Lack of backpsi = burnt valves???

[soloithtz]

The question is simple does a lack of back pressure ie, running open pipes create an issue with burning out valves in the future? If not valves anything else that could be damaged running an open system on an I4 engine??

[Eric Baker]

It can be detrimental to the engine if done for too long without proper precautions taken. I just found THIS article that describes it pretty well. In short, if you run the engine with just a header and nothing else done, like a tune, it will run lean and that could lead to burnt valves.

[soloithtz]

So is it possible to get a Powercommander that is mapped for this kind of a set up to avoid running too lean? I know that they make them for the various slipons but my bike has been taken a step further with a mid/Y pipe that is open leading back to the Jardine GP1.

[Stromper]

You will never reach the 1/2 million mark

[Cerberus]

It can be detrimental to the engine if done for too long without proper precautions taken. I just found THIS article that describes it pretty well. In short, if you run the engine with just a header and nothing else done, like a tune, it will run lean and that could lead to burnt valves.

just for laughs i started reading the linked page, got two paragraphs in and found it was wrong..
so don't take what it says too much as truth.

re: backpressure, the truth.

First of all we have to define some parameters here.

Backpressure is only one variable in the multivariable equation that is an engine.
Fuel air mixture is another variable, as is ignition timing, RPM range compression ratio, air temperature, volumetric efficiency, and that just hits the high points.. there are still things like intake port runner design, combustion chamber design, piston crown/dish design... ..but i digress.

The point here is that all these variables are highly interrelated. Changing one variable in an equation effects the whole equation. That is what one reply was referring to; remapping the fueling to compensate for changed flow dynamics.

Exhaust system design is always a compromise.
Ultimately, all engines are air pumps, and the more air they move, the more fuel you can add, and the more power you can make. Most people are familiar with the term "tuned port", but most don't know what it means. Simply a tuned port is a runner whose diameter and length are "tuned" to a frequency (rpm). This is why tuned port systems make great torque but pulse reversion issues cause them to starve the engine for air at higher rpms.
What most people don't consider are the physics involved in exhaust system design. An exhaust header is a tuned system in its own right, and similarly to the tuned port intake systems, it is largely effected by reversion waves.

Now, most people think about the 4 cycle engine in relatively simple terms, which is fine, but over simplifies a complex system. The simple fact is that valves start opening much earlier than is ideal, because the valve train needs to be accelerated from stationary to moving, and closes much later than is ideal for the same reason. This means that the exhaust valve starts opening before the piston has even reached BDC of the power stroke, dumping some power (pressure) at lower rpms, because at higher rpms, the window of time within which to vent the exhaust is so short that it has to be initiated as early as possible..
Here's where the design of the exhaust is relevant.. too much restriction in the exhaust path will result in incomplete emptying of the exhaust and ineffective inertial scavenging (and subsequent initiation of the incoming fuel air charge during valve overlap)
By running an open header (per your question) you are venting even more of that combustion pressure at lower rpms, and costing some torque in that range regardless of remapping to compensate for flow dynamics.

Now, about burning valves, that is usually caused by either running too lean (which can be one of the effects of changing your exhaust flow dynamics) or insufficient valve clearances, which has absolutely nothing to do with exhaust, period.

So, yeah, remap for the open pipe and you'll be fine, but you will lose some of the bottom end power and will have to wick it up more to make the power, which will turn heads in street trim...

[Danz19899]

the guy above me is right. It might burn the valves if you dont get it tuned for the pipe, but otherwise you should be fine

[Stromper]

Small chance you will have a power dip somewhere in the range in the middle 3 to 5 K

[scubasteveRR]

so If you get a slip-on and do not get a power commander you are causing damage to your engine?

Or is a slip on not enough change?

[soloithtz]

Thanks for all the info guys I plan on getting the PC soon and then head to get it dyno tuned

[Cerberus]

so If you get a slip-on and do not get a power commander you are causing damage to your engine?

Or is a slip on not enough change?

usually, any exhaust change you make is not going to be significant enough to damage the engine..
but it can happen.

[soloithtz]

Thanks! I plan on getting the Power Commander just to be sure

[6 Fingered Man]

usually, any exhaust change you make is not going to be significant enough to damage the engine..
but it can happen.

Except on a 2 stroke, throw a pipe on it, lean it out and let the carnage ensue, always jet your two strokes for the pipe/temperature.

[Cerberus]

Except on a 2 stroke, throw a pipe on it, lean it out and let the carnage ensue, always jet your two strokes for the pipe/temperature.

touche!
i was think 4 cycle exclusively, but good point.