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2500 rpm at 55 mph. Is that about right?

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Skulptorchaz

Number of posts : 227
Location : So. East Indiana
Registration date : 2015-05-08

2500 rpm at 55 mph. Is that about right?

Post by Skulptorchaz on Mon Feb 13, 2017 7:18 pm

Now that I got her going down the road, and not getting hot, I'm wondering if it should be pulling THAT high of rpms going down the road?
I'm running a 292 with the stock trany and 10 bolt rear end. I understand the 10 bolts were 336 (?) geared. Rolling and counting confirms that pretty close. I dont have a lot of experience with this combo but it seems a little high in the rpms. Is it?
I'm planning on putting a 700R in it, when I can come up with one but, I had also been thinking about a 350 turbo since I have a couple and they are quite a bit less to freshen up. But if I'm pushing 2500 at 55, I think I need to go with a 700. I definitely think I have enough motor to push it.
Is this about the rpm I should be seeing? Is it high for a 292?
Thanks guys..
Chaz
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jrinaman

Number of posts : 790
Location : zelienople,pa.
Age : 53
Registration date : 2011-03-10

Re: 2500 rpm at 55 mph. Is that about right?

Post by jrinaman on Mon Feb 13, 2017 9:37 pm

without overdrive, that is normal. when our vans were built, everyone rode around at 3000 rpm's and never gave it a thought. now, we are used to our cars lower cruising rpm's and we think our van motors are screaming, but your not even half way to redline. had a '67 c40 that turned 5500 at 45 miles an hour, I would run it there daily for hours at a time. what is your speed at 5500 rpm's?
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m1dadio
Chevy Guru

Number of posts : 1719
Location : Victoria B.C.
Registration date : 2008-10-06

Re: 2500 rpm at 55 mph. Is that about right?

Post by m1dadio on Mon Feb 13, 2017 9:43 pm

You have to measure or look to see what rear gears you have. 2500 is a little high but often what was normal for these vans when gas was 13 cents a gallon.

I would consider a 200R4 because its the same length as your current trans and you wont have to shorten the drive shaft.

I have a 342 gear with a 700R4 and at 55 my rpm is about 2200 in fourth and drops to about 1800 when the converter locks. How much it drop with converter lock up is a direct function of the stall speed of the converter.

Do the math 2500 to 1800 thats 28% reduction you are under heavier load at 1800 maintaning 55 so its not a 28% fuel savings but could be a 20% savings at highway speed.

my 2 cents worth

M1D
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panelmanrd

Number of posts : 764
Location : kcmo
Age : 56
Registration date : 2009-10-04

Re: 2500 rpm at 55 mph. Is that about right?

Post by panelmanrd on Tue Feb 14, 2017 6:49 am

mine with a 3.36 gear and a 700r4 does about 2200 at 70 mph
don`t spend enough time a 55 to check the rpm at that speed
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boogieman

Number of posts : 69
Location : New Mexico
Registration date : 2015-10-12

Re: 2500 rpm at 55 mph. Is that about right?

Post by boogieman on Tue Feb 14, 2017 11:42 am

im not sure what my rear end is, 3speed manual with 250/6 im turning 3200@70 with 215/75 r14 tires and i feel like im hurting it a bit...
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Eds-68-Chevy

Number of posts : 64
Location : Massachusetts
Registration date : 2011-10-17

Re: 2500 rpm at 55 mph. Is that about right?

Post by Eds-68-Chevy on Tue Feb 14, 2017 12:43 pm

Mine has a Chevy 350 with a turbo 350 trans and a 10 bolt rear end with 4.11 gears. It does about 3500 rpm at 65 mph....It's a rough ride on the highway for long distance trips.
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Skulptorchaz

Number of posts : 227
Location : So. East Indiana
Registration date : 2015-05-08

Re: 2500 rpm at 55 mph. Is that about right?

Post by Skulptorchaz on Tue Feb 14, 2017 1:50 pm

Thanks Gents.
I did some numbers crunching on a chart: http://www.csgnetwork.com/multirpmcalc.html and it confirms your numbers panelmanrd. (2213 with my 25'' tires)
I am just wondering if that is a good RPM for a 292? I'd kinda like to find that optimum cruising rpm without lugging it. I'm not sure who can tell me the optimum rpm of a fresh, stock 292?
I did post on "stovebolt.com" a question but, have not heard anything yet.
Thanks guys!
Chaz
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jrinaman

Number of posts : 790
Location : zelienople,pa.
Age : 53
Registration date : 2011-03-10

Re: 2500 rpm at 55 mph. Is that about right?

Post by jrinaman on Tue Feb 14, 2017 3:00 pm

http://6066gmcguy.com/inline6.html here are the h.p. and torque specs for the 292. gross and net figures are at a lower rpm than the small blocks, gross torque at 1700 rpm's, about half of what a v-8 would be. the v-8 may have more torque at 3500 rpm's but most are much lower at 1700. that being said, you can gear higher than a v-8. optimum rpm depends on what you want. best milage would be achieved slightly below 1700, best performance would be closer to 4000 rpm's. I am running a 292 with 200r4 and 336 gears, my 292 is not stock so power curves would not be the same, even with a bigger cam, I gained no performance with 411's so put the 336's back in. I am also turning around 2200 @ 70 mph and would not hesitate to gear higher 'if' I cared about milage.
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Skulptorchaz

Number of posts : 227
Location : So. East Indiana
Registration date : 2015-05-08

Re: 2500 rpm at 55 mph. Is that about right?

