[Mark 2JZ]

Hi guys so I’m in the middle of downpipe/midpipe design and I’m at the point that I can decide how to merge them and where.

I was originally gonna fab it how the HKS twin kit used to come out of the box, with the downpipes merging together before the midpipe, leaving the rest of the system modular.

but now I’m considering moving the merge further back in the system, just before the catback, as Mr. Henderson has done on his monster. I can fab it either way if it makes a difference in my setup.

basics of my setup are 3.0L, 10:1, e85, big plenum, Kelford v202d cams,1700cc/twin 450’s, and twin GTX3071R Gen2. From the turbo 2” compressor outlets they merge to the 75mm/3” HKS Type-R fmic to 3” exit, up to my 4” transition to the 4” throttle body. The twin manifold is from suprastore and it has long runners to tial v-band entry flanges to each .82 tial housing. Maybe this is irrelevant to what I’m asking but just including these details anyway.

from each turbo are twin 3” downpipes. so my two questions are what’s the best location for the merge, and is a merge collector (that has the pinch) better than just a Y-pipe that transitions the two ? does it really matter ? I’d imagine I’d end up somewhere with 800+whp at least with my setup but idk…. ive read that the merge collectors like this are typically used at the end of NA big displacement longtubes. is the theory the same ?

either way I’d need to join to 3” pipes to a single 4”.

this one below i already have

they both have the same entry and exit dimensions but one is a merge collector and the other is simply a collector. if I’m overthinking it then let me know. Visually the merge collector (top picture) looks like a smoother transition but the pinch just before the 4” section has me curious. For NA use they mention the venturi effect being useful but would it just be a restriction on the post-turbo side of things ?

Thanks guys,
Mark

 

[Casey James]

Mark,

I’d definitely run the two 3” down pipes further down such as you said Ken did. This only helps with your response time but also power levels. And you want to run them to the type of merge collector as the 2nd one you posted as it will help with any scavenging affect going on. The first one simply is just forcing each other flow into each other at the bottle neck.

For a NA car this is more important because you want to take advantage of the scavenging to maximize power. This is how I maximized my NA build putting over 500whp in a A4 with only 347ci.

On a turbo car, such as a twin turbo setup and on a inline 6 this goes beyond my understanding of physics I’ll have to admit. But I’d assume and without a doubt take the bottom style merge collector any day of the week.

 

[HiloDB1]

I'm interested to see pics of your kit as it sits. Sorry I dont know or have input on your downpipe merger but maybe you can contact @Griffon as he makes a twin kit and might have some answers for you.

 

[Mark 2JZ]

This is what i came up with for the pre-intercooler side of things, dual 2” to single 3” (the couplers are just there so I was able to hold them on my bandsaw. There not much pinch as the bellmouth almost exactly matches the outer edge of each tube and very little was sacrificed in the center for them to merge and interfere as little as possible.

so I’m guessing I should make one instead of using that shiny vibrant one I have ? Thanks for your input Casey.

Hilo, on my build thread I have recent pictures of how it’s been coming along. I’ve actually chatted some with Griffon/Joe quite a bit on FB messenger he’s been helpful as well. his kit emulates the merge as HKS as done, just before the midpipe starts. All i started with was the suprastore manifold and am fabbing the rest (although slowly)

I’m okay with the little extra fab work needed for the 4” midpipe to be replaced parallel 3”, but am doing my homework to get these details right to help with power/efficiency whenever possible.

 

[Casey James]

Nice job on the charge pipe merge!

You should be able to find one premade already. It’s a common size. Unless you just want to make one lol.

 

[HiloDB1]

View attachment 272890
This is what i came up with for the pre-intercooler side of things, dual 2” to single 3” (the couplers are just there so I was able to hold them on my bandsaw. There not much pinch as the bellmouth almost exactly matches the outer edge of each tube and very little was sacrificed in the center for them to merge and interfere as little as possible.

so I’m guessing I should make one instead of using that shiny vibrant one I have ? Thanks for your input Casey.

Hilo, on my build thread I have recent pictures of how it’s been coming along. I’ve actually chatted some with Griffon/Joe quite a bit on FB messenger he’s been helpful as well. his kit emulates the merge as HKS as done, just before the midpipe starts. All i started with was the suprastore manifold and am fabbing the rest (although slowly)

I’m okay with the little extra fab work needed for the 4” midpipe to be replaced parallel 3”, but am doing my homework to get these details right to help with power/efficiency whenever possible.

