I apologize in advance for this quite long post. I appreciate any advice you guys can offer, as I'm sorta shooting in the dark here. Hopefully I'm asking the right questions. TIA. Okay, so I've got a couple ideas rattling around in my head, and I wanted to see what more experienced people think. I am building a set of EJ205 heads that, short of a catastrophe, I hope to not take apart again and hope to continue running through possibly more power upgrades - like eventually a 2.5L shortblock and a larger turbo. I am thinking that its worth doing most everything that will give me appropriate gains now while the heads are being built. Problem is, I'm not 100% about what things will be good for an aggressive DD and which won't, since I don't intend to build a track car out of my RS and I'm concerned that if I make the wrong modifications I will be quite unhappy with the results. Also, this will be my first turbo'd car, so I have no solid idea of how the power is going to feel in this car and what I may most want to improve - so I'm basically shooting guesses out my ass here. I think that what's important for a DD is a broad powerband that starts low with quick spool. I think what I don't want to do is sacrifice a bunch of low end for a bunch of top end. However, it seems power can really fall off towards the top end in a stock setup, and there may be gains to be had without sacrificing street driveability. Motor will be installed with a VF34 turbo, stock TMIC, walbro, injectors (PE650's IIRC), catless exhaust, tuned. Tranny will be stock wrx until (if/when) it breaks, at which point I think I will stay with some stock length or longer aftermarket gears since I freeway drive a lot. I think long-ish/stock-ish gears and enough and early enough power to push through them well would be good for an aggressive DD, no? So, I'm investigating the various things I can do to stock heads, like PnP, cams, valvetrain, etc. I've already purchased some PnP'd heads that Chimera did (some pics & flow numbers of my actual heads here: http://forums.nasioc.com/forums/showthread.php?t=1565101). So, PnP Heads - what are the effects? * Will my peak torque point move left or right or not at all? * Will I make more or less power down low? up high? * Will I improve or reduce fuel efficiency? * Will my spool characteristics change significantly? * Are there other important differences, or especially downfalls, I am overlooking? * Are there other mods that tend to work particularly well in conjuction with PnP'd heads? (e.g., should I be considering PnP/coating more of the flow path - IM, exhaust, turbo. Would cams really open up the flow?) Next, cams. Hearing how great cams could be on a N/A subie, I naturally wondered if I could see benefits from them in a turbo application. Searching around a bit seems to suggest that all of the "hotter" cams are going to rob me of spool and hurt low end quite significantly. Also, the cost might be prohibitive. I've read that the STi cams have more lift, and can pretty easily be put in the wrx heads. I've also read that longer duration is what can kill spool and therefore low end power, but that the STi cams have the same duration as the wrx cams. Others, though, suggest that STi cams will still hurt spool somewhat because of a lack of overlap. I saw a before/after dyno of someone throwing STi cams into wrx heads (http://forums.nasioc.com/forums/showthread.php?p=26048302#post26048302). It looks like power came on the same with STi cams, and stayed higher after the peak. That person obviously has more (and unknown) mods (400 ft/lb). So, STi Cams - what are the effects? * Will I likely see a similar improvement from STi in my setup as the dyno plot linked above^? (More power after the peak, no significant loss before the peak, peak at same RPM's). * Will I improve or reduce fuel efficiency? * Will my spool characteristics change significantly? * Are there other important differences, or especially downfalls, I am overlooking? * Does my turbo start to become a significant restriction to airflow at higher rpms, to the point of negating the gains I might see from cams? Also, are there other cam options I should consider (I am willing to consider options within $100-200 of the cost of STi cams)? Next, valves. Here I'm a little more clueless, but I may need some new valves and I definitely need a valve job, so I think, "Would there be any benefit for me to oversized valves?" Well, would there? So, oversized valves - what are the effects? * I'll leave this open, since I really could use some schooling here. Is this a good or bad idea for a DD and why? * I think I understand that it will increase my flow, but are there other factors I'm missing? * Are there downsides to oversized valves? Next, valve springs. I think this is where I'd like to draw the line. I don't think there is an appropriate price/performance tradeoff here. I think this will throw me too far out of budget. I mean, wouldn't the main/sole benefit be a higher rpm? So, more HP but I just don't think I care. I can't imagine where on the street I will care about reving higher than 7k. I don't care so much about the max numbers. I also am not interested in doing something for the sake of saying I have it in my car. I just am trying to learn which mods I could make to the heads as long as they're being rebuilt that will support my overall goals for the car. Also, no strict budget, but every $ spent on parts prolongs the swap. Again, thanks in advance. All advice is appreciated.
One last question. If I decided to buy used STi cams, is there anything in particular I should watch out for (common things that are wrong with used cams)?
