So I am having boost creep issues on a 76mm turbo and BMW engine, 4" exhaust with a single precision 46mm gate (have a tial 44 too, in case I have to add a 2nd, tried both gates).

A 2.9 psi spring creeps up to 12 psi by about 6500 RPM ,and a 13 psi spring crept up over my boost cut limit (250 kpa). The problem is, the further from my desired pressure spring I use, the slower the turbo spools (because it opens earlier) - but I can't run close to the spring weight because it creeps up. So a 9psi spring is resulting in 18 psi or so by 6500 RPM in 3rd... which is where I want to be boost wise, but it doesn't peak and hold, it makes like 1 bar by 5000 and gradually raises up.

So, an engineer recommended I tie the wastegate into the downpipe/exhaust to increase the energy on the backside of the turbine wheel.

Thoughts? Right now it dumps to atmosphere - not a fan of the sound but it was easier.

 

that would only make it worse

 

recirc will add backpresure may help slightly with boost control

 

Picture of the manifold?

 

thats what said engineer is saying - since the energy released from in front of the turbine wheel is so much hotter than what traditionally comes out of the turbine wheel (via downpipe), it should create a good amount of back pressure.

 

This would help, and especially if you could show wastegate placement w/dumptube. Recirculating will likely make it worse. I was able to cut my boost creep down significantly by making a very short wastegate dump tube that comes through the hood. If you end up modifying the manifold to add another gate, make sure the runner to the gate is angled with the flow of the exhaust gasses, rather than just a 90 degree angle.

Edit: You're quick lol

 

With that picture, it makes so much sense why it is creeping. There is no easy way for the exhaust gasses to flow out of that wastegate in that location. While pressure obviously plays a role, you want to rely on that as little as possible.

For instance, look at this lovefab manifold. The runner for the wastegate is integrated in a way that allows for easy flow out of the manifold.



I don't see your problems getting much better without a design change or huge wastegate.

 

Right now the dump tube is about 12" long and has some slight bends in it but nothing drastic but not as short as possible and not straight.

I am going to tie in this wastegate. I have a 2nd 44mm on hand, though it will be a PITA to take the head off and add a 2nd gate... but if I have to... then I have to.

What do you guys think about something like this:



Blue tube being a tie in to the single wastegate.

 

Plumbing the WG back in to the exhaust will be more restrictive and may... MAY help reduce boost creep.

However, adding a restriction to the system and decreasing your overall VE is not... NOT the best way to go about this. Your single WG appears to be plumbed correctly and should be flowing as much as it can; you say the dump tube is relatively straight. This leads me to believe you just are not gettting enough flow from a single WG to keep up with your compressors output so I would suggest a 2nd WG. Can you not use the space to the right of the flange on the header for the 2nd WG?

Good luck.

 

Thank you Alfa - I have been thinking about this a lot recently. Its a bit of a catch 22 in effect. I think I have several drawbacks in my system:

1) The collector is pretty short - therefore the spool is pretty fast as the exhaust is shot right up into the turbine housing, but without much "common area" I have a hard time venting the exhaust from there as a whole, its very "regional" if you will. So venting 2 cylinders leaves the middle two free to decide where they go (likely into the turbine housing) and the opposing side definitely spooling into the turbine housing.

2) WG placement - I chose the area I did because I have friends using that spot with great success. My friend can regulate his boost to 12 psi or so on the same turbo. The difference is I have a 4" downpipe and exhaust and he has a 3" down pipe and exhaust with the WG tied in.

3) People say raise the boost level above the creep level. This doesn't seem to work as I have noticed. I am going to try a little more with the MBC (Hallman Pro RX) but I think I figured this paradox out. As I increase the boost controller up toward the creep level, he creep level creeps higher. The turbo spools faster since the WG isn't opening as early, which in turn sends more air into the motor faster, which makes more energy, which spools the unit faster, repeat. When I creep at 9 psi spring pressure I made 18 or so by redline. When I hold the spring closed to make (hypothetically) 16 psi, then that energy comes through in even more amounts, again, creeping up.

Of course this could all be wrong - this is just my brief experiment/findings. In my mind it would make sense that if I raise boost to 16 psi through a MBC it should creep only to 22, but given that the WG opens later and bleeds off less as it spools, maybe thats incorrect. I will admit I was hasty with the MBC adjustments. Cranked that bad boy down 2 turns from open and saw no results. Said eff it and turned it like 8 turns. Saw overboost hahah. So, maybe I should try it more this week.

Saturday I am going to tie the WG in to the exhaust. Kind of excited to get rid of that annoying open dump sound, so even if it doesn't cure my boost issue, it'll sound better.

Thanks honda world for their boost creep insight

 

Your manifold design & wastegate placement is responsible for your boost creep.

Add another wastegate and call it a day

 

In this case, +1. 2/3 of your runners are shooting towards the turbo before they can vent out the VG. Hondas have this same problem on the old DRAG manifolds that have the WG halfway down runner #1 instead of just before the turbo (centered where it collects).

If you ADDED that blue tube, it would probably eliminate boost creep. If you moved it to that spot, you may still get some for lower boost. Adding a 2nd WG in that huge space in front of the collector would work wonders.



As far as adding boost when it creeps, you are supposed to do that with the MBC, not spring. A good MBC will open the WG as far as it can if it creeps too far, yours doesn't seem to allow that. Sometimes the vent hole on the MBC is too large.

 

I can't add the 2nd WG to the front side of the collector - that's where my oil drain and all is at, along with my compressor outlet.



Seewutimean?

Whatcha think about adding that blue tube or the WG off of that blue tube area.

 

nice v-stack





re-circ'n the dump tube will make the dump more restrictive, and will increase your creep issues... try to make your dump tube as straight and short as possible, dump it to atmosphere.. if it doesnt resolve the issues you might need to add a larger gate or another gate all together.