3" over axle exhaust

[Jeff73Mach1]

I am looking to replace my exhaust. Since I built a 393 stroker at 11.5:1 compression and stuck a big solid roller cam in it, my 2.5 exhaust to the mufflers and 2 1/4 out over the axles is just not cutting it.

I'm moving a lot of air and would like to put a mandrel bent 3" system in.

If you have done so from a kit and were either happy, satisfied or otherwise, I'd like to know.

Please do not tell me about backpressure and scavenging, I am familiar with the concepts and have done my research-This is a 600 horse engine and it is not going to follow the rules for a mildly built engine. I don't mean to sound like a know it all-I don't think I am, but I am not looking for advice on those issues.

I am looking to find a kit that fits well and is of good quality.

And thanks as always

 

[mjlan]

I'm curious about this as well. My car is getting an old FRPP crate 460 I have and 2.5 won't be enough for that either.

My plan is 3" to the mufflers and try to fit a set of off the shelf 2.5" mandrel bent tailpipes out the back...

 

[coreysvt]

I don't think there are any off-the-shelf 3'' exhaust kits for our cars. Ive been wrong maybe once before though.

 

[lduke12]

Yeah not sure either, i am running 3.5" for my 521 stroker so i purchased 4 45degree mandrel elbows from summit, plus two 4' long straight pipes into 3.5" flowmasters and then dumps straight to the ground after that.

 

[turtle5353]

Jeff, if your dead set on a 3" exhaust your best bet would probably have one custom built for you at a good shop. I had my system built and love it. I am only running the 2.5" system but im in your ballpark with the 600hp. I haven't noticed any real ill side effects of the 2.5" cruising around the streets, but when I do want to open it up and run it I just hit the button for the electric cutouts and bang! ready to go. The thing is scary sounding with open headers. Just an idea for ya. I had from my headers back custom bent, with x pipe, magnaflow type mufflers, electric wireless cutouts, and slash cut tips, all stainless installed with parts and labor for around $1100. The cutouts are nice too because you can just crack them a little or halfway or wide open or anywhere in between. 3" might be fun snaking up over the axles. Good luck with the project and keep us posted on how it goes.

 

[PAPPY HAROLD]

If you can find it please let me know. I have been facing the same issue, I tried 2 1/2 with a pair of so called low restriction mufflers and the car was so rich I couldn't stand to be in the shop with it. Took them off and it was fine. I'm running 466 with all the trimings and an 850 double pumper, I really don't want to dump it under the body.

 

[TommyK]

The Magnaflow 2.5" stainless system for 67-70 mustangs works on 71-73's without modification with the exception of the head pipes which, as with any system will need some fitting depending on header configuration. I suspect the 3" version will fit as well but don't have personal experience with it.

 

[71mach1lady]

wish we knew that before we got their builder kit

 

[tommy]

jeff im running 3 inch on mine its a 393 with a big solid flat cam cHi heads and 11 to 1 comp my mate and exhaust mechanic wizz built it in an afternoon hooked up to my hooker headers it sounds awesome and goes like a missile he said it was no big deal to build unfortunatley for you he is here in oz i ll get a vid with sound up later this week totally recommend 3 inch its killer

 

[Finmach]

Done it with 3 1/2" exhaust. 2 1/8" headers with 3 1/2" collector. 3 1/2" flex couplers, 3 1/2" x-pipe, Delta 40's and 3 1/2" over axle with stainless exhaust tips. Flex couplers does their job so the exhaust was done very rigid, you can do pull ups by hanging from the pipes. Picture is taken in the early pages of the Mach 1, there's the gravel shield still been mocked-up, there's the ol' 9" rear etc. I made the exhaust for the blower usage, otherwise the 3" would have been wiser IMO but it can be done with 3 1/2" - it is very streetable with stock height rear. With 2" lowering the exhaust was too close to the rear housing and it was way too low. With 1" lowering leafs it was streetable, only after I changed to sheetmetal rear housing with back braces the exhaust over's are close to hit to the bracing. If I would still have the original rear with 1" lowering - no problemo. Once I change the delta40's to dynomax ultraflows I'll make more room for the axle over's since there is room to be used.

You'll notice the fuel cell casing, it's narrower than the orginal fuel tank, so it gives you some extra clearence too.

 

[Jeff73Mach1]

jeff im running 3 inch on mine its a 393 with a big solid flat cam cHi heads and 11 to 1 comp my mate and exhaust mechanic wizz built it in an afternoon hooked up to my hooker headers it sounds awesome and goes like a missile he said it was no big deal to build unfortunatley for you he is here in oz i ll get a vid with sound up later this week totally recommend 3 inch its killer

Are your shocks staggered?

I have a good exhaust builder buddy if I can ever catch up with him.

 

[TommyK]

wish we knew that before we got their builder kit

I should clarify that the kit only works with the standard rear shock layout, not staggered shocks.

 

[71mach1lady]

I should clarify that the kit only works with the standard rear shock layout, not staggered shocks.

Thanks for clarifying that, it makes the builder kit look better again

Sure looks like you could make the 3" work with the staggered shocks looking at the room around our 2 1/2"

 

[Mesozoic]

I had my local exhaust guy fabricate my system in full 3.0" aluminized tubing. Looks and sounds great, even includes a 3" X-pipe.

 

[tommy]

jeff im running 3 inch on mine its a 393 with a big solid flat cam cHi heads and 11 to 1 comp my mate and exhaust mechanic wizz built it in an afternoon hooked up to my hooker headers it sounds awesome and goes like a missile he said it was no big deal to build unfortunatley for you he is here in oz i ll get a vid with sound up later this week totally recommend 3 inch its killer

Are your shocks staggered?

I have a good exhaust builder buddy if I can ever catch up with him.

not staggered

 

[Jeff73Mach1]

I guess I should have reported back sooner.

I relocated the staggered shock to the standard position, all it took was drilling a hole and adding a bit of reinforcement. After that getting the tailpipes out the back was no problem for my exhaust guy-I like doing as much as I can myself, but bending exhaust pipes is above my pay grade.

We even managed a set of 3" manual cut outs between the headers and the H pipe.

I don't think that it would have been nearly as straight forward without relocating the shock