twin turbo vnt15's alh

e84 · Jun 4, 2015

I think I've thought of a way it would be possible to attach 2 vnt 15's to the alh with easy modification to the exhaust manifold... one turbo for two cylinders each. this VS two vnt 15's lined in series back to back instead of parallel like I described above, which would work better? How much hp could one expect?

Pondering this thought because I have two vnt 15's right now.

Here's the premise

You cut away what I circled on both turbos but on different sides, weld/fix the remaining hole.

Then one with the right side cut connects to the far right and the one with the left side cut connects to the far left (when viewing from the back of engine and turbo). Then you have them staggered and they should fit. Would two cylinders even cause enough pressure to provide boost? You could use the one n75 with a t in the line to control vnts/boost to both. Then it's a matter of working out the piping. Presumably the intake mani wouldn't have to be modified for this setup?

What you guys think? If it is somehow made to work how much power you think a twin vnt 15 setup like this could produce?

e84 · Jun 4, 2015

extremely crude picture of what I mean. I checked and there's plenty of clearance on the passenger side of the engine bay.

Matdman · Jun 4, 2015

That would be really cool if you could pull it off. I think the VNT 15's turbine wheel is small enough to be able to be spun by 2 cylinders. You'll probably get more lag with twins than a single. I'm interested in seeing what you do for IC and intake piping.

e84 · Jun 4, 2015

Matdman said:
That would be really cool if you could pull it off. I think the VNT 15's turbine wheel is small enough to be able to be spun by 2 cylinders. You'll probably get more lag with twins than a single. I'm interested in seeing what you do for IC and intake piping.

honestly probably not going to try it for a while... was more or less just asking for input on it... am I hitting pipe on this one or is it plausible.

50harleyrider · Jun 5, 2015

Do some research on compounds in the cummins forums. Don't see how two vnt 15 will get you anything but headaches.

Rembrant · Jun 5, 2015

Wouldn't you only get 50% of full exhaust flow through each individual turbo, which of course means 50% intake flow through each turbo, which added together, still only equals 100%?

You'd also need two airboxes, and two of everything between the two turbos and the intake manifold? I mean, in order to make best use of the dual turbos?

Then there's the D shaped ports in the head and exhaust manifold...meaning you couldn't run the right half of the manifold on the left half of the engine. Sure, the studs would line up, but the ports wouldn't...not properly at least.

Just thinking out loud of course

.

Rem

e84 · Jun 5, 2015

Rembrant said:
Wouldn't you only get 50% of full exhaust flow through each individual turbo, which of course means 50% intake flow through each turbo, which added together, still only equals 100%?

You'd also need two airboxes, and two of everything between the two turbos and the intake manifold? I mean, in order to make best use of the dual turbos?

Then there's the D shaped ports in the head and exhaust manifold...meaning you couldn't run the right half of the manifold on the left half of the engine. Sure, the studs would line up, but the ports wouldn't...not properly at least.

Just thinking out loud of course.

Rem

I would think you would generate more exhaust flow because you would be generating more boost....I have to double check the ports/studs at first glance it looked like it would line up but it was dark out when I checked lol.

[486] · Jun 5, 2015

There was a guy sorta kinda doing that in a beetle a few years back, think he was using an hx35 as well though.

Mighta just been completely full of it though, kinda disappeared.

Curious Chris · Jun 5, 2015

And why not just put in a single larger turbo? I love my VNT 17/22.

94cobra2615 · Jun 5, 2015

I see no benefit.....

totalloser · Jun 5, 2015

Waste of time. Parallel twins are basically similar to a single larger turbo. But the flow would be so far out of the operating spectrum it would be a slug if you could do it- Which you cannot due to the iron manifold being functionally un-weldable.

Twins are good for a specific purpose- smaller turbo sequential (one flows into the other) with a larger turbo gives you the response of a little turbo with the flow of a big turbo. This really is only worth doing when you get into the 20+ psi range since below that most engines can have good response from a single small turbo.

Add to this issue that variable geometry turbos already perform some of the functions of a compound system by delivering a much better boost map. Besides, unless you are going to open up the engine, twins would be worthless since the engine could not handle the boost without serious mods such as dropping compression ratio and studs. By then you are probably bending rods, too.

