DDP - To recirc, or not to recirc.

[87witmoreboost]

I have read several threads about downpipe options. I just installed a Cooleeze 3" DP with elbow. I ran it open the first night until I could have the test-pipe welded to the cat-back the next day. The power of open 3" downpipe, to 3" DP and 3" test pipe WITH catback was DAY AND NIGHT DIFFERENT. I was extremely let down when I drove away after getting it welded up.

I am now considering other DP options as I hear the BIC DDP is rated at 29WHP over other DP's. I really don't want a loud exhaust, which is why I went with stock cat-back. I didn't realize how much it would still restrict it though. This being said, I really don't want an open DDP - too loud.

The question is this - Does the open DDP make much more power than a recirc DDP? Would it even be worth it for me to go from my 3" cooleeze to a recirc? My boost (no boost controller) went from around 9psi with open downpipe, back to 7psi all welded up. I know that 2psi could be 20whp or so, and make the difference. So, if I then set a MBC to 9 psi, would it make me as well-off as 9psi on a DDP?

I truly do not understand how a downpipe raises stock boost. The only idea I have is that it affects the pressure differential on the wastegate actuator somehow, making it require more boost to open. Someone who knows - please tune in.

In summary:

1. Is an open DDP going to make a noticeable amount of power over a recirc DDP?

2. Will I see a difference from my 3" Cooleeze megamouth (integrated elbow) to a recirc DDP?

3. Would a MBC to 9psi and my Cooleeze give me the power of a DDP at 9psi?

4. Why does a downpipe raise boost?

 

[theKnifeArtist]

There's a lot to explain, but one thing i'll say is that my DDP gave me boost creep in the winter. The much larger exhaust flows so much air that the stock wastegate has a hard time coping with it and thus, it cant and it starts to creep up.

 

[87witmoreboost]

There's a lot to explain, but one thing i'll say is that my DDP gave me boost creep in the winter. The much larger exhaust flows so much air that the stock wastegate has a hard time coping with it and thus, it cant and it starts to creep up.

I wish someone would chime in an explain WHY the pressure on the backside of the wastegate affects what actuator is doing.

Intuitively, I would think that the lower pressure on the wastegate (better flow=higher_velocity=lower pressure) would result in a LARGER pressure differential on either side of the waste. It would seem to me that the actuator is designed to push open at a 6.8psi differential based on the stock exhaust/elbow, and the better flowing exhaust brings the turbine pressure down, LOWERING stock boost. Obviously, this doesn't happen. But, I really want to know why.

Calling someone with a brain...

IJ?

 

[Nocheez]

I'm no hippy, but you should recirculate it back into the exhaust. No need to spew even more crap into the environment than we already do, you know?

 

[blk92suprat]

I had a BIC DDP and swapped it out for a standard BIC downpipe.

I only noticed a slight decrease in throttle response on the highway but without all that noise.

The ddp is real loud past 3k.

Im very satisfied with my Standard BIC DP.

 

[Kckazdude]

If your trying to stay quiet then go with a recirculated DDP. The difference isnt that much between them.

 

[87witmoreboost]

I'm no hippy, but you should recirculate it back into the exhaust. No need to spew even more crap into the environment than we already do, you know?

Haha - It's all getting out there whether is blows straight down the open DDP or out my muffler.

No cat here.

 

[starscream5000]

You car is able to expel gas better with a free flowing exhaust. The exhaust gas go through faster. Faster exhaust gas travel, faster spinning turbo. Faster spinning turbo, more boost. The stock WG was designed along with the rest of the motor's setup to control 6.8 psi ONLY. With a free flowing exhaust it cannot cope with the faster traveling exhaust stream, thus the boost raises up some more. Make sense? It does to me, that's how I look at it, it may be wrong though...

