Exhaust upgrade parts selection - do I need 3"? - Team Camaro Tech
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post #1 of 36 (permalink) Old Nov 13th, 18, 05:32 PM Thread Starter
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Exhaust upgrade parts selection - do I need 3"?

With holiday sales coming up, I'm trying to decide on what exactly I want to get to upgrade the exhaust on my '68.

The engine is a 383 with a Weiand 142 making 5-6 psi of boost. (Cam specs here: 12-560-4 - Nitrous HP) On the engine dyno without all the accessories and open dyno headers, it made 560 hp and 585 tq. Back in the car with the 1.5" primary shorty headers and 2.5" exhaust with no crossover (and all the accessories) power is down pretty significantly and I'd like to get some of it back.

From my research, my engine's power output is right above the point where it's recommended to upgrade to 3" tubes, but not by much. From watching all the Engine Masters dyno tests, it looks like I should pick up somewhere between 30-45 hp by swapping to 1.75" long tube headers, 3" exhaust with x-pipe, and free flowing mufflers from the basic small system I have now. Sounding mean at WOT is great but I want it to be a pleasant cruiser at 1500-2600 RPM as well. The car has stock suspension. Only things non-stock on the underside are subframe connectors and the 700R4 crossmember. The connectors sometimes drag when going over a dip in the road at speed and I'd rather not add more things that will drag. Probably need stiffer suspension at some point..

My plan so far is:
- THESE Hooker headers because they're the new design that's meant to fit cleanly around all the obstacles like the steering box without having to hammer on them and already has a spot for my wideband sensor.
- THIS 3" exhaust system since it's a good price, stainless, has an X-pipe, and I've read several good reviews of those mufflers.

Is that a good plan? What would you do differently? Think for my car it's worth the time, money, and effort? Better to just do the header swap and a 3 to 2.5 reducer somewhere along the way? I don't see any 1.75" headers with 2.5" collectors for a 1st gen. What else do I need to consider?

Thanks!


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post #2 of 36 (permalink) Old Nov 13th, 18, 05:45 PM
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Re: Exhaust upgrade parts selection - do I need 3"?

Looks pretty good, donít know about Pypes stuff but if itís a straight through (not chambered) muffler it will work.
I think the fact you are using shorty and 1 1/2 primary tubes is the biggest issue, so long tube headers alone will help I think drastically. You could probably use 1 5/8 primary tubes but I had 1 3/4 on a similar build that worked well.
I would go 3Ē exhaust for sure, but whatever your collector size is at least start with that, to the X. In this case 3Ē collector and 3Ē exhaust should be money.

God luck with it!

Sean

1968 rs with an old school 354" SB2.2 pump gas motor.

Repetition does not transform a lie into a truth.

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post #3 of 36 (permalink) Old Nov 13th, 18, 06:09 PM Thread Starter
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Re: Exhaust upgrade parts selection - do I need 3"?

The Race Pro mufflers are straight through. Their description says it's actually their quietest muffler, but flows the best. I can get the kit without mufflers and choose my own as well, but from what I've read, they're pretty good.

Seen a couple less than fully positive reviews on the fitment of Pypes kits in general. Not a whole lot specifically for this car. I'm actually surprised, I figured every company out there would have a kit for a first gen, but there actually don't seem to be many. Other than Pypes, I see a Flowmaster kit with an H-pipe and 44 series mufflers which I've read drone pretty bad, a Dynatech kit, and some Summit/Jegs branded kits.


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post #4 of 36 (permalink) Old Nov 13th, 18, 06:22 PM
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Re: Exhaust upgrade parts selection - do I need 3"?

Imho keep the headers you have go 2 1/2Ē back with an X or H pipe and youíll be good to go.

I see no reason for larger primaries or 3Ē going back that may complicate installation clearances
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post #5 of 36 (permalink) Old Nov 13th, 18, 10:33 PM
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Re: Exhaust upgrade parts selection - do I need 3"?

I had an exhaust shop do mine locally, so consider that, then you donít have to mess with poor fitting kits. They fit high and tight, and I had them build it the way the program we ran the motor through said was best, or close to it. Kits are usually a compromise.

Well designed long tubes will basically always make more torque below peak rpm. Generally unless you are having a custom exhaust assembled go long tubes. Without running a program like pipemax or the like itís just guessing, but there are standards that work, itís just an SBC after all.
Run a pipe out of the header the same size as the collector also, or gradually reduce it if need be. A big step is not helping anything.

Just some basic stuff, but I think you are generally losing low end torque and the primary is a bit small.

By the way, what is peak rpm?

Just one mans opinion.

Sean

1968 rs with an old school 354" SB2.2 pump gas motor.

Repetition does not transform a lie into a truth.

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post #6 of 36 (permalink) Old Nov 14th, 18, 01:11 AM Thread Starter
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Re: Exhaust upgrade parts selection - do I need 3"?

I just kinda assumed the labor involved would at least double the price and figured I could get a kit designed specifically for the car and do it myself. Especially if we're talking custom built headers as well. But it's true, there's nothing like custom built for the application.

