Road race header
11-23-04, 11:00 PM
#1
Road race header
Well, I finally decided that the header my 12a will get is going to be a Racingbeat road race header. The only thing Im not sure about yet is the length of the primaries. I am ordering the header and also a Racingbeat collector and an extra flange but my question is, with the scavenging effect in mind, what is the best length to make the two primary pipes from the header to where the collector is attached? I dont plan to run any presilencers or mufflers before the axle so I dont care how long it says seperate but am more interested in power.
11-23-04, 11:20 PM
#2
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I did a fair bit of reseach on this topic prior to purchasing my system. It seems that on aI 12a NA the longer the better, that is why I elected for dual system all the way.
Cheers Sue
Cheers Sue
11-24-04, 03:32 AM
#5
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At work but dont have my RB catalog here.. so cant remember the long collected numbers exactly.
If you want to go Long collected.. collect around 118. If you want to go short collected.. you need to NOT get the Road Race Uncollected. It is considered 26" by RB IIRC. You need to collect at something like 18-22..
So SHort collected.. just get the Short collected RB header and do what you want after that.
Long collected.. if you have the flow and want it quiet.. get the RB long collected. Otherwise collect at 118 or so.. and YES.. that will put the muffler at the END of the bumper in most cases.
On the 85 ITA car I had a long collected 118" into a 3" then into a Edlebrock RPM performer ceramic packed SS muffler (streight shot).
Made 100 HP and 101 FTlb of torque.
Then bolted on the Long collected RB exhaust. The one with the precilencers and the RB muffler etc. COuldnt tell it was runing in comparison to the other exhaust.
Made 102HP and 98Ftlb of torque.
Needless to say the long collected running UNDER the axle made equivalent power to the QUIET over axle RB exhaust.
Difference? I noticed a barely discernable change in power in the mid range in corners. The RB has less.
On the street.. I can drive hard like a FOOL.. and no-one knows.. cause the Goddamn Holley Blue Fuel pump is louder than the exhaust.
I prolly have the dyno sheet SOMEWHERE.. maybe EvilAviator has it....
If you want to go Long collected.. collect around 118. If you want to go short collected.. you need to NOT get the Road Race Uncollected. It is considered 26" by RB IIRC. You need to collect at something like 18-22..
So SHort collected.. just get the Short collected RB header and do what you want after that.
Long collected.. if you have the flow and want it quiet.. get the RB long collected. Otherwise collect at 118 or so.. and YES.. that will put the muffler at the END of the bumper in most cases.
On the 85 ITA car I had a long collected 118" into a 3" then into a Edlebrock RPM performer ceramic packed SS muffler (streight shot).
Made 100 HP and 101 FTlb of torque.
Then bolted on the Long collected RB exhaust. The one with the precilencers and the RB muffler etc. COuldnt tell it was runing in comparison to the other exhaust.
Made 102HP and 98Ftlb of torque.
Needless to say the long collected running UNDER the axle made equivalent power to the QUIET over axle RB exhaust.
Difference? I noticed a barely discernable change in power in the mid range in corners. The RB has less.
On the street.. I can drive hard like a FOOL.. and no-one knows.. cause the Goddamn Holley Blue Fuel pump is louder than the exhaust.
I prolly have the dyno sheet SOMEWHERE.. maybe EvilAviator has it....
11-24-04, 05:08 AM
#7
Senior Member
Originally Posted by Hyper4mance2k
I heard 67" is the best for peak power.
Granted things like extreme PP engines etc will require shorter collection lengths... but unless you are the less than 1% running something at the highest levels of performance available.. that would be the incorrect collection point.
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11-24-04, 06:53 AM
#8
Now why doesn't RB recomend running larger than stock piping in their short collected exhausts? This honestly goes against my logic. I figure if I run the RB short collected then the RBpresilencer, then open it up to 2.25 or 2.5 then over the axel and through a straight through muffler I should to be good for more power then their system, right? I don't understand why they don't recomend larger diameter piping.
11-24-04, 09:24 AM
#9
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a friend of mine said it had to do with torque...and getting rid of exaust gas...he made the analagy of trying to blow through a piece of 3 inch pvc...you cant generate any velocity due to the fact that you dont have enough back pressure...is is the same when your exaust is too large...no back pressure...no torque...bad performance.
the system a ferrari has is ideal...where a waste gate opens up at a specific exaust pressure level...allowing the exaust system to provide variable back pressure over a wide range of RPM. this is why ferraris have 4 exaust pipes...2 straight thru...2 which open up when you stomp on it...it is also why a big blaring V12 ferrari can pass emmisions and noise restrictions...baby it and all that nasty exaust goes through the nice green quiet pathway...
the system a ferrari has is ideal...where a waste gate opens up at a specific exaust pressure level...allowing the exaust system to provide variable back pressure over a wide range of RPM. this is why ferraris have 4 exaust pipes...2 straight thru...2 which open up when you stomp on it...it is also why a big blaring V12 ferrari can pass emmisions and noise restrictions...baby it and all that nasty exaust goes through the nice green quiet pathway...
