Inliners International Forums General Discussion Engines Glasspacks

I think this is the right forum. I am considering a pair of 3" dia. x 2 foot long, 3 bolt flange, purple horney, flowmaster glasspacks. In your respected opinions, would this be a good fit for a chevy 250?
Ken

If loud is what you want,then you picked the correct ones.
Is there a reason for 3" ones,really built engine?

If you can fit 36" ones that would help quiet them down,but having 3" exhaust is going to be tough to keep quiet,plus reducing low end & mid range torque.

Having two, 2" glasspacks will work,but get as long as you can possibly fit to be sorta quiet.

I have a large 3" Gibson type round straight through muffler on my turbocharged Syclone,it is loud when you step on it,& having a turbo is like have another muffler.



MBHD

I ran my 270 from the headers into a single 3' collector, then to a 3" Flowmaster, and then out the side in front of the back wheel. It was too loud and I lost both low end torque and RPMs at the top. It sounded cool. These things need some back pressure to run right.

MBHD & Beater,
The engine is a 250, .030" over, RV cam. I saw the mufflers on the internet, brand new, $45.00 for the pair. It seemed like a good buy, but I wasn't sure if they'd work for me. I don't want to be too loud. I don't need the grief from the HP or local sheriff.

Thanks.
Ken

Try Dynaflows. I traded my flowmasters for these and I got a mellower sound without the drone at highway speeds.
Al

3 inch duels is way to big for a 6 cylinder, max size for duels would be about 2in, even then that might be considered a little big, 1 3/4 would be better suited. Considering that most 250 engines only had single exhaust and it was a 2in pipe. Even 2in duels with glass packs can be loud and obnoxious. Check out summitracing, they have a several mufflers under $30 each.

I had 2" straight pipes on the 270 that went all the way to the back bumper. It sounded great at idle and when I was on it. The rest/most of the time it was too loud. I put 28" glass packs on and I was surprised at how much quieter it is. It's still noisy and maybe too loud for the guy behind me but I like it. When I get old I'll put some 36" glass packs on. I only got one ticket the whole time I lived in Oakland was when I was trying to bounce the front wheels off the ground at Broadway and MacArther In my '48 Fleetline. The cops were pretty busy with Angles, Hippies and Panthers back then.

Just because the factory installed 2" single exhaust does not mean it was breathing good.

IIRC,Clliford catalog recommends two,2" pipeing for a street car.

It was pretty loud when on it,that is way Clifford recommended running a "Y" pipe & to run single exhaust.

I also ran that,but it sounded more like a 240-280 "Z" car,& that was going with 2.5" single exhaust system.

I had Clifford headers, 2" dual exhaust with two turbo mufflers all the way to the bumper. It ran great,great bottom end ,mid & top end power. This it not too big running 2".

At the time my Camaro ran low 14's in the 1/4 & was a daily driver w/9 to 1. 250 C.I. engine. 3 speed on the floor OG tranny.

MBHD

They do make adapters to change the diameters...
If you take it into a muffler shop to do the work, they should be able to expand the end of the pipes to allow you to run 2" pipes with 3" mufflers.

I do not think he bought the 3" glasspacks.

Some muffler shops can also reduce the pipes OD,like I has done for my mandrel bent supercharger feed pipe,it was 3" & a shop reduced the OD to 2.5",nice & smooth transition I would say also.

MBHD

Think its mainstream thinking now that backpressure is a myth. Running 3" would likely mimic an open exhaust, which is actually ideal, given proper engine tune, based on current thinking. Sure, opening up the exhaust would likely make the engine feel soft in the lower rpms but with tuning, it should recoupe if not increase the low rpm tq.

Plus a larger pipe will offer a deeper quieter tone vs a smaller diameter pipe, as the sound waves will slow down vs the smaller diameter pipe would likely increase the velocity.

All I can say is what the sticker on my rear window states;

"LOUD PIPES SAVES LIVES"

Just because it's Mainstream doesn't mean it's right!

I had a flowmaster 40 series my friend gave me and it was terrible no matter what vehicle/engine I had on it, I got out ith a headache every time. Not just the loudness, but the frequency. I have a glasspack on my single exhaust now, not a purple hornie, but a different brand. Red Devil or somethin, I know it is Red. It sounds just fine coming out at an angle behind the rear tire.

