Manifold primary size OPINIONS -

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Old 03-06-2019, 09:17 AM   #1 (permalink)
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EDIT • Sorry for the long post, I kinda started rambling, but I guess this is the best way I can lay it all out. Incase anyone has further questions in order to give solid advise •

This isn't happening anytime soon, but hoping to have a good friend of mine fabricate me the perfect manifold for my setup I'm planning. I've already found the both flanges I think I going to go with. My buddy probably has some sch.10 1.25" & 1.5" weld els, etc laying around. Plus I'll just order more from vibrant or wherever he gets his stock from. Basically it shouldn't be very expensive.

Okay so I'll have to tell you a bit about my setup and plans before I get into my beliefs on why I should run one size over the other...

This car is a 99' LX sedan that now has a D16Y8 that I rebuilt eight years ago. Since then I've maybe put 15,000 miles to it. The block internals had 60k on them along with the valves. The rest is a mystery, but was all refreshed properly. Cylinder walls looked amazing! So considering it wasn't being used, I decided to put this engine swap in there while I did an auto to 5spd conversion. I'll be driving it daily NA in the mean time, but I do have most of a turbo kit pieced together the way I want it. Eventually I'll finish collecting stuff, get Hondata s300 and then install everything.

This will be AC & PS friendly. That's my main goal honestly.

The kit consist of a:
td05-14b (compressor clocked, internal wastegate actuator assembly deleted, turbine inlet & wastegate area ported)

2" j pipe (cut to arrange it coming off compressor outlet on a 90 degree instead) TO a 2.25" 180 degree pipe TO front mount intercooler TO 2.5" cold side piping

RFL style BOV

Ebay external waste gate

2.5" downpipe
2.25" midpipe/axleback
OEM FA civic Si muffler

Now I'll explain my plan. Obviously it's a pretty basic setup, but I am being picky and want it how I want it. For example the transition in intercooler piping size. I believe that really matters for a setup like this. Having the hot side before intercooler smaller than the cold side after. Anyways things like that I made sure to take into consideration while collecting parts.
Why did I choice a DSM turbo? Well first of all it was given to me (I was seeking one out however), so with a rebuild it'll be ready for use again. Other than it being a great size for my goals and application, there are other reasons why.
Mainly the turbine housing. The wastegate outlet is separated from the turbine outlet, meaning I'll be able to run an external waste gate there. I truly dislike just about every cast manifold option on the market today. Mostly because of the waste gate placement and terrible merge. So I've completely ditched the option of wastegate off manifold/non internal gate turbos.
I mean if I could find an old Edelbrock manifold I would be SUPER hyped and run it forever, but those chances of finding one are slim. Plus I would need an adapter anyhow. It's just a nice one with good merge and turbo placement. High quality too.
As for tubular manifolds, XS Power makes one with a DSM flange, it would probably last and its a good price, but unfortunately I highly doubt it would work for my AC needs. So HERE I am officially deciding to go with a nice custom pipe manifold.

My goal with this is to have quick spool. I do have other d16 long blocks and such laying around, so I will be building at least a bottom end with SpeedFactory no notch H beam rods (138.63mm) & Vitara piston combo. ARP headstuds of course.
This is for some tried and true insurance that has been tested time and time again. I don't plan to go too crazy. Figure I'll definitely need to upgrade clutch throughout the process. Otherwise fairly simple.

Even though I am shooting for quick spool I do understand there will be a lower RPM range out of boost (basically NA) so I'm hoping my setup will accommodate that. Currently the stock y8 I rebuilt is probably at 9.8-9.9ish compression due to head milling. Also when the time comes, the higher compression from the longer aftermarket rods/vitara combo will raise compression compared to standard rod length with those Pistons. Being around 8.8:1 (instead of 7.8:1). Either way, higher compression will help with out of boost RPMs and spool time. Assuming I get it dyno tuned by a legit person.

The concern I'm having is the primary pipe sizing. With 1.25" sch.10 (1.442" ID). That should promote a quicker spool, but could sacrifice top end power, which I am not worried about. The downside I see here is out of boost I'll be at a loss of flow.
With 1.5" sch.10 (1.682" ID) I feel out of boost it would perform better, and open up room for more power that the built bottom end could easily see if I want it to (they say boost is addicting LOL). It would likely be easier for my friend to fabricate too considering the head flange I found is machined ready for that piping, plus the merge collector might be less difficult to construct if all piping is same size. The downside would be more lag.

I tried wrangling up every idea I could to get the best of both, but I'm kinda scratching my head here. I'm not an engineer. I do know what I'm doing with most of this stuff though and have searched plenty online. Even read about how if effects EVOs and 2jz builds. Learned a bunch, but I'm here trying to find experienced d series turbo folk and fabricators that might see this and have some input on the topic.

Thought about transition tubing. Bumping from 1.5" to 1.25" using a sch.10 reducer right off the head flange. I could still get a standard flange and press a reducer down on one end to ovalize it. But at that point I might as well get the better machined flange. I'm not sure what to do about the collector though. Keep it 1.25" or bump back to 1.5"??? Going this route would make a short runner AC/PS manifold fabrication rather difficult unless maybe I went with a mini ram horn style. So part of me wants to just rule out that idea as cool as it may be.

I did forget to mention no matter what I'll be running this particular turbo kit on a stock internal longblock at first (The one I rebuilt and barely used). Plan is anywhere from 7-10psi.
Like I said above, that will change eventually...
When I switch to a built block I might go crazy and buy a REAL Evo 3 16g from (on sale), along with a REAL Tial wastegate and turn up the boost some (at least 13psi), but I can't predict the future hah... I'll most likely end up buying the turbine housing instead and have Austin there work on the 14b compressor housing for me.

I'm going to attach some pictures in the first reply of this thread. Examples of the flanges I want to order, external wastegate location, and manifolds I am getting ideas from.

Last edited by DomkeBoy; 03-06-2019 at 11:37 AM.
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Old 03-06-2019, 10:25 AM   #2 (permalink)
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EXAMPLES with pictures

1st pic- turbine housing modified for external wastegate

2nd & 3rd pic- dump o2 housing mounted on turbine housing with wastegate

4th pic- head flange

5th pic- turbine flange
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Old 03-06-2019, 10:40 AM   #3 (permalink)
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More examples...

1st, 2nd, & 3rd pic- the manifold that got my mind turning. Has 1.25" (can post a link to a thread about it from years ago)

4th pic- as similar manifold, but more offset, probably easier for AC fitment (generally what I'm going for)

5th pic- Transitioned primaries (not a honda manifold
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