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Author Topic: exhaust diameter  (Read 17642 times)
caddycarlo
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« Reply #15 on: January 30, 2008, 11:33:40 PM »

Also how much pressure is there pushing the exhaust through the pipe. Seems this would allow for a smaller diameter


 I have heard in the past that you could see as much as 3 lbs at the point where the tube meets the head ......... so I drilled a small hole and hooked up a pressure gauge to a line and taped it to the windshild ........ I then drove the car all out thu the first three gears while someone watched the gauge ........ this was with 1 3/4 tubes and 4 inch ex and motor and blower ( so a far anout of hp) full load ......... we saw 0 pressure ....... none at all .......... I have sence got a better guage that is only a few lbs and reads in tenth of a lb to try again ........I know it has to have some pressure but I do not think it is much .............


I almost forgot the other part ........ you do not want to forse the airspeed up by going to a smaller tube as to make a higher airspeed will take more pressure at the start of the tube and this pressure will leave ex gas behind ......... though I have seen gains in low rpm hp with smaller tubes it has always cost the engine in high end power .........
« Last Edit: January 30, 2008, 11:37:47 PM by caddycarlo » Logged
caddycarlo
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« Reply #16 on: January 30, 2008, 11:39:00 PM »



Taking CC's example of 3.5" dia collector,  A=9.621 sq in  x  115 cfm/sq in  =

1106.43 cfm  /  2.2 cfm/hp  =  503 hp  is what a 3.5 " pipe will flow with zero

loss. 

More hp needs a larger pipe dia.

where does the 2.2 cfm/hp come from is that vissard ?
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Nick Campagna
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Posts: 180



« Reply #17 on: January 31, 2008, 03:30:26 AM »

    I agree that the pulses in a std 'non-180deg' header are not uniform in time. That is the first place the peas in a straw breaks down. It is just a vehicle to get an idea of what is going on while the pulses are still contained. Dissipation of the pulses can be accelerated by the use of a slow increasing taper to the pipe. This whole design is not an easy simple model, I just wanted to point out that the sum of all areas of the 4 pipes is probably too big for a single exhaust pipe. Like having a 10 foot collector length. Merge collectors and longer exhaust might be the answer.

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Is the defect in what I see, or in what I'm seeing with ?
MTS Marty
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Posts: 282


« Reply #18 on: January 31, 2008, 08:21:15 AM »

I think the pressure, or lack there of is an indication of a free flowing proper exhaust system. There must be pressure at the exhaust valve opening and the head port when the valve is opening and the burnt gasses are being pushed out. At that point a smaller cross section is needed. Also downstream the gasses begin to cool and take up less volumn. Not sure how to figure all this into a standard equation 
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sMiles
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Posts: 321


« Reply #19 on: January 31, 2008, 08:33:41 AM »


I can't devote the time to reread all I have posted links to,  but,  the SuperChevy link states the 2.2cfm/hp (Vizard) and the DynoMax link corroborates this if you take the values on the right side of the page and work backwards in the math.

Vizard states the 2.2 # is a functional rule of thumb guide (my words) covering all but 1% of engine data examples used.

When I was at PRI I spoke with the Flowmax crew regarding my exhaust sys and they also acknowledged the 2.2 cfm/hp as a valid guide in choosing pipe dia and muffler flow in a system to achieve zero loss.  

In addition to cfm considerations,  dB levels are lower with greater muffler case volumes and the use of resonator boxes in a zero loss system.   Larger than necessary pipe diameters create increased dB levels

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sMiles
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Posts: 321


« Reply #20 on: January 31, 2008, 09:01:47 AM »

I think the pressure, or lack there of is an indication of a free flowing proper exhaust system. There must be pressure at the exhaust valve opening and the head port when the valve is opening and the burnt gasses are being pushed out. At that point a smaller cross section is needed. Also downstream the gasses begin to cool and take up less volumn. Not sure how to figure all this into a standard equation 

The Speedtalk links provide considerable discussion by exhaust pros internationally.   I recall one stating, in a tuned header system without muffler, there MAY be an advantage in using a primary pipe area 10% smaller than the port area.  This only applies in a tuned system anticipating a negative pressure wave return at a specific time (affected by pipe dia and length) when the valve events allow its scavage effect.

With your blower engine, the tuned header exhaust system offers no advantage since it is pressurized.   The first link in my post discusses Log exhaust manifold systems characteristics that would apply to your Nash build but not as favorably to a turbo system (not constant pressure).