11-24-04, 11:51 AM
#10
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Back pressure is never good for power. The reason you stickwith the smaller diameter pipes is to keep velocity up. You keep the velocity up in order to maximize exhaust scavenging. A pulse of exhaust has more MOMENTUM if it is travelling fast thru a 2" pipe than if it were travelling slow thru a 3" pipe. Momentum is needed so that when the exhaust cylcle is completed at the engine, the gas is still moving away from the port creating a vacuum behind it. During port overlap (when intake and exhaust is open at the same time) this vacuum draw air thru the combustion chamber from the intake port. This clears out more stagnant gases from previous combustion cycle out of the motor leaving more volume for the nice fresh intake charge. Hence, more power. Please read further on Paul Yaws web site:
http://www.yawpower.com/febtech.html
http://www.yawpower.com/febtech.html
11-24-04, 02:31 PM
#11
Good read, but that still doesn't answer the question would up sizeing the exhaust after a RB header & presilencer, would there be a gain in power. I don't care about torque, this is a hp question. Wouldn't it benifit from a larger pipe diamater. If not why does everyother car in the world allways upsize the exhaust when modifing the engine. There is much more exhaust being produced after modifications, so sholdn't a larger exhaust help rid these extra gasses?
11-24-04, 05:45 PM
#12
Okay, if no mufflers before axel it is gonna be extremely LOUD as in race car loud wear ear plugs but that's what some peoples want. Go with the road race header, dual 2" O.D. mandrel bent tubing side by side then up and over the axel. Then a flowmaster collector: dual 2" into single 2.5". And your muffler which I reccomend a Magnaflow.
The collector on the racing beat muffler is low tech. The 2 pipes merge into a same size pipe; that's the restriction and although I did own one, and the complete RB road race exhaust system is streetable big time, I do reccomend the aforementioned rear muffler.
Now to Hyper's question. When I switched from the RB rear muffler to aforementioned flowmaster collector and Magnaflow 2.5" inlet/outlet straight thru 6" can yes, I saw a lot more power and motor liked to rev. It did make more noise too and I had to lift when I saw the fuzz so as not attract TOO much attention.
Whatever you can do to reduce exhaust pressure yet still have good scavenging will help out. And when I ditched the RB dual presilencers for dual 2" O.D. pipes boy, did that make her sound MEAN and the motor did rev better. But RB does say each of those presilencers only takes off 3hp on a n/a street motor.
The collector on the racing beat muffler is low tech. The 2 pipes merge into a same size pipe; that's the restriction and although I did own one, and the complete RB road race exhaust system is streetable big time, I do reccomend the aforementioned rear muffler.
Now to Hyper's question. When I switched from the RB rear muffler to aforementioned flowmaster collector and Magnaflow 2.5" inlet/outlet straight thru 6" can yes, I saw a lot more power and motor liked to rev. It did make more noise too and I had to lift when I saw the fuzz so as not attract TOO much attention.
Whatever you can do to reduce exhaust pressure yet still have good scavenging will help out. And when I ditched the RB dual presilencers for dual 2" O.D. pipes boy, did that make her sound MEAN and the motor did rev better. But RB does say each of those presilencers only takes off 3hp on a n/a street motor.
11-24-04, 06:09 PM
#13
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Originally Posted by Hyper4mance2k
Good read, but that still doesn't answer the question would up sizeing the exhaust after a RB header & presilencer, would there be a gain in power. I don't care about torque, this is a hp question. Wouldn't it benifit from a larger pipe diamater. If not why does everyother car in the world allways upsize the exhaust when modifing the engine. There is much more exhaust being produced after modifications, so sholdn't a larger exhaust help rid these extra gasses?
Exhaust tuning is largely about deciding where you want your peak power (within reason).
11-24-04, 06:48 PM
#14
Basically it comes down to money, If I could afford it I would buy the whole system but Im not running any presilencers or anything right now so I dont think it will be a problem. Since I have 2.25" exhaust already and I think Id like run two 2" pipes that collect before the axle, and just attach to what Ive got, how much of a performance gain is there running the collector after the axle rather than before, is it really worth it? and also there is no point of going to a 2.5" from the 2.25" really is there? I know there may be small gains in both those areas but is it enough to make a difference? what should I do?
11-24-04, 07:48 PM
#15
Originally Posted by Gen1onr
Since I have 2.25" exhaust already and I think Id like run two 2" pipes that collect before the axle, and just attach to what Ive got, how much of a performance gain is there running the collector after the axle rather than before, is it really worth it?
