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Old 02-12-2017, 02:44 AM   #1
pop_LMP
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Top speed?

Hey guys

I've got a 1981 c10 with an 350 small block and a gear ratio of 2.73 (planning on getting a 3.73 with positrac)

I've pushed 100mph but I broke my original needle on speedometer.

I'd like to know how fast I can push it without ruining my engine.

Thank you
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Old 02-12-2017, 04:39 AM   #2
Nick_R_23
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Re: Top speed?

Speed isn't going to be your limiting (or breaking) factor, RPM will. Speed is just a byproduct of RPM x gear ratio. Exceeding the RPM limitations of your engine is going to be what damages it. The 3.73 gears will lower your top speed but accelerate quicker and have more power to push your truck to its (new) top speed with less effort.

However, for what reason does your truck need to be pushed to 100 mph? Also, at that speed, I would first worry about suspension, tires, and brakes being rated for those speeds, way before I worried about the engine.
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Old 02-12-2017, 10:03 AM   #3
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Re: Top speed?

4.11s and no overdrive for my 86 means my engine is racing at like 70. That's about the fastest I ever went. Years ago when I owned a f150 the thing would start to get really floaty at 90. I can honestly say I've never done 100 in anything I've owned.

What always scares me is throwing a driveshaft or blowing a tire at that speed
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Old 02-12-2017, 10:50 AM   #4
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Re: Top speed?

Quote:
Originally Posted by abig84 View Post
4.11s and no overdrive for my 86 means my engine is racing at like 70. That's about the fastest I ever went. Years ago when I owned a f150 the thing would start to get really floaty at 90. I can honestly say I've never done 100 in anything I've owned.

What always scares me is throwing a driveshaft or blowing a tire at that speed
Racing!!
Put some earplugs in!! LOL!!
That's only 3400 rpm.
Hardly turning over!

As for speed, I've seen 140 mph a few times. Once in a LS6 chevelle and a few times in a '06 charger daytona.
Live a little!
Get out there and live on the wild side!!
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Old 02-12-2017, 03:44 PM   #5
Alex V.
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Re: Top speed?

The theoretical top speed of my '85 1-ton with TH400 and 4.10's, just by engine redline+gear ratios, etc., is 110. Being a 454 it might have the power to hit that, but on our trucks in stock form the engine will usually just come to the limit of its air supply or the valve train will reach its limit (valve float) before the technical redline. With especially high gears like your 2.73's the wind resistance may dictate, basically, "terminal velocity" just because the engine doesn't have the power to push it any faster, before it hits redline or valve float territory.

I've had my '85 to 85 once - I still had plenty more throttle but just didn't keep going. I believe it could hit 100 but that's a lot of big components spinning real fast so I'd want to know it's all in real good shape before trying.
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Old 02-12-2017, 11:15 PM   #6
Ziegelsteinfaust
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Re: Top speed?

Years ago I had a 75 C10 rcsb. I built a strong torquey 350 with 2.43 gears for DD mpg. I also lowered the truck 4/6 or 5/7. I drove a lot of hwy back then for work at odd times, and OD trans were to expensive for me back then. So pep off the line was not as important as it had none to speak of.

It would run 110 for quite awhile as I took it to Vegas a couple of times, and ran 90-110 most of the way. At 110 with my motor it was running out of steam to keep moving the air, and turned gas into noise faster then speed after 100. It was perfectly stable at 100, but you have to have a well sorted out suspension with stuff shocks.
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Old 02-13-2017, 02:31 PM   #7
cheap
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Re: Top speed?

My 77 C10 SWB with a mild 350 and a 3 speed with a 3.73 gear has made it up around 120 a few times, but running my engine a like 4800 for extended time periods seemed a little sketchy.
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Old 12-31-2018, 04:08 PM   #8
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Re: Top speed?

Not sure my c10 is the best vehicle for top speed runs it’s got half an inch of play in the back axle. Done 170mph in my old bmw m3 though. That was sketchy tires only rated to 155. Thought I was going to go up in a fireball and was not used to judging breaking distance at that speed
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Old 12-31-2018, 09:35 PM   #9
akart
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Re: Top speed?

There are limiting factors. My tires are rated for 100 MPH. with my 4:11 rear end,that's 4320 RPM,quite doable. I do 85 MPH often,that's 3672 RPM and a bit more sometimes and there is a bunch left. Could go faster I guess but I wonder what other systems I might over stress. I'd like my truck to last. I also have flat hydrolic lifters and they shouldn't go much over 5000 RPM with that set up or you could get valve bounce which is the valve hitting the piston. If you want to go really fast use a roller cam and the double springs, (this is getting expensive).
Be happy w/100 MPH
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Old 12-31-2018, 09:57 PM   #10
74CustomK20
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Re: Top speed?

I've done roughly 100 in my k10, and it was quite sketchy. Had a 350 from a Camaro and 3 speed auto. 4" lift with 35's n 3.08 gears. It did it, but I only did it once. RPM will destroy a motor, but speeds just is what it is.
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Old 01-01-2019, 03:22 AM   #11
rideair
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Re: Top speed?

A thread started two years ago, by someone on a mobile device asking how fast can you go? Has only posted that one time, lets hope they did not find out the hard way.

pop_LMP, you still with us?
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Old 06-11-2019, 07:37 PM   #12
Sparky dave
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Re: Top speed?

Yup Marty got to 88 mph and broke the space time continuum!
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Old 06-12-2019, 10:14 AM   #13
blazer2007
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Re: Top speed?

I took a 400 mile trip,no freeway and was cruising nice at 70-75 and was getting passed all day like I was standing still by new trucks pulling fifth wheels, even up hill they were passing me,how embarrassing
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Old 06-12-2019, 05:10 PM   #14
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Re: Top speed?

Got my 83 up to what i thought might be 100 and i swear i saw the 4 Horsemen
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Old 06-13-2019, 04:47 PM   #15
demian5
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Re: Top speed?

I have 3.07 in my 70 c10 with 31" rear tires and a 350/350 combo. i dont think I would have the balls to redline it, I imagine that could be about 140 MPH...
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