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Discussion Starter #1
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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Looks pretty good, don’t know about Pypes stuff but if it’s 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 3” exhaust for sure, but whatever your collector size is at least start with that, to the X. In this case 3” collector and 3” exhaust should be money.

God luck with it!
 

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Discussion Starter #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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Imho keep the headers you have go 2 1/2” back with an X or H pipe and you’ll be good to go.

I see no reason for larger primaries or 3” going back that may complicate installation clearances
 
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I had an exhaust shop do mine locally, so consider that, then you don’t 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 it’s just guessing, but there are standards that work, it’s 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.
 

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Discussion Starter #6
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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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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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 I’m 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 (1/2” 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 it’s still a gain.
 

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Discussion Starter #11
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.


AT THE COLLECTOR :grin2:
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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Brett - Leander, Texas 1969 SS396
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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


Brett......
 

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I also installed the American thunder 3” 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 don’t mind. I have an overdrive transmission.
 

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Just to compare.... I have 1 7/8" primaries on a 364" along with a 3" kit with Ultra-Flo's.

Runs and sounds good IMO.

IF you have the kit and its what you want.....do it. It will not hurt performance going bigger.
 

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Discussion Starter #17
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.

Did you use the mufflers that came with the kit and if so how did you like them?


I also installed the American thunder 3” 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 don’t mind. I have an overdrive transmission.

Thanks, sounds like a very similar setup to what I'm planning (tank, tires, trans, etc). Did you have stock suspension?


Just to compare.... I have 1 7/8" primaries on a 364" along with a 3" kit with Ultra-Flo's.

Runs and sounds good IMO.

IF you have the kit and its what you want.....do it. It will not hurt performance going bigger.

I don't have any of the kit yet, just making plans. I won't be back in the states with the car for several months but I was hoping to take advantage of some Black Friday sales and get some parts ordered if I could decide on stuff that I think has a real good chance of fitting. May not be worth the risk and I should just wait, but either way I want to have a plan. I'm certainly not worried about hurting performance. Just trying to decide if it's worth it and if the parts I selected are good.




Any of you guys running 3" pipes have any ground clearance issues that you didn't have before? Anything else I'm not considering?
 

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Any of you guys running 3" pipes have any ground clearance issues that you didn't have before? Anything else I'm not considering?
On my 406 I had 1 3/4” super comps with 3” collectors and 3” out the back behind the X. Magnaflows. No ground clearance issues.

The current set up on my 354” is a custom built lemons header that are 1 7/8” stepped to 2” with a 3 1/2” collector, 3 1/2” to 3” stepped X, 3” out with magnaflows. Sounds awesome and not crazy loud at all. The X makes a big difference at cruise and idle in sound, mellows it out.
The headers fit so amazing they are actually super tight under the car, exhaust is hard to see from the side.
The headers have a big impact on exhaust fitment.

I had flowmasters but grew really tired of the sound and they are not the best for making power. But if you like the sound then that’s what you like.

You can throw anything on your car and the exhaust will get out, but if you don’t want to leave power on the table don’t take shortcuts like a huge step behind a collector that is probably too short already. I don’t like leaving power on the table, and with a motor making 550 horse or better it doesn’t sound like you do either..😉

Sound is subjective, so listen to some clips if you can.
 

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Brett - Leander, Texas 1969 SS396
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Yes, I used the mufflers that came with the kit. I liked the sound, and I had cutouts on the Chevelle. The kit worked so well that I bought another for my Camaro, but they are 2.5" as I don't have the HP I had in the Chevelle. I am installing the exhaust this weekend. I also bought these low profile cutouts from Kindig

Brett.....
 

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No clearance issue that I found yet.
Being larger diameter, you need to take time to tuck in better at a few spots ;)
 
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