Tuning: What's the Trade-Off?

[Captain Snooze]

Why do manufactures leave power on the table to be had with after-market tunes? I don't quite buy the quality of fuel reason because I'm thinking that the ecu can make on the fly adjustments for quality of fuel (this is just my hypothesis, no evidence). Is it for emission reasons; what happens to emissions after a tune?

Thoughts?

[Basket Case]

Fuel quality, emissions, longevity of components.

[husker741]

I think that they do it so when you do it and potentially cause harm to your vehicle, they don't have to pay for it.

[BlueDubbinTDI]

Originally Posted by Basket Case

Fuel quality, emissions, longevity of components.

This. Just ask VW owners. Those 2.0T engines leave about 40hp/60tq on the table with just a $600 tune. Maxing out an engine can shorten its life dramatically as it makes every moving part and system work much harder, doubling routine maintenance costs as well.

[wheelhaus]

Originally Posted by Basket Case

Fuel quality, emissions, longevity of components.

QFT again.
Consider it from the manufacturer's perspective, their goal is to build cars that people want to buy, and then sell a f*ckton of them and profit. If those engines in tens (or hundreds) if thousands of cars are tuned close to the edge of performance, it means manufacturers would sell them for much higher prices than we see today, or without much of a warranty at all because many, many engines would see failure in one form or another. Why? most owners don't want to deal with all the little details and things we enthusiasts actually enjoy. They want a dumb car to get from point A to B, with the cheapest fuel and tires and brakes that never wear out.

The VAST majority of owners don't buy cars for the same reasons enthusiasts do. We want to take an existing platform of choice and make it better in ways we individually see fit. That being said, everyone has different tastes. So there's little point to a manufacturer tuning an engine to the bleeding edge (or even close to it) because we'll still change it anyways.

And besides, it gives us that warm fuzzy feeling when we make all those improvements making the car "better" (read: more purpose built) because it makes us feel smarter than those OEM engineers... (:

[IAmNotTheDriftKing]

Well, the parts won't last as long. But as long as you make sure the tune you are getting is running somewhere along the lines of stock compression then it should last somewhere along OEM. If it runs rich you are even better off. Just don't let it run too lean!!!

[pche]

Originally Posted by IAmNotTheDriftKing

Well, the parts won't last as long. But as long as you make sure the tune you are getting is running somewhere along the lines of stock compression then it should last somewhere along OEM. If it runs rich you are even better off. Just don't let it run too lean!!!

I'd like to see a tune that can change compression...... Running rich is not as harmful as lean but definitely not "better off".

[IAmNotTheDriftKing]

Originally Posted by pche

I'd like to see a tune that can change compression...... Running rich is not as harmful as lean but definitely not "better off".

Sorry didn't mean compression, I meant AFR You knew what I meant though.

I am just going by the assumption that cars that run rich usually do so to help keep the engine from blowing itself up. I am not sure what can happen from running rich other than losing power, gas mileage, and carbon build up. The engines longevity should be preserved. . . probably.

[arghx7]

A few things to think about with "leaving power on the table" :

The main tune and hardware are developed in a lab on an engine dyno. The engine doesn't behave quite the same way in a vehicle on a chassis dyno. Air and fluid temperatures are different, not to mention that frictional losses and especially backpressure can be different. You may have most of the design completed before the engine is ever in a car. This is because manufacturing something takes a couple years lead time.

The rich AFR at heavy load is to keep the cat and in some cases exhaust valves from overheating during heavy vehicle acceleration and in engine dyno durability tests.

Somebody somewhere had to pick what fuel to develop the hardware and tune on. If it's US certification fuel, it's 97 RON or roughly 92 pump octane. That's better than some gas pumps and worse than others.

There are NVH, emissions, and fuel economy constraints. For NVH, it can be the rate of combustion pressure rise (fast pressure rise is noisy). This relates to spark and injection timing among other things. For emissions, enough scavenging through cam phaser tuning can hurt the catalyst. For fuel economy (also CO emissions), the AFR can be tuned leaner than the AFR that gives best torque--think about closed loop delays.

Originally Posted by pche

I'd like to see a tune that can change compression...... Running rich is not as harmful as lean but definitely not "better off".

Any time you retard the intake closing timing beyond intake BDC at a given engine speed, you are reducing effective compression ratio by blowing air back out the intake port. The effective volume decreases. However, later intake closing timing gives more time to fill the cylinder at high speed. This is due to inertia of the air. The big factor here is the pressure drop (restriction) across the intake valve... this varies with engine speed, load, valve position, etc. That's why a high lift VTEC cam lobe might close the intake valve at 60 degrees after bottom dead center, even though there's less effective volume and lower compression when you do that.

In a similar fashion, advancing the exhaust opening timing reduces the expansion ratio and hurts fuel economy. However, advancing the exhaust opening timing helps evacuate more gases and can affect pumping work. It's always a tradeoff.

[pche]

Originally Posted by arghx7

A few things to think about with "leaving power on the table" :

The main tune and hardware are developed in a lab on an engine dyno. The engine doesn't behave quite the same way in a vehicle on a chassis dyno. Air and fluid temperatures are different, not to mention that frictional losses and especially backpressure can be different. You may have most of the design completed before the engine is ever in a car. This is because manufacturing something takes a couple years lead time.

The rich AFR at heavy load is to keep the cat and in some cases exhaust valves from overheating during heavy vehicle acceleration and in engine dyno durability tests.

Somebody somewhere had to pick what fuel to develop the hardware and tune on. If it's US certification fuel, it's 97 RON or roughly 92 pump octane. That's better than some gas pumps and worse than others.

There are NVH, emissions, and fuel economy constraints. For NVH, it can be the rate of combustion pressure rise (fast pressure rise is noisy). This relates to spark and injection timing among other things. For emissions, enough scavenging through cam phaser tuning can hurt the catalyst. For fuel economy (also CO emissions), the AFR can be tuned leaner than the AFR that gives best torque--think about closed loop delays.



Any time you retard the intake closing timing beyond intake BDC at a given engine speed, you are reducing effective compression ratio by blowing air back out the intake port. The effective volume decreases. However, later intake closing timing gives more time to fill the cylinder at high speed. This is due to inertia of the air. The big factor here is the pressure drop (restriction) across the intake valve... this varies with engine speed, load, valve position, etc. That's why a high lift VTEC cam lobe might close the intake valve at 60 degrees after bottom dead center, even though there's less effective volume and lower compression when you do that.

In a similar fashion, advancing the exhaust opening timing reduces the expansion ratio and hurts fuel economy. However, advancing the exhaust opening timing helps evacuate more gases and can affect pumping work. It's always a tradeoff.

I knew someone was gonna call me out on my vague statement........ Let me try this again, tunning, with ignition timing would not change the mechanical compression.

[StormTrooper]

You also have the improvement on following years to consider...