I definitely think I'm losing power/torque with the small primaries right now. Pretty much nobody even makes 1.5" headers anymore. 1 5/8 at the smallest and those are used on milder builds. Mine isn't a monster by any means but it's also not a basic 350 with a cam and intake. Chassis dyno numbers were down close to 30% from engine dyno numbers (400 at the wheels vs 560 at the crank). I know there are more variables in a chassis dyno and most of the loss there is drivetrain. But still, I expected to see maybe a 20% loss.

Peak hp is at 5600 RPM. If I keep my foot in it it'll rev past 6000 before the 700R4 decides to shift.


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post #7 of 36 (permalink) Old Nov 14th, 18, 02:35 AM
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Re: Exhaust upgrade parts selection - do I need 3"?

my engine showed 540/515 on the dyno with 1 3/4" long tube headers. that is what I have in the car with electric cut outs , x pipe and 2 1/2" stainless out the back
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post #8 of 36 (permalink) Old Nov 14th, 18, 10:30 AM Thread Starter
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Ever had it on a chassis dyno? Are you happy with the performance? At what point does it neck down from 3 to 2.5 inches?


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post #9 of 36 (permalink) Old Nov 14th, 18, 11:13 AM
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Re: Exhaust upgrade parts selection - do I need 3"?

I was actually referring to pipes behind the collector as far as having them welded up by a shop. I actually had to have headers built, but with a common engine type system I would use off the shelf headers.

I wanted a specific pipe set up so no kits are available, but I would still consider an exhaust shop, but Iím also picky, the kits always seem poor fitting somewhere in the system.

If you reduce the pipe size do it gradually with a tapered reducer if at the collector. I went from collector size to my X, and used a Dr. Gas X that steps at the X then took the reduced size (1/2Ē in my case) the rest of the way.

It can be done more simply with a kit no doubt, but I personally always figure if you are going to do something think it through and do it right, it may only be a small gain in power but itís still a gain.

Sean

1968 rs with an old school 354" SB2.2 pump gas motor.

Repetition does not transform a lie into a truth.

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post #10 of 36 (permalink) Old Nov 14th, 18, 11:51 AM
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Re: Exhaust upgrade parts selection - do I need 3"?

Quote:
Originally Posted by SOAR B-1 View Post
Ever had it on a chassis dyno? NO! Are you happy with the performance? HELL YEA! At what point does it neck down from 3 to 2.5 inches?
AT THE COLLECTOR
you will never touch the dash when I say 123 GO
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post #11 of 36 (permalink) Old Nov 14th, 18, 12:31 PM Thread Starter
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Re: Exhaust upgrade parts selection - do I need 3"?

So I definitely want to do the header swap. In addition to the pipes being too small, the finish is wearing off and they're pretty ugly. And like I said, the current exhaust is 2.5" straight back, no crossover. Seems like kind of a waste to replace the whole exhaust with tubing of the same diameter just to add a crossover. I guess that's where it'd probably be better to just have a shop add one vs replacing everything. The other non-performance reason I wanted all new piping is that the car used to have a fluid leak at the front of the diff and it flung gear oil all over the exhaust pipes and mufflers for who knows how long with the previous owner before I fixed it. So that looks pretty nasty as well. I don't know exactly what type of mufflers the car currently has, so couldn't say if they're a bottleneck or not.

So basically, I'm between upgrading just the headers with a gradual 3 to 2.5 collector extension, leaving everything else as it is (and maybe having an H-pipe welded in and seeing if a wire brush can clean up the burnt on fluid) or doing the full new 3" exhaust with X-pipe.


Quote:
Originally Posted by flat tire View Post
AT THE COLLECTOR
you will never touch the dash when I say 123 GO

Side note, what tires/transmission/rear gears do you have to put the power down?


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post #12 of 36 (permalink) Old Nov 14th, 18, 04:40 PM
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Re: Exhaust upgrade parts selection - do I need 3"?

m20 MUNCIE
p 295-50-15 cooper cobra
I also run drag shocks on all 4 corners with 5 leaf rear springs
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post #13 of 36 (permalink) Old Nov 16th, 18, 09:03 PM Thread Starter
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Any other thoughts regarding the options here?


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post #14 of 36 (permalink) Old Nov 17th, 18, 04:06 AM
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Re: Exhaust upgrade parts selection - do I need 3"?

I changed to 1-3/4 primaries and purchased the American Thunder 3" kit for my 72 Chevelle and it went in fine. Don't know if there are more issues with clearances on the Camaro. This was after I had Midas put in a custom system and I was happier with the American Thunder kit. It was engineered to fit, whereas at the muffler shop I was at the mercy of a dude trying to knock it out as fast as possible and I was not happy with some of the work. I was glad I went with 3" for the 454 & 6-71 Blower. As far as the custom work, your results may vary, as I probably just got a less experienced guy on a Saturday with a hangover.

Summit-Flowmaster American Thunder 3" exhaust with H pipe - 17201


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post #15 of 36 (permalink) Old Nov 17th, 18, 11:38 AM
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Re: Exhaust upgrade parts selection - do I need 3"?

I also installed the American thunder 3Ē kit on my 69 Camaro with thre h pipe and stock tank. I have 275 60 15 tires. The fit was great. No rubbing great hangers. Used band type clamps instead of crush clamps on the mufflers for easy removal. Welded the rest in. Great kit. Might be too loud for some I donít mind. I have an overdrive transmission.
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