Hey guys,
I've been trying to come up to an alternative to running hi flows with longtubes. I've heard that, contrary to many statements I've seen on here, hi flows basically eliminate all gains created by longtubes. So what I've decided to do is to have some sections of pipe made that basically fit in place of the catted pipes, something interchangeable. Has anyone with a c4 and longtubes done this?

 

Speak up. The Feds are listening.

 

Longtube headers will give you a significant gain whether you run cats or a straight pipe.

 

Unless you have some monster motor in there thats trying to push out a volume of exhaust the size of Texas the high flow bullet cats might rob you of a couple of ponies.
Besides that you are replacing your exhaust system because of failed componnents - right!

I put LT, bullet cats, straight pipes to stock lt1 mufflers. Did it for several reasons:
Right thing to do
Have to smog every year
Exhaust meets the DB levels at the race tracks
Its quiet enough it can sneak in during "quiet hours" at most tracks
I like the sound

 

Well my plans were to have flanges welded on both ends of the catted pipes and both ends of the test pipes, that way I can put them on for inspection and take them off for track use

 

Just my .02 but that seems like a waste of time. As mentioned the gain is almost nothing hp wise. Your exhaust will probably be louder though if that's what you want. But, if you must do this band clamps might be a better choice than flanges. You'll be buying gaskets every time you swap them out.

They're called high flow cats for a reason......

 

Here's my concern. I own an Acura RSX Type S, and on the forums, it's always been said that using a hi flow cat defeats the purpose of longtubes. Idk if this is because it's an I4, but they have dyno sheets proving upwards of a 15whp loss with the cats in place. Keep in mind, I'm referring to a setup tuned for a catless system. I would tune my vette for the test pipes

 

Here is something for you to consider:

If you were to go to lets say long tubes with 1 5/8" primaries rather than 1 3/4 you would pick up some additional low end torque however if you completely remove the cats .... you're going to loose back pressure and while you may gain a few rwhp at the top of the rpm range there is a good chance that with the reduction in back pressure you will loose torque over several thousand of the low and mid rpm range.

What accelerates cars down the road is torque and what you want to do is increase the area under the torque curve.

Get yourself some longtubes, keep the high flow cats you'll feel it in the sotp and still do your part for the environment

 

I dont want to start anything here but I still dont get this back-pressure thing. How can back-pressure help the engine at all (torque curve)??? I think what makes sense is that the faster the air is moving unrestricted, the more torque and HP you will get...

 

Um simply not true. I have experienced this loss of tourqe due to open exhaust many times. Enough time to know that backpressure is extremely important and that you do not want to completely eliminate it. If you like the seat of the pants feel at low end. You wont have that as much as the power moves up in the band. I never liked that experience. Kills my low end and I can feel it. The reason backpressure is necessary is for exhaust gas scavaging. How it works exactly I have no idea but I know it is important in regards to building low end tourqe

 

I dont want to ruin 94lt1vette94's thread by getting off topic but I though gas scavenging was when the gas that is moving down the exhaust pipe pulls the gas that is behind it due to Bernoulli's principle? How does back-pressure help scavenging?

 

Scavenging is the process of pushing exhausted gas-charge out of the cylinder and drawing in a fresh draught of air ready for the next cycle in automotive usage. This process is essential in having a smooth-running internal combustion engine. Modifying the exhaust system, (i.e. modifying the exhaust gas velocity by changing exhaust tube diameters) can detract from the "ideal" scavenging effects, and reduce fuel efficiency and power if not properly planned out and executed. To increase scavenging potential, the entire path from intake to exhaust(i.e. all powertrain parts) to tailpipe must be tuned in sync with each other. This will ensure that the air flow is never interrupted. The acceleration and deceleration of thus exhaust gas is what will hinder the scavenging potential. For example, fast flowing heads and a tunnel ram intake combined with a badly planned camshaft and exhaust system will cause the air to "slow down" and "speed up" throughout its journey, thus reducing its scavenging potential. So, to increase scavenging potential, the air must maintain a positive linear acceleration curve.


When I put these cutouts and the stock system back on my car I lost a few rwhp. If I ran the car with the the cutouts wide open I didn't gain hardly anything. But if I open the cutouts about half way instead of all the way I picked the lost hp back up. Below is probably the reason why.

http://answers.yahoo.com/question/in...7205124AA91jnC

 

Great post! Here's my question now: Say you are using the sam exhaust system and longtubes. Wouldn't you make more power with a system tuned for the test pipes than a system tuned for the hi flows?

 

The difference would be minimal and wouldn't require a different tune.

 

There just isn't a lot of power to be gained in fooling around with the exhaust system. I'd concentrate on the motor itself if you're after more power.

 

Thanks for the great info! So the whole backpressure thing is useless (for the most part). Its all about scavenging and the proper airflow through the engine. So ideally you want an open intake tube with the same diameter as the intake (or a little bigger) then you want the air to travel to the cylinder as smooth as possible with minimal 90 degree bends and stuff to cause turbulence. Then you want the exhaust gases to exit as smooth and unrestricted as possible with pipes that dont bend too much (or bend gradually). Then you want them to collect in the proper size collector so that the exhaust gases are flowing quickly but unrestricted all the way out the tailpipe... That would be an ideal system right?

 

Sweet, thanks guys. How much are random teck bullet cats? Would it be better to get them in 2.75" or 3" because the collector will be 3", but the system itself is 2.75"

 

Pretty much IMO. That's also pretty much what GM gave the LT1's.

 

Get the 3".

I'd just Google the cats and get the best price. There are cheaper ones than RT though but it's one of those you pay for what you get things. Good Luck!

 

Here is sorta what RT cats would look like hooked up to your lt collectors. This set up is from stainless works