Shooter63
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| posted on 1/9/16 at 05:36 PM |
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Diy exhaust manifold
After getting some wild prices to make an exhaust manifold I'm thinking of making one, some of the manifolds I've seen seem to use
different size tube within the pipe run ie start at 47mm diameter then half way to the collector increase to 50mm. Can anybody tell me the idea
behind it, as I presume it's a gas speed thing. The plan is to make a 4-1 by the way.
Shooter
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Talon Motorsport
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| posted on 1/9/16 at 06:04 PM |
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The arguments about exhaust design started with the first internal combustion engine and will probably run till the end of time .......there now
follows the can of worms and about 100 posts on the matter.
I would say buy a CNC laser cut manifold plate and then just buy 40-42mm pre bent tubes and just make it fit the car rather than worry about
performance too much.
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Jimbo77
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| posted on 1/9/16 at 06:14 PM |
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I'm no expert but I think the increase in pipe diameter would be to reduce the exhaust gas pressure and therefore reduce the temperature. I
couldn't say why that would be needed though!
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mark chandler
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| posted on 1/9/16 at 06:19 PM |
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^^^^^
As above, the car is simply to short to allow you to follow the calculations, get a handful of 1 1/4" or 1 1/2" mandrel bends and make
something that looks useful, knock up a nice collector and drop into your silencer.
Here's some pictures where I made up a turbo manifold
https://get.google.com/albumarchive/102680160261680183167/album/AF1QipNxT94cbJPGxU-hvKzMZRf5t3Kg9Dl4Bgi6QcUF
You have to watch your assembly order to ensure you can access all the bits to weld up, building the collector like this welding from the inside then
cladding allows you to weld the tubes, separately then bring it all together.
[Edited on 1/9/16 by mark chandler]
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SPYDER
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| posted on 1/9/16 at 07:36 PM |
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There could be another reason for a step-up in diameter.
When I made my manifold I deliberately had a step up so that the end of first bend could slip
inside the next part. It all holds together for welding and no butt welds.
I made a wooden jig which mimicked the head flange and collector to aid fabrication.
1 3/4" going up to 1 7/8" into the collector.
Rather than make a proper merge collector I bought an ex R400 one off ebay for £40.
Yes, I know the primaries are rather short and the pipe lengths aren't the same.
Available space was the major factor.
It doesn't seem to be causing a problem.
There are 1 1/2" collectors on ebay for less than £40!! 252502348017
A pronounced step can inhibit "pulse reversion". Apparently.
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Rocket_Rabbit
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| posted on 1/9/16 at 08:11 PM |
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quote:
Originally posted by SPYDER
A pronounced step can inhibit "pulse reversion". Apparently.
It certainly does. I am currently about 20-25bhp down on my F20C thanks to a 4-2 then immediately a 2-1 after it. This is giving the pukse reversion
you speak of and 10% power just gone!
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SPYDER
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| posted on 1/9/16 at 08:29 PM |
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Anti reversion manifold
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SPYDER
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| posted on 1/9/16 at 08:36 PM |
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Strange, isn't it, that most designs try to use the pulses and go to great lengths (geddit?) to capitalise on the effect of the reflected pulse
but others are trying to prevent them!
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ken555
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| posted on 1/9/16 at 09:07 PM |
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quote:
Originally posted by SPYDER
Strange, isn't it, that most designs try to use the pulses and go to great lengths (geddit?) to capitalise on the effect of the reflected pulse
but others are trying to prevent them!
Then there are us with mini siamesed exhaust ports !
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coyoteboy
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| posted on 2/9/16 at 08:43 PM |
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Cursory thought is that reversion is just the anti-effect of wave tuned headers (or badly sized ones) and is heavily dependant on valve
timing/duration. In the ideal situation you time your negative pulse to match the exhaust and intake timing to help draw additional air into the cyl
(or at least better clear it). If you screw that up, or at certain rpm on a well tuned one, the positives will time up and you will push exhaust back
into the cyl and intake. It's all just geometry based. If you can't help the runner lengths, anti reversion steps may help.
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snapper
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| posted on 3/9/16 at 08:15 AM |
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David Vizard experimented with anti reversion stubs
I believe gas reversion and pulse signals whilst linked are different
I did have some calculations done on a manifold I had modified, it was very close to perfect considering the engine/cam combination
I did mistakenly go for a 3" pipe
Apologies for the long post but thanks to Tom from Turbosports forum.
