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K20A2 Turbo Preparation

3295 Views 38 Replies 6 Participants Last post by  waccoon
Heyo, I'm new here and I am currently working on a K20A2 boosted swap RX7 FD3s. There are some question I want to tackle but not sure where I should head towards so I thought I could bring it up here.

So the motor is a K20A2 out of a RSX Type S, it has roughly 158,000 kms and I am getting the long block.
Anyways, so I know I am definitely not going to drop the engine in and just boost it right away. I am looking to tackle these problems.

Refreshing Engine
  • ARP Headstuds
  • Timing chain kit
  • Oil pan gasket Might get new oil pan for clearance?
  • Valve cover gasket?

Delete/Disable VTEC, VTC
- During boost application, I understand that VTEC will not work as good with force induction. As I'm looking to throw in around MAX 17psi on stock bottom end, so is there a way I can disable VTEC? or swap out camshaft?

Turbo Recommendation
  • Currently I own a T04Z HKS turbo for a 13b REW and is planning to just buy a exhaust manifold and make it work. But I heard that this is way to large for a K20 and I should go for smaller T3 size turbo.
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  • Also want to know how much the K20A2 motor can hold for power. (Not looking to exceed 350whp) (Reliable > Power)

Goals of the car
So the RX7 is going to be a 6 speed manual (RX8 Tranny), with K20A2 Boosted motor. Car is going to be used as a daily driven fun car from point A -> B.

Concerns eliminated
Some of you might ask, how is the engine going to work? PMC motorsport got a swap kit readily for a RX8 tranny and in my understanding RX8 is similar to the RX7 FD3S tranny. Wiring harness will be done custom through a website, I forgot who but there is one. And ECU will possibly be AEM or Link.

Yeah, I know this is a lot to ask for but it'd be nice if anyone who has prior knowledge can give me a hand and let me know what I need to prepare before boosting this baby.
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I wouldn't delete the vtec, it gives you great idle and low speed drivability with great high rpm flow. There's no good reason to delete vtec with the goals you have. You could delete the vtc if you don't have an ECU that can run it, if you do have a vtc capable ecu then again there's no good reason to not use it. It can help broaden the power curve quite significantly
My understanding is that VTEC during boost is not a good thing. Heard it will kill the motor and I don't mind losing the VTEC anyways. I think the ECU can disable it.
Welcome to @waccoon. This is a very nice project, getting rid of the Rotary for a turbo'd K20 awards you a CO2-reduction award :cool:! The Mazda 13B engine sounds nice, but that is almost all what can be said about it, Felix Wankel may be of an different meaning. I pull my hat for keeping the concept alive to Mazda, but they made with the SkyActive and SkyActiveX such a big step forward, the Wankel concept is more a keeping the scene alive, but that chamber has a hard time to get compliant to actual Emission limits.

Why this? Don't you like the stock ones? Didn't you want to keep the longblock as it is?

Keep it.

Wrongly understood. The iVTEC functionality gives your engine, like @Bjorn posted, a much greater operational bandwidth. I've tuned many boosted applications, where only drag applications may need a VTEC delete because of the valvetrain weight, never based on the technology, just based on redline limitations. I would be interested which guy spread such information's, which really have no technology basis.

We seen on daily's up to 20 psi, but this need good tuning not to seizure the pistons and piston rings. Most tuners are not able to get it above 12 psi reliable, as they just don't know what it takes to get there.

That won't hold the torque, the RX8 tranny will fail under that torque without upgrading the too weak parts of it. It would be better to upgrade to a ZF-box or e.g. an BMW DCT 😜.

Infintiy vs Thunder? In case of that, take the Infinity 506, even it is a princess in some areas.
Wow the amount of knowledge you have is just incredible. The build goal for this car is to use parts that minimize fabrication and maximize available parts. The AEM or Link is both PnP ECU that i’m looking at. Nothing fancy cut the work load in half. RX8 Transmission is widely available and I am aiming for daily driving application with casual high boost. Car would likely stay 4-10 psi on regular days. Goal for this car is to reach “Vancouver BC, to Cali US,” so high power is not needed. Although VTEC is good, but I prefer simple and safe than complex and hassle, the end result of this build should be able to represent cutting corners but not sacrificing efficiency and safety, and by that disabling VTEC and not risking dropping a valve is a better ideology for me. Yes keeping the long block stock is the goal, but minor improvements that doesn’t significantly change the characteristics of the k20 is acceptable, such as headstud upgrade and head gasket. Piston, rods and crankshaft are major upgrades that I don’t see the need of doing so. Thanks for the info thou that helps a lot.

