eclou

Being long tubes, the exact length discrepancy is much less critical than on a short tube because the percentage mismatch is minimal. Not all long tube "equal length" headers will be exactly equal length.

Mr. Vanos

That's why you should be sticking to EVOSPORT parts baby!

But seriously, 414 base is actually on the low side for the car. On average, the car should be baselining in the 424 range on a Dynojet. I'd be curious the see the A/F numbers.

SleeperX

Correct me if I am wrong, but isn't the conversion factor to determine how many HP you put out at the crankshaft about 15%. So if you are putting out 408hp at the wheel you would be putting out 469hp at the crank. Our cars are supposed to put out 469hp at the crank so anything above 408hp would be above average. Am I thinking of this wrong?

Mr. Vanos

Your logic is not far off. Actually, 15% drivetrain loss is more inline for manual transmission cars. For cars with auto boxes and torque converters, it's more like 17-18% loss. But to address your question about the 469bhp, that number is really a marketing number that Mercedes-Benz puts out so that the SL55 remained the flagship 55 car. Truth be told, the E55 is not only faster than the SL55, but makes the same power...we've proven this on the dyno time and time again!

SleeperX

Grumpy666

Minimal discrepancy for long-tube headers would be on the order of an inch or two - not a foot. The difference between the first tube and last tube on the SS headers is significant. If all tubes are not the same length, they're not equal-length headers.

SleeperX

I found the following 2 posts on the Sl55 forum. It seems that a forum member with a SL55 only saw 15hp increase from his Renntech ECU and pulley upgrade. If you read his second post you will notice that he picked up an incremental 47hp with a new intercooler pump. Does that make sense to anyone on this forum..

https://mbworld.org/forums/sl55-amg-sl63-amg-sl65-amg-r230/143675-renntech-pulley-ecu-installed-questions.html

https://mbworld.org/forums/sl55-amg-sl63-amg-sl65-amg-r230/149186-fixed-intercooler-pump.html

eclou

Yes technically true but a 5-10% difference in lengths of approx 48" primary runners is going to have negligible exhaust scavenging disparities compared to the shortie and mid length headers with 50-75% difference in lengths in 12-16" primaries. The differences are even less critical in forced induction than in naturally aspirated motors.

rflow306

Yes it does, the car had a bad inter-cooler pump. Which is the reason the car had such low dyno numbers after the initial ecu and pulley install.

Grumpy666

Thank you - you have just made my case. Take another look at the SS header and you will see that the tube exiting the left port is about 50% longer than the tube exiting the right port. Plus, based on the distance brtween ports, the primary tubes are about 30" long, not 48".

Your comment about FI vs NA is not entirely accurate. All FI does is to provide a larger pressure delta when the intake valve opens compared to NA. There will still be an impact from cylinders with better scavenging, which will make that delta larger than cylinders with poorer scavenging. It's a function of fluid dynamics - given the same port diameters, the system with the greatest pressure will have the greatest velocity and, hence, flow the most. That translates into uneven A/F ratios between cylinders, which doesn't allow for maximum power.

eclou

By your eyes you thought those were tri-y's. Now you estimate the #7/8 primary is 50% shorter than the #1/2? Sorry but the discrepancy is not that great. Unless someone wants to run it with a tape, all guestimates are going to be questionable.

With FI the the increased pressure differential makes the scavenging effect become a decreasing factor to flow. If it were really that important then the stock cars should run horribly with the stock log manifolds. And unless I am missing something, our cars run quite well.

Grumpy666

No, you are misstating what I said - I said #1/2 is 50% longer than #7/8 - BIG difference. Below is a visual aide to help you understand. The red vertical lines bisect #7/8. IOW, each section between the lines represents 50% of the total length. Now, compare one of those sections to the section between the left-most red line and the green line. Looks like I actually was wrong - it's more like #1/2 is 60-70% longer than #7/8. My mistake.

eclou

That would be a fine approximation if they were 2 dimensional objects, and we were measuring the distance on a straight ruler from from a to b. Like I said previously, until you run a tape it will be impossible to accurately assess the length of each runner. Regardless, the mid/shortie Evosport header, even if it is equal length primaries, is not nearly long enough to match the resonance of the exhaust and has almost no collector transition.

Grumpy666

OK, fine, but it doesn't take a rocket scientist to see that all the pipes have very similar bends, and if straightened out, they would closely match my approximation.


You have this backwards - headers are not designed to match the resonance of the car's exhaust system (which in this case is probably somewhere around 1600-2000 RPM). They're designed to enhance the torque curve. The exhaust system should be designed to screw this up as little as possible. That means sizing it to have minimum impact on ezhaust velocity and with minimal restictions.

