turbo people....need some help, back pressure issue.

[one eyed willy]

so i have been turboed for about 3000 miles. custom built kit from scratch.i had about 1000 miles on it before i bent a rod and had to get the motor forged.when i first built the kit i was running a turbonetics 38mm wastegate, and a 2.5" downpipe. i was having issues with holding boost, when the rpms got high the boost would drop off a few PSI, so i would hit 10 psi, then by red line it would be down to 7-8psi. we noticed this on the dyno and some thing where done in te tune to help it out, it helped some but did not fix the problem entirely.I always though that the turbonetics wastegate was spiking in the lower rpm and then coming down as it got higher in the rpms to normal.


so to fix this problem (i thought),when i put the new motor in i upgraded to a 44mm wastegate and a 3" downpipe.re-routed the wastegate to allow much better flow.well, i still had this same problem, so i started thinking that maybe whats going on is too much back pressure and its forcing the wastegate open, there for loosing boost. so i switched to a 11 psi tial spring, it helped a little. then i hooked up a spare boost gauge to a copper tubing i plumbed into the exhaust pre turbo. im showing 28-29 psi in the exhaust when im showing about 8 psi in the manifold.

from what i have been told, you want a bout a 1.5:1 ratio of back pressure to boost, so if i was at 10 psi, the most back pressure i should want is about 15. so im at a 3:1 ratio , which im pretty sure is causing the wastegate to get forced open.(and probably what caused my bent rod)

so when i fixed my head gaskets this past week, i also swapped in a .96 exhaust housing on the turbo, thinking that the .68 i had on it was my restriction. but it didnt really help much at all.

so im trying to find out if anyone else has done a back pressure check? what size pipes you guys are using and where can i free up my back pressure at?im running 2.5" from the manifold to a "y" , then 2.5" to the turbo in front of the engine, then 3" downpipe to mid car where it splits into towo 2.5" pipes with bullet mufflers.

im going to take a new reading on the back pressure with the new exhaust housing, then im going to un bolt one of the pipes that come off the down pipe and see what that does. but if that fixes the problem then i dont know what ill do to fix it permently.

i have done a full cold side test using pvc end caps and pressurized the whole cold side to 20 psi with no leaks, i capped off the turbo intake and the intake pipe going to the TB. so i know the entire cold side is tip top and tight.i know the exhaust side is tip top and tight becuase of the back pressure im getting, if there was a leak causing the boost to drop then i would have way low back pressure.

 

[CataclysmGT]

You don't need such restrictive mufflers (bullet mufflers? they are still chambered design, no?) when you have a turbo, as the turbo will reduce noise significantly itself.

 

[Vashthe3rd]

Willy if you're not running a full 3" I'd recommend it.
I'm running the Magnaflow 3" and the entire car feels SO much more opened up. Like it's gone from breathing in a hot steam room to a fresh breath of winter air. Brings all the piping to 3" except for just the 2.5" neck on the end of my Y-pipe. The magnaflow system bolted right on which I was happy about.

I'd suggest that first and foremost. A larger diameter exhaust pipe always helps a turbo car (within reason)

 

[one eyed willy]

You don't need such restrictive mufflers (bullet mufflers? they are still chambered design, no?) when you have a turbo, as the turbo will reduce noise significantly itself.

doooood, i took the muflers out one time just to hear what it sounded like, it was absouletly aweful, i turned around with in 100ft and went home to put the mufflers back in there.it was hideous!!!

 

[quick60]

i have borlas 3" straight thru mufflers, and tell you the truth its not that bad,

what boost controller do you have

 

[gijosh28]

Turbos are kind of a new concept to me. My wife has had two SRT-4s, and both had this problem where the boost would fall off a couple psi in the rpm band. I just figured it was normal. I had a 3" turbo back exhaust on one of the neons with no cats and no mufflers whatsoever, and it still did it. I never though much of it, so I am subscribing to this thread. I want to see what comes of all this.

Vashthe3rd: Any links to exactly what exhaust youre running? Any sound clips of your car at idle, revving a little, drive by, and in car? I would love to hear how this sounds.

 

[one eyed willy]

what boost controller do you have

AEM

Willy if you're not running a full 3" I'd recommend it.
I'm running the Magnaflow 3" and the entire car feels SO much more opened up. Like it's gone from breathing in a hot steam room to a fresh breath of winter air. Brings all the piping to 3" except for just the 2.5" neck on the end of my Y-pipe. The magnaflow system bolted right on which I was happy about.

I'd suggest that first and foremost. A larger diameter exhaust pipe always helps a turbo car (within reason)

what size piping comes from the manifolds to the turbo?

 

[US-1]

You need a full 3" exhaust through a pair of straight through mufflers. Find a pair that sound decent even if you have to swap them out a few times.

 

[5.0Shocker]

You need a full 3" exhaust through a pair of straight through mufflers. Find a pair that sound decent even if you have to swap them out a few times.

+++++1
I tried Summit, E-bay mufflers, and a few others before I got it right on my last car...

 

[ChevyKiller]

You need a full 3" exhaust through a pair of straight through mufflers. Find a pair that sound decent even if you have to swap them out a few times.

Absolutely. I've posted it many times before, but here it is again...

My whipple set up made 626 rwhp @ 20 psi. After redoing the exhaust to a true 3" - this was the dyno - same car, same mods - just exhaust set-up change...



