I heard today from a very honest and intelligent mechanic that on Cummins engines with only a straight pipe, there is not enough backpressure on the engine and that it could possibly cause turbo damage (he told me exactly what would happen, but i dont remember what it was.)

Has anyone heard of or experienced such an issue?

 

No such problem exists. Only helps doesn't hurt.

 

not true it is fine

 

also find yourself a new mechanic if you are using him

 

Backpressure and diesel don't belong in the same zip code.

A GASSER needs backpressure.........Cummins don't.

 

dean the turbo would provide enough back pressure if the cummins needed any. gas engines won't run right without back pressure.

 

Hmm. How do those racers get by? F1 cars, fuelers, NASCAR racers. Four stroke gas burners DON'T respond well to changing from muffled to un muffled, but that's just tuning. They don't BENEFIT from back pressure.

 

yes, the turbo in the exhaust produces the back pressure

 

On my klx650, I put in a higher compression piston, cams, port and polish. The big bore bike responded VERY well to uncorking the exhaust and letting it breath through an open megaphone (yes it is loud).

I uncorked it before and after the mods and both times, huge difference in power and drive ability... the only problem was hearing loss for about 2 days... not good when you're working in an engineering firm, they think you're ignoring them...

 

Gassers will run fine without backpressure depending on engine modifications. Factory vehicles are tuned for a certain amount of backpressure (higher cylinder pressure). If you slap a wide open system on them, they no longer run right. It is less so today with engines that basically tune themselves to the external conditions, but a valid point none-the-less. Race cars are designed for lots of air, lots of fuel, and minimal exhaust restriction. Muffled or non-muffled is creating different backpressure because of different restrictions.

The point in a diesel is to get backpressure away from the turbo as that will restrict is ability to compound pressure on the inlet side (and can possibly damage it IIRC).

 

the race cars are made with specific headers so they have just enough back pressure.

 

i would reconsider that statement......

 

Oh boy, that mechanic is perhaps not as smart as you thought! He appears to have little understanding of the 4 stroke principal. 4 stroke engines are only hindered by back pressure. Any pressure is implying you added a resistance to flow - you are slowing down the flow of exhaust and ruining the benfits of scavenging the cylinders which WILL cause a power loss. The goal of any good 4 stroke exhaust to achieve maximum velocity with the minimum resistance to flow for the engines intended operating range.

I often see people mix up 4 strokes with 2 strokes.....a 2 stroke is another operating principal altogether and does require a certain exhaust back pressure to run properly.

 

On any supercharged or turbo charged motor (engine) minimum back pressure is the goal. Why do we put 4-6 inch pipes on our trucks?? It doesn't matter what fuel is used. If there is pressure in the exhaust you will be degrading maximum power.

I think there is misunderstanding as far as back pressure in unsupercharged or naturally aspirated motors too. There are pressure waves that can help or hinder scavenging but if there is a constant back pressure you will not achieve cylinder scavenging as a result of the pressure waves. Maybe I should clarify, not as good scavenging. It is very closely tied to pipe diameter and length. If you hang a muffler on , you pretty well have killed any tuning.

As was noted, a stock motor is tuned to run as well as possible within closely defined parameters. If you go and remove the muffler for example, it opens up the exhaust system and the tuning may or may not be able to adjust for the free flowing exhaust. As a result someone says that the system needs back pressure to run. Well true to a point. If you can adjust the mixture to compensate for the lack of the muffler you will increase power to the extent that the muffler was robbing.

 

Absolutely true! That's why Two Strokes CAN achieve maximum possible power with a quiet system. In the 70's, I was the 'prototype engineer' at Torque Engineering. I developed two-stroke tuned exhaust systems for a living. My personal scooter was a Kawi triple that was 1/2 dba quiter than stock, and made 45% more horsepower than stock. Torque's pipes for the little RD 350 pushed the bike from 24 HP to 32 HP with no other changes, and did it without making it louder. Unfortunately a lot of the squids riding those things equated noise with power, and our pipes didn't sell all that well. Oh, they were kinda' ugly too... that didn't help.