Psss, I actually have two rx7 and the other one still have a 13B :p
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Ok, you will get only the half CO2-award 😂

If you really looking for a K-series which only works in low speed cam (redline latest at 6500 rpm) you can go with a PNP Infinity 305 ECU, which is price worth, but has no High Side switch to control VTEC. That means you run allways in low speed cam. Any K-series guy will lift know at least one eye brow and ask what is this guy aiming for, but I am just telling you what price-wise reduction option you can go. At least 600 USD less compared to an Infinity 506 class ECU.

Your K-series engine will not drop an valve if you upgrade, which is duty with boost, the stock valvetrain accordingly. You valve-less guys have a crazy connection to piston driven ICE's 😜 . I am actually developing a 360 flwhp-2-Liter-NA engine, which has a redline of 10,500 rpm and I am neither planning on a valve drop, nor did I've experienced one on a well designed and applicated K-series engine. Valve-piston-clashes happen only when exceeding the limits by misshifts, wrong tuning, wrong maintenancing, wrong cooling and so on. My actual 2-Liter development-use-only NA engine redlines at 9500 rpm, I am already exceeding the valve spring limits of 8800 rpm according TODA. It didn't destroy my engine because of the safety factor of the valve to piston clearance are well chosen.

But I feel I still have issues to understand your engine setup. So let me create a picture of what you planted into my mind:
  • K20A2 engine, turbo'd on a stock longblock
  • delete VTEC = disable high speed cam, consequence of the short valve opening duration will be a reduced engine speed bandwidth thermodynamical and mechanically as the low speed profile seat velocity is designed for exact that purpose (= low engine speed)
Is that correct?
Somewhat close to what I want. I live and is based in vancouver BC, I don’t know much about K engine builders nor I trust a lot of them. Coming from a rotary background it’s been taught that you don’t always trust people in the trade and go based off your own instincts determining who is genuine and who isn’t. I apply the same rule to the honda scene where I go with the less problematic side and less work for less power because I believe is less hassle. But after what you recommended and further research I think I can give it a try. ECU setup is also a problem as I am running a complete different wiring harness and is not confident with wiring things myself. Luckily some company had created a engine harness swap kit so I will go with that, probably a AEM Infinity.
Great, let us know if we can support you with something.
My question would be,

Any tuners you know that you can refer me to?
What I should do to refresh the engine before boost application?
What concerns is there when I mount the motor few degrees off, due to transmission swap plate?
Oil pan clearance, (Recommendation for low profile)?
if your background is in rotaries than I understand why you are so wheary, but rest assured; the k series is a VERY simple engine. even the VTEC and VTC systems are just a series of solenoids which control oil pressure. like the others said, disabling VTEC doesn't make a tone of sense reliability wise. whoever told you that was likely refering to the fact that disabling VTEC will aid spool time on big turbo applications
Yeah, my general question is that what I should do to refresh the engine before boost application. ARP headstuds and timing chain has to be replaced and install. These are the known issues I know to fix and avoid but is there anything else I can prevent?
Car would
I'm assuming you know about the chain tensioner? if not, here's some required reading. I'm sure the others can chime in on what brand they've found success with, though I'm sure any of them will do just fine, I.E Hybrid Racing, Drag Cartel, K-Tuned, or Skunk2.

you mentioned the car will see a max of 17 PSI correct? in that case, the MAP sensor will have to be upgraded to a 4Bar sensor, whether that be to the Hondata, Skunk2, or K-Tuned is your pick
I understand the problems with chain tensioner and I would look into it further, thx for the info. Since I am planning to go AEM in terms of ECU, I would also go for AEM MAP sensor if there is one just everything would be AEM to cut hassle and possibility cost.
I am an engine designer, builder and tuner, I neither can recommend you going to a competitor, nor I can't recommend you myself per terms and conditions.

Depends on the maintenance schedule and OPL. In general K-series engine loves to get a new timing chain, tensioner and oil drive chain above a 100,000 km. A new TPS, best a hall technology based one, would be a good thing. And of course the obvious testing stuff: compression and, leakdown test, visual inspection of cam lobes, valve lobe adjustment, upgrade the valve springs as boost reduce the seat pressure significantly. No oil filter experiments, filter quality is A and O in endurance preparation. No Penzoil, Castrol, or whatever oil stuff with overriding oil weights. Only serious oil qualities: Amsoil SS 5W30, Ravenol RSP 5W30, Quaker State Full Synthetic 5W30, Mobil1 0W40. I have or still actually run all those in long term endurance tests in several applications from race to drag till DD on NA and FI engines. When bearing clearances, temperatures of oil and material combinations fit I would keep viscosity around a SAE 30 quantity. The stock bearing clearances and oil cooling does fit to that. If you add a nice oil cooler to your setup to keep oil temp. below 125 °C at the sump under any conditions then you and your engine are well prepared.

