Rb26 Low Mount Tubular Manifolds - Do They Make Any Difference?

[Lithium]

Awesome job! Looks fantastic, shame there are no power gains there but still a very sweet project and it'd be nice to think you may have improved response etc, +1 for video clips so we can hear the goodness

We learn nothing by doing the same thing all the time.

[joeyjoejoejuniorshabadoo]

nice work matty! cant wait for the next deca!

[MrStabby]

They are things of beauty, but perhaps you compromised low end response by using a larger runner ID? I'm thinking these may be more suited to a much higher than 350kw setup. Its all about fluid momentum...

[femno]

Yep easily 25 hours in them...if I was to make any more id have the merge parts milled...those took ages. Its just the fact that the 3mm thick stainless takes so long to grind and cut through.

When you say larger, larger than what? The ID isnt alot bigger than the runners on the cast manifolds, but have you seen how much open space there is inside the factory 'merge'? Its massive. Most manifolds made by other guys all use 1.25" Nominal Schedule 40 materials, so thats why I decided to use that size.

Theres also the issue of the port areas being MUCH bigger than the area of the 1.25" pipe. I havent calculated it but its alot. Say If I went to 1" pipe, the difference between the port and the runner sizes and areas would be massive. Have a look at the photo of the head flange after de-burring. You can see the runner ID is alot smaller than that of the port. So as these were the first ones I kept things to what I knew worked so it wasnt a total waste of time.

I agree with the momentum point, well, maybe not so much momentum but moreso velocity, its possible I could machine some port size-to-1" reducers and put them somewhere and use the 1" pipe with them, that may give some better results or maybe shift the curve a bit to the left without restricting top end power with my measly 350kw. When ive got a spare few weeks, and ive forgotten how much of a pain they were to make then maybe ill have another go...

Interesting fact: Burns stainless in the U.S ('top notch' exhaust guys) suggested to use 5/8" tube for my setup. haha.

[MrStabby]

When you say larger, larger than what? The ID isnt alot bigger than the runners on the cast manifolds,

I'm just searching for possibilities as to why the improvement is small. I would have expected more, and larger runner ID is the only explanation I could come up with.

Theres also the issue of the port areas being MUCH bigger than the area of the 1.25" pipe. I havent calculated it but its alot. Say If I went to 1" pipe, the difference between the port and the runner sizes and areas would be massive. Have a look at the photo of the head flange after de-burring. You can see the runner ID is alot smaller than that of the port. So as these were the first ones I kept things to what I knew worked so it wasnt a total waste of time.

Are your ports stock or bigger? Are you talking cross section area? Makes sense to have port and runner IDs the same, so fair call on your choice of size.

I agree with the momentum point, well, maybe not so much momentum but moreso velocity, its possible I could machine some port size-to-1" reducers and put them somewhere and use the 1" pipe with them, that may give some better results or maybe shift the curve a bit to the left without restricting top end power with my measly 350kw. When ive got a spare few weeks, and ive forgotten how much of a pain they were to make then maybe ill have another go...

Given what you've said above, its probably only worth the effort if the stock runners have about the same cross sectional area as the 1". For experimentation, could you work in mild steel to make fab easier?

[femno]

My ports have been matched to the factory gasket port size; so theyre not huge or anything.

Again maybe in a while if I have nothing better to do I could maybe do some 1" runner items, mild would be a little easier, maybe even use thinner wall stuff just for ease of fab...machine up some nice port size-to-1" 'cones' and use those. At the moment im concentrating on getting the car ready to get back onto the race track.

I also have the issue of #6 runner being very close to the heater core in/outlet and consequently dont have my heater connected. It was impossible to design for it as I didnt have any measurements when the motor was actually in the car. Will be coming up with a solution pretty soon as the colder months close in.

For those who asked ill grab the next opportunity when someone is driving near me to take a video.

[Ben26]

Hey Mat,

Did you ever get a video or up the boost / make any more changes?

Cheers,

Ben

[Lithium]

What are the odds this gets bumped - after not thinking about it for years I had a flash back to it last night while pondering some exhaust manifold design ideas we are looking at trying with one of the cars I help with, definitely finding it a bit less surprising that there wasn't any improvement with this after a few more years of learning stuff and looking at data for things :(. Still very cool, but

[Ben26]

Interesting, what did you find Lithium / what are your thoughts on twin tubular manifolds? 

I recognise that modern singles with an equal length manifold will likely out perform 99% of twin setups, however I love the idea of twin manifolds for the racing nostalgia to group a etc

[Lithium]

1 hour ago, Ben26 said:

Interesting, what did you find Lithium / what are your thoughts on twin tubular manifolds? 

