t28 turbine port

[twotonetsi]

hey guys. ive been all over lookin into boost creep problems. ive tryed all but porting and external wgs. im really trying to keep it internal, since there is no reason why i should need external on a big28 from force performance. as she sits with 3" turbo back, no cat, ported 2g manifold/o2 housing, intake, bov, 1g tb, hardpiping, smic, and boost source ran directly to wga it boost creeps. it hit and hold 13psi strong at 2700. it holds it till bout 4k and starts creeping really high! im going to try porting. has neone ever tryed this on a t25/t28 before? i would like to know what diameter the flapper for wg are stock, the size that it was changed to, and ne other helpful hitns on this. i have read all there is pertaining to 14b/16g turbines and i wanna know the specifics to the t25/t28 if possible. thanks

 

[kenamond]

I ported my FPB28 and have no significant creep with a 3" catless turboback (2.5" to the end of the flex). With boost set at 12psi, it hits 14psi at redline. I didn't open up the WG hole other than clean up the bumpy cast surface with a 40-grit flap wheel. I did take a lot of material out inside the housing to make the turn into the WG hole more gradual. I also ported the mani and O2 housing. I've posted pics in a bunch of threads.

 

[bmoha2]

My FP Big T28 hits 17-18 psi easily but has never creeped. It has been very consistent. I'm running a DNP SS tubular manifold, SS tubular atmospheric dump O2 sensor housing, Buschur racing SS 2.5 inch downpipe, 2.5 inch SS hi flo cat and then a Thermal research 3 inch catback exhaust. I was thinking about going to a test pipe or just having the exhaust exit out the front driver's side. I'd like to look at your setups more closely to see the differences between them. Is it because of the lack of a cat? Or does the 3 inch turbo back make that much of a difference? What other mods does your car have?

 

[kenamond]

Any decrease in exhaust backpressure will contribute to creep, because the turbine flow has an easier time. However, if you're dumping your WG to atm. from the O2 housing, the WG doesn't even have to go through the exhaust (unless I'm misunderstanding your setup). Also, you say you have no creep, but you're running 18psi. Have you tried running 12psi? It might be that your setup does creep...to something between 12psi and 18psi.

I've done some pretty aggressive porting of the WG entrance in my housing, and that technique has been proven to help reduce creep. Below is a pic of my housing after I ported.

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[bmoha2]

Artwork! Might be why you're a wiseman. You understood my setup right. Atmospheric dump O2 sensor housing. I've come to think of boost creep as uncontrollable boosting... Is that correct? I've always been able to control my boost levels with the combination of boost controller and pedal. I've never had boost develop at a rate I wasn't expecting or suddenly go very high. I think the first setting on my Blitz dual solenoid boost controller is set at .96 bar, slightly less than 14.3 psi if I remember right, depending on barometric pressure and elevation. I lost my bar to psi conversion program when my hard drive died and forgot where I got it from. I don't really have anything set that is less that .96 bar. I suppose I could reset one of the four stages (user programmable) into it and see what it does. I haven't messed with it in a long time. Now where did my English to Japanese translation dictionary go? Damn all Japanese instructions! I'm just kidding a bit. I'm pretty sure it's not creeping but you do have me wondering. Maybe I will play around with it a bit.

 

[kenamond]

Artwork! Might be why you're a wiseman. You understood my setup right. Atmospheric dump O2 sensor housing. I've come to think of boost creep as uncontrollable boosting... Is that correct? I've always been able to control my boost levels with the combination of boost controller and pedal. I've never had boost develop at a rate I wasn't expecting or suddenly go very high. I think the first setting on my Blitz dual solenoid boost controller is set at .96 bar, slightly less than 14.3 psi if I remember right, depending on barometric pressure and elevation. I lost my bar to psi conversion program when my hard drive died and forgot where I got it from. I don't really have anything set that is less that .96 bar. I suppose I could reset one of the four stages (user programmable) into it and see what it does. I haven't messed with it in a long time. Now where did my English to Japanese translation dictionary go? Damn all Japanese instructions! I'm just kidding a bit. I'm pretty sure it's not creeping but you do have me wondering. Maybe I will play around with it a bit.

