LSA or Duration to fine tune glasspacks??

-
Don't buy them for their handsomeness.Buy them for what they do to the sound. Before you weld them on, do a slip-fit test to see,rather hear, the difference.
But before that;
If you have the resources, you might also try a swedged pipe to convert what you have now, to a 3inch round outlet. The pipe should be about 15 inches long. Then slide it up and down your pipe, to tune it. Stop when you like it. You kindof have to do both pipes to get the stereo effect. When you are finished that,crush them down to oval, and start again. I like ovals.
 
Last edited:
AJ/FormS said:
Don't buy them for their handsomeness.
Buy them for what the do to the sound. Before you weld them on, do a slip-fit test to see,rather hear, the difference.
Click to expand...
I'm going to tune the glass packs by ordering the right custom grind cam. I just need to know what LSA/duration and order of events to get the glass pack to thap instead of thip
 
The sound is not in the cam. Well not in the sense of the tones. The timing of the exhaust opening certainly plays a role, if you are looking for the energy, and the late closing intake allows some compression back into the intake, where it messes up the AFR, and makes the common lope as the ignition tries to keep up. But building an engine or camming an engine for the sound out the tailpipe is kindof strange,to say the least. As to tonality,you will get the biggest results with tip shapes and size of tailpipes. You cannot of course duplicate the lope. But honestly cams under 225* in a hiC engine have very little lope at normal idle speeds.From there to 235ish you still have to idle them down pretty far to hear it.Really the cam needs to be up around 240/250 before it becomes noticeable at a normal idle speed, of 750ish. But by this time the cam is fast taking you out of the realm of streetability. Do you really want a race-cam in your streeter? I bin-der/done-dat, and it was fun while it lasted(one summer), but I'll probably never go back there.Naw a nice streeter has a 230ish or smaller cam, 360 plus cubes, and some hi-flo heads.With a well matched Scr, this makes very little lope at a normal 750ish rpm. You need that 750ish rpm to keep all the fluids pumping, and possibly to keep the brake booster ready to go.And of course with an auto, the TC will drag it down around a hunert rpm. So, if you really want the lope, get yourself a 292/292/108, or something along those lines (heaven forbid, a Thumper), idle it down to 650,and let the tuning begin.But when you find out the power doesn't start til up around 5000 rpm, and the beast don't like to pull below 2500 to 3000, well hey, you got yourself a nice lope, right? Did I mention that cam burns a lotta gas? Well it doesn't actually burn all of it.heehee.Some of it burns in the pipes on the way to the mufflers, and if you do it just right, you can blow one clean off! And some of it stays in the mufflers when you shut it off. There it mixes with condensation,forms acids and soon you will have that ugly 4-banger sound, as the acids eat holes in your holey glass-pacs.lol. Ok now I'm just being mean,sorry.
Yeah so, to quote another guy,good luck with that.

Personally I like a nice thoop-thoop-thoop-thoop-thoop. And I know exactly how to get it; Take one 1969 340 short block, and throw away the cam. Stick a teener cam in it dot-to-dot,lol. Bolt on a set of open chamber teener heads, a CI intake with a TQ.Add a set of fenderwell headers,two to 2.25 inch very straight pipes to a pair of cherry bomb shorties.Add very straight under the axle 1.875 pipes out to the rear bumper. Take an 18 inch length of cardboard, and roll it up until it fills the end of the pipe. Drill a hole vertically up thru both sides and drop a 3inch nail down thru it so the cardboard doesn't go AWOL. Repeat on other side.Start her up and crank the idle down to 500; There you have it; thoop-thoop-thoop-thoop-th
I can almost guarantee that when you hear it you will nearly die laughing.
Now put you some 340 springs on those teener heads and some 3.55s out back.Pop the pins and let her fly. In a sub-3000 pounder like a 65 long-roof Valiant, the laughing will stop, as your brain tries to figure out what just happened. Then you will begin laughing all over again.
thoop-thoop-thoo
This cannot be, can it?
Hey that was me in 1975. I still remember it fondly, almost like it was 40 years ago....
 
Last edited:
71DodgeDemon340 said:
Not sure lol it has a lunati vooodoo cam in it. The engine builder recommended staying around a 280 duration. lemme see if i can find the cam specs. Keep in mind this is with hi po manifolds and accurate true duals with two gibson performances mwa mufflers


  • Advertised Duration (Int/Exh): 268/276
  • Duration @ .050 (Int/Exh): 226/234
  • Gross Valve Lift (Int/Exh): .494/.513
  • LSA/ICL: 110/106
  • Valve Lash (Int/Exh): Hyd/Hyd
  • RPM Range: 1800-6200
  • Includes: Cam & Lifters (#71977PR-16)
Click to expand...
Can we have more please? I really, really, like the sound of that thing
 