Equal-length EVO headers would be an excellent choice for this car, since the shorter pipes would enhance torque in the mid-to-upper RPM range, whereas longer pipes would have more impact on the low-to-mid RPM range.

rflow306

To general of a statement. The biggest question should be is the header for a street car, race car or a combination of both and will the header give me room to grow. That will determine the best header design.
The reason we are not seeing larger gains with the SS long tubes is either tuning or the tube diameter is to large. A shorty header will never work as good as a long tube header.

eclou

The way to enhance the tq curve is precisely by matching the resonance and exhaust pulse frequencies. It is one and the same.

Dyno after dyno on LT1, LS1, LS6 motors n/a and FI have shown relatively insignificant gains in power from shorty and midlength primary tubes. These motors are operating a similar displacement and rpm range as the 55k motor and should theoretically have similar exhaust characteristics. Coming from a bowtie backround, I am surprised that you are unaware of this. I found a major difference between Gibsons and Pacesetter longtubes on my Z71.

The EVOsport style headers are made to work with the primary constraint of available space and packaging, especially with regard to maintaining the ability to bolt up to the converters. That design, similar to Gibson or Edelbrock shorties pays off very, very little over a stock manifold. The Evosport style was also shown to give negligible gains on smaller displacement 3L I-6 BMW motors as well, which generate less exhaust pulses per revolution and will optimally benefit from a shorter primary.

SleeperX

Interesting.. If the inter-cooler pump was bad why did the inital dyno numbers look correct. I am not sure I understand this.

DJE55

I have the EVO headers on my car that you say make very little improvement over stock. So why is my car the fastest in the 1/4 with just pulley/ecu and headers? Why is my 60' quicker than even Derek's car on NSO? I was thinking the headers were helping me?

eclou

I am not saying that they will provide some gain over stock, but it will not be close to the gains of a long tube. Did you ever run your car with just pulleys and ecu? If not, then it would be impossible to ascertain what the headers contributed.

Grumpy666

You seem to have some confusion about exhaust resonance. Every system will vibrate at a resonant frequency when excited with an external stimulus. Take a tuning fork, for example. When you hit it, it vibrates at a specific freuqncy. It doesn't matter how hard you hit or what you use to hit it, it will always vibrate at that one frequency. The resonate frequency of a car's ehaust system is determined by the volume of the system between the exhaust valve and the first major restriction (e.g., a baffled muffler), and the pressure pulses from the explosions in the combustion chambers. The pressure pulses are the external stimuli. Headers will have virtually no effect on the resonant frequncy, nor does the resonant frequency have any effect on how the engine performs. The resonant frequency is the drone that you hear cruising in 5th gear between 1600 and 2000 RPM.

What does have an effect on how the engine performs are the pressure pulses that are traveling up & down the exhaust system. When a pulse leaves the combustion chamber (at near the speed of sound), it travels through the exhaust system until it hits the end of the tail pipe. As it reaches the end of the pipe, it leaves a finite volume and enters an infinte volume (wrt the exhaust system). As it does this, a rarefaction wave (low pressure) reflects back up the exhaust sytsem to the closed exhaust valve. These waves continue to reflect back and forth until they lose energy and dissipate. IIRC, it's the third harmonic of the initial pulse that you want to have at the exhaust valve when it opens. The low pressure from this wave is what causes the scavenging effect.

The same applies for the intake tract, only you want a pressure pulse at the intake valve when it opens, not a rarefaction. This was first discovered by the Dodge Ramchargers back in the early 60's, which was reflected by the velocity stacks they used on their intake systems. Their name comes from the ramming effect of the intake charge.


I am not going to debate this with you, other than to say I have seen the opposite, both first-hand and in various car magazines. Nor will I spend time with a web search to confirm it.

rflow306

The initial dyno was kind of on the low side, several cars here have made from 420 to 440 stock. The thing is at stock boost levels on the dyno the ic pump issue tends not to show up. The minute you add a pulley a bad pump will not flow enough fluid and kill power due to high iat's.

