k24a2 Stock (what's really best?) (VTC/Intake Manifold)

[iDom]

OK, now I have been looking at information for about a year and a half now, and what I am (thinking) is this:

(k-pro, duh)
- k24a2
- 45-50* VTC Actuator
- RBC IM
- JRRH/Test Pipe/HKS Hi-Power

Plans:
I like OEM reliability. So, I don't wanna open the head up and put new cams in, I don't care for that (at least right now)

Questions:
VTC Actuator
I have been reading a lot about this lately, I was originally not even concerned with this, but I see that the benefits of getting a higher degree VTC is worthwhile..
- Just to get things right, the stock VTC on the TSX is 25*, correct?
- Also, I have read on Hondata that they have been experimenting with the VTC actuator out of the RSX-S which is a 50*, right?
- In the reading, I read that a 50* VTC is not "safe" with the k24a2 because of the valve/piston clearance in the event of "over rev'ing/mis-shifting".. They suggest a 45* VTC..
- Question(s): Is this all true? Anyone want to shed some more light on this? And, is there a VTC that is at a 45* from the factory rather than 50* ?

RBC
I have also done a lot of reading about this as well.. From various dyno sheets, all I see is that there is a greater significance in the loss of Torque in the low end with the shorter, fatter runners of the RBC (with just a bit more HP up top) than the longer, thinner runners of the RBB.
- Also, all dyno results I see of stock k24a2's typically only rev out to 7,500 RPM and there is a loss of HP, and a very large loss of Torque at the end. So, that's all the more I plan to rev mine out to.
- I know it is recommended to get the RBC, especially for boosted applications, but for what I want to do, I am wondering if I really should or not..
- Question(s): Anybody want to shed some new light on this in addition to what I have said? I see some good numbers with the PRB. Basically, after a tune, is there going to be significant gain in performance based off of what I want to do between the RBB/RBC/PRB IM's?

[AttarixEp]

The VTC. Most will say 45* including myself, for a safety zone. Some will say go all the way, they've never had issues. I like my safety zone. K-pro is reliable, but accidents happen.

The k24a2 head when compared to the K20a2 head is almost identical. The springs are a little weaker, The high speed lobe is a little smaller. The K24 is built for tq. The k20 is built for top end. Swapping in a full k20a2 valvetrain with TSX cams will yield higher rev limits. However you will need the RSX-S oil pump as well to gain full potential.

With the RBC manifold, get at least a 70mm TB.

[iDom]

Yea I definitely want a 45* but I want to buy it as a 45* rather than 'attempt' to make a 25*/50* a 45*.. Know what I mean?

[AttarixEp]

Through K-pro, it's simple. When you're tuning your timing advance's, you limit it to 45*. It just keeps the gear from rotating the full 50. I opted for that over modding the 25*. Some places I talked to about it were even hesitant to modify the 25* when I asked about it.

[iDom]

Through K-pro, it's simple. When you're tuning your timing advance's, you limit it to 45*. It just keeps the gear from rotating the full 50. I opted for that over modding the 25*. Some places I talked to about it were even hesitant to modify the 25* when I asked about it.

Yea, it would cost me more time/money probably to modify the 25* than the relatively cheap $125 50* actuator.. I usually get OEM parts at a cost discount from a nice guy at a local Honda dealership so maybe it'll be even cheaper too.

[AttarixEp]

Gotta love discounts!

[Ba82Ep3]

Modding the VTC isnt hard. Its a nice chunk of metal to mod, but the Hondata page shows you how to do it. The purpose of modding the 25* to 45* is to have a PHYSICAL stop... not just a programmed stop. I have seen the discussion both ways as well... some say its ok others dont. I ran a modded 25* with my TSX pistons in a k24a1 but in the end i dont feel i needed to.

Also if youre just NA you wont really need to advance to 45* to make power. You could honestly just leave it as is. You wont really be able to unlock the FULL potential of a modded 25* until youre boosted or have opened up your intake and exhaust paths beyond OEM. Also, k24a2 intake ports are closer to k20a2 intake ports... that isnt a bad thing... but there is less OEM flow than the k24a1 head. Something to consider when looking for...

... manifolds... i was really impressed with the versatility of the PRC with a k24. It was definitely better than a PRB. Nice broad powerband from 2.5krpm on up to about 7krpm. I just recently got my hands on an RBC for myself (going to RRC) for more testing... but the few k24a2's i have tuned with an RBC and 25* VTC were dogs compared to a comprably equipped k24a1 with more VTC.