Boost creep: If all of the exhaust flow goes through the turbine, boost goes up and up and up and up. To keep it from going higher than a certain point, some of the exhaust is diverted around the turbine. That's what the wastegate is for. If not enough exhaust can be bypassed, the boost level goes higher than you want. That's boost creep. It all boils down to the WG design. The 16g WGAs suck if you want to run below 15psi, because they don't open the WG lever enough. That, combined with the "desire" of the 16g to boost at 20psi combined with the WG passage cast into the housing make creep on those turbos commonplace. But it usually isn't a problem until the backpressure downwind of the O2 housing is decreased (full 3" turboback for example) which makes it easier for exhaust to get through the turbine and places additional burden on the WG system as a result.

1bar is roughly 1atm which is 14.7psi. If you run a vaccuum line straight from your j-pipe or compressor outlet to the WGA nipple and completely bypass your boost controller, you should run around 10-12psi. That's easy enough to test. If you can hold 12psi or whatever to redline, you don't have a creep problem. But I suspect that your WG setup may do a better job than the stock O2 housing and internal gate design. I personally believe that the best solution for a WG if you see creep is to use an external gate mounted on an aftermarket O2 housing that routes the dumped WG flow back into the DP in front of the flex section or similar. In this setup, the internal WG flapper is removed and the hole can be enlarged without worrying about a flapper covering it all.

 

[hypnoticpimp]

I had the same problem as you twintonetsi... i had an unported o2 housing tho...Once I switched to a Megan Racing o2 housing (did a lil porting on the wastgate hole) the creep is gone or should i say not as bad. I have my boost controller on the lowest setting and i boost to 15 psi , setteling to 13-14 by redline...Is this still creep?

 

[kenamond]

I had the same problem as you twintonetsi... i had an unported o2 housing tho...Once I switched to a Megan Racing o2 housing (did a lil porting on the wastgate hole) the creep is gone or should i say not as bad. I have my boost controller on the lowest setting and i boost to 15 psi , setteling to 13-14 by redline...Is this still creep?

That's probably a bit of creep, but since it's settling on 14psi (mine is, too), you're probably still good on stock fuel. I'd verify with a logger, though. Don't run too lean. Mine starts at 12psi and creeps to 14psi. Front O2v look fine, so I'm not too worried. I still see knock but that's an old problem I had even at 9psi boost on stock exhaust (no creep).

It's all about bypassing enough exhaust flow around the turbine. You may be able to do this at 12psi and 4k rpm, but depending on what the turbo is fighting against (O2 housing and exhaust), the effectiveness of the WG may not be enough for 12psi and it creeps higher. Hopefully, the creep is something your fuel system can cope with.

 

[tenn-gsx]

I have a t28. I have NEVER been able to boost less than 16-17 psi. I have ported exh mani, Ported o2 and 3 in dp and exhaust. I wasnt too concerned about it tho because that is the boost i wanted to run.

 

[kenamond]

I have a t28. I have NEVER been able to boost less than 16-17 psi. I have ported exh mani, Ported o2 and 3 in dp and exhaust. I wasnt too concerned about it tho because that is the boost i wanted to run.

That's the key; boost creep isn't a problem if you can handle that level of boost. Easiest fix: live with it.

 

[twotonetsi]

i agree on just tuning for it if u can keep boost below 20, but when this one hit 24+ thats too much. im going to try to port before the split to wg and wheel a lil as well as the flapper and hole just for security. i am still trying to find the diameter of the stock flapper and hole for wg before removing the turbo. if any one has one laying around, can u measure it. thanks.

 

[kenamond]

I just measured the WG on my T25. The outer diameter of the flapper is pretty close to 1.3". The ID of the WG hole is around 0.975". I have more faith in the flapper diameter than the WG ID, but they're both not exact. I couldn't get my dial calipers around the flapper completely, but that's pretty close. I had to eyeball the calipers and WG hole, so that's probably not perfect. I don't know if they change the WG on a T28, though.

EDIT: You can't undo porting. Before you port, you should atleast make sure your WGA is functioning properly. Take a pressure tester to the WGA nipple and see if/when it opens and if it extends the arm all the way.

 

[bmoha2]

What that porting means I am not sure. I bought it not very used from another member on here. One thing I do know for sure is that the Talon was running terrifically today! Wahoo! That's the best it has run since the engine fire a few years back that totaled it. I am not a car mechanic. I work in a totally unrelated field and have been modifying and now rebuilding this car solely from knowledge gained thru this website and others. I am pretty sure I couldn't have done it solo without this website! I did this without the help of any service station.