I actually have the older tubular manifold, not the cast one. I don't see modifying it for an external wastegate—I'd rather just sell the kit and buy a proper external gate kit. To be honest, it would likely just be a 35R-based kit with a TiAL v-band housing and a single gate plumbed back in. I don't really need to deal with dual gates and all of the associated pain in the ass with plumbing. I'm building a SIMPLE set-up.

It's more likely I will at least try to port this wastegate, open it up to 40mm at least and remove the divider, port the inlet path a bit, and try that out. It will likely depend on the cost of the housing.

The water injection thing has been discussed, but honestly it both goes against the "simplicity" ethos, and if that's where I was interested in going I could just throw that on top of my twin turbos to solve the IAT issue and be done, and sell about $5k worth of stuff.

IDK, mechanical water injection systems seem pretty simple to me, but it is your car and your choice.

I think the 2.75 metal exhaust gasket in your 3" exhaust is worth a shot. It's seems extremely simple.

Your saying you don't want to try the gasket because it goes against everything that you have done. Your original dyno run at 13 psi was part throttle at 390ish hp right?

What if the exhaust gasket works, and your car makes 400 at 13 psi wot? Would you still not be satisfied?

He's saying the last time he fought this problem, it took a 2" restrictor to stop the creep and he felt a definite drop in power...and that he is at least going to try the restrictor since it is easy but he is not expecting much. What I got out of it at least....

Except your 99 twins can't match the power curve of the 8374 from 3500 rpms +(the whole area you use on track). The water meth is about as simple as it gets. I've installed 10+ AEM kits with zero issue. It really is the best solution to your problem. I'm sure you would like to not get walked by Z06s and GTRs on the straights.

Except at 400+ RWHP the diff and trans become as consumable as oil when being tracked hard on sticky tires.

Jason

^You say this based on......?

Not necessarily disagreeing, more curious.

I beg to differ

What constitutes as sticky tires? I've been tracking for years at ~400whp and have had no such experience with my drive-train. Trans has been fine and my diff, though has a carbonetic LSD has been completely trouble free. No extra cooling, just regular fluid changes.

Edit:
ptrhahn, as you already know I am converting my EWG setup to an IWG. A long with a large streetport, I'll be running a 3.5inch DP, 3.5inch MP to a FEED ti catback. My goal is to hold a steady 15psi for track days and like you I am a fan of simplicity. No AI, E85, etc. Ill report back as to how the system handles my high flow setup and maybe we can compare notes.

It may be down to individual driving style, track characteristics, or just luck, but lots of track guys have noted the phenomenon. Sticky tires would be Hoosiers or other similar slick-style R-compounds

I'll be interested to see how your set up works. This was the purpose of this thread, rather than to psychoanalyze me or my expectations.

One theory I have is that my port is "small" port, mostly intake with very little/no exhaust porting.This is done to maintain exhaust velocity, and I'm wondering if that in combination with an ultra-short manifold, good flow everywhere else, and just a particularly strong motor (as evidenced by making 30-50 more hp than other similar setups), contribute to spinning the turbo up at high rpm. Think of it like putting your thumb at the end of garden hose... the flow of the water increases velocity.

Same phenomenon happens with stock twins with actuators when you free up the exhaust.

Bringing back this post alive, Pete were u able to find a solution?

None thus far.

Working with Elliot on an extra housing to try porting. I wouldn't expect a definitive answer for a bit, as it'll take a while to get it, figure out how to port it, and pull the kit and reinstall.

I'm also looking at water injection kits—I still don't want to run that or high boost on the track for heat/durability reasons, but having tasted 17psi on the street it would be nice to have that option.

Just to add something on this thread:

I just installed my 7670 IWG on my stock-ish port FC with a turblown cast manifold, 3.5" downpipe, and a small (probably restrictive) air filter.

turbosmart actuator with a 7psi spring

boost is rock solid at 7psi, boost might have gone up to 8psi at redline in 4th gear.

Ptrhahn, I am probably the "other" guy Elliott was referring to. I bought my iwg8374 from him, however I made my own manifold. It is a copy of his. My boost creep is far more severe. On cool days I can see as much as 26psi. I upgraded the ignition to the smart coils thinking I might have been blowing unburnt fuel over the turbine. Didn't work. I also made a 2nd manifold with larger diameter runners thinking there might be a velocity issue. Didn't work. I am dumping a crap load of water/meth in. My knock levels under acceleration never get above the teens. I am running a 100% stock port motor. I was thinking the same as you, too much velocity. At one point I wired the wastegate wide open. Spool up was very slow but still creeped the same above 6k. I have a 3" open exhaust. I put a 2.75" restricter in the exhaust. It didn't change much. A couple of pounds at best. I quit worrying about it sense my knock levels were good. I just make sure to top off the AI tank every time I take it out. I have to say the acceleration is incredible at those boost levels. Please keep us informed if you find a solution.

I spoke with an engineer at Borg Warner today, and he indicated that I ought to take a close look at the turbine housing wastegate passage for potential casting issues (wouldn't take much of a booger to plug that 35mm pathway up), and/or if I were to get a 2nd housing to port, swap it in and run it as-is first to compare.

The other suggestion was to run the 9180, because the larger turbine would flow more. BW will make you a custom turbo with the 9180's 80mm turbine wheel, and the 8374's 83mm compressor, but it ain't cheap.

P

I've looked closely at my turbine housing and WG runners. I really didn't see much room for improvement. There is only a minimum of material that could be removed underneath the door. Like you said, I think you would have to remove the divider in order to gain any amount of area.