No engine runs better with more backpressure. A certain cam, cylinder head and carb combination may suffer from reversion that a smaller exhaust can cover the effects of so it seems to run better. Or you can do the research and put together the right parts that work well together and have more power and efficiency when you are done. This is another myth along with the "torque motor" myth and the "engine cools better with less coolant flow" myth that modern science and engineering have debunked.

Yes and we all know how modern science is absolutely right. Wait is that snow? How could that be call Al! I'll go along with some of that for a race motor, and I agree that the components must work together, but we are talking about changing one aspect of an already built engine. Should we all pull or thermostats?

3 inches is too big for that motor unless you are running a single exhaust.

You want to keep the exhaust gas velocity high.

Folks who say 'no such thing as backpressure' are off base IMHO. Why not just run without exhaust manifolds or headers at all? Now that would be zero back pressure for sure. Try running a motor like that and see how well it runs.

Big pipes are of the 'more is better' train of thought.

In my bike shop guys would come in all day, wanting fatter and shorter pipes. And then wonder why their bike lost all their punch.

Rant off, sorry 'bout that, but my vote is for a pair of smaller diameter units.

Can't go along w/that way of thinking.

Next you will be saying you can run 2" primary tubes on your headers on a 250 C.I. engine, it equals less back
pressure ,right?
MDHD

A pair of three inch mufflers on a 6 is way too big. I have two inch glasspacks on my Nova. I noticed a small loss power. Even the 18" are pretty loud on my car.

Exactly. You cant run open pipes for one reason, noise.
Throw in emissions, then you require a certain length of pipe. Obviously, if you must run a length of pipe, you would want the size to compliment the engine output by running optimal size for optimal exhaust velocity.
The reason the gusy bike runs like chit is because the carb was tuned for certain engine characteristics which in stock form, goes all the way to the end of the tail pipe. Open up the pipe diameter, youve changed how the engine performs. You couls stop here and make the assumption the engine performs poorly due to the pipe diameter or you could tune the carb and reap the benefits. But as im gonna suggest in my next response, the pipe diameter for a certain length outside the cylinder head, I believe to play a more dramatic roll. I think folks understood this more so years ago on the ATV, as an exhaust upgrade was followed with a recommendation in increased jet size.





No. I believe the primary tubes/length on the header or diameter of the exhaust manifold play more of a role as to how the power is made than anything else, I believe this is the critical part. There is a reason why headers length and diameter vary and companies put alot of R&D into such. Exhaust pipe diameter and length is something else all together. Now the exhaust pipe on the other hand, only reason Id imagine size would matter is as stated above, your trying to make emissions, sound components mesh with engine output and all the while compliment the engines performance....which means, maintain exhaust velocity over a given length of pipe/restrictions. Obviously too small would be a restriction, thats just good old common sense.



Doesnt mean its wrong either.

Greetings . . .

I have found this article on Exhaust Theory instructive.

Same with this post and resulting links over on MX6: Exhaust Theory for . . . (rough language aside) a later response includes some CFM ratings for different diameter pipes and some arithmetic on calculating engine exhaust CFM that I am not sure I understand yet . . .

regards,
stock49

Since the articles reflect what I was trying to say, Id have to agree with them, right or wrong.

Yup,,,
it says,the the theory of bigger is better is incorrect way of thinking.


MBHD

You're right, Hank, bigger isn't always better. When I had my old Chevelle, it had an RV cam, Clifford intake and Clifford long tube headers with 2 1/2" collectors. I used a 2 1/2" intermediate pipe connected to Cherry Bomb glasspacks with 2" exit pipes and brought the exhaust pipes out just in front of the left rear wheel. That setup worked really well, wasn't overly noisy, and sounded really sweet, especially when I got on it a little bit. And it wasn't entirely by accident. I had a Holley carburetor book that had formulas in it for designing an exhaust system for maximum efficiency, and I used those formulas to build the exhaust for my Chevelle. I suspect that they're about the same ones that stock 49 posted in the thread above. At any rate, the formulas really do work, and you'll get a lot better results if you use them for figuring out what diameter and length of pipes you need for the exhaust system on your project car or cars.

So, given a moderately hot 250 (with offy intake, Edelbrock 4bbl, Comp 260 cam, flat top pistons, Lump port head, bigger valves, and the head work that goes with that, Clifford tube headers, and dual exhaust, what size exhaust should I be using behind the headers?

