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| | | | Joined: Jul 2011 Posts: 74 Wrench Fetcher | | Wrench Fetcher Joined: Jul 2011 Posts: 74 | I have a 1948 1 ton chev panel with a 235 engine from 1958-1962. It also has a 457 rear end. I put on a tac to see what rpms I am running. At 45mph I turn 1400 rpms-at 50 mph I turn 1800 and at 55mph 2000 rpms. I still have some left but I think I am close to top end. Does this sound right and at what speed or rpms should I run this engine. | | | | | Joined: Sep 2001 Posts: 29,269 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,269 | 4.57:1 ? 2000 rpm at 50 mph seems pretty low rpm? What type of tach were you using? Does it have a switch to set it for 4/6/8 cylinders? I think that 2500 rpm +/- 200 rpm is a nice zone. | | | | | Joined: May 2005 Posts: 487 'Bolter | | 'Bolter Joined: May 2005 Posts: 487 | Something's weird. That combination of axle ratio and rpm would require 55" tall tires. A more common tall truck tire of 31" should give about 2500 RPM @ 50 MPH. (assuming you don'y have an OD transmission)
regards,
Leon | | | | | Joined: Feb 2002 Posts: 12,029 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Feb 2002 Posts: 12,029 | yes, what they said - at 55 with a 4:57 rear you will be "close to top end", which would be around 3000 rpm - are you sure you have the tach hooked up correctly? and it's not an 8 cyl tach?
Bill | | | | | Joined: Apr 2005 Posts: 1,107 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 1,107 | im running the same gear ratio in my 40 with 16" wheels that are 30" tall. im running 2550 rpm @ 50 mph. this has been confirmed many times using my westburg tach, gps and a speed/rpm calculator. with this combination at 60 my engines turning close to 3100 rpm. | | | | | Joined: Dec 2003 Posts: 2,733 Shop Shark | | Shop Shark Joined: Dec 2003 Posts: 2,733 | I suspect your tach is for an 8 cylinder engine. If it's getting 25% fewer impulses then the lower number makes more sense. At least this is my KY windage swag. | | | | | Joined: Oct 2006 Posts: 1,847 'Bolter | | 'Bolter Joined: Oct 2006 Posts: 1,847 | what is a KY windage swag?
| | | | | Joined: Apr 2005 Posts: 1,107 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 1,107 | its an eastern thing  | | | | | Joined: Sep 2001 Posts: 29,269 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,269 | SWAGs or not, it looks like a hit and run post.
We may never know the outcome.
| | | | | Joined: Oct 2006 Posts: 1,847 'Bolter | | 'Bolter Joined: Oct 2006 Posts: 1,847 | I thought KY was in the south...I just realized I don't remember any of my 5th grade geography | | | | | Joined: Sep 2001 Posts: 29,269 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,269 | It is east of the Mississippi and south of the Mason-Dixon line.
For those who use Civil War terminology, it was a border state that sought neutrality but gave up on that and petitioned for Union support/control.
| | | | | Joined: Oct 2006 Posts: 1,847 'Bolter | | 'Bolter Joined: Oct 2006 Posts: 1,847 | OK thats about where I was thinking, besides consulting a map. What I found out is Kentucky windage is a reference to adusting your aim on the fly for the wind while shooting a rifle, whilst swag is scientific wild @$$ guess. that was actually two jabs...
Last edited by brokenhead; 09/19/2012 7:04 AM.
| | | | | Joined: Jul 2011 Posts: 74 Wrench Fetcher | | Wrench Fetcher Joined: Jul 2011 Posts: 74 | The tac is right now and I turn 2500 rpms at 50 mph with my 4;56 rear end. I have had it up to 57 mph which gets about 2800 rpms and I think close to the top. I am going to a show with my 1948 chev 1 ton panel with a 235 and want to know if 2500 rpms will be fine for a 3 hour trip. Thanks for any help. | | | | | Joined: Feb 2002 Posts: 12,029 Cruising in the Passing Lane | | Cruising in the Passing Lane Joined: Feb 2002 Posts: 12,029 | I wouldn't expect any problems, I'm sure I've cruised at higher RPMS than that for extended periods with a 235 .... assuming the engine is in reasonably good condition
Bill | | | | | Joined: Nov 2006 Posts: 2,544 Shop Shark | | Shop Shark Joined: Nov 2006 Posts: 2,544 | You will be fine as long as you have good oiling and it doesn't get hot. The noise that your hearing is the way it used to be, we have all been spoiled with our newer vehicles and all the sound deadening insulation they have in them. | | | | | Joined: Jul 2012 Posts: 93 Wrench Fetcher | | Wrench Fetcher Joined: Jul 2012 Posts: 93 | Amen... and all the super low (numerical) low gear ratio/overdrive drivetrains. | | | | | Joined: Feb 2008 Posts: 108 'Bolter | | 'Bolter Joined: Feb 2008 Posts: 108 | Does anyone have a 6 cylinder tach that they would be willing to sell? | | | | | Joined: Dec 2000 Posts: 3,399 Gas Pumper | | Gas Pumper Joined: Dec 2000 Posts: 3,399 | They are pretty cheap on Ebay. Most of the ones listed have a 4-6-8 cylinder switch on them. I just got one recently and paid about $20. | | | | | Joined: Jul 2014 Posts: 362 'Bolter | | 'Bolter Joined: Jul 2014 Posts: 362 | I found a pretty sweet looking Mercury Marine tach for a 6 cyl with a 5k rpm scale on eBay for less than $50 last year (mounting kit cost more than the actual tach). They're out there, just gotta wade through all the other stuff to find them. I ended up searching "6 cylinder tach" after looking at too many V8 tachs that did not have the 4/6/8 switch... PIC | | | | | Joined: Dec 2008 Posts: 1,922 'Bolter | | 'Bolter Joined: Dec 2008 Posts: 1,922 | If you begin to feel a new roughness or buzz, slow down and take a look under the vehicle for something loose, leaking etc.
Otherwise 2,500 is fine. | | |
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