My JRRH literally sat on my exhaust tunnel after my k24 swap. I removed all heat shields looking for clearance and relocated my shift cables... nightmare. Im not saying that is the case with all of them, but i had to bail on the JRRH for my setup. I would really like to see someone on this site score an ASP header for a build like this. $$$

If you want a *50, i have one ill hook ya up with. Just LMK.

[Slip_Angle]

I've done a fair bit of experimentation with the k24a2 and so far here is what I've found worked best.

K24a2 /w 2006 TSX cams. If you have an 06+ motor, you already have them.
KRRH
RRC Intake Manifold - Keep the torque, gain the HP. (vs RBC, RBB, PRC and PRB)
50* VTC (MAX VTC on this setup is 40)
High Flow Cat (test pipes are awful)
CAI (long tube)

[K20A EP3]

Dave you think i will have to worry about piston/valve contact with my set up or are you going to limit it to 45* in the tune?

[Ba82Ep3]

Already got it covered for ya Chris... ; )

[K20A EP3]

appreciate it man. but you think if it were to go to 50 id have a problem? id hate for that to happen and have to redo this again lol

[bchaney]

From what I've read, the RBC and 45/50deg VTC work hand-in-hand. If you get an RBC, you'll need more VTC flexibility to harness it's full potential.

[gtolio]

Anyone have a good thread for which OEM manifolds came in which cars?

It seems like such a simple request, but a search yielded nothing. :mredface:

[iDom]

What motor mounts were you using that your JRRH wouldn't fit? I was planning on getting some innovative MM when I swapped it in.

Also, what cars come with the RRC and the PRC manifolds?

[iDom]

I've done a fair bit of experimentation with the k24a2 and so far here is what I've found worked best.

K24a2 /w 2006 TSX cams. If you have an 06+ motor, you already have them.
KRRH
RRC Intake Manifold - Keep the torque, gain the HP. (vs RBC, RBB, PRC and PRB)
50* VTC (MAX VTC on this setup is 40)
High Flow Cat (test pipes are awful)
CAI (long tube)

May be a noob question, but why a cat over a test pipe? I always thought that less restriction = win

[AttarixEp]

There's a good thread on honda-tech testing RBC, RRC, and skunk2 manifolds on an n/a k24.

[RHCP0801]

got a link?

[gtolio]

There's a good thread on honda-tech testing RBC, RRC, and skunk2 manifolds on an n/a k24.

There was a good article like that in Super Street also.
http://www.superstreetonline.com/techarticles/sstp_1002_k_series_intake_manifold_shootout/viewall.html

What I'm looking for is a breakdown of all OEM k-series manifolds showing which cars they came in from the factory.

[AKEP]

Also if youre just NA you wont really need to advance to 45* to make power. You could honestly just leave it as is. You wont really be able to unlock the FULL potential of a modded 25* until youre boosted or have opened up your intake and exhaust paths beyond OEM. Also, k24a2 intake ports are closer to k20a2 intake ports... that isnt a bad thing... but there is less OEM flow than the k24a1 head. Something to consider when looking for...

... manifolds... i was really impressed with the versatility of the PRC with a k24. It was definitely better than a PRB. Nice broad powerband from 2.5krpm on up to about 7krpm. I just recently got my hands on an RBC for myself (going to RRC) for more testing... but the few k24a2's i have tuned with an RBC and 25* VTC were dogs compared to a comprably equipped k24a1 with more VTC.

for NA and supercharged apps hondata suggests that most power is made at the higher end (toward 50*) of VTC, considering you have high flowing exhaust. But with a turbo setup, the backpressure from the turbine keeps your powerband in the 20* area. im guessing you would only benefit from anything over 30* during low rpm acceleration, if at all.

I would go for a PRC manifold over a PRB, when I had the PRB it felt like the motor just couldn't breathe, it made my k24a2 feel like junk. I ended up with RBC only because i didn't want to deal with the sharp bend in my IC couplers, plus i was going to be boosted, low end was made up for quick boost. I still want to port the RBC and bore the TB. I don't have any experience with the PRC to speak on it. just tot throw that out there. I imagine it would help my partial throttle power out when puttin' around the city, but its not bad at all with the RBC. Prolite wheel probably doesn't help that feeling either. I regret nothing, the car drives beastly.

quick question though, is the flow measured in the heads without valves in on a bench? or is this all theory based on dyno numbers? cause i've read some things and i don't think it has to do with the head castings (port sizes) or locale of ports in the chamber, as i'm pretty sure i read that the dimentions were identical minus a small detail in the bowl. a reliable source told me a secret and i'm trying to back what he told me but i can't seem to get a straight answer from anyone.

