Torque Exhaustion

Thrlls · 09-28-2009, 11:21 PM

I have an 84 3.2 and installed a Flowmaster 2 in/out....it's a little on the loud side, but I want to be heard in this small car.

Anyway, the only mods I have that affect the motor is the S.Wong Chip, TRE Headers, and a lighten flywheel.

My questions are:

Am I losing torque due to the dual exhaust with OEM intake?
Would capping one of the outlets help to increase torque, or it doesn't matter?

I would invest in a CAI, but the OEM seems to be pretty good as is.

I know I lost some torque due to the light flywheel, but the exhaust is easier to address at this point. I also realize by capping one side the exhaust will be a little quieter.

My concern is I'm letting out more air than I'm taking in, kind of like taking a breath, then opening your mouth wide and letting out air...I think!

Joe V · 09-29-2009, 04:51 AM

Woody,

I've an '84 also with a stock banana muffler. Took it to the muffler shop to have the 2 out mod done (where the right side is cut and a tip is welded on). I could not bear the noise. And it felt like a dog!! A slow one at that. I know it's a different exhaust system all together, but I just had to share my experience with "more flow".

Hang loose!

175K911 · 09-29-2009, 05:33 AM

Woody- a couple of questions:

What size headers did you use? If they're 1-3/4" then you're going to loose a lot of torque, they're too big.

Which Steve Wong chip do you have? Is it one of his maps that is designed for headers and a free flowing muffler? If not, you need different software. The change of exhaust makes a big difference in the fuel/spark requirements of the engine. If I run an off the shelf chip with my 1-5/8" headers and M&K muffler, the car is flat in the midrange. Running software designed for this combination really fattens the torque curve expecially over stock.

I run a lightweight pressure plate and throttle response is much nicer, no way I lost torque from that.

I'm betting on the software. Steve Wong should be able to fix that for you.

javadog · 09-29-2009, 06:10 AM

Quote:

Originally Posted by Thrlls

I know I lost some torque due to the light flywheel,

No, you didn't. The flywheel has no effect on the production of torque by the engine. The engine will feel different, but that isn't the same thing.

No engine really needs more back pressure. Ask yourself how many race cars you see (that do not run in a series where noise limits are imposed) with anything but open pipes. The answer is none.

Having said that, exhaust tuning is a complex science and there can be both positive and negative effects from altering characteristics of any exhaust system. The easiest way to answer your question (and the only one that isn't an educated guess, at best) is to stick the car on a chassis dyno and see what changes when you cap a pipe. Be sure to note the air-fuel ratios, as you want to make sure that the changes that you see are related to the exhaust change only and are not affected by non-optimum fueling at various points. Chassis dynos are pretty common nowdays and not expensive to rent.

JR

stlrj · 09-29-2009, 09:33 AM

I don't think it's really necessary to put the car on a chassis dyno to see if capping a pipe makes a difference. The old reliable butt dyno should do just fine.

The air fuel ratios must have already been optimized by Steve Wong, so monitoring that might be a waste of time.

Cheers,

Joe
86 3.2 transplanted into a 74.

javadog · 09-29-2009, 09:38 AM

Quote:

Originally Posted by stlrj

I don't think it's really necessary to put the car on a chassis dyno to see if capping a pipe makes a difference. The old reliable butt dyno should do just fine.

The air fuel ratios must have already been optimized by Steve Wong, so monitoring that might be a waste of time.

Cheers,

Joe
86 3.2 transplanted into a 74.

Your butt must be a great deal more sensitive than mine. I don't think we're talking more than a few horsepower. If the A/F ratio is good with one exhaust configuration, it might vary a little with the other. Maybe not a great deal, but...

I've done tuning with a stopwatch and my butt, in years past. I now much prefer a dyno. Each to his own...

JR

stlrj · 10:22 AM

Quote:

Originally Posted by javadog

Your butt must be a great deal more sensitive than mine. I don't think we're talking more than a few horsepower. If the A/F ratio is good with one exhaust configuration, it might vary a little with the other. Maybe not a great deal, but...

