Road speed with a 3.73???

[woodscavenger]

I have ripped my truck down to the frame rails. Now would be the time to swap my rear end or possible consider an S10 T5 tranny swap. Obviously a rear end swap would be easier. I have a 3.73 rear end. My current tranny is a 4 speed. What type of reasonable top end am I looking at on this truck so I can decide if I need to go that route?

[Young Ed]

I've got a 3.90 and tall 16s on my truck and can go 60-65 easily. You'll be good with that 3.73. I have a 3.73 in my coupe with 15s and that one cruises nicely too.

[greg g]

figure it all out here.

http://www.4lo.com/4LoCalc.htm

[grey beard]

Several of us on this forum are running the stock 4:10 rear axle ratios with tall (31-inch) radial tires. Not too bad a ride, and 55 seems comfy to me. JMHO

[Tony_Urwin]

Sorry, Dave, I beg to disagree. 55 mph is OK if you are a Sunday driver. 55 mph may be top speed if your suspension needs a rebuild. But 55 mph is definately not OK when you are driving at night and you have a pair of 18 wheelers on your tail. I've been there and it surely is not comfy.

Get the 3.73 if you can find one.

Sorry to be contrary. I just had a fight with the wife.

[greg g]

I have to agree with Tony. I run 4.1 to 1 in my coupe, I am running 225 75 tires and I will run it up to 70 o the clock for short bursts. What concerns me is even at 65 on limited access highways, I am probably 10 to 15 mph slower than 80% of the traffic. Even on regular highways, most traffic is running 60 to 65, so the closing rate isn't to bad on grade level roads. But I wouldn;t want to be on a highway where I was taped out at 55 with traffics closing from the rear at 15 + mph and having no reserve. That said, with tall tires and 4 .11's you should be able to drive at 60 all day long.

[woodscavenger]

Now I want you guys to realize this is a B1B truck. I am guessing the gearing in the tranny is a bit lower than the coupes. I was figuring I would for sure have to swap things out to get a truck that could do 65-70 on the highway however from what is being said I may be lucky. Do any of you guys with trucks have any input?

[Young Ed]

I've got 215 85r16s and a 3.90 behind a stock 218 .030 over in my pickup. 70 would be pushing it. 65 is doable.

[greg g]

I thik you will find that high gear is 1 to 1 car or truck. Your lower gears might be different but high is pretty much 1 to 1 for road vehicles.

[Vintrader]

There is no question that you can make a B Series run 65 - 70 but I am not sure I would want too......The suspension, front end and most of all BRAKES....are very old technology even if they are in perfect working order where designed for lower speeds

(Remember the national speed limit in those days was under 50 MPH).

I am very happy to stick to the side roads and enjoy the view and the ride. Dutch

[bts_dodge49]

Any idea what RPM you would be turning at 55 Mph with 4.11 and 15" tires? What is red-line for these flat heads? Any idea what a comfortable crusing RPM you should shoot for?

Thanks,

[Reg Evans]

For me 2500 rpm for cruising is comfortable. What size are your 15" tires?

P235's are going to turn slower than P205's.

[woodscavenger]

Vintrader, I appreciate the concern about the brakes. I will be ordering a disc brake kit before it goes on the road. As far as the supsension does anyone have any advice?

[bts_dodge49]

Hi Reg, tires are 235/15. What would be redline on a stock flathead??

Thanks

[Reg Evans]

Any idea what RPM you would be turning at 55 Mph with 4.11 and 15" tires? What is red-line for these flat heads? Any idea what a comfortable crusing RPM you should shoot for?

Thanks,

According to the rpm calculator posted by Greg G at 55 mph with 235/15 tires your engine would be turning at 2630 rpm.

By "red line" do you mean when will your engine scatter it's parts all over the road?

[greg g]

Hp is rated at 3600 rpm. The factory used to pull engines off the line and run them on a test bench for 50 hours at 3600. So are you looking for a top RPM to twist it, ar for a reliable cruising rpm. I have heard that 85% of HP RPM is bassically an all day deal. So take 3060 Rpm go back to the calculator I posted fill in your details, tire diameter, gear ratio, trans ratio, leave the transfer case blank, it will figure things out for you.

If you extrapolate the figures the factory bench test was equal to about 3000 miles.

[Young Ed]

Wow at 3000RPM my truck comes out to 69.xx MPH and the coupe 66.xx. Not bad.

[bts_dodge49]

Thanks guys.... this gives me a good idea of where I can run this safely. It's deceiving because at 45 Mph it sounds like it's revving pretty good..

[greg g]

Only cause you're used to riding around in a modern, well insulated, geared down modern car with an OD top gear. My wife's car is only turning 2800 at 72 mph. Barely off idle for a 6000 rpm redline on the tach.

[Reg Evans]

The calculator says that at 2800 rpm "Ole Yeller" ,my 52 1/2 ton with it's 3.0 rear ratio, is moving along at 82 mph. I don't like to drive the truck more than about 60 mph so I guess I'm use to hearing the engine at only ~2100 rpm. Yup Greg....that splains when I hear one of these engines running at more than about 2500 rpm's I feel like it's gonna fly apart.

[Tony_Urwin]

Reg, how does "Ole Yeller" do off the line? Is the acceleration adequate with the 3.0 rear?

[Young Ed]

Reg do you have a 4spd in that thing? I always thought you could put a lower gear in a 4spd pickup and then have to actually use granny as a normal gear.

[Reg Evans]

Reg, how does "Ole Yeller" do off the line? Is the acceleration adequate with the 3.0 rear?

Tony,

I also have a 50 Chrysler 251 installed in the truck so Ole Yeller does fine off the line and up long grades.

[Reg Evans]

Reg do you have a 4spd in that thing? I always thought you could put a lower gear in a 4spd pickup and then have to actually use granny as a normal gear.

Yes Ed. It has the stock 4 speed and granny still isn't necessary to get rolling so it's essentially a 3 on the floor. 1st gear is still pretty much a stump puller.

[Dennis_MN]

Grannie Gear is also usefull in Parades. Just put it in super-low and enjoy the view.

http://www.sullivan.us.com

Dennis