3D Printed Parts

[Magpie]

I can't wait to test the curved trumpet!

Another issue with the stock jenvey setup for our RHD cars is using a 40mm trumpet. This is about 50mm too short for optimum length. Whilst this is not an issue with mild cams it becomes a negative when big cams are used. As stated Jenvey do make a shorter body and this COULD allow longer curved trumpets to miss the booster etc. I never got around to testing this, but testing with 90mm trumpets DOES work!

Is there a market for an air box that fits Jenvey trumpets on a RHD MX5 not likely, it would be more of a niche market unless an arrangement was made with a Jenvey distributor. However this would require more R&D to prove the concept, why is it better than what is currently available and performance gains. Based on what is available a price around $300 could ba accepted by the market.

[gslender]

My understanding is this...

Optimum ITB intake length is measured from valve face to trumpet outer face, so reducing throttle body and extending trumpet (in the same overall space) makes no difference. If you need more length than either curve up or remove what's in the way.

CAMs are not the only factor, the exhaust headers are also part of the equation and the entire header, cams and intake need to be tuned together to really bother about worrying about specific trumpet lengths.

Would like to understand the specifics on how you tested a 90mm trumpet? If you can put them on and drive around, why take them off? I guess it might have been "dyno" tested and without brake booster installed - right?

Jenvey are based in the UK and commonly sell to RHD market, so whilst LHD is big in the USA, they do sell a few kits in RHD markets and an ITB airbox made for Jenvey fitment that is $500 and is guaranteed to fit a RHD MX5 (with minor changes for space needed) would probably sell equally as well as the $2000 ITB kits that are needed to go with them. Obviously it would not be a high volume item, but then again, how many performance mod parts are?

I'm not sure if 3D printed plastic is the right option for the airbox, but if the 3D model is correct, can I get it made from other material? what's the point of making something out of 3D printed plastic is the material isn't really suitable for production use? I thought the idea was to prototype out of plastic and if correct (it fits) you'd then pay to have it made out of some other more suitable material (at a greater cost).

G

[gslender]

Optimum ITB intake length is measured from valve face to trumpet outer face, so reducing throttle body and extending trumpet (in the same overall space) makes no difference. If you need more length than either curve up or remove what's in the way.

...and I believe 450mm is the goal for an engine that hits redline at 8000. Measured from valve face to trumpet face.

2nd harmonic from 6500 to 8000 giving 10% extra pulse strength
3rd harmonic from 4750 to 5500 giving 7% extra pulse strength
4th harmonic from 3800 to 4250 giving 4% extra pulse strength

Even with that, there is ALWAYS a gap where the harmonics don't overlap.

[Magpie]

The 90mm trumpets were tested on a dyno with no airbox. At least for my build they smoothed out the toque dips at 3500 and 5500. This was what was calculated that the 90mm trumpets would do by Pat at competition Systems.

Further discussions with Pat suggests that the 40mm trumpets are a compromise for a RHD MX5 to fit an airbox.

[gslender]

Runner length is the only thing that matters with change trumpet length.

Input length is 12 inches
For 2nd harmonic, RPM range is from 9790 to 11880 with a pulse strength of 10 percent
For 3rd harmonic, RPM range is from 7356 to 8407 with a pulse strength of 7 percent
For 4th harmonic, RPM range is from 5735 to 6413 with a pulse strength of 4 percent

[madjak]

Abs plastic should hold up fine for use in the engine bay as long as it doesn't get hotter than 100 -120 degrees. Its stronger than the pla I have been using and if temp is ok structurally abs is strong. Since the throttle bodies transfer heat heat from the head I'm pretty sure they will be close to that temp on a hot day when pushing hard. They do get nice cool air running through them. Anyone care to take some temp readings?

The stock air box and intake will most likely be some form of abs.

As for printing the best is probably the abs. If temp is an issue then you'll either have to print a mould or take a mould or part from a plug.

[madjak]

Here you go. Still needs to have the support structure sanded or trimmed off the face.

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Magpie, pm me your address and I'll post them out. The two parts clip together nice and tight but you can change the rotation between the two to trial any orientation you like.

20140926_083401.jpg

Next print... I broke my plastic trim inside the tombstone when removing the stereo. I'm printing a replacement trim that will be a direct screw in replacement allowing for the mounting of a 2mm carbon or aluminium sheet. It will also fit 3 x 2 1/16" gauges across the width.