I knew a dude, who knew Daryl, and his other brother Daryl who used to own a 1971 Chevy Chevelle, they would swear up and down you CAN super turbo tune a pair of glass packs. What they would do is take the plug wire off the #1 cylinder, to get that bdump bdump bdump psssst out of the left bank. For the right side , you take a 1 1/2 inch hole saw , and with the car running , you start cutting holes in glass pack . They usually end up with 6 working from left to right. Depending on how you have your firing order set up , this will give you a very tunable sound. bdump bdump psssst BLAH BLAH bdump psssst BLAH BLOOP BLOOP bdump bdump psssst etc etc. Now the super turbo tune secret is to get your rpms down to around 350 to 400 without killing the engine. It has to be able to idle without dying. This is when the toothless chicks come running, bb duh AP - bb duh AP - BLAAAP - BLAAAP - THUUUUMP - THUUUUMP - PSSSSSSS - THAAAAP - PSSSSSSS - THAAAAMMMMP - BLOOP - BLOOP . long story short, you can super tune glass packs with any duration or LSA
 
Chained_360 said:
Can we have more please? I really, really, like the sound of that thing
Click to expand...

More specs or more videos? Lol

I wouldn't spend the time trying to tune the muffler to the engine and vise versa. You should be able to choose a muffler be happy with it and leave it be
 
AJ/FormS said:
The sound is not in the cam. Well not in the sense of the tones. The timing of the exhaust opening certainly plays a role, if you are looking for the energy, and the late closing intake allows some compression back into the intake, where it messes up the AFR, and makes the common lope as the ignition tries to keep up. But building an engine or camming an engine for the sound out the tailpipe is kindof strange,to say the least. As to tonality,you will get the biggest results with tip shapes and size of tailpipes. You cannot of course duplicate the lope. But honestly cams under 225* in a hiC engine have very little lope at normal idle speeds.From there to 235ish you still have to idle them down pretty far to hear it.Really the cam needs to be up around 240/250 before it becomes noticeable at a normal idle speed, of 750ish. But by this time the cam is fast taking you out of the realm of streetability. Do you really want a race-cam in your streeter? I bin-der/done-dat, and it was fun while it lasted(one summer), but I'll probably never go back there.Naw a nice streeter has a 230ish or smaller cam, 360 plus cubes, and some hi-flo heads.With a well matched Scr, this makes very little lope at a normal 750ish rpm. You need that 750ish rpm to keep all the fluids pumping, and possibly to keep the brake booster ready to go.And of course with an auto, the TC will drag it down around a hunert rpm. So, if you really want the lope, get yourself a 292/292/108, or something along those lines (heaven forbid, a Thumper), idle it down to 650,and let the tuning begin.But when you find out the power doesn't start til up around 5000 rpm, and the beast don't like to pull below 2500 to 3000, well hey, you got yourself a nice lope, right? Did I mention that cam burns a lotta gas? Well it doesn't actually burn all of it.heehee.Some of it burns in the pipes on the way to the mufflers, and if you do it just right, you can blow one clean off! And some of it stays in the mufflers when you shut it off. There it mixes with condensation,forms acids and soon you will have that ugly 4-banger sound, as the acids eat holes in your holey glass-pacs.lol. Ok now I'm just being mean,sorry.
Yeah so, to quote another guy,good luck with that.

Personally I like a nice thoop-thoop-thoop-thoop-thoop. And I know exactly how to get it; Take one 1969 340 short block, and throw away the cam. Stick a teener cam in it dot-to-dot,lol. Bolt on a set of open chamber teener heads, a CI intake with a TQ.Add a set of fenderwell headers,two to 2.25 inch very straight pipes to a pair of cherry bomb shorties.Add very straight under the axle 1.875 pipes out to the rear bumper. Take an 18 inch length of cardboard, and roll it up until it fills the end of the pipe. Drill a hole vertically up thru both sides and drop a 3inch nail down thru it so the cardboard doesn't go AWOL. Repeat on other side.Start her up and crank the idle down to 500; There you have it; thoop-thoop-thoop-thoop-th
I can almost guarantee that when you hear it you will nearly die laughing.
Now put you some 340 springs on those teener heads and some 3.55s out back.Pop the pins and let her fly. In a sub-3000 pounder like a 65 long-roof Valiant, the laughing will stop, as your brain tries to figure out what just happened. Then you will begin laughing all over again.
thoop-thoop-thoo
This cannot be, can it?
Hey that was me in 1975. I still remember it fondly, almost like it was 40 years ago....
Click to expand...
This is a great post! Thanks A/J, it really moved me closer to making a decision. I wonder what density of cardboard would be required to keep the defuse from catching fire yet keep the concentricity of the cylinder from going out-of-roundness? Now, as far as the 340 springs, keeping the Datum of the perpendicularity true to parallelism in circumference to the teener head will keep the idle low yet quality of sound great!
Again, thanks!! :)
 
71DodgeDemon340 said:
More specs or more videos? Lol

I wouldn't spend the time trying to tune the muffler to the engine and vise versa. You should be able to choose a muffler be happy with it and leave it be
Click to expand...
I've chosen my muffler. Thrush glass pack from Farm & Fleet. 24.95 each. Not happy with the thip thip thip. I've tried the turbo muffler, still thip thip thip. I figured my cam is the culprit. I've now thought of moving LSA or duration (not sure which) to create the thap thap thap of boldness that I'm looking for. I figured I'll order a custom grind cam, but first I must set the order of events for the function of the camshaft. You see???
 
