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RPMs at 65mph?

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whitezracer

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What is everyone running rpm wise at 65 in there blazers with 700r, 35s and either 4.10 or 4.56 gears? I am trying to decide what gears to go with to get these junky 3.08 out of my blazer but I don't want it to be screaming at 60 and above because I still dd it alot.
 
I don't quite recall my rpm's but I think it was around 1700-1800 at 65 mph. 35's, 700r, 4.10's. It was a little better performance than the 3.73's I replaced and the engine was a little happier.

I'm at 6500' so power is a little lower.

Since then, I put on 33's and keeping the 4.10's and 700r. RPM's are now around 2000rpms at 65 and it drives a lot better! 75 mph is no problem now and the tranny doesn't hunt up and down at all. Engine is a lot happier on this setup combo.

I'd say 4.56 gears for you. 4.10 will be adequate but 4.56's might be a little better for you.
 
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Basic calculator:

700r4 (.70OD at 65mph)
35" tires
4.56 gears
65mph

1992 rpms

And really the important one, at around 45mph would be 1970rpms @45mph (with 3rd gear 1.00). Your round about 3-4 OD hunting speed.



With 35" tires and 700r4, I wouldn't want anything taller than 4.56. In fact 5.13s sound even better at 2241rpms @65mph. (personal preference) 4.10 would be the tallest gear IMO to use with 35s. But people do it all the time with 3.73, and even 3.08. You're just lacking power, and straining your trans. This of course I'm ONLY referring to the 700r4.


With the 700r4, I'd be more concerned with proper 3-4 OD/lock up rpms/pressures than highway rpms. With your above parts sernario, as far as highway, you'd be safe from 3.73-5.19, not being a problem for your engine.

And for another example:

Stock setup (and I'll use the assumption of stock=safe)

700r4
3.08
31" 1519rpm
29.5" 1596rpm

Both tires examples are .70OD @65mph.
 
I would like to keep the rpms around 1900-2000 at 65 so I was thinking the 4.56 from the calculators I have used but I just wanted to see if anyone had some real life experience to be sure the calculator is correct.
 
whitezracer said:
...I just wanted to see if anyone had some real life experience to be sure the calculator is correct.
Click to expand...

Ya I dig that.



But, just to say, the calculators are basic math. It WILL be those numbers, real life or on paper. With the exceptions being for example, buying a "35" inch tire, but it actually measuring 34.5", or something like that. Which is the case most of the time. But that'll be an insignificant rpm change..
 
whitezracer said:
I would like to keep the rpms around 1900-2000 at 65 so I was thinking the 4.56 from the calculators I have used but I just wanted to see if anyone had some real life experience to be sure the calculator is correct.
Click to expand...

most guys doing 700r4/35" tires or bigger like 4.88 or 5.13 best .

this keeps the 700r4 from hunting gears at highway speed.

but its all up to you .
 
Stock 5.7, 700r4, 4.56:1 and 35's. No tach so no help there. But the truck weighing 7k makes the trans hunt on the slightest hill at 65mph. I would have liked 4.88:1 a lot better. And it would wheel better with those gears.
 
kennyw said:
:haha::haha::haha::haha:

How many issues did they have under warranty?
Click to expand...

:haha: It cracks me up though. 1500rpm. That's just off idle speeds :rolleyes: THOUGH that's cruising/coasting at 65mph flat terrain, in that scenario it SHOULD be lowest rpms while driving in any vehicle. That or change your mph and gear, should be similar.
 
MrSchaeferPants said:
:haha: It cracks me up though. 1500rpm. That's just off idle speeds :rolleyes: THOUGH that's cruising/coasting at 65mph flat terrain, in that scenario it SHOULD be lowest rpms while driving in any vehicle. That or change your mph and gear, should be similar.
Click to expand...

1500RPM works out just fine for us Diesel guys. I spend my days wishing GM had made a 14BFF with 3.42 or 3.23 gears. 3.73 is no fun... :whistle:







:haha:
 
700/4.88/"38"s (closer to 36.75" on the ground)

2200 rpm @ 70

All depends on the engine whether or not the trans hunts. A lot of pedal input on hills means a lot of TV cable input on hills = gear changes. My 400sb is super mild, the 700 fully built and holds overdrive well. lol my overdrive starts ~42 mph and holds easily.
 
My '89 Suburban had factory 3.42 in it with 31/10.5-15 tires.

Didn't do too bad, never really noticed any hunting with gears then, it did much better with fuel mileage then than it does now being lifted with bigger tires.

Running 4.10's now, with BFG A/T's 317/70-17 supposed to be about 35" in size.

RPM's run about the 2000 range at 65, I don't/haven't driven it much faster than that much, it seems like it struggles to maintain speed when running up in the 2500 rpm range, like I can almost watch the fuel gauge dropping when doing that. The 2000 range with this tire and gear combo has a certain sound to the engine that just sound comfortable, maybe I'm weird, I dunno.

Not sure what size the tires are on the Avalanche, it's only 2wd though, I know at 65 the rpms are much lower because it runs about 2100-2200 at 75, and this thing cruises real nice there too.
 
sweetk30 said:
I am sure others have posted up them before here.

try sale section 1-tonmudder I think . :dunno:
Click to expand...

Searching for 1-tonmudder yielded quite a few drivetrain parts, but I didn't see anything advertized with 3.42/3.23 gears. But it's good to know they exist (not sure how I missed that to this point). Now just to find one... :thinking: :doah:
 
Only thing I have to add is that I once parted out a truck that had a 14ff with 3.21 gears. I really should have kept them!
 
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