Jump to content
  • Sign Up

Avalanche Exhaust Mod


Recommended Posts

Posted

I followed up my FIPK Mod and installed a Flowmaster 70 series (and a chrome tip). I Seemed to have lost the "High-End" response I use to have. My Avalanche use to "Jump" at the slightest tap of the peddle.

:angry:

I have heard of people who weren't happy with an exhaust install having the shop "work" with them to make it right? Guess I'll be having one of those "confrontations" tomorrow with the shop who did mine.

Any suggestions appreciated!

 

Sad Brad in SoCal

 

 ???

Posted

I'm confused.  I consider "jump" at tapping the throttle as low-end response - lots of torque at low RPM, not high-end response.  A couple of folks in this forum cited a loss of low end torque with Flowmasters.  I assume that the torque curve is shifted upward in RPMs, which is a shame since, in my opinion, the 5.3 already has it's peak too far up the RPM scale for a truck engine.

 

Did you do a full cat-back or just the muffler (and tip)?

Posted

All of my power gains came in the low end when I put my Flowmaster cat back on.  

 

Something similiar happened to a buddy of mine.  He has a 98 Jeep TJ and we put an intake kit and a throttle body spacer on and he gained all kinds of power.  We put the cat back on and he lost his lowend jump off the line.  However, in the long run he is getting better gas mileage.

Posted

I've heard a few people talk about losing low end torque by opening the exhaust.  How can this be true?  I've been trying to figure this out on the internet and friends I work with.  (I still can't convince myself one way or another ???)  If you open the exhaust, this allows the exhaust gases to escape on the exhaust stroke and thus less pressure on the piston.  With less pressure on the piston on this stroke, that makes a less resistive force the piston (and the rest of the cylinders) has to overcome and thus more force (torque) on the crankshaft.

 

If I remember correctly with a mechanically governed diesel engine (semi truck Caterpillar engines), when you start putting a load on the engine you slow down the RPMs.  Slower the RPMs->slower piston->more time to inject fuel and better distribution of air/fuel->more fuel->more KABOOM!!!  With gasoline the air/fuel mixture is nearly constant, no matter the RPM (and it takes place outside the cylinder).  The thing that changes is the amount of throttle (air intake and thus fuel).  To add another obstacle, you have a lot more freedom to change spark advance, fuel injection duration...etc. with EFI on gasoline and diesel engines.  UGGGGGGGHHHHHH!!!!!!  I'll have to ask again at work tomorrow.

Does anyone else have a theory on this?  Does anyone know why the max torque is at such a high RPM?  Does it have to do with emissions?

Posted

I think I can answer part of your question.

Low end power vs. high end power. In order to make power at any rpm range, the intake and exhaust velocity has to be high enough to get the mixture in the cylinder, well mixed, and then scavenge it out forcefully. This has to be accomplished by moving the air mixture very quickly.

If you open either end up to far, i.e. big carb, open intake manifold, big tube headers, large diameter exhaust pipe, the air velocity in that particular section slows down because it carries the same volume at a slower speed. So if you put an exhaust system that is too big to keep that velocity going, the air just kind of "eases" it's way out and does nothing to help scavenge, or suck, the remaining air out. As the rpm's come up, the air gets moving and the scavenging effect is realized.

Hope this helps.

Posted

Did you go with a single 3inch in and 3inch out?.   I have read about power loss on the 5.3's with this set up.   I installed the Flowmaster 70 on my 2001 Tahoe 5.3 ( your stock exhaust is like mine was ) and have lost no power ,  I am pretty sure I have gained.     I went with a single 3inch in and dual 2.25 outlet  with 18 inch length 3inch dia tips straight out the back.   It sounds great and has a real deep tone.

Posted

I'm not certain on the size of pipe. I show up at the local muffler shop and ask the guy to throw on a 70 series and a tip. He cut the stock muffler out and threw the flowmaster on. Same side exit as stock!

 

Brad

Posted

Listen to Friz:

 

 Essentially, you are breathing too easily.  Want to prove Friz right?  Get some very coarse steel wool or something like that, jam it in your pipes.  (Or better yet use a soup can or something that will slip over your exhaust pipe)...of course...cut a hole in the bottom of the can...  There are a kajillion ways to do this...you could even engineer a 3" gate valve over the end of your pipe.

 

WARNING:  Do this for TESTING purposes only.

 

Try to restrict the flow of exhaust a little bit....see if your low end perfromance improves.  Betcha you will be surprised!

 

There are mechanical wizards around that build racing engines that can actually calculate this crap for you.  They are the experts on what a little "turn down" on your exhaust pipe will do.  Basically there is an optimum balance between intake and exhaust and you have missed it.

 

A stock engine is essentially perfect from the factory.  Any mod you make to the intake needs to be accounted for in the exhaust & vica-versa.

 

Hey..get it perfect...I am surprised that K&N doesn't have an exhaust pipe recommendation to go with their breathers!

 

Dean

Archived

This topic is now archived and is closed to further replies.



×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.