I own a '89 GTA 350 tpi. Don't get me wrong, I love my flowmaster cat back, but never dynotested the car before or after the install...
Could anyone help me with some no=umbers for their aplication?

Thanks a lot!!

 

Flowmasters are slightly restrictive than other mufflers, but u will feela power gain.

 

There HAS to be a gain over the stock exhaust system.

 

n/m.. what he said ^^^

 

I do believe it flows better than stock, but this only mod to a stock car don't seems to produce any power gains. So, has anyone some numbers before/after instalation?

 

I have the 3" catback took off the cat. and an 80 series muffler. I don't know a hp or tq number but it added 3mph to my trap speed in the 1/4

 

A freer flowing exhaust system will alter your HP/TQ power curve...It will put more emphasis on high end power, while rlowering some lower end TQ.

It would be like this:

Before: (not real numbers)

1000rpm: 100Hp 175TQ
2000RPM: 130HP 200TQ
3000RPM: 170HP 250TQ
4000RPM: 200HP 275TQ
5000RPM: 250HP 260TQ
5500RPM: 240HP 240TQ
6000RPM: 200HP 190TQ

After:

1000rpm: 110Hp 160TQ
2000RPM: 132HP 190TQ
3000RPM: 170HP 250TQ
4000RPM: 220HP 275TQ
5000RPM: 265HP 260TQ
5500RPM: 260HP 260TQ
6000RPM: 210HP 200TQ

This is dyno proven...Less backpressure t generate low end torque.
That is, IMHO, why iit is not as easy to smoke the tires off the line with LT's and 3" pipe with the same engine and other mods.

 

what he said

 

i have the blowmaster cat back on my car and hollowed out the cat at the same time and felt no difference in power. i will be getting rid of it shorty for a random tech muffler.

 

I heard only good things about hooker systems. why don't you get this one? is cheaper too...

 

i'm just get the random tech muffler and have a exhaust shop weld it on with some borla tips. i thought about getting the hooker cat back but i want a straight flow muffler.

 

i like my edelbrock.

 

Backpressure increasing torque is an old wive's tale. Kinda like leaving a battery on concrete will drain it faster. It's just not true.

The only thing that can be done to increase low RPM torque by changing the exhaust would be to increase the scavenging affect. That's it. And the more you increase the scavenging affect, the better the rest of your exhaust needs to flow.

Backpressure is bad. There is no benefit by having it. It lowers the VE%, causes poor MPG, and poor TQ and HP #'s.

The old thinking that backpressure increases torque has been construed from the fact that an engine that is built soley for use below 3500 RPMs is not effected by backpressure. That would be a tractor, a plow, or a semi, etc. There's never enough RPMs to really build any backpressure, so it will never effect the output of the engine.

AJ

 

You are right, backpressure doesn't increase torque, but lack of backpressure malters teh power curve, as illustrated by my post above. Adding more backpressure over a stock system would have the opposite effect on low end torque......Since it kills high end HP, it would also kill low end TQ.

 

Your imaginary numbers make no sense. Torque is measured on a dyno, horsepower is calculated from the measured torque. Horsepower calculations are based on the formula:

<B>(Torque x RPM)/5252 = HP</B>

Thus your first chart should look like this:

1000rpm: 33.3 HP 175TQ
2000RPM: 76.2 HP 200TQ
3000RPM: 142 HP 250TQ
4000RPM: 209 HP 275TQ
5000RPM: 247 HP 260TQ
5500RPM: 251 HP 240TQ
6000RPM: 217 HP 190TQ

Horsepower and Torque will <B>ALWAYS</B> be equal at 5252 RPM, not 5500 RPM as your chart indicates. Study the above formula to see why this true.

Your second chart is even wackier. At some RPM points you show torque decreasing(in comparison to the first chart) and horsepower increasing. At other rpm points you show identical torque measurements(in comparison to the first chart) while hp increases. Neither of these is possible. Again, check the formula above for the reason why this is true.

