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Discussion Starter #1
I'm stuck at home and thinking way too much....
Does anyone have any experence with exhaust blow off valves, or another way to relieve pressure, progressively, when it builds in the exhaust system.? The last three feet of my exhaust necks down to four 2-inch pipes and with new heads and a new cam, it's not enough any more .

This is the layout: This is a street/strip car
509 BBC: 1 7/8 headders, 3-inch collectors to 4-inch single chamber Flowmasters to 3-inch perforated Y pipe resonaters with duel 2.5 inch outlets… so far so good…

Same set up on both sides - 2 pipes out on each side, then the last 3 feet, it goes to two, 2 inch pipes on each side.

So I am thinking about fabricating a little expansion chamber on each side, between the two tailpipes, ahead of the 2-inch,and then using something like this Tial turbo blow off valve to relieve pressure, as it builds. These run on vacuum but I figure I can let it open under pressure, with springs. I think the aluminum will live with the air blowing over it.
bovhead.jpg


I dont have room for 2.5 inch all the way back, An electric cut out is not an option.

So will this approach work? Is there a better way?

How much pressure is in my exhaust system, at WOT? / 10 pounds? 50? any guesses?

thx!
 

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Discussion Starter #3
OK I'l post some visuals later..... but regular cut outs are not the plan. I want to come up with a progressive type of cut out that opens more with increasing pressure. Kind of like a return style fuel pressure regulator that works against a spring.
thx
 

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Discussion Starter #5 (Edited)
Wastegates are expensive because they are high heat solutions. I dont think the pipes 6 feet away from the collectors are going to be too hot for aluminum that will be hanging down in the breeze. I think the BOV is good for 300 degrees and that's with a viton seal in it. If I have this right, I won't need that seal anyway, since it's for the vacuum operation. There must be a heat coating I can put on the BOV piston to keep is sliding.

IMG_7860.jpg
Same on both sides. I want to build a 4-inch pressure chamber between the two pipes where they exit the muffler and put the BOV there.

IMG_7858.jpg

I don't have room for two 2.5 inch pipes on each side in the trunk
 

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I'm stuck at home and thinking way too much....
Does anyone have any experence with exhaust blow off valves, or another way to relieve pressure, progressively, when it builds in the exhaust system.? The last three feet of my exhaust necks down to four 2-inch pipes and with new heads and a new cam, it's not enough any more .

This is the layout: This is a street/strip car
509 BBC: 1 7/8 headders, 3-inch collectors to 4-inch single chamber Flowmasters to 3-inch perforated Y pipe resonaters with duel 2.5 inch outlets… so far so good…

Same set up on both sides - 2 pipes out on each side, then the last 3 feet, it goes to two, 2 inch pipes on each side.

So I am thinking about fabricating a little expansion chamber on each side, between the two tailpipes, ahead of the 2-inch,and then using something like this Tial turbo blow off valve to relieve pressure, as it builds. These run on vacuum but I figure I can let it open under pressure, with springs. I think the aluminum will live with the air blowing over it.
View attachment 83125

I dont have room for 2.5 inch all the way back, An electric cut out is not an option.

So will this approach work? Is there a better way?

How much pressure is in my exhaust system, at WOT? / 10 pounds? 50? any guesses?

thx!
I think you'd be better off by getting a copy of PipeMax and playing around with it a bunch. It costs less than that bling pictured above.
You've got an approximate 600HP engine that appears to be ok with 1 7/8" primaries but really wants a 3.5" collector where yours are at 3".
The 4" exhaust pipe is added weight.
The 3" y pipe/resonator inlet is another slight bottleneck. Not much but smaller than ideal nonetheless.
4 - 2" tailpipes will never be a restriction.
 

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Discussion Starter #7
Pipemax would be great to work things out with, but i'm a mac guy and it's a pc program. and I'm trying to make this work through mufflers. Does Pipemax do mufflers?
No 4-inch pipe, all 3-inch back to the 2.5s
Are you sure the 4 - 2-inch tailpipes pipes arent hurting it? When I compute the area (one side) it goes from 7 inches for the 3-inch, to 9.8 with the 2- 2.5 and then down to 6.25 for the 2 - 2 inch. I just cant imagine that working at 6500 or more.
thx!
 