Just went and took a look at your build. Really nice! I actually ordered a kit with @Griffon Joe at Black Lotus. As he doesnt include the hot side piping in his kit I was curious how you were doing your merge.

 

[Mark 2JZ]

Yeah for the charge piping it’s totally up to the end user. HKS included a Y pipe for the intercooler merge piping but depending on how you want to clock the turbos and have your intake pipes situated it’s left totally open ended from so many variables with everyone’s setup. That’s why I like these cars so much 🤣 when i happen to catch another supra somewhere the first thing I always look at is the engine bay. It’s interesting to always see people’s approach to things, conventional or not.

i think I’ll try to make one, similar in fashion to my charge pipe merge, but even shallower of an angle. if not there’s always that black flowmaster merge i posted (readily available) not too pretty but if it works it works.

 

[KenHenderson]

Some pics for context (already shared with @Mark 2JZ) :

Piping on top was our first attempt, which was replaced by the piping on the bottom.

@Mark 2JZ, I'm sure you already know this, but the downpipes in the HKS twins set-up kit are 70 mm in diameter. I mention this because you plan 75 mm piping and in case you are in need of more space and flexibility.

With respect to your power goals, and from @SP Engineering files, Blackie made 1115 whp on C16 @37 psi (8.5:1 HKS stroker, twin GT 3240 turbos, 272 cams, PortFlow head, HKS Racing ti)

Kendal Yamamoto's QS TRD wide body (Turbo cover car) made 826 whp with HKS 2835s which he switched out to Blackie's set-up except for HKS 280 cams. With the new twin GT3240 set-up and HKS 280 cams, he made 1101 whp @34 psi, one of the lowest boost levels for 1100+ whp I've seen even to this day.

The High End Top Secret car we discussed earlier, with twin HKS 2835s installed and tuned by SP Engineering, made 820 whp all in.

All of this is to say, your power goals are, likely, quite conservative given your high compression motor and peripherals. So, if you need the space 70 mm downpipes would afford you, don't be concerned about their ability to meet your power goals. The cars referenced above were all 8.5:1 motors and were built long before high compression motors and E85 became a thing (my 1115 whp run was made late summer in 2004 to provide a frame of reference).



Ken.

 

[KenHenderson]

@Mark 2JZ, you're putting lot more thought into this than I did but, then again, I understand because you are doing all your own work. Once SPE and I agreed on the concept, that was my only input until [email protected] sent me the above pics and said "behold" 😎.


Ken.

 

[Mark 2JZ]

Ken, as always I appreciate your input ! This is great info as i wasn’t aware of that particular detail, the 70mm HKS downpipes that is. I plan to attempt to fit 75mm dp’s as the fab work carries over to my VVTi engine on a stand (I’ve measured the hard points i have to avoid (firewall/motor mount/frame rail/crossmember etc) if it starts to become forced with angles or doesn’t fall in to place as planned I can retry with 70mm.

i may continue with this thread, if allowed, in regards to big twin idiosyncrasies, for example, can i just use a factory 2JZGTE oil return “Y” (the flanged piece that bolts to the upper oil pan) and just weld on -10an fittings to it?

like this:

I think I tend to underestimate my goals so I won’t be too disappointed when the time comes. I’ve sure had to sharpen my learning curve in quite a few things over these past few months, since going this direction 🤯

cheers 🍻

 

[Kingtal0n]

From reading fluid mechanics books I would say that most of the merge stuff works exactly like you think it does- shitty merges induce alot of turbulence and the smoother ones will work better. Never abruptly change the size of a pipe section. Most flow will be turbulent anyways but there is additional energy losses when fluid flow is disrupted due to a merge or any kind of change to the pipe really, even wall roughness matters. The book often says we will automatically assume that flow is turbulent so the engineer is forced to work with 'worst case scenario fluid flows' and if anything happens to become laminar its just a lucky boost to flow rate.


Turbo engine can benefit from scavenging during the onset of boost at low mass flow rates, due to exhaust gas velocity which does "flow work" on the back of an exhaust valve or turbine nozzle. There is definitely low end engine torque available to keeping a section of exhaust closed off until the engine can make us of it, as evinced by cut-out systems and the OEM twin setups which block off part of the exhaust at first, making more precise use of kinetic or internal energy.

