Afi b16 turbo kit unstable boost

EITCP · Post by **EITCP** » Fri Apr 24, 2009 3:25 pm

i got one customer with AFI ramhorn turbo kit (t3t04eturbo) on his b16 civic. the car has ramhorn mani, 38mm wg, open dumbtube and 3\" exhaust. I tried only stock WG spring setup and it gave me boost from .7 bar (9psi) to .9bar(14psi). why? will i have more problems on higher boost also?? sceenshot of my datalog is attached

naturalalloy · Post by **naturalalloy** » Fri Apr 24, 2009 9:26 pm

The wastegate is not able to flow enough to hold low boost. It's a function of valve size, exhaust restriction, and exhasut flow to the WG. A bigger wastegate or a better manifold design would help if it's not a desierable low boost curve for your customer. Personally I like boost creep in first and 2nd gear since it gives you better traction from a more gradual torque increase. And no it won't do it as much or at all at higher boost levels since more exhaust goes throught the turbine rather than out the wastegate.

JaredKaragen · Post by **JaredKaragen** » Fri Apr 24, 2009 10:44 pm

notice the correlation with the AFR line and boost line... but both of them on a graph with injector duty and see how they relate... I think it's the extra fuel giving you a little more spool... and what is a \"stock WG spring\"??? is it an internal gate? either way... what is it _supposed_ to be?

EITCP · Post by **EITCP** » Sat Apr 25, 2009 1:59 am

WG sprig should be around 0psi, i didnt check. it is external 38mmWG and dumbtube is opened into atmosphere, not back into downpipe

JaredKaragen · Post by **JaredKaragen** » Sat Apr 25, 2009 4:23 am

0psi? I assume 10psi is it aftermarket or name-brand? I had issues with the little screws inside that hold the diafragm cup to the plumger... there were 4 of them... they liked to back out and cause my WG to raise PSI slowly.... the more they backed out, the more the PSI increased.

naturalalloy · Post by **naturalalloy** » Sat Apr 25, 2009 8:48 am

here's a B16 with the same turbine and same wastegate with a .7bar spring. It creeps from 9psi to 11psi by redline. There is a rich spot at 6200 rpm but otherwise the airfuel was flat in vtec. I have seen this on lots of B series with small wastegtes that come off the manifold at almost 90 degrees like your AFI one.

Adam Hopkins · Post by **Adam Hopkins** » Sat Apr 25, 2009 12:23 pm

The only way I know how to fix it is to upgrade to a 44mm waste gate. If you have a 4-1 merge collector and a 38mm wastegate it is almost guaranteed to creep on lower boost levels. I have to explain to customers all the time that tuning or a boost controller can not fix a creeping issue.

Post by **Bugermass** » Sun Apr 26, 2009 11:11 am

you can also try putting more timing in it.. If you are too conservative on the timing it can cause boost creep just as quicjly as being too rich. I did a 240SX with a SR20 swap yesterday, it was super rich when it came in and was making like 12 PSI of boost on wastegate and about 160HP, all i did was lean it out to where it needed to be and added timing until it made best power, ended up making 182HP and boost was steady at 8PSI.. So just by adding timing and getting the fuel right the boost dropped 4 psi.. but then again I have seen ALOT of suposedly top notch manifolds that boost crept no matter what we did.. Anyone can make a manifold that works, but making one thats actually designed well is another story.

combz · Post by **combz** » Mon Apr 27, 2009 9:26 am

i have not seen it with my own two eyes.. but the RC autoworks manifold has a good wastegate exit design. They use part of a weld el, so thats its curved and does not just have an abrupt 90 degree. http://www.rcautoworks.com/catalog/images/img_8069r.JPG cant really find a better pic of it.but it supposedly eliminates boost creep. We built a skyline manifold recently with that design, and we'll see how it works.

naturalalloy · Post by **naturalalloy** » Tue Apr 28, 2009 1:02 am

Manifold design matters but flow through the turbine is a much bigger factor. Look at all the stock turbo setups, they have restrictive turbines, horrible wastegate position and size yet can control boost pretty well. If you put a turbo with a stg1 turbine wheel on this AFi manifold you could get a ruler flat boost plot.

EITCP · Post by **EITCP** » Tue Apr 28, 2009 3:45 pm

Today i've tuned the car. it produced 350WHP at 20psi, measured on a mustang dyno. Boost wasn't stable neither at higher boost levels. But what can i do else than to tuned it like it is. Thanks for help, people. It seems that a problem comes from too small WG.

naturalalloy · Post by **naturalalloy** » Tue Apr 28, 2009 9:55 pm

The boost creeps at higher boost too or you mean it fluctuates? what's your boost control setup?

EITCP · Post by **EITCP** » Wed Apr 29, 2009 2:41 pm

boost creep. boost control is with ectune/mac solenoid, boost by gear. I didn't enable it as closed loop as i am not very familiar with it.

naturalalloy · Post by **naturalalloy** » Wed Apr 29, 2009 4:42 pm

can't you just adjust it so the boost goes down in the higher RPMs? I'm assuming you are looking for a flat boost plot.

Post by **calvin** » Wed Apr 29, 2009 5:21 pm

rpm based boost compensation(duty adjustment)?