Does a drag race only car need exhaust boxes?

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Markh

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My 340 drag only dart has exhaust cut outs with plates that unbolt.
The car was ran on a rolling road for a base line figure and the afr showed a steady 12.
The car then had 2 runs with the cut outs opened. Afr dropped to 11 and then 10. Hp was down 5% and torque down 10% on both runs. Carb is a 750dp. If the carb was rejetted to get the afr back to 12 would the hp and torque be better with the open exhaust or does a car make more power with exhaust boxes over an open exhaust? Or do I need a bigger carb? I suppose what I want to know is what is going to make the most power, an open exhaust or one with boxes or is it not that simple?
 
Sounds like you answered your own question.

Tune it for open or closed.

If you tune it for open it may or may not have more power / torque. You will have to test to know.
 
If an exhaust box is a muffler then no, you don’t need that.

You need a 36 inch collector extension.

If an exhaust box isn’t a muffler then I haven’t a clue what the hell we are talking about.
 
As above, gonna have to tune for open or muffled. How well a cutout works depends on where it is. Closer to the headers is better. See enginemasters cutout episode.
Most times if an a collector extension (directly off the header) isn't used, midrange torque will be hurt, sometimes dramatically. I have no idea if they work off of a cutout.
I have always raced with mufflers, and our local strips (supposedly) require them . I don't believe a properly sized and free-flowing exhaust hurts performance much, if at all.
 
Rat Bastid said:
How long were the collectors?
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Shifting it a 8000 1050's at 130 weight 3850 with driver



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Markh said:
My 340 drag only dart has exhaust cut outs with plates that unbolt.
The car was ran on a rolling road for a base line figure and the afr showed a steady 12.
The car then had 2 runs with the cut outs opened. Afr dropped to 11 and then 10. Hp was down 5% and torque down 10% on both runs. Carb is a 750dp. If the carb was rejetted to get the afr back to 12 would the hp and torque be better with the open exhaust or does a car make more power with exhaust boxes over an open exhaust? Or do I need a bigger carb? I suppose what I want to know is what is going to make the most power, an open exhaust or one with boxes or is it not that simple?
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From the header, where the 4 tubes connect is called the collector. From here, the length of the collector will dictate the amount of low rpm torque the engine will make. Top end power may increase slightly.

The length of the collector should be tested on dyno for best length to maximize torque. Once this is a know length, you can run it open or add a torque cancellation box and then continue with exhaust pipe to where ever you want to end the system.

If you want to add a muffler, the muffler itself must flow at least 1.2 the amount of cfm flow as the HP the engine makes in HP.
I suggest a center in and out muffler for the path of least resistance. This should very well create a zero loss exhaust system.

A car that runs 12’s is kind of broad. High 12’a or low 12’s?
In general, getting into the 12’s requires approximately 400hp.
Search for a muffler that flows a minimum of 400+ cfm. Then pick up a pair for the car.

AFAIK, or remember, there isn’t a turbo muffler on the market that flows 400 cfm. Perhaps dynomax?
Hookers Aero Chamber flows 441.
AFAIK, the straight through glass pack style muffler like ghe Hooker or Dynomax “Max Flo” mufflers are able to move 1,000 cfm.
Rat Bastid said:
If an exhaust box is a muffler then no, you don’t need that.

You need a 36 inch collector extension.

If an exhaust box isn’t a muffler then I haven’t a clue what the hell we are talking about.
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The exhaust box, IMO, of which he is talking about is a pressure wave cancellation box.

I don’t know how you come up with a blanket statement or needing a 36” collector extension. The extension length should be dyno tested. It will vary in length per each engine tested due to changing perameters of each engine. Ending with the header used.
 
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rumblefish360 said:
From the header, where the 4 tubes connect is called the collector. From here, the length of the collector will dictate the amount of low rpm torque the engine will make. Top end power may increase slightly.

The length of the collector should be tested on dyno for best length to maximize torque. Once this is a know length, you can run it open or add a torque cancellation box and then continue with exhaust pipe to where ever you want to end the system.

If you want to add a muffler, the muffler itself must flow at least 1.2 the amount of cfm flow as the HP the engine makes in HP.
I suggest a center in and out muffler for the path of least resistance. This should very well create a zero loss exhaust system.

A car that runs 12’s is kind of broad. High 12’a or low 12’s?
In general, getting into the 12’s requires approximately 400hp.
Search for a muffler that flows a minimum of 400+ cfm. Then pick up a pair for the car.

AFAIK, or remember, there isn’t a turbo muffler on the market that flows 400 cfm. Perhaps dynomax?
Hookers Aero Chamber flows 441.
AFAIK, the straight through glass pack style muffler like ghe Hooker or Dynomax “Max Flo” mufflers are able to move 1,000 cfm.