After some googling, i've found some more crazy flow figures, but still inconclusive because they were flowed differently. not exactly controlled testing. i know this is somewhat off topic but it has to do with a1 vs k24a2 flow going along with an rbc. rbc and k20a2 head go hand in hand with high rpm flow, where both crv and tsx heads fall off. same with lift, the rsx is more advantagous at higher lifts than both tsx and crv again, but they both outflow at lower lifts, the crv leading tsx, where partial throttle driving would feel much better.

so one would say your choice of intake manifold would depend on cam choice and rev limits, where you would choose a head based on which bottom your mating it to, give or take an a2 oil pump of course. porting negates any of this as cutting enough material brings all heads to the same flow regardless of cams (minus the element head). and depending on how much they flow you would match them up with the most efficient manifold. and seeing that a z3 head (for example) flows 292 CFM @ .500 lift @ 28 inches and the RBC manifold is rated at 320 CFM (i think? cant find a reference...) - well looking for the reference completely threw me off my tangent on whatever it was i was trying to say, but maybe you guys can pick up what im puttin down. im not saying any of the manifolds are better than the other for OP, but the choice should be based on what he plans on doing. things start to add up in the end, esp if your going boosted. 20 cfm doesn't seem like much at 290 or 280, but at 1 bar that turns into 580 and 560 CFM, a ported head seeing 320 CFM and manifold seeing 360 CFM is seeing 640-720 CFM, you get the idea. ok suprise firedrill gotta go. peace.

[Ba82Ep3]

appreciate it man. but you think if it were to go to 50 id have a problem? id hate for that to happen and have to redo this again lol

I dont think so, but if you would feel safer i could always mod your 50* like i did my 50* for my 2.2 build...


What motor mounts were you using that your JRRH wouldn't fit? I was planning on getting some innovative MM when I swapped it in.

Also, what cars come with the RRC and the PRC manifolds?

RRC= JDM
RBC= USDM
PRC= JDM
PRB= USDM

The RRC is to the RBC as the PRC is to the PRB. The USDM version looks very similar to the JDM version... but the JDM is always better it seems. JDM always carries the higher pricetag too.

Katman on k20a.org was the one that spearheaded that article. There is a corresponding thread along with it... but its got a lot of BS convo in it too. Its informative, just takes time to read it.

Something to keep in mind. A manifold like the RRC/RBC is designed towards the upper half of the rev range. More air, more fuel, more power. While a 2.4 draws in more air than a 2.0, you wont rev it out like you would a 2.0.

For discussion sake, lets say the 2.4 at 7500rpm pulls in the same amount of air as a 2.0 at 8200rpm. If you build (plan for) your 2.4 to rev to 8000k and above, then the RRC would be your choice. If you plan on driving your 2.4 on a daily basis, arent concerned with peak whp#'s and want to have a nice solid powerband so you dont HAVE to rev it out (isnt that why most people want more TQ anyways?), then IMO the PRC is hard to beat. It made 220hp on the original JDM k20a. It makes great midrange AND performs up top. Whats not to love?

[Ba82Ep3]

...well looking for the reference completely threw me off my tangent on whatever it was i was trying to say, but maybe you guys can pick up what im puttin down. im not saying any of the manifolds are better than the other for OP, but the choice should be based on what he plans on doing. things start to add up in the end, esp if your going boosted.

And this is what it always boils down to. You have to know what you wanna drive before you can build. Theres enough info out there to cause anyones head to spin into a coma trying to decide just that.

Know what you want... realize its limitations (and your wallet)... build it and love it. I get joked all the time because i have three engines and several head sets. "What is all this shit for...?" Each one will be an engine for its decided path... because one cannot be all three.

[StockTexasEP3]

Can anyon explain the differences between RBC, RBB, PRC and PRB? I've done some googling but all I can find are that theyre different intake manifolds... What do they mean?!

[Blah1219]

Prb - ep3, dc5
prc - ep3r
rbc - fd2, fa5
rbb - tsx
rrc - fn2

[RHCP0801]

I dynoed my k24a2 with the rbb manifold, the stock tsx mani and made roughly 20hp less than I did when I slapped on the rbc. I also gained tq with the rbc. Final numbers on my 06 k24a2 was 230 198, with the rbb I only made 201hp

[Ba82Ep3]

The RBB isnt designed to have air run through it as fast as possible to make power (not TQ). If you lost TQ with the RBB... odds are you were using too much cam advance. Its a catch 22... the RBB doesnt like a lot of cam advance (why do you think it only comes with a 25* VTC from Honda?), but you need to use it to make power. Changing the mani is the first step in this case... if better dyno #'s are what youre after.