Ill see if i can get some more. Not taking her out that much being as its been nasty out. I need to get me a go pro
 
Cam has no effect on tuning glass packs......you are working on the wrong end.Start your motor till it gets to operating temperature and then shove a water hose in the tail pipe and turn on the water. ..repeat for other side if dual exhaust...your glass packs are now tuned.
 
If,... I was to run a GP, it would be as a resonator, well after the 3-pass, and it would be under the trunk about a foot or so from the end of the pipe, and followed by probably a turn-down,turned out a bit.By the time the exhaust gets this far along,it has cooled off a lot, and lost most of it's energy. So now it is ready to have the hi-frequency annoying sound energy, sucked into the matting
 
TXDart said:
Cam has no effect on tuning glass packs......you are working on the wrong end.Start your motor till it gets to operating temperature and then shove a water hose in the tail pipe and turn on the water. ..repeat for other side if dual exhaust...your glass packs are now tuned.
Click to expand...
Yes" it does : High overlap(yes it exists,get over it...), inferior ignition in the '60's glass pack heyday, would load up the packing to burn out prematurely, giving that "wonderful glass pack rap rap rap sound" .... Seen people replicate with water soaking the mufflers,driving & heat cycle 2 or 3 times...Made a lot of noise,had a lot of "too loud ' tickets...Trust me,he earned it....
 
318willrun said:
If a person wants to fine tune the sound of glasspacks, would LSA or duration have the greatest effect on fine tuning the sound of the glass pack to make it sound more like a glass pack should sound?
We all know on a 4 cylinder sounds like a terrible weed eater because of the order of the exhaust pulses. We know we can delay or speed up the order of exhaust pulses with the cam. So which would be the best way to accomplish this, LSA or duration?
Click to expand...

I've been thinking about this and here's my idea:

An overtly rich fuel mixture, bleed in some excess air just before the mufflers, maybe a tad more fuel, spark plugs set up at the muffler exit to ignite the mixture..........I think you'd have the sound
 
JBurch said:
I've been thinking about this and here's my idea:

An overtly rich fuel mixture, bleed in some excess air just before the mufflers, maybe a tad more fuel, spark plugs set up at the muffler exit to ignite the mixture..........I think you'd have the sound
Click to expand...
Interesting, very interesting. But, I ask myself "would it be easier/cheaper to swap cams?" If so, then what LSA (or duration) to get the perfect tuned glass pack? I'm sure overlap has nothing to do with it.
 
318willrun said:
Interesting, very interesting. But, I ask myself "would it be easier/cheaper to swap cams?" If so, then what LSA (or duration) to get the perfect tuned glass pack? I'm sure overlap has nothing to do with it.
Click to expand...



Look, you gotta get the seat duration first. It's gotta be GM big, like 320-330*'s. Once you get that, you blow the LSA way out, like 116-118. Now your starting to cook. Once you settle that, you gotta split the damn overlap. So install that ***** about 122-124 ICL so that pig closes real late on the intake and you open the exhaust real early.



That's what you gotta do to get what you want. Hell, been doing it for years. And not only will you get "that" sound, you will get 54 MPG and run 11 flat on pizza cutters. It will also idle at 57 RPM, rev to just past 8k and impress all the seat covers you can find.


Now you are good to go.
 
Last edited:
"Jam-a-Cam"
If you really want to tune those mufflers, you should jam a cam in those glasspacks.
The bigger the lobes, the softer is will sound...
For ultimate sound, jam a Hemi-cam in them.

Only then you're right, overlap has nothing to do with it... :D
 
yellow rose said:
Look, you gotta get the seat duration first. It's gotta be GM big, like 320-300*'s. Once you get that, you blow the LSA way out, like 116-118. Now your starting to cook. Once you settle that, you gotta split the damn overlap. So install that ***** about 122-124 ICL so that pig closes real late on the intake and you open the exhaust real early.



That's what you gotta do to get what you want. Hell, been doing it for years. And not only will you get "that" sound, you will get 54 MPG and run 11 flat on pizza cutters. It will also idle at 57 RPM, rev to just past 8k and impress all the seat covers you can find.


Now you are good to go.
Click to expand...
I think yellow rose has something here.... I guess i'll might call a custom cam grinder with these specs..
 
It's getting harder to separate the facts from the fiction, honest curiosity from blatant misinformation, drama, comedy and truth. What was the original question again? I think we need to start-over.I'm so lost and confused.Will somebody throw me a life-buoy!
 
You must log in or register to reply here.
-

Back
Top