Peak power at 7.3k was optimistic and probably in the middle high 6k
Notice that pipe lengths can vary due to 1st, 2nd, 3rd etc, harmonics
RL31 manifold
Manifold made to suit an RL31 rally cam, 332.5mm intake length and 49.5" exhaust length, the theory works realy well.
Max diameter of inlet port at manifold head face 39.5 mm. Max dimensions of exhaust port at manifold face 35.5mm X 27 mm. …
Bore, 93.045
stroke, 76.95mm
number and size of valves, 8, 4 inlet 44.4mm 4x exhaust standard pinto 36mm 2x valves per cylinder
RPM at which peak power happens. Any ones guess but 7,300 expected
Expected peak power, 170bhp
Camshaft timing etc. 304* inlet 297* exhaust
46/78 74/43
12.7mm lift inlet @ 106* atdc
12.44mm lift exhaust
10.6 to 1 compression
Cosworth rods
V6 cast pistons
1.875" primaries
2.125" secondaries
2.5" system
Calculated dims
Re: Manifold calculations
The output from the second program gives me the following lengths
32.8" primary pipe length
38.5" inches to end of exhaust pipe
Primary diameter = 1.5"
Main exhaust diamter = 2.5"
Tuned Inlet length = 13.2" 335mm
The measurements in both messages are from the manifold face and not to the valve.
The secondary pipe length is very important when developing power and should be considered as nearly as important as the primary length.
Re: Manifold calculations
Hello Paul,
Here are the first calculations that I have done.
The exhaust pipe diameter recommended is 3" which is too big in my opinion and should be 2.5". The primary pipe diameter is 1.487 to 1.612
which you may think is small but this is a good diameter for torque and should work well.
I will send you another message with the output from my second program including the inlet lengths if you are using twin webers or throttle bodies.
Regards
Tom
--- Single Primary Pipe Specs --- for 127.723 CID from 5100 to 7600 RPM
Diameter= 1.487 to 1.612 Length= 29.9 to 32.2 inches long
--- 2-Step Primary Pipe Specs ---
1st Dia. inches= 1.487 Length= 14.9 to 16.1
2nd Dia. inches= 1.612 Length= 14.9 to 16.1
--- 3-Step Primary Pipe Specs ---
1st Dia. inches= 1.487 Length= 10.0 to 10.7
2nd Dia. inches= 1.612 Length= 10.0 to 10.7
3rd Dia. inches= 1.737 Length= 10.0 to 10.7
--- Header Collector Specs (Conventional Straight Tube) ---
Diameter= 3.010 Tuned Lengths= 16.5 best and 8.2 or 32.9
-- Total Exhaust System Tuned Lengths (Primary ends to TailPipe end) --
Best HP/TQ Tuned Collector Lengths= 16.5 , 32.9 , 65.9 , 131.8 inches long
Worst HP/TQ Loss Collector Lengths= 24.7 , 49.4 , 98.8 , 197.7 inches long
Note=> measured from where the Primary Pipes end inside the Collector to
the point the tailpipe exits into the atmosphere.
Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness
---- Primary Pipe's Harmonics ----
1st Harmonic = 129.6 inches long ... typically never used
2nd Harmonic = 49.5 inches long ... longest recommended
3rd Harmonic = 29.9 inches long ... highly recommended , best Torque Curve
4th Harmonic = 21.0 inches long ... shortest recommended
5th Harmonic = 16.0 inches long ... typically never used
6th Harmonic = 12.7 inches long ... typically never used
7th Harmonic = 10.4 inches long ... typically never used
8th Harmonic = 8.7 inches long ... typically never used
---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 131.8 inches long ... longest with Mufflers and TailPipes
2nd Harmonic = 65.9 inches long ... longest recommended with Mufflers
3rd Harmonic = 32.9 inches long ... more bottom-end Torque
4th Harmonic = 16.5 inches long ... highly recommended , best Torque Curve
5th Harmonic = 8.2 inches long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 4.1 inches long ... reduced Torque , not recommended
29.9" to 32.8" x 1.5"
Collector to end 8.3"
Pipe to can 18" overlap 4"
Can 14"
Tail pipe 10"
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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coyoteboy
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| posted on 5/9/16 at 11:58 AM |
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quote:
I believe gas reversion and pulse signals whilst linked are different
I don't believe they are, but I'd be willing to be proved wrong.
Reversion is caused by differential pressures (upstream being lower than downstream), those pressures are caused by the pulses. The pulse timing is
caused by the valve timing and runner length etc.
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