Some details on my car
1991 GTA - 3460lbs with me in it
421 sbc - engine dyno'd at 586TQ@5200, 686HP@7200 (nitrous combo engine)
Powerglide with 3.75 gears and 275 drag radials
Exhaust is 1 7/8 Ed Quay long tube headers, with 3" collectors, then merged to a single 4" over the axle and thru a flowmaster 40 series muffler.

Went to the track with and got a best of 11.39@119.4 thru the exhaust.
I'm having a converter problem (not quite right for my combo).
My converter guy told me to uncork the exhaust, as he thought that was the problem.
Went again a few weeks later, with open headers, and did 11.13@122.5.

So I did pick up with open exhaust, but I am amazed that the 4" exhaust was holding me back.

I want to run an exhaust combo on the street. (maybe not with spray down the road)

I'm thinking 3.5" collectors , then thru some mufflers and dump before the axle.

Is dual 3.5" exhaust going to be better than single 4"?

 

The 4” exhaust wasn’t the restriction....it was the flowmaster

 

I would try dumping the flowmaster to see how open 4” does first

 

Toss the chambered muffler and sell it to somebody with a family car.

 

Yup, the flowbastard.

 

Not as high strung as the op's. But I switched from a 3 inch spin tech to a 4 inch dynatech and it feels like it picked up 50 horse. That's only on a stout 358 fwiw

 

i am using 5.7" restrictive exhaust in my Hemi ram 1500 which I am using for Roadside Assistance Services, but for you 4" isn't a restriction so you may consider that. for more details check their manuals book or on wikipedia there must have detail about it.

 

A 4-inch exhaust is not restrictive. It's reducing velocity which reduces low RPM torque.
Bigger is not always better...

 

4.30 gear 28" tire for that high reving motor and with the right converter youll easily be trapping 125-127mph.

 

I have a nitrous plate (sledgehammer) waiting to spray onto this engine.
Gonna start out with a 150 shot and go higher.

I'm switching to 4.11, which should be good to 150mph

 

Don't go with an open headers unless you plan on adding an appropriate length of collector extension. Otherwise you'll REALLY be disappointed.

 

I'm not following you

You saying that open headers(after the collector) would be worse than having a pipe on the end of the collector?

 

Yes. The exhaust is a tuned pressure pulse. Most sbc stuff will like 15-18” total collector + extensions depending on combo and rpm

 

Ever driven your car with it's new headers to the muffler shop to have an exhaust system installed? Generally (or in all cases I've been involved with), the engine is flat below something like 4000 RPM.
It's exactly as Orr describes it. It's all about tuned length. The same holds true for intake lengths as well. This is why the OEM TPI gives up at higher RPMs but torque is very good.
With no collector extension, torque production goes down the toilet because the length is less than ideal. And a header with nothing past the flange is most definitely less than ideal. The same holds true for having a collector that's too long as well.
There are programs, such as PipeMax, that will let you input your engine specific data and it will churn out optimal lengths or multipliers of the best length. Some will be directed at maximizing torque, I.E. smaller diameter and longer lengths as compared to maximizing peak HP as in larger diameters and shorter lengths.

 

since this is an all out race car, and you're launching at a high rpm, I wouldn't worry with how much low end torque and exhaust velocity I have. I'd run a 4" pipe with no muffler, or a straight through muffler with no baffling. if tuned length pipes made for better race engines than open headers, funny cars would have collectors and exhaust pipes instead of open primaries.

 

Thats totally different. Blown funny cars cant get enough gas out fast enough at those power levels. Blown cars in general dont tend to tune exhaust

look at any competitive naturally aspirated engine class and you will see collector lengths or megaphones, or some style of advanced merge collector shape

 

Again Orr has it. Any competition engine will have a tuned collector. In classes or if track restriction mandate mufflers, you'll find the muffler design is incorporated into the overall length. A baffled muffler will behave one way while a straight through design will behave another.
As for funny cars or top fuel, believe me, there's a lot of thought that goes into the design, length, diameter and shape of the zoomie header. All of the tuning is in the primary.
As for the OP, if he can maintain a specific rpm for the entire run, and that rpm falls in with the stub of a collector that a simple open header provides, then he's golden. But that's not likely to be the case.

