TeamRX8

iTrader: (25)

you just fail to comprehend the reality of the situation; consider it like this, if you push on a 1 ton block of stone with 10 lbs of force and 100 lbs of force, yet it doesn't move in either case, you have accomplished the same thing regardless

I have never said that there is no power in the exhaust system, just that you can accomplish it without resorting to overly complex and/or expensive tubular configurations that do not apply in this particular instance

Bse, I was ignorant enough to prove it out for myself back in 2006 so put that in your blowhard pipe and smoke it


.

bse50

Sure, because you experimented with various lengths other than what your rulebook allows?
Like all the bullshit spread by almost everybody about our intake manifold's design being the best when it clearly isn't from a sheer performance point of view?

Do us the favor Team...

PhillipM

If that's your view of fluid dynamics Team, no wonder you left it at a log header.

olddragger

iTrader: (3)

has anyone built a shorty header with 2 inch ID primary pipes?

etzilon

If you remove the engine mount, you can do this

TeamRX8

iTrader: (25)

technically, yes

I understand both physics and fluid dynamics enough to know how impossible it is to pull a vacuum on a closed, low volume chamber in this particular application. You are not thinking the process through, just jumbling together some theory without comprehending the physical reality

etzilon

P1v1t0=p0v0t1

PhillipM

You don't know enough to realise that you don't need to pull an absolute vacuum on a chamber that's still exhausting then.

olddragger

iTrader: (3)

has anyone actually measured the backpressure present in the various exhaust systems being commonly used?

Too bad we cant have variable diameter exhaust pipes.

TeamRX8

iTrader: (25)

But I do and have stated so previously. It's readily accomplished without going to all that complexity and trouble. The whole high velocity scavenging theory is out the window. Without overlap there can be no scavenging. High velocity then only inhibits flow. You are trying to rectify the very condition you have created.

olddragger

iTrader: (3)

I agree with Team on this one. Just a free flow exhaust with no back pressure is going to be the best you can get here.
Still--I have no creditability so my opinion really means squat.

olddragger

iTrader: (3)

i measured my exhaust back pressure today.
i have the oem header, mazmart twin resonator midpipe and RB catback. For those of you who dont know I run the Pettit SC with approx 300 rwhp.
At idle i am at 0
During full acceleration it is at 4psi.
From what I understand--that is not bad.
So if I do get a little more gain after building my exhaust system--it is not from relieving a lot of back pressure.
Exhaust pulse strength demonstrated on the gauge was interesting.

olddragger

iTrader: (3)

this is a dead forum

TeamRX8

iTrader: (25)

You're just not good with technical stuff. It's not personal.

etzilon

Ok, ok... I'll bite, OD :-)

Where did you take the measurements from? Since you have a system that resembles OEM from what I can read, was it at the mid pipe, before of after the resonator, or somewhere else? BTW, do you still have the OEM choke between midpipe and catback?

How 'quick' is your sensor? We get to see a lot of 'pulses'/sec at high RPMs, so you're probably seeing just the attenuated pulses blended together.

Lastly, how do we use this info to build a better header?

Beodude

iTrader: (3)

If he measures it close to the muffler, the pulses will even out, and be more of a constant flow.

I've been reading this, and I'm very interested in what you are doing OD. I just don't ever have much to add!

olddragger

iTrader: (3)

i will be the first one to admit that I have a lot to learn on the tech side. i have learned a lot, but I still have a long way to go. I keep trying and I have learned to not take things personnel, it is frustrating at times when I ask honest questions and either get the run a round or sarcasm. But it is the internet........
I have the mazsport 3 inch dual resonated midpipe to a RB cat back system--no midpipe choke, its a flange that doesnt use the oem gaskets. I have the oem log exhaust header
No cat of course. The mazsport resonators are a straight flow through that maintain 3 inches throughout.
I measured my back pressure at the 2nd o2 sensor bung between the resonators using a simple boost pressure gauge. The engine was fully warmed, i didnt measure the egts.
At idle it was zero, under full acceleration I get to 4 psi of back pressure from 3K rpm forward , i was making 7 psi of boost at the time and right at full maf voltage. a/f's are in the high 10's to very low 11's. None of my exhaust is coated or wrapped. I do have heat shields on top only.