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Pipemax would be great to work things out with, but i'm a mac guy and it's a pc program. and I'm trying to make this work through mufflers. Does Pipemax do mufflers?
No 4-inch pipe, all 3-inch back to the 2.5s
Are you sure the 4 - 2-inch tailpipes pipes arent hurting it? When I compute the area (one side) it goes from 7 inches for the 3-inch, to 9.8 with the 2- 2.5 and then down to 6.25 for the 2 - 2 inch. I just cant imagine that working at 6500 or more.
thx!
Have done the math to figure the area of 4, 2 inch pipes? I think you will be surprised.
 

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If you do decide you need relief then what about a spring controlled plate kinda like the burst panel on the front of old roots style blowers. The springs will push the plate closed but will open with the back pressure created. More back pressure then it opens the "plate" more and will stay open as long as the exhaust dictates its need. It would be more of a pressure regulator vs a pressure release that quickly releases then closes just to need opened again. If that makes sense. Lol
 

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As the exhaust cools it slows down and the pressure increases, as the exhaust goes from one size to a larger size it slows down and the pressure increases, that's why most exhaust systems have smaller tail pipes out of the mufflers so that the velocity increases and the pressure drops, just something to think about.
 

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How much back pressure do you think the system will have that light springs could open the system?

I’m thinking of a Holley Vac secondary spring kit and sort thru them, but those might be too lite.
 

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Discussion Starter #13
If you do decide you need relief then what about a spring controlled plate kinda like the burst panel on the front of old roots style blowers. The springs will push the plate closed but will open with the back pressure created. More back pressure then it opens the "plate" more and will stay open as long as the exhaust dictates its need. It would be more of a pressure regulator vs a pressure release that quickly releases then closes just to need opened again. If that makes sense. Lol
yes that's exactly what I am talking about. The BOV is just a cylinder with windows in it that slides up and down. It vents the size of a 2 inch pipe. They are $35. I'll find the right spring
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You can measure exh backpressure fairly easy. If you have a O2 bung you can rig up a fitting to hook up a fuel pump - vacuum gauge to read pressure in the exh system. Anything over 2-3 psi on the gauge under WOT is costing power. Have done this on daily drivers when diag low power complaints.
 

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Discussion Starter #15
As the exhaust cools it slows down and the pressure increases, as the exhaust goes from one size to a larger size it slows down and the pressure increases, that's why most exhaust systems have smaller tail pipes out of the mufflers so that the velocity increases and the pressure drops, just something to think about.
So why would I want a bigger collector if I am running through a muffler? I dont understand that part.
thx
 

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So why would I want a bigger collector if I am running through a muffler? I dont understand that part.
thx
You race this car??
You worry about some of the dumbest shit....
If you think that system is costing you 50-60 HP over a better one, you'd be wrong....
Just drive the phucking thing and smoke tires.
 

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So why would I want a bigger collector if I am running through a muffler? I dont understand that part.
thx
I don't know that your system looks like, but I would think that you need a collector the right size and length then a reducer to your "exhaust system".
 

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Discussion Starter #19
I don't know that your system looks like, but I would think that you need a collector the right size and length then a reducer to your "exhaust system".
My 'collector' is about 18-in of 3 inch pipe, from the headder flange to the muffler and 3-inch to the resonator, then duel 2.5 inch back to the duel 2-inch section at the end. I'm trying to keep this quiet and still let it breathe..... think 'sleeper'
thx
IMG_7860.jpg
IMG_7855.jpg
 

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Discussion Starter #20
You can measure exh backpressure fairly easy. If you have a O2 bung you can rig up a fitting to hook up a fuel pump - vacuum gauge to read pressure in the exh system. Anything over 2-3 psi on the gauge under WOT is costing power. Have done this on daily drivers when diag low power complaints.
Excellent idea! **** I will try this, thx
 
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