lexaltezza

As usual nothing has been going according to plan with this car so far. I had originally cut the resonator out and replaced it with straight pipes. The exhaust was immeidately more alive, but more muscle car sounding which is a bit out of character for this type of car.

Just recently I ordered a x-pipe through Vadim and had it installed. The car was immediately almost like stock again. The difference from straight pipes to an x-pipe was night and day. The sound was a bit smoother, but overall quieter. Not exactly my cup of tea. However, I thought the car felt a bit quicker in the lower rpm's, which I was not expecting. It feel like it had more low end torque.

Now here's the kicker. I used the Dynolicious app on my Iphone to measure some 0-60 times. The best time I can get now is 5-5.1 seconds with it being about 90 degrees today. In March I was getting consistent 4.4-4.5's with it being 65-80 degrees.

At first I figured it would be the temperature, but I didn't think you could lose .5 second or more. Could the x-pipe be the culprit?

Here is the data from the app for the heck of it:

March, Today

0-10 .78 .89
0-20 1.56 1.69
0-30 2.18 2.38
0-40 2.85 3.15
0-50 3.67 4.06
0-60 4.57 5.07

JustPete

Sounds to me like the x-pipe threw the pulse tuning off. But that's a pretty dramatic change which leads me to believe it's throwing a sensor off and the ECU is doing some retarding.

von32897

Tezza,
Man, you've been playing with that exhaust forever. Should've left it with straights. Anyways, hope you figure out the problem bro.

azncarjunkie

last pic i saw of vadim's xpipe was that it was way too restrictive (total pipe diameter) compared to other xpipes or straight pipes. would make sense that you'll gain a little bit on the low end but lose a TON on the higher end.

The reverse is true for those little japanese imports that put on larger exhausts. they may gain a couple of HP on the higher end but typically lose several HP in the more 'useable' low-mid range. You might have just done the reverse of what those numnuts oftentimes do.

if you're looking for a technical description, i'd go along the lines of added backpressure helping low-end, and choking the high end when it really needs to breath. as mentioned above, the pulsing could be adding to the jacked-upness

Full Throttle

For forced induced engines the best exhaust is no exhaust at all. Removing restrictions in the exhaust will not make your car slower.

rick2964

Very true about forced induction. This is one of the few times bigger is better plus the exhaust can get very hot under boost. My 55 is stock but my blown bigblock in my other car has 2 1/4 primary header tubes and 4 inch exhaust!

azncarjunkie

This is wrong.

Supercharged engines like the 55 still rely on 'normal' exhaust physics which includes backpessure. going 'too big' WILL result in a loss of power especially in the low/mid range. there may be a slight increase at the higher rpm range, but the loss in the power curve would completely negate any negligible gain in the top end.

On turbocharged motors, the theory of no exhaust is true since turbochargers work off the pressure difference between inside the manifold/compressor and the exhaust.

stop spreading internet stupidity.

JustPete

That's always been my understanding as well.

Nick Name

Can you explain that a little more, please? My basic school physics tell me the less resistance the motor has in the exhaust, the easier the motor can breathe.
Why do you need backpressure at all?

Nick

Full Throttle

Incorrect
"stop spreading internet stupidity"

Full Throttle

This is correct

You dont, the moment positive manifold pressure is created the exhaust needs to be as least restrictive as possible. Especially with Roots blower that make their peak boost at very low RPMS

06A180Man

Just go back to the straight pipes and sound, if tweaking is all about gaining or losing just a fraction, why bother ?

azncarjunkie

The point of an exhaust to a car isn't just for reducing sound or piping the fumes away from the driver.

Exhaust and intake alike follow the laws of fluid dynamics. I'll explain it so someone like Full Throttle can understand...

Think of drinking a soda through a small straw. If you drink really fast and then remove your mouth, there were still be some soda that forces its way up and out through the straw. If you use a much bigger straw, you'd need a much larger force to have the same thing happen since there is much more volume of soda inside that straw.

