2012+ Honda Civic Si RBC Intake Manifold Test


There has been an ongoing debate about the pro’s and con’s of swapping the 8th gen Civic Si intake manifold onto the 9th gen Civic Si without any real concrete testing. Just butt dyno reviews, bromancing and numbers being thrown around with no context. So basically your average day on an enthusiast discussion board.

We’ll be having none of that here — I requested a 2012+ Civic Si that had a Full Race exhaust and Full Race 3″ catless downpipe, running the stock intake as our “base” to start from. We also got the the PRL SRI for the stock IM & RBC so that testing would stay consistent — and we tested the PRL SRI before installing the RBC IM.

So in short the testing involves:

  • PRL SRI on stock intake manifold.
  • RBC intake manifold w/ PRL SRI (to see difference over stock manifold).
  • ZDX throttle body.

Now the ground rules are simple:

  • The vehicle must be fully retuned after each major modification change on the vehicle.
  • No “snorkel modding” the intake out of the engine bay to artificially reduce intake air temps (reducing air temps will indeed increase HP — the goal of this test isn’t to show you this). The goal is consistent and realistic testing (particularly to demonstrate differences from mod to mod).
  • Two to three pulls are done on the “final” tune to ensure the engine has “settled” and the pulls are consistent between attempts — maintaining this requirement ensures comparisons between the various mods we are testing are consistent.

Long and productive Saturday: eight hours without the car leaving the shop dyno and over 70 dyno pulls later, we had concluded testing.

Now on to the results.


Stock tune vs VitTuned

stockintakeThis is how the car came in today. Equipped only with the Full Race 3″ Exhaust and Full Race 3″ catless downpipe.


I baselined the car on the stock tune and we got just shy of 180whp (the dyno baselines 162-165whp for a bone stock 2012 Si). Not bad at all for two simple exhaust bolt ons. The stock intake had been retained and this example demonstrated why I recommend keeping the stock intake if you can’t afford FlashPro/Tuning yet — the car actually runs mostly OK with the factory airbox on the vehicle. Obviously doesn’t make “best power” for the mods, but the car drives and performs well day to day.

I proceeded to fully tune the car — and the power went up nicely with a cleaner power curve throughout the rev range, stopping just shy of 190whp — with gains of 11-14whp through the top end over the factory tune.


Stock intake vs PRL SRI

prlsri_stockimI proceeded to install the PRL Motorsports short ram intake (SRI) on the vehicle. Fitment was perfect and install of the SRI was a breeze — requiring only a couple of basic tools.prl_sri_vs_stock_intake_stockim

Back to the laptop I went and more tuning commenced. I was pleasantly surprised by the solid low end gains from 1700 rpm til 2500 rpm — as much as 12 ft lbs of torque to the wheels will definitely be something you can feel during normal stop and go driving. Slight loss from 2750 rpm to 3000 rpm though — nothing major. And no real gains until after ~ 5700 rpm, with a maximum of 4.5whp was had from 6750 rpm til 7000 rpm. Not a bad gain for a simple mod — I’ve seen much worse performance from some intakes on this platform (worse than stock intake at times).


And now the RBC intake manifold!

prlsri_rbcimOn to what we’ve all been waiting for! I dug back into the engine bay and worked on installing the RBC intake manifold PRL graciously supplied for testing — as well as their adapter for the kit. This install is a bit more involved than the SRI and required a larger variety of tools — and about 2-3 hours of shop time to install.

Once the intake manifold was on, the RBC IM version of PRL’s SRI was bolted up and the coolant system was burped. This step is very important — the coolant system must be properly burped. I’ve had customers send me datalogs with 280 degree Fahrenheit coolant temps after doing work on the car that involved draining the coolant system — which just guarantees a blown head gasket and very costly repair. I recommend using this kit, or something similar, to assist with purging the coolant system of all air: Spill-Free Funnel.

Back to the laptop I went for another session with the Hondata rbc_vs_stockim_prlsri_on_bothFlashPro. And here are the results!

  • Below 2100 rpm there is as much as 12 ft lbs of torque lost when using the RBC intake manifold.
  • From 2100 to 3500 rpm there are minor torque gains (1-6wtq) when using the RBC intake manifold.
  • From 3650 rpm until 5750 rpm there is nothing but bad news when using the RBC intake manifold — as much as 15 ft lbs of torque lost!
  • After 6200 rpm is some good news — we begin to see minor gains, based on “peak” numbers, we only got a 6whp gain using the RBC.
  • At ~7150 rpm there is a 7whp gain.
  • At 7500 rpm there is a 11whp gain.