I've done tuning with a stopwatch and my butt, in years past. I now much prefer a dyno. Each to his own...

JR

A few horespower may not be that noticeable but torque is what he's looking for and should be felt without the need of artificial devices to tell him what would be obvious.

Thrlls · 09-29-2009, 10:30 AM

Mahalo Joe for sharing your experience with your exhaust.

175K911 - I don't remember what size headers I have, but I'll check the reciept, and as for the SW chip I did inform Steve of the exhaust and flywheel, and can only assume he gave me the correct one.

javadog - good to know I really didn't loose any torque due to the light flywheel.
I agree with what you say about the race cars with open pipes, but they are not running OEM intakes either. They are taking in more are as well...making a larger air pump.
I also agree I should probably find a dyno somewhere here in the middle of the Pacific and do a comparison test of single vs dual.

stlrj - Mahalo for your input also, and it's actually my butt dyno that's making me feel I lost some torque prior to the changes.

This exhaust issue can be exhausting to say the least and will take all advice into consideration...you all have been a great help to me!

MAHALO!

JP911 · JP911's Garage

Experimenting with mufflers on these cars can certainly be exhausting (of time, effort, and money). Different engine setups (cams, compression, induction) require different types of exhaust setups. In my case, headers plus a stock 2-in, 1-out muffler made the best HP and torque...opening up more outlets on the muffler actually cost me approx 10 HP and 8 ft.lbs of torque. It would be interesting to see what would happen if you bolted up a stock (2-in, 1-out) muffler.

javadog · 09-29-2009, 11:55 AM

Quote:

Originally Posted by Thrlls

javadog - good to know I really didn't loose any torque due to the light flywheel.
I agree with what you say about the race cars with open pipes, but they are not running OEM intakes either. They are taking in more are as well...making a larger air pump.
I also agree I should probably find a dyno somewhere here in the middle of the Pacific and do a comparison test of single vs dual.

What works in principle on a race engine works for you, as well. Anything you do to move more air through an engine, whether it is opening up the intake or the exhaust will make more power. Most of the tuning effects of an exhaust are not relevant when you are talking about exits from the muffler.

There are several dynos in Honolulu, if you want to go down that route.

JR

wowzer911 · 09-29-2009, 09:59 PM

I have tried several muffler setups and on a couple of them a loss of torque was noticeable.
So yes, it is possible that this could also be the case for you.
I currently have an M&K dual out, but one side is capped for both noise reduction and the fact that there is no HP increase with the dual out vs. single out on my particular muffler.

Thrlls · 09-29-2009, 10:49 PM

Quote:

Originally Posted by javadog

What works in principle on a race engine works for you, as well. Anything you do to move more air through an engine, whether it is opening up the intake or the exhaust will make more power. Most of the tuning effects of an exhaust are not relevant when you are talking about exits from the muffler.

There are several dynos in Honolulu, if you want to go down that route.

JR

I think I'm missing something here, so please forgive me if I sound...out of tune.

As you say moving air through an engine will make more power, but wouldn't that have to be relatively equal coming in as going out?
Granted mufflers have other restrictive issues as well, especially OEM, and then there's the CAT as well as additional piping.

Here is where I'm not understanding the logic of what I have.
My intake is somewhat restrictive (taking in warm air through a box) but my exhaust is much less restrictive (headers/Flowmaster muffler).
Ultimately wouldn't it be best to get as close as possible to being equal with intake and exhaust?
I know race cars all have headers/straight pipes, velocity stacks, blowers etc. and I guess the opposite of what I have would be to have a turbo or super charger and an OEM exhaust...for some reason that doesn't sound right, but I'm not certain it isn't.
Once I get a dyno done I'll know more.

Thanks again for you advice/suggestions

docrodg · 09-30-2009, 03:05 AM

You are right, equal in and out is ideal. The engine however has valve overlap, and exhaust gases exit under more pressure than the engine sucks in intake charge. That makes exhaust design a PITA.

