Shift Speeds/RPMs question
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Shift Speeds/RPMs question
My 1988 F150 XLT, 302, AOD, 3.55 axle, extended cab with a tachometer, shifts gears fairly smoothly (most of the time) when the tach is at about 2000 rpms, and after the gear shift, the rpms drop to about 1300 rpms, going up again to 2,000 til the next shift, or into overdrive. In the city, at about 55 km/hour (about 33 miles/hour), the tach registers about 1300 rpms. On the highway, at 110 kms/hour (66 miles/hour) the tach is at about 2100 rpms.
I have two questions: Does this sound normal, given that other posts have talked about the 302 engine reaching optimum torque, etc. at about 3500 rpms? And what is the optimum level of rpms for this motor at highway speeds to achieve good fuel economy/efficiency, avoid carbon build-up and promote long motor life?
Thanks for any feedback.
Frank.
I have two questions: Does this sound normal, given that other posts have talked about the 302 engine reaching optimum torque, etc. at about 3500 rpms? And what is the optimum level of rpms for this motor at highway speeds to achieve good fuel economy/efficiency, avoid carbon build-up and promote long motor life?
Thanks for any feedback.
Frank.
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Joined: Mar 2002
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From: Bonita Springs FL
Those numbers sound about right. My 3.08 geared truck runs a little lower than that on the highway.
Just because a motor's peak torque is higher up the the RPM range, doesn't mean you want to run it that high all the time. That's just where it happens to make the most torque - this is why most people prefer the 300 when faced with a choice between the 302 and the 300. The 300 makes torque at a much lower rpm, 1900 or 2000. It's much more useful in a truck.
On the highway, I would say anything between 1600 and 3000 is a healthy speed with respect to long engine life. Obviously, the lower the RPMs, the better your mileage will be.
Just because a motor's peak torque is higher up the the RPM range, doesn't mean you want to run it that high all the time. That's just where it happens to make the most torque - this is why most people prefer the 300 when faced with a choice between the 302 and the 300. The 300 makes torque at a much lower rpm, 1900 or 2000. It's much more useful in a truck.
On the highway, I would say anything between 1600 and 3000 is a healthy speed with respect to long engine life. Obviously, the lower the RPMs, the better your mileage will be.
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Thanks for your reply. If running at lower RPMs (ie. about 1800 to 2200 on the highway) is better for mileage, is there any risk of motor carbon--I have heard that running too low contributes to carbon build-up, but don't know what "too low" means in this context. Also, if carbon does build up, does an occasional run at higher RPMs burn that off, or is that an old wives tale? I occasionally use STP gas additives, which claim to reduce carbon build-up, but have heard mixed reports about their effectiveness. I would appreciate any opinions or advice on this, and in general, how to keep my truck running well for as long as possible. I do regular oil changes, try to fix small problems before they get worse, do a tune-up about every 30,000 miles and regularly keep all fluid levels topped up. Thanks.
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From: Topsfield, MA
That seems right...2100ish at 65 mph is good..thats exactly where you want to be. Don't worry about carbon buildup or anything...those speeds are what the engine was designed to run at on the highway. The max torque on the 302 is more towards 3k rpm than 3500 rpm...but it still has pleanty of torque at 2100ish rpm for highway. Don't bother with those gas additives either...they don't really do anything. They have special stuff for cleaning injectors and it's really not a probelm.