The exhaust box, IMO, of which he is talking about is a pressure wave cancellation box.

I don’t know how you come up with a blanket statement or needing a 36” collector extension. The extension length should be dyno tested. It will vary in length per each engine tested due to changing perameters of each engine. Ending with the header used.
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Because it’s easier to cut some off than to add some. Plus, all the testing I did at the track (will do some dyno testing of this stuff when my junker goes on the pump) showed that going under 18 inches almost always hurt 60 foot times and I never really found any loss at 42 inches.
 
Rat Bastid said:
Because it’s easier to cut some off than to add some. Plus, all the testing I did at the track (will do some dyno testing of this stuff when my junker goes on the pump) showed that going under 18 inches almost always hurt 60 foot times and I never really found any loss at 42 inches.
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It’s per header size and combination of the engine and now that you have it in the car, at the track is good, the dyno is great, but a blanket statement is not good.

To add to the mix of parameters you stated less than 18 inches is bad seems to apply to a certain set up and not all or even many. This is a very particular move when it comes to length of exhaust header extension pipe.

Some engines are numb, others very cranky over the pipe length.

When your engine hits the lie detector, IF you can, if you have another set of headers, swap them out and I’ll bet there is a change in header collector length for each header on the same engine.

I don’t see very often this being done. The few times I have seen it only leaves me baffled and above I stated why. The only time I can actually say, this XX length of pipe is what will work is because this is what the racer has done and it’s ether a track tested or dyno proven move. Otherwise I have to say, test it.

No one parameter has stood out except there is a benefit to running a header extension pipe most of the time of some length. I can say I have seen a trend.

The only place I can point to is the “Engine Masters” TV show with Freiburger/Dulchich/Brulè when they did this test. The headers used were dinky 1-5/8 & 1-3/4. Header extension pipe lengths were very different between the two headers on the same engine.

This is what David Vizard discusses in his book and on a on line video which you can find easy enough I think. He goes into header collector pipe extensions, pressure wave cancellation boxes & the rest of the exhaust system.



When time allows at my son in laws shop, we are working on my ‘79 Magnum. The exhaust is half way done. It’ll be done when it’s done since he has to make money first and service his clients needs. He has commercial accounts and average Jane and Joe’s walking through the door. So…. When he has time and is t dead tired from the week……

I’ll make a video on it.
 
My car is a street/strip deal and has been 6.25 @ 110 with the exhaust off, probably 50-60 pounds. The exhaust is 3" with mandrel bends, and dumps at the rear axle with Pypes SS Race Pro's.

The last race it ran was a street car deal so I ran it with the exhaust on. The boards were off and we weren't supposed to get a time slip. Someone screwed up and they gave us out time slips during the first round. My car ran 6.33 @ 109 on what I didn't think was a great pass. The second round it made a very good lick and I feel like it probably ran very low .20's but didn't get a slip.

A good exhaust system will slow a car very little. Having said that, my 60' is always slower with the exhaust on.
 
I'd tune for what ya got... I like to see 12.5 @ WOT... I'll live if I see 12.4...
 
If my car was faster uncorked (and I would be surprised if it is) I think it will be because of the weight difference of removing the exhaust.
I would use the 18"header extensions that came with the headers when I bought them.
 
Thanks to Dana67, Rat, 33Imp, Oldmanmopar, Rumblefish (Rob) and Justin for taking time to post.
It was after watching the Engine Masters cut out episode that prompted me to open up the cut outs to see how much better it would run without exhausts. My lack of knowledge meant that I never thought it would cause the engine to run lean (or lose power)
My plan now having read all of the replies is to install AFR gauges on both banks, run 42" long pipes and a pair of straight through mufflers at the end.
Looking at the Duster pictures posted by Oldmanmopar, I will probably fit an H pipe as well.
Really appreciate all your replies.
 
and thanks to j par (who I missed in the previous post) I realise now how important what the AFR is a WOT
 
My car is a bracket car only, it never sees any street time. I have multiple length collector extensions that I swap around according to the weather and track conditions. There are going to be nay sayers out there who disagree with me, but I know what works for ME. Everyone has their own ideas and things that work for them. Try your car out multiple ways and see what works best for you.
 
The "S" bends coming off the headers were made by using 4 turn downs bought through summit. I slipped on on the header and clocked them then added another backwards. You can clock them to fit through the torsion bar cross member exhaust indents. They are the same as the turn downs coming off the mufflers. So I used 6 total on the exhaust. The 3 1/2 exhaust slips on and off the headers and the "S" easy. No clamps they are bolted together using tabs facing opposite directions with hole for 1/4 20 bolts. We were able to remove and add different length pipes after the "S" The car ran faster times with the full exhaust. 829 at the crank at 7900 RPMs using a 950 quick fuel on the dyno. The car picked up changing to a 1050 quick fuel.