The same thing happens in your exhaust at the exhaust valves. Exhaust trying to exist your pipes will create a low pressure area (think of a mini-vacuum) at the other end of your exhaust which is at the motor's exhaust valves. When those valves open up, the exhaust trying to escape your pipes will help 'pull' the spent exhaust exiting your cylinder while also helping in the 'fresh' air/fuel in (assuming there is some valve overlap which there probably is).

Full Throttle is correct that you want to maximize the amount of air pushing into your motor (high pressure at intake valves). For optimizing, you also want to utilize a properly tuned exhaust (low pressure at exhaust valves). Fluids/Air will flow fastest between higher differences of high/low pressure.

Our motors aren't pushing enough air that a full open exhaust would be warranted or desired.

JustPete

Maybe I'm way off base here because I don't know the MB Kompressor system all that well. (All my experience has be NA) but ...

Doesn't the Kompressor system kick in around 1500 rpms? Without either some sort of bypass system in the exhaust, I could be wrong but, an open or too large an exhaust would just kill low rpm performance.

When the Kompressor engages, does it engage at full boost? If not, you still need properly tuned exhaust dynamics to not kill performance ... especially torque, which for me personally is more fun than horsepower.

I'll let the experts confer here, I'm just scratching the ole noodle, but I always thought you needed a proper balance of back pressure for the greatest velocity and scavanging with this type of SC setup. (And maybe I am putting the horse before the cart because the velocity/scavenging is what creates the backpressure) I know with a Roots you can just run open headers and be done with it.

azncarjunkie

You mentioned two very key words. velocity and savaging. Managing exhaust is just as important as the intake.

If you're running enough boost, I could imagine where open headers would be more beneficial. I'm curious why you're saying that with a roots blower 'you can just run open headers'. That sounds like old-school muscle car mentality where you don't worry about exhaust tuning, but overcome it with more boost. I thought roots was more of a lobe design compared to our screw design. Don't know some of the particulars beyond that and would be quite curious why.

Full Throttle

Out of curiosity how much power does your car make. I would like you to post back to back dyno graphs from the same car, on the same day, same dyno that supports your claims. Many of us have built MANY turbo and supercharged platforms *in the real world* and we know what gains to expect from given mods and tuning. On no other supercharged or turbo setup does free flowing exhaust lose power. There is no reason to assume it will on a K55 engine either.

azncarjunkie

"No other supercharged or turbo setup does free flowing exhaust lose power".

I'm not sure if you meant to use both SC and TC in the same sentence. But this is a clear statement that you don't understand the dynamics of each.

Turbos work WAY differently than superchargers. Understand the difference and then talk. You can't put them in the same category since the exhaust manifolds alone are are completely different design. Forced induction IS NOT the same.

If you're ONLY talking about SCs.....and ONLY about peak horsepower then in most situations you would be right. Unfortunately that's the same mentality that most rice-burner idiots think when they put a 4" exhaust on their honda civic. i.e., A 2% increase at 5% of the power curve with a decrease of 10% over the middle 20% but you can 'claim' a 2% increase in max HP. So while you're mostly right, you're still unfortunately wrong.

I don't need to post dynos because the "claims" that I'm making are scientific facts. The ball is in your court to prove science wrong, not the other way around. Do some google-searching and I'm sure that you'll see that you're unfortunately wrong. It's not that big a deal, just a common mistake people make when comparing SC and TC and thinking forced induction is simply forced induction.

FYI, I'm on a stock 55 motor. If you're hunting for credentials, I've spent plenty of time with REAL fabricators of 1k+hp street cars along with NHRA. Not your typical plug and play, bolt-on, enthusiast knowledge.

azncarjunkie

Notice I'm not getting into a lot of things like valve timing/overlap. The simple point to understand is that a properly designed exhaust actually helps evacuate spent exhaust fumes from the cylinder to prepare for the next boom-boom. If you want to take it to that level then I suppose we could.

