Funny how I hear all of you guys talk about how the L just loves backpressure. Just to be clear about this, that is a completely false statement. The closer the backpressure gets to 0 the more power the L will have. Now scavenging is a completely different story. Flame away I'm ready to defend this to the death of it.

 

you are probably right, because everytime i start to feel backpressure, i quickly try to reduce it to zero (if there's no one around)

 

good to have you back MRBBQMAN!!!........or something......JR

 

Here is an example for you. 1997 Honda Valkyrie with stock exhaust dynoed and 100 HP and 102 ft/lb of torque. This person put a 6 into 6 exhaust with no baffles in it (way too loud btw) and LOST 10 hp and 10 ft/lb of torque. Some backpressure is required.

 

so does this mean that the whole argument about flowmaster mufflers reducing back pressure can be discarded? I would love to put a few flowmasters on the L because they do sound great, but after hearing that I will lose power then I'd rather stay stock.

 

Nope....I'm with air1

The trick is to reduce back pressure to "0" ..BUT maintain air speed or velocity.

Most of the time reducing back pressure means just puttin bigger pipes on it. This will kill air speed.

So....no back pressure + high velocity = more power.

Oh and I will defend this almost to the death or something
Dale

 

InS0mNiAc
I was thinking about flowmasters myself, but I haven't heard them on a L. What do they sound like? I've had them on the last four Fords I have had and loved the sound they made.

 

What would mean 0 backpressure ? No exhaust whatsoever? Just exhuast shooting out the heads? I dont think it would gain or lose any horsepower, because it wouldn't run.....?

 

I'm not sure what they would sound like on an L, but on my gt stang it made it sound like I had a damn big block in it! I love them and was pissed when I heard that they didn't go well with the L's. But who knows now, there was supposedly a whole back pressure issue with them but with this news now, I wonder if it was all just a bunch of bull! Can anyone clear up the flowmaster issue?

 

well its not so much that your losing any torque, its that you move the torque range up a little.. like you might lose 5ftlb at idle but you gain that back in the higher rpm ranges...so all in all it really depends what you optimal rpm range is, ie. you could move your optimal rpm range all the way up to 4000-8000 but you wouldnt be able to use it because its so high. but see you also have to get that bad air out before you get the new good air in...headers and full exhaust help with that a lot. i agree both with and against the backpressure theory to an extent. i mean y do the fastest lightnings run long tubes? a machinist/automotive engineer told me his "theory" on backpressure, and he said if you do lose lowend torque its very minute and youl make up for it in hp and highend torque. it makes it easier for you motor to accelerate to a higher rpm too.

just my 2 cents!

id like to hear the tuners point of view on this?

 

I've got flowmasters. I'll be putting on a Bassani soon, which sounds much better in my opinion.

 

Backpressure is needed to fill the pipes and keep airflow going smoothly. Obviously if the pipes are too small you lose power because the exhaust cannot get out quickly enough.

When the pipes get bigger it takes higher RPMs than before to fill the pipes so the power curve moves up. How much higher depends on the pipe size vs. engine size.

For single outlet 2.5" to 3" seem to work best for most of our vehicles, with the PSDs needing bigger pipes obviously.

Factoring in the mufflers gets a little trickier because of the different sizes and designs. The best bet here is to see just what has worked for different people. I wish I had been on this forum a few years ago. I spent a lot of money experimenting to get what I wanted.

 

To those of you asking about the Flows.

IMHO the reason why they don't work so well on and L is because of the Cats.

Traditionaly Flows have always shown a bit of back pressure over other makes of mufflers, but a flow bench can't duplicate what is happening on the car. On the car the Flows always seem to run better than other mufflers and with that awsome sound too.

But hears the catch, anycar I have messed with, that had a cat converter OR a turbo on it, always ran best with an open center straight thru muffler.

My opinion is if you take the cats off the truck the Flows would work great, Cats on and all bets are off.

I guess all that wiz bang pulse wave stuff that Flowmaster rants about probably does work......but only "without" something in there way. Dale

 

 

air1kdf: I agree with you that backpressure hurts performance, and less is better.

Redshift: the reason the honda lost hp was because going from a tuned header (stock) to 6 open pipes he lost SCAVENGING, not backpressure. A well designed header will use the last exhaust pulse to help pull the next one out of the head. In effect, it's like vacuum, NEGATIVE backpressure.

I suggest that what some see as a loss of performance is due to 2 things: The rpm at which optimum flow (and scavenging) is achieved has changed with a freer flowing exhaust, it isn't lost, just at a higher rpm. And if you see a loss in boost pressure it's because the air mixture isn't being stacked up trying to get into the cylinders, it can flow in better and easier because the exhaust isn't still fighting the backpressure trying to get out. The result is less PSI on the gauge, but as much or more air flowing, and with less heat buildup in the intake.