How many RPM's...? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

motocrosschump · 09-07-2005, 06:46 PM

at 70mph? My speedo is broke so I have no idea how fast I am going.

I have used this http://www.angelfire.com/fl/procrastination/rear.html and it says it will take 3700 RPM's to run 70. That seems like alot.

235/50/15 3 speed and 3.73

I measured the diameter of the tire and its 24.5 inches.

cableguy0 · 09-07-2005, 06:56 PM

those tires are tiny and yes those rpms are correct. why are you running such a short tire. a normal 235/75/15 is the stock size on these trucks and measure out to about 29 inches. that alone would help significantly with keeping the rpms down on the highway

motocrosschump · 09-08-2005, 11:46 AM

Is it safe to run 3700 RPM's constantly?

farside847 · 09-08-2005, 11:49 AM

Quote:

Originally Posted by motocrosschump

Is it safe to run 3700 RPM's constantly?

Good question.... What would be considered "redline" for a stock engine?

Ogier · 09-08-2005, 12:19 PM

Redline on a stock smallblock is somewhere around 5500 or so.

it is safe to run that high of an RPM for a while, but, you are putting a lot more wear on your Engine and Transmission doing so as well as burning a lot more gas.

Changing the gears in the rear axle may seem like an expensive proposition, but it will pay for itself in the first six months in gas mileage alone.

farside847 · 09-08-2005, 12:29 PM

Quote:

Originally Posted by Ogier

Redline on a stock smallblock is somewhere around 5500 or so.

it is safe to run that high of an RPM for a while, but, you are putting a lot more wear on your Engine and Transmission doing so as well as burning a lot more gas.

Changing the gears in the rear axle may seem like an expensive proposition, but it will pay for itself in the first six months in gas mileage alone.

What is a "good" freeway RPM? 2500? I run at 3000 RPM at 65MPH and I feel bad doing it. Feels like Im pushing it too hard.

*FormerMember* · 09-08-2005, 12:42 PM

Depends on where the torque band is in your engine.

Most say thay 1700 to 2100rpm is about right. I tend to like 1850 with a stock older 350.

Lugging your motor isn't good, nor is overrevving.

69Goody · 09-08-2005, 01:25 PM

I too am around 3500, but that is since I put my 3.73 in the rear. Prior to that, I was right around 2400 on 2.73 rearend, around 27" tires, and a TH400 trans.

I want and will keep the 3.73, but I will be installing a new 700R4 (overdrive baby) to address the RPM/Fuel issues.
That will change my setup dramatically and give me a 30% improvement in OD and a bit taller ratio in First Gear from 2.48:1 to 3.0:1.
My best cruising gear ratio now is 1:1 in 3rd gear, but I'll be getting .70:1 in the OD gear. I expect to drop my 70mph RPM down to about 2300 or so.

The problem with all of this is the required changes due to different length trannys and the size of the yoke. The 700r4 is longer than the th400 and the yoke is smaller than my 400. But I think it will be worth it.

motocrosschump · 09-08-2005, 05:11 PM

I guess that is a good excuse to put 20's on it

09-07-2005, 06:46 PM	#1
motocrosschump Registered User Join Date: May 2005 Location: Texarkana, AR 71854 Posts: 397	How many RPM's...? at 70mph? My speedo is broke so I have no idea how fast I am going. I have used this http://www.angelfire.com/fl/procrastination/rear.html and it says it will take 3700 RPM's to run 70. That seems like alot. 235/50/15 3 speed and 3.73 I measured the diameter of the tire and its 24.5 inches. __________________ 2006 Titan SE Crew Cab Daily Driver 2005 Mazda Tribute (Wifes car) 1969 C10 SWB 350/3 Fleet "Max" 1969 Chevelle 2 door 350/3

09-07-2005, 06:56 PM	#2
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	those tires are tiny and yes those rpms are correct. why are you running such a short tire. a normal 235/75/15 is the stock size on these trucks and measure out to about 29 inches. that alone would help significantly with keeping the rpms down on the highway __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

09-08-2005, 11:46 AM	#3
motocrosschump Registered User Join Date: May 2005 Location: Texarkana, AR 71854 Posts: 397	Is it safe to run 3700 RPM's constantly? __________________ 2006 Titan SE Crew Cab Daily Driver 2005 Mazda Tribute (Wifes car) 1969 C10 SWB 350/3 Fleet "Max" 1969 Chevelle 2 door 350/3

09-08-2005, 12:19 PM	#5
Ogier Chopper/Painter Join Date: Jul 2004 Location: Medford, Or. Posts: 284	Redline on a stock smallblock is somewhere around 5500 or so. it is safe to run that high of an RPM for a while, but, you are putting a lot more wear on your Engine and Transmission doing so as well as burning a lot more gas. Changing the gears in the rear axle may seem like an expensive proposition, but it will pay for itself in the first six months in gas mileage alone. __________________ With regards, Ogier 1969 Chevrolet C20 - Resto-Custom started!!!

09-08-2005, 01:25 PM	#8
69Goody Registered User Join Date: Jul 2004 Location: Southern Tip of OHIO 45680 Posts: 49	I too am around 3500, but that is since I put my 3.73 in the rear. Prior to that, I was right around 2400 on 2.73 rearend, around 27" tires, and a TH400 trans. I want and will keep the 3.73, but I will be installing a new 700R4 (overdrive baby) to address the RPM/Fuel issues. That will change my setup dramatically and give me a 30% improvement in OD and a bit taller ratio in First Gear from 2.48:1 to 3.0:1. My best cruising gear ratio now is 1:1 in 3rd gear, but I'll be getting .70:1 in the OD gear. I expect to drop my 70mph RPM down to about 2300 or so. The problem with all of this is the required changes due to different length trannys and the size of the yoke. The 700r4 is longer than the th400 and the yoke is smaller than my 400. But I think it will be worth it. __________________ Only the Mediocre are always at their best... '69 GMC LWB 406, TH400, 3.73 Posi' Things I've learned from my truck...If I was an automaker, my vehicles would be overpriced, run rough, and get 5MPG.

09-08-2005, 12:42 PM	#7
FormerMember Account Suspended Join Date: Feb 2004 Posts: 3,051	Depends on where the torque band is in your engine. Most say thay 1700 to 2100rpm is about right. I tend to like 1850 with a stock older 350. Lugging your motor isn't good, nor is overrevving.

09-08-2005, 05:11 PM	#9
motocrosschump Registered User Join Date: May 2005 Location: Texarkana, AR 71854 Posts: 397	I guess that is a good excuse to put 20's on it __________________ 2006 Titan SE Crew Cab Daily Driver 2005 Mazda Tribute (Wifes car) 1969 C10 SWB 350/3 Fleet "Max" 1969 Chevelle 2 door 350/3



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