Engine rpm @ hwy speed??

[Jdbfish]

Any idea about what rpm a 350 with a turbo 350 tranny, 255-50-15 tires, and 4:10 rear end would be? What about 3:73 and 3:08?
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[70blackfish]

with those tires i would say 3600 at 65mph

[jocko]

255-50-15 is only 23.9" tall. Here's the rpm at 65 and 75 mph for the different ratios you asked about:

[Jdbfish]

Thanks guys!,,, Jocko, where did u get that calculation table?
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[SS Tim]

Did it yourself for any variation.

http://www.summitracing.com/expertad...tio-calculator

[Already Gone]

Originally Posted by jocko

255-50-15 is only 23.9" tall. Here's the rpm at 65 and 75 mph for the different ratios you asked about:

Are you sure on the tire height, cause I come up with 25.02 for a height on 255/50 15

255 millimeters= 10.02 inches
50 Sidewall height 50% of height = 5.1 inches
15 Rim Width

10.02 + ( 5.1 x 2 ) = 10.02 + 15 = 25.02 tire height
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[Jdbfish]

Yeah, I got 25 inches as well. I used the same calculation formula as u
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[Already Gone]

Originally Posted by Jdbfish

Yeah, I got 25 inches as well. I used the same calculation formula as u
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If you went to a taller tire ( 28/29 inches) your RPM's will go down by 300/500RPM depending on your highway speed.

[Jdbfish]

I'm gonna have to do something. This thing is really wound up at highway speeds. Not sure exactly what it's turning but gonna put a tach in to see. Debating on exactly what my best option is on a very tight budget. 700r4 tranny or different rearend or both? Thinking about trying to go to a 3:08 rear first and then a 700r4 later after I have some time to save up for it. Opinions please?
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[PanelDeland]

Most seem to be happier with a 3:73 with the 700R4.It really depends on how much hiway driving you plan on.I think the general consensus is that the 3:08's and OD are a bit hi for town cruising while the 3:73 and OD are beter there.Most of the later models I see are 3:42 with the OD unless equipped with the towing pkg or optional 3:73.As said above.tire size can make a big difference.

[DreamRyder1963]

Originally Posted by PanelDeland

Most seem to be happier with a 3:73 with the 700R4.It really depends on how much hiway driving you plan on.I think the general consensus is that the 3:08's and OD are a bit hi for town cruising while the 3:73 and OD are beter there.Most of the later models I see are 3:42 with the OD unless equipped with the towing pkg or optional 3:73.As said above.tire size can make a big difference.

I have a three speed with 3.08 gears on my truck. It definitely prefers the highway over city driving. I tend to do a lot of down shifting in the city.
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[Jdbfish]

Most of my driving is highway speeds. My dilemma is which way to go? 3:08 rear swap or 700r4 swap?
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[Already Gone]

In my opinion the best all around route for hiway /city and the occasional blast off from a stoplight would be a 3:42 ratio with a 700R4 and a 27 to 29 inch tire. To do all that with new parts is costly so at this point I think your best bet is go with a 3:08 and get some taller tires, even a 235/75-15 tire is tall enough. I have a 3:08 ready to go in my BB truck cause running around the city like I do with 3:73's costs lots in gas.
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[gvw5400]

Just a thought, actual RPM may be a bit higher than the charts indicate. Unlike manual transmissions and later model automatics,[700r4, 4L60, 4L80 eta..] T350 autos have some slip/ stall through the convertor even at highway speeds. I am a manual transmission guy but maybe some of the auto trans experts on here can weigh in to give an opinion on how much this raises the RPM in question. all the best, Dirk

[Jdbfish]

Thanks for all the input. Not sure what I'm gonna do yet.
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