The Truth About Cars » torque peak The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. Tue, 15 Jul 2014 10:00:12 +0000 en-US hourly 1 The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars no The Truth About Cars (The Truth About Cars) 2006-2009 The Truth About Cars The Truth About Cars is dedicated to providing candid, unbiased automobile reviews and the latest in auto industry news. The Truth About Cars » torque peak Piston Slap: A Fear of Falling? Mon, 22 Apr 2013 11:00:20 +0000

Michael writes:

I am a longtime TTAC reader, but do not comment very often. However, I have a question that perhaps you and the B&B can help me with. I am the owner of a 2011 Kia Soul +, 14,XXX miles. Been a great vehicle so far.

My issue is that my workplace happens to be located DIRECTLY off of a major street/highway. This means that from the time I put the car in gear and pull out of the parking lot, I need to be up to 60mph within about 10 seconds or get run over. No side streets to take and no time to gently warm up the car under load.

Even in the oppressive Houston heat, the car would take several minutes to warm up by idling in the parking lot. I have not been doing this, but if I need to, so be it.

So, am I killing my engine by getting it up to such speed on a cold engine? The car does warm up within a couple minutes once on the street, but I do not want to do any damage in the meantime. What says you??


Sajeev answers:

A good rule of thumb in Houston: one of the worst things you can do is idle a cold motor instead of driving it, putting a load on it. Not necessarily true in places where engine block heaters are necessary, but definitely true here.

So, relatively speaking…

Unless you’re full throttle, wringing it out to redline, etc. you’re warming up the motor well enough.  I was in your place when I wrote about the Dodge Attitude for a surprisingly cold December in Houston. My new job was in an office building on US 59, plenty of throttle was needed when leaving. Mostly because it was a somewhat high speed, limited visibility merge to the feeder road.  I cringed when I wound out my (low-ish revving) Lincoln Mark VIII to 3500-4000rpm sometimes, but it really didn’t matter.

Even if I stuck around there, I am sure my 175,000 mile Lincoln would still be just as happy as it is today.  Too bad I wasn’t happy and the Cutting Crew CD in my stereo was not only broadening my musical horizons, it possessed a song that encapsulated my fears: mostly about the job, but kinda about that freeway merging from the parking lot, too!

Click here to view the embedded video.

What you are experiencing is a Fear of Falling, but I digress…on a KIA Soul, two bits of advice:

1. Use synthetic oil, a full synthetic.  You should have no problems switching at this mileage, so just do it.

2. WHEN POSSIBLE: accelerate onto the feeder with enough throttle to say near your torque peak, which is 4,200 RPM.  If you can remain in that area for the majority of your runs back home, you’ll never have a problem at all.

Do those two things (the second one as much as safely possible) and you’ll be just fine. Go ahead, jump.  No fear here.

Send your queries to Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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Piston Slap: Of Power Curves and Turbo Boost… Mon, 17 Dec 2012 12:32:47 +0000 Chris writes:


In a couple recent Piston Slap articles you’ve mentioned that when driving car with a manual transmission its most efficient to accelerate with the engine near its torque peak, then cruise in the highest gear possible. This raised two questions in my mind:

1. Does the engine’s torque peak vary based on throttle position? From what I understand, power and torque curves are generated at wide open throttle. But would the torque curve look different at, say, 50% throttle? I’ve heard that exhaust backpressure can affect the torque curve (maybe this is a myth). Could throttle position have the same effect via intake vacuum? Speaking of intake pressure, that leads me to my real question:

2. How does your strategy of accelerating with the engine near its torque peak apply to a turbocharged vehicle? My car has a turbo and according to the manufacturer the torque peak is 2000 rpm. But clearly it’s not always capable of generating max torque at 2000. If I’m loafing along at 1800 rpm and floor the throttle it takes a very laggy second or so for the boost to build and its definitely past 2000 rpm by the time it starts really generating power. I’m thinking there must be a different torque curve for part-throttle acceleration, when the engine is either off-boost or not making full boost. I think this would also apply to an engine like Audi’s supercharged V6, where the supercharger can de-clutch from the engine under low load. Any thoughts on the most efficient way of accelerating in a turbo? Better to accelerate “on boost” at relatively low rpm and relatively wide throttle? Or accelerate with less throttle, keeping it out of the boost (but probably winding the tach up more to avoid moving at a snail’s pace)? Or just forget the whole thing, floor it and enjoy the wild turbo-torque surge?

If these are stupid questions, please disregard. These are just things I ponder while sitting in traffic… Keep up the great work!

Sajeev answers:

This is a fantastic question that I am totally not qualified to answer…but that hasn’t stopped me before, and it hasn’t stopped you lovely people from reading, so let’s do this thang!

Point #1: Yes, throttle position will affect the torque peak. Because an engine is basically just an air pump, if you have less throttle you have less air, less fuel and therefore less power.  Thankfully, with the advent of electronic fuel injection there are multiple mappings: older systems have a full and a part throttle program, and newer systems probably have several.  So I betcha you can maximize an engine’s efficiency at just about any throttle opening. Every application is a little different, and many are tuned to maximize performance with a computer reflash from an aftermarket programmer.

As a rule of thumb, and I’m ready to get slammed by engineers for saying this, backpressure (or a lack thereof) does indeed affect the torque output of an engine.  More importantly: backpressure isn’t a good thing, finding the ideal exhaust velocity to minimize backpressure while keeping the speed “slow” enough to not hurt torque output is crucial.  That’s why, in the past 10-15 years, we see far higher quality exhaust systems in all OEM applications: no crush bends in the tubes, cast iron manifolds that are shaped more like aftermarket tubular headers, and mufflers/catalytic converters that aren’t a significant restriction.**

Point #2: turbocharged motors are just like point #1 when it comes to power in part throttle applications. And every boosted application out there is different. Once again, and even more so, tuning makes ALL the difference in the world.  Because the turbo is a muffler/restrictor in the exhaust system, you want as little restriction behind it to ensure maximum efficiency: hence why the Dodge SRT-4 is muffler-less from the factory.

My gut feeling is that with any modern car, turbo or not, you need to give it more gas to cut through the slop of electronic throttle control/torque management to get into your torque peak quicker.  Spend less time accelerating and more time cruising, with traffic conditions in mind of course. That doesn’t mean you run wide-open throttle, either. There’s a happy medium out there, somewhere.

Off to you, Best and Brightest: I’m ready, I’m wearing my flame suit.

**Grab a catalytic converter from the 1970s-early 1990s. They neck down, restrict air flow, etc far more than the goodies I see today in cut-away diagrams at the auto shows.  We have come a long way, baby.




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