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Another RSP thread - with a twist

17K views 88 replies 15 participants last post by  Them Witches 
#1 ·
First time poster, spent far too long reading lots of interesting threads on intake manifolds.

However times have moved on and I thought you might be interested in my little project.

My car is an S1 elise with a K20a2, it currently has the PRB manifold and the RRC wont fit without cutting the bulkhead.

Then I discovered the RSP, not only does it look okay on paper but more importantly it is a modular design so I can take it apart to tweak quite easily.

I have seen several posts on here where people have cut the back off and welded it up and done similar to the trumpets, even seen people CNC machining new trumpets but all of that is either beyond my skill set or budget.

So this evening I set up a mini photo studio



Resulting in 109 photos of the trumpets, example below



I then imported those into 3DF Zephyr and after an hour or two of custom making image masks I was able to generate this splodge:



The rings of blue dots are the camera positions and the image mask process basically cuts out the block of wood the trumpets are balanced on. The wood is on a lazy susan (turn table) on an oversize clear plastic protractor. After each photo I rotated the part by exactly 10 degrees and took another photo, after 36 photos I rotated the part.

The splodge is a point cloud, the software has compared all of the photos an identified specific points that it can see in all (well some) of the photos and it uses these points to understand the 3d model.

Next step is to refine the point cloud:



And then generate the model



This can then be exported into your modelling software of choice. Because I am on freeware that would be Blender:



Its pretty lumpy and bumpy.

Next step is to basically trace it in the modelling software so that the whole thing is tidied up and then tweak it so it matches the dimensions of the actual part. Place particular emphasis on bolt holes etc.

I've found this to be a nice easy way to get to a 90% model that can be refined because freehand measuring things like curved surfaces can be tricky.

So why bother, where is this going?

First step will be to 3D print a new plenum back plate that does away with the resonance chamber, I can run this a while to check/prove reliability as it will be easy to see if its damaged.
Second step will be to print a set of 20mm trumpets with nice elliptical edges to open up the top end.
Third will be to experiment with different trumpet designs / angles to see if flow can be evened out / improved.
Then try and find a way to add a dual plenum to the back plate to feed the plenum.

Once the design has been tested (including dyno time) and reliability proven the last step will be printing a custom flange and runners as part of a full working printed inlet manifold to maximize.

I'm expecting all of this to take some time but i'll keep this updated if there is interest :)
 
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#2 ·
Welcome to K20a.org mrluke!

First step will be to 3D print a new plenum back plate that does away with the resonance chamber, I can run this a while to check/prove reliability as it will be easy to see if its damaged.
Second step will be to print a set of 20mm trumpets with nice elliptical edges to open up the top end.
Third will be to experiment with different trumpet designs / angles to see if flow can be evened out / improved.
Then try and find a way to add a dual plenum to the back plate to feed the plenum.
Amazing what can be done out of digital pictures. I am interested in the quality. Did you measure the bolt pattern in the model and compare it to the real bell mouth bolt pattern?

A very good basis for your design approach is this paper here: RET_Bellmouth_Sept.pdf (profblairandassociates.com)
 
#3 ·
Welcome to K20a.org mrluke!

Amazing what can be done out of digital pictures. I am interested in the quality. Did you measure the bolt pattern in the model and compare it to the real bell mouth bolt pattern?

A very good basis for your design approach is this paper here: RET_Bellmouth_Sept.pdf (profblairandassociates.com)
Thank you and thanks for the paper :)

The accuracy is really very good, you're talking about fractions of a mm really. The biggest issue is my photo quality isn't great so the software struggles to find the edges of the dark grey object against the slightly darker grey background. I scaled the model to an overall length of 250mm and checked the widest diameter across the trumpets, 64.6mm in the model and 64.6mm in real life.

The picture below shows my model and the cad scan overlayed so you can see the differences



As you can see its mostly around the edges with little pockets on the surface finish. I think I may have more success using a green screen as the background rather than black so will try that in the future.

And here's the model looking slightly prettier. Renders aren't my forte, I just make and print the parts lol.



