headers length

[sinus]

If you wish to keep the original characteristics, you have to shorten the length corresponding to the reduction in velocity of sound due to the colder gas.

This is my question! I know that sound is slower at lower temperatures of gasses, but I have no idea what temp. we have at the end on marine exhaust-collector. I know:"Measure it", but is not so simple for us. We did not made holes for measurments and now we have double pipes, water betwen...

Round of our exhaust from foto I have no idea of secuence. Engine is basically job of my brother, I am only help to calculated resonance lenght and if I remember well have originally busas exhaust same configuration and same sequence, this we did not change at all. Look strange, but I am hear explanation for this and it work. Basic I did not work on engines, I am work mostly on boat. Brother is work more on intake lenght, headers lenght and tune engine with injectors for adecuate lambda nr. he is calculated exhaust for best efficiency betwen 7.000 and 8.500 rpm, which are most used rpms. For same lambda like originally busas he is oppen injectors for 12% or 15% (I do not remember now.) becouse of better air flow thru engines.


Casted headers we will made 4/1 becouse of simplicity and becouse of enough torque at start. We will made it closed cooling lop with same cooling liquid like for engines and oil. With expecting temps. Betwen temperature of cooling liquid betwen 80 and 100 oC will be exhaust gasses for sure warmer like with 23 oC sea water and more warm mean more energy for sucking gases from engines.

 

[jehardiman]

So, if you cool your exhaust (with the original pipe length), the pressure pulses will take longer to pass through the pipe. The effect is a reduction of the optimum rpm, just as if the pipe length had been increased slightly. This means that you may get exactly the right power characteristics with standard lengths and cooling; i.e maximum torque comes in at a slightly lower rpm. If you wish to keep the original characteristics, you have to shorten the length corresponding to the reduction in velocity of sound due to the colder gas. The exact amount of shortening necessary is depending on the heat transfer, but I have seen the difference to land in the 3 to 5 percent range with a cooled manifold.

It is true that the pressure pluse will speed up in the cooler exhaust, but with the new density comes a lower volume flow down the header tube. Don't you need to keep the velocity up to keep up the mass flow out of the cylinder to provide proper scavenging which points to a longer, smaller, diameter. There then would be a trade off between backpressure at the exhaust and inlet runner pressure. Unless the engine is blown, wouldn't that drive a longer header pipe?

 

[baeckmo]

It is true that the pressure pluse will speed up in the cooler exhaust,

Now you got it "upside down"; the pressure pulses travel slower in lower temperature. The scavenging is all about pressure pulses, less about mean flow velocity. When the exhaust valve opens, a pressure pulse will travel through the pipe with the critical velocity, ie speed of sound at the prevailing conditions. When it meets an area increase (the Y-junction), part of it will reflect as a negative ("suction") pulse going back towards the exhausting cylinder. The other part will travel down the connected branch and is reflected as a positive pressure pulse when it meets a closed valve. This pulse (in a four stroke) must not reach its origin until that valve has closed.

The representative mean flow velocity is reached when all gas particles have been "passed" by the pressure pulses. The mean flow velocity may vary between roughly 40 m/s and up to 100 m/s, while the pulse speed (equals the speed of sound in the gas) is about 420 to 500 m/s.

The trick is to tune the pipe length so that the low-pressure pulse arrives at the valve during its closing phase, thereby creating a low pressure in the cylinder.

The figure I mentioned (length correction about 5 %) comes from dyno-testing of two-liter fourcylinder engines that exist both as marine engines and car engines. The marine manifolds were fabricated by welding water jackets to the steel exhaust pipes, while the auto manifolds were iron castings. The exhaust ports were grouped (1+4) and (2+3) and these two groups joined after about 1 meter (ooho just a vague memory....should be checked), depending on the characteristics wanted, and finally dumping into a common 2" pipe.

 

[sinus]

The figure I mentioned (length correction about 5 %) comes from dyno-testing of two-liter fourcylinder engines that exist both as marine engines and car engines. The marine manifolds were fabricated by welding water jackets to the steel exhaust pipes, while the auto manifolds were iron castings.

Nice info, I am expect bigger diference.

