250i6 mods for Highway Driving

Tdwmaxwell · 2025-01-22T00:11:14-0500

At the moment I drive a 1982 C10 with the 250i6 and the SM465 transmission, don't know what rear end. I'm looking to make it a bit more comfortable as a highway cruiser. I've been doing more highway driving recently and it feels like I put a lot of strain on the engine (I don't currently have a tachometer so I have almost no idea what my RPMs are). I've been thinking about doing an engine swap to a V8 but was wondering if I should try changing the gearing first. Any recommendations about what I should try to make highways more comfortable?

Grit dog · 2025-01-22T01:06:45-0500

If it’s an original 6cyl I’d be surprised if it has steep gears. But if that’s what you’re referring to, a V8 won’t help high rpm’s.
If your issue is just it doesn’t have enough power then more power is the solution.

ali_c20 · 2025-01-22T01:08:26-0500

Welcome from Austria. Are you happy with the original engine and want too keep it? If yes I would install a tachometer (I prefer to have a tach in all of my cars) and check the rear end ratio. Tire size is also related to engine rpm.
You can use a Engine rpm calculator to get the rpm for current setup and the effects of the changes you want to make. No need for a tach then.

With that data I would see what needs to be done to achieve the desired goal.

This one has a list of popular transmission gear ratios:

https://www.crawlpedia.com/rpm_gear_calculator.htm

Vbb199 · 2025-01-22T06:54:49-0500

Look in the glovebox and take a pic of the sticker and upload it. We can figure out your axle ratio from the SPID....
Or, compare for yourself.

I believe it'll be a GUx code, like for example, GU6 is 3.42, and GU4 is 3.08.

Assuming its the original rear gears, we can go from there and reccomend a change that'd suit you

mcarlo86 · 2025-01-22T13:26:37-0500

Up in this part of the world, if a C10 came with a SM465 4 speed and a 6 cylinder, it usually had 3.73's. That being said, check your SPID label if it is still there. If it had a 3 speed manual or automatic, then they often had higher gears like 3.08 or 3.42. My dad has a '76 C10 with the 250, 465 transmission and 3.73's with 235/75R15 tires. It cruises nicely at 60-65 mph and will run 70 fairly easily, but probably wouldn't be my choice for interstate/freeway driving. If you do have 3.73's, then finding an overdrive transmission would help a lot. That all being said, a 250 will handle 3,000 rpms just fine and it really isn't adding "strain" to the engine. They handle rpms better than a 292 does.

250i6 mods for Highway Driving

Tdwmaxwell

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Grit dog

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ali_c20

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Vbb199

B-rate Hillbilly Customs

mcarlo86

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