Johncy2000

Hey guys, I just put in 3 inch piping from the primaries to the mufflers and feel a difference in power, but does it lower boost a little bit due to the increased diameter of the exhaust? I remember on my evo I switched to 3 inch piping and lost a couple psi due to larger piping. Don't know if its the same with our superchargered E55's.

Bramage

I am not an expert here, but I will think it through.

Boost is created through the supercharger, and builds up in the intake and surge tanks. When an intake valve opens, that boost is shooved in, and then the intake valve closes. Following detonation, the exhast valve opens and releases the gases.

Valve overlap aside, I do not think a bigger exhaust, or no exhaust pipes at all for that matter would have any affect on an SC boosted engines actual boost PSI. BUT

Backpressure does play a big roll in the torque equation, and therefore, you could gain or lose power due to this type of modification. Some swear with 3", while other find more power (faster 1/4 mile ET's) with a smaller diameter. (2.5 - 2.75)

The trick with these cars: Finding the sweet spot. Not all 55's react to a mod or a tune the same. So it is really a matter of testing, datalogging and changing one small thing at a time if you are looking for the most you can get.

This is a different scenerio than with a turbo.. Turbo will not spin as fast if the velocity of the exhaust gases is lowerd (bigger tubing) Hope this all helped

Johncy2000

THanks for the info Bramage. My car has been noticably faster after the piping. The reason why I was asking this question is because a while back Vadim or whoever was talking about 190mm pulley because of loss of boost pressure with exhaust mods. I guess that's not the case.

Bramage

He would know way more than me. However based on my logic, I dont see a relation. I may be wrong, and I am certain that someone else will jump in here. Contrats on the extra power!

Johncy2000

Thanks Bramage. Car's a beast now. Can anyone chime in on this theory?

skratch77

you loose boost when more air is flowing threw the engine,s/c is still making same boost,but if you had a gauge it would show a boost drop from the added flow/volume efficiency of the exh.

sneakyneon

Boost is a measurement of restriction. When you decrease restriction boost will decrease. So yes, things like headers, bigger pipe and High flow mufflers will potentially reduce boost.
That being said, just because your boost decreases that does not mean performance will suffer. HP is made by air flow.

emoving

So could you actually be reducing the stress on the SC while maintaining the cars performance by using the 3 inch pipe?

Johncy2000

My car seems quite faster with three inch piping. When I start modding, this will for sure add more insurance on S/C efficeincy as boost drops slightly.

bassn_07

Right now I'm only running a 2.5" exhaust system with my floored fab headers. It came this way and so far I've never felt the need to change. Everyone has told me to go bigger but I just haven't seen enough evidence to switch, at least not yet. Now with more members going faster and quicker I'm starting to pay more attention.

My biggest concern would be giving up my 60' times at the track....any thoughts?

Jakpro1

Well known guy here on the forum claims going 3" killed his bottom end torque. Said you could really feel the difference but didn't have any dyno numbers.

Went back to 2.5" and said it was much better.

Interesting.

skratch77

I noticed a loss around 1600-2200 rpms with the kleemanns and primary cat delete.

E55Bullet

I doubt that changing the piping would affect boost what so ever, now change the headers and yes, a loss in boost...In my non professional opinion the only thing its going to change is sound. A lot of people think that running 3 inch is a must. I am not one of those people. Stock I believe is 2.75 and is connected to my headers. Alan is running 2.5, so I do not think 3 inch is necessary at all.. Just my .2

-Chad

sneakyneon

Yes depending on how much of a restriction the stock pipe has. There is going to some point of no gain, 3 inch may have a gain but 4 inch won't or a stock car my see no gain with 3 inch but a modded one would. I haven't seen a soild answers on our cars to whats proven as of yet...

Johncy2000

My car feels faster with 3 inch. My lowend is still great.

Hammer Down

Your lower end will still feel great because we have so much of it and the only way that you are going to find out is to have dyno'd it before and after.

Johncy2000

That's very true. Its hard to tell loss in power or torque with our cars because they are so ferocious. But gains can be felt pretty easily with me. Should I get Kleemann headers and hold off on rims. they are the same price and I think throwing headers in with my custom dyno tune, pulley, H/E, and pump would be marvelous but I want to look good going fast as well.

Hammer Down

Since you are going to have Jeremy custom tune your car I would add the headers now so he can dial it all in at the same time. Don't worry about the rims because you will be moving fast enough to look good!

beauphus

i went from stock piping to 3" back and gained slighly in HP all through the range but lost bottom torque (approx 20). only reason i removed is it wasway too loud on my cls with bmh headers...

Johncy2000

Headers it is. I'm just worried about the primary cats. Can I keep them with the Kleemanns on. I want to know if this is possible. If not then I might go with PLM headers then.

BenzoBoi

If you decide to go with the Kleemann headers, you will lose the primary cats. Why don't you just add a set of high flow cats in it's place? That way you'll have a set of cats in your exhaust system if that's what you're worried about?

Johncy2000

Do I need cats with an o2 bung or should I just get the tune to eliminate the o2 and get cats without a bung in them. Thanks for the advice Benzo.

I found these:
http://www.etrailer.com/Catalytic-Co....html?feed=npn

BenzoBoi

If I'm not mistaken, the extra pipe that comes with the Kleemann headers (gets rid of the primary cats) should come with the O2 bung on it already. So you shouldn't need to find a high flow cat with a bung in it. Just ask Jeremy to get rid of them for you if you want the easy fix.

Johncy2000

Thing is I wanna have cats on my car. I think that means cutting the header where the o2 bung is and welding a small spun HFC with an o2 bung. I wonder if this can be done.

Or I can have the headers installed with the downpipes in place then, since there is an o2 sensor already on the down pipe, I would cut the o2 sensor pipe and weld it on the the downpipe. Then connect the bottom part of the primaries to the rest of the exhaust system. The cats would be further back so I wonder if the o2 sensor would reach the new location. If not then I would somehow have to extend the o2 sensor.

emoving

I have Kleeman headers and I still have CATS.