RPM vs Load

[guest001]

once I finally, completely tune my car a dyno run just to see you be interesting.

but doesn't it change in different gears? or no.

^yeah, that's kinda what I'm saying. That's what I usually do all the time, but since I've been on here I've been driving on the highway 55-60, 61, 62 max and I'm seeing big gains. also I've been paying more attention to speed, instead of just load.

highly recommend a vacuum gauge to anyone that doesn't have one already.

[DRW]

From my experience if there is a light load on the engine, use low rpm. If you need more power, use higher rpm. Overally try to keep the rpm as low as possible without lugging the engine, and without using more than about 3/4 throttle. On fuel injected engines, keeping the throttle light keeps the ecu in closed loop where the A/F ratio stays at 14.7:1. If too much throttle is used, the ecu goes into open loop where it runs extra rich. A basic A/F ratio gage can show when the ecu/engine is in open/closed loop, so you can see when the engine is running outside of it's most efficient zone.

It's good to have more gages so you know what's really happening, instead of guessing. Every car is different, what works for a big engine won't neccesarily apply to a small engine. A supermid, scangage, or even a datalogger are valuable tools.

I don't recomend trying to drive with the engine rpm spinning at peak torque since most engines make peak torque high up in the rpm band. For normal driving on flat roads you shouldn't need maximum torque to move the car. For example, here's a dyno chart similar to mine: http://www.dsmtuners.com/gallery/sho...searchid=28509
Notice peak torque is at about 3500rpm. Typically I shift gears below 2krpm, sometimes I'll shift at 1500rpm and I'm seeing a nice improvement from when I used to shift around 2,500-3k rpm. Here's the thread where I started shifting at low rpm, the whole thread is good, but the experiment starts at post #23 where I observe fuel use at different rpm with no load, www.gassavers.org/showthread.php?t=3140

BTW another word about that dyno chart. It shows a certain feature common to turbo cars, that the peak torque occurs about 200 rpm after the turbo reaches full boost. I don't know if that's true of a low boost turbo on an engine that was originally designed without a turbo though.

[kamesama980]

Originally Posted by guest001

once I finally, completely tune my car a dyno run just to see you be interesting.

but doesn't it change in different gears? or no.

the torque curve is from the engine, it won't change in different gears. the only way it might is with a turbo that will spool at a lower rpm in a higher gear.

Originally Posted by DRW

From my experience if there is a light load on the engine, use low rpm. If you need more power, use higher rpm. Overally try to keep the rpm as low as possible without lugging the engine, and without using more than about 3/4 throttle. On fuel injected engines, keeping the throttle light keeps the ecu in closed loop where the A/F ratio stays at 14.7:1. If too much throttle is used, the ecu goes into open loop where it runs extra rich. A basic A/F ratio gage can show when the ecu/engine is in open/closed loop, so you can see when the engine is running outside of it's most efficient zone.

It's good to have more gages so you know what's really happening, instead of guessing. Every car is different, what works for a big engine won't neccesarily apply to a small engine. A supermid, scangage, or even a datalogger are valuable tools.

I don't recomend trying to drive with the engine rpm spinning at peak torque since most engines make peak torque high up in the rpm band. For normal driving on flat roads you shouldn't need maximum torque to move the car. For example, here's a dyno chart similar to mine: http://www.dsmtuners.com/gallery/sho...searchid=28509
Notice peak torque is at about 3500rpm. Typically I shift gears below 2krpm, sometimes I'll shift at 1500rpm and I'm seeing a nice improvement from when I used to shift around 2,500-3k rpm. Here's the thread where I started shifting at low rpm, the whole thread is good, but the experiment starts at post #23 where I observe fuel use at different rpm with no load, www.gassavers.org/showthread.php?t=3140

BTW another word about that dyno chart. It shows a certain feature common to turbo cars, that the peak torque occurs about 200 rpm after the turbo reaches full boost. I don't know if that's true of a low boost turbo on an engine that was originally designed without a turbo though.

noone said drive at the peak torque. that's crazy talk (unless you're racing around for fun). IF you need to load the engine down (hill climbing with a full car) up the revs to that area. I thoroughly agree about keeping the revs as low as you can without lugging the engine for steady cruising and light acceleration. gradually use more rpms as you gradually accelerate faster.

peak torque being slightly after peak turbo PSI is going to be pretty consistent across stock turbo cars and modified turbo cars as far as I can think about it. the turbo is going to be what's getting the air into the engine so the engines output is going to be directly tied to it. there are of course going to be some exceptions...big cam for high rpm power with a large turbo and electronic wastegate to get it to spool fast and hold the same psi longer but that'd be a weird engine to drive and it'd take deliberate action to make as weird of a torque curve as that would be.

Most cars don't go into open loop till 80-90% throttle. Not a big concern for most people here.