So what can we gather from this? There is a hefty trade off when using this intake manifold on the 2012+ Civic Si. You are basically sacrificing a lot of mid/low end for a powerband that carries better after 6000 rpm.

So pick your poison: what are you using the car for?

Racing? Then technically speaking this car will be a bit faster when keeping the revs above 6000 rpm.

Daily driven stop and go “fun” car? The torque with the stock IM might benefit you more.

The choice is yours — as with everything in life, we do what we do with our toys for our own pleasure and enjoyment.


Wait, let’s make a joke and put a huge TB (ZDX/J37) on the car and see what happens?

zdxtb_on_rbcimNow I really have no idea how TB swaps got so popular on bolt on motors. The simple fact is this — items like throttle bodies, injectors (yes I’m looking at the guys claiming RDX injectors are necessary with an RBC IM swap), etc, are nothing more than SUPPORTING modifications, and ONLY benefit you when the motor has a flow requirement that is now surpassed by the items on the car. To say the stock 9th gen throttle body is a restriction on a bolt on 9th is simply a JOKE. The following comparison demonstrates as much. For the marginal gains (1hp) that is had up top with the TB, as much if not more is lost in the mid/low end.

But so and so put a TB on and it pulls so hard…. sorry, please schedule an appointment to have the butt dyno re-calibrated.

Hopefully this has been an insightful test for us all.


What’s all this cost?

  • RBC Bored to 70mm for ZDX and CNC Bored for 9th gen injectors – $420
  • PRL RBC Adapter Kit – $135
  • ZDX TB (when purchased as kit option from PRL) – $220
  • PRL SRI – $200
  • Shop labor (if not installing on your own) — 3-4 hours ($240-$320 here)


I’d like to give a big thanks to PRL Motorsports for supplying us with all the goodies for this test.

Thanks Ernesto for supplying the test vehicle — enjoy the mods and the tune!

Deatschwerks DV2 1500cc Injector Review

Deatschwerks announced their DV2 line of injectors — 1200cc and 1500cc variants — not too long ago. I was fortunate to be one of the first to get the word about these injectors from DW and I was excited to get my hands on both sets to do some testing on my shop vehicle.

Foremost, I want to talk about the 1500cc variant — I’ll touch on the 1200cc set briefly later.

The test vehicle is a 2001 Honda S2000 powered by the F20C on an AEM Infinity stand alone. The fuel system is very simple — the OEM Honda fuel return system with completely stock fuel lines, with a Walbro 485 fuel pump in tank, an AEM FPR and AEM fuel rail sitting over the Deatschwerks DV2 1500cc injectors.

My goal? To make over 600whp (on a dyno that baselined 195whp for the car bone stock) with a Comp CT4x-5862 turbocharger.newmotor_20psi_pump_vs_24psi_e85

Mission? Accomplished. On E85 the vehicle put down over 600whp at 24psi and 525whp on 20psi running 92 octane pump gas.


That is fantastic power for a very simple setup — it’s a 2.0L bottom end with a 58mm turbo and only “drop in” fuel system upgrades (no plumbing new lines, etc).  The only fault in the fuel system is the high fuel pressure at idle — I’ll touch on that later — and the injectors have performed amazing nevertheless.

I am able to run a very wide range of power without swapping parts — no injector swaps, etc. The injectors DW supplied me have been more than plenty for my goal, with room to push to 700hp with a higher base pressure and a different pump/fuel line setup (the Walbro 485 doesn’t do so hot at high base pressures).

Unlike the 2200cc injectors we have been stuck with in the past if you wanted to do a 600whp+ flex fuel vehicle, the 1500’s don’t have the drivability nuances we’ve become so accustomed to — no insanely unstable idle due to the pops and misfires, no weird shuffling at light loads or on deceleration. Even on pump gas — where it is virtually impossible to get a set of 2200cc injectors to behave without running the vehicle at a super rich target lambda.

On E85 the 1500’s have a very slight pop at idle . On pump gas — they are a little “poppy”, but not so much that it deters from the idle or attracts unwanted attention to the car stop light to stop light. Much more than acceptable — they actually make the car very enjoyable to drive without having to put up with drivability nuances. In fact, whether it be on pump gas or E85 — squeezing the throttle rewards you with a smooth powerband, strong spool and very predictable power delivery without the odd “oops the motor missed” as you touched the throttle.

