Now that I have my larger tires, I have a couple of questions. I never paid attention to how many rpm's I was running at 65 mph with the stock 255/70-16's and my 3.55ls. I was wondering if anybody knows how many? The second question is for some of you guys who are running 315's or 35's with the 3.55ls (jmtruck,Bigredliftedfordman,Nitrox,cpdice). Do you guys use overdrive at 65 mph or on the freeway, or do you just leave the switch off? I have noticed that in drive I am running around 2500 at 65 mph and in overdrive I'm running at about 1800. It would seem to me that lagging the engine would be more damaging. Thanks for the help evrybody.

Lok

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1997 F-150 Supercab 4X4,Royal Blue,4.6 V-8, Tow Package,3.55 LS,
K&N FIPK,Performance Accessories 3" body lift,Superchip,
Gibson Supertruck Exhaust,Smitty Nerf Bars,
16X10 Eagle 589's, 315/75-16 A/T's,
Alpine CD,Alpine 5 Channel Amp,PPI 5 X 7's,
Boston 10" Sub.

Pics at: http://www.f150world.com/loknload/

 

Well on my truck with the stock 255/70 16's in overdirve auto trans at 65 mph I run around 2000 on the tac with 3.55 open end rear end gears.

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2000 F150 XLT Reg. cab
4.6 Triton Engine
4x2 3.55 rear end gear
sliding rear window
automatic keyless entry
white styleside short box

 

Lok,

I have been driving my truck with the overdrive on. With the overdrive off, the RPM are to high to get decent gas mileage. At 70 MPH (1900-2000 RPMS), I do not have as much problems with it downshifting. At 65 MPH (1700-1800 RPMS), it will shift into 3rd on a very slight grade. I do not think that this will hurt the engine, but I am keeping a close eye on the transmission. My truck came with an auxiliary transmission cooler. I figure that the cooler should keep the transmission temperature down. Therefore, I just let the transmission shift as it wants to.

Hope that this helps!

CPDICE




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1997 F-150 Lariat
4x4 ORP ext cab
4.6 auto
3.55 gears
3" body lift
35x12.5x16.5 BFG AT KO'S
16.5x9.75 Eagle 143's
Vent visors
Westen nerf bars,
tube bed rails
custom dual exhaust w/3.5" X 24" ss tips

 

Thanks for the replies. I have the tranny cooler too. Maybe the combination of the new tires and actually being able to hear the exhaust makes it seem like the engine is lugged down. I usually run with the OD on until the tranny starts hunting for gears. Thanks again.

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1997 F-150 Supercab 4X4,Royal Blue,4.6 V-8, Tow Package,3.55 LS,
K&N FIPK,Performance Accessories 3" body lift,Superchip,
Gibson Supertruck Exhaust,Smitty Nerf Bars,
16X10 Eagle 589's, 315/75-16 A/T's,
Alpine CD,Alpine 5 Channel Amp,PPI 5 X 7's,
Boston 10" Sub.

Pics at: http://www.f150world.com/loknload/

 

The beauty of the 5.4 L V8 is the ability to produce good torque at low revolutions, the only time I get worried is when traveling about 45 MPH, with the tranny in overdrive, the engine is doing about 1100-1200 RPMs, I usually keep mine in 3rd gear below 45 MPH.

The 5.4 L engine should be fine anywhere over 1400 RPM, at this engine speed it should have healthy oil pressure, some horses and just over 70% of the total torque.

So if you are not pulling heavy stuff, use the gas pedal and let the tranny shift by itself.


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2001, F150 SuperCrew, 5.4, Limited 3.55, Trailer Tow, 4R70W Tranny, 255-70-16, Captain Chairs.
Assembly Date 10/4/2000.
++++++++++ Modifications ++++++++++
** Gibson Side Swept Stainless Steel - Cat-Back exhaust. **
** K&N Filter **
*************** AUSTIN, TEXAS ***************

 

Unless you've 'chipped' it, your tranny will downshift rather than letting it over-torque istself, so...

...as long as it's not annoying you with excessive downshifts, you're fine.

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Y2K™ Jim - N8JG@Hotmail.com

Toreador Red, Keyless XLT SC SB 5.4L E4x4 4wDisc/ABS, 3.73LS, Skid, HD 7700# Towing, LT-245's on Chrome, Tube-Steps, Captain's, 6CD, Tonneau, named: "Nick"