PTE

Grumpy: Now you are getting where I really wanted you to go. The firing order on a M-113 N/A or F/I motor is 1 5 4 2 6 3 7 8. I believe that albert is on to something.
Beside dyno testing , there is real world testing. To bad we couldn't build a car around the perfect exhaust system??. Back in 67 I had a Ford Fairlane w/ 390 GT. Hooker sent me a set of the racing Headers. The left & right rear cyl. exhaust tubes , crossed under the oil pan . What a Pain in the A$$ to install. We also painted the collectors with a soft leaded house paint. Ran the car hard and got it good and Hot . Looked for the burnt circle on the collector , extention. That was the point of the exhaust gas reversion. Outgoing met up with the returning pulses. We would cut it off there.If we changed the cam , we have to do it all over again. Todays car engines now have cams that vary its timing , intake manifolds that change runner length. Making it even harder to select the right exhaust header. I choose a header that used large tubes and a big collector > Length & diameter . Along with a convergence cone inside of the collector.. My car was restricted to what I could use . Just no room in the engine bay .I picked up 36 ft lbs of torque & 20 hp at the rear wheels. That was on a 5.5 N/A motor. I wonder if divergence rings would help on Shorty style headers??My meds are running out. ___PTE___ got to go

eclou

This is where you are totally confused. The scavenging effect which headers are tuned not based upon a wave reflection from the end of the tailpipe at all. The effect comes from the wave reflection at the 1st convergence of the primaries at the collector. The gas particle/pressure wave/sound wave has the option of traveling 5 different ways - the back upstream inlcuding the other 3 primaries or downstream to the muffler.

It is at this point (end of the primary tube) the pressure wave should come into a collector which allows expansion. With no formal collector, there will be minimal expansion. The expansion then sets up a reflection "suction wave" which will travel back up the primary to the exhaust valve and ideally should arrive during valve overlap and NOT exhaust valve closure. The key is that the relfection wave is tuned by the primary length, the frequency of the wave is dependent on the # cylinders and rpm. Most V8's are ideally tuned in using primary lengths of 30" or more. Only when the rpm is approaching 8k would a V8 be optimally tuned with primaries in the 20's" range. The reflection from the end of the tailpipe is completely insignificant by comparison.

There are some simple calculators out there for figuring ideal primary lengths and diameters. They have nothing to do with engine bay space. http://www.wallaceracing.com/header_length.php

rflow306

You guys are practically saying the same thing only using different terminology.

Lets explain it to everyone else on the board.

We are dealing with gases and pressure waves only. The absolute pressure differential between the cylinder and the atmosphere determines gas particle speed. As the gases travel down the pipe and expand, the speed decreases. The pressure waves, on the other hand, base their speed on the speed of sound. While the wave speed also decreases as they travel down the pipe due to gas cooling, the speed will increase again as the wave is reflected back up the pipe towards the cylinder. At all times, the speed of the wave action is much greater than the speed of the gas particles. Waves behave much differently than gas particles when a junction is encountered in the pipe. When two or more pipes come together, as in a collector for example, the waves travel into all of the available pipes - backwards as well as forwards. Waves are also reflected back up the original pipe, but with a negative pressure. The strength of the wave reflection is based on the area change compared to the area of the originating pipe.

These are things you both have stated but worded different. Now the differences which is were eclou is correct you want to time the negative wave pulse reflection to coincide with the period of overlap - this low pressure helps to pull in a fresh intake charge as the intake valve is opening and helps to remove the residual exhaust gases before the exhaust valve closes. He is also correct that this happens at the end of the tube not the tail pipe. Typically this phenomenon is controlled by the length of the primary header pipe. Due to the 'critical timing' aspect of this tuning technique, there may be parts of the power curve where more harm than good is done. Again this is something you both have stated and grumpy has given us the link to headersbyed which stresses this last statement.

So what do we have after this long physics discussion is what I have been saying from the beginning, is the car a street car, race car or a combination of both, that will determine your header design ie tubing diameter, tubing lenth and collector diameter.

The last thing for everyone to understand a shorty header whether equal length or not will never compare to a well designed long tube. Dje55 has shown us that the evo's work good and they do there is no arguing that. I think his car would pick up some more with a long tube header. Why? because I have never seen a well designed long tube not give any gains over a shorty header.

Grumpy666

This argument only holds true if the headers are open to the atmosphere (i.e., no exhaust system). If there is an exhaust system in place, the boundary conditions at the header pipe/collector interface are too similar to generate a rarefaction wave of any magnitiude - it will be minisule in comparison to the wave reflected at the tail pipe/atmosphere interface, where the volume differential is huge. There is also a larger pressure differential at the tailpipe boundary, which adds to the reflected wave's magnitude.


This is wrong. Sound waves travel faster in cooler air, not slower. Cooler air means denser air, which means the air molecules are closer together. The closer the molecule spacing, the faster the wave propagates. This is why sound travels faster in solids than air.