What turbo are you using? I cant answer all of your questions, but I'll try to answer some. I would say that any pnp would improve fuel efficiency and gains in power. But for a DD, 1mm oversized valves be WAY overkill. More airflow in and out of the combustion chamber = more power. I'm not familiar with the flow characteristics of wrx heads, so I cant recommend that you get pnp or not. It doesnt sound like for your goals you wuld want dual valve springs. Yes, reving upwords of 9.5k would be awesome but for a DD.....meh prolly not. Some higher lift cams require dual valve springs, milder cams do not. If I was in your position and had extra cash laying around, I would get a delta regrind or BC 272 cams and probably an intake and exhaust pnp clean-up on the heads. If necessary, replace the valvetrain with oem.
turbo: vf34 - for now, eventually I will probably want to upgrade, but that's a vague, far-off notion for now.
a 272 cam will slightly shift torque curve to the left and allow more gains at higher rpm. IIRC there is a happy equilibrium between turbo size and cam aggressiveness.....but thats about the extent of my knowledge. Someone should elaborate on this.
I am listening so closely.... I plan on using the stock valves, and stuff, I also plan on using a 2.0l block for now, but I plan on staying with a tdo4 for the first summer after I install my goodies. Now, if I am using a pipsqeek turbo, does it make sense to go with 272 cams? or should I stick with stock nobby sticks?
If I can get this seconded - that oversized valves are way overkill for my setup - then I would gladly cross it off my list and put the $300+ back into other areas of my budget. This is my main general guiding principle, but my small experience with vehicles has taught me that things are usually far more inter-related and therefore complicated than this. Hence the questions. Trying to uncover any gotch-yas that might arise from naively piecing multiple engine mods together. I do have such a set of cleaned-up/PnP'd heads in my possession now. And, thanks for the input.
Fuel economy is a function of the efficiency of the motor at a given RPM that you are cruising at, along with a couple things like drag, rolling resistance, etc.. Smaller ports are going to be more efficient at lower RPM ranges and lower flow rates with less overall pumping losses throughout the system. The velocity is higher and thus more efficient at lower RPMs such as cruising. This is why motors with small ports and risers make so much torque down low and fall off up top, like my 22T heads. Also, cams and port sizes and work together to be efficient in certain ranges. Larger ports and higher duration cams are going to be efficient at higher flow rates, thus making more power at higher rpms. If those are the heads from Nick, I wouldn't worry about killing your off-boost torque too much and the overall drivability. I looked at them and they are smaller than the stock ports on the EJ25D heads I'm putting on. You're not going to rev that high reliably with a subaru motor anyways. Unless you like changing lots of rod bearings. Also, duration is what gives you your extra flow. Lift somewhat, but it is minimal. Look at a flow map of any head, and see how the flow levels off with more and more lift. Flow rate is an exponential. This is also why higher ratio rockers on a pushrod motor don't do a whole hell of a lot compared to changing the camshaft. Your turbo is going to be the major restriction in the system. Unless you know where you want to make your power and how much you eventually want to make, a fancy heads, cams, and valvetrain shouldn't be on your radar. Put that money towards a nice engine management system and datalogging setup to maximize what you have. Being limited by your management setup would be quite frustrating to me if you have the hardware for more. Cover your bases with solid electronics and drivetrain components to exploit what you have reliably, then go from there.
I shot this to ya via pm, but here's my take after thinking about this a bit. The VF34 is a "moderate" turbo on the 2.0L. With a good tune, it will not lose much power up top, if any. Especially with those P&P heads. From that thread you posted, I think this is the best post in the thread. Jeff is correct in stating that you will lose spool but gain top end power due to the difference in overlap of the STI cams. IMHO, shortening the powerband on a 2.0L is not what you want to do, especially with a degree of "unknown" top end power gains.
Hmmm .... that makes it a tougher decision. I don't know if I want to risk powerband width and low-end for marginal gains up top. Eventually, I think I want to bolt on a 2.5L bottom end and upgrade the turbo - but I'll be driving the 2.0L for at least a year, probably 2, before that happens. If I didn't do cams, and only installed the PnP heads, what kind of gains could I realistically expect over stock heads? If its really not much, perhaps I'll save the PnP heads and get a non-DD Subaru project on deck. Can't really rally with the hot-ass RS ....... and I could use a beater L to give me more time to swap ........ evil ........
You know.... the quicker you can get air in, the sooner you can make power. This is exactly what AVCS does. Allows air to come in sooner. AVCS acts like a cam with more duration, or say early lift. You should NOT have to worry about low end grunt. My heads where ported on the intake side and are pretty large for gulping in initial air. I run a 2.2L. I had no drivability issues. It definitely doesn't feel like a 2.0L. The port work being done to the valve seats really helps off boost driving. It allows some better air flow in and thus more fuel and more power. The EJ205 heads are good heads to port out for ULTIMATE DRAG setup running BIG CAMs and no need for AVCS. They have a lot of meat to make the ports big. Not much room for +1mm valves. HP comes from flow in and out of the motor. You really have to build the head to your application. It can't be good for EVERYTHING. You have to drive and live with it. Kind of like I lived with a 8cm^2 hotside for my EVO3-16G. Sacrificed a little spool up time for some breathing up top. It was like a mini 18G.
