Early A exhaust fitment?

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vntned

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So I'm in the process of finishing up my 360 build to swap into my slant dart. 360 .060" over, 9.8:1cr, Comp XE 268, unported 587s with 1.88s, LD340 intake, 3.55fd, 26" tire. It's a non power steering car that's been converted to a 4spd. I've decided to use 340HP manifolds as opposed to headers, mainly for the sake of simplicity.

The question is: Will a 2.5" down pipe fit on the drivers side, or am I limited to a 2.25" pipe?

Also, is there any need for a dual 2.5" vs a dual 2.25" with my build?
 
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Open headers compared to 2.25 duals and 3.0 duals. No difference until 5700 +-1%
first number is HP, second is torque. 2.25 is a much easier fit.

Chassis Dyno Chevy 355 9.8cr 355HP headers
Note: Dyno tests measure rear wheel horsepower not flywheel horsepower.

Open Headers Borla 2 1/2-inch Borla 3-inch
RPM HP Torque HP Torque HP Torque
rpm--open--tq-----2.25----------3.0---------
4500 213.3 248.9 211.5 246.9 209.1 244.1
4600 236.2 269.7 236.2 269.7 236.0 269.5
4700 239.6 267.7 240.7 268.9 239.0 267.1
4800 239.2 261.7 242.1 264.9 243.1 266.0
4900 237.5 254.5 242.8 260.3 242.9 260.3
5000 238.6 250.6 240.3 252.4 242.1 254.4
5100 236.4 243.4 240.1 247.3 239.4 246.6
5200 235.1 237.4 238.3 240.7 239.4 241.8
5300 235.6 233.5 238.1 235.9 238.8 236.6
5400 231.3 225.0 234.2 227.8 240.3 233.7
5500 229.5 219.1 231.8 221.3 233.4 222.9
5600 226.1 212.1 231.8 217.4 231.4 217.0
5700 222.6 205.1 224.6 206.9 227.9 210.0
5800 214.6 194.3 222.7 201.6 222.6 210.6
5900 213.3 189.9 216.7 192.9 218.1 194.2
6000 216.9 203.9 207.9 189.9 214.1 187.4
Average 229.9 234.2 230.4 230.8 231.3 231.6




Noise Level Inside Car
Open Headers Borla 2 1/4-inch Borla 3-inch
RPM dB RPM dB RPM dB
2000 96 2000 80 2000 82
4000 104 4000 91 4000 92
6000 115 6000 95 6000 96
 
thats pretty weak for a "hopped up" Chevy SB. standard intake, 9.8 pistons, Comp 275 cam and headers...at the wheels.
 
vntned said:
Could please explain the compression effecting pipe size?!
Click to expand...


I think your biggest problem will be getting the down pipe to clear the torsion bar if you're going to use the large hole (2 1/4") driver 340 manifold. Also, if you use mandrel bends coming out of the manifold it will make a big difference. That's why I started making the 120 degree 340 down pipe for the manifolds I sell. I make it using mandrel bent 2 1/2" pipe, the one I buy is the tightest mandrel bend that you can buy
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Without this mandrel piece you'd either have to crush the pipe to make the bend or use smaller pipe.:

Treblig
 
First off, I recieved my pass side manifold yesterday! Thanks for the fast shipping!

Secondly, I do intend on using the large hole drivers side manifold, which I have also acquired.

Next, does that down pipe you make work on a Early A with a 4spd?!
 
vntned said:
First off, I recieved my pass side manifold yesterday! Thanks for the fast shipping!

Secondly, I do intend on using the large hole drivers side manifold, which I have also acquired.

Next, does that down pipe you make work on a Early A with a 4spd?!
Click to expand...


To be honest I've sold so many manifolds to so many FABO members that I can't remember how many were for early A bodies. I'm pretty sure I've sold some of the 120 degree down pipes to early A owners but off hand I really don't remember any specifics. I do know that the torsion bar on the early A bodies is in about the same spot. I also know that some early A owners use the Shumacher (sp) motor mounts, this usually raises the engine a little giving you more torsion bar clearance for the 120 degree down pipe. You could also use a spacer on a regular motor mount. Unfortunately (or maybe fortunately) I own a '69 Barracuda so I don't have access to an early A body. I depend on the early A members for their input on the manifolds/down pipes I sell them.
As far as being a 4sp....it doesn't matter because the 340 driver exits way up front next to the starter as you can see in the pics:

I'm selling a set of 340 driver/360 magnum passenger manifolds to "rockramcharger" (FABO member) for his early A. He has sent me a deposit and should be getting his order in the next few weeks.

treblig

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vntned said:
What do you charge for your down pipe?
Click to expand...


I charge $75 plus shipping. I would sell it cheaper but the only way I can keep the price down that low is if I buy a 2 1/2" mandrel bent donut and cut it into three pieces as shown earlier. Then I have to pay to get a piece of pipe "flat flared" and then buy the flange adapter. The flange adapter must be installed before I weld the 120 degree piece of down pipe to the flat flared pipe. Anyway, I spend about $55/$60 on parts and pieces and have to cut, weld and grind for about 2 1/2" hours to complete the piece.

So it's really not worth it for all the time, labor and parts but I do it to help other FABO members. Where else could you get a 340 down pipe custom made out of 2 1/2" mandrel bent pipe??

The first one I made for my Barracuda cost me well over $100 because I bought I section of mandrel bent J pipe and only used a short section of the bend, as I got more requests for this piece I had to find a way to get the price down for everyone else. If I hadn't found the mandrel bent donut it would cost over 100 dollars. There are very, very few muffler shops that can make a mandrel bend and that would be willing to do all the cutting, fitting/welding and test fitting until they got it right...... at least not without charging you an arm and a leg.

The one in these pics was made last week for FABO member "alist". I used my last piece of donut and will have to order more donuts.

treblig

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