I recognise that modern singles with an equal length manifold will likely out perform 99% of twin setups, however I love the idea of twin manifolds for the racing nostalgia to group a etc

Always learning, looking for/analysing data and hearing other peoples experiences so really it could always change - but at this stage my view is that in this instance by increasing the distance from turbine to the valves you are sacrificing exhaust energy for no reason.  There will be wasted heat which could be put into driving the turbine so more exhaust gas is required to generate the same amount of work... and also the greater runner volume means that it will take more time to build drive pressure.  The fact that the bends and merges are cleaner probably offset some of the loss from that, but I am pretty convinced that the length of the runners would do more harm than good.  The fact that you are collecting with 3 cylinders means that the exhaust pulses are lined up nicely anyway so the volume etc isn't needed to manage collisions, that length runner isn't needed to reduce turbulence so realistically the same idea COULD be applied with much shorter runners much more effectively.

So yeah, avoiding the twins versus single debate - my comment can be applied to the sheer size of the manifolds versus what they need to do.   

If you were bent on twin manifolds and wanted them to perform well I'd lean more in the direction of something like this: 

 

 

 

[Ben26]

Yes me too, its great learning from other people experiences and trying to put together your own understanding to then test in practise. 

Ok, that definitely makes sense, but I wonder if the runner length determines the optimum speed the turbine will operate at, ie alter where the turbo chargers are at peak efficiency, and therefore tune the runners length depending on turbine size, rpm limits, cam sizes and boost pressure. This is something I would like to play with. 

It makes sense what you are saying based on how a turbocharger works, and definitely when your only collecting three cylinders per turbocharger as opposed to 6 with a single turbo manifold. 

A somewhat important part of the runner length / shape to me is also sound however, and I have found that the longer the runners, the more I like the sound. Maybe not something everyone cares about. 

[GTSBoy]

Heat loss can probably be more than sufficiently mitigated with ceramic coating though.

I think beyond that, the question is not really amenable to thought experiment. The variables are non-linear and it's not really possible to say which one has the bigger effect at the exact conditions in play. Would make a lovely episode of Engine Masters though.

[Lithium]

2 hours ago, Ben26 said:

I wonder if the runner length determines the optimum speed the turbine will operate at, ie alter where the turbo chargers are at peak efficiency, and therefore tune the runners length depending on turbine size, rpm limits, cam sizes and boost pressure. This is something I would like to play with. 

A somewhat important part of the runner length / shape to me is also sound however, and I have found that the longer the runners, the more I like the sound. Maybe not something everyone cares about. 

Hmmm not sure how the runner length would affect the turbocharger's efficient speed?   Some of those other things I can see interacting with each other to a degree but compressor efficiency and optimal turbine speed I don't really see the runner length doing much.   

I very much understand choosing things which deliver sound etc that you dig, though...  like realistically nothing is ever going to be perfect performance wise so if there are things which are going to make it more fun to you then by all means.  Does my head in when people try to justify their preferences arguing until they are blue in the face when "I just like it this way" is a perfectly acceptable reason for choosing their own mods 

 

1 hour ago, GTSBoy said:

Heat loss can probably be more than sufficiently mitigated with ceramic coating though.

I think beyond that, the question is not really amenable to thought experiment. The variables are non-linear and it's not really possible to say which one has the bigger effect at the exact conditions in play. Would make a lovely episode of Engine Masters though.

I am pretty sure I didn't say exclusively heat.   A lot of it is theory but I feel there is quite a bit of reason to assume it has plausibility to it - not least that we have data already provided in this thread showing very carefully designed and nicely built manifolds with smooth curves and nice merges showing that it would be generous to say that it didn't gain... realistically that's probably charitable when I would guess in some instances like this if the "stock manifolds" result was the "after" in the comparison then it could have been arguably called a great success.

Like anything it will come down to various variables, what the target is etc.  If I had seen these headers before this test with what I've seen now (excluding this test) before this test was done and asked what would perform better overall I wouldn't be confident in much other than the tubular ones would likely sound cooler.... 

Edited July 10, 2019 by Lithium

[Ben26]

12 hours ago, GTSBoy said:

Heat loss can probably be more than sufficiently mitigated with ceramic coating though.

I think beyond that, the question is not really amenable to thought experiment. The variables are non-linear and it's not really possible to say which one has the bigger effect at the exact conditions in play. Would make a lovely episode of Engine Masters though.

Yea ok, interesting. Agreed, trialling a few different length runner designs and thicknesses with the same turbo setup would make an interesting comparison. 

[Ben26]

11 hours ago, Lithium said:

Hmmm not sure how the runner length would affect the turbocharger's efficient speed?   Some of those other things I can see interacting with each other to a degree but compressor efficiency and optimal turbine speed I don't really see the runner length doing much.   

I very much understand choosing things which deliver sound etc that you dig, though...  like realistically nothing is ever going to be perfect performance wise so if there are things which are going to make it more fun to you then by all means.  Does my head in when people try to justify their preferences arguing until they are blue in the face when "I just like it this way" is a perfectly acceptable reason for choosing their own mods 

 

I am pretty sure I didn't say exclusively heat.   A lot of it is theory but I feel there is quite a bit of reason to assume it has plausibility to it - not least that we have data already provided in this thread showing very carefully designed and nicely built manifolds with smooth curves and nice merges showing that it would be generous to say that it didn't gain... realistically that's probably charitable when I would guess in some instances like this if the "stock manifolds" result was the "after" in the comparison then it could have been arguably called a great success.