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caddycarlo
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« Reply #21 on: January 31, 2008, 09:28:21 AM »

I was just rereading the first speedtalk one on the log manafold .........  kind of makes you wonder .......... I have run the car with 4 inch ex and N/A  .............. two things running thu my mind   .............. one if a properly sized ex helps make hp then why do most cars speed up when you take the ex off even with a 350 engine and duel 2.5 ex ?    and also in that on both my car with the 4 inch and my buddys johns with a blown sbc and 3 inch ex when you now take off the ex system the car slows down .... john even fussed with timing and jetting to no avail ........ he then added resonators ( due to new local sound level laws ) and it all changed now droping the ex helped to the point that he has added electric cutouts .........  so I agree that the system can be tuned to help but I think from what I have seen that the tuned size is bigger then you think ........

second thought is about flash ........ when I was looking at his headers for the first time I was awe struck as he runs 2 3/8 header tubes ........ when I asked he said he wanted to go to 2 1/5 inch but was not sure he could get  it to fit .............. when I said something about 2 3/8 being to big he laffed and said he has had a bunch of headers on the car with each one being bigger and that in each step he went faster ...........


I my SBC stuff I have run some big headders and not felt like they helped at all and have even gone smaller and picked up et ....... but every time I have gone bigger on the rest of the ex system it has helped ........... so what is it that effects what the ex system wants ? and the only thing I can think of the the opening point of the ex valve and the blow down of the cyl before you get to BDC ...... if you blow down early like I tend to do then I think it changes what you need in an ex system .......


as a side note my 1 3/4 headder on the monte has only a 3 inch collector then I go up to 4 inch pipe ........ I was going to make some 2 inch headders with a 4 inch collector for the new engine but I think know I will test it first then do the new system then test it again and see what happens ............................
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sMiles
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Posts: 321


« Reply #22 on: January 31, 2008, 12:19:24 PM »


If removal of the ex sys after the collector results in improved performance I think it points to a sys with a flow restriction after that junction. The muffler itself (flow not pipe size), a change in tail pipe dia, or restricted bends in the piping, and, in some sys, the length of the sys to open end (causing the arrival of the negative pressure wave return to the comb chamber at wrong time relative to valve events, preventing its scavage effect).

In the second case of your sys and Johns,  the as installed dimensions and flow of the total sys shows it is giving the intended effects.  Johns resonator addition changed the equation .. if the resonator was simply another 'muffler without guts' design without sufficient interior volume and the junction of the piping into the resonator was not as discribed in the links (see the pictures in the SuperChevy link),   this would tend to degrade the sys performance.

Flash's sys may be responding as it is due to the length of the sys remaining unchanged and the only the dia changing .. the negative wave form returning to the cylinder is arriving at a increasingly opportune time relative to the valve events with each increase in primary pipe size dia.  Can you be confident that the only change made is in the header design ?

On your sbc stuff .. what you have written seems consistant with the info in the links above.   I particularly like the Log Manifold thread logic, even N/A, since my car is street/long cruiser use and I want quiet quiet not just legal quiet system.   I am designing a 5" log with 8" primaries that stick into the log 2" and dump straight in.   The log is 20" long,  attaches to a collector pipe 5" dia on the log end tapering to 3.5" over a 36" length to attach to a muffler with a case 8.25 x 11.5 x 25" having a 3.5" exit pipe size.   This sys will give max blow down, minimum/no return wave, no sys length sensitivity, max volume for sound reduction.   The total volume will exceed 11 x the displacement of the engine, 496ci.

Your Monte sys sees the 4" as a 24% larger resonator, particularly if you have projected the 3" past the connection with the 4" (see the pics in the first link).
If you haven't done this I hope you will do this after you baseline test the existing sys and retest to see the comparison.  Which brings me to .. my ex ports are 1.5 x 1.625 or 9.75 sq in.    If i were to try the 10% smaller logic, the ID of the pipe needs to be 1.67", after measureing several common ex pipe sizes,  the 1 7/8" OD pipe is very close to this ID.  I was surprised to find that 1.75" was to small for my needs even at a 10% smaller size.  The 2" pipe covers the ex port shape and dimension.   On the log header I may go to the 2" primary as it also fits the flange opening nicely.   A 2" on your sys will have an equal tot sq in primary tube area as does the 4" collector per bank of cylinders.

I am simply sharing my thoughts, logic. and understanding of this complicted subject .. thanks for listening ..

Miles

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caddycarlo
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« Reply #23 on: January 31, 2008, 01:39:31 PM »

I agree with what you have said ........... and like you some of what I have posted is just me thinking aloud ............... most systems that make loud debates on forums are very comlicated subjects that we attempt to simply enough to make better chooses on parts and sometime it works and other times something else is changed and then it does not work ............ and without a great deal of testing it is hard to say if what we beleve is "the" truth ...........

