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While assembling my car, I figured out that the downpipe that Huronspeed provides with their T4 truck manifold kit will not work with my setup. I installed a UMI K-member and there's just no way to make it work. Nothing wrong with their product, it was a perfect fit when I mocked it up with my factory K-member. Since that's the case, I'm no longer going to handicap my power output with a .96 A/R turbine housing. I ordered a 1.25 A/R housing from VS Racing, and I'm having a full custom exhaust built.
I have an idea of what I want to do, but I'm not sure if it's feasible or will work well. Basically, my idea is to have a 4" dump pipe made that will come off the turbo and dump under the front of the car, with an exhaust cutout at the end. I'm not doing a fender/bumper exit because I want this thing to be close to stock appearing. I'll then have a 3" down pipe fishmouthed into the side of the 4" dump pipe and routed down between the block and K-member engine mount stand, then connect to the rest of the exhaust. The exhaust only exists to make the car quieter on the street while cruising, so it doesn't matter if it chokes off power - however, I don't want it to be so restrictive that it's useless. I'd like to set it up so it opens under boost, that way whatever exhaust is under the car is a moot point.
Will building it that way work? It seems like a reasonable plan, but I've only had experience with one turbo vehicle previously, and that was my old WE-4 Turbo Buick. This thing is going to make triple the power that had, and I want to make sure I do this right the first time.
I’ve had down pipes that just turn down and point at the ground in front of the engine. Do not recommend. You should really consider getting it out from under the car.
for the cutout you can get a normally open one with a vacuum actuator run the manifold pressure. It will suck it closed at cruise and idle and automatically open under heavy throttle.
I was planning on having it point outward and down towards the bottom of the front bumper, adjacent to the front tire. Basically in the same general direction most people route their dump pipes, just not through the bumper/fender.
I’ve had down pipes that just turn down and point at the ground in front of the engine. Do not recommend. You should really consider getting it out from under the car.
for the cutout you can get a normally open one with a vacuum actuator run the manifold pressure. It will suck it closed at cruise and idle and automatically open under heavy throttle.
I have found that with a decent size cam, those vacuum cutouts rattle pretty badly.
Pro-Flow claims fully OPEN at 6 to 7 PSI
Should work really nice.
Let us know how they work out .... You going to use a single ?
What size ? 3.5 or 4 inch ?
Sounds similar to my plan. I have a 5.3 with a LIL John stage 1 turbo cam, its 222/227 with 113lsa. I don't see vacuum being a problem so using a vacuum cutout.
So the plan is:
Huronspeed 4" fender exit with 4" vacuum cutout to block it off. 3" exhaust to back of car,
Sounds similar to my plan. I have a 5.3 with a LIL John stage 1 turbo cam, its 222/227 with 113lsa. I don't see vacuum being a problem so using a vacuum cutout.
The plan is:
Huronspeed 4" fender exit with 4" vacuum cutout to block it off when cruising. 3" exhaust to back of car, with an OBX exhaust. Also adding a 200 cell metallic cat to it and a Thrush 20" stainless glasspack. I might spring for a Borla transverse muffler too (pn 40474 or 400499) Its got a bigger body and there are complaints its too quiet so it might be quiet enough for me. Lol
PS: if you use a vacuum cutout you can add a vacuum pump to force it to close when you want. You could also install a solenoid to keep it from seeing vacuum so it stays open when you want. I'll probably do both.
Yes, I plan on just using a single 4" one. That should be more than enough, I figure. Since turbos seem to choke flow more at higher boost levels and turbo speeds, having it open up around 5-7 PSI will be perfect. I'll update this thread when I get it running, but that may not be until next spring at this rate.
Question: If I'm setting it up this way, where should I mount my O2 sensor bung? Huronspeed mounted it down their downpipe a little ways, but that's not going to work if my exhaust is favoring the dump pipe. I don't want to mount it too close to the turbine exit, but for proper flow into the exhaust when the cutout is closed, the downpipe will need to be fishmouthed in at an angle and that's going to place the fishmouthed point pretty close to the turbine outlet. Should I just place it at the midpoint of the Y? Will having the O2 that close to the turbine throw readings off?