I've currently got 2.5" with 2.5" mufflers. It's a little on the loud side but I don't have any tailpipes on it yet. It jsut stops at the mufflers. The problem is that when I built the frame, I did not realize that few mufflers are straight inlet and outlet. The mufflers I got are Center in, offset out and will have to go ultimately because I don't want to redo my cross member.

I've been thinking about glass packs but now I'm thinking my 2.5" pipes are too large. This is a street driven roadster with a moderately hot engine and I'm not into droneing exhaust or fart cans.

I can easily step the collector output down to 2" or even 1 3/4 if that is what is needed for quieter sound and low end torque. This motor will rarely see 5000 rpm and probably not even 4000 unless I'm showing off.

I also did not plan on my muffler being 4 1/2" thick and now it hangs below the frame. That's one reason I was thinking of a 3" OD glasspack. I've even been thinking of building a custom muffler but would rather not.

Your thoughts and ideas would be appreciated.

If space is limited, do what I did. I have 2 1/2" exhaust with Langdon's Headers. I used "Chambered Mufflers" These are the same mufflers that are used in the late 60's side pipes on a Corvettes. They were also used only on ZL1 Cameros. Nice rumble at idle and cruise and at open flow when you floor the gas pedal.
Inexpensive too. I purchased mine from the corvette place in Illinois, Mid America Corvettes. http://www.mamotorworks.com/
I remember they where $30 a piece. You can order them with 2.5"in & out or 3" in&out and either 18" or 22" long. The diameter of the muffler is only 3.5"

Call and ask for the mufflers only. The online price id much higher because it is aluminized and has extra tail pipes on it.

RapRap

If you want a compact center in/out muffler that muffles (but isn't 'too quiet') the Hushpower IIs are a nice piece.

I've heard them on (and off, for frame of reference) of a V8 Flathead Ford.

Not the same sound as a 6, but it was qieter, without any of the 'gurgle' that some mufflers give. Had a throaty rasp to (with them on, and more so with them off).

That's the only experience I have with them, but I'm contemplating a set for a 6 powered car we have, going to have to try them sometime.

I never said bigger was better. You may have forgot that I wrote dual 3" would likely behave as an open exhaust. The article only suggests pipe diameter in regards to velocity, makes no assumption about the need for an exhaust pipe, only assumes you would be using one.

The link would suggest as I had, attention should be paid to velocity, if trying to move the exhaust over a given areas, we all agree.

What it didnt state and I was implying, is there really is no know way to determine when velocity is lost nor when a given pipe diameter would behave much like open exhaust. Granted I was speculating but Id imagine a stock 250 with dual 3" would behave much like a stock 250 with open exhaust. Considering a single 3" by most, would be considered good for 300hp. Throw in the reality that slower moving sound waves produce a deeper tone and Id personally find the tone (too large pipe) more pleasing than a sharper/higher/louder tone. Considering the low power output to start with, the difference is likely to be negligible either way you go if properly tuned.




If you wanted to get highly technical, you would likely have to use multiple diameters of pipe, not just one. As you would want a smaller diameter pipe as the exhasust cools over a given length.

Kerry...

Check out the Dr. Gas/SpinTec website. They have some mufflers that are only 2 - 1/2" tall. They also offer mufflers that are straight-through. I haven't heard one of these in person, but the theory looks interesting.

Just a few random thoughts
One 3" pipe flows the same as 2 - 2" pipes if calulated as you would for pressureized liquid flow. I think the advantage of one three inch pipes is less surface area to cool the exhaust gases and to cause friction losses along the pipe wall. If you go to 2 - 3" pipes I think your flow loss due to lack of velocity would hurt your low end performance at least on an unblown engine. The effects on a turbo charged engine might be less.
The effects of 1 5/8, 1 3/4, and 2" pipes on small block chevys was studied years ago by the larger header companies and they discovered that the operating RPM range made a major difference in what was required.
This is why exhaust extractors for high performance engines are normally tuned for a given rpm range usually narrow.
Just for fun figure how many cfm a 250 turning at 1000rpm puts out, then figure the cfm of the same engine turning at 7000 rpm and see if you think the pipe diameter requirements would be different.