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high rpm on freeway??

smartcarkiller

smartcarkiller

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Dec 10, 2008
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Tacoma Wa.
So I have a 72 blazer with a 383 stroker, th350, np205, 35inch toyo mts and 4.11s in the rear. When I am doing 65-70 on the freeway my tach says its like 3500 rpms. I know it doesnt have overdrive but it seams like it should run around 2500 rpm. Any thoughts???
 
That could very well be right if your tires aren't actually 35's.. you also got to figure that since the th350 doesn't have a lock up torque converter you will be spinning a little more than what actually makes it to the wheels.

I haven't ever seen a 35x12.5r15 that was actually 35" tall...

I don't think most gear calcs take the torque converter into account..
 
yea i know the tires are not exactly 35" but I don't see how much difference it makes, I have a 2500 stall converter on it if I am correct. As far as the tach goes I cannot be sure if its 100% right but it sure aint running at 2800 rpm.. besides I thought a stall converter only affects the way it runs from a standing start. trannys have always baffled me as to how they work. is there any way I could have weird gears in my tranny that could be causeing it? I know it has a shift kit but again I don't think that affects the over all speed.
 
Not certain how relevant this it, seeing as I'm running what I thin is stock size (31x10.50 R15) but my first time on the interstate yesterday was scary, as soon as I hit the speed limit, I immediately checked my gauges, fearing most are idiot gauges with no function, but my oil pressure was PEGGED and it's the stock 0-60psi, and my temp gauge which normally stuck at the first notch after "C" no matter what I was doing was already at the middle notch and climbing, unfortunately my deistination was to be or not to be in the family (mother in laws B-Day dinner) and I was across two towns, and took the side roads there, I was puckered the whole way.

and she was SCREAMING, had people staring out of every vehicle, so i'm nto sure how normal all that is or isn't.

i'll be keeping an eye on this thread to see if anyone sparks off with something I can rule in or out of concern for ever touching the interstate again, I'm gonna definitely be dropping in a NV4500 per suggestions of Rusty, those 2 extra forward gears are what I need, especially for a lot of our summer trips we have planned.
 
All my gauges are aftermarket(not great but why pay more than I have to) and everything is good there, my temp runs right about 140-160 and my oil pressure is a solid 50 psi. I live in Tacoma and I drive to Seattle which is about 30+- miles quite often and never have any problems other than it costing me 20 bucks each way and not fitting in any parking garages. I just really want to take it over to eastern Wa. this summer but don't want to if I have to run 3500+ rpm all the way there.
 
smartcarkiller said:
All my gauges are aftermarket(not great but why pay more than I have to) and everything is good there, my temp runs right about 140-160 and my oil pressure is a solid 50 psi. I live in Tacoma and I drive to Seattle which is about 30+- miles quite often and never have any problems other than it costing me 20 bucks each way and not fitting in any parking garages. I just really want to take it over to eastern Wa. this summer but don't want to if I have to run 3500+ rpm all the way there.
Click to expand...

see, that's EXACTLY the reason I was concerned, Cause my truck was absolutely SCREAMING, like, ears ringing for a few hours after, I thought the 3rd gear would have been easier on the motor, I mean, don't get me wrong, I'm pretty sure GM wouldn't have allowed them to go off the lots like that if they were gonna blow up after a few interstate runs, but then again, who here has a fully stock exhaust? I sure don't, 2 3/4 piped through 2 packers, last 18" is a 3 1/2 chrome tip on each side, full length though (Echos like you wouldn't believe).
 
I have 40 series flowmasters and the are loud but not straight pipe loud. are you manually shifting through gears, I ask cause it seems like you are not hitting high gear if its screaming that bad. I know I'm in high gear but it shouldnt be as high rmp as it is.
 
Well, without any slip, at 65 - 70 (with tires that are actually probably closer to 34), you should be 2600 - 2800 RPM respectively. You will get a little slip, but it should still be ~ 2900 at 70. Two thoughts come to mind initially...

- if your stall converter is a cheap one that could be your problem. Cheap stall converters slip a lot.

- did you correct your speedo gear? Are you going faster than you think?

Other than that your trans could be slipping or your tach could be off, etc...
 
I got 315's which is just short of a 35, 4:10's and a th350. In third gear and at 55 I am at 2500 rpm, 65 about 2750 ish. My tach isn't 100% accurate but from the sound of it it's pretty close.


But yes, overdrive with a lock up would be great.
 
smartcarkiller said:
So I have a 72 blazer with a 383 stroker, th350, np205, 35inch toyo mts and 4.11s in the rear. When I am doing 65-70 on the freeway my tach says its like 3500 rpms. I know it doesnt have overdrive but it seams like it should run around 2500 rpm. Any thoughts???
Click to expand...

Are you positive you have a 4.11 rearend?
 
79Midnight said:
see, that's EXACTLY the reason I was concerned, Cause my truck was absolutely SCREAMING, like, ears ringing for a few hours after, I thought the 3rd gear would have been easier on the motor, I mean, don't get me wrong, I'm pretty sure GM wouldn't have allowed them to go off the lots like that if they were gonna blow up after a few interstate runs, but then again, who here has a fully stock exhaust? I sure don't, 2 3/4 piped through 2 packers, last 18" is a 3 1/2 chrome tip on each side, full length though (Echos like you wouldn't believe).
Click to expand...

Sounds like you're in second gear.
 
I'm with andyblack, when my 700r4 was starting to go a couple years ago it wouldn't go into 3rd or 4th. Unless there is something funny going on with your converter I'd start by looking at the trans. What's the fluid look like?
 
yea I know the gears are 4.11 because I have the matching dana44 gears in a box in my garage, just havent got around to installing them yet.I thought about that too and did the old spin the wheel and count the times the pinion turns trick.
 
I'm not saying it's not, but my trans feels fine, again, reality and how it feels are separate truths sometimes, the stall converter........I've done nothing to it, and I doubt anyone else has either, so not sure there, I do sometimes go through the gears myself, but not always, i'm used to driving a manual, so it's kind of habit.

Smartcarkiller, I didn't mean to hack this thread on you like that bro.
 
Avery4jc said:
I'm with andyblack, when my 700r4 was starting to go a couple years ago it wouldn't go into 3rd or 4th. Unless there is something funny going on with your converter I'd start by looking at the trans. What's the fluid look like?
Click to expand...

I checked it last week, it was pink-ish, just checked it and it's brown-ish pink-ish, I assume that's possibly the problem, what sucks is I can't afford a fluid change right now
 
somethin aint right there for sure.i got 4.10 manual trans and 35s, but same 1:1 final gear ratio and im around 2800-3000 at 65.i just try to keep it around 60..i dont like to run over 3000 for longer than 50 miles tops.i almost always try to keep it under 3000 rpm actually.
 
if the original poster did not have the speedo corrected, he might be going faster than the speedo says.

Or make sure you shifted out of 4-low. ;)
 
So is the speed you are telling us the actual speed or the speedo speed? Because if you are actually going 78 MPH then RPM would be closer to 3200, or about 3300 with 5% slip. Which is what I was referring too before.
 
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