Extractor Design Theories.

[LittleRedSpirit]

Hi guys and girls.

 

I'm considering getting some custom extractors made, or finding a nice aftermarket set somewhere. I'm chasing torque, which most people tell me will mean 4-2-1 design with the longest runners possible, for a 4age. Lets please focus this discussion around inline 4 motors, I'm sure there is a whole different set of theories for V style motors and more cylinders.

 

Is there anybody on rollaclub who can lend me their ideas, either as a professional who makes such things, maybe you had a set made which were good or bad for whatever reason. Just please feel free to give me the benefit of your experiences or wisdom on the subject.

[KEI069]

Ok, I'm sure some people will disagree with me here but the only extractors that work properly are 4 into1

design pipes with equal length runners. Power and torque will both be gained across the entire rev. range.

the 4-2-1 style pipes referred to as tri-y's are mainly used to replace broken/cracked manifolds or when

space it at a minimum. Although these pipes do give an increase over a standard manifold they wont out

perform a properly made tuned length 4-1 set.

There is an equation to work out the length of the primary pipes which i don't have handy at the moment

but i will try to find it for you.

 

Cheers Justin

[love ke70]

have you checked out bills site?

billzilla i think it is

bill sherwood i think is his name?

pretty sure he covers all the exhaust stuff in his very lengthy 4a info...

[twitchy]

here is some borrowed info... :P

 

A 4-into-1 design is perhaps the most traditional design. This design is common to the US market and is well used within the drag race fraternity. The basic principle behind the design is that the scavenging effect within the collector cone effects the three remaining pipes (in a V8 half), instead of limiting the pulse to the very next pipe in the sequence. This generally results in a header that performs very well in the mid-range to top end of the engines performance.

 

A TRI-Y on the other hand splits the firing order evenly and uses the secondary pipes as sequential collectors. This results in generally a greater scavenging effect due to the fact that scavenging is achieved at 2 different points in the header design, firstly at the primary to the secondary collector and secondly to the secondary outlet collector. Generally this improves torque in the lower to mid range performance of the engine.

 

Both designs are usually more efficient than a standard manifold and both offer distinctly different advantages.

[vagen]

from my days building Datsuns I ran into a set of numbers for tri-Y extractors primary = 18-24" secondaries = 24-36" I always went with the shorter end of the scale because I needed a bit more top end than bottom. I always used 1 3/8" primaries and 1 3/4 secondaries with a 2 1/4 collector

[Sam_Q]

KEI069: yep I completely disagree

 

there was a performance workshop manager that had a 3sge engine that I spoke to a long while back that tried everything and they made the most power everywhere with a 4-2-1.

 

Toda themselves quote a 3% top end gain with their 4-1 but at a massive 15% loss in the mid compared to their 4-2-1 set they sell.

 

For lengths look here and all the links on the page.

 

http://www.my-acoustic.com/Car/intake_exha...ust/exhaust.htm

 

The basic answer is the longest pipes you can fit.

 

I if I ever get anough motivation (maybe never) will make some pipes with 750mm primaries, 425 secondadries and have my cat just after the flex pipe.

[Jason]

Just though Id say this its been on my mind for a bit.

 

Instead of 'forcing' the motor to make power where ever you want. Why not match the exhaust VE to the intake VE? I'm not sure VE is right maybe flow efficiency or even better flow momentum.

 

Say, you have your engine and it makes toruqe where ever with the exhaust off / or no joining headers. Then try to match a realist header system to where it makes the most torque? This is dyno territory but I thought it might be some food for thought.

Edited April 21, 2009 by Jason

[philbey]

With your engine's VE, I believe a well designed set of headers (obviously combined with the right cams, valves etc) will improve your volumetric efficiency thanks to the scavenging effect? The idea isn't to force your engine to make power wherever you want (as implied) but rather to optimise your VE based on what cams, carbs, jetting etc you are running.

 

For example , If you've set up your cam and carbs for 6500+ power, then you want to combine it with the right exhaust that improves your VE at those revs.

[snot35]

If you want hard copies, the book "Four stroke performance tuning" by A. Graham Bell has a great chapter on exhausts, with a few formula for calculating length based on displacement, camshaft timing etc. There is so much good stuff in that book, I highly recommend it.

[Felix]

If you want hard copies, the book "Four stroke performance tuning" by A. Graham Bell has a great chapter on exhausts, with a few formula for calculating length based on displacement, camshaft timing etc. There is so much good stuff in that book, I highly recommend it.