 

Another update - personal best!

Ran at the track on motor, off the trailer.
1.67 - 60ft
7.14@99.6
11.01@124.3
That was with open headers and short turn-downs

 

Glad you're making progress. But I don't understand how a 690 Hp engine only traps 124 mph. That's more like 550 Hp real world. Maybe it's worthwhile to revisit gearing and converter selection?

 

I have a nitrous cam and converter.
My converter is super tight.
Even with a 150 shot, at the 1/4, it is 4.5% slip.
It wants more nitrous

 

124 is pretty good being a nitrous cam converter deal. Most heavy nitrous cars are somewhat turds on motor

 

So the 690 Hp is on nitrous?

 

I have 3.5 inch over the axle with a full size straight-thru muffler. Didn't seem to hurt me at 550 Hp na. It's hurting me a lot at 700 Hp na. I only got numbers up to 4k rpm and then tires spun on dyno, but the torque curve was way up after dropping exhaust after the y-pipe merge.

I haven't gone duals because it's loud as hell on the street. It already hurts my ears now.

 

I took that to mean 686 hp on motor alone. Normally at that weight i would expect closer to 130’s mph, but gearing and tight converter can suck it down

 

No, my engine dyno'd at 685

 

Old wives tale, or have you actually seen it happen?

I think OEMs use small exhaust because they want the car quiet. Any testing I've seen shows higher flowing exhaust lifts the whole torque curve, but the header design can definitely cause a loss of torque (the bigger isn't always better concept). Paying attention to header primaries, merges, collectors, and extensions is where you get the most payback.

And I've also heard that muffler selection is about more than just flow rates. Pressure waves reflect back to engine differently depending what style of muffler is used. For example, the whole length of exhaust out the tailpipe has to be considered with a straight through muffler. But a chambered muffler kind of acts like a pressure wave termination box which makes the engine more blind to everything after the muffler. In other words, the pressure waves are acting on a different length of exhaust, changing the timing that it hits the exhaust valves.

 

Oh, close enough. My mind remembers nice round numbers easier than down to the decimal.

Seems like you've lost an excessive amount of power from engine dyno to the real world. Can that really be explained away with converter or is there something else going on? I know your car flies on nitrous. How much nitrous are you using?

 

It’s possible, converters do weird things

i believe in his other post car went 9.47 at 141 on a 150 shot ramped in. Thats a hell of a gain 124 to 141.

for reference i went 119 on a 400’whp 383 and 128 on a 150 shot

 

Wow, that is huge gain and puts things back in balance. I had no idea a converter could make that much difference.

 

My converter is suited for 350 shot of nitrous.
Nitrous cam/converter/gears (4.11) really makes the car doggy on motor.

To utilize the motor, I should have 4.56 or higher numeric gears.

 

I am paying close attention to what you guys are discussing here. Will be putting the 150 shot on my car next months, and then the big project this winter is to spec. out and build a suitable exhaust from end to end. looking forward to the exhaust tech talk !

 

Id be curious how much the exhaust changes the nitrous runs...i know in the boosted world a lot of guys go very fast on 4“ exhaust. My self switching from dual 3” to single 5” didnt seem to change much in power and et but to be fair i never maxed out the 3” combo.

nitrous cyl pressure will find its way out but am curious. I think na is much more sensitive to the sizing.

 

Converter and gearing aside, my thinking is that only way to have a streetable exhaust, that is one that won't split your ears, is to go with cutouts at the appropriate place in the collector or y-pipe (if a single to the back is involved).
Not only is exhaust pulse tuning a reality but if the motor spec is right (with a cam and heads capable of making that happen) but the gains are proven.
Even with a full dual or large single arrangement ( one that doesn't impede flow and ultimately reduce output ), the exhaust tune goes out the window. The reflected wave is so diminished by the time it returns from the tail pipes that it has little effect.
Opinions may vary.



I would take this and the probably undersized single over...



..this. Even if this has enough capacity to suit the horsepower involved.
The tune for either would be different in order to realize the maximum benefit of the 5th cycle.