The real story lies in the dyno curve... not just max whp/wtq numbers.

[gtolio]

The real story lies in the dyno curve... not just max whp/wtq numbers.

So true, and so many people fail to realize this or don't care.

A good curve is so much more important than peak numbers.

[iDom]

So true, and so many people fail to realize this or don't care.

A good curve is so much more important than peak numbers.

Yes I completely agree, I want a good smooth curve throughout the rev range.
Also, my intentions are a DD with some pick-up.. 215-230whp would be great, while keeping things as OEM and reliable as possible.. 7,500 rev limit.

[gtolio]

Yes I completely agree, I want a good smooth curve throughout the rev range.
Also, my intentions are a DD with some pick-up.. 215-230whp would be great, while keeping things as OEM and reliable as possible.. 7,500 rev limit.

Keep in mind that the stock tach is off by about 400rpm at redline, so what it shows will be different. I believe my fuel cutoff is set to 7,600, but the tach shows right at 8 when it cuts.

If you set it to what you want in kpro, you'll be fine.

http://www.youtube.com/watch?v=9mua5-CNjLM

[iDom]

Keep in mind that the stock tach is off by about 400rpm at redline, so what it shows will be different. I believe my fuel cutoff is set to 7,600, but the tach shows right at 8 when it cuts.

If you set it to what you want in kpro, you'll be fine.

http://www.youtube.com/watch?v=9mua5-CNjLM

Yea I would always know to shift when it hit the 7 on the tach with the stock ECU because it was off a little. 7 was about perfect with the 6,700 stock rev limit.

That's a good idea though, 7,600-7,700 and just rev it to 8,000 on the tach.

[gtolio]

Yea I would always know to shift when it hit the 7 on the tach with the stock ECU because it was off a little. 7 was about perfect with the 6,700 stock rev limit.

That's a good idea though, 7,600-7,700 and just rev it to 8,000 on the tach.

Yeah, it just happened that way by coincidence on my car, but it's really nice for drag racing.

[StockTexasEP3]

Prb - ep3, dc5
prc - ep3r
rbc - fd2, fa5
rbb - tsx
rrc - fn2
Damn, I literally had no idea. Thanks

[Slip_Angle]

If you use a spun core cat you get the best of both worlds. No flow restriction up to 400whp (based on the model of cat you choose) and no stink, raspy sound or CEL.

[Slip_Angle]

I dont think so, but if you would feel safer i could always mod your 50* like i did my 50* for my 2.2 build...


Something to keep in mind. A manifold like the RRC/RBC is designed towards the upper half of the rev range. More air, more fuel, more power. While a 2.4 draws in more air than a 2.0, you wont rev it out like you would a 2.0.

For discussion sake, lets say the 2.4 at 7500rpm pulls in the same amount of air as a 2.0 at 8200rpm. If you build (plan for) your 2.4 to rev to 8000k and above, then the RRC would be your choice. If you plan on driving your 2.4 on a daily basis, arent concerned with peak whp#'s and want to have a nice solid powerband so you dont HAVE to rev it out (isnt that why most people want more TQ anyways?), then IMO the PRC is hard to beat. It made 220hp on the original JDM k20a. It makes great midrange AND performs up top. Whats not to love?

This is true with the RBC but not so much with the RRC. On K24's the RRC maintains the torque of the RBB and increases HP across most of the range.

I have a comparison dyno of the RBB vs RRC. I'll see if I can find it and post here.

I believe I make 221whp and 185wtq with the RRC.

[AKEP]

for the record if you go boosted, my k24a2 was still making power at 7500rpm. idk about NA tho.

[iDom]

I'm just going to use the PRB from my a3 and the stock VTC, and once I get the money, a SC and the higher degree VTC.

[Ba82Ep3]

:thumbu:

No need to spend $$$ on something that will likely sit on the shelf later on. Just dont feel bad when you do drive her and she feels pretty weak above 7krpm. The performance is there... just not unlocked yet.

[Ba82Ep3]

I have a comparison dyno of the RBB vs RRC. I'll see if I can find it and post here.

Bump for this info!

So many people have reported different gains with the RRC over the RBC. At some point you have to assume a % of that will be lost to inconsistent/incomplete testing/tuning variables. IMO though, if the RRC>RBC as the PRC>PRB... even if it is just a little bit its worth it. But is it worth it to the tune of $350?

I know the PRC was much better than the PRB...

[iDom]

Well as long as there's a significant difference in the a3 and the k24a2 then we'll be good haha. I just don't wanna put on an RBC IM and mess with the radiator support and the hood and the brake booster port and everything else because I plan on SC'ing it anyway and then the new VTC