The main reason for the engine angle setup spec is the oil suction capability. Think from there and you can see the answer for any conditions. Do a test with water, you will see it.

There are low rider oil pans available on the aftermarket. Check it out. In any case, you need to clear the steering kinematic, you will have a customized or at least a specifically produced oil pan. Look at the Honda S2000 and Mazda Miata K-swap aftermarket.
Thanks for all the info, a lot to take in but community provides a lot for information.

From my understanding, these are thing I should be purchasing and replacing. (Engine Specific)
Timing Chain Kit, Link
ARP Headstuds, Link
Headgasket, (Haven't Decided)
Fuel Rails, Link
Oil Pan, (Need to check clearance)
Wiring Harness (Specific to FD3S), Link
ECU, Link (Has inhouse 7Bar MAP sensor) OR AEM ECU idk.

And this list would be thing I have to purchase for boost application.
Turbo Manifold/Intake (Custom or whatever works lol)
Wastegate (Turbosmart?)
Wideband (AEM)
Turbo (Pre Purchased),
Intercooler, (Depending on clearance, V-mount or Front)
Oil Cooler,

Other than that I would also like to retain certain stuff such as,
Lose OEM Dashboard, Replace LINK Display

And custom stuff for clearance
Custom engine mounts w/subframe
Steering extend
Custom transmission mounts

Anyways the list goes longer and longer and it will be a hassle. But yeah pray for me and my wallet as a University Student as this build will be super long and tedious.
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if you only want a 350HP turbo, there is no reason to not use a Doctronic or Hondata ECU on a K20a2 engine loom. They can control all the VTEC/VTC things you need and even offer boost by gear.
it also means you can use the OEM engine loom. You just need to connect about 7 cables to the car to make it work.
We talk about a few hours to map a turbo car with good base maps availabe for the Honda ECU platform vs. many many hours on a custom job on a Link ECU where few can help you.

VTEC delete is only ever useful if you need to exceed much beyond 9-9500 rpm. This is only done in very light weight cars, mostly race cars (<1500 pounds) or pure drag cars. There is not a single reason I can come up with to delete VTEC in a daily driver. Not a single one.

Turbos love VTEC on a k20. As there is a rather low pressure gradient across the engine, the set-up is not that changed vs a naturally aspirated set-up regarding lift, duration and overlap.
Superchargers and NA also love VTEC. You get 2 engines in one. A torquey and well mannered engine from idle to medium revs your mom would drive to the shops with ease and a wild animal on 300 deg cams reving 8500 rpm delivering power to the limited.

For your 350-400HP build, you might enlarge the ring gaps a tad for track work. For a DD, there is no reason to even open the engine. Just do the timing chain and tensioner. No ARP studs necessary.

For a longitudinal engine install, you need a special oil pan and baffle set-up.

You will also need a suitable RWD intake manifold with the TB on the correct side.

spend a few hours reading here. Don’t transfer too much engine insides from the rotary world to the K20 or K24. They are entirely different beasts.

here is a video of a k20a2 turbo incl. VTEC running some 500HP. a 400HP build will sound about the same and rev as high: fun’s starts ar about 3.10 min.

You might consider a k24 if you prefer less revs and more torque, especially off boost.
Yeah, I've gone off that route of deleting VTEC. I will keep VTEC as for different engine usage.

For ECU, I want something a lot more customizable. Hondata and Honda brand name isn't my forte as I want wider programmability. AEM and LINK is perfect as for the tuner I might MIGHT go with and the wiring kit also has an option for me to purchase it so might as well go for it LOL. The K20 is my first choice cus a 13b is a 1.3L little monster, and I want something similar to a 1.3L. I know B series are also good but who really wants 90's technology. Anyway thx for the info but I am still looking to open the engine and machine the head while I'm at it.
The K20a2 head and its ports are already extremely well flowing as is. It is therefore extremely easy to mess up flow. @LotusElise knows a thing or two about this as do others.
As an example making the port dividers sharp edged and narrow makes the angle the air is entering the ports extremely critical. If off by only a little, you create turbulence as air flow detaches on one side of the port divider. If you look at most intake manifolds and ITB set-ups, you can see that pretty much every runner comes it at a slightly different angle, e.g to provide clearance to the pulleys and water pump. The more rounded port divider is much more tolerant trading the direction of the incoming air. If you machine these dividers, you should consider the angle of each intake path. Hardly anyone does that. they just hack them with their Dremel. Even the CNC machining only makes sense if you know your intake IMHO.

