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Old 10-06-2022, 10:04 AM   #1
72SB
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Column Mounted Tach-250 RPM?

Had this Autometer 2300 tach on another car I changed the gauge package in years ago. My dash cluster does not have a tach nor center clock, so I decided to put this in (pic). Just switched the dip switch inside for 6 cyl

My 4.1 is stock using the 1 brl Rodchester but I do have a Pertronix kit in dizzy. I read HP & TQ info is:

Max Brake Horsepower: 170 @ 3800 rpm
Max Torque: 283 @ 1600 rpm

What is the Max RPM these engines can rev to?
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Old 10-07-2022, 04:06 PM   #2
RichardJ
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Re: Column Mounted Tach-250 RPM?

What do you mean by "Tach-250 RPM?"

Your 170 hp, 283 tq specs are more like 292 specs. Those numbers are a little optimistic for a stock 250.

This page shows some specs, https://en.wikipedia.org/wiki/Chevro...-Thrift_engine, but I'm not really sure of their accuracy. On their chart, on the right column, has references to the GM Heritage archive pages that don't exist any more. They turned the Heritage pages into a store. Dumb asses.

In your pictures, the tach is reading about 800 ? You should have it idling about 600-650 rpm. A smooth running six should have no problem idling down about 450-500, but in my case the oil pressure starts dropping below 500rpm so I keep my 292 at about 550rpm.

I don't know what max is for my engine. It pulls best 1800-2800 so most shifts are somewhere in there.
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Old 10-08-2022, 05:25 AM   #3
67 twins
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Re: Column Mounted Tach-250 RPM?

Your question shouldn't be how high will they rev. As you can see these inline 6s make peak torque at 1600 rpm, therfore there is no reason to ever turn more than 3000rpm. You will have more power available by upshifting. Seems counterintuitive if you are used to peaky V8s but that's the way it is. Besides there is no power up there anyhow on a stock engine the power drops off precipitatiously. Look at the bright side that power starts at 800rpm.


This is for a 292 a 250 has a similar torque curve just lower numbers
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67 C10 283 T5 swapped longbed fleetside = wife's daily driver
67 C20 292 (originally a 250)4speed longbed fleetside w/original wooden bed=my project truck
67 C10 283+.060 (so a 292 as well)T5 swapped longbed fleetside=my DD
72 C1500 Sierra Grande 350 TH350 longbed fleetside=wife's fair weather truck
Can you tell we are fans of longbed fleetsides & 67s
Chris

Last edited by 67 twins; 10-08-2022 at 05:36 AM.
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Old 10-08-2022, 09:25 AM   #4
72SB
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Re: Column Mounted Tach-250 RPM?

Depending on what site you refer to for engine specs, this site indicates the "1972" 250 makes (varies by year): https://www.enginefacts.com/chevrolet250/

1972 with 1 Barrel Carb
Max Brake Horsepower: 130 @ 4000 rpm
Max Torque: 205 @ 1600 rpm
Stroke: 3.53
Bore: 3.875
Compression: 7.7
Firing Order: 153624

My ? is how high can the 250 safely rev?

My sense is 4500 RPM as it peaks HP at 4k rpm...according to above specs. Don't intend to drive it that high RPM. Valve springs are original, and cam is what it is so no benefit revving past 4k rpm

Now with tach installed I find my "normal" shift is about 2800 rpm and cruising at 65mph I am at about 2800 rpm. I had this tach on another car and assume its accurate but it's not a high $ tach. Motor runs so quiet it was hard to tell by ear if it was revving to high on fwy so since I had it, I put it on to see what RPM's actually are.

I had previously set my idle at 650 using my timing light (spec for manual trans per sticker on core support). This tach shows closer to 750-800 at idle so I will revisit idle adjustment. Pic shown was right after startup with engine not yet at operating temp
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Old 10-08-2022, 09:45 AM   #5
67 twins
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Re: Column Mounted Tach-250 RPM?

Rev it to 4000 or 4500rpm if you like but all your doing is wasting gas & making more noise. You're not moving the truck along quicker.
I think you're paying to much attention to HP figures. Torgue is what gets work done. The idea of HP was invented to sell engines.
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67 C10 283 T5 swapped longbed fleetside = wife's daily driver
67 C20 292 (originally a 250)4speed longbed fleetside w/original wooden bed=my project truck
67 C10 283+.060 (so a 292 as well)T5 swapped longbed fleetside=my DD
72 C1500 Sierra Grande 350 TH350 longbed fleetside=wife's fair weather truck
Can you tell we are fans of longbed fleetsides & 67s
Chris
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Old 10-08-2022, 09:56 AM   #6
72SB
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Re: Column Mounted Tach-250 RPM?

This truck is just a cruiser. Not looking to drive it balls out. My ? was just how high a stock 250 can rev safely. I have other SBC cars that are built and shift at 6400 (about 500 rpm after peak HP for that motor) at the track but rarely on the street do I ever go that high in those cars

I can feel, like any motor, when it stops making power and just "noses over" which is right at 4k ish. Don't rev it that high normally
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Old 10-08-2022, 10:34 PM   #7
'68OrangeSunshine
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Re: Column Mounted Tach-250 RPM?

250s can rev higher than 292s. I keep a red marker on the Tach at 3500. Over-revving a 292 can cause the Harmonic Balancer to spin off its mark, wobble, or separate.
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