I definitely agree with your assertion that less backpressure will increase low-end torque. However, qualifying this statement by saying "this is dyno proven", when it appears you do not understand what a dyno does(measure torque, calculates HP) makes me wonder how you came to this conclusion.

Finally as you increase low-end torque(by reducing backpressure) it becomes increasingly easy to smoke the tires off the line(to the point of being annoying even).

 

<B>Backpressure increasing torque is an old wive's tale.</B>

This old myth is probably based on a misperception. Since the effect of backpressure is cumulative - more exhaust flow will increase backpressure - it should logically cause more restriction as rpm's increase. Thus when backpressure is decreased, the benefit will be perceived to be greater at higher rpm's, and less noticeable at lower rpm's.

So once the "free-flowing" exhaust system is installed, the higher-end gain is easily noticeable, but the lower-end is not. This would fool some into thinking that they have gained top-end HP, at the loss of low-end torque.

The other problem lies with dyno data. Dyno's don't lie, but the data can be misinterpreted. For instance: if you gain 5 lbs/ft torque at 2000 rpm, the dyno would calculate this as a gain of 1.9 hp. Fairly insignificant to most people. But if you gain 5 lbs/ft at 5000 rpm, the dyno calculates this as a gain of 4.8 hp. Still a small gain, but more noticeable to those who quickly glom the HP numbers while overlooking the torque curve.

At any rate, I have yet to see any proof(from a dyno or any other source) that a decrease in backpressure will not increase torque and HP throughout an engines operating range, if changes are made to take advantage of the gains(rejetting the carb, burning a new prom). Since backpressure can be defined as 'a positive pressure opposing the flow of exhaust gasses away from the engine', it makes sense with less backpressure, less exhaust gases will remain in the engine. This in turn means more air can enter the cylinder, and more fuel will be needed as a result. If these changes are not made, the engine may be running leaner at and below the torque peak, which in turn may cause a loss of some torque at and below the torque peak. Above the toque peak, volumetric efficiency drops off, and the leaning effect would be decreased.

 

To return at the first ideea, about Flowmaster's cat back, I've finded out that the 80 series muffler is good only for low rpm cars (ours...). a 4th gen won't benefit from the use of a 80 series muffler because seems that it cannot outflow even the stock GM muffler... Still it has a fabulous sound. Let's be serious, a free flowing muffler cannot have flowmaster's specific muscle car low growl...
Still I'm proud of my Flowmaster cat back because it fits well my slow(I mean "stock...") GTA!!

 

Hey 88IROCs,

Wouldn't it be easier to say "You're right. Increasing backpressure does not increase torque"?

It really doesn't matter why people once thought, or still think that it does. All the matters is, it isn't true.

Remind me to never ask you why the sky is blue..... OK?

I'm just pissin' with ya. That's a good explaination. I'm just tired of trying to tell people, who were told by farmer Billy Joe Jim Bob that backpressure is good.

AJ

 

The increase in low RPM torque would be due to Flowmaster's patented scaveging affect. The 80 series is just made to increase the scaveging, but doesn't flow much better than stock because it's also made to be more quiet than the 40 and 50 series. More baffles = less flow.

Plus I'm sure that the crossflow design doesn't help either.

AJ

 

the 80 series IS the loudest.

 

Oh..... is it? Sorry.

I don't know a whole lot about Flowmaster. I think they are too trendy for me, so I never really followed the specs of there different series.

Well I guess I'm wrong again.

AJ

 

Wouldn't it be easier to say "You're right. Increasing backpressure does not increase torque"?

Yup, it woulda.

But you been around here long enuff to know that some people regard the backpressure myth as gospel(cuz the guy down at Pep Boys told 'em so). I won't even try to convince those folks it's wrong. But I figured I'd throw in my .02 on how I think the myth got started.

 

I've never understood Flowmaster's claim of a scavenging effect in their mufflers. This may be a lack of comprehension on my part, but I have a couple of conceptual prolems with their claim:

1. By the time exhaust gases reach the muffler, they are so lacking in mass and velocity, that I can't comprehend them having the energy to create a negative pressure(scavenging) pulse.

