project with 302 needs exhaust....and future part list.

I bought my Comet with a Maverick front end, incomplete 302 swap, incomplete small bumper swap, and all around incomplete. It is getting close to running and I need exhaust from the headers back. The engine is a 1971, appears to have been rebuilt with iron heads, has a torker 289 manifold, holley with vacuum secondary, MSD coil, hooker long tube headers (1 5/8 tube, 3" collector). I do not know if there is a cam or any work done on the heads. Compression test with pb blaster shot into cylinders (engine hasnt run in more than a few years) yielded 170 (high) 150 (low) and 160-165 for the rest.
In the future, I would like to install gt40 heads, mild cam, higher stall converter, and 3.25 to 3.55 posi. Currently I have 2.79 open, and will use 14" Indy Slots. Should I run 2.25 exhaust, or 2.5? Also, has anyone tried to run the 2.25 off the headers and combine the two to a 3" single over the back axle and out the back? If I never plan to rev over 6K would a single 3 be enough? It would save a little weight and be simpler......slightly less volume in the back half, but are the exhaust gasses cooler by then and need less space?

 

2.25 exhaust is good to almost 400hp, 2.5 to over 450hp. If you are going to use GT40 heads the 2.25 will be fine. Usually if the pipe size is reduced, it is after the muffler. I think you will have better luck running two 2.25 pipes versus one 3, but that is just my opinion, and since it is your car, my opinion is worth 0.

 

I ran 2.5 I have 6901 hookers and I bought a set of mustang tail pipes and a couple straight peices and flowmasters. Just had to tweek the tail pipes alittle and the straight front pipes alittle. They came out pretty good.

 

There is a shop near by that sells mandrel bent pieces. I am going to check them out after I take a few measurements. I have a chopsaw that just needs a metal blade and a buddy will loan me a welder. I will see what their price is vs. carry out of parts, but it appears the prevailing wisdom is dual, and for what I have going on, probably 2.25 inch. See Jason, your opinion is worth at least $.02 !

 

Now if I can just convince the wife.

 

Well, the guy at the shop with the mandrel bender charges $800 for a complete system. He builds a crush bent system that fits perfectly, uses it as a template, then fabs the mandrel mandrel system. The guy does absolute A-1 work, but I am going to scratch my head a bit before tossing that much cash at it.

 

Wow that sounds expensive but exhaust work is not cheap,when I had mine done a few years ago it cost $350.00 to run 2 1/2" and 2 mufflers and weld in a set of frame connectors . I would have to try and do it myself before I spent that much money on exhaust .

 

If any shop I was considering told me that they needed to waste that much time and piping?.. just to build a template for a mandrel bent system?.. I'd be shopping elsewhere. Anyone who's worth their "custom exhaust" salt and has decent enough spacial recognition skills should be able to make it from point A to point B without much waste material and re-cuts.

I myself have learned to cut slightly less than required(leave some extra radius in place).. and then simply grind it off against the side of the cutoff blade to sneak up on the perfect angle/fit. Takes more time and some finesse.. but much less errors/compromises and waste product. Don't forget the H-pipe too.

 

A Guy quoted me $1200 for custom headers on my 347 and I told him to do it...he backed down...
sometimes they price things as a "don't want to price" on a Mav/Comet...

 

Hi Stumanchu:
We've built exhaust setups using the "J" and "U" Mandrel Bend Pieces which we cut and welded in house
using the pieces sold by SUMMIT Racing . These pieces work great for the " X" pipes also. The headers on my Comet were from a early Mustang and we had to re-route five of the pipes to make it work out .. After "Fitting" I had them Ceramic Coated and it was worth it .. they still look good . Also , $800.00 is STEEP .. for a header system.. I believe
SUMMIT also sells headers that would work for you without all that expense.
JMO
Cometized
( Chip )

 

I thought that was pricey too. Can a regular wire feed welder do a decent job on aluminized pipe? The guy said I would need one with a gas bottle? I can borrow a wire feed if I buy some wire.....what kind of wire should I get? I am leaning towards doing my own; the learning curve doesnt scare me yet.

HA! There was a guy who bought 25 mandrel bent 180s while I was looking at the parts and scratching my head! He must have been from a shop somewhere......I should have followed him out the door and got a quote from him.

 

Wire feed would weld regular exhaust pipe just fine if you use welding gas but aluminized pipe is a different story you need an entirely different set up, why are you thinking about using aluminized pipe. If you dont use gas and use flux core wire it will look like it has been buggered on. Doing it outside with gas can be a challenge because of wind blowing gas away so be prepared to take it down to get a good job all around the pipe. It would be nice if you could use slip fit joints as much as possible.

If you are planning on going over rear axle and out the back be prepared for a challenge as that is the hardest part not much room

 

As far as welding Aluminized Pipe you shouldn't have any problem if you use a M.I.G. ( Metal Inert Gas ) Welder..
Its a Wire Feed Welder and so far we've made 5 exhaust systems using a MIG welder. The aluminized pipe has a
'coating' which burns off the instant you begin the weld .. and if you're welding in " Bungs " we surface clean the
area first with a small air sander wheel and then proceed. There are good deals online for a small MIG welder setup if you plan to do a lot of your own work .
Cometized
(Chip)

 

Hey Stu:
If you're going to install GT40 Heads.. try to get the ones that have the Spark Plug Holes facing the SAME as a
stock head . There are other GT40s that have a spark plug hole facing the opposite and they're a PITA to work with
as far as reaching a spark plug , running wires . etc. etc. Just my opinion;
Cometized
(Chip)

 

Chip you are talking about the GT40s vs the GTP40s. Look for 96-97 explorers for the GT40s.