There's a bit more work to do before its a finished part, the edges need tidying up so that it looks smooth rather than faceted. But for a couple of hours in CAD i'm pretty happy with where I have got to.

I'm not going to spend much more effort on this design because I don't want/need to print trumpets that duplicate the originals. This is good enough to get the dimensional accuracy, next step is to create an elliptical profile in both stock height and shortened lengths.
 
#6 ·
Thanks :) much cheaper than a scanner but I am very jealous of what they can do with them, the real time scanning is pretty cool. Not very accessible for a hobbyist though.

Seems you rises a bit more of my interest with that result. Just the radii weren't build up correctly, especially at the bell mouth.
The software struggled to work out where the edges of the trumpet were which reduced the accuracy.

What did happen to the parallel cut on the bolt bores? De-rendered?
The model has two parts, the first is the underlying geometry and the second is a texture file. On the image its the texture file that hasnt been compiled 100% correctly, its overlapped the holes slightly to make them out of round. Again this has been from the software struggling to identify where the metal stops. Ultimately this is easily overcome because we know that the holes need to be round, we can measure the diameter from the part, When I add the holes to the model I make sure there are all at the same height, the scan will indicate the horizontal position and then its just a case of double checking against the actual part to make sure they are perfectly placed. But again we are into fractions of a mm here.

I assume this is a test case for you to investigate the approach for further projects, isn't it? Wouldn't you be faster by to measure and draw it into 3D with that bell mouth flange?
I'm not quite following. The new bell mouths I will draw free hand and add to the model as my first tweak but things like matching the curvy flange are much easier to do with this technique than from the part with a ruler :).

The plan is to 3d print a functional set of trumpets that can be installed on the car. This will be by outsourcing the printing to a large company that have the latest tech available at affordable prices.

We used a 3D laser scan tool (80 kEur) to transfer a head into 3D CAD, the effort to render it correctly would so high we skipt it, maybe we had the wrong technology. But on free form shapes ghost differ, there the real advantage lays to dig out with such technologies. Would nice to see how it works there, e.g. on a more complex runner design of the RSP IM.
I can see a head being somewhat difficult to render if you are trying to include all the cooling galleries etc. If you are just looking for airflow then it shouldn't be too bad, depending upon whether you want to accurately recreate the variances in each cylinder/port or just do one and mirror it 4 times till you get a good fit.

Very good, I hope the Blair paper helps on that.
I'll use their profile for the bellmouth

Do you have an idea how long you want to have the runners, for the runner length tuning?
From what I have seen there are multiple ways to calculate ideal runner length and the outputs vary enormously. I have come to the conclusion that the calcs will only land you in the ball park and dyno testing is required to get the perfect length.

My thought is that the issue with the RSP manifold is that runner #1 blocks the TB opening. Fine at lower rpm but at the top of the rev range it makes the flow path too difficult. Hence why people cut them down to a 25mm runner length and regain the top end.

If I can add a dual plenum onto the back of the RSP and cover up the existing throttle opening then maybe the stock length trumpets will show a benefit over the shorter lengths. Given my use case i'm probably aiming for a peak HP at around 7.5k.
 
#7 ·
So I have modelled the elliptical profile from the paper:



However they aren't going to fit the RSP manifold.



They are also 1 diameter high so circa 50mm which means they will obstruct the TB opening as well.

Once I have got all of the elements scanned I will start looking at CFD to narrow down the options.
 
#8 ·
So I have modelled the elliptical profile from the paper:
However they aren't going to fit the RSP manifold.
They are also 1 diameter high so circa 50mm which means they will obstruct the TB opening as well.
Welcome to the engineering world. Theory and Practice, here the engineering began to span the bridge between both: clearance limits and theoretical recognitions to implement. If you read carefully the paper you will find the that Blair has a heart for engineers, as he already foreseen issues and made general design rules to follow. I would follow that.

I am no friend of 3D CFD, as the results are too depended on modeling approaches of boundary layers and mathematical requirements to get it started or to be able to calculate it. It doesn't include the fuel droplet spitting and it's effect of vaporization during that back and forward process. So I wouldn't mind about doing 3D CFD. BTW, most CFD codes look into stationary conditions, but the conditions here are by far not stationary. Modelling this correctly will cost some days or even weeks to calculate one single inlet event with respect to Plenum pressure and mass movement :D.