"Upgrades" to turbos often aren't really upgrades. This is a very commonly misunderstood issue. Bigger will flow better, but perform worse at lower load and rpm. A lot of folks don't mind more lag and are happy, some are bummed when they discover the boost lag from the bigger turbo. Also, without appropriate fueling mods to match a bigger turbo, virtually no performance increase is to be had.

VGT and ball bearing turbos bend these rules a bit. Ball bearings by reducing low load parasitic drag for better response, and VGT by choking exhaust to spool the turbo at lower load levels, and opening it back up to allow adequate exhaust flow and limit drive pressures as needed.

[486] · Jun 5, 2015

totalloser said:
if you could do it- Which you cannot due to the iron manifold being functionally un-weldable.

I welded a wastegate pipe onto mine, haven't actually used it yet, but it welds okay with 316 stainless filler.

totalloser · Jun 5, 2015

To *the most skilled welders*, such welds may be reliable. But still inferior to simply fabricating a complete mild steel manifold.

Those that can reliably get a durable high heat iron weld are the rare exception rather than the rule. This is why I chose my words carefully when I referred to the process. However, I could have been more clear, and I recognize it is technically possible.

e84 · Jun 6, 2015

totalloser said:
Waste of time. Parallel twins are basically similar to a single larger turbo. But the flow would be so far out of the operating spectrum it would be a slug if you could do it- Which you cannot due to the iron manifold being functionally un-weldable.

Twins are good for a specific purpose- smaller turbo sequential (one flows into the other) with a larger turbo gives you the response of a little turbo with the flow of a big turbo. This really is only worth doing when you get into the 20+ psi range since below that most engines can have good response from a single small turbo.

Add to this issue that variable geometry turbos already perform some of the functions of a compound system by delivering a much better boost map. Besides, unless you are going to open up the engine, twins would be worthless since the engine could not handle the boost without serious mods such as dropping compression ratio and studs. By then you are probably bending rods, too.

"Upgrades" to turbos often aren't really upgrades. This is a very commonly misunderstood issue. Bigger will flow better, but perform worse at lower load and rpm. A lot of folks don't mind more lag and are happy, some are bummed when they discover the boost lag from the bigger turbo. Also, without appropriate fueling mods to match a bigger turbo, virtually no performance increase is to be had.

VGT and ball bearing turbos bend these rules a bit. Ball bearings by reducing low load parasitic drag for better response, and VGT by choking exhaust to spool the turbo at lower load levels, and opening it back up to allow adequate exhaust flow and limit drive pressures as needed.

triple aaa post.

Dimitri16V · Jun 7, 2015

Turbos need to be in series not parallel

[486] · Jun 7, 2015

Dimitri16V said:
Turbos need to be in series not parallel

Not even in common practice is that true, there's some toyota inline 6 with two huffers being fed by 3 cyl each (2jz?), and countless v config motors with one per bank.

Generally, two smaller turbos will spool quicker than one larger one. Tuning the vane actuators wouldn't even be all that terrible, just a couple EMP gauges and then tweaking the actuator rod length. Tune the travel limit stop with the initial EMP spike on tip-in.

To the OP, go for it. If nothing else you'll learn a ****load of things along the way. I sure am learning a lot on my ghetto compound setup.

Baxter'sTDI · Jun 8, 2015

Yeah, I say try it! It sure looks good on paper and it doesn't cost me a thing to watch...

e84 · Jun 12, 2015

[486] said:
Not even in common practice is that true, there's some toyota inline 6 with two huffers being fed by 3 cyl each (2jz?), and countless v config motors with one per bank.

Generally, two smaller turbos will spool quicker than one larger one. Tuning the vane actuators wouldn't even be all that terrible, just a couple EMP gauges and then tweaking the actuator rod length. Tune the travel limit stop with the initial EMP spike on tip-in.

To the OP, go for it. If nothing else you'll learn a ****load of things along the way. I sure am learning a lot on my ghetto compound setup.

meh I'd rather not try to reinvent the wheel here. especially considering I'm not exactly that experienced in this field. will probably just go with the traditional vnt 17/22 down the road.

