I'm thinking of putting straight pipes on my car. No cat. No muffler. When I have to pass emissions i'll stick the old one back in there. Good idea? Bad idea?

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1982 Berlinetta
2bb 2.8l V-6
4 spd. Dog **** SLOW!!

 

it's not going to sound right and you need some back pressure.just get aftermarket headers.

 

backpressure is the enemy, It will sound like sheit though.

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91 RS W/carbed 350, Vortec heads, performer rpm, Comp cams Xtreme energy 280 grind. BFG Drag radials. 3.42 posi,Corvette servoed 700r4, ****ty stock converter
13.24@104

 

What the hell are u talking about??!? BACKPRESSURE IS GOOD

 

amount of backpressure that is good or bad depends on your car.

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beau-t-ful yellow 85 iroc

 

Backpressure is bad...it is a complete myth that should be exterminated like the plague.

What people are confusing is VELOCITY with backpressure. You need to maintain the right velocity to obtain maximum torque. This is the argument behind too large of headers or too large of an exhaust system. On smaller engines they don't maintain enough velocity to obtain maximum torque at lower engine speeds.

Backpressure is when you have restrictions that do not necessarily maintain optimum velocities. Similar to shoving a potato with holes in your exhaust system. Yes, you have backpressure, but you have no velocity. An extreme example, but old pellet type catalytic convertors or certain mufflers do just that. They increase backpressure, but do nothing for velocity.

1 5/8" headers vs 1 3/4" headers introduce very little backpressure, but the 1 5/8" headers maintain higher velocities. At lower rpms this promotes torque. At higher rpm, the 1 5/8" headers become saturated with exhaust gas due to the volumes they can hold from the cylinder, and produce less power at top rpm. At this point they introduce backpressure and kill performance.

Conclusion, backpressure is BAD!

 

I wouldnt really do that,it would sound like poo-poo.But if you wanna stil do it at least dont take off the cat so it will kinda be muffled.But i recommend getting a super turbo dynomax muffler.It makes your v6 sound like a v8.Sounds really good,too!Also is cheap,around $55 from summit.(www.summitracing.com)

 

Glenn,

Just to amplify on what you said: I think a lot of people think backpressure is the same thing as a negative pressure(scavenging) exhaust pulse. The negative exhaust pulse, which is created when the exhaust plug enters the collector, is absolutely essential in establishing good velocity for the exiting plug and scavenging burnt mixture from the cylinder(which in turn promotes cylinder filling).

Smaller pipes can often create a stronger scavenging pulse, at lower rpms, because the exhaust pulse enters the collector at a higher velocity. However, the trade-off is that the smaller pipes create more restriction as the rpms increase. As is true with almost all engine components, the size must be chosen based on the engine's intended operating range. Going big can actually cost you power in your intended operating range, if the exhaust size is not properly matched to the rest of the engine.

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He who hesitates,... is lost!

 

At least put in some glasspacks on or an Edelbrock RPM Series muffler. Both are practically straight pipes with perforations and sound damping material in the muffler cavity. It'll sound a lot better than just straight pipes.

 

This myth of "backpressure" and good street throttle response is completely backwards. The correlation is spurious at best. "Inertia" is the guilty property where headers are concerned.

The "backpressure" that is seen in a small diameter header tube is caused by the column of gas not wanting to move RIGHT AWAY when the slug of exhaust gas comes out of the port.

In other words, the slug comes out but the gas in the tube is at rest and will compress before it moves. Once the column of gas in the tube starts moving, it will want to keep moving. THIS property of inertia (a mass of gas in motion) is used later in the exhaust cycle to create a relative vacuum and scavenge the combustion chamber. There is a certain RPM range at which the compression and rarefaction waves are ideally suited for scavenging. This is when the header tube is "resonating". Header tubes that are too large will not have sufficient velocity to prevent the rarefaction wave from pulling the exhaust back into the cylinder. Hence, sucky performance on the street.

A properly designed exhaust manifold works just the opposite way. It is designed to offer no reaction at idle and low RPMs. A good exhaust manifold has almost no runner and a large open space for expansion. The slug comes out with no column of gas to push out of the way and lots of room to spread out. The drawback comes in the form of turbulence and lack of a column of moving gas to scavenge as RPMs go up. Somehow, people look at the backpressure problem and jump to a false conclusion about what makes low RPM torque.

The presence of backpressure reveals the deficiencies of either design. Loss of LOW RPM performance, after installing headers, is NOT caused by lack of backpressure! Loss of street performance is caused by the inertia of the gas in the tube and the carb not being jetted properly for headers. Most stock carbs are not calibrated with headers in mind. Again, loss of performance and jumping to a wrong conclusion about backpressure.

Bottom line: The myth of performance and backpressure is completely backwards.

[This message has been edited by jrr (edited November 27, 2000).]

 

Finally, more people are finally debunking this myth about "backpressure". Yes, you can have an exhaust system that is TOO BIG, (a 4" Mufflex cat-back system on a 2.8 V6) but it isn't because of backpressure that a smaller systems works better, as explained by all the people above.