There are only so many ways to set up a shorty 3 into 1 manifold whilst maintaining stock location you know, but the devil is in the details... The MMP manifold starts off @ 32mm ID, tapers up to 36-39mm ID or thereabouts shortly afterwards, and then necks back down to to the equivalent of sub 29mm as it goes into the hotside, hardly ideal IMHO. i do agree however, that a high-performance TT setup is absolutely the way to go on our cars, which is why I went that route to begin with
you are right the devil is in the details and you are also right Twin Turbo is the way to go. We have owned many N54s twin turbo and also single turbo and also both types of turbos at the same time, and hands down the twin turbos are way funner to drive than the single turbos and with all the twin turbo options including 53mm ball bearing twin turbos we are starting to make now, any whp goal can be achieved with MMP twin turbos. Also we like generally what you are doing with the turbos although as you can see below we would make several key improvements like we have in our design but imitation is the best form of flattery and I must say your turbos are a striking resemblance to the MMP 1K turbos.
As far as manifold details….The MMP manifold perfectly matches the N54 head exhaust runner ID at 33mm and is a smooth transition to 45.1mm then merges to a 50.1mm collector. This smooth merge is only accomplished with a casting and we use the best investment casting process and highest-grade stainless-steel materials for our casting. Below you can see a pic of the cross section of our casting and how it matches the runners and merges for the best aerodynamic flow possible and least pressure losses. MMP manifolds combined with our turbine housings truly are the highest flow of any twin turbo setup for the N54 including the ones you present here.
I think you use a machined flange with machined insert welded in and cut and bent 1.25" sch 10 tubes welded together, correct me if I’m off please. You also would have to match the 33mm ID port size of the N54 with the counterbore for the insert, not sure what the N53 is but it is probably similar maybe you can measure it in the head just past the counterbore for the exhaust port insert and advise the size. the 1.25" sch 10 tube you use is 36mm ID. also from your flange to the ID of your pipe there is not a smooth transition as you can design with a casting, it is most likely a step change in diameter due to fabrication limitations that step change in diameter is very bad for flow as it causes flow separation and pressure waves and pressure losses add up there. My 45.1mm pipe ID size in my casting is 57% greater flow area than your 36mm ID pipe. also your collector is visibly smaller than mine. I would guess around 40mm ID but maybe you can clarify the size. If it is 40mm ID my 50.1mm ID is also 57% more flow area than your merged collector which again is less pressure losses, more flow, and more power from the manifold. I took a stab at modeling the cross section of your manifold based on the specs you provided to show what I think are the differences and posted the pic of the cross section below, but please let me know if I need to correct something for comparison purposes.
The manifolds I designed I did as the highest flow area diameter possible based on the bolt pattern restrictions. If I could have done larger I would so I believe they are the largest possible with a bespoke casting design and using investment cast methods and not sand casting is absolutely required for the high end surface finish and precision needed since pushing to the largest size pipe not to interfere with bolt pattern so even .5mm tolerance matters for the casting otherwise will run into problems quick which is why our 1K turbos uses these investment cast stainless steel manifolds with our 1K turbos.
Also your cast turbine housing you mentioned you use 6.6cm^2 for the AR area, our turbine housings have a 7cm^2 AR area so again ours flow more and are optimized through CFD for our high flow manifolds, high flow collector size and large 4646 GT28 high flow 9 blade turbine wheel TD04 turbos with our high flow native TD04 compressor housings.
You are right the devil is in the details and this is the most details I have shared about our design anywhere but since you posted some info on our design as if you knew all the details I just wanted to make sure you had all the right information for comparison purposes.
Also nice work on the custom N53 head mating to the N54. I look forward to the flow bench numbers. Was the n53 head ported or is it as stock? The N54 head work we did over 2 years ago and posted about in another forum showed the N54 head did flow terribly and could be improved by over 40% at .5” lift with a porting job on the head as we did it. We saw flow increased from 167CFM at .5” lift 28inhg pressure drop to 235CFM which we were very happy with those results using the stock N54 valves and of course non of the headaches to solve when fitting a non standard n53 head to an N54 bottom end but we like to see the effort and new things being tried. Once we saw the great results 2+ years ago from the N54 head porting we started offering them for sale at $2000 which was a huge decrease from other options on the market at the time offering a ported head for $4000. Since then others now offer it and the market has come down more in line with reality.
We look forward to seeing more results from your testing, good luck.