2. Even if the scavenging effect could be created, what is supposed to be scavenged. For the scavenging pulse to do any work, it has to reverse direction(by reflection of the pulse, or by collapsing the pulse) in order to draw(suck) gases towards an exit. The only place I can conceive this happening would be at the y-pipe or the header collector. However the distance travelled to either of these two locations would surely dissipate any energy in the scavenging pulse, rendering the whole exercise fruitless.

Then again, I spent a good part of my high school physics classes experimenting with altered states of consciousness. So maybe I missed something important.

 

More than likely it's one of those one time occurances that happened on one 1.3L Mazda 4cyl. You know, it happened that one time, when they did that one thing, and the temperature was at 65.82* Farenheight, and there was one slit second of scaveging that happened right at 3246.32 RPMs, when the earths rotation was @ 42.86 deg. and the barometric pressure was.......ETC, ETC.

The sad part is, that's all it takes to be released from false advertising. Like K&N for instance. "Gain up to 50HP". Well that's just it. "Up To" being the key words there. Some engines might gain 1 HP, but that falls within their claims. Nowif they said "Gain at least 1 HP", and someone showed that their car only gained .8 HP, then they could sue K&N for false advertising.

AJ

 

Hey, don't bag on Pepboys like that! Leave that to the employees like me.

 

Has anyone ever decided to consider exhaust velocity! A larger exhaust that is installed to increase top end power by REDUCING back pressure will limit the low end EXHAUST VELOCITY. This slow down in exhaust speed at low RPM reduces the low end scavenging effect and causes a driver noticed power loss. By installing a larger exhaust for top end power one has moved the power band UP! Those who say back pressure is needed for low end power have mistaken back pressure for EXHAUST VELOCITY AT LOW RPM that scavenges exhaust from the cylinders. People think that "hey I put on a smaller exhaust and my low end power picked up, I must have needed back pressure". NOPE, you needed exhust velocity to REDUCE back pressure and scavenge the cylinders! Hope this helps!

 

camaromike is right, when I put my flowmaster catback on I lost some low end torque, but it pulled about 4000rpm A TON better. so.........do you want to leave fast then not go anywhere or leave just a tad slower and get somewhere? you can't always have the best of both worlds. you just gotta make you decision on what ya want? fast off the line and now pull about4000rpm or so? or a little bit worse 0-60times but an overall better 1/4 mile time? just thought I'd share my thoughts

 

<B>A larger exhaust that is installed to increase top end power by REDUCING back pressure will limit the low end EXHAUST VELOCITY</B>

If we were talking about the primary tubes or the collector, I would agree with you. But we're not. We're talking about the cat-back. Any reduction in size here will reduce exhaust velocity through the y-pipe, the collectors and the primaries. Regardless of the engines rpm.

Proper sizing is critical in the primaries and the collectors(and smaller is not always better), but beyond the collectors reducing backpressure should be your only goal.

 

<B>camaromike is right, when I put my flowmaster catback on I lost some low end torque, but it pulled about 4000rpm A TON better</B>

When I put a flowmaster system on my first IROC, I gained at the low-end and at the top. When I upgraded to a 3.5"/Borla system I gained even more at the low-end and at the top.

 

88Irocs, I agree with you in most cases. I was focused more on the header and y-pipe side of things but if the headers or y-pipe are too large then a smaller cat back can increase low end HP by making up exhaust velocity and scavenging the y-pipe more efficiently.

 

All a smaller catalytic will do is increase increase backpressure.

In the primaries and collector, downsizing can increase exhaust gas velocity(at the risk of increasing backpressure). Which will increase the effectiveness of the scavenging pulse.

The collector exits and to an extent the y-pipe, will affect the velocity with which the exhaust gases exit the collector. This is critical in creating the most efficient scavenging pulse.

