Ok, after starting my 434 with the 3.5" magnaflows it seems as if I need an alternative to quiet this car down. I'd like a full exhaust that's both quiet and doesn't restrict this motor. Now i've always been interested in Vizard's comments regarding exhaust flow, wave tuning, and the design of his terminator boxes so here's what a friend and i've come up with. This is for my 434 which should be in the 650-700 fly wheel horsepower range.

The car has 3.5" merge collector headers and a sb2.2 intake. Being that the sb2.2 intake has short runners I figured the lower rpms could use a boost of power to bring average power up via exhaust tuning and my th400, 4000 stall, and 4.56 gears will have some somewhat significant rpm drops (from 7500 to 4600ish in 1st to 2nd and 7500 to 5000ish from 2nd to 1st). That being said i've got approximately 18" of 3.5" pipe from the primaries to the terminator boxes (18" collectors so to speak). The terminator boxes are 4"H x 8.5"W x 18"L. This give me a cubic inch size of 612 which is well over the required volume of 8 times the cubic inches of one cylinder (434 cubes in this case) as per vizard's recommendation. Now here's where it gets tricky.

Since I want this thing quiet the smaller the diameter of tail pipe out the back the better i'm sure. Dynomax claims their 2.5" mufflers flow 1133 cfm each. I only need a total of 2.2 cfm per horsepower total muffler flow which in the case of my projected power is 1540 cfm or 770 cfm per muffler (this is based of off 700 project fly wheel horsepower). Now theoretically these 2.5" mufflers will work perfectly.

What do you guys who follow vizard's exhaust articles think of all this? Do you think the 2.5" tail pipes will be restrictive with this kind of power?

Sure would be super cool to have a real quiet exhaust system which didn't restrict this motor hardly at all!!!

Nick

P.S. Here's the muffler i'm speaking of.

http://www.dynomax.com/

http://www.dynomax.com/ecat/ecat.asp?page=180

 

Great stuff. In case you missed it, there was a good thread in the External Section in March that discussed this.
https://ls1tech.com/forums/generation-iii-external-engine/465206-better-than-x-h-pipe.html

 

Also, Vizard's terminator box is 8x the volume of 1 cylinder per side. In other words, your 434 would need 868ci of volume to replicate atmospheric.

 

IMO, mandrel bent 2.5" tails could easily support 675 RWHP before even beginning to look like a restriction....maybe even more. When my electric cutouts (muffler by-passes) are closed forcing all my exhaust thru stock GM titanium mufflers I am only down like 5-6 HP (on a 535 RWHP car) and thats considering the fact these mufflers have 2" internal baffling! A 2.5" pipe has way more cross-sectional area (about 50% more) than a 2" pipe so you should be in great shape there. Just focus on smooth gradual bends and transitions to really maximiize the larger pipes effectiveness. Also, dont forget the exhaust gases have cooled considerably by the time they reach the tailpipes and the smaller tailpipe just keeps the velocity from falling off a cliff which I feel aids in better scavenging as well. I think you will have higher average power with a 2.5" tail than a larger 3" might provide at the power levels mentioned above....

Look foward to hearing about and seeing your finished results...

Tony

 

We have had success with terminator boxes with 3.5 inlet and 3.0 outlets. A LOT of heat gets into the boxes which it radiates especially toward the floorpan. Insulate the floor well. Of course all of that radiated heat cools the exhaust and reduces the exhaust cfm so smaller outlets and mufflers work.

For your 700 fwhp I'd use 3 inch T-box outlets all the way back to the Ultraflows which I hope are behind the axle. By that time, the exhaust gasses will be a lot cooler and your 2-1/2 mufflers might be enough. I'd start with 3 inches and see how quiet it is. For the 2.5 inchers I wouldn't reduce the pipe size until just before the mufflers.

We used a bellmouth (trumpet) outlet inside the boxes to help direct flow.

Collector length is very important as you said. Have you used a program like "Pipemax" to help determine optimum length?

 

Thanks for the input guys.

Old SStroker, i'm not using pipe max, but am trying to use common sense and observations of other combinations with similar power and rpm ranges in selecting the actual collector length. I may play with it a little to be honest but want to start there and see what happens.

I planned to use a bell mouth which will actually run inside the outlet side of the box a few inches as from what I can tell this is how vizard likes it. I'm still deciding on going with 3" or 2.5" but based on the opinions on both side i'd almost rather error to the bigger side as I don't want to loose power. I may run the 3" version of the magnaflow muffler which is 18" long case. On another s-talk thread a gentlemen indicated that there was almost no restriction with this muffler on a 700hp big block and said it was the quietest as well.

I did not plan to run tail pipes on this setup as there is really no room for them so dumps will happen before the axle.

 

Gottcha, it's 600+ cubic inches per side

 

Yeah, our trumpets extended to within a few inches of the inlet pipe so most of the flow tries to pass right thru. The "all outdoors" chamber causes the reflection you are trying to get.

Engine Masters' folks mostly all use 3 in. Magnaflows well over 800 hp.

 

Any pics out their of those boxes we speak of here?

 

No, not yet. Waiting to get the digital back from a fellow employee and then will have picks up on my photo buckett page!

 

subscribing.

 

how about a tear drop shape?something like the shape of a heart.a single pipe at the end which then would go into a duel pipe.the heart shape should give an expansion chamber to both inlets,since you have a left and right hump.the natural shape should mold the air into a nicely shaped venturi,helping to speed things along inside the chamber.just think of the shape of a candle flame.a box of any shape is just going to bounce sound waves all over the place.a tear drop shape would guide them.if your bouncing sound waves,your bouncing the flow around to.

 

IIRC thats what David Vizard recommended, a heart or tear shape

 

TTT - has anyone pursued this idea yet on an F-Body?

 

Guys, they are on, I just haven't taken any pictures. If you ever check the for sale section you've noticed taht i'm deciding to get out of this whole project for a variety of reason. I'll try to get some pics of them on the car though before I take them off. They will be for sale along with the rest of the exhaust if anyone's interested.

 

To the top

 

Well did they work? Were they quieter than the magnaflows?

 

The boxes themselves do not serve to make the car quietter, but allow the use of smaller diameter mufflers which in turn quiets the system. Yes, the entire system is much quieter then it was when it was just the 3.5" magnaflows on there.