Variety is the spice of life. I am gonna eliminate taper on mine while still employing the stock, integral MHI gate exclusively, fully ported turbine housing and a modded FP 18# actuator.

I don't like the TurboDumb inline(post turbine housing)gate design. I am also gonna run more than 1/2 an evelet of preload. But, to each his own.

 

The IWG75 is an actuator for internal wastegates, so I think he's talking about stock replacement WGA and not any kind of external setup.

Anyhow, maintaining a flat boost curve is not always easily acheived or desirable. Exhaust manifold pressure at 7000 rpm starts increasing pretty dramatically after about 25 psi of boost.

 

Yeah proper O2 housing design. Like the merged CBRD dump setup , and some of the better open dumps such as the Shearer one or the RT Ernie dump and a few others help eliminate taper. Flange size and contour plays a big part at the bypass outlet. Hell, some of the traditional housings duch as Titek and even the cheaper S.S. designs are fine if the crossover port is large enough.

The way I see it the first log jam is the 10.5 turbine housing's bypass port design itself. It is way restrictive and the lead-in radii need to be opened up. I just dont see much sense in adding on an external gate downstream of the factory internal gate.

Chad and Blouch configured the wheels to work optimally with the factory integral gate without any boost taper. Is the O P's 3B ported? Which WGA is fitted, the factory MHI or the CBRD HD unit?

I am thinking that maybe the OP should try raising WG preload level and install the HD CBRD actuator. He should check with Chad on which O2housing/dump design is critical. design dumpis less restrictive.

Porting the entrances from the turbine inlet area at the turn-in to the bypass port(s) helps bypass flow. Also, since this is a larger displacement stroker motor there is a larger volume of exhaust flow at any given RPM compared to a smaller 2L engine.

When porting the turbine housing on a 16G used on a stroker motor I would pay special attention to unshrouding the turbine outlet area relieving any shrouding of the turbine exducer and as Chad says a free flowing O2 housing is important. On a 2.3/2.4L I might even go with a 3.5" turbo back exhaust.

 

Yeah you are right Fred. My bad. He did state IWG. I prefer the FP 18 or 25# units to the turbosmart though. I haven't tried the CBRD HD actuator yet so I cant comment. I think my 3B is fitted with one though....so I will let you know.

Usually boost taper is not a function of insufficient bypass port flow which tends to cause boost creep not taper. Taper can be related to insufficient WG spring pressure though. So maybe that is what Benja is refering to.

 

since your turbo is not yet installed, could you post up pics of your turbine housing port job?

 

sparky, the reason i taper is because i track the crap out of the car. Like i am REALLY REALLY REALLY hard on it. I only do 2-3 hot laps at the very most with cool downs in between each session. At most i do 2-3 sessions. That is why i had them tune it with 2-2.2.5psi taper. If i were to hold 27.4psi the entire time, I am pretty sure something will blow up. 100% certain. I have very bad luck with my motors. Exhaust Gas Temps, engine temp, oil temps, water tempps will all skyrocket. I am 80-90% of the time between 6000-8000rpms. On the lower speed corners im above 4500rpms.

Also I am confident that if I did want it to hold with no taper, it would be achievable, but for my uses it was not what i wanted. If it was my daily street car to beat around in, then sure i would want a more aggressive tune because a few pulls here and there on the street won't hurt.

Track abuse is the absolute worst on a car.

Look at my signature.

 

And technically it doesn't really taper if you look at both graphs. It is more of a spike of boost at the lower end (<4000rpms) for torque then levels out after 4000rpms and pretty much stays there and holds the entire time.

 

Yes, Zhong correct and ditto. Now I understand what you are doing. After posting my response, I got to thinking last night that your taper was probably programmed into your race tune via ECU/BCS.

So, it is not a turbo/engine related aberration at all. But, rather you pull boost via your tune because of sustained WOT on the straightaways and the resultant high EGT's, etc. Thanks for clarifying.

With an MBC it would not be possible to roll off boost on the top end, or take advantage of the increased torque due to the intentionally induced spike the way you are able to control it through your tune.

 

Fred: Believe or not I am a complete nerd as far as posting pics on the forum. Sorry.

However, send me your cel #/whatsapp, or email address in a PM and I will send you the images. I already took a pic of the turbine inlets and they are very nicely matched up to the gasket. I bought the turbo used and it apparently has the CBRD port job.

I may do some deeper porting up into the scrolls but I haven't checked that deep yet. I will radius the bypass entrances and flip it over and gasket match the turbine outlet area and the flapper pocket.

 

Upload into Photobucket, and get the Link, then post the link here...
Its not direct, but not too indirect, after you do this a few times it becomes routine.

Than we can all see...he he he

BBK-B spools incredibly well, but bare in mind, new BBK-B spools incredibly well...if it is over 1 year old it may not be same technical spec, and it may spool slower. CBRD does not advertise technical improvements, but do implement them regularly.

Its prefect turbo for 2.3 on E85.

 

The turbine inlet area is pretty nicely ported and port matched as is, by CBRD. I just always do some additional porting on the shortside radius of the transitional turn into the WG bypass port.

Actually, since it is a TS housing, there are two bypass ports one each originating in each individual TS inlet chamber. These originate separately but then they siamese by the time they reach their exit point at the flapper valve seat.

Due to my old age I am overwhemed by laziness. Hence, I only port the entrance to one of the two bypass ports. I only grind the shortest of the two. The one that is located on the the TS chamber wall closest to the flapper valve and then I only open up the lead in radius.



This is enough to help the exhaust gases make the 90* directional change from the scroll centerline to the centerline of the WG bypass port. This minor transitional grinding just helps bypass flow.

I will try to post up some pics soon. Sorry for taking the thread a bit off course and into the rough.

 

I've had one laying around for a while now, here's some cell phone pics.

 

Thanks for the pics. I was curious to see how deeply it had been ported on the inlet side and what had been done on the outlet side.

 

my BBK-B took a crap. Got some shaft play on compressor side. Sending to BBK-B for repairs. It is also allowing oil to push to intake tract and intake manifold.

 

Sucks to hear. Do you have a clue as to what caused the problem?