Originally Posted by Gen1onr
and also there is no point of going to a 2.5" from the 2.25" really is there? I know there may be small gains in both those areas but is it enough to make a difference? what should I do?
Just tell us you'll use a good Flowmaster or Magnaflow collector. The collectors most muffler shops fab up with crimp bent tubing flows like crapola.
11-24-04, 10:17 PM
#16
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what about running two pipes 2" through 2 presilencers under the car to two seperate mufflers, not joining them at all? I was contimplating on this fact for awhile due to my muffler blowing up issues.
11-25-04, 02:52 AM
#17
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The answer in sorta laymens terms to the questions on where you collect the exhaust.
Ever drive the car with a bad bog or hesitation.... Or better yet.. one with a Holley on it. Or even a Fouled plug.
You floor it.. and it is accelerating.. and making noise.. developing power.. hunning along.. then it suddenly clears up and goes ZING right to redline.
The Zing is basically what you are getting with properly collected/tuned exhaust.
The BEST method to understand it is a 2 stroke dirtbike with tuned exhaust.. like any built in the last 10+ years.
You roll onto the power down low and it goes.. and goes well.. then it just suddenly makes a ripping noise as it gets "on the pipe" and all hell breaks loose.
You put a tuned AFTER the axle collected Long collected exhaust and you will have that. It is really remarkable.. almost like No2 when it comes on the exhaust at like 5K.
A Proper short collected will do the same.. but it is more sensitive as its margin for error is a lot closer.
Basically.. you are collecting the exhaust at a point where the exhaust pulses are hitting the collector a point so that.. as it hits it.. and you get a reversion wave that travels UP the pipe to the engine.. it hits the engine at the same time as the new pulse is exiting, keeping it in there for a moment longer.. then it flees down the pipe. If tuned properly the wave hitting the engine hits when one is hitting the collecter. Then both waves travel back up and down the pipes colliding at the short point, and then they bounce off each other again and the process continues.
You also have to remember at the same time you are having the collection point have a reversion wave shoot up it from the other pipe further adding waves to the equation.
If you really start thinking about the waves bouncing back and forth.. remembering that it looses energy after each colision.. and the two of them fighting.... it gets really hairy. If you think og it like a 1 cylinder/rotor.. you can mentally follow the pulses easier.. but you add two and it gets even more interesting.
All these velocities, and pressures all are dependent on the bends, and the diameter of the pipes. If you have a bend in one pipe and not the other.. the tuning is toast. You need to re-figure everything compensating for velocity changes because of the bend. Also if you have pipe diameter changes that too will effect the exhaust drastically.
In essence.. a "Perfect" system would realistically be short collected.. being 2" ID (In a Bridge or larger engine) Colleceted at the proper length for your porting design.. (IE length of collection shortens as the porting gets more radical) Then after the collection you would have your 2.25" collector that would very gradually increase in size as it travels back in the car till it enters a Muffler at 3" and then exits at something like 5" ala N1 style.
The reason for this.. the exhaust will travel out the pipe.. but will not want to travel back up the pipe.. it will have EXCELLENT scavenging.... then you also will have the exhaust decreasing in velocity and temperature (pressure is dropping as well as dissipation) as it travels down the ever largening pipe (megaphone) then as it enters the muffler it is traveling much slower.. and has had time for sound dissipation.. (The tinny noise of the supersonic air escaping the initial port opening) As it hits the muffler.. another expantion chamber because of size.. as well as the packing material inside a muffler acts as a displacement INCREASER.. (come out my hard core audiophiles).. Then by the time it hits the 5" outlet.. it is traveling very slowly.. and has attained a very deep tone. The tinniness should be decreased a lot. YES.. it will not be quiet.. but it will be a LOT less harsh... and power development should be awesome.
The 20B exhaust for EvilAviators is in that basic design.. but it is Turbocharged.. so therefore is losing a lot otf noise. Post muffler.. 3"downpipe.. then a Burns 3" merge that splits the exhaust into 2..3" pipes. These travel out to two FULL SIZE N1 mufflers. The area of the pipes continually is getting larger.. via the 3" split.. then into the two large volume mufflers. It should be quiet at normal driving. Under boost and WOT.. It will NOT be so quiet.. but you really dont care at WOT now do ya..
Uncollected.... Unless you Tune the length of each individual runner.. you may as well have a thermoreactor and no header. Because you are getting ZERO tuning. Yes it will flow out better.. but it will give ZERO scavenging.. unless you get REALLY lucky and by some freak chance it is the right length. (Around 115-120" for the exit of the pipe.. and the muffler will change the effective length)
(Wow that was long.. sorry bout that)
Ever drive the car with a bad bog or hesitation.... Or better yet.. one with a Holley on it. Or even a Fouled plug.
