[mrluke]

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

 

[LotusElise]

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)

 

[mrluke]

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.

 

[drtye]

I like it. Really neat approach instead of fancy 3d scanning and proprietary software.

 

[LotusElise]

...64.6mm in the model and 64.6mm in real life.

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. What did happen to the parallel cut on the bolt bores? De-rendered?

But for a couple of hours in CAD i'm pretty happy with where I have got to.

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? 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'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.

Very good, I hope the Blair paper helps on that.

Do you have an idea how long you want to have the runners, for the runner length tuning?

 

[mrluke]

I like it. Really neat approach instead of fancy 3d scanning and proprietary software.

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.

 

[mrluke]

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.

 

[LotusElise]

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 .

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?

 

[mrluke]

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.

 

[Them Witches]

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

 

[Scider]

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

 

[mrluke]

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.

 

[drtye]

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.

 

[LotusElise]

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.

There are tons of tests comparing RRC vs RSP in different bell mouth lengths on different setups you can find here: RBC vs RSP(euro type R) intake manifold | Honda / Acura K20a K24a Engine Forum, especially I like the comparison of member 6spd_EK on pages #9 and #10. For my experience it isn't worth a penny to test different lengths below 30 mm difference. That said the there are 2 maybe 3 test cases: original, shorted by 30 or 60 mm. The effects what 6spd_EK found was coming from different sides: better inflow condition into the plenum, better inflow into the runners by well designed bell mouths and increased peak power engine speed with an aligning higher peak power. So maybe the 30 mm shortened runner isn't worth the effort too.

BTW and again...

What engine speed is in your specification?

As Scider said, length is the most important factor regarding peak power settlement as well as the other harmonic orders down low the revving band, therefore my introducing question.

 

[LotusElise]

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.

drtye, you may remember the 6spd_EK RSP plenum? You find them here: (1) RBC vs RSP(euro type R) intake manifold | Page 34 | Honda / Acura K20a K24a Engine Forum . I never saw the results, I lost the contact to 6spd_EK. Maybe you have the FB contact or any other? He lives in the mountains of the sate of NY. Not to far away from your place if I am not wrong 🤔?!

 

[drtye]

drtye, you may remember the 6spd_EK RSP plenum? You find them here: (1) RBC vs RSP(euro type R) intake manifold | Page 34 | Honda / Acura K20a K24a Engine Forum . I never saw the results, I lost the contact to 6spd_EK. Maybe you have the FB contact or any other? He lives in the mountains of the sate of NY. Not to far away from your place if I am not wrong 🤔?!

Yeah, I remember that testing, can't remember if I ever saw results either... I do not have any sort of social media to speak of. NY wouldn't be too far away....

 

[mrluke]

There are tons of tests comparing RRC vs RSP in different bell mouth lengths on different setups you can find here: RBC vs RSP(euro type R) intake manifold | Honda / Acura K20a K24a Engine Forum, especially I like the comparison of member 6spd_EK on pages #9 and #10. For my experience it isn't worth a penny to test different lengths below 30 mm difference. That said the there are 2 maybe 3 test cases: original, shorted by 30 or 60 mm. The effects what 6spd_EK found was coming from different sides: better inflow condition into the plenum, better inflow into the runners by well designed bell mouths and increased peak power engine speed with an aligning higher peak power. So maybe the 30 mm shortened runner isn't worth the effort too.

Thanks, I have read through the thread a few times, its the main reason i'm sharing my progress on this forum

I could only really see one before and after dyno of a modified RSP.

Which gives fairly minor gains from 5,750 through to 8,500 with the caveat that the low cam tune wasn't altered to suit the RSP.

BTW and again...
As Scider said, length is the most important factor regarding peak power settlement as well as the other harmonic orders down low the revving band, therefore my introducing question.

Given my use case i'm probably aiming for a peak HP at around 7.5k.

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.

A peak anywhere between 7.5k and 8k would be good, i'm not specifying an exact target because I haven't seen any calculations yet that have proven to be that accurate.

The whole idea was around getting a manifold to perform as well as the RRC but still fit into a lotus without cutting a hole in the bulkhead Or for those already with an rsp maybe it unlocks some performance for less than the cost of a new manifold.

 

[LotusElise]

Which gives fairly minor gains from 5,750 through to 8,500 with the caveat that the low cam tune wasn't altered to suit the RSP.

That is what it is. Reality is a challenger 😉

A peak anywhere between 7.5k and 8k would be good, i'm not specifying an exact target because I haven't seen any calculations yet that have proven to be that accurate.

Like Scider mentioned above, exactly that is what the series RSP already does, it let the 2 Liter engine peak at 7800 rpm. More displacement = lower peak power engine speed.

The whole idea was around getting a manifold to perform as well as the RRC but still fit into a lotus without cutting a hole in the bulkhead

The RSP plenum flange bolt pattern causes the clearance demand of around 275 mm head to plenum flange end. No room to reduce that. The firewall/bulkhead has to be moved. What you could do is what I've done, doing a complete own IM. Otherwise, aftermarket could supply some more or less well developed IM which are definitely less challenging in clearance. But think of this, moving the bulkhead is a DIY job of around 100 Euro and two days of work. Better do this then landing in a dead end road.

Maybe you do a DIY plenum for the PRC IM, sort of central feed plenum, which would likely improve power significantly. This IM is the only one of the row of OEM ones which fits without any issues in a '02-'05 Elise chassis.

 

[mrluke]

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.

Trumpets:

Back plate:

Plenty of tidying up to do but not far off ordering.

 

[LotusElise]

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.