backpressure

**99-SS-Conv** · 01-09-2007, 08:48 AM

before I do this does anybody know if I have LT headers no cats custom x-pipe and glasspack dumps will my engine get f'ed up due to backpressure or will that be fine?

**JEFF01Z** · 01-09-2007, 09:33 AM

No backpressure = good

**99-SS-Conv** · 01-09-2007, 10:48 AM

good for the engine?

**9t8z28** · 01-09-2007, 02:52 PM

You should have a little backpressure. Thats a good setup. Your engine will be fine. Now if you were to run just open headers, that would be no backpressure.

**BlackLT1Z28** · 01-09-2007, 09:22 PM

Glasspacks? That will be almost as loud as open headers.

**0rion** · 01-09-2007, 11:02 PM

Originally Posted by BlackLT1Z28

Glasspacks? That will be almost as loud as open headers.

we'd already had this discussion in another thread. Glasspacks = bullet mufflers.

Old timers and a few youngun's still call them glass packs. Back in the day that was the muffler to run. It helped knock out the windows in the car next to you when you got on it.

To the original poster.
That's a very common setup for people going true duals. I would invest in some decent ear plugs ( although at 52 that's probably the same as sweeping a barn floor

) and tape or glue everything in the car down so it doesn't vibrate.

**nhraformula** · 01-10-2007, 05:40 AM

backpressure=myth

**0rion** · 01-10-2007, 06:51 AM

Originally Posted by nhraformula

backpressure=myth

agreed.

**9t8z28** · 01-10-2007, 07:06 AM

Originally Posted by 0rion

agreed.

Can you please explain?

**LS2Tuner** · 01-10-2007, 08:46 AM

Originally Posted by JEFF01Z

No backpressure = good

Take a look next time you go to the track and notice how many 7 sec. door cars run mufflers.........Then again it will depend on weather or not there is any really fast cars there......... You actually build MORE power with a "good" exhaust than with nothing.

Open headers is for the deaf old guys......
The exhaust helps scavenge out the exhaust gasses which speeds up the process which builds volocity which builds power!!!!

**SSTODD** · 01-10-2007, 09:10 AM

There have been tests that say over the axle set-ups are worth more than just "dumps". Again the dyno can lie but it makes sense to have a full exhaust on all but the most extreme drag cars.

**9t8z28** · 01-10-2007, 09:21 AM

Originally Posted by nhraformula

backpressure=myth

So there is no difference in backpressure from open headers and full exhaust?

**LS2Tuner** · 01-10-2007, 09:26 AM

Originally Posted by 9t8z28

So there is no difference in backpressure from open headers and full exhaust?

YES THERE IS A BIG DIFFERENCE!!!!

**9t8z28** · 01-10-2007, 09:50 AM

Originally Posted by LS2Tuner

YES THERE IS A BIG DIFFERENCE!!!!

Yes, I know! That is what I have been trying to say!!!!!!!!!!!!!!!!
I wanted a response as to why backpressure was a MYTH!!!!!!

**JEFF01Z** · 01-10-2007, 12:54 PM

Yes there is a difference. Will it harm the engine at all.. yes and no. It's not really a myth. Different setups require different exhaust setups to show its full potential. If you have 10" hg of back pressure your car is going to run like crap and it is really bad for the engine, your engine actually having to work to push the exhaust gas out and not fully scavenge the cylinder during the exhaust stroke.

4 stroke engines are not quite as affected by it as a 2 stroke engine is. There is no real benefit of having back pressure. A full exhaust will create some back pressure, but it is so little that it can be meaused in inches of H2O. The benefit of the exhaust system is the expansion chamber, typically this the muffler on most cars. It creates a pressure differential and increases velocity of the gases, thus scavenging the cylinders of exhaust gases better. This is also why headers LT headers add a good amount of power. The collector is the expansion chamber and the exhaust flow into and out of the collector creates a lot of velocity and is low pressure area because you are going from a 1.75" pipe to a 3" pipe. There are different types of headers and each one effects the power and torque curve the engine differently.

Running open headers is not really going to benefit you at all, if it does anything it might slightly decrease the power on a stock engine. There is no control of the expansion because it is going to atmopshere and creates such an increase in velocity you won't benefit from it unless you are moving just massive amounts of exhaust, such as a total race engine that is not even close to being able to drive on the street.

For the most part any setup you use to run on the street will benefit from a full exhaust with one exception... Turbos. Turbos work most efficiently when there is no back pressure and no exhaust system. This increases the velocity exiting the turbo, making the turbo more efficient.

Hope this sheds some light on this. And by all means if I am wrong about something please correct me.

**9t8z28** · 01-10-2007, 01:32 PM

Originally Posted by JEFF01Z

Yes there is a difference. Will it harm the engine at all.. yes and no. It's not really a myth. Different setups require different exhaust setups to show its full potential. If you have 10" hg of back pressure your car is going to run like crap and it is really bad for the engine, your engine actually having to work to push the exhaust gas out and not fully scavenge the cylinder during the exhaust stroke.

4 stroke engines are not quite as affected by it as a 2 stroke engine is. There is no real benefit of having back pressure. A full exhaust will create some back pressure, but it is so little that it can be meaused in inches of H2O. The benefit of the exhaust system is the expansion chamber, typically this the muffler on most cars. It creates a pressure differential and increases velocity of the gases, thus scavenging the cylinders of exhaust gases better. This is also why headers LT headers add a good amount of power. The collector is the expansion chamber and the exhaust flow into and out of the collector creates a lot of velocity and is low pressure area because you are going from a 1.75" pipe to a 3" pipe. There are different types of headers and each one effects the power and torque curve the engine differently.

Running open headers is not really going to benefit you at all, if it does anything it might slightly decrease the power on a stock engine. There is no control of the expansion because it is going to atmopshere and creates such an increase in velocity you won't benefit from it unless you are moving just massive amounts of exhaust, such as a total race engine that is not even close to being able to drive on the street.

For the most part any setup you use to run on the street will benefit from a full exhaust with one exception... Turbos. Turbos work most efficiently when there is no back pressure and no exhaust system. This increases the velocity exiting the turbo, making the turbo more efficient.

Hope this sheds some light on this. And by all means if I am wrong about something please correct me.

No you seem to have layed it down pretty heavy. Nice write-up!

**99-SS-Conv** · 01-10-2007, 03:18 PM

very good info

**ss~zoso~ss** · 01-10-2007, 04:49 PM

as stated above, no back pressure is 100% good for turbo equipped cars

**0rion** · 01-11-2007, 01:09 AM

back pressure explanation

I read that a while back and it seemed to make sense to me. I grew up always hearing that running free flowing exhaust or open headers would burn valves. This guys explanation just made sense to me. He might still be wrong but it makes sense to me.