I spoke for a while to the guys at spd performance, and the summation is that since we have no overlap/a siamese port and I am supercharged-the only thing to do is to get the exhaust out. No "tuning" with megaphones, reverse cones, etc etc. Concentrate on pipe size and no restrictions.
My primary tube size (1.75) was also recommended by them and they recommend a 3 inch collector with either a 12-15% transition.
I like them because they were honest and told me up front that I probably would not see much of a change by using a true merge collector versus a well made regular collector. He said that the most benefit would be in the design from the collector back. This we know, but he had a few suggestions. I will follow those and reveal them as they are done.
Regardless I am going to purchase a basic merge 3/1 collector for them --it is going to be between 12-18 inches long ( they are still crunching numbers) and it will be made of 321 SS.
You cant get rid of all exhaust back pressure with a street driven car, but the backpressure I am seeing can be improved on per spd. My goal is a max of 2psi.
It does look like I will not be using the RB catback.
Does this explain things better? If more info is needed--just make me aware and I will get it.

etzilon

Thank you for the info. I ask because I am researching where to start on a custom exhaust project for my NA RX8. It will not be street driven.

The only idea I have not read about is leveraging scavenging to help pull exhaust from the siamesed port. It might just be a stupid idea; many stupid ideas have been discussed but this one (at least to my recollection). Shortening/lengthening the middle runner to dephase the pulse compared to the outside ports is what I thought out.

If you have thought about it/heard about it, let me know. The bandsaw will still be powered off for the next 3-4 weeks.

PhillipM

That what my manifold is setup like.

olddragger

iTrader: (3)

when I spoke with John at spd performance ( they are like Burns) he is thinking that the Siamese port exhaust pulse volumne is not something to be concerned about. He had more advice concerning this weird engine about what happens after the Collector.
After the header collector, the goal is to reduce the resistance to the exiting gasses by the exhaust system. The resistance in the exhaust system comes from several sources 1- drag from the surface area within the exhaust system,2- all the twist turns in the exhaust system. Each time the exhaust system forces the gas mass in the exhaust to turn, it requires energy. Just like the intake.
Designing an exhaust circuit with the least amount of turning possible reduces this resistance to flow.. You can reduce the drag caused by the surface area by reducing the length of the system also. An open header or the "zoomies" on a dragster are examples of systems that use both tactics, as is the use of wider radius bends in aftermarket performance after-cat exhaust systems. Of course, there are limits on how far you can shorten the exhaust system on a street-driven vehicle.
Another tip for exhaust system performance is to look for a low-pressure area in which to dump the exhaust. This is one of Smokey Yunick's tricks. On street-driven vehicles, most people just choose the oem site.
I have a feeling I will be concentrating more on the collector back part of my system and i probably will not be using my RB cat back. He did agree that since I run a single exhaust system that a 3 inch OD pipe would be good to have and it should not slow the exhaust flow to any degree of concern.
SPD makes their collectors on demand. The final decision will be agreed on tomorrow. After that I start on all the other stuff.

etzilon

Keep us posted about your progress. 12 degrees or lower?

In "typical" headers (all I have seen on this site and on the 'net), the siamesed port runner has the same OD as the outer runners, so even if the velocity is higher at the middle port exit (due to the smaller exit), once it gets to the runner, it is reasonable to think that the actual gas velocity on the middle runner will be slower than on the outer runners due to the transition to a relatively higher volume zone. I think it needs all the help we can give it. How? Not sure. Perhaps with a low angle, long collector with a dephased middle runner :-)

Since this is all happening in my head (i.e. hypothesis), it shall be proved/disproved in practice.