There is a reason these can do 240HP NA with just bolt ons with their stock 300+ CFM intake and 200+CFM exhaust flow capability.
You even get them to 300HP NA with careful choice of measures and some $$.

For a big turbo circuit track build, you might consider inconel exhaust valves, but only if you are chasing the big numbers, i.e. 500 wHp+

Getting monster power out of a K20a2 with forced induction is one of the most easy things to do for a reasons. 400HP turbo k20 is essentially DIY in your garage without the need to even open the engine. YT is all over these. And they even last.

The company that rebuild the cylinder head I am using in my K20 Elise, they are mainly working VW/Audi rally cars incl. some their former WRC effort, had a look at the ports and plainly said it is best to leave them as is as the are huge and very well designed. You do not hear him saying this about many other automotive heads he comes along regularly.
The only thing they did in preparation of recutting the valve seats was a slight cleanup of imperfections on the transition from intake port to valve seat. There was a tiny edge.

17 PSI will get you to well over 400HP, likely 430-450, in a DD without having to to anything to the engine. For a track engine, I'd fit Mahle forged pistons and steel rods.
A chap I know runs a 4xx Hp k20a2 turbo in his Lotus Exige MK1 in Austria. It is mainly used on track. We speak about once a year about engine stuff and experiences with parts. He designed also engine conversion parts for the Lotus K-series swaps. He even runs Honda OE bearing shells. No need to upgrade. They only really fail if you run out of oil pressure. This is a major point you need to pay attention to for a track build as it happens easily.
His experiences with forged pistons from 2618 alloys were not the best. He was using CP AFAIR. The pistons are sturdy and perform, but after 2-3 seasons, they start to burn oil as the ring groove clearance starts widening. The material is too ductile and soft.
Since running Mahle forged pistons, a 4032 class of alloy, this is no more of an issue. As the thermal expansion coefficient is lower, it also allows to run smaller piston to valve clearance again minimising oil consumption, piston slap and associated wear.
For sure, what I meant to work with the heads is just pure machining, no more no less. The reason why I am opening up the engine is due to the fact that it is 185k kms and want to make sure I refresh as much as I can. The main play of this build is to REFRESH not REBUILD* the motor as I am looking for stock. I understand people wants to build their motor and shoot through the moon, but I am not much of track person. Occasion one day track even for the year is more than enough for me since I work at a gokart place. For people who are concerned about my exhaust manifold., here is a link for it and they make it for rx7 fd3s too :D. After everyone's suggestions, I am getting a much clearer picture of where I am heading towards this build. (ALTHOUGH VERY PRICY) but it should be worth it. One more question is that what injectors and ignition should I use? Boost application <<<<
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Here are my two babies :), black one is expecting the K20 and the blue is perfect as is. 350whp 13b stock port, borgwarner 8374 turbo :D.
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Hey, coming back with some updates and upgrades? on the process if it entertains you guys.

Sent the head to machine shop and got the whole package for leak down test, pressure test, valve grind shit like that. Came back bout 700~ CAD which is within expectations. But the catch is that the machine shop guy told me I should upgrade springs and valve. There is a significant cut down in material for the valve when I saw, and when comparing to a CRX motor it shows at least a differences in material around 0.5mm? Anyho, that's the update for the head, the block itself. Scotch brite is a handy tool to remove any carbon build up on the piston and mating surface of the head gasket. Nothing major with the block just usual clean up.
Brought another K20 but A3 this time for spare parts like water pump housing and alternator. Also intake manifold in the meantime until I get a RWD RBC or whatever the rating is. Other than that, also got the subframe down and ordered a tranny adapter that binds up straight onto the engine. Idk what other updates I can give expect some photos?
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The valve margin on my K20A2 is thinner than the CRX motor. So the machine shop recommended me to get new valve and springs. Supertech apparently is what they told me for the springs. I'm in the cross road of thinking wither should I upgrade both or just the springs. My goals are to do low boost and even might as well just to run NA for the time period until I gain the funds to push forwards towards Force Induction. Timing chain guides are fine? but I will probably change them to new guides and chains regardless.
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Ah, thanks for the clarification of the word margin here (y).