Like anything it will come down to various variables, what the target is etc.  If I had seen these headers before this test with what I've seen now (excluding this test) before this test was done and asked what would perform better overall I wouldn't be confident in much other than the tubular ones would likely sound cooler.... 

Well the velocity of gas coming out of the manifold drives the turbine right, so you would think different velocities of air would have a different effect on the turbine in my mind?

Yea im not going to pretend that some modifications I make are for aesthetics or sound haha. Most are functional but hey the whole experience is not just about perfection otherwise we wouldn't own skylines!

 

 

[Lithium]

1 hour ago, Ben26 said:

Agreed, trialling a few different length runner designs and thicknesses with the same turbo setup would make an interesting comparison. 

Hell yeah, honestly the amount of things I wish I had the time money and skill to put together and try because there are PLENTY of commonly accepted routes which I feel like could potentially be improved on - but would not push for people to try, or try myself without having more certainty.   And just for trying to see what happened haha.

1 hour ago, Ben26 said:

Well the velocity of gas coming out of the manifold drives the turbine right, so you would think different velocities of air would have a different effect on the turbine in my mind?

Not just velocity, but essentially yeah - it does.   This conversation could get very big very quickly, and no doubt the line between knowledge and opinion can start getting blurred but my 2c on that particular comment is that you shouldn't control velocity with runner length, the longer the runner the more time the exhaust has to shed energy.   When "tuning" a steady flow rate through a pipe you usually adjust the diameter of the pipe, the length usually has more to do with synchronizing events and balancing up other factors involved with managing the bigger picture.  

 

Edited July 10, 2019 by Lithium

[MBS206]

9 minutes ago, Lithium said:

Hell yeah, honestly the amount of things I wish I had the time money and skill to put together and try because there are PLENTY of commonly accepted routes which I feel like could potentially be improved on - but would not push for people to try, or try myself without having more certainty.   And just for trying to see what happened haha.

Not just velocity, but essentially yeah - it does.   This conversation could get very big very quickly, and no doubt the line between knowledge and opinion can start getting blurred but my 2c on that particular comment is that you shouldn't control velocity with runner length, the longer the runner the more time the exhaust has to shed energy.   When "tuning" a steady flow rate through a pipe you usually adjust the diameter of the pipe, the length usually has more to do with synchronizing events and balancing up other factors involved with managing the bigger picture.  

 

Velocity, and volume. 

Hence why retaining heat is important as it keeps the volume larger. 

Length as Lithium mentioned is about timing, at which point diameter also plays a part, but you're looking for the other side of the pulse to be at an exhaust valve when it opens to be a "vacuum" and help scavenge everything out of the cylinder, which let's you get more into the cylinder, which gives you more bang, which gives more exhaust, which gives faster turbo, which gives more inlet flow which gives more bang, and the cycle continues... 

 

The ID of the runner can also bring the spool up rpm up/down, but then it can become the choke point, not the turbo, in the higher rpm, hence it's all a balancing act. 

[Ben26]

Yep, understood and agreed with both of you, diameter of the runners has more influence on the pipe velocity, however flow rate varies dramatically with length of the pipe. Half the length of a pipe and expect double the flow rate. 

All very interesting, now who has the budget and time to test all of this with different length runners and pipe diameters on the same turbo setup and see what happens!

[Lithium]

5 minutes ago, Ben26 said:

 Half the length of a pipe and expect double the flow rate. 

So what benefit do you think there may be in having a lower flow rate?

And yeah, very interesting stuff.   Hoping we can try some stuff out with a design on a car we're doing, but the problem is there won't be any comparisons - it will just be part of an overall setup so hard to know what will contribute to what.  

Edited July 10, 2019 by Lithium

[Griffin]

16 hours ago, Lithium said:

Always learning, looking for/analysing data and hearing other peoples experiences so really it could always change - but at this stage my view is that in this instance by increasing the distance from turbine to the valves you are sacrificing exhaust energy for no reason.  There will be wasted heat which could be put into driving the turbine so more exhaust gas is required to generate the same amount of work... and also the greater runner volume means that it will take more time to build drive pressure.  The fact that the bends and merges are cleaner probably offset some of the loss from that, but I am pretty convinced that the length of the runners would do more harm than good.  The fact that you are collecting with 3 cylinders means that the exhaust pulses are lined up nicely anyway so the volume etc isn't needed to manage collisions, that length runner isn't needed to reduce turbulence so realistically the same idea COULD be applied with much shorter runners much more effectively.

So yeah, avoiding the twins versus single debate - my comment can be applied to the sheer size of the manifolds versus what they need to do.   

If you were bent on twin manifolds and wanted them to perform well I'd lean more in the direction of something like this: 

 

 

 

Does anyone have any thoughts / experience with these manifolds? I'm going back from big single  to twins t517z on Gtr atm. Was looking at these manifolds from gcg but not much info around.

Does the coating still work on stainless as it does with cast / mild steel?