The exhaust is off the car since the car was totaled in an accident and is not being reused on the new car. The headers are 2" tube hookers and have a damaged tube from the accident . The new car is getting 2 1/4 zoomies exiting the front fender for a alcohol/nitro mix engine.

The complete exhaust with the tail pipes and tips with hangers are for a mini tubbed 108 WB car . I have adapters for standard heads , W2 Heads , Batten or Indy heads . So this exhaust was used on different engine combos.

 
Markh said:
and thanks to j par (who I missed in the previous post) I realise now how important what the AFR is a WOT
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Remember the AF gauge isn't the end all just a tool. Reading your plugs is very important...
Also remember that atmospheric pressure of the day... I remember one day at the track I was just off by half second no matter what I did and come to find out it was really bad air that day...
Who would have though....
 
Markh said:
Thanks to Dana67, Rat, 33Imp, Oldmanmopar, Rumblefish (Rob) and Justin for taking time to post.
It was after watching the Engine Masters cut out episode that prompted me to open up the cut outs to see how much better it would run without exhausts. My lack of knowledge meant that I never thought it would cause the engine to run lean (or lose power)
My plan now having read all of the replies is to install AFR gauges on both banks, run 42" long pipes and a pair of straight through mufflers at the end.
Looking at the Duster pictures posted by Oldmanmopar, I will probably fit an H pipe as well.
Really appreciate all your replies.
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You did notice in that enginemasters episode that Freiburger admitted that he choked that motor with the mufflers/exhaust he chose? (Presumably to make the cutouts look good. In their 1000hp muffler test, they had one setup that MADE power, over uncorked! ).
 
Saw a guy racing a 67 El Camino a few years back, with an iron head rat. I was told race weight at the starting line was 4300 lbs. Didn't believe it, till I saw the driver get out. 450-500 lbs. Not sayin...but....LOL.
 
pittsburghracer said:
How the heck did you get a duster to weigh 3850 pounds. Cheese n rice.
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Well every option the car came with was in the car it was loaded minus air. It was all original metal no glass parts. Complete mild steel cage took 2 of us to carry it without the swing outs or rear down tubes. Large after market stereo with 4 huge magnets. Heavy wall 3 1/2 inch exhaust with mufflers and tail pipes. Full factory bucket seat interior. Every hose was braided . . Oil and Trans coolers. Stabilizer bar still in place. Trunk mat and spare with jack in trunk.

And most important if you look I said with driver. You never asked me what my son or I weighed. He is 6'4" around 240. I am just a tad rounder. If you look close at the one video you can see it is turning the tires through second. It did not hook on the feathered street driven tires.

The new car will be very light all chrome moly steel we are only using the roof ,firewall, and quarters, AJE front race suspension with Strange light weight brakes. The rest from glass tech. The engine now will be all alluminum, Titanium, internals except for the light weight crank. Ordered the titanium valves tonight they are on sale right now $140.00 each. Everything else is here
 
Oldmanmopar said:
Well every option the car came with was in the car it was loaded minus air. It was all original metal no glass parts. Complete mild steel cage took 2 of us to carry it without the swing outs or rear down tubes. Large after market stereo with 4 huge magnets. Heavy wall 3 1/2 inch exhaust with mufflers and tail pipes. Full factory bucket seat interior. Every hose was braided . . Oil and Trans coolers. Stabilizer bar still in place. Trunk mat and spare with jack in trunk.

And most important if you look I said with driver. You never asked me what my son or I weighed. He is 6'4" around 240. I am just a tad rounder. If you look close at the one video you can see it is turning the tires through second. It did not hook on the feathered street driven tires.

The new car will be very light all chrome moly steel we are only using the roof ,firewall, and quarters, AJE front race suspension with Strange light weight brakes. The rest from glass tech. The engine now will be all alluminum, Titanium, internals except for the light weight crank. Ordered the titanium valves tonight they are on sale right now $140.00 each. Everything else is here
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My buddies street duster with a 440, Pa sticker, cage, steel everything but hood, stock glass, heater, stock trunk annd wheel wells, inner fenders in the car, stock suspension with super stock springs, and 250 pound body was a hair under 3500.
 
pittsburghracer said:
My buddies street duster with a 440, Pa sticker, cage, steel everything but hood, stock glass, heater, stock trunk annd wheel wells, inner fenders in the car, stock suspension with super stock springs, and 250 pound body was a hair under 3500.
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All I can tell you is that is what it weigh when I drove it over the scale at the track. From what I remember my 70 Duster original 340 auto car weighed a tad over 3200 No cage or options . I know My orange 71 Duster was quite heavy. Add ons and all the options add up quick.
 
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