Regarding the length approaches. Here simple approaches like Speed of Sound wave front calculations up to 1D-engine simulation are rational. The interesting is, the first differ not too much from the last and every misses the reflection flexation and efficiency. The last was also not included by Blair, he just looked at the flow properties, not into the oscillation properties. Something, many approaches misses. What engine speed is in your specification?
 
#9 ·
Little more progress on the next part, model is a little more interesting this time. Still with the basic photogrammetry setup and my rubbish slightly blurry photos.





This shouldn't take too long to get to a part I can print so that I can see whether the manifold will fit into the lotus or not. Might need an extra spacer on the throttle body to help that clear.
 
#10 ·
Good thread to follow. Respect for all the information and graphs. The RSP IM has been a ponder for me Just as the RRC & RBC IM's. If I could have my druthers I would have all three with a Fully Worked PRC/PRB IM's for my R&D heavily directed compulsive behavior to Honda's material. I am going to do another Fully Ported PRB IM for entertainment in the next few months for my next project.

But what I could do if I could get my hands on an RSP or RRC IM to work on... I really feel I could make some good power with those manifolds with my particular style of porting matching to the head, knowing where to remove stock, and meditating with the intake manifold listening to what it wants to do. What it wants to do with the bolt-ons you are throwing at it... And how using the custom work justifies the means.

Questions :

1) How straight are the bends in the intake track & exhaust track ?

2) How bends ends in each system ? What type of bends?

Honestly, if the engine isn't flowing on In. & Ex. I don't think the PNP will helps that much. Sorry my 2cents.

Subscribed to the thread
 
#11 ·
Buddy of mine used to build engines for Mugen UK, his input on the RSP manifold was that removing the freeze plugs on the resonance chamber wall was worth a couple hp. Same guy brought my RSP manifold over when he moved stateside ;)

I've studied more SAE papers than I can count related to intake and exhaust design, and spent a few months playing with 1-D GT Power models getting my masters. My conclusions:
  • Intake manifold design is not something that can be magically calculated with a single formula.
  • Runner diameter directly impacts ram tuning for high engine speeds, large diameters = lower flow velocities / less ram tuning. Small diameters increase velocity, but if you approach mach, flow decreases.
  • Runner length is the largest contributor to resonance tuning. IM Runner length bumps VE in bands at several engine speeds, based on 1st/2nd/3rd etc. order reflection timings, and valve event timing.
  • Choosing a runner length aimed at your peak power engine speed may give you that impressive peak number, but almost definitely have large torque losses, resulting in less power under the curve
The RSP manifold came on the K20Z4, rated power at 7800 rpm, so if you're expecting a lower peak power speed than that, I'd personally keep the same length, if not go slightly longer on the trumpets. I generally work under the assumption that Honda/Mugen have done their homework on manifold design ;)
 
#12 ·
Buddy of mine used to build engines for Mugen UK, his input on the RSP manifold was that removing the freeze plugs on the resonance chamber wall was worth a couple hp. Same guy brought my RSP manifold over when he moved stateside ;)

I've studied more SAE papers than I can count related to intake and exhaust design, and spent a few months playing with 1-D GT Power models getting my masters. My conclusions:
  • Intake manifold design is not something that can be magically calculated with a single formula.
  • Runner diameter directly impacts ram tuning for high engine speeds, large diameters = lower flow velocities / less ram tuning. Small diameters increase velocity, but if you approach mach, flow decreases.
  • Runner length is the largest contributor to resonance tuning. IM Runner length bumps VE in bands at several engine speeds, based on 1st/2nd/3rd etc. order reflection timings, and valve event timing.
  • Choosing a runner length aimed at your peak power engine speed may give you that impressive peak number, but almost definitely have large torque losses, resulting in less power under the curve
The RSP manifold came on the K20Z4, rated power at 7800 rpm, so if you're expecting a lower peak power speed than that, I'd personally keep the same length, if not go slightly longer on the trumpets. I generally work under the assumption that Honda/Mugen have done their homework on manifold design ;)
I agree 100% with every point you make in your post (!).