Last edited by LS1Formulation; Jun 6, 2024 at 01:01 PM.
No, you wont hurt it being close to turbine. You actually want it close. Mine is about 6 inches from the turbo and it works good. With the dump you dont want it anywhere near open atmospheric air otherwise you will read lean.
Some guys that run divided manifold setups actually run widebands before the turbo so they can see each bank. But the accuracy of the widebands is thrown off once exhaust backpressure rises(boost) so they are only there for driveability and cruise.
The pneumatic valves don’t rattle at all in my experience as they are firmly spring loaded in the closed/open positions. The cheaper electric ones (and even the nicer ones) eventually rattle. But the nicer electric ones don’t rattle for a long time and are adjustable. HPE badlanz are great for electric dumps IMO. Great customer service and they have replacement parts sold reasonably.
I wouldn’t listen to the above comment about wanting it close to the turbine. They are not designed to run in temps that high. If you read the manuals they state 14” minimum form the turbo. Mounting closer shortens the life, as mentioned. I found you can run 02 heat sinks and stick them pretty close and sensor life still is decent.
I agree with your plan as well, but I’m not a fan of the 3” full exhaust system. I like to run tiny crush bent 2.5” (I’ve even run 2.25”) to a factory style muffler. That way you can have a “Stock sounding car” or a race car. Best of both worlds. Not to mention a crush bent 2.5” or 2.25” system is less than half the cost and less weight compared to a 3” race exhaust.
You do need the valve that’s “normally open” and closes with vac for these setups. Usually, the exhaust system is too restrictive to open the boost activated “normally closed” valves.
EGTs should not be hot enough in the downpipe to hurt an O2 sensor.
Assuming OP is using a Bosch wideband, they are rated for continuous 1700*F, and intermittent 1850*F. If his EGTs are that hot in the downpipe he will have more problems than burning a wideband out.
Coupled with the fact that he is using an open dump, he will want it close to the turbine for a better reading.
Right from the Bosch spec sheet "The lambda sensor should be installed at point which permits the measurement of a representative exhaust-gas mixture, which does not exceed the maximum permissible temperature. Install at a point where the gas is as hot as possible. Observe the maximum permissible temperature. As far as possible install the sensor vertically (wire upwards). The sensor is not to be fitted near to the exhaust pipe outlet, so that the influence of the outside air can be ruled out."
If you look at the installation manuals they suggest otherwise. Can't say why there is such a huge swing between the sensor manufacturer and what the WB02 companies are stating should be done. I assume its sensor life related.
innovate
AEM
NTK
I use a heat sink like these when placing it close to the turbo outlets. And I still only get a few years out of a sensors before they start reading wonky. Innovate is the worst IMO. something to do with a crappy heater circuit I believe. AEM and PLX have been the best for me personally.
Last edited by Forcefed86; Jun 11, 2024 at 03:44 PM.
I'm going to be running what came with my Terminator kit, which I believe is a Bosch. Either way, the whole thing has to be custom fabbed, and I'm trading my fab guy a DOD delete and cam swap on an L76 sitting on an engine stand for a custom full stainless dump + full stainless exhaust. May as well make it look good, lol. I'll keep my O2 placement in mind when having it built, for sure.
Gotcha... Issue is the sound for me. 3” piping is loud compared to 2.5 or 2.25. With a nice flowing 3” system, I doubt you’ll see much difference between the Dump being open/closed.
Gotcha... Issue is the sound for me. 3” piping is loud compared to 2.5 or 2.25. With a nice flowing 3” system, I doubt you’ll see much difference between the Dump being open/closed.
I had a full 3" exhaust on my last car and there was a huge difference in seat of pants feel between open and closed cutout.
My QTP cutout was right under my feet and worked well, lasted for years too.
My innovate WB was just north of that maybe 16-20 inches and it lasted for four years until I sold the car.
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Have to build custom downpipe/dump. Thoughts? 