Porting still affects off-boost fuel economy. There is no way around it. The low end grunt of my 22T heads made everything else seem like a dog. Granted, it like comparing a Neon motor to an LS1, but the comparison is relative. A motor's efficiency is dependent on where exactly it is efficient, which relates directly to its cam profiles and port profiles. Large ports and more aggressive cams mean less efficient highway cruising. Basic higher order math. You want me to get into calculus and fluid dynamics here, I will if I have to, but would prefer to not. Serious engine builders build an engine around a specific camshaft. That is how much a cam affects the rest of the motor. You said you drive a lot with your own car for work, so I'd stay with a somewhat low rpm friendly setup.
To add..... Good examples would be like running the STOCK cam on heavily ported heads. You'll notice some power gains, however being the stock cam it can only allow so much air into the engine. Not much help in the higher RPMs because the cam can only lift so much and have so much duration. BIG cams on a stock head would a kind of opposite if the heads where a bottle neck. The cams would help flow as much as it could until the heads choked any more air from coming in. However you will see gains up top where the efficiency comes in with the cam. My build. I'm trying to make everything flow well from intake manifold, head porting, equal length exhaust.....however staying with stock AVCS cam. Well...the cam for me would cost me some power if staying with stock. If upgraded, I would see a much bigger jump in power because of the good air flow of the supporting mods. As one would put it; take more advantage of the ported heads and better intake manifold.
Here, I'll throw in my $.02. Heads are something you do not want to build for down the road. As they effect your car NOW. It isn't like putting in forged pistons so that later you can run a big turbo and throw more boost at it. You build heads based on your FINAL application. Camshafts are the same way, and their gains are monumentally different depending on when in the power band you intend to make power, and how much power you intend to make when you do. A VF34 will hold not boost till redline, but it isn't going to outflow your WRX heads, especially the ported ones you have. Regardless of camshafts you use, you're still going to see about the same top end. Your gains will be negligible and you'll likely sacrifice some low end grunt, something the VF34 is good at. Stepping up to a larger turbo, like a 20G or larger, any turbo that is efficient at higher boost pressures on a 2.X liter engine, will yeild exponentially higher gains with cams...again, assuming that you are camming and boosting for top end. 272 cams are a midrange/topend cam. They provide more to the midrange/top at a sacrifice to the low end. If your turbo starts to taper to redline (as the VF34 will) you are losing turbo efficiency when your cams are trying to give you more efficient flow. A 20G does not taper up top, it can be ridden flat across the band, since it is still efficient at the top of your RPM range, the cams will provide more efficiency. But don't take any of that as "Camshafts with a VF34 will make it run like crap." It'll run fine, but it'll be alot of wasted money on parts that wont necessarily give you any gains at all. And you MAY lose some of your low end grunt for the sake of 10 more ponies up top. For a daily driver, you'd be better off keeping that lowend tug, and sacrificing a few higher RPM ponies that you'll likely rarely use anyway. Keep in mind where you yourself spend most of your time in the RPM range. More than likely as a DD car, you're between 0-5000rpms. That is where you should want your power to really be kicking...where you'll use it. If I were you, and I had a plan for a really fun daily driven car, and I had those heads, I would: 2.5L STi shortblock Your P&P'd Heads stock WRX camshafts (I have a set if you need them) P&P everything you can, headers, uppipe, downpipe, intake mani, throttle body, TGVs, port match EVERYTHING 20G Turbo. External Wastegate If you can, get some pistons for that 2.5L block that will raise compression a bit. 9.1 would be fantastic. Torque torque torque. Higher compression will push your torque spike to the left a little, keeping those stock cams will keep your low end grunt, you've got good flowing heads, so use that 20G to force tons of air at it. Get a map for 92octane and a map for E85. Boost the piss out of it. I think that for a daily driver, the 20G STi is pretty much, bar none, the best mix of power and performance. If you've ever driven one, it just feels like the car should have came that way. The power is smooth, not too pushy, holds the power through the entire band, and is very responsive.