My intention at the moment is to remove the resonance chamber, smooth it off and bolt it back on as a rounded plenum. Are you saying that it would be beneficial instead to keep the extra volume from the resonance chamber?

From other peoples dyno experiments my views on runner diameter are that too narrow quickly becomes a restriction at higher rpm whereas runners that are slightly too large don't appear to cost power elsewhere in the rev range so in short, too big is safer than too small. However for now my runner diameters are pretty much fixed by the RSP.

There also appears to be a relationship between runner length and diameter i.e. a runner that is short and narrow may be okay, but as you make it longer you need to increase the width otherwise it chokes. I'm thinking of it as runner diameter being a course / rough adjustment with the length being more of a fine tune.

This channel has been a fantastic resource, all testing no bs.



If I can hit peak at 7,800rpm that would be lovely. Limiter is around 8,300rpm i'm not planning at pushing much if any higher than that right now.

The only issue with the runner length is the throttle body inlet location



I think this is why people are seeing benefits from reducing the runner length. At the top end its too much of a restriction to the flow.

Plan is to have a few different trumpet sets to run on the dyno to try and see what is going on. Will be interesting to compare standard length trumpets with a side and rear inlet.
 
#13 ·
I have thought about that as well, in regards to TB placement. I would love to test out a blanking plate and modify the lower resonance chamber to adapt the throttle body, probably in a dual plenum design but really just looking for improved throttle body angle of attack.
 
#15 ·
#20 ·
Bit more progress, would like to get the back plate ordered up this weekend and probably a set of trumpets for mock up / fitment check.
Very nice 👏.

Are you going to cut out the overlapping bell mouths? I would recommend to cut them at the touching. As they are symmetric they will form at the cut line exact the same shape, which makes it flow-wise much better. Just in case you do 3D print outs, on a single bell mouth fab approach, you would do that automatically.

How much volume to you provide for the plenum? The plenum volume is beside the shape of it the 3rd free parameter. You can design it via Helmholtz-resonance (cylinder displacement vs plenum volume) or do an 1D calculation method approach. In any case it is always power support vs. throttle response. If you don't race slalom races, where throttle response and control is most important, a rule of thumb would be around 2-4 Liter are ok for most applications. Maybe that helps.
 
#26 ·
I don't believe the PRC is a modular design? So somewhat trickier to modify in the way that I can the RSP.
Yes, it is no modular design, but it has a way better clearance design as basis for your requirement to fit into the Lotus engine bay. As an extreme example you can find this here: Aggressive as fuck RSP custom "center feed" plenum | Honda / Acura K20a K24a Engine Forum

So last night I pushed the button on the trumpets and a new back plate. 2-3 weeks until arrival, depending upon Brexit.
Looks nice. But maybe you need to push the button a second time. How do you want to place bolts into the flange or do you place threats with screw nut. Anyway both will get challenging. I would design bigger bore diameters around the bolt axis in vertical to get the screw's mounted.
 
#28 ·
Allen socket head bolts with a tool like this might be able to reach around the bells,
Definitely drtye. This allen socket approach would safe some clearance, but the bore diameter of the cut out of the bell mouths is the same as the flange bore. The screw head is always bigger to give a surface to be able to transfer the bolt force right down. I assume at least a 2 mm bigger radius. With the actual design it won't be possible, it has to be reworked. Just my two cents.
 
#29 ·
Thanks.

I'm pretty sure the bolts will be accessible one way or another, there's plenty of room under the bells and the holes shown are 8mm to allow for inserts whereas the bolts are 6mm (well 5.8).

As suggested can always change to cap heads :)

That said these are only a mockup, i'm not expecting them to be a final product but hopefully I can mount them and start testing for durability.

But I will happily bet you a beer that I can install the bolts without too much bother.
 
#31 ·
M6 threads.

I dont want bolt the plastic directly so it will have metal (likely brass) insert which is much more robust. Therefore the holes are oversized to allow for installation of the inserts.

