When Bigger ISN'T Better: Plenums AKA Intake Manifolds

The bigger your throttle body and inlet manifold is, the more air your engine can flow, the faster you go right? Yeah nah.

A guide to throttle body sizing, getting even air distribution within 1%, major design considerations, intake volume vs capacity and if an intake/plenum chamber alone is all you need to make more are all topics Shannon Rogers from @plazmamanracing runs us through during our visit to The World Time Attack Challenge where the team was supporting a new Mitsubishi Evo X product launch.

Where he and the Plazmaman team see the limitations of factory setups is also discussed along with how some head designs and packaging issues just don't allow better solutions as well as a the golden rule Shannon tries to get customers to follow which is to focus on the best combination for the application, not just a combination of the biggest parts you can find.

With this in mind an aspect that is so often overlooked when focusing on the shiny things under the engine bay is also discussed with engine builders and tuners alike forgetting to address the pedal ratio when drastically changing the inlet setup.

If you only take one thing away from this interview it should be that going for the biggest intake manifold chasing the biggest power number you can on the dyno is going to get you a nice piece of paper (noting there's always a bigger fish!) and a probably horrible car to actually drive.

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TIME STAMPS:
0:00 - Common Upgrade
0:23 - Shannon Rogers - Plazmaman
0:58 - Main Design Considerations
1:37 - Reasons To Upgrade
2:04 - Aesthetics
2:21 - The Only Mod You Need For More Power?
4:04 - Design & Validation
4:50 - Overall Power Isn't Better
5:24 - Inlet Runner Length
6:31 - Volume Vs Capacity
7:09 - Throttle Body Sizing
9:09 - 800hp - 1000hp - 1500hp & 2200hp Sizing Examples
10:22 - Pro Tip: Measure Pressure Drop BEFORE Changing
11:08 - Fuel System Restrictions
11:49 - Fuel Distribution Concerns: Dual/Staged Injection Setup
13:33 - Flow Distribution: Within 1% Where Possible
14:40 - FG Manifold Example
15:01 - Don't Assume, Get Some Data
15:20 - Plazmaman, They're Everywhere
15:38 - Thumbs Up, Learn More. Do It. Now. The Old You Would Have.
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#highperformanceacademy #plazmaman #intakes #plenum #intakemanifold #dangertomanifold #wtac #enginesetup #learntotune #enginebuilding101 #dontletthesmokeout #wiring101 #dieseltuning #datanerd #gofasterwithdata #racecraft #learndriveoptimise #motorsports #plazamamanracing

[hpa]

Check out the previous [TECH TOUR] chat we did at Plazmamans facility. Link at end of video.
TIME STAMPS:
0:00 - Common Upgrade
0:23 - Shannon Rogers - Plazmaman
0:58 - Main Design Considerations
1:37 - Reasons To Upgrade
2:04 - Aesthetics
2:21 - The Only Mod You Need For More Power?
4:04 - Design & Validation
4:50 - Overall Power Isn't Better
5:24 - Inlet Runner Length
6:31 - Volume Vs Capacity
7:09 - Throttle Body Sizing
9:09 - 800hp - 1000hp - 1500hp & 2200hp Sizing Examples
10:22 - Pro Tip: Measure Pressure Drop BEFORE Changing
11:08 - Fuel System Restrictions
11:49 - Fuel Distribution Concerns: Dual/Staged Injection Setup
13:33 - Flow Distribution: Within 1% Where Possible
14:40 - FG Manifold Example
15:01 - Don't Assume, Get Some Data
15:20 - Plazmaman, They're Everywhere
15:38 - Thumbs Up, Learn More. Do It. Now. The Old You Would Have.

[grahamerosewarne]

Bigger isn't always better. Glad to hear from a Bloke involved in the trade of manifold replacement. Awersome content as usual from HPA 💯 AUSSIE FAN 🆒🇦🇺

[plazmamanracing]

Pleasure to be apart of this, We appreciate the support you guys provide.

[jdmjesus]

Thanks for this. Been trying to tell the Honda boys for years that a bigger throttle on a stock Honda isn't going to make it faster, it's an uphill struggle though.

[mikejovi]

Have been banging on about this subject for a long time.. specifically to do with rb25s and the greddy style manifolds.. even with bigger turbos say my gt3076 vs a gt35 making the same peak power at same beak boost the difference in power under the curve is far superior on a standard manifold. Sure eventually the other type will allow more and if your worried more about the way it looks ok.. but for a street car... 💯 No point.. better to spend money elsewhere

[jdesigns]

OMG OMG OMG!
I'm SO happy this videos are back!

[capnthepeafarmer]

I'm sure you get this all the time, Andre, but you're such a good interviewer! Very professional and genuinely interesting and relevant questions!