One thing though is that I can't think of a single post here (at thirdgen) where someone actually has determined the correct collector extension length (as determined by PipeMax or similar) and gone with it. Which is kind of odd really. Plenty of hardcore drag racers here but no stories. Could have missed them I suppose.

 

How short? And how did you arrive at the length?

 

Wouldn't you know last night there was an Engine Masters episode on TV where they experimented with header extension length? It was a 500 Hp 358 SBC. Extension length had a strong effect below engine peak torque, and pretty much no effect above peak torque. That was true with two different size headers. The "burnt paint line" theory was junk.

 

Exactly. Imagine that hitting your converter.
Keep in mind also that the length can be tuned for results directed towards HP and RPM.
Point is, with a full exhaust, and that's in the conventional sense with no termination boxes or whatever, all of that is gone. You're only relying on at least having enough exhaust flow capacity to not be a cork.

I never put too much cred in that . Interesting though in that it shows there's been experimentation over decades of racing.

Yesterday I saw some import tailpipe where the stainless tip was burnt blue. That's a really long collector...

 

Problem is on a heavier nitrous combo I think the exhaust tuning stuff is not as significant.

now 300-350 shots isnt super heavy. But i know guys messing with 600+ shots and dont seem to benefit in header and collector tuning, they just want it out as fast as it can get out

i dont know many doing full exhaust with large nitrous. I second the idea of running cutouts if you can get them under the car at a reasonable length from end of primaries

 

There was another Engine Masters episode testing dual and single exhaust (on a 600 Hp big block? can't remember for sure). Now that was even more interesting to me because it hit closer to home.

Interestingly enough, the smaller single exhaust actually did really well compared to dual 3" exhaust, provided proper muffler selection. But single exhaust was super sensitive to muffler choice. Dual exhaust was far less sensitive to muffler choice. That makes sense since all the engine exhaust is going through one muffler vs. sharing of two mufflers.

So, high power engines with single exhaust need to pay super close attention to muffler choice.

 

Turnout was about 9"
How did I arrive at that length?
Lol, it was long enough to turn the exhaust from underneath the car.
Absolutely no science to it.

I can't use cut-outs...
The one track I race at, has a muffler/Db rule

 

Was that short turn down after a muffler?

As pointed out by Qwk earlier, you can incorporate a muffler that connects to the header collector directly. A straight through design (Cherry Bombs come to my mind as opposed to chambered) would behave as if it was a piece of straight pipe. So if the muffler meets your Db spec, it might be possible to get that "open header" effect. The short turn down after has to be factored into the overall length calculation.
The problem is packaging. It's difficult to fit mufflers with dumps before the axle. Overall length wouldn't be more than 24" (as per a Pipe Max spec'd collector length) and that puts it all up against the trans crossmember (on average) .

 

No, at the last race, that turn out was right on the collector. No muffler

 

One thing to consider, if you haven't already, is to determine the flow capacity of the entire exhaust. It's been demonstrated that about 2.2 CFM per HP produced is needed to allow the dyno results to be realized once in the chassis. As the flow diminishes, so too does maximum output.
In your case, with 680 HP, that's over 1300 CFM. For the record, the best number I could come up with a 40 series Flowmaster was less than 500 CFM. That's a problem not unlike my own.

As for a short turn down, depending on it's length, it could be worst thing for torque production or it could enhance it. A difference of a few inches either way can make a difference.
In case you're interested, I've a few lists that might allow you to get an idea of what a highly functioning exhaust might involve.

For the record, there are some here that might say that this doesn't amount to a hill of beans because they've tested and their results speak for themselves. Good for them. I like to science things out and rely on the engineers and racers that have beaten the path already.
Maybe at approaching 700 HP, there's an embarrassment of riches and those fine details aren't of any consequence.
I've proven to myself with back to back tests how much by-passing the muffler can be worth at the track. At a hopeful 400 CHP, I was looking for any and all advantages then.














Food for thought.

As for a simple collector extension, this PipeMax screenshot is from a project I was working on for someone. This isn't an SBC but will give you an idea how tight the spec can get on length.
Check out the shortest collector extension and how close the best to worst cases are.

