J10 headers for 3in exhaust?

[82camo401j10]

I crashed my hot rod, gremlin x, 550 hp 401. Putting the 401 in my 82 j10.
Gotta have 3in exhaust! My long tube headmans exit so close to frame and Tranny,
I don't think they can fab 3in to attach? Was thinking shorty headers might work?
Anyone got 3in, or even 2.5 in duals from headers?
My current 360 exits through 2in. Dumps in front of rear wheels.
Help?

[Ristow]

i had 2.5 from the hookers back on my J20.

http://www.ifsja.org/forums/vb/showpost.php?p=1446315&postcount=150

[82camo401j10]

i had 2.5 from the hookers back on my J20.


http://www.ifsja.org/forums/vb/showp...&postcount=150

My front shaft on drivers side, makes a tight fit, right by the wires and fuel, and brake Lines. Never thought bout going both drown one side? I'll check in to that.
Gotta figure how to use 3in. When I went from 2.5 to 3 on this engine in my gremlin, it felt like another 100HP above 4000rpm!

[wiley-moeracing]

Odd? I really think you will not need 3 inch pipes. Your Gremlin was 1/2 the weight of the j-10, you will need a little backpressure to help scavenge the exhaust(unless you plan at being full throttle 100% of the time). Your engine must have a very radical cam to be making that kind of horsepower at that rpm so you may find it will be hurting you when installed into the truck. You will need some bottom end out of your motor to get things rolling and the difference of 1/2 inch should not make any difference in power in that scenario.

[82camo401j10]

Odd? I really think you will not need 3 inch pipes. Your Gremlin was 1/2 the weight of the j-10, you will need a little backpressure to help scavenge the exhaust(unless you plan at being full throttle 100% of the time). Your engine must have a very radical cam to be making that kind of horsepower at that rpm so you may find it will be hurting you when installed into the truck. You will need some bottom end out of your motor to get things rolling and the difference of 1/2 inch should not make any difference in power in that scenario.

Yes you may be right? It red lined @ 7K, pulled HARD from 2500rpm.
I've advanced the cam 2deg, and added Rhoads V-max adj lifters to tame it below 3500rpm, then full lift and dur comes back.
Crawled under mine yesterday and figure I can kinda copy your system?
I'll have to turn my driver side over right under the collector, but theirs room on the pass side for both tubes above crossmember.
Thanks for the pics, they my be my fix?

[82camo401j10]

I'm going to try 2.5 back to mufflers(3in flowmasters), then 3 out the side.
My old system had restrictive (compared to FM), mufflers, and non mandrel bent ells.
This should flow equally well?
Ps-the truck is progressing, have BM shifter in floor and working.
Replaced steering box, and shaft.
Built camo door panels, and headliner.
Repaired tank and fuel gauge now works.
Replaced TC output seals.
Rebushed front sway bar and links(This dang thing corners now like on rails with the
235/70s on!
Still gotta rebuild tilt colum , parts on back order.
Scrapped my winch front bumper, and used my gremlin rear!
Trying to repair all I can before engine comes out!
Thanks all!

[Ristow]

flowmasters??!




barf!

[rang-a-stang]

I have 3" coming out my headers. Passenger side comes out and goes straight back. The driver side crosses over just under the trans pan, they Y together just forward of my case, single 3" pipe, passed the case, into a single Borla under the passenger seat (single 3" in, single 3" out), down the inside of the frame over the axle, and dump aft of the passenger wheel. My exhaust shop had to D shape the pipe as it passes my case but there is room there for 3" pipe.

If my gas tank was not under the driver side I would have done 3" true duals with an X under the transmission. The only place it is hard to fit 3" pipe is past the transfer case.

[DarkMonohue]

I crashed my hot rod, gremlin x, 550 hp 401. Putting the 401 in my 82 j10. Gotta have 3in exhaust!

Ehh...well, maybe. Maybe you don't gotta. We can come back to that.

My long tube headmans exit so close to frame and Tranny, I don't think they can fab 3in to attach?

A good exhaust shop is invaluable. Really skilled and experienced exhaust guys can work miracles (conversely, hacks can ruin anything). Improvement may be possible. Maybe you could redirect the header collectors to make the system fit and/or work better.

Before you go any farther, are your Hedmans correct for a late model FSJ with the front diff on the driver's side? If they are for a truck with passenger drop t-case, like in Ristow's example, all bets are off.

Was thinking shorty headers might work?

They may make fitment easier, but you'll definitely pay a price in power, especially in the midrange, which is much more critical in a pickup truck than in a street toy or drag car. That also raises the question of what your intended use is. Putting a 7000-RPM drag engine in a four-wheel-drive pickup is unusual. Is this a mud racer or puller or sand toy or something?

My front shaft on drivers side, makes a tight fit, right by the wires and fuel, and brake Lines. Never thought bout going both drown one side? I'll check in to that.

The fuel tank is on the driver's side of the truck, so unless you are relocating the fuel tank, the only realistic route for exhaust is down the passenger side.

Gotta figure how to use 3in. When I went from 2.5 to 3 on this engine in my gremlin, it felt like another 100HP above 4000rpm!

Any chance you have before and after dyno charts? Dynos sort the facts from the "feels like". The butt dyno ("feels like") has misled many of us. I have been fooled into thinking I found a big gain in top-end thrust when what I really got was a big drop in midrange grunt. Instrumented testing is the only way to know.

Odd? I really think you will not need 3 inch pipes.

