Long-tube header & exh. system dia. recommendations?

[TheEddie]

I want to take full advange of this '85 Z24's low-down torque and hi-MPG characteristics .  This truck will be naturally aspirated, stock cam, Weber.

 

I'm planning use of a tri-Y full-length header, low-restriction welded-up mandrel-bent exhaust system, and a low-restriction muffler.

 

1.  Header manufacturer recommendations?  Primaries, secondaries, collector diameter?  Or do I have a choice?  Pacesetter's catalog shows 1.5" primaries, 2" collector--no try-Y design, boo-hiss.

2.  Exhaust tubing diameter(s) recommendations?   Pacesetter's header is 2" OD at the collector--pipe the rest of the system in 2"?  I'd hate to have to go any smaller than 2", but high-velocity effciency is the watchword here and the widdle itty-bitty pipe ain't gonna show nohow.

3.  Muffler recommendations?  I like a throaty rumble, sorta loud-ish, but not obnoxious; SuperTrapps and the like would not work for me.  The muffler needs to be in line with the piping, somewhere toward the middle of the system, larger inlet/outlet (rather than smaller), below the bed and forward of the rear axle (short wheelbase, short box, regular cab).  Heh-heh--got something kinda special in mind for those exhaust tips... :thumbup:

 

Eddie

[datzenmike]

I want to take full advange of this '85 Z24's low-down torque and hi-MPG characteristics . This truck will be naturally aspirated, stock cam, Weber.

 

Eddie

 

Then you don't want or need a header. This is something for racing using a modified motor that needs to get rid of a high volume of exhaust. The Z24 makes it's torque at 2,800 and up. It's not a high revver Just a nice stainless 2" mandrel bent pipe with a large 'muffler'.

 

At low speed/rpms the stock exhaust is more than large enough for the amount of gasses flowing through it. You want the exhaust gasses traveling as fast as possible but the pipe size large enough that it not restrict flow. I think the Z24 720 uses a 2" pipe. Too big a pipe will slow the exhaust and you will loose power at medium speeds.

 

 

As the Z24 barely makes much usable power above 4,500-5,000 the 2" pipe is fine. A header will increase flow but at an RPM that is never going to be used. You could reduce the restriction of the muffler by getting a larger one or maybe a 'turbo muffler'. Do not get straight through cherry bomb type, instead get one with baffles and glass insulation to absorb the sound. If you don't have emissions testing you could remove the cat and fit straight 2" pipe in it's place. 

 

Header...

Expensive at $50 per hp gained at high RPMs you don't drive it and won't feel.

Don't fit well unless spending $200+ on a good one and then don't always seal properly

Produce increased under hood temperatures from the increased surface area.

Nosier than the stock manifold.

They rust in a few months and rust out in a few years and need maintenance unless ceramic coated... add $100

 

For arguably a few hp gained at high revs, the cost, the day plus spent installing, the noise, the floor heat and the fact that you did all this and no one can see it when driving? Not worth it. My advice... don't throw away that stock exhaust manifold, you WILL want to put it back on.

 

Instead spend the money on a brake or suspension up grade, lower it, some shocks to improve the ride quality, up grade the headlights or some nice seats...

[Farmer Joe]

i would stick with the stock exhaust manifold. 

 

youll loose most of that well neeed lower end torque, wvwn with a longtube header. 

 

keep the stock manifold and use the stock headpipe. 

 

a 2inch exhaust system with a turbo muffler would be nice. any bigger than 2in is a waste with a 2.4L. 

[TheEddie]

Thanks.  Kind of fingered that an equal-length header wouldn't work all that well. 

 

If memory serves (sez the poster-boy for early-onset Alzheimer's), back in the day, the nickel-dime guys were creating a home-brew tri-Y by retaining the OE cast-iron dual-out upper, and substituting a longer fabricated tubing 2-into-1 section, then going into the system. 

 

Use the stock headpipe on the OE Z-24?  Wouldn't a longer pair of "secondaries" merging into a collector enhance the low-end?  I need to run some numbers--off the top of my head, I'd think they need to be somewhere around 16-18" long; shold be worth a couple of lbs.-ft. anyway.  Nissan had to have known this, but built the shorter OE "Y" for ease of packaging as an acceptable tradeoff.

 

Again, I was looking for tri-Y header designs; sorry to confuse things by throwing Pacesetter's equal-length design in there!  I just needed some somebody else's diameters so I wouldn't have to hit the books!

 

Trust me, I have absolutely no intention whatsofreakin'ever of running a glasspack;  I got that out of my system long (long, long ago, when dinosaurs walked the earth)--these days, the muffler would be (as David Vizard recommends) a Flowmaster, or Walker Super Turbo, or DynoMax et al, set up anti-reversion style.

 

Eddie

[Farmer Joe]

yeah a tuned headpipe off the stock manifold would be cool. like a 510 headpipe. 

 

i was going to do that with my KA swap, but ran out of room to run the 2 longer pipes off the manifold. 

[datzenmike]

To tune for that low an RPM you'd have to carry the tuned length pipes in a trailer out back. :lol: Actually 75" @ 2,800 and 45" long at 3,500 rpms. That's almost 4 ' long

[TheEddie]

Yep, it's doable--the hard way--so obviously I gotsta do it.

 

Essentially, all we're looking at is a dual 1.5 exhaust system off the OE manifold, tied together at some point 75" or so rearward.  This can work--a dual-inlet/single-outlet Flowmaster-type silencer, positioned just in front of the rear axle.  Provided somebody makes a dual-1.675 inlet/2.0 outlet, anyway.  

 

Sheesh, this can be pieced together from mild steel mandrel bends sourced from just about anywhere.

 

Now what would be really cool would be an long runner IR intake--like SR's have.

 

No, WAIT!:  Doable with DCOE's.  WARNING!!!  PROJECT CREEP!  Just got out of cheep mode.

 

Eddie

[datzenmike]

Dodgde did this back in the '50s.

 

[TheEddie]

WOWSERS!

 

They must've read the same book I did  (Scientific Design of Intake and Exhaust Systems, Dr. Philip J. Smith, PhD).

 

Dodge's big problem with that design was gasoline droplets falling out of fuel/air suspension on that long ride, which, BTW, was of a length tuned to enhance low-end torque. 

 

EFI fixed the drop-out problem, which is one of the huge benefits of FI.  On their late-'80's-early-'90's pickup used an inline-six with an IR manifold with a total intake tract total length of 53 inches...talk about your low-end!

 

Current EFI motors are using ram-tuned intakes, as well as extractor exhausts.  Well.  The semi-tuned extractor exhaust, as we've figured it out today, I can build on the cheeep while I figure out the rest of my new toy.

 

Eddie