And here is the car with a 100 shot on top...



How the car breathes makes all the difference in the world when it comes to boost...

 

[Vashthe3rd]

what size piping comes from the manifolds to the turbo?

I'm fairly sure it's 2.5" for the sake of exhaust velocity.
I know the downpipe is 3"

You need a full 3" exhaust through a pair of straight through mufflers. Find a pair that sound decent even if you have to swap them out a few times.

I'll say that for a cat-less car the 3" magnaflow cat-back sounds great. 2.5" inlet so it bolts up to the stock cats if needed but it's designed with O/R exhausts in mind. Comes with open resonators and 5" tips (sounds big but it fills up the rear fascia cutouts nicely)

I'm going to get an exhaust clip up at some point, I'm waiting to get a new wideband and a dyno tune. I'm going to get a baseline dyno to see how much just the exhaust helped with the previous tune, then get a re-tune and see what happens.

I think Bassani also carries a 3" cat=back. Price for them range around 500-600$ at best brand new, I got mine with just a little dust on them from someone buying then not using them for 300$

Willy you might be able to get away with just fabbing up yourself some 3" diameter piping, or go with a side exhaust.

 

[one eyed willy]

i have a pypes mid muffler set up now. so from the turbo back it is 3" and then it splits into (2) 2.5" pipes and then thru the mufflers, they are the straight thru bullet mufflers, not bullit like ford bullit. i thought most of all the turbo kits for our cars used 2.5" pipe going to the turbo,so thats what i used.

1) im going to remove a section of dp to see if that helps
2) change out the wategate
3) move the bung closer to the turbo and away from the "y" section (wheres its at now)
4) redo the up pipe to the turbo

im hoping it gets worked out before making it to option 4, id hate to have to fab up a new pipe,it was a real bitch making the first one.here are some pics,take a look.

 

[Vashthe3rd]

yea I'm pretty sure it's all 2.5" to the turbo and then I'm 3" all the way back. Honestly willy nothing is going to release back pressure like opening up the pipes.

Honestly your fabbed up piping is so great at first glance it's almost identical to the Hellion system. Just making that observation lol, never noticed it. But yea your backpressure won't change much without bigger pipes and with the bigger turbo the open pipes will help all that much more.

 

[Freaknazty]

turbosmart e-boost has a rpm correction factor setting to cure the problem you are having bro .....

 

[Wes]

I just had a couple pressure taps made up that fit in the O2 sensor holes for this very purpose. Either Beau's car or another will be the first candidate of them this week.

That wastegate placement and routing looks a tad sketchy to me. Mike @ Powerhouse will have some good, authoritative feedback regardless.

Like Beau said, the eBoost can compensate but I wouldn't use it as a bandaid for a larger problem. I'd be interested to see EGT data from about 1" off the face of the exhaust port.

Wes

 

[retfr8flyr]

I think some of your problem is the way the wastegate is routed back into the exhaust. It's hard to tell from the photos but it looks like the wastegate pipe runs into the main pipe at almost a 90 degree angle. I think this is where you pressure backup is coming from. Before you start jumping through hoops with the rest of the exhaust try disconnecting the wastegate pipe and let the gate run open to atmosphere. See if that lets your boost level remain steady.


Earl

 

[one eyed willy]

I just had a couple pressure taps made up that fit in the O2 sensor holes for this very purpose. Either Beau's car or another will be the first candidate of them this week.

That wastegate placement and routing looks a tad sketchy to me. Mike @ Powerhouse will have some good, authoritative feedback regardless.

Like Beau said, the eBoost can compensate but I wouldn't use it as a bandaid for a larger problem. I'd be interested to see EGT data from about 1" off the face of the exhaust port.

Wes

any suggestions on the wastegate piping?
where should i grab the reading for the back pressure, at the turbo?
i think the egt's are up there with this kind of pressure,im starting to think this was the cause of the bent rod, too high egt's and too much back pressure.

i have thought about going to the eboost,but jebus that thing is expensive!i still need to bypass the aem and run it straight off the turbo.

 

[Wes]

any suggestions on the wastegate piping?
where should i grab the reading for the back pressure, at the turbo?
i think the egt's are up there with this kind of pressure,im starting to think this was the cause of the bent rod, too high egt's and too much back pressure.

As a somewhat gross simplification you can think of your exhaust gasses as flowing water and then imagine the wastegate as a way to bypass some of this water. What happens when the wastegate is at a 90* to this flow?

The advice above for temporarily disconnecting the wastegate to exhaust section is good.

Your test of removing the exhaust and measuring backpressure is great as well.

At this point a boost controller would be covering up a real problem. You should be able to work it off the spring for the time being and not see the high pressures that you are.

Wes

 

[one eyed willy]

hopefully i can dig into it tomorrow evening and get back to you guys.thanx for the help.

 

[jroc07gt]

Turbos are kind of a new concept to me. My wife has had two SRT-4s, and both had this problem where the boost would fall off a couple psi in the rpm band. I just figured it was normal. I had a 3" turbo back exhaust on one of the neons with no cats and no mufflers whatsoever, and it still did it. I never though much of it, so I am subscribing to this thread. I want to see what comes of all this.

Vashthe3rd: Any links to exactly what exhaust youre running? Any sound clips of your car at idle, revving a little, drive by, and in car? I would love to hear how this sounds.

srt4s do it cuz the turbos are so small. sometimes a adj wga can help.