Boost Creep. Enlighten me

AkursedX · Post by **AkursedX** » Fri Feb 04, 2005 9:00 am

I read a lot of turbo-car-related forums (rx-7, mr-2, and for my VW) and I have heard of the term "Boost creep"

Now I think I kind of have an idea of what this is, and why it's a bad thing, but I know there are a few people around here who eat sleep and breathe turbos and I figured I could stoke your ego a bit by asking you guys to explain it to me.

Also, is boost creep only common in small displacement motors. I hear the most about it on rx-7 forums. Would an improperly tuned (Like most of the Turbo Fieros on Fagland) turbo Fiero have to be concerned with boost creep?

Standard · Post by **Standard** » Fri Feb 04, 2005 1:47 pm

Boost creep usually means that your wastegate is too small. It's not bypassing enough exhaust so the boost 'creeps' higher as the rpm's rise. It's pretty common on the DSM's, also.

Post by **eHoward** » Fri Feb 04, 2005 6:19 pm

Poor manifold design is also a big contributor.

Standard wrote:Boost creep usually means that your wastegate is too small.

donk_316 · Post by **donk_316** » Fri Feb 04, 2005 10:27 pm

Is that intake manifold or exhaust manifold?

My first thought was exhaust manifold wastegate piping design or lack there of.

Shaun41178(2) · Post by **Shaun41178(2)** » Fri Feb 04, 2005 10:49 pm

Wastegate is on tEh eXh!! GOSH!!!!!!!!!!!!!

But yea its usually because of a excessively small wastegate.

First two posts were right.

Standard · Post by **Standard** » Sat Feb 05, 2005 12:09 am

eHoward wrote:Poor manifold design is also a big contributor.

Do you mean poor wastegate placement, or are there other factors?

donk_316 · Post by **donk_316** » Sat Feb 05, 2005 12:35 am

Standard wrote:
eHoward wrote:Poor manifold design is also a big contributor.
Do you mean poor wastegate placement, or are there other factors?

Thats what i was trying to say...i KNOW the wastegate goes on the exh side.

trigger · Post by **trigger** » Sat Feb 05, 2005 4:44 am

it can also be due to poor tuning. you can actually have unburnt fuel burning off in the exhaust manifold and therefore still spooling the turbo.

Post by **eHoward** » Sat Feb 05, 2005 11:24 am

It is poor placement of the wastegate on the manifold.

I will get my crayons out or maybe just repost some pictures from FieroXs website later today.

Standard wrote:
eHoward wrote:Poor manifold design is also a big contributor.
Do you mean poor wastegate placement, or are there other factors?

AkursedX · Post by **AkursedX** » Mon Feb 07, 2005 8:25 pm

Ok, so if you are flowing more air (Intake, bigger exhaust, headwork) without turning up boost, are you more susceptable to boost creep? My guess is yes.

Post by **eHoward** » Mon Feb 07, 2005 10:35 pm

Ok:

Not so OK:

Ideal:

Doug Chase · Post by **Doug Chase** » Wed Feb 09, 2005 9:42 pm

eHoward wrote:Ok:

Not so OK:

Why? It doesn't look to me that the flow to the wastegate would be significantly different between these two.

I agree that your "ideal" would be better for wastegate flow. On the other hand, having a big hole on the outside of a bend is bound to disrupt flow to the turbo. What I don't know is how much difference that would make.

Post by **eHoward** » Wed Feb 09, 2005 10:00 pm

First, it is flowing opposite the direction of the exhaust in the manifold.

second, it really should be in the middle of the 3 tubes instead of off to one side. Rational or not, in my mind it makes more difference in the 6 cyl version then the 4. Those outside two tubes arent going to get wastegated at all on the 6.. . Having different manifold pressures in each cylinder caused by the uneven wastegating is not going to be good at all for tuning.

about ideal, it is ideal for wastegate location and routing. I do imagine that air will stack up and become like a wall in the tube that leads to the wastegate until it opens. SO it should behave like a smooth bend until that time. My daydreams are anything but a CFD program though.

I havent had much luck finding a *bad* . .. . i am sure i will though.

trigger · Post by **trigger** » Thu Feb 10, 2005 3:05 am

hey howard, you wouldn't happen to know anybody that has a valve seat for a tial 35mm wastegate laying around would you?

donk_316 · Post by **donk_316** » Sat Feb 12, 2005 11:26 am

I thought about this a while back, I was thinking of adding a second Deltagate to my setup so I wont have this problem.

Like one for each bank of the V6 (35mm each) would totally eliminate the issue plus look pretty trick.

Obviously its overkill but for the price it would be fuck all to add.

Post by **eHoward** » Sat Feb 12, 2005 11:54 am

nope.

trigger wrote:hey howard, you wouldn't happen to know anybody that has a valve seat for a tial 35mm wastegate laying around would you?

Post by **eHoward** » Sat Feb 12, 2005 11:58 am

ON a car that is tuned to teh raged edge, I dont think dual wastegates would be a bad idea.

donk_316 wrote:I thought about this a while back, I was thinking of adding a second Deltagate to my setup so I wont have this problem.

Like one for each bank of the V6 (35mm each) would totally eliminate the issue plus look pretty trick.

Obviously its overkill but for the price it would be fuck all to add.

A variation of the above rams horn manifold using dual wastegates:

Yeah I understand that youre talking about a V6 (and probably placing each wastegate on a log manifold) and not an inline 4 set up as I posted but I still think 2 on the merge collector is the way to go on both configurations.

donk_316 · Post by **donk_316** » Sat Feb 12, 2005 12:05 pm

Man O man those manifolds are sure sweet, beats the hell out of cast iron logs with a crossover

Indy · Post by **Indy** » Sat Feb 12, 2005 5:38 pm

Somewhat O/T, but what is this header made out of that it has the gold hue to it? I was thinking Inconel, but I'm not the brightest.

Awww hell, I'll just start a different topic with my other Q's.

Nate

donk_316 · Post by **donk_316** » Sat Feb 12, 2005 6:12 pm

I would say its Titanium, cause it looks like my bikes exhaust.