3500, no point in going higher...

 

I would guess the factory redline on a 258 to be somewhere in the 4500 range. Torque and HP cross at 5250, not 3500, but that's irrelevant. What determines redline on a stock engine is where you can expect it to mechanically fly apart, or the valves to float. Cam selection is one of many factors which will affect where your HP peak occurs, but that has nothing to do with redline, either. Again, I'd say if you spin it faster than 4500 you may be playing with disaster.

As for your timing, the mechanical advance normally starts at about 1000 rpm, so adjusting the idle from 400 to 700 shouldn't affect the timing. However, it could depening on how worn your mechanical advance mechanism is. It only take a minute to recheck it, why not just do it

 

Whoops! Checked my FSM, for 1975 258 Net bhp is 110 @ 3500 rpm. Net torque is listed as 195 at 2000 rpm. This is obviously for an engine with the stock cam. One of these days I'm going to get the fact that the old memory just ain't what it used to be.

I still don't see much point in revving above 3500, although it won't hurt anything to go higher. Although my engine will easily rev to 4500, its just kind of pointless.

 

Thanks for all of the replies. It is a brand new hei that I just installed a month ago so the mechanical advance should be in good shape. I would just check it again but I do not own a timing light yet. The motor felt like it didn't want to go any higher than 3400. Maybe worn out valve springs or the restrictive exhaust? Later on I plan on upgrading to a 2 barrel carb and intake, a 4.0 head and maybe one of comps extreme 4x4 cams.

 

There are a lot of reasons an engine won't rev up, most have to do with airflow restriction in the exhaust or intake. Make sure the air filter is clean. Unbolt the exhaust from the manifold and see how it revs. If those are OK, a dirty fuel filter or carb can limit rpm. You have a new distributor, verify that you have somewhere around 30 degrees of timing at about 3000 rpm with the vacuum connected. You can get a cheap timing light at most auto parts stores. It's an essential tool, everyone should have one. Try to find one with an advance knob, they make it a lot easier to check total advance.

Of course, it's also possible the engine is worn out enough that it just doesn't have the poop to push the vehicle. It'll take some investigation to make that determination.