I tend to agree so far. Turbo guys (extremely sensitive to backpressure) can make 300+ wheel horsepower through a single 2.5" system before it becomes a restriction, so dual 2.5" tubes really should be more than adequate, provided the system is built right, and provided good mufflers are used. If you use crush-bent tubing and restrictive mufflers , then you might have to make up for it with bigger pipes and correspondingly bigger restrictive mufflers.

...you will need a little backpressure to help scavenge the exhaust...

This I don't agree with. This is a complicated subject which has been misunderstood for decades.

Backpressure absolutely does not help scavenge the exhaust, but exhaust pipe diameter that improves velocity at a chosen engine speed does. Now, the tricky bit: a pipe diameter that is small enough to improve velocity at lower engine speeds may also be small enough to cause backpressure at higher speeds. Rest assured, the resulting backpressure is an unfortunate side effect of smallish pipe size; it most definitely is not what's causing improved scavenging or increased torque.

It also bears mentioning that scavenging is affected much more by the diameter of header primary tubing than by the diameter of the tubing after the collector. Too small a main pipe diameter can, of course, choke off the breathing at higher engine speeds and loads, but going too large is less critical *if the header is sized correctly*.

However...

Your engine must have a very radical cam to be making that kind of horsepower at that rpm so you may find it will be hurting you when installed into the truck. You will need some bottom end out of your motor to get things rolling and the difference of 1/2 inch should not make any difference in power in that scenario.

Agreed. 100%.

Assuming a well-designed and built mandrel bent system, with appropriate headers (primary tube diameter and length suited to your engine and your intended use) and a well-designed and installed H-pipe, X-pipe, or collector to join left and right banks together, along with straight-through (or very nearly so) mufflers, dual 2.5" pipes should be more than adequate.

On the other hand, if you get a crush-bent system with no crossover cobbled together at Felony Frank's Discount Mufflers and Neck Tattoos, and you handicap it with restrictive mufflers, you have a lot of issues working against you. In that worst-case scenario you might benefit from larger tubes to accommodate larger restrictive mufflers and compensate for the crappy bends.

Flowmasters are kind of like Fram filters or McDonalds hamburgers - ubiquitous but terrible. People default to them because they recognize the name, and you can find 'em anywhere, and they're cheap. Despite their name, they don't flow very well, and I don't believe that they could outperform a muffler that flows better. Personally, the sound alone is enough to turn me off. It's not a matter of being "too loud" - the tone they produce is just unpleasant in every way.

There are other mufflers that perform as well, or likely better, and produce a much nicer sound. Straight-through mufflers like Magnaflow or Borla are excellent performers, but can get a little noisy, and I don't want to be the guy that torques off the whole neighborhood every time I come home. My personal favorite is the Hooker Aero Chamber. They flow like crazy, they're built like a bank vault, and they sound fantastic on damn near anything.

[82camo401j10]

The FM mufflers are being used because leftover off crash car. That car was my toy for 30years. This is my replacement toy. I have a cj for dirt play. This will be a (farm truck kinda sleeper). I'm looking for similar sound to gremlin that crashed.
Their ant no cruising, or street racing hear anymore. But their is Lots of unplaned red light play.
And I just like going through the parking lot sometimes and setting off alarms.
I'm to senior (62) to be doing this still but I do. (Still ride a RM 250 also).
The truck will c some work duty, but mostly run local errands.
The enging ant really a race engine, 500hp, even 15years ago could be built dependable .I regularly drove up to 100miles from home, day trips.
And I think the 2.5, no crushed pipe back to the 3in mufflers will flow just as well.
My old 3in system had the shrinking ells and homemade X pipe.
I don't think there room for a X, but a crossover will be attempted.
And as far as backpressure ,as stated before, going from 2.5 with junk mufflers,
To 3in, felt like another hundred HP above 3grand.
Thanks for all the interest.
I'll post viedo on utube when done. Should be running by early fall.

[DarkMonohue]

Thanks for the extra information. That all makes sense.

If you want to reuse your existing 3" mufflers but don't have room for a dual 3" system, you can still have the 2.5" pipe swedged up to 3" for the muffler inlets and outlets. That kind of gives you the best of both worlds. You get pipes that fit the vehicle and mufflers that flow a little extra.

Since both pipes are going to be on the passenger side, probably right next to each other, you can just build a little chamber that they both run into and out of. That will perform the same function as an X-pipe but will take up less room.

Please do share some pics and a video when you get it together. Sounds like a fun project.

[82camo401j10]

Thanks for the extra information. That all makes sense.

If you want to reuse your existing 3" mufflers but don't have room for a dual 3" system, you can still have the 2.5" pipe swedged up to 3" for the muffler inlets and outlets. That kind of gives you the best of both worlds. You get pipes that fit the vehicle and mufflers that flow a little extra.

Since both pipes are going to be on the passenger side, probably right next to each other, you can just build a little chamber that they both run into and out of. That will perform the same function as an X-pipe but will take up less room.

Please do share some pics and a video when you get it together. Sounds like a fun project.

So basically a shoe box with2, 2.5 inlets,and outlets? Instead of X ?
Is this way better than just a simple crossover between the 2 parellel tubes?
I've never had an X, just a crossover.
Remind me of the benefit from either?
More tq?
More top?
Smoother idle?

[DarkMonohue]

Yep, just a short box, or two pipes side by side with an open chamber between them.

I don't believe that there would be a significant difference in performance or sound between a small box-shaped plenum as I have described and a compact X-pipe. It's just an idea that may (or may not) make packaging easier in tight quarters.

As I understand it, an X-pipe tends to produce a smoother sound than an old style H-pipe style crossover. Either one is better than no crossover at all. I haven't looked into performance differences. Dyno proof would be necessary to make any definitive statements on that.