BobnOH · Jun 12, 2015

good choice.
2 units would need to be hooked up in parallel and isolated per side, a nightmare.
The hybrid 17/22 is plenty beefy

[486] · Jun 12, 2015

BobnOH said:
2 units would need to be hooked up in parallel and isolated per side, a nightmare.

plenty of twin turbo stuff dumps both compressors into the same intercooler

VWdrummer · Jun 12, 2015

while we are at it lets just go for a quad turbo setup. Two parallel vnt 15's run sequentially through two Vnt 17/22's. jk I am very interested to see where this post goes...

e84 · Jun 14, 2015

VWdrummer said:
while we are at it lets just go for a quad turbo setup. Two parallel vnt 15's run sequentially through two Vnt 17/22's. jk I am very interested to see where this post goes...

lol if someone wants to go first and do a writeup I'm down... when it comes to cars I'm more of a follower than a leader.

DSMOS · Feb 26, 2018

this is quite interesting, though the i think that 50% of exhaust = 50% of power, and subsequently 100% of power. very interesting idea though... it reminds me of engine downsizing, some engines being built have one turbo per cylinder

UhOh · Feb 26, 2018

I believe that all the later diesel trucks run compound turbos.

PakProtector · Feb 28, 2018

There is no reason to do twins...save for building more pressure than a single is capable of. With a VNT17 and perhaps an HY35 you could make a go of it. CI engines can take all the boost a compressor can make...but SI engines will suffer pre-ignition in normal street-able tunes. IOW there is no need to series rig a gasoline engine's turbo's. CI, given ability to tolerate the resulting pressures can go get boosted as long as there is fuel to burn...

cheers,
Douglas

UhOh · Feb 28, 2018

Compound turbos are used to achieve larger boost pressures (big turbo), but higher boost tends to require larger, slower-to-spin-up turbos, so smaller turbos are used to get boost starting sooner (especially at lower RPMs).

Doubt that multiple turbos on an ALH is going to be worthwhile, Even IF there could be a gain it would likely be insignificant compared to the later, single turbo performance offerings (like the 17/22?).

wonneber · Feb 28, 2018

I would try getting a headers type exhaust flange and some bent tubing pieces the correct diameter.
Cut and tack weld until things fit.
Run exhaust cylinders 1 and 4 to one turbo, cylinders 3 and 2 to the other.
Pipe the two boosts into 1 cooler.
Manual waste gate and go.
Sounds to simple to me.

jeffpepin · Aug 8, 2020

i have been while attacked by the same idea , Exept ive imaginated that blending turbos should be efficient , i have a homemade tune that push my vnt15 over 25psi , theses babies run max 20 000km before melt but it prove that 4cyl with an extreme tune is overkill an oem turbo so basicly , 2cyl + a tune can drive a vnt15 like oem stats

I THINK the secret in this idea is by doing a custum intake in manner to have 1 turbo drived by 2 cylinder and flowing air to 2 cylinder insead of four and same for other turbo .,then need a way to blend theses to a logical setup to avoid running 2 cyl without boost and 2 other with if anything goes wrong

if anything goes wrong with one turbo , other will continue his job and will lost 50% boost ,

a 2.0l AEG gazzer 8valves hexaust manifold fit bolt on on alh , can be modded to feed turbos

i donk know at this time if cloning N75 Harness with somes diodes can be possible

but at this time is more like doing it just because i want to build it , exept if it have somes majors missconception of this project , my little finger does'nt stop to say '' its logicaly possible '' but ,,
the main idea is tanking 2 oem turbo to working in COOP mode ,, should result same performance has now exept without overexploiting turbos

turbocharged798 · Aug 10, 2020

Isn't the max boost of a VNT15 ~18 PSI? So what exactly would one be gaining by doing twin tubos? I guess lower EMPs but you are still limited to 18 PSI....

mittzlepick · Aug 10, 2020

I've got twin vnt17's and 8 tires people think I'm nutz also

twin turbo vnt15's alh

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