Exhaust Work Question
 

Finally redoing the temporary exhaust setup I threw on my 87 F150 for the winter. It's getting a new system from the oxygen sensor H-pipe back. My question is how do I get that pre-cat cut out of there? I was able to get the lower inlet pipe cut, but I cannot find a way to get to get a sawzall or hack saw in to cut the upper inlet pipe or the 3" outlet pipe. Any ideas would be greatly appreciated.

Hmmm... when I cut out my cat we had no problems... We used a hacksaw because we were quite close to my propane tanks haha. What exactly is blocking you from making the cut?

The frame and tranny bellhousing are getting in my way with a hacksaw no matter how I go at it. Might just be my crappy hacksaws haha. Maybe I'd have better luck if I got the front end off the ground since the truck is a 2wd?

https://cimg3.ibsrv.net/gimg/www.for...c71412f360.jpg

This might be an option. Leave the cat, cut the back out, weld in a plate with 2 pipes coming out.

[QUOTE=eakermeld;14375997
This might be an option. Leave the cat, cut the back out, weld in a plate with 2 pipes coming out.[/QUOTE]

I've never seen it done like that before, but my cat is for sure plugged and I'd rather not have an expansion chamber so it's gotta go one way or another lol.

That pic is my truck. My cat was plugged up real good till I done this. This also serves as some-what of a crossover or "x-pipe". Just curious, what do you mean by an expansion chamber?

Basically it's a chamber in the exhaust where the exhaust gas can expand and add more backpressure. They're used on 2-smokers to improve power output.

Have you tried a small cutting wheel (e.g. 4" mounted on angle grinder) or the "wrap around" (chain link style) pipe cutter ?


Backup is to go with the tried and true oxy/a torch.........

I understand now. And I may have stumbled on to a power maker! This truck runs and pulls fantastic. I know 460's need some back pressure to have good low end torque, but need to breathe for upper end HP and mileage. It seems this is the perfect combo for mine. It romps and stomps and pulls anything I hook behind it and will get between 10.5 and 12 MPG doing it! I have been doing other little things as I go and it only gets better. It may not work for everybody, but you don't know till you try!

Grrr... It's NOT back pressure you need...

Why, why won't this myth just die already!

Exhaust is a series of pressure waves with high and low pressures - peaks and valleys. There is also a mass that goes with it to create momentum. When all those pulses exit the exhaust system there is a reverberation or a back pulse that goes back to the engine. There's a lot more to exhaust systems then just dumping toxic fumes out the back. You need to manage the velocity and also the thermal energy.

So... When someone chops out a muffler and the car runs like crap because they've upset that careful balance, they assume it just needs a cork in the system to run better... Big, open pipes can kill the velocity and allow the exhaust to cool down and become more dense. So it piles up in the end of the pipe.

Longer pipes in general are a good idea because with velocity you can increase scavenging due to the mass of the exhaust stream. Any large change in the cross section of the exhaust looks, to the engine, like the end of the line. Mufflers also build heat and help thermal management. It also helps smooth the pulses out. This is where crossovers, x-pipes, etc all come into play and it's also the theory of the Tri-Y headers. Get all the pulses to nicely line up and smooth out. However, this is always changing because of the changing in RPM. Larger engines and higher RPM engines need larger pipes to manage all the air and keep the velocities in the sweet spot. X-Pipes, crossovers, etc can be placed in different locations to favor a specific RPM. IIRC the further back they are the more it favors the low end.

There is a ton of science to this and it has nothing to due with corking up the pipes - aka back pressure. Sorry for the rant but it's one of my pet peeves. It's right up there with people who bash brands without any specific first hand reason. My father refused to even consider a Ford, saying there were junk because he learned to drive in his father's poorly maintained 1949 Ford around 1960 and it kept breaking down. I finally got him into an Explorer and he loved it.

Thanks for that info. I love to learn new stuff. So what do you think about my setup?
https://cimg2.ibsrv.net/gimg/www.for...1b0c91d7b9.jpg

https://cimg3.ibsrv.net/gimg/www.for...c71412f360.jpg

https://cimg4.ibsrv.net/gimg/www.for...61f5103dbf.jpg

https://cimg5.ibsrv.net/gimg/www.for...641197d889.jpg

https://cimg6.ibsrv.net/gimg/www.for...d940916fc0.jpg

https://cimg7.ibsrv.net/gimg/www.for...3fba0ce81a.jpg

To much? Not enough? This thing runs great but if I'm leaving something on the table I'll rip it all off and build something else. More power is more smiles!

Glasspacks aren't the best flowing, but after the gutted cat I don't know if they'll cause you any issues. Mandrel bent pipes look good. I'm assuming 2.5" pipes? After that cat you can probably get away with 3" and not effect the low end.

Looks good overall and I don't think you're leaving much on the table if anything.

Yeah I did some looking around as well and found out the same crap with glasspacks after I put them on my truck (opps) Honestly they sounds nice when I'm flat footing the truck but if i had known they would drone the way they do at certain rpms and flowed less I would of just told the guy who made my exhaust to not of put them in and just straight piped it. :-X04

Good to hear, thanks for all the good info!:-drink