 

[Mark 2JZ]

Kingtal0n, your input is much appreciated as well. After researching further I’ve decided to order that Flowmaster Y-collector. It has a very shallow entry angle (over a nice length) between the two and doesn’t have the abrupt “pinch” of the vibrant merge mentioned above, nor does it sacrifice volume between the two before the “bellmouth”. It also would save some time since it’s prefabbed.

Let’s make it happen 💪🏼

 

[Mark 2JZ]

Some pics for context (already shared with @Mark 2JZ) :

Piping on top was our first attempt, which was replaced by the piping on the bottom.

@Mark 2JZ, I'm sure you already know this, but the downpipes in the HKS twins set-up kit are 70 mm in diameter. I mention this because you plan 75 mm piping and in case you are in need of more space and flexibility.

Ken,

From your photos i see you have two wideband bungs, did you notice much difference in AFR from each cylinder bank ? I wasn’t planning on it but with the merge happening further down I may wire up a second wideband, as I believe my AEM Series 2 ems has the provisions for it. I think it may even be able to be wired up through the oem harness (on a stock CA 2JZGE there’s 3 o2 sensors, one on each header group 1-3,4-6, and in the oem cat). I don’t think there’s any way fueling can be adjusted for separate banks but I’m it may be good for me to monitor that for peace of mind….

 

[Casey James]

Mark,

Here’s my answer to the twin oil return. I used PHRs billet oil return. It’s designed for the turbo and catch can oil return. We simple just used another AN fitting reducer to keep them same size because the catch can I believe was a -10.

 

[Casey James]

Oh, and I think you’ll be happy with the flow master merge. It’s what I used and it tested to out perform other merges in the LS v8 world back in the day. Like you said, ain’t pretty but who’s going to see it?

As for Ken’s merge SP did an amazing job for custom. You can see how they kept the pipes straight going into the larger pipe and looks tapered as well(pics may be deceiving my eyes). His merge offers up the scavenging effect.

 

[Mark 2JZ]

Thanks for the follow up ! Yeah I read up on it across other platforms and that seems to be across-the-board a great collector. Some V8 platforms mentioned it even changes the sound slightly (in a good way, somehow) ? I’m very interested in how this will sound, all said and done.

 

[KenHenderson]

Ken,

From your photos i see you have two wideband bungs, did you notice much difference in AFR from each cylinder bank ? I wasn’t planning on it but with the merge happening further down I may wire up a second wideband, as I believe my AEM Series 2 ems has the provisions for it. I think it may even be able to be wired up through the oem harness (on a stock CA 2JZGE there’s 3 o2 sensors, one on each header group 1-3,4-6, and in the oem cat). I don’t think there’s any way fueling can be adjusted for separate banks but I’m it may be good for me to monitor that for peace of mind….

@Mark 2JZ ,

I replaced my first-gen HKS A/F Knock/Amp with its second-gen A/F Dual-Bank Knock Amp, which provides more precise AFR readings for 3 cylinders each than the first-gen model did for all 6 cylinders. For my purposes, it was an affirmation of SPE's tuning of Blackie way back in the day.

At cold start, there can be as much as 0.6 tenths difference in the AFRs of the two 3-cylinder banks. Completely warmed up, the AFR never varies by more than 0.2 tenths, usually less, and, at speed, the difference is virtually indistinguishable.

This is all very old school stuff that modern EMS technology has overtaken. I still have the first in America HKS F-CON V Pro V.3.1 EMS in Blackie. Change may be coming after Eau Rouge 3.0, but I've thought that before until I have taken her out for a drive. 😎

Here's another bad, old pic when I still had the Momo Race steering wheel in the car. The Knock/Amp is positioned in front of (but slightly lower) the factory odometer:

Hope this helps.


Ken.

 

[KenHenderson]

@Mark 2JZ ,

Found a slightly better pic of the AFR, Dual-Bank Knock Amp:

Ken.

 

[Mark 2JZ]

Ken, that definitely helps, as always. I did some reading and apparently i can run a single wideband on 1 downpipe, but not at the ragged edge of AFR tuning. If i can, I’ll put both.

oh man, more period correct photos/parts to save to the hard drive in the ol’ noggin. If I could only remember other things so easily outside of supra-knowledge.

 

[Mark 2JZ]

Okay more to add, this is what I have so far for the charge piping, but the charge pipe from the #2 rear turbo is close to the #1 wastegate branch. Nothing touches is it fine ? I’m guessing it all gets hot anyway in this area, is it similar to the compressor outlet being super close to the #1 runner on single setups ? There is an air gap.