And if the biggest fault I can find with the 1500’s is that on deceleration in rare situations running pump gas I’d get some shuffle — I can easily blame it on the high fuel pressure at idle & low load. With the Walbro 485 in tank, the fuel volume is so massive the small factory return line can’t keep up when the engine doesn’t demand a lot of fuel — this increases the fuel pressure to over 70psi on this car, resulting in effectively a 1900cc injector in these situations. Yet — I was still able to fix the shuffling with a tuning trick, without going to the same extremes as a 2200cc injector.

Better yet — a fuel return line upgrade will bring the fuel pressure down to actual base pressure and clean up that behavior. This isn’t something I’m wanting to do on the car as I have not found it to be necessary — the drivability is fantastic and I just don’t want to change a thing at this point.

Short comment about the DV2 1200cc injectors: they are perfect. In every aspect. If you’re not looking for 600-700hp they’re a great choice as well. I made 575whp on E85 on the 1200’s squeezing them to 100% duty cycle.

Whatever you’re looking for — both injectors are fantastic and I would definitely recommend.  As with all the products I’ve tested and support, these injectors are on the VitTuned Store.

K Series Mapping: Why so many revisions for a proper map?

A question I get very frequently here at VitTuned. The short answer is very simple: do you want it done right, or do you want it done fast (and lazy)?

For the long and descriptive answer, let’s take a look at an example of a Hondata FlashPro (same idea with Hondata KPro and KTuner maps) map. The heart of the tune is the ignitcammapion, fuel & cam angle mapping, with the proper VTEC point being the final slice of pie.

The following graphic depicts these basics — but the thing to note is there are actually *10* ignition and *10* fuel maps, at various break points. So now at the very heart of the tune are 10 of each of the “big ones” (ignition/fuel) that need to be properly mapped for the vehicle & its modifications.

Now we can begin to understand why so much work — not only do you have to do all the individual mapping, you then have to combine it for a “final” fully tuned map, adding in any further tweaks necessary to smooth out the motor’s operation as well as doing any necessary part throttle tuning whimapsle the power tuning has been going on.

To the right is a screenshot of how many “revisions” a proper all motor map involves — this was a tune done in person on the shop Dynapack dyno. Every log is either a WOT pull or load based part throttle mapping while the vehicle was on the pack. Took about 34 “revisions” (IE, changes to the tune before more logging & testing was done).

This is how I do every tune, every single one. Whether it’s your basic stock K series vehicle or highly modified turbo built motor beast. Do it right, or don’t bother doing it at all.

I’ve seen some claim they tune like I do — short story is they may try to duplicate, but they can never replicate.

Let’s dig a little bit deeper.

The most important thing to note is the fuel mapping — on a setup that breaths very well there can be as much as a 30-40% difference in fueling between the 0 degree cam break point and the 50 degree cam break point. Even if you set up the cam angle map to have a mostly “fixed” cam angle map — guess what? The cam still moves, it’s a simple mechanism that’s powered by oil pressure — not to mention the phasing between the high cam and low cam (VTEC on and VTEC off) maps. Then what happens if the ECU ever limp modes for any reason? It will default to the 0 degree maps in the ECU during fail safe scenarios.

So let’s take for example a map where every single cam break point is the *exact* same, they are identical or very nearly so. Or fuel maps that were put together with no thought — I have yet to see a single K series motor that will demand the exact same fuel at every break point. In three words — it is impossible. As the cam angle moves, the VE (volumetric efficiency) of the motor changes, and as a result the fueling demand drastically changes which is then depicted in a map with properly tuned fueling.

Now what happens in this scenario? The cam will phase, the motor’s fueling demand will change, and you’ll start to experience some drivability concerns — some hesitation there, some weird lag here. What if the ECU limp modes? You’re left with a potentially undriveable (if not unsafe to drive) vehicle.

I’ve heard several excuses for lazy K series mapping — “AEM doesn’t  do it like this” (or insert “Blah blah stand alone doesn’t do it like this”) or “you’re obviously getting your information from someone who’s never seen anything but Hondata”. That is by far some of the worst excuses I’ve seen for laziness on this specific platform. And to break some hearts — I tune over a dozen different engine management systems. Simple fact is — you tune Hondata like Hondata, AEM like AEM, SCT like SCT, HPTuners like HPTuners, etc. Every EMS has it’s intricacies — you learn them all, or in my opinion, don’t bother touching it if you don’t have the motivation to do it right to begin with.

So I’ll leave you with that — you can have fast & lazy, or done right (but takes a bit more work). Ultimately it’s the customer’s money paying for the work & experience they’d like to receive.