^ maybe shaving half a mil' off everything would make all the difference? Half a mill on a 40mm hole with a divider in it is quite a bit of material. Is there any way to make the door open further? Move the pivot point on the actuator arm in a touch?
This of course coming from the guy who shat himself and swapped his IWG hotside to an EWG, but I already had wastegates and a manifold to work with. An acquaintance is going to be using one of these and its a bit of a concern.

Well, the "door" itself is 42mm, but the diameter of the hole is only 38 or 35mm (I've gotten conflicting info), if you could shave 1-1.5mm around the outside (making the diameter effectively 2-3mm larger, then subtract the divider and the material around the four radiused edges of it, you've got a bit more material.

I'm not knowledgeable about how one would calculate this sort of thing, but taking 4psi off of 16 is 25%, which isn't small.

the 26 lbs of boost that Ernstudet22 is seeing is craziness. It just doesn't make sense that there would be such a wide range (11 to 25 lbs) of results in relatively similar cars. There must be some other factor at play.

Well im guessing that if you took around 0.5mm off the sides of a 38mm hole and divider (leaving plenty there for the door to seat) you'd get about 10% bigger cross-sectional area.

Im not going to pretend to understand the dynamics of wastegat flow and manifold pressure, but I would be guessing that taking into account surface friction on holes that small, 10% more area would equate to more than 10% more flow, especially if you took out even more material than that the rest of the way down the volutes and polished it all up a bit...:dunno:

Yeah its doing my head in the wildly different results people are getting. - could a difference in the castings be a part of it??

"a wide range (11 to 25 lbs) of results in relatively similar cars. There must be some other factor at play."

absolutely.



one variable is the turbo manifold. (first off i don't know what manifolds are being used, maybe they are all the same...) if, however, if the do differ they could effect all dynamics.

a well designed manifold will allow the turbo to spool earlier, make more power and therefore be more difficult to control... such as in Peter's case.

a poorly designed manifold will tend to choke the exhaust flow therefore driving the compressor w less net force. the result being an easier to control boost factor.

this may or may not be THE answer but it is a factor. it may prove to be ironic that the manifold is so well engineered from a flow aspect could be your problem.




WG sizing and rotaries

BG engineers are no dummies. WG sizing is walking a narrow line. too small and you can't control boost, too big and you can't control boost.

notice the factors considered by BW when sizing the IWG highlighted in red...

"By using a conservative flow coefficient assumption, we can predict how
much flow will pass through a wastegate port of a specified diameter,
motivated by the expansion (pressure) ratio across the turbine stage.
Using this method, the wastegate can be sized on a match-by-match basis. This
procedure was followed for a wide range of matches (displacements,
power levels, engine speed ranges, turbo sizing) at the beginning of the
project. It was decided that a 31mm port (36mm valve head) would be
sufficient for the smaller turbine housing, and a 36mm port (42mm
valve head) would be used for the larger housings. 36mm may not
sound that much larger than 31mm but in fact it’s 35% more flow area.

nowhere do you see engine type as in piston/rotary.

the rotary produces both more flow and more violent impactful exhaust impulses than the piston engine due to VE and the peripheral exhaust port.
i have no doubt that the rotary requires a different WG setup than a piston engine.

boost creep occurs when WG bypass flow requirements exceed 40% of total exhaust flow.

adding to this challenge is the, uh, diminutive size of the WG.

a 36 mm WG is 1.57 sq inches area

the two exhaust ports are 6.085 sq inches.

i run and recommend a Tial 60 mm WG on my manifold.

a 60 mm is 4.382 sq inches and easily controls boost of a GT4094r at 16 psi.

i do think that with a well flowing manifold, a high energy rotary exhaust flow, a very efficient low mass turbo, a single 36 mm WG will quickly reach a point where it can't bypass 40%.

you are there and i doubt porting the hole will solve your problem.

note BW's statement:

"In extreme cases, the EFR wastegate port will not be large enough. It is
sized to provide capacity for up to 40% of the engine mass flow to
bypass the turbine wheel. However, on applications using very low
boost pressures on large engines, little turbine power is required to
satisfy the boosting task and as a result the need for wastegate flow is
extremely high. In this type of scenario, there may be no other solution
than a very large external wastegate."

Howard

Thanks Howard,
The one interesting thing about the BW language is the part about 36mm hole being signicantly larger than a 31mm hole—35%. I don't think thew hole can be enlarged much more than half that 2-3mm, with the existing flapper door. But maybe that's maybe 15-17%. If you then remove the divider, and the radiused edges, maybe you get to the 25% required to get (mine at least) to the safe-margin-on-pump-gas threshold.

It also looks like BW has started making an 9174, but not an 8480... the latter being BW engineer's suggestion to have a larger (and thus harder to spin) hotside.

if you're considering changing turbos what about going the other way to a 7670 with the same .92 hotside? You would likely be running higher boost levels like you are now, but you'd be making your desired power levels there.

I don't see that as worth it. My twin turbos made 390rwhp @ 15-16 psi. I'll just put them back on.

that certainly makes sense, I just figured the 7670 would give you the benefits of less heat, less complexity, more reliability (supposedly) that you were looking for compared to the twins...just making about the same HP.

I hope it works out for you, I've been eyeing the switch from twins for a long time and it doesn't seem like there's a bullet-proof single turbo setup for track guys yet. They all have some trade-off. Good luck and keep us posted.