I also liked how the 2 inch pipe fit the port which is why I desided to go with that size on my new headers rather then the 1 3/4 inch that has been on the car for 20 years ..... either way I have to make new ones before long ......... but I felt when I made these that I had to heat and stretch the tube to make a good joint ......... I have also played with the idea of some steps and or anti revertion ...... and yes I liked the area match of 4 2 inch tubes and a 4 inch tube


I could make a add on 3 inch pipe that I could test same day as a bolt in if it was not too long ...... what do you think the min length should be ?

also does anyone have any ideas for an exit at the bumper for a 4 inch tube as stright does not look right ...........


one thing I ran across what this ........ yes two stroke stuff.......





http://wikiscootia.wikidot.com/expansion-chamber
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Stiney
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Posts: 114



« Reply #24 on: January 31, 2008, 02:17:45 PM »

I found this interesting....


"What is REALLY interesting is the "pressure wave termination box" (or resonator box). What this is is a large volume box (muffler, empty, etc.) that is at least 8 times the volume of one of the engines cylinders. In the V8 case, as large as the engine displacement! It's inlet pipe extends into the box, and the end of the pipe is the end of the collector that the open header would have for best performance. What this does is make the rest of the exhaust system virtually have no effect (pressure wave wise) on the headers. If you have little backpressure behind the resonator box (piping, muffflers, tailpipes, etc.) the engine will lose no power. Without this box, the rest of the exhaust just causes the collector to get REALLY long, as far as the engine/header combo is concerned."


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dave brode
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Best of 11.66, 113.96, 1.59 sixty


« Reply #25 on: January 31, 2008, 02:23:48 PM »



also does anyone have any ideas for an exit at the bumper for a 4 inch tube as stright does not look right ...........



Hi Scott,

Fabricated from mandrel bend tailpipes, I assume? Can you tuck it up into the chassis at the rear? If so, you could cut a tight bend, sliced off and hook them down like a stock tailpipe. Might not hurt flow much.

Dave
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3960 lb '71 C-10. 11.7-1 CR 514". PEP I beam rods floating MTS 18cc dish Probes, Elgin solid cam, home ported heads, MTS 2.19/1.84", Potter/Probe shaft rockers, edel 2115, 4781 850. Switch-pitch TH400, 12" 1800/3200 Tri-Shield convertor, 4.30 gears. Best so far of 11.66, 114.8 mph and 1.59 sixty
sMiles
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Posts: 321


« Reply #26 on: January 31, 2008, 03:09:03 PM »

http://www.superchevy.com/technical/engines_drivetrain/exhaust/0505phr_exh/photo_20.html

This pic shows the relationship of the parts.  I seem to remember the inlet pipe needs to extend in past the nearest end wall of the case, whether its a muffler or a resonator, and the inlet/outlet pipe size needs to be an inch larger than the incoming pipe dia., the bell mouth adaptors are important design element.

The 4" tube at the back can be turned down 45* and cut off parallel with the  ground,  angle the pipe to the rear corners turning the end down 45* and cut off.   

Something fabricated:  two lengths of 4" ,  bend two close 45's in the same plane ("S"),   cut in half length wise,  take one side from each and give to the other,  turn cut edges to each other,  weld together & fill in vacancies,  one end fits to tail pipe , bumper end is rectangular 2" x ?" opening.   I could be all wet on this one ..

Stiney ... where did that quote come from ?
« Last Edit: February 02, 2008, 08:16:07 PM by sMiles » Logged
caddycarlo
Guest
« Reply #27 on: January 31, 2008, 03:12:00 PM »


Dave
I will try to get a picture to help but I was trying to get away from the turndowns becouse our track has a lot of dirt and it just turns it up from the flow and I get dust everywhere and also I am getting old so I thought I would put a radio in the car and so I wanted to dump the sound out away from the underside of the car ...................
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caddycarlo
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« Reply #28 on: January 31, 2008, 03:18:40 PM »

I have seen that before and when I did my truck I took the cats and dumped the insides out and pushed the pipe in like in the picture the added an x pipe after the cats after that was the edebrock mufflers I was running and then a y pipe and a stock single tail .......... and now it drives like it is open header and is just as quiet as a stocker it worked great ................. much better then the edebrocks with no cats and a duel exit
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sMiles
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Posts: 321


« Reply #29 on: February 02, 2008, 08:15:06 PM »

Thats great to know, CC,  since the sys has similarity to my plan.  The very low noise level is the goal.   The 'Y' pipe and the single pipe .. did you increase the tail pipe dia after the junction ?   I'm thinking it would look cool to have only one tail pipe .. more in keeping with the  '47 vintage.

When I suggested the 45* turn down, I should add the cut is parallel to and at the same level as the bottom of the tail pipe,  no downward dimension.

« Last Edit: February 02, 2008, 08:25:42 PM by sMiles » Logged
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