HiFlite999

iTrader: (2)

3) Reversion waves. Without careful simulations and/or a lot of testing, it's nearly impossible to guess at a best system. Mazda's metal hints strongly though that reversion is a problem because of the rather HUGE step they build in at the runner/manifold transition.

olddragger

iTrader: (3)

thats an interesting thought, but I am thinking that it was less to do with reversion than the cooling affect that step has on the exhaust port?
We have several things that work in favor of not providing an environment for reversion pulses. 9K rpm, individual intake runners and long intake runners are three of them.
Its true that there are an increase in the number of reversion pulses as the rpm is increased, but it is also true there is less time for these pulses to re-enter the intake track. The dominate variable in this set of conditions is time. Stated another way, the degree of encroachment to which reversion pulses can go back in a counter-flow direction is shortened with increased rpm. So I am thinking but i dont know for sure that reversion is not that big of an issue with the present oem design. Adding a supercharger further reduces that risk

Here is a useful table in trying to determine exhaust pipe size ( post collector)
at my hp level it looks like I am where I need to be with the 3 inch OD

Calculations and Comments by Dave Stadulis of SMSP Exhausts Relating Flywheel HP to Exhaust Cross-
Sectional Area (Diameter):
quote:
Here are the numbers for 16g tubing:
OD (in.)....ID (in.)...Area....%Increase......HP.......HP/in^2
2.25........2.120.......3.53.....0%............... 200.......56.66
2.50........2.370.......4.41.....25%.............. 275.......62.34
2.75........2.620.......5.39.....22%.............. 318.......59.00
3.00........2.870.......6.47.....20%.............. 400.......61.83
OD is exhaust outer diameter, ID is inner diameter, Area is tube cross-sectional area, % Increase is
increase from the prior OD, HP is Flywheel hp, and HP/in^2 is hp per square inch cross-sectional
area.
For the 2.75 in. tube, I assumed 59 HP per square inch of flow area, I used Larry's numbers for the
others....you are talking HP at the crank :
2-1/4" for up to 200HP @ the crank, 2-1/2" for 275HP, 2-3/4 for 320HP...
or 60HP (at the crank) per square inch of (cross-sectional) flow area.
This 60HP/in^2 is to get you in the general vicinity. It also is based on the inside diameter of the
tubing not the OD (i.e. 2" in your example). The ID for 2' 16g tubing is 1.87" and this will yield a limit of
165 crank HP. 2-1/4" 16g (212 HP), 2-1/2" (265 HP). Now you can get different sized tubing such as 2-
1/8" and 2-3/8" to fine-tune a vehicle but you can't get cats and mufflers in those sizes so you should
go up a size when building an exhaust in those cases.

why include this table....? because exhaust velocity is also important. To slow of a velocity also increases the risk of reversion. Its a balancing act for sure.
--------------------

HiFlite999

iTrader: (2)

If you're talking about the cooling effect of expansion, that would also happen with a smooth transition.

Intake? Nothing to do with intake. Reversion waves will happen regardless, at any place there is a sudden change in the velocity of the pressure wave. What works in our favor is having zero overlap. Scavanging in the normal sense of the automotive world, cannot happen.

Zero overlap. Exhaust essentially seperate from intake.

The pressure wave moves at the speed of sound, the gas itself moves much more slowly. Reversion comes from the pressure wave, not the gas flow. The speed of sound depends on temperature. ( Speed of Sound ) Temps are much higher in rotary exhausts, the reversion effects cannot be compared with recipes.

olddragger

iTrader: (3)

I understand what you are saying, but by adding a supercharger more exhaust is being pushed out. All other things being equal this helps with maintaining velocity doesnt it? From what I understand significate reversion is more likely the slower the gas flow?
No overlap--yep separation between exhaust and intake--or is it? It the conventional sense it is, absoulutly. Yet, dont we have a small amount of exhaust gas that recircluates--correct? So by design we have so called built in reversion? Need evidence--pull an intake We have intake reversion for sure. It would be worst with shorter runners etc.
.
How do you reduce reversion? Is reversion having a negative affect on our engine? Again I am not sure because how do you determine exhaust reversion is occuring on this engine? Measure BSFE/VE versus torque? The normal signs and symptoms will not be there due to the no overlap.

Agreed== every automotive exhaust system will have some reversion--regardless.
Good discussion?