Regarding valves and valve springs. For a 10 psi setup there is no sense to invest in new valves, the OE ones can stand it. What you should definitely do is to upgrade the valve springs to cover the bigger forces at the valve due to the higher pressure on the fillet (backside of the valve). These need to be compensated by higher spring pressure values to keep the cam and valvetrain all the time connected under a good force level, supporting the suppress of valve bounce.
Thanks for the info, I was looking into Supertech and Skunk2 valves. My understanding is that all it matters for the valves are that they are close to 100lbs pressure. I was looking at price vs quality and doesn't seem to see much of a differ. ^Idk if any of them make sense. But I was thinking to invest into Skunk2 (311-05-7380) as it was the cheapest with valve springs and retainer. But Supertech (SPRK-H1021D) is just $10 more. Any advice here?
I have myself no personal experience, but many of my tuning customers have Supertech stuff installed. I had only a few with Skunk2 springs. During the tuning and consultation I never saw any issues with these.

Run on these springs several years, about 20.000 miles.
Very interesting, as if this build is replica to what I'm working on LOL. I am not sure if I have a RBC intake manifold or not, but I don't think there is much of a difference once I go force induction anyways. He is using a hondata, which is pretty cool. I'm leaning towards a ktune or hondata depending what the wiring harness provides, but other than that it seems like supertech is the way. It's 10 bux more like I said so might spend the money.
On a boosted application there is likely not much difference between the manifolds as length only plays a role on NA MAP's, above a pressure ratio of 1.4 it is very mass related. Flow properties are counting more.
That's exactly what I'm thinking. Another question I have in mind is the e85 and 93 potential. I know for sure this car would be used on more or less a daily or weekly basis and do not want to risk detonation due to high compression. Any solutions you have heard of or could point me towards?
Of course, there are high sophisticated solutions possible. I developed quite a few technologies at an OEM for the combustion development to suppress knock. But you named already the most simple one, using Ethanol or a blend with gasoline of it to move the knock margin to a more advanced IGT just by increasing the vaporization energy demand and a bit faster combustion velocity.
The thing is where I live doesn't have e85 all the time. Is there other way to prevent pinging? As I said, 93 should be the maxium at all time. With that said, 93 is still prone to detonation. I guess it comes down to the tuner's ability to do so? Also another question is where I should draw the line in ECU tuning. The goal I want is a daily drivable car, which means AC/PC would be available. With the AEM, I feel more comfortable knowing the ability it provides but it seems like hondata does a similar job. Is there any suggestions in terms of ECU choice. I am still trying to figure this out
You can prevent normal knock always with IGT (ignition timing) retard. There are other well known methods like additional injection of water, methanol or a blend of both to cool the entrancing gas mixture, which should be of course also done by a huge intercooler.
I see, seems like IGT and larger intercooler would be my first choice. I do understand methanol is the best effort, but with the goals of this car it seems very out reach to use methanol. If this is a track car then for sure e85 all day baby. xd
You tune yourself?
Nope, probably with a tuner. Would not want to do tuning myself at all. Flexfuel is not an option for me as for now so I guess hondata for now?. A separate question is the wastegate. I am thinking of going a similar turbo for the forum you showed me. T67. As 10psi is my goal ish so 44mm external waste gate is more than sufficient?
it gives you great idle and low speed drivability with great high rpm flow. There's no good reason to delete vtec with the goals you have.
Think it's been established in prior comments that deleting VTEC is a bad idea. Not going that route anyways. But since I kind of ghosted everyone for the new years, I feel like I owe everyone a update on what the project is currently at. With much confidence, I can say the phase 2 of the project is mostly achieved. That means able to put the engine and transmission in the car with no fabrication works to do.

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Here is a photo of the engine bay without the motor, if you look closely there is no transmission mount due to mazda's design.C:
Subframe which holds both engine mounts and control arms are on and off most the time due to fitting issue but also subframe is the only part of the build that needs welding and fabrication.

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Here is the half block sitting inside the RX7 with no fitment issue regarding to the fire wall. The subframe as you can see if currently off the car since the gravity loves to pull the whole drivetrain down but I've successfully install it and will provide pics and updates later.

Regarding to the build, I have brought the following items to ensure the build is enroute.
  • AEM Infinity ECU
  • ARP Headstuds
  • SuperTech Valve springs with OEM style guides
These parts except the ARP heads studs are all BNIB (Brand new in box) and has not seen daylight for a while just like me.
The following parts are what is needed to finish the first start up for the build.
That's kinda it :C hope yall appreciate the build at this point
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What clearance between valve stem and guides are you aiming for?
No clue, am letting the machine shop do all the measurements for me. Including giving me a thicker head gasket
The crank assembly is stock?
Yes bottom end is completely stock. I don't plan to move it nor plan to touch it except installing ARP fastener because I got it for free.
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