[davidparker]

Excellent point that is lost on so many. Bigger is not always better. Bigger often makes it lazier and less fun to drive. Maybe it makes great numbers on the peak of the dyno, but if you lose all of your low and mid-range power to gain it, was it worth the trade?

Perfection is striking a balance that gets you the most improvement through your usable powerband.

[joels]

Been porting engines for a long time. When it come's to intake manifolds the 2 most important things are "smooth" airflow, and cylinder equalization. You want all air turns to be as smooth as possible with no turbulent ridges or "steps" in between parts. You want all cylinders to have equal flow from the air source all the way through the cylinder head and out the exhaust, and the intake manifold is the first critical piece to accomplish this. As far as plenum capacity things get a bit more complicated but you want to essentially do is "shape" the plenum to make sure the back cylinders are getting the same airflow as the fronts and can meet the flow needs of the cylinders. This will determine the size and shape of the plenum based on the application. Bigger is not always better.

[timmurrayy]

The Plazmaman intake manifolds for the 4G63 are odd designs. The long runner manifold is marketed to suggest more midrange torque due to the runner length but it has a massive internal volume. Their site suggests this is to support rpm in the 10, 000+ range. If you’re spinning the engine that high, why the long runners? The other design is much closer to the Hypertune manifold with short runners which favour top end power but this has a small(er) volume which according to plazmamans long runner marketing would not be ideal for high rpm. I called the them to discuss it, and the bloke was like yeah nah they’re both good aye. Couldn’t give me any practical advice on which one would suit my aims, but did say the long runner version made over 800hp… confusing AF.

[Takeitlightly]

If people read HVAC standards and Air Velocity standards based on fittings it will work beautifully on induction system...as well as exhaust...you gotta know what are velocity reducers like elbows are and tight bends and by how much...whats the target requirement or air velocity and how are all the fittings together cause pressure drop. Ashrae standards are great resource.

[S]

They're right on the money when it comes to going too large in the plenum size as well as the throttle. I actually prefer to over size my throttles some as I like a touchy pedal within reason. But going back to the plenum, the Helmholtz theorem is a very good guide on idea size for the application and in my experience, going bigger than needed makes the engine very unresponsive and soggy to drive, even with a larger throttle in the mix.

With throttle size, I generally used a program like dynosim to simulate where a throttle starts to choke, then pick the size a few mm or closest above the min and use that. The power figures mentioned for throttle size in this video are a foreign language to me, since I only have built and hotted up NA engines.

I found at least with sims and actual real dyno/road testing on some engines, 60mm NA is good for around 300hp, 65mm was good for 340hp and 70mm could support 400+ pretty well unrestricted. I never went any further than that since my engines can't support or even will need anything bigger than 68mm in real life. When boost is added, the stock 60mm is heaps as mentioned in the vid.

[PhamVans]

Works good if you are pushing in enough air aka PSi.

Of course the fun part of this is figuring out where that line is. Whether you want a flat torque curve or something that will spike.

[NKPGarage]

I love the Plazmaman manifolds, quality is absolutely amazing! I just got my Plazmaman manifold in for the 1997 1FZFE Land Cruiser that I am building!

[vipercrazy-]

I have regularly checked my plugs every 1k miles or so to adjust cylinder fuel trims, with a stock runner/replenum and 23psi I still ended up around 5-6% on one or two cylinders until the plugs started to look similar. I wish I knew how the factory manifold did, it may have performed the same.

[MafiaboysWorld]

The issue I've found with these have been the plenum runners. Motive showed in their video they had only 22mm runners which is ridiculously short and only good for top end. I've also seen dyno results from Goleby on a 1JZ that he put up on FB and the loss of power under the graph was more than the top end gain you got. 👍

[madvtecyo]

I have seen dynos of people adding a bigger plenum and actually losing power, needing to run 3 extra PSI to make the same power of the stock plenum. Dyno on an s2000. A lot of intake plenums are just for looks

[dilsher]

Its very simple and most people can't get their head around it, a long runner will always make more power over all and will usually fall off around 5500-6000 depending on the length ofcourse . A shorter will only make more power at higher rpm, there is no sorcery behind it . Your average street driven 500-600hp build does not need a fancy $2000 manifold infact you are actually loosing driveability and power if anything .

[stuartcarter]

Ok here’s the skinny
I spent 3 yrs on methanol engine development on the dyno
Let me tell you
Some bogg std manifold from an evo or even a NA car with boost up to around 30 psi is hard to beat
Unless you start into dual plenum style only then will you see real gains
I’m sure some of these plenum’s work
But in the real world when your at the club sport level
Just try to size everything correctly and you ll make good hp and the thing that wins is torque
Just look at WRC and LeMan Audi diesel s etc

[totensiebush]

wait... a 4psi pressure drop across the TB is reasonable? That sounds WAY larger than I'd expect. I would have expected even a 1psi drop to be an indication of an undersized TB.