And FWIW I'm aware of unmodified elise's with the RSP manifold fitted, we'll see.
 
#32 ·
I love delivery day! Wasn't supposed to be here until Tuesday :D









I did manage to get all the bolts but the bottom two were a bit awkward to tighten. Cap heads would work but now I have the physical part, making the cutout larger doesn't look as bad as it did in the 3d model so i'll do that.









Blown away by how accurate the hole placement is.

 
#33 ·
Nice progress mrluke 🆙! Are you satisfied with the surface roughness of the bell mouths? How do they align with the runners? I can't see it clearly in the picture.

Cap heads would work but now I have the physical part, making the cutout larger doesn't look as bad as it did in the 3d model so i'll do that.
As I suggested 😉.

Are you going to do a back to back test on the dyno with it?
 
#39 ·
Would this fit the bill?
Ultrasint PA6 FR (Flame Retardant) 3D Printing Material
Looks like it's melting point is 201C and flame retardant. Limited by printer bed size.
Wow, you are up early and well informed. Thanks for the link. I skimmed it, many properties of it looks promising. My feeling says I would still need notched brass inserts to enforce the bolt bores to spread the blot forces far wider into the material. I am not sure about this.

There must have been a lot of work in getting your inlet manifold made up!
103813


It took some effort, yes. Costs for my prototype was around 2000 Euro only for fabrication and material, a bit expensive, but worth the results. Made already 180 whp@5250 rpm (or 180 ftlb@5250 rpm at the wheels), not bad for a 2 Liter NA engine shortly after VTEC.

For comparison the actual print cost for the trumpets is under £50.
That's another world, the same of alu would be under 50 GBP when producing as cast type. Sounds very good!

The benefit of the nylon part is that if needs be it could be sanded fairly easily to improve the port match, it might even be worth making the ID slightly too small so that they could be hand finished.
So it doesn't smear when it get sanded?

Wow, thanks for the link. It seems it may worth a deep dive into it for the next IM, which is planned for raced 87x99 NA engines.

Thanks for the inspiring links guys!
 
#38 ·
There must have been a lot of work in getting your inlet manifold made up!

The benefit of the nylon part is that if needs be it could be sanded fairly easily to improve the port match, it might even be worth making the ID slightly too small so that they could be hand finished.

For comparison the actual print cost for the trumpets is under £50.

I'm not sure if this nylon is going to be the final material, waiting to see how it deals with the temp. However I have a fallback option of Nylon 12 CF which can be heated to 143c under 18bar load before it deforms by 0.25mm. Which I am more confident would be up to the task. Failing that there are things like Ultem.

Even the plain nylon can hold 4.5bar at 150c so we're certainly in the ballpark of possibility.

Details on the Heat Deflection Test:
Heat Deflection Temperature: Definition & Values at 1.8 Mpa (264 psi)
 
#41 ·
I would 100% of the time er on the side of caution and use the inserts. With that thin of a flange it wouldn't be worth the risk even if the material was up to the load/stresses. The fasteners not being torqued enough would be moreof a concern and potentially backing out into the manifold. Even with chemical thread locker.
 
#43 ·
I haven't figured out specifically what the manifolds are printed in yet, but I did find this:
Higher melt nylons: PA12 → PA6/66 → PA6
High T engineering plastics for engine and tooling: Ultem → PEEK → PPSU

Edit:
PA12, followed by a sealing process called "Imprex"
 
#44 ·
Wow i'm shocked that PA12 is holding up to that sort of abuse! Ultem, Peek etc i've been looking at.

I'd be interested in where the steel inserts come from, are they bespoke made for each project?

The Imprex seems to improve porosity so something to keep an eye on.

Interested in any other info you have :D Thanks for the contribution!
 
#45 ·
From what I recall, they look like standard slotted, unthreaded spacers to me (McMaster-Carr). Anything bespoke would only up the cost. The brass inserts are probably standard off the shelf bits too, likely something with a knurled OD to take an epoxy set.

Unfortunately I don't have any information on what design changes we make for RP manifolds vs. their standard black plastic production cousins.