The catalytic converter cannot create a scavenging pulse of it's own. It does however, create backpressure, which can be felt upstream, all the way to the collector. That backpressure will reduce the velocity of exhaust gases into and out of the collector, which will diminish the scavenging pulse and it's effect.

And as I mentioned before, backpressure will increase as exhaust gas volume increases. So having lost more top-end power, I believe a lot of folks mistakenly identify this as a gain at the low-end,... not realizing that they have lost power across the board.

 

since all of ya are talkin bout exaust systems....

about a year ago when i got my car, i had an old rusty 92 flowmaster on it. i thought to myself, fugk it, i'll cut the muffler off. so i did...will i gain HP/TQ by doin so was it a bad idea?

 

88Irocs, I don't have a CAT! HeHe! Don't think you should have one either!

 

Oh G0D, this again. Listen, this back presser thing has more people confused then the tax code. BACKPRESER IS BAD, for the most part. If you totally eliminate back presser (or just get to the point that you have almost none) you WILL LOSE low end torque! But that just will not happen on a car with a full length exhaust. Don’t think you’ll lose torque, get a bike, something with a smaller motor that is low on torque to start with like a 883, and pull the pipes off. YOU WILL LOSE LOW END TORQE! But to get to this point with a car it would take large tub headers, run it with open collectors. Other then that ANY thing you do to reduce back presser on our car WILL BE HELPFULL! BACKPRESOR BAD, NO BACKPERSOR NOT GOOD, for low-end torque.

 

NeedAZ, you obviously did not read my earlier post. The reason your 883 lost torque, when the exhaust was removed, is because you lost exhaust velocity that scavenged the cylinders.

88Irocs, to respond to your theory of the exhaust after the y-pipe not affecting cylinder scavenging. I think you missed the fact that two pipes meet at the y-pipe. Exhaust velocity from one bank will help scavenge the other. On a conventional dual system you would be correct. Make the exhaust big as possible past the collectors but......... Why do X-pipes work so well and make such dramatic increases in torque?! Shared muffler capacity and bank scavenging is why. One half of the engine will pull a vacuum into the X-Pipes' opposite side. Pretty cool, huh!

 

i love the people who think that a muffler makes the difference between a fast car and a slow car. build a nice motor and choose the muffler you like the sound of best, as long as it isnt restrictive and fits the application, its fine. Also, leaving your stock clogged cat on and expecting a freer flowing muffler to help isnt gonna do a lot without a high flow cat as well. just some food for thought.

 

ROFLMAO the 80 series are three chamber flows. Have you ever heard a 40 series two chamber???? Look in the summit or jegs and they will tell you the noise levels on the mufflers. If you ever heard a car that went from a 80series to a 40 series two chamber you woudl crap your pants.

flomaster one chambers sound like open headers Well pretty close

 

<B>Why do X-pipes work so well and make such dramatic increases in torque?! Shared muffler capacity and bank scavenging is why. One half of the engine will pull a vacuum into the X-Pipes' opposite side. Pretty cool, huh!</B>

I doubt by the time the exhaust makes it to the x-pipe, that it has the energy(mass x velocity) to create the negative pressure area behind itself to scavenge the adjacent pipe to any great degree.

Where x-pipes(and to a lesser degree h-pipes) benefit exhaust flow is by balancing flow between the two pipes(which I think you alluded to). Because the the Chevy small-block does not have evenly spaced firing pulses between the cylinder banks, the exhaust flow on each side is very uneven, this causes peaks and valleys in the pressure rate in each pipe. These peaks and valleys both cause restrictions to smooth exhaust flow. The x-pipe smooths the pressure rate and lowers the overall restriction. It is important to note that the closer to the collectors that the x-pipe is placed, the smoother the flow and the less the restriction. 180&deg; headers attempt to do much the same thing, by routing the exhaust from the out-of-sequence cylinder on each bank to the collector on the opposite bank. This evenly spaces the exhaust pulses on each bank, smoothing exhaust flow and reducing restriction. However, because of their cost, complexity, and reduction in ground clearance these headers were nevr popular with any but the most hardcore racers.