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Exhaust Tube Sizing: I did your Arithmetic for you!!


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#41 Justinp551

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Posted 22 February 2012 - 02:58 PM

Interesting solution. I like it. When I get the car together and running smoothly I will build a 2.5" to 3" exhaust and post dyne results back to back. Thanks for the idea Leon. I have come across the megaphone idea on a few different threads. Will research it a bit further.

#42 Justinp551

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Posted 22 February 2012 - 03:07 PM

And best place to find a 13" 2.5" to 3" megaphone?

#43 Leon

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Posted 22 February 2012 - 03:21 PM

Interesting solution. I like it. When I get the car together and running smoothly I will build a 2.5" to 3" exhaust and post dyne results back to back. Thanks for the idea Leon. I have come across the megaphone idea on a few different threads. Will research it a bit further.

No problem. Some dyno results would be great!

And best place to find a 13" 2.5" to 3" megaphone?

I've used Burns Stainless in the past, check their site.

You can have a custom one made, cut up an existing one, or make it yourself. For option 2, you can buy one that has too small of an inlet and/or too big of an outlet, do some quick math, and cut them to size.

#44 1 tuff z

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Posted 22 February 2012 - 04:06 PM

Mild or ss, check cone engineering, here is a link to their transitions / cones pdf, inexpensive...

And best place to find a 13" 2.5" to 3" megaphone?


David
"A lot of people go through life doing things badly.  Racing's important to men who do it well.  When you're racing, it... it's life.  Anything that happens before or after... is just waiting."  1971 film "Le Mans"  driver Michael Delaney, played by Steve McQueen


#45 Justinp551

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Posted 22 February 2012 - 08:29 PM

Thanks for the input guys. John C's pic of the megaphone stated 13". And suggestions on a more desired length?

#46 johnc

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Posted 23 February 2012 - 07:55 AM

That was just an example picture. 13" is not a hard and fast number and I actually don't know the proper length for an open megaphone on a L6 engine. Never built one.
----- John Coffey, Fabricator at Benton Performance, LLC

#47 BluDestiny

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Posted 23 February 2012 - 08:50 AM

If you want full 3in, just cut the MSA header back. It transitions from 3" to 2.5" really roughly
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#48 Leon

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Posted 23 February 2012 - 11:30 AM

Thanks for the input guys. John C's pic of the megaphone stated 13". And suggestions on a more desired length?


That was just an example picture. 13" is not a hard and fast number and I actually don't know the proper length for an open megaphone on a L6 engine. Never built one.

Furthermore, the proper length for one guy is not necessarily the proper one for the next. In order to properly size your megaphone, you must take into account the causalities posted in this thread (longer megaphone = wider bandwidth/smaller magnitude, and vice versa) as well as perform resonance calculations, taking into account gas temps, pipe diameter, valve timing, etc. This, along with your goals (location and width of powerband) will determine megaphone size and location.

Of course, you can always say the hell with it, and slap it in there. Just don't expect to get exactly what you want.

#49 Justinp551

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Posted 23 February 2012 - 11:49 AM

Oh boy in over me head now. Haha. Just looking to make the exhaust as efficient as practical without using a race team budget. Fresh N42 combo with CAI and small increase in cam. Cleaned up and refreshed n42 head w/ MSA 6-1 headers. Stock FI. I understand the theory of the megaphone and am all for fabbing it. 2.5 to 3" megaphone- With that small of a step... What general length should I be considering. Leon I understand the different requirements on desired performance. Just looking for that "general" recommendation if one exists. 

#50 Leon

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Posted 23 February 2012 - 12:28 PM

I'll reiterate the generalizations, from which you can then approximate "where" and "how big". Longer means you get a boost over a longer range of rpm, but at the same time it decreases the amount of extra torque. A bigger difference in inlet/outlet diameters will increase the effect, but since you have already set your inlet and outlet diameters, then you can't do anything with that. Placing the megaphone upstream shifts its powerband influence to higher rpm, and placing it further downstream shifts its influence to lower rpm.

Now, if you want take the suggestions given in David's (1 tuff z) link, they imply that a 9 degree transition is a good compromise. Whether that's true or not is up to interpretation, but it's a start. Given that you're not going to be doing testing of different exhaust combinations, I think it's safe to say that you'll be in the 7-9 degree range.

If you do the math, the length comes out to about 1.6 inches for a 9 degree taper, if I did that correctly.

Edited by Leon, 23 February 2012 - 12:30 PM.


#51 Justinp551

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Posted 23 February 2012 - 01:43 PM

Thanks Leon. That was the info I was looking for. Thanks for the additional theory info as well.

#52 vega

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Posted 22 April 2012 - 07:44 PM

What about trying to achieve a specific sound? The affect of an H pipe, the affect of an X pipe, chambered muffler vs straight through.

Any thoughts on these links?

http://victorylibrar...ader-tech-c.htm

http://www.bgsoflex....bestheader.html

Is it possible to "tune" the exhaust so that the v8 will sound like a v6? I think so to a point based on the configuration. From what I can tell the 4.3 vs the 5.7 sbc will sound the same with the correct exhaust seeing that a 4.3 is a 5.7 with 2 cyl lopped off. The difference I have found is the larger displacement tends to create a deeper tone.

example;

vs


They give off a similar type of exhaust tone BUT the v8 5.0 is just simply deeper.

