Anyone know a formula to calculate the exhaust flow rate of the Lightning. Variable equation for boost?

 

Nobody?
How do you know if the aftermarket mufflers flow enough?

Does this sound correct? displacement X RPM / 4 (4-cycle) = exhaust cfm.

Sounds to simple, what am I missing?

 

The denominator would be 2 rather than 4 as there is an exhaust purge every other revolution. But would you get a full purge? Then again, I think you get flow-through on a normally aspirated engine with a high performance cam (i.e. unburned fuel/air flows through the exhaust valve because of cam overlap).

As the supercharger is positive displacement, and everything that goes in the intake must come out the exhaust, could you figure exhaust CFM from the s/c flow rates?

Both of these methods might change with RPM and backpressure.

 

DH,
Thanks for the input.

Does this sound correct for a ball park figure?

330ci (motor) + 112ci (blower) = 442ci displacement

442 x 5500 (rpm) / 2 (4 cycle) = 704cfm

704cfm / 2 (dual exhaust) = 352 cfm per muffler

The part I am not sure of is how boost PSI effects this figure.

How does 352cfm for duals or 704cfm for a single muffler stack up against the various brands out there?

 

Nope, not even close. It just doesn't work that way. It has to do with cam duration, boost, etc.

The only way to know for sure is to find out how much air is going in at max RPM's. A tuner should be able to tell you how much.

I'm not sure why you want to know though. An Escort's stock muffler will flow the air, it'll be under a lot more pressure though.

I'm guessing what you're really asking is what is the pressure before the muffler, with every muffler out there. This still won't help you because of scavanging, and the noise factor, etc.

So this question is too open. If you want less back pressure, run straight pipes, if that's too loud, run race mufflers, if that's too loud, run something else. But there is no simple math equation for this, and even if there was what have you gained?

Just trying to help.

Kurt

 

What I am trying to figure out is at what point is a muffler costing you power. There is always a compromise between noise and performance. I also know that a certain amount of back pressure is needed. How much is the magic question.

My point is there are lots of choices of various cat-back and mufflers to choose from. Most are adapted from a regular 4.6/5.4 application. This is the cheap and easy way to market a product, but is it the best for our application?

 

What you are missing is the expansion of hot gases. I think you have to find mufflers designed to work with a motor of the same hp. The real problems is that mufflers are designed to damp certain frequencies. The muffler designed for a Mazda rx7(rotary) is different from the one for a Honda s2000(twin cam 9000 rpm) from a Mustang(large displacement, low rpm most of the time) even though they all have similar hp and cfm coming down the exhaust.

Hope this helps

Andy

 

There used to be someone on this board that worked for Flowmaster I believe.

Using some basic ventilation measurements, you could at least identify the pressures in an exhaust system. You would then pretty much have to have dyno data for each combo so that you could correlate pressure with HP or torque. It would be interesting to see the static or total pressures at various rpms for a stock exhaust; straight pipe and any other aftermarket combinations.

Honestly, the tests would be a pain to due but if your interested I could go into length about what it would take. In fact, come to KC and you can use my test equipment. You're on your own for the dyno, exhaust systems and labor!

Its the kind of ***** I would like to do if I hit the lottery and had the time to play around with stuff.

 

If your shooting for max hp at a certian rpm? You have to take into account the exhaust temps along it's path too. There is a "sweet spot" at which you should open it up. I believe the idea is to have a gradual decrease in delta P and temp. And after that "sweet spot" you just want to dump to atmosphere.

But that more pure dragracing stuff not street.

 

Silver also figure that we are at a absolute psi of atmosphere of 24.xx psi [I think]As you increase boost you are increase atmosphere psi [in theory]So if you have a 300 cid and boost to 6[25% of atmosphere]you increased the size of the motor up 75 cid so now you have a 375 cid motor.This is how I would work it.Plus you will increase the compression ratio the same %.Stan

 

Thanks guys. I knew that I had over simplified things. I have been running the Magnaflow 12468 for about 15k miles and begining to think it is too restrictive at WOT. Also thinking that a modded truck is moving too much air for a single muffler to handle. I like tha Bassani X-pipe with dual muffler but don't like the price. Plan to play with some exhaust combinations this winter and see if I come up with a little more mph on the top end.

 

Silver-Bolt

I really like the dynomax race magnums I have on my L. I went with an H-pipe because I didn't see a whole lot of engineering behind the X-pipes out there. Simply welding pipes in the shape of an X doesn't give you Dr. Gas performance.