You floor it.. and it is accelerating.. and making noise.. developing power.. hunning along.. then it suddenly clears up and goes ZING right to redline.
The Zing is basically what you are getting with properly collected/tuned exhaust.
The BEST method to understand it is a 2 stroke dirtbike with tuned exhaust.. like any built in the last 10+ years.
You roll onto the power down low and it goes.. and goes well.. then it just suddenly makes a ripping noise as it gets "on the pipe" and all hell breaks loose.
You put a tuned AFTER the axle collected Long collected exhaust and you will have that. It is really remarkable.. almost like No2 when it comes on the exhaust at like 5K.
A Proper short collected will do the same.. but it is more sensitive as its margin for error is a lot closer.
Basically.. you are collecting the exhaust at a point where the exhaust pulses are hitting the collector a point so that.. as it hits it.. and you get a reversion wave that travels UP the pipe to the engine.. it hits the engine at the same time as the new pulse is exiting, keeping it in there for a moment longer.. then it flees down the pipe. If tuned properly the wave hitting the engine hits when one is hitting the collecter. Then both waves travel back up and down the pipes colliding at the short point, and then they bounce off each other again and the process continues.
You also have to remember at the same time you are having the collection point have a reversion wave shoot up it from the other pipe further adding waves to the equation.
If you really start thinking about the waves bouncing back and forth.. remembering that it looses energy after each colision.. and the two of them fighting.... it gets really hairy. If you think og it like a 1 cylinder/rotor.. you can mentally follow the pulses easier.. but you add two and it gets even more interesting.
All these velocities, and pressures all are dependent on the bends, and the diameter of the pipes. If you have a bend in one pipe and not the other.. the tuning is toast. You need to re-figure everything compensating for velocity changes because of the bend. Also if you have pipe diameter changes that too will effect the exhaust drastically.
In essence.. a "Perfect" system would realistically be short collected.. being 2" ID (In a Bridge or larger engine) Colleceted at the proper length for your porting design.. (IE length of collection shortens as the porting gets more radical) Then after the collection you would have your 2.25" collector that would very gradually increase in size as it travels back in the car till it enters a Muffler at 3" and then exits at something like 5" ala N1 style.
The reason for this.. the exhaust will travel out the pipe.. but will not want to travel back up the pipe.. it will have EXCELLENT scavenging.... then you also will have the exhaust decreasing in velocity and temperature (pressure is dropping as well as dissipation) as it travels down the ever largening pipe (megaphone) then as it enters the muffler it is traveling much slower.. and has had time for sound dissipation.. (The tinny noise of the supersonic air escaping the initial port opening) As it hits the muffler.. another expantion chamber because of size.. as well as the packing material inside a muffler acts as a displacement INCREASER.. (come out my hard core audiophiles).. Then by the time it hits the 5" outlet.. it is traveling very slowly.. and has attained a very deep tone. The tinniness should be decreased a lot. YES.. it will not be quiet.. but it will be a LOT less harsh... and power development should be awesome.
The 20B exhaust for EvilAviators is in that basic design.. but it is Turbocharged.. so therefore is losing a lot otf noise. Post muffler.. 3"downpipe.. then a Burns 3" merge that splits the exhaust into 2..3" pipes. These travel out to two FULL SIZE N1 mufflers. The area of the pipes continually is getting larger.. via the 3" split.. then into the two large volume mufflers. It should be quiet at normal driving. Under boost and WOT.. It will NOT be so quiet.. but you really dont care at WOT now do ya..
Uncollected.... Unless you Tune the length of each individual runner.. you may as well have a thermoreactor and no header. Because you are getting ZERO tuning. Yes it will flow out better.. but it will give ZERO scavenging.. unless you get REALLY lucky and by some freak chance it is the right length. (Around 115-120" for the exit of the pipe.. and the muffler will change the effective length)
(Wow that was long.. sorry bout that)
11-25-04, 12:56 PM
#18
Fantastic post Scott.
If you wanna run two mufflers, at least run a X pipe right before the mufflers. That way you get exhaust scavenging as the exhuast from each pipe hits the center of the X. Magnaflow makes a real nice X pipe.
I think if you did that with dual presilencers leading up to it and two supertrapps side by side after the X pipe you could be onto something. But it would be expen$ive.
If you wanna run two mufflers, at least run a X pipe right before the mufflers. That way you get exhaust scavenging as the exhuast from each pipe hits the center of the X. Magnaflow makes a real nice X pipe.
I think if you did that with dual presilencers leading up to it and two supertrapps side by side after the X pipe you could be onto something. But it would be expen$ive.
11-26-04, 09:14 PM
#20
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so basically running a road race header to two presilencers all the way down to two seperate mufflers is bad? I'm alittle confused on this while thing. I would think doing it that way would be in a since good.... some one PM me on this one.