 

Another update!
I went to the track on Sunday.
Drove to the track, did 8 passes, and drove home

This is my combo
sbc 421, powerglide, 4.11 gears, and nitrous
1 7/8" primary Ed Quay header, to 3.5" collectors, then merged to a single 4" over the axle to a Dynomax 4" muffler
https://www.summitracing.com/parts/wlk-17225
Did a 150 shot with a ramp, a did a 6.13@113.12 , with a 1.37 60ft
Previous best was 6.07@112.9 - no ramp
Then did 250 shot with a really soft ramp, and went 5.85@118.5 - 1.32 60ft
Previous best was 5.72@118.9 with a tighter ramp.

Best 60ft of the day was 1.284.

In conclusion, the muffler did not restrict any power/flow compared to open headers or open headers with 6" race bullets.
I had a couple people tell me that my car was pretty quiet, lol.
Time to spray 300 with the full exhaust

 

You got me wondering again how much is given up with less CFM / Hp. Packaging exhaust in our cars can be a beach, you know.

Found this data collected for a specific engine combo that was tested. I don't know how well this holds for other engine combos. I'm around the 1.5 mark with my engine, so conceptually ~85% of power potential with my single exhaust. I really don't think I'm down that much though. My chassis dyno numbers were dirty (tire spin), but at the same time were too good to be down more than single digits. I should try to get a 1/4 mile trap speed before this summer ends.

https://www.musclecardiy.com/perform...to-tail-pipes/

 

Dynomax ultras are good mufflers. I used one on my 383 and it did help quiet down that car. I used two on my twin turbo sbc with dual 3”. Super quiet. I ran one 3.5” on my 6.2 truck, also very good deep sound but not overly loud

 

That's a Vizard graph. And yes, it is a guideline though of diminishing returns. At the top end, clawback of the lost power is less than a full on cork.
As I demonstrated with a quick back to back experiment several years ago, simply bypassing my muffler offered up almost 2 MPH in the 1/8th. That is an extreme example of a full on cork.
What people fail to miss, or so it seems , is that it's not a question of just having open headers. It having open headers with a specific collector length. And then, it's only useful if the overlap triangle is sufficient so as to provide the sought after scavenging.
There's no doubt in my mind Qwk, that if you could dyno your engine with a well sorted header and then compare it to your full exhaust, you would see double digit gains. Tuning accordingly goes without saying.

 

Just for clarification, you did say there was no science to the length of the collector with or without mufflers correct?
As mentioned, you could be helping as much as hurting open exhaust performance.
Quick car nonetheless. Well done

 

I was waiting to see some pics of Ed Quays SBC headers 1-7/8" Stepped 2" w/ 3.5" collectors, but I found a used set of Lemons(jet hot coated) headers in that exact size. One collector had a hole in it so I replaced both and did some high temp paint refurbishing and baking in oven. Mufflex took care of the dual 3.5" - 5" howe Y- collector, 5" cutout and connected to the 4" hooker max flow muffler. I know the 4" muffler isn't a restriction as I trapped 127mhp a few months ago plus killed clutch on next pass and this was with crushed hooker super comps 1-3/4". I really think the headers and super long y-pipe un choked the engine alot because its even quieter now. If I picked up 1-2mph in the 1/4 id be more than happy. Hoping to be in the 10.80 range in the next few weeks!

 

John, I am going to need you to take all that off your car and drive it up here to my garage! It is exactly what I need!

Just kidding bud, looks good. and I am very eager to see it perform in person. Let me know when you are going to the tracka nd if it is Atco or Island, maybe we can make some passes together. Then we will swap exhausts in the pits and see the wild difference! !!

I am keeping close watch of this thread, as this winter I will be doing a full blown exhaust system overhaul; everything comes off. Big long tubes, big y-pipe, and a 4" with a cutout.

 

How far from the ends of the primary pipes would you say that cut out is?
I'm curious whether its contributing to and taking away from the tuned length pulse.
I could run this through an older version of Pipe Max that I have to see where the specific collector lengths would fall with the given engine combination. In theory what you've done here is create a certain collector length with the cap off and that is where the exhaust valve will see the low pressure reflected pulse originate.