 

 

I totally agree. Also read anything you can get from David Vizard.

 

For a street engine 4-2-1 extractors are the go. In general they pick up the low to midrange at the expense of a few HP up around peak revs compared to 4into1's. For a street motor peak HP is nowhere near as important as the area under the curve. Realistically you are only hitting peak revs a very small percentage of the time you are driving.

 

Just like carbs and cams, extractors are just another component that should be matched to the rest of the overall package.

 

LittleRedSpirit, what did the gearbox you are running originally come out of? you can't get a close ratio gearset to keep the motor further up in it's powerband on changes?

[Jason]

With your engine's VE, I believe a well designed set of headers (obviously combined with the right cams, valves etc) will improve your volumetric efficiency thanks to the scavenging effect? The idea isn't to force your engine to make power wherever you want (as implied) but rather to optimise your VE based on what cams, carbs, jetting etc you are running.

 

For example , If you've set up your cam and carbs for 6500+ power, then you want to combine it with the right exhaust that improves your VE at those revs.

 

Ya. Ill reword saying the same thing :P

 

Take exhaust out of the equation and you max VE will be your peak torque, therefore matching extractors where ever that may be. So you really setup your base torque/power curves by the intake and exhaust just tweaks it.

 

So this is how I see it, say your best VE is at 4000rpm but you want torque at 2000rpm, by designing a exhaust to get more at 2000 will start to strangle the torque at 4000. You could say your distributing the power more evenly, Id say its wasting intake tuning.

 

 

IMO the best exhaust would be four independent runners. You don't wont to disturb the momentum of each cylinder.

[love ke70]

you are better using the reverberation to scavenge extra exhuast from one cylinder by running them in a tri-Y or 4-1

[Corolla1]

I have recently built a set for the 4AGE in my Ke70. here are some pics,

 

I used 1 1/2 primarys 375 mm long

I used 1 3/4 secondrys that are approx 160 long.

 

I could of made the secondys longer, but i was told that the secondrys had to be a little bit under half the length of the primarys.

 

I am using this set of extractors just to get my engine running.

 

if you want more info on my extractors PM me or look at my project thread,

 

Cheers Jarrod

[KEI069]

I know everyone has their own opinion on this topic, but i have run my own exhaust shop for

about thirteen years and have proven many times that 4-1 extractors work. The formula for working

out the extractor design is quite involved. I will do my best to explain.

 

as the exhaust valve opens- just comes of its seat- it generates a pressure wave in the manifold

itself. This is a positive wave which travels down the pipe- it is not exhaust gas, but a wave

travelling within the gas, at the speed of sound.When it reaches the end of the pipe it suddenly expands

and as it does, by the laws of physics a reverse wave of negative pressure starts to travel back

up the pipe.

that wave travels up the pipe back into the cylinder and arrives with a certain amount of withdrawal

power because its pressure at that point is considerably lower than existing cylinder pressure. The art of

tuning or designing exhaust manifolds is to create a length and size of exhaust pipe so that this negative

pressure wave arrives back at the combustion chamber just during the point of overlap- just when the

piston has come up on its exhaust strokeand has finished pushing the gas out of the cylinder.

So the basic formula for choosing first of all the primary pipe length is

5100 x ET

primary length = RPM x 6

 

ET is the timing in degrees of the exhaust valve from when it starts to open up to TDC - the amount before

BDC plus 180 degrees. RPM is the speed at which you wish to tune the engine, in most cases the point

at which you know the engine is going to develop maximum power.

This is the primary pipe length in inches form the exhaust valve head, so don't forget you must subtract

the lengthof the exhaust port from the actual pipe.

The primary pipe should contain twice the swept volume of the cylinder with which we are working.

Suppose cylinder volume is 500cc therefore twice swept volume is 1000cc

Divide 1000cc by 16.4 to bring it to cubic inches

Divide by 3.14 to find the square root. multiply by two

This gives us the internal diameter of the pipe.

Always work up to the next available pipe size to allow for bends in primary pipes that create a restriction.

All four pipes should join into a collector. the finish of the primary pipe should be as sudden as possible

so the pulse wave itself knows where it is finishing.

In summary if you can be bothered workin this out you will have a set of properly tuned extractors

that work.

Have fun.

[Jason]

Wow thats awesome! Would you have any before/after dyno sheets of your extractors for curiosities sake?