Post by Skulptorchaz on Tue Feb 14, 2017 6:37 pm

Awesome!!! THANK YOU!!
That is what I was hoping to find out. I was just wanting some ball park optimum figures to shoot for. I'll definitely go for the 700R4 over the TH300 now but, I doubt I will do anything to the rear..............unless the occasion arises where I have to get into it. Then maybe.
Thanks a bunch!!
Chaz
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Skulptorchaz

Number of posts : 227
Location : So. East Indiana
Registration date : 2015-05-08

Re: 2500 rpm at 55 mph. Is that about right?

Post by Skulptorchaz on Fri Feb 17, 2017 7:45 am

Well, a guy on "stovebolt" says to NO WAY put in a 700R4. I'm not sure how dependable his info is but, I beg to differ with him. I'm going to try to find a 700R4.
Thank you guys for all the help and time.
Now, to figure out the interior............. Shocked
Chaz
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jrinaman

Number of posts : 790
Location : zelienople,pa.
Age : 53
Registration date : 2011-03-10

Re: 2500 rpm at 55 mph. Is that about right?

Post by jrinaman on Fri Feb 17, 2017 8:26 am

what is his reason to not use the 700r4? I have had both the 700r4 and the 200 4r in mine, the 200 is an easier install and uses the same driveshaft. I had a shaft for a th400 so I didn't need to have one made for the 700 and chose the 700 because 1st gear was lower than the 200, after installing it, I was less than pleased with the rpm drop from 1st to 2nd. on either tranny, you most fabricate brackets for the t.v. cable. it is not a kick down cable like your th350! many have died early from improper brackets or adjustments and they have a bad reputation due to that, yet the last forever in the original vehicle. what carb you have will determine what bracket you need.
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Skulptorchaz

Number of posts : 227
Location : So. East Indiana
Registration date : 2015-05-08

Re: 2500 rpm at 55 mph. Is that about right?

Post by Skulptorchaz on Fri Feb 17, 2017 10:00 am

A really good friend of mine owns an auto repair place and is the local tranny authority. He tells me the 700 would be better. I trust his expertise and the fact he knows I am an "overkiller". Smile The drive shaft is no problem to remedy. I have done a couple and another friend balances them for me. It will just be a little more work. The rear mount will be no problem either. (I own a welding fab shop since '86.) I have a cable mount that I can fab as well. If it has to do with metal, I am all about it.
The RPM, between 1st and 2nd, you speak of is interesting tho. Do you think ALL 700's are that way?? I know the '88's to '92's are a bit more heavy duty (size of the splines, I'm told). I'll ask Jim about that too.
And you are right on the money about the cable. It's excellent you try to make people aware of that! That is a tranny killer. My friend comes to my shop to set mine up before I even drive it. I have swapped a few of them into my Hot Rods.
Thanks for the heads up!!!! I really appreciate the help, time and concern!!!
Chaz
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m1dadio
Chevy Guru

Number of posts : 1719
Location : Victoria B.C.
Registration date : 2008-10-06

Re: 2500 rpm at 55 mph. Is that about right?

Post by m1dadio on Fri Feb 17, 2017 8:36 pm

The drive shaft is no problem to shorten however you will then need to consider some for of track bars to keep the rear end from rolling. The 19" long drive shaft will mean the rear end can flex only a half a degree before you get drive line vibration. I guarantee you will have vibes either rolling or on acceleration depending how you angle the diff. This is because the drive shaft becomes too short.





If you think the diff dosnt flex on those wimpy 2" leaf springs watch this video before I installed track bars.
spring wrap is common, the shorter the drive shaft the less tolerant it is

http://illiweb.com/fa/pbucket.gif?sort=3&o=4

the factory set up will allow about an 8* to 10* flex with a torquey V8. the 19" drive shaft can accept about 1.25* mathamatically speaking

with the track bars its allot more stable but still about 3* flex
http://illiweb.com/fa/pbucket.gif?sort=3&o=1

m1d
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jrinaman

Number of posts : 790
Location : zelienople,pa.
Age : 53
Registration date : 2011-03-10

Re: 2500 rpm at 55 mph. Is that about right?

Post by jrinaman on Fri Feb 17, 2017 10:21 pm


never noticed any vibration from mine, however, I did have another slight problem. I was not able to repair this on site. since I had to fab a bracket anyway, I lowered the rear of trans. a little so that angles were slight and matched each other.
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Skulptorchaz

Number of posts : 227
Location : So. East Indiana
Registration date : 2015-05-08

Re: 2500 rpm at 55 mph. Is that about right?

Post by Skulptorchaz on Sat Feb 18, 2017 8:43 am

Wow Gents, GREAT STUFF!!! That is an awesome couple a videos Dadio! Great actual footage to go by!!
Yeah, they are wimpy 2'' springs and on top of that, I only have 3 on each side as the PO took them out to lower it. I have the others in a box that came with it. I have thought about having a "single" made but not sure I want to go that route.
I'll have to look into a trac bar set up but, do you know of anyone setting it up with a 4 link? Pictures of that would be awesome. Triangulated, preferably. I'm a fan of slammed vehicles and as much as I like "form", it also has to ''function". My vehicles are "drivers". When I build the trany mount, I will set it up for the ride height and build for the correct degrees in the drive shaft. (I've set these up before.)
BTW Dadio, your mill sounds really healthy. My 292 sounds good, for what it is, but, there's NOTHING like a healthy V-8!! This is actually my first Six in 41 years of driving. If it has one in it when I buy it, it's ripped out right away. I decided to try try a Six this time but, I yanked out the 194 and at least put in a "stump puller". Smile
Thanks again gents!! This helps a bunch in getting the plan together.
Chaz

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