When I was in college, we didn't treat our formula car intake at all, but it has a short life expectancy. For reference, temperature wise we control intake charge to 100 degF and coolant temps to 200 degF as best we can, they'll generally see a bit more charge temp at peak power and if the controllers are messed up (which isn't uncommon).
 
#46 · (Edited)
So slight update to my "studio" now using a box painted with black 3.0 rather than a piece of wood. Idea being that its easier for the software to tell what is the part and what is background.



Which appeared to work quite well, i'm getting better at this now.

First two pictures are in the software:





And this is the exported textured mesh in Blender.





Really impressed with the quality, there's a couple of small holes to fill in where I didn't get good enough photo coverage but generally the whole piece is much crisper.

The runners have about the first 50mm which is accurately modelled then after that they go solid. I dont really see this being a major issue and was actually expecting the runners to be solid pretty much the whole way.

Now I have to remake this as a simplified and tidied up model, the actual generated mesh is too dense to work with as is.
 
#48 ·
Small update.

This is by far the most complex part I have modeled and its taking a little while.

I'm not particularly interested in the outside features as this is only really for CFD.

Modelling to do list/WIP
- Runners are a constant radius
- Flanges to be squared up
- Overlength runners to be trimmed
- Plenum interior is only a mock up, needs tidying

This is the current state of play:

Combined


Just the model


Combined


Model


And a bit of a catch up.

You've probably spotted it in the model but I have chopped up the flange on the manifold to fit my k20a2:



I've also spent far too long cutting up little brass spacers for the bolt holes:





That'll be okay for these prototypes but definitely something I need to find a better solution for going forward. Ideally i'll find some similar sized unthreaded spacers and then adjust the flange thicknesses to suit.

Printing is mounted up and i've added some temp strips that will show the maximum temperature they have reached.

One on the bottom closest to the printed parts and likely to get hotest


And one on the runner because it will be easier to see when the manifold is installed


Printing should be okay up to about 150c. These strips measure from 70c to 110c. In reality I don't think I will even get a reading on this top mounted one.

I'll add hotter strips if need be.

Manifold should be going on the car this week to start durability test while I finalise the CFD model.

Once the plenum model is up and running i'm going to work on improving flow distribution between the runners by trialing slightly angled trumpets. Once I have a few that work well they'll be printed for back to back testing.



I'm not sure what you mean by adding a wall to the surface?
 
#50 ·
Oh I see.

Unfortunately it isn't that easy, the scan has a very high number of points, in the region of 1 million. This makes it very difficult to work with. It's like working on photoshop with a 1 pixel brush.

I have to create a new model that effectively traces the scan but has more sensible geometry.

Sent from my Pixel 3 XL using Tapatalk
 
#52 ·
Bolt clearance was tight but okay, until I put the the bronze spacers in which made it more difficult so I opened the holes up with the soldering iron.

Going forward I'll order cap head bolts to minimise the impact on the trumpets. They'll also be 5mm shorter so they don't have to go through the trumpets to put them in the holes.

Sent from my Pixel 3 XL using Tapatalk
 
#53 ·
Going forward I'll order cap head bolts to minimise the impact on the trumpets. They'll also be 5mm shorter so they don't have to go through the trumpets to put them in the holes.
Sounds like a solution. I like your idea of using a temperature indicator. Would be nice to know which surface temperature mine has. BTW, the Testo company is just a one and a half hour away from my place. I've used many emission and temperature measurement tools of them, they stand for higher quality equipment for a more fair price. Many of the service guys of my former engine company I worked for use them to tune the emissions correctly during service of the gas engines. Anyway, a good idea to use such an indicator.

Which process did you use to place the bronze spacers? Looks like a thermal heating process, but I am curious about the details :).
 
#56 ·
Its been slow work but the manifold is pretty much modelled, i'm going to add a throttle plate and I have some small areas of geometry to tidy up but its pretty much there.

The runners now have more of a conical shape to align with the port shapes and I have pretty much done the internal face of the plenum.

Plenum



Original trumpets added



Printed trumpets and backplate



I've had a bit of delay getting the manifold fitted so next post could be results or it could be CFD watch this space.
 
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