I'm pretty sure you've heard of variable intake runners for low rpm and high rpm intake air management. We're pretty much discussing the same fluid dynamic concepts, just for exhaust rather than intake.

Please do some research before responding though. You might actually be influencing some people into believing you.

Full Throttle

OMG i just spit coffee all over my monitor.


I have done research on all the above 600whp turbo and supercharged cars i have owned in the past. Supras, Cobras, DSM's, EVO's..ect the list goes on. But I will step aside and let you get back to your bench racing, Its quite entertaining.

azncarjunkie

Oh god....I'm assuming you're going to argue next that gravity doesn't exist either.

Your inability to enlighten the rest of the forum with facts is a demonstration of your level of knowledge. 3 of the cars that you listed are turbo cars which clearly work on different exhaust mechanics than N/A or SC. If you have gotten some of those motors over 600whp, then you should already know how critical manifold design is and the pros/cons of longer/shorter manifold tubing for TC cars and why it's so different than SC.

You really should stop talking. Your contributing to the dumbing down of America. God knows how many people from this form are going to regurgitate your idea of "For forced induced engines the best exhaust is no exhaust at all." For the sake of humanity's future not falling into stupidity, just admit that you were wrong in categorizing SC motors and TC motors into the same category and move on.

Or perhaps I should argue for you since you're incapable of doing so. Your blanket statement is wrong no matter how much you try to argue it. You would be correct when you reach the point where you are boosting at a high enough level where valve overlap allows the boosting pressure (high pressure) to more quickly move into/out of the cylinder and overcome any benefit of scavenging. Or in simple terms, the benefit of boost 'pushing' the exhaust out is significantly greater than the benefit of exhaust 'pulling' it out--this is of course assuming valve timing allows it.

Understand the whole picture of Forced Induction. Not just the hyper-performance/boost portion and the world will be a smarter place.

azncarjunkie

For the rest of the people that might be reading for the sake of learning remember that valves open and close so exhausts and cylinders work in pulses not a seamless flow of air as most people incorrectly assume. Therefore there are always areas of high pressure and low pressure just outside of your exhaust valves (just like if you drop a rock in water, the ripples represent high and low pressure). You're always trying to create the lowest pressure possible outside of the exhaust valve and the highest pressure possible outside the intake valve. the physics of this world dictate that a fluid will always move from the area of high pressure to low pressure at a higher velocity the greater the difference in pressure.

Using the rock in water example, it's easy to see that by confining the exhaust you will effectively have a greater high pressure and a lower low pressure than that of a wide open exhaust (the energy will disperse/diffuse in a fan shape). This is why a properly tuned exhaust can take advantage of a large low pressure pulse to scavenge.

Full Throttle

You can make as many personal attacks as you wish. It really does not matter to me. You have no experience with any thing that has made any amount of power with mentioning. You're just magazine page flipping bench racer. Until you can post back to back dyno figures that support your claims all your long winded babblings are moot.

azncarjunkie

"claims". You're the one claiming that open headers is the end all be all for any FI motor.

Asking for proof against simple science. True genius. Go ask a muscle-car shop that specializes in SC....maybe you'll learn something.

Vadim @ FD

Our X-pipe replacement has no effect on tuning of the exhaust.

It simply replaces stock resonator with an X-pipe design that alters the sound, not power. Our X-pipe is dual 3'' vs. fatcory dual 2.75'' and internal diameter of the merge is over 4.5'' overall diameter, hardly what I would call restrictive.

15F difference in temperature can easily account for performace difference.

Lex, try it in the same weather and you will be back to where you were.

Have fun!

juicee63

Are you running the car in C mode?


In order to really compare the two number sets you need temp range within 1-2 degrees.

Was the March run 65 or 80 or 70?? Was the July run 90 or 99 or 95?

If it was 65 in March and 90 in July this will cause a huge performance drop. If it was a 5 degree difference than something is wrong with your car.