Racecars use open pipes because they are running at high RPM so the gases in the cylinder have a lot of momentum, an open exhaust lets them flow out, while the high RPM will close the ex valve before much of the intake charge follows (less momentum). In addition, the headers are designed to give just the right amount of backpressure (a very tiny amount) so that a muffler is not needed. On a street car you are not running flat out, this changes things. Less momentum, and more time for the intake charge to follow the exhaust gases out during the overlap. A street car needs some backpressure in the exhaust so that the engine does not lose as much intake mixture out the exhaust pipes. The amount is small, but it is needed and a bit more than a racecar, that is why too big a pipe hurts your power. Too much backpressure and you don't get good exhaust scavenging out of the cylinder and that contaminates the fresh charge. Some stock mufflers however are over-restrictive because they also have to keep the sound level down by damping out the pressure waves.

Mufflers affect airflow and hurt your power by restricting it too much or not enough. The construction of the muffler must allow for good airflow. I have a book somewhere on exhaust design and the testing of mufflers was illuminating. Testing on Dyno and Flowbench of stock and aftermarket mufflers for US Muscle cars showed that the aftermarket mufflers designed for agressive sound flowed less air and hurt horsepower. The reason is that although they are "Straight Thru" mufflers the sound is made by fins sticking out into the air path that cause turbulence, thus cutting out the airflow to a large degree and creating too much back pressure. "reverse Flow" mufflers (like on a cadillac) were the best tested as they allow somewhat free airflow without turbulence. Generally, the louder the muffler, the more turbulence, the more turbulence, the more restriction. Pass the magic line for a specific engine and the restriction becomes a performance killer. Too quiet a muffler can cause problems as well as they may restrict flow and cause too much backpressure.

You may be flowing too freely on the exhaust, causing a portion of the mixture to go out the pipe as well, more at lower RPM. My guess is that when you really get her moving she has much better performance at high RPM. A couple of things to try:
1. Block off one outlet and see if it improves.
2. Block off only a part of one outlet and see if it gets better or worse from 1.
3. If 2 is better then start playing with exhaust tips that are smaller than the muffler outlet, find the right size and you will be able to tune it in.
4. If 1 is better then try the stock muffler again, it might be "just right" depending on the construction of your flowmaster.

javadog · 06:22 AM

Okay, I don't want to get too deep into this because I type slow and I've covered this several times before. There are several misconceptions floating through this thread...

I'd suggest that, if you want to understand the relationship between and exhaust system and camshaft timing, go buy a book on the subject. Something like "Scientific Design of Intake and Exhaust Systems." It's been published forever and covers the basics quite nicely. There are others. The bottom line is that with any system, there will be many places where the pressure pulses in the exhaust system interact with the timing of the closing of the exhaust valve and as a result, cylinder filling. Each cross sectional change in the exhaust system will introduce pulses. By the time you get to the exit of the muffler we are talking about, a dozen other things will have already affected the exhaust flow. It's the pressure waves, more than the overall flow, that are of concern.

JR

Edit: One other thing. The volume of exhuast gases will be higher than the volume of intake air. Part of this is due to the chemical reaction that takes place. The by-products of combustion have a volume about a third greater than the volume of oxygen consumed. Also, the exhaust gases are at a much higher temperature and we all know that gases expand with temperature. Don't confuse mass with volume.

Thrlls · 09-30-2009, 05:41 PM

Mahalo Doc & Java!

What your are saying is making sense, and I see I have some reading to do to fully understand the exhaustive issues with intakes and exhausts.

Now to get my car to a dyno for some testing.

You gottah love this Forum!

Again, MAHALO NUI LOA!

Porsche Head · Porsche Head's Garage

I found the same thing, seems like less torque with the Dansk dual out.

I recently went to Kragen to get exhaust reducers (2.5"->2") and stuck them in the tips. I noticed a smother torque curve.

I also welded up a spring loaded valve version based on the same reducer but have not tested that yet, the card in under major brake and suspension work right now.

I also welded up a block off cap using the reducer and put a screw in to keep it in place. Not tested yet but I have options.