Again, thanks to all you guys for throwing info at me. readymix, that sounds like a very good idea of where I'd like to go with the car - 2.5L bottom, bigger turbo, etc... Also, I'm not talking about throwing some BC 280's in here. The STi cams caught my eye because it seemed like they could keep low end about the same while allowing more gains up to if the turbo could flow enough. The more I listen to you guys, the more I question that. And, yes, I would have to say that power over 5k rpm is power I will only use on rare occasion on the street, and it won't be nearly as important to have as responsive power on tap down in the neighborhood of 3k rpm. Since its not a track car, I won't be all that concerned about the small amount of extra power to be had after 5k. Plus, it sounds like my turbo is still going to be the limiting factor by far. I was looking back at the dyno graph Jeff posted when he had RS tune for the VF34 (http://mnsubaru.com/forums/showthread.php?t=29681) and that plot doesn't seem to fall off all that quickly anyway. So, let me ask this. I have been thinking about doing as much of this as I can, too. When you say P&P everything, would I be aiming for just smoothing things out and making a nice clear path for air flow? Or are we talking about reaming out giant gaping holes to increase overall airflow? I would think smoothing would be the main purpose - to get that air flowing with as little turbulence as possible and get it moving through that turbo. Yes? I notice you didn't mention porting the turbo. Worth doing? I would think. Also, what about heat coating? Snake oil? Gains too marginal? Or worth it? Talking about powder coat looking kind for doing like headers and up-pipes and whatnot.
I'll touch on the stuff that I can answer. The VF34 in his graph doesn't fall off QUICKLY, but look at where in the RPM range it makes full boost, and how much boost you have after that peak. It hits 18psi quickly, but by 6000 rpms it has dropped about 5psi. It holds till 5000. If you put cams in there for midrange/topend, you're adding efficiency where the turbo is losing efficiency. Pointless. Like I said, your gains will be minimal at that point. Your goal should be to be as efficient as possible while not being too complex or expensive. Do you really want to go hunting around for used camshafts that will give you negligible gains in an area of your RPM range that A) you rarely touch and B) your turbo really doesn't make its power? Of course not, that's wasted time, wasted money, and wasted power potential. Stock cams on a WRX will be fine for a 20G, and while you would gain some power up top, it would be at a loss to your lowend/midrange power...and that is where you want your power to be. So I'd build for where you WANT power. Your stock cams are gonna open up and move in the 2000-5000rpm range, as they should, since that is where the stock car is supposed to shine. Let's keep that power band in that area if we can. As far as porting goes, I would say smooth the transitions from pipe to pipe. Less turbulence = more efficient flow. You've got heads that are designed to flow more, so lets keep the flow going throughout. Smooth the throttle body ridges, smooth the intake runner to TGV mating area, clear out the TGVs and TGV separater plates (remove those), and then port match the TGV exits to the intake ports on the heads as much as you can. On the backside, do the same with the exhaust manifold input ports from the head...match the exhaust port to the head, not the other way around. Smooth the transitions through the cross pipe and the uppipe and the uppipe/turbo flange. Any smoothing you can do in the hotside will be good. I wouldn't worry too much about the inlet and input side of the turbo. Coat/Wrap the exhaust manifold and uppipe, and the first 1/3 to 2/3s of the Downpipe. It isn't snake oil. Heat wrap keeps the heat IN the pipes. That is where you want it. Thermal energy drives your turbo. It also drives the exhaust flow out of the car. By keeping the heat in, you keep that thermal energy contained and moving. It also keeps engine bay temps down, which is another good thing. Radiant heat increases intake temperatures. Cooler/denser air goes IN, hotter air is pushed throught he turbo. All good things.
Good posts by Mixx. This appears to be due to the tune. I haven't tuned a VF34 on this set up, but I have tuned many similar sized turbos. That size turbo most certainly does not need to taper as much as Jeff's tune did. Ron is typically less aggressive with boost for a street tune, and I respect that, but I would be comfortable tuning a VF34 to hit 20-22 PSI peak and holding about 18-19 to redline. With that type of boost and a moderately aggressive timing curve, it will make peak power at around 6k, and will only begin to fall off after 6500-6700. With all that said, this is still most certainly true.
True, but my point, as you pointed out on your second quote, was that a VF34 is going to have negligible benefits from aggressive camshafts because its efficiency isn't at the top of your power band. A more agressive tune will obviously yield more boost up top with less drop off, but at that RPM range the turbo isn't going to be able to feed a volume of air that would required camshafts. The fact that it does taper up top shows that it isn't a 'top end power' turbo.
nate the reason he didn't tune to 22-23 psi is because the stock tmic is restricting it and not allowing to boost anymore than that with a good curve
Heat is an issue, and is a function of surface area. And then there is airflow volume, at some point, an intercooler will not be able to flow more CFM due to turbulence and volume capacity. Think of a drinking straw and a 3" pvc tube, the volume capacity of the straw is much smaller than the 3" PVC tube. The same goes for intercoolers, at some point, the airflow capacity of the intercooler will be reached. I don't have numbers for CFM capacity for the stock intercooler, but I can tell you it is likely designed to flow enough for the TD04 without alot of headroom.
