Setup:

Built B18B
AFI Street Kit (T3/T4 .57 Trim)
Ram Horn Mani
Tial MV-S with 7.25 psi spring
Tial Q BOV with 8 psi spring
WG is fed from a pressure only port (I tapped my charge pipe)

Problem:
Went for tuning today and was aiming for about 9 psi since I am running stock MAP. Ran good but the wastegate would not hold steady at ~7 psi but would go right to 10-11 psi. My boost guage did not even hang up around 7 psi - it went almost directly to 10-11 psi for a second, and then my boost cut-off would engage (put in by my tuner)

Troubleshooting:
- Completely removed my manual boost controller to make sure it wasn't hanging up
- Removed dumptube to make sure it wasn't adding resistance
- Confirmed the spring was 7.25 (the box says it is, and it looks beige, but I will triple check and take it apart tomorrow)
- applied pressure to the pressure port, with a guage inline, and it began to crack at about 10PSI (this was with the WG out of the car - so no exhaust pressure - so I assume this is OK)

Noe of these tasks worked. My tuner wants me to replace the MAP with a 3 bar and tune higher and hope the WG will begin to control at some point. It's tough to tell if it will b/c now I have this boost cutoff and no matter what it kills the engine at ~10PSI


Any ideas what I have going on?



[Shown with no dump tube here]

 

with the poor wastegate placement it is usually hard to control boost even with a 44mm gate in that position. Even if you put a 3 bar it is still going to creep out of control.

Send it back to whomever made the manifold and have them fix it.

 

ram horns tend to creep.
sorry thats all the help i have for ya

 

they tend to creep due to poor wastegate placement/design.

Look at full-race's manifolds and you will see how they tear-drop the inlet into the wastegate to fix this issue. Its the little difference's like that that make full-race the best at what they do. Everything else is just half-***.

 

I thought boost creep would be if I hit somewhere around my spring setpoint, and then slowly "creeped" past it to say 10 or 11 psi. I am boosting right to 10-11 psi instantly.

And honestly I don't see much of a difference between the Full Race Mani, is it the angle of the port that helps? It is nearly in the same position from the looks of it.

 

Here's a pic for reference. You can see the tear drop that Miller is referring to. I have a AFI sidewinder manifold on my car with two MV-S gates and it runs around 11psi with 8psi springs.

http://www.full-race.com/catalog/ima...t%20t3%202.jpg

 

it can be either way, i had a 38mm on my topmount and it would do exactly what yours was doing, it would run right past 12lbs and keep moving. i put a 44mm gate on it and it holds 12lbs rock solid in all gears except 4th gear 6k rpm it starts to creep up to about 15lbs or so to redline.

 

I also had boost creep problems with my old ramhorn manifold and a 38mm gate. I chopped that off and welded a 44mm flange on there and it fixed it.

How do you have the vacuum lines routed?

 

you can try to recirc the dump, it should help with creeping

 

sorry to thread jack but i have an older full race ram horn manifold, and it doesnt quite have the tear drop like miller indicated... but i have a 44mm wg? do you guys think ill be experience boost creep? do i need to get my manifold reworked so i can avoid this problem? here is a pic of my setup...thanks again

 

^^^^ we cant tell you if it will creep or not, my friends old FR Ramhorn was exactly like yours and never creeped.

My old Neukin Ramhorn (no teardrop for flow priority, just a straight right off the collector) on the 13psi springs would hit 16psi and creep to 20 by redline with a Tial 44mm, glad I run E85.....

 

No offence to some of you guys, but i think it had less to do with the wastegate placement(don't get me wrong it is important). Then with turbo/turbine housing sizing.

Think about it if you were to run a t3 turbo with a .48a/r stage 1 wheel you would have more back pressure then a t3 turbo with a .63a/r stage 3 wheel.

Now with that said it is easier for the exhaust gas to go through the turbine then to bypass it. As the pressure difference will be less across the turbine then with a smaller more restricive turbine wheel/housing combination.

So if this is know then it is hard to fault a manifold company, correct?

 

its true indeed....i noticed a huge difference from the previous fr manifold to this new one.

 

sounds like you have a 10psi spring in there. pull it apart and confirm the color. totally possible the spring was labeled wrong or something.

i dont care if you have an 80mm pipe feeding the wastegate.....if the gate opens at 10psi on the bench, its not going to open any earlier than 10psi on the car.

full-race manifolds are the def. the ****, but thats not going to help in this situation.

 

Pulled out the spring - it is beige which is the 7.25 spring. I am going to try switching to a smaller spring size. Basically sounds like I have about 4lbs of unaccounted boost so if I drop my spring down a bit hopefully it will steady out where I want.

One other thing:

Looking at this mani above, and this link http://www.full-race.com/catalog/ima...t%20t3%202.jpg I honestly dont see a difference between manifolds. YES I have seen the tear drop on their site, but this is a vent port and I find it hard to believe the small tear drop would improve bleed-off.

 

Vac lines - T'd into the brake booster for my vac manifold and I run the BOV and Boost Gauge off of that. WG is supplied with pressure only from a bung in my charge pipe with 1/4" tubing about 3' long

 

my AFI sidewinder has one 44mm wastegate and it creeps past 17psi!!

 

Did anyone read my post.

 

agian, take the gate off, go do a 3rd/4th gear pull and see how much boost you get.

 

you must not know much about "fluid dynamics", looking at the outside wont help you understand, if you looked inside the collector of a manny with a teardrop you would see the difference..... the gases do not have to make that 90 deg turn to exit the collector but instead have a much smoother path to exit the collector.

 

Yes, doing that tonight...

Also
I throught about a smaller spring but I don't think that will help since it is cracking - just not controlling. right?


I can only hope turning up the boost to 12-14 will help since I just bought the 3 bar MAP. But after that I am out of feasible options short of hacking up a brand new mani.

 

Ok, I pulled the WG completely off and did a 3rd gear pull to maybe 5-6K and made about 4PSI of boost. I could not due a 4th gear pull - too damn loud, and I think I proved your point. Basically I have to add 4PSI to my spring pressure and I should be able to control to that?


So 7.25 spring, and 4psi of boost with no gate = about 11 PSI minimum.

Do you agree with this?


So I can get the weakest spring (4.35), or just tune to 11 PSI are my 2 basic options....? Do you think it will hold this pressure (11) or may I still see creep even after that point?


Thanks for the help.

 

What a/r is the turbine side?

 

if your seeing 4psi at 6k, its a manifold problem and its probably going to get worse with RPM.

throw a 2nd gate on the manifold

 

.63 on the turbine
.60 on the compressor






Well, I have my Rev limiter set at 7500, so I can't imagine I will see much more than that. It was a struggle to get it to the 4PSI. I would have taken it higher but it was evil loud...