I did a search which anwsered the majority of questions, but I still cannot determine if an engine (lt1) runs optimally with lots of backpressure or will acheive more power with a free flowing exhaust. For example with my current setup I beleive the flowmasters are restrictive, however I want to go to a straight through muffler (ex. bullets) I have been told by some that If i do this my car will be a dog off the line because of no back pressure, but others tell me it will flow really good and I should see significant gains. This all seems really here nor there, I would like to know the logic in the backpressure debate.

Thanks in advance

 

Your bottom end loss will be minimal if you could even feel it at all. All engines will benifit from less back pressure. You will see the benifits in the higher rpm range. And when you think of it, what race have you ever been in where you've stayed in the lowest 1/4 of your rpm range for the whole race?

Ken R.

 

Only two strokes are going to significantly benefit from backpressure

 

Here is a thread I started a while ago.

It should cover everything you want to know. I highly recommend the book as well.

http://web.camaross.com/forums/showt...highlight=Myth

 

The benefits of small amounts of backpressure are only seen in engines with very large cams with alot of overlap. The danger is overscavenging. If you have a cam with alot of overlap, well-tuned headers, and a well-matched intake, you can actually draw your intake charge out of the exhaust. A little backpressure can help with this situation, but the ideal solution is to modify cam timing.

My point is that with a street LT1 cam and intake, too little backpressure isn't going to hurt you.

 

I don't mean to step on anyone's post, but I want to get a clarification:

If backpressure is HELPING an engine, there is an error with valve timing,
and/or intake & header dimension.

IOW, a proper system will have zero back pressure but proper length intake/exhaust
dimensions with IVO, IVC, EVO, EVC timed perfectly.

(of course this is limited to a specific RPM window)

Backpressure will exist at some moment in time and must be figured into the
picture.

Tuning the backpressure out of the window of RPM the motor spends most
of the time is the main objective.

 

i have yet to see a 4stroke engine ever benifit from backpressure. ever.

so long as the conservation of mass laws apply; Mass in = Mass out.
Last I checked, the end goal of all exhuast/intake tuning (heads, cam, rockers, exhaust setup) is to get as much air into the engine. air in = air out (or damn close to, lets assume steady state here)

Although extrodinarily dynamic, its still pretty simple and this rule ALWAYS applies: Its a pump. The goal is to get as much air in and out of it in a given time frame as possible.

Please do not confuse "exhuast tuning" and "backpressure."

but hey, i've been wrong before. maybe i'm missing something.

 

No you aren't wrong.How many Pro stocks have you seen running full exhaust.

 

Only reason the "backpressure" helps has nothing to do with the backpressure you changed the secondary length of the exhaust system and the motor didn't like it.

Time to go buy the new Pop Hot Rodding and read the article by Vizard in there on exhaust systems if you still think freaking back pressure makes power anywhere.

Bret

 

Vizarrd?

ehh maybe.

 

I've never seen one individual test so many exhaust systems in my life.... The guy is in his element putting together a bad *** street car exhaust.

I'm not the only guy on here who will reffer you to him, Mindgame, OldSStroker etc...

I wonder if NateH read that article and would like to comment since he is the resident exhaust guy around here.

Bret

 

Thanks guys, its crystal clear now, zero to 69, that post is what I came up with when i searched before i posted this thread, I am going to install my bullets which is going to give me a straight through exhaust aside from the xpipe. Thanks again for quality posts, (really notice the difference between the advanced tech and general tech)

 

I would say back pressure hurts power , what you want is velocity. Too big a pipe and you create back pressure , have the right size pipe and you have good ehxaust velocity.

 

To big a pipe does not create backpressure, it relieves it.

 

Vizzard rocks. He has a very scientific approach and the guy must live in the dyno cell! As far as back pressure goes, I agree with what's been posted about it being a bad thing, relatively speaking. But you have to keep in mind that the funtion of an exhaust system on a street car is different from a race car, in a variety of ways. Noise suppression and emissions are big considerations. Still, less back pressure = better, but the system will be compromised by having to serve multiple functions besides exhaust scavenging.

If I were doing a high-po NA 4th gen, the exhaust system would get a lot of attention. And eventually, I will get around to doing something else as it is (with boost and N2O). The stock configuration, with a single convoluted pipe running the length of the car, is so far from optimal that it's pitiful. Problem is that there is so little freakin' room to put a better system. So far, I haven't seen one I really like and a custom job would be needed. Big $$$ unless you can skillfully bend and weld tubes, which I cannot.

Rich