 

[MOTOWNMKIII]

efficiency = performance.
nutshell
go recirc DDP. I kinda wish I had. I'm just running a standard 3" DP with stock cat back...not so impressive lol

 

[suprahero]

If you're slightly worried about the noise, go recirculated because it is freaking loud. I had an open downpipe and I never really got used to it.

 

[starscream5000]

If you're slightly worried about the noise, go recirculated because it is freaking loud. I had an open downpipe and I never really got used to it.

That's the key word

 

[ILikeCarsYesIDo]

I like my open DDP.

 

[suprahero]

<<<<<<Pansy

Now I have an open wastegate but for some reason it doesn't bother me at all. I love the sound of it.

 

[starscream5000]

<<<<<<Pansy

Nah, I am.

I hated my open test pipe when I ran it. It was loud a fuck, you KNEW the car was turbo. And everyone watched you drive by. Too much attention.

The only thing I miss was the extra 10-15 WHP I had with it. I lost about that much (felt like it anyways) when I put on my RSR GTII.

 

[rtrdpenguin]

Just my 2 cents...

Go with recirculated. I went with the open DDP and regret it due to loudness (some exhaust gases will still leak from the little wastegate tube when the gate is closed unless your metal plate is exactly flush with the turbo's exhaust housing). The power gains are supposed to be about the same, though I've never seen dyno sheets of the open DDP and recirculated DDP side-by-side. It does sound cool when the wastegate opens with an open DDP but it gets old pretty fast.

 

[Poodles]

:withstupi

I will being going to a rec. DDP in the future some time...

Normal DDP is fun, and it tends to make you drive to get better gas milage. Gotta drive nice not to be loud :biglaugh:

But... WOT 5th gear pulls with a DDP are amazing :love:

 

[bluezone]

the whole idea of a ddp is that your not blowing exaust gasses from the waste gate across the path of the exducer flow of the turbine. thus the flow doesnt get disrupted. velocity is your friend with a turbo exaust exit. so much so that the stock size waste gate port cannot bleed off enough manifold exaust pressure and volume, under high denisty atmosphere conditions.
recirulated may not be as effective in preventing boost creep, but a little porting of the waste gate opening might help this problem.
me i'm going recirulated.

p.s. bigger down pipes hold more volume so there is a larger area containing the same amount(volume) exaust gas. now if the pressure on both sides of the exaust housing were the same. the main force acting on the turbine wheel would be volume. but with a pressure differential(what a turbo was designed to work with). the higher pressure gas in the manifold accelerates down the volute and out past the turbine in an effort to equlize to the lower pressure in the down pipe. in doing this the gas trades pressure for velocity. this velocity is traded off to the turbine wheel. which turns the turbine wheel faster.
so a bigger down pipe allows a bigger energy transfer to happen.
this is an over simplification, but i hope it gives you an idea of how this works.

anyone care to add to or correct any of this.

 

[rtrdpenguin]

:withstupi

I will being going to a rec. DDP in the future some time...

Normal DDP is fun, and it tends to make you drive to get better gas milage. Gotta drive nice not to be loud :biglaugh:

But... WOT 5th gear pulls with a DDP are amazing :love:

You know, you bring up a good point. I had been trying to think of one good reason the open might be better than the recirculated... it really does make me stay light on the throttle! People around here are easily scared by loud noises so I have to keep quiet =)

 

[Poodles]

I've nearly drove a soccer mom in her mini van into a ditch...

She was going way too slow, took a right turn, 3 lane road, she went in center lane, I went to left lane.

Wastegate opens right at her open window, she veers over halfway into the breakdown lane next to the right lane...

Beyond that, it's irritating in daily driving...

 

[blk92suprat]

yup.. I totally agree

I drove it easy to avoid being loud. It does draw too much attention for my taste.
Doesnt help with limo tints either.

I was under the impression before I bought it that it would only make noise at high rpm's. Once it hits 3k+ it was making noise.

I swapped for a reguar BIC downpipe. I enjoy the sleeper supra better!