 

[PAR]

Most folks know about the importance of exhaust gas scavenging, but there are a lot of other things to consider. Automotive primary lengths are roughly standardized at 32" - 36", before they dump into the 4:1 collector. The photo above shows a "tri Y" setup, which is dubious at best, considering testing results and the marine application. A much better arrangement is the 180 degree tuned header setup. essentially the pipes are arranged to be the same length and next to each other 180 degrees apart in the firing order, so scavenging effect is the greatest. The idea is 4 equally spaced exhaust pulses, per collector on a V8. Anyone that's seen a F1 car's headers understands why it's usually called a bundle of snakes.

Aside from scavenging and primary length, you should also look at collector length and diameter, keeping the heat in the pipe, preferably centered, engine output and operating range (you might not want a 4:1 header at all). Other things to think about is exhaust gas contamination (reversion), port matching, effective torque curve utilization, primary tube diameters, collector diameter, flow velocity etc.

So, what are the engine spec's, what will be it's RPM range and any idea of flow rate or velocity, etc.? If it's going to be the typical, high RPM, high output marine engine, you'll want a proportionately shorter and larger diameter collector, with primaries, tuned to length. If flow is high enough, you might find better results with no scavenging attempts, but just "dump" pipes, much like seen on aircraft, where a high RPM, high output engine isn't incumbered with the restrictions of a "formed" exhaust. Given the little I know about your engine, a 32" primary that's 1.5" to 1.75" in diameter, with a 2.75" diameter, 6" long collector will get it done, but without a full set of spec's, this is just a quick guess without doing any math. The penalty for a too big diameter primary and/or collector is less harmful than too small, at the RPM ranges I suspect you'll run.

 

[sinus]

Hello;


Are next datas enough to say which lenght and configuration is best?

We have double classic 1.3l Suzuki Hyabusa engines. Unfortunately it is something wrong on server and have troubles to put fotos on forum, will try in this way:

Double Suzuki GSX1300RK1, datas for one:
- maximum power 178 bhp at 9500 rpm
- torque 125 Nm at 7200 rpm, but at 4.500 rpm it is almost 110 Nm and than keep it betwen 125 Nm and 120 Nm to the end rpm
- maximum 10.500 rpm, soft limiter. We go up on 11.800 rpm, which is highest permited level
- becouse of other inox intake tubes and exhausts like on foto before, we have better airflow and we need to pick up injectors for 15% to reach optimum lambda, it mean at least 12% more power like originall.
- headers are calculated for 6000 rpm (Not 7.000 rpm like I said day before) and above and all pipes have same lenght, foto above lay.
- pipes from last Y to the valves are 800 mm (32 inch)long and it should work from 6.000 to the end, the best round 7.000-8.000 rpm, which are calculated for cruising with 40-50 mph. Diameter of pipes it is the same like at bike.
- valve diameter intake 33 mm (1,3 in), 2 for piston
- valve diameter exhoust 27,5 mm (1.08 in), 2 for piston
- cam height intake 36,78-36,848 mm (1,448-1,4506 in), exhaust 35,48-35,548 mm (1,3968-1,3995 in)
- valve intake open 43 degrees B.T.D.C., intake close 58 degrees A.B.D.C.
- valve exhaust open 62 degrees B.B.D.C., close 24 degrees A.T.D.C.
- bore 81 mm (3,189 in)
- stroke 63 mm (2,480 in)
- piston displacement 1299 ccm (79,3 cu. in)
- compression ratio 11:1
- fuel injection sistem, lambda 12,7 if remember well.
- intake tube lenght I do not know on this moment.

Engine have first reduction from crank shaft to clutch teth whell and it is 1,596. Than we use other gear ratio of 1,285 and at the end is ZF with ratio 1,569.
It mean next torque on prop shaft:
- at 1.245 rpm = 643 Nm
- at 1.550 rpm = 665 Nm
- at 2.000 rpm = 720 Nm
- at 2.500 rpm = 800 Nm
- at 3.000 rpm = 770 Nm
- at 3.600 rpm = over 700 Nm
Torque it is calculated with standard power from standard diagram, not with our 12% more juice, and standard exhaust is maded for higher rpms.


Becouse of really good hole shot we thinking to made shorter pipes with minimum at 7.000 rpm and perhaps to use bigger maximus with 15-5/8 diameter for better efficiency at cruising.