That in mind what would one need to make a sbc sound like that 5.0? short headers, and h pipe and a particular muffler? To me it sounded like he used an x pipe because it sounded as if the pulses were equaled out. Seeing that an H pipe was used I would assume that the LSA on the cam was higher in the 112-115+ range making the vehicle idle better.

Personally I am attempting to find the smallest diameter primaries I can use until it chokes the engine, also I am curious on if my plan to use shorter headers for sound alone is going to dis-benefit my motor. The header I found has equal length primaries at 17.5 inches which according to the headers by ed equation is too short with a 1 5/8s inch diameter primary (assuming 1 5/8s inch primaries are as small as I can go with out choking the motor). The recommended size is 34 inches.

The motor is a 333ci motor, 195cc intake ports, team g single plane manifold, the cam will run from 2300rpm-6900rpm.

Any thoughts or suggestions there?

Btw great thread learned more by reading these three pages than I have for the past 3 weeks on the subject.
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#53 Leon

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Posted 10 September 2012 - 08:18 AM

Dyno Testing a 260Z - Part 2

This is an analysis based on my dyno testing from yesterday (9-8-12).

Test Parameters


The reason behind testing was to baseline the Nissan Motorsports header/dual pipe exhaust against the stock manifold/single 2.5" that I baselined on page 2. Also tested was the same setup with advanced (from stock) timing, then with air cleaners removed, and finally with EDIS/Megajolt controlling ignition.

The settings are as follows:

  • early 260Z with 1972 L24/E88 that was installed by the previous owner
  • stock cam and internals
  • triple 40DCOE-18 Weber carbs with K&N-style filters (no heat shield)
  • Cannon long-runner manifold
  • Nissan Motorsports header with crush-bent true dual 2" pipes
  • Mobil1 synthetic 10W-30 in engine, Redline 75W-90 in transmission (GL-4) and differential (GL-5)
  • Stock 260Z distributor or Ford EDIS run by Megajolt for ignition
Testing was done at Dito's Motors in South San Francisco on a Dynomite load-bearing dyno. Robert and David are great guys to work with!

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Test Settings: Same as page 2, but with a Nissan Motorsport header and 2" twice pipes

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http://www.youtube.com/watch?v=36GsOl_Q45M&list=UUmNR_gGDK0GX_MagE8szLJA&index=2&feature=plcp

Results:

SOLID lines are the initial baseline
DOTTED lines show the new exhaust

Attached File  Dyno Plot.png   44.43KB   68 downloads


The new setup made a peak of 130.5lb-ft @ 3350rpm and 115.8hp @ 5600 rpm, compared to the initial baseline of 136.3lb-ft @ 4100rpm and 120.8hp @ 5150rpm.

Analysis

The results are not unexpected, the single 2.5" did better than the separate duals. It is worth to note that the Nissan Motorsport header brought the torque peak down by about 750rpm when compared to the stock manifold and 2.5 pipe setup! This is caused by the header's very long primaries. The powerband feels like a mini-V8, gobs of torque down low, but still likes to rev. However, mid-range torque took a definite hit.

Final Thoughts


The twice pipe system does not have a merge collector, which would give gains across the board. Integrating a merge collector can also shift and improve the torque peak.
The next iteration of the engine will be jetting the carbs (more for partial throttle cruise, WOT AFR is 11-12), putting in a more aggressive cam to take advantage of the header and to let the engine breathe better at higher rpm. I'd also like to build a single-pipe system utilizing this header. Eventually, I will build up an L28 to drop in.

Other Notable Data (not exhaust related):
  • Advancing distributor timing gave peak gains of 2.1lb-ft (132.6lb-ft) and 4.3 hp (120.1hp)
  • Removing the dirty air cleaners gave additional gains of 3.4lb-ft (136.0lb-ft) and 4.2hp (124.3hp)
  • Using EDIS/Megajolt to tune the spark curve gave another additional 4.4lb-ft (140.4lb-ft) and 3.6hp (127.9hp)


#54 madkaw

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Posted 10 September 2012 - 09:33 AM

Leon,
Are you saying you were 11-12 AFR's WOT on this pull?
Seems a bit rich-losing a bit of HP there?
Don't give the up the duals man!
Steve,
9/71 240z. 2.4 -.40 over, balanced. E-88 Bigger SS valves, stage 2, 6x2 header, true dual exhaust. BW t-5 , STI LSD 3.90- triple Mikunis 40mm

#55 Leon

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Posted 10 September 2012 - 10:12 AM

Leon,
Are you saying you were 11-12 AFR's WOT on this pull?
Seems a bit rich-losing a bit of HP there?
Don't give the up the duals man!

Yeah, a bit rich so I'm probably losing a few more horses. I'll try to rejet for 12.5-13:1 AFR and see where it gets me.

Don't worry, the duals will stay for now!140lb-ft at 3500rpm from an L24 on an load-bearing dyno is pretty healthy, nonetheless.:D




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