[gslender]

The 90mm trumpets were tested on a dyno with no airbox. At least for my build they smoothed out the toque dips at 3500 and 5500. This was what was calculated that the 90mm trumpets would do by Pat at competition Systems.

Further discussions with Pat suggests that the 40mm trumpets are a compromise for a RHD MX5 to fit an airbox.

Something always bothered me with that claim - trumpet / runner length calculations don't measure up with that outcome.

For runner length to have had a positive impact on the engine at 3500 and 5500 you'd have to have 600mm runners. A 40mm to 90mm trumpet change isn't going to make up that difference, and doesn't push any harmonics around in that rev range. Whilst I'm not saying Pat at competition Systems or the team at Automotive Plus don't know what they are talking about, I am saying that the maths and science behind why runner length is important doesn't correlate with the outcomes you are chasing.

Might be worth asking why they think another 50mm can account for such a significant improvement when it doesn't match with the well known and published information on runner length calculations - see for yourself on Bowling & Grippo http://www.bgsoflex.com/intakeln.html

[madjak]

I would have thought for a high reving, high flowing engine that shorter lengths would be better. Putting the 90mm throttle bodies on and 40mm trumpets! Probably would kill torque down low but I don't plan on being in that rev range much!
My other issue is a curved trumpet actually has multiple lengths. So on the shorter edge on this trumpet would be 75mm, on the longer edge 105mm with the center line being 90mm. I'm not sure how that would impact on harmonics etc. I could get creative and angle the end bell so that all lengths are the same.

Has anyone looked at the TWM 48mm ITBs? they are a total length of 8.5" or 215mm. I think that matches the Jenvey 118mm bodies + 40mm trumpets + Inlet Flange.

[plohl]

Can't be bothered embedding it.

https://www.dropbox.com/s/6cfcxct6bro53di/2012%20differenet%20lengths.PNG?dl=0

40mm changes to intake length made a lot of difference. From CBR600f4i

[madjak]

Nice... thanks plohl. That is a much bigger impact than I was expecting!

Whats the T2010 curve as that looks the best one to me for race purposes! And 11,500 Rpm... what engine is this, a motorbike engine or something?

You can see the longer trumpet getting way more torque down low but at a massive hit higher in the revs. Just need a sliding trumpet on an actuator.

edit: Spelling

[Black_Penguin]

The 26b 4 rotor engine used in the Mazda 787b le mans car had variable length intake runners for a better torque curve.

[sailaholic]

It's a 600cc honda CBR bike engine. The longer trumpets get rid of the torque dip in the middle that would make the car difficult to drive.

I'd suspect you'll spend more time at mid revs then you think. Biggest Area under the curve generally gives best performance unless you have a track with lots of big straights where you peak power is fighting aero


Sent from my iPhone using Tapatalk

[gslender]

Can't be bothered embedding it.

https://www.dropbox.com/s/6cfcxct6bro53di/2012%20differenet%20lengths.PNG?dl=0

40mm changes to intake length made a lot of difference. From CBR600f4i

Yeah, but that's exactly my point. 40mm isn't going to improve the engine problems at 3500rpm. At 7000rpm for a bike engine like that perhaps but just not understanding how it can help with lower rpm problems when the intake runner length is just way, way too short and adding 40mm isn't enough to even remotely come into what would be ideally needed to positively improve low rpm pulsing. If you were going from 40mm to 200mm then I'd agree that would be absolutely needed, but 1.5 inches isn't enough to make the runner lengths tuned to the RPM band that is the problem.

On that bike, the longest intake didn't help with torque dip/drop below 6,500 - it made it worse. The engine now has (with the 328mm intake) a much worse torque drop below the 6,500 mark.

Overall, I'm suggesting that adding 40mm would help with max output at 8500rpm, but should do close to nothing for anything below. If it isn't, would be curious to understand the science behind why... given that cams, fuel and spark should be the same, why is 40mm magically doing something that all text books on air flow dynamics suggest shouldn't be making any difference.

G

[Caffeine]

We have a new Objet 1000 printer at work, that can print up to 1000x800x500mm

We have around a dozen or so printers of various types. I've found the ones that print in ABS to give quite strong models, with acceptable surface finish. They finish is obviously better when cleaned up and finished with some mr surfacer or similar.