Improve cylinder head airflow?

[JD@af]

One of the limiting factors for power potential, especially in small displacement engines, like those Honda manufactures, is cylinder head airflow. What are some of the best approaches to improving airflow? I know there are many, many options here:

• Porting
• Oversized valves (or a simpler option is using a set of intake valves on the exhaust side)
• High lift/duration cams
• Increasing redline

For all motor, and separately, forced induction applications, what do you think are the best methods for moving more air through the cylinder head? Thanks in advance for you input-

-JD

[texan]

The principles are the same regardless of induction method... through pressure differential and velocity try to cram as much air into the cylinder as posible, and then evacuate that as completely as possible with the smallest pumping losses incurred and enough velocity to get a little scavenging going without causing reversion OR blowby. Of course there's also the tennant that all this must be accomplished over as large an RPM range as possible to maximize engine efficiency and power output. Now I was in the middle of writing this long drawn out post (as you know I am prone to doing) when I realized I'm not entirely sure what you are asking! I consider you one of the most knowledgable people I know online, and I also figure you know about the basics behind head porting, forced induction and why the engine's intended application will dictate what should be done for optimal performance. Reading your post, I will try to give a basic repsonse until you further clarify things.

Improving maximum power output on a fixed displacement NA motor is largely about RPM, and secondarily about optimizing the system for good airflow at that increased RPM. RPM is where it's at, which is why Honda and F1 motors routinely spin to much higher RPM than their larger displacement counterparts of similar hp output. The balance of that is in seeing to it the induction and exhaust systems are up to the task of efficient flow at high airflow levels, which is primarily a function of velocity and diameter. Any modern intake port can flow well, the question is can it flow efficiently at a given rate? Likewise, any cam profile is likely well thought out in it's application, the only question lies in what that application is. VTEC gives us tremendous ability (some overstate VTEC's importance, most understate it IMO) to use very aggressive cam profiling on the big lobes without killing low RPM power, especially if you run these setups on high compression motors (we can get into why compression is so important later).

When it comes to forced induction though, the rules are very different. Since all turbos and superchargers help tremendously in terms of airflow ability on the intake side, the focus on head porting, cam timing and manifold choices had better shift to the exhaust side, where either you are asking the stock system to flow increased amounts of air without increased restriction (in the case of supercharing), or you are asking it to do so with increased often times greatly increased restriction (in the case of turbos). Cam timing is also specific to both applications, as a supercharged motor will be more forgiving to big duration cams than the backpressure hindered turbo system. And of course each system and setup is still going to be optimized for a particular RPM range, as you can't have hard parts be equally effective at one flow rate vs. 5 times that flow. Compression is again very important here, and so is intercooling, particularly in the turbo applications. Why is best left for another discussion, but I hope this helps answer at least a part of your question. Peace

[JD@af]

The basic reason for my question is that I was thinking about what limits power production, piece by piece (keep in mind that the following list is vague and generalized). Seems that your first big obstacle is airflow, which can be answered by power adders, higher flow intake and exhaust components, etc. many of several options (or increasing cylinder pressure, via high compression pistons, FI, nitrous). Your next problem becomes mechanical reliability, which calls for building up your bottom end, and perhaps some head work (valve springs, retainers). Seems that following that, it's all about optimizing fuel tuning; usually a good stand-alone engine management system being the next step to unleashing power.

Now if you've taken all the steps above, in a supercharged B series engine, according to a very knowledgeable friend of mine in "the business," you theoretically hit a horsepower wall at about 400 (that's bhp, by the way). Though we all know about the differences between turbo and supercharger power potentials, I was wondering about how one of the most powerful B series engines in the world does it: Ed Bergenholtz's CRX is powered by a B18C1 (fully prepped, of course) that supposedly puts 720 horsepower to the wheels (accounting for the 15 to 16% power loss due to drivetrain friction, this means a peak output of 828 to 835 bhp, which equals the highest output B series engine I have ever heard of)!!

So how do you surpass that 400 mark, and at least move further towards Ed bergenholtz’s daunted peak horsepower? Granted, with a turbo, you'll be able to make much more peak horsepower than with a supercharger. But even still, it seems that once again you must look to increase airflow (or cylinder pressure) in order to increase power production. I’ve heard repeatedly that large cam lobes are the enemy of power production once your engine’s breathing is aided by forced induction (hence the reason I addressed the issue separately for both all motor and FI applications), and using a positive displacement unit like a roots blower, increasing rpms also becomes a no-no once you approach 14K to 15K blower rpms (or certainly by the time you hit 18K rpms, when the bearings are likely to slip). So I was wondering about what to do next.

As you can probably guess by now, I am half-curious about where I can expect my power to run out, and what I can do to get more, assuming I eventually get bored with what I have now (or if I really want to pursue a goal of having an 11-second car). My cylinder head is already ported, and my exhaust system (header and exhaust itself) is still in the works at Hi-Tech, so from my original options, that leaves the addition of oversized valves to increase airflow, and perhaps bigger cam lobes, arguably, with VTEC disabled. More at this point as a hypothetical than anything else, I figured I would ask around to see what I could do down the line, and maybe gain a little insight into what Ed has up his sleeves Thanks as always.

[texan]

Honestly, I can't even imagine how you would get 400hp from a supercharged B18C1, at least not using a JR based kit. The blowers just won't flow enough air at reasonable temps to accomodate that, it takes around a minimum 15 psi of intercooled boost on a turbo setup to produce such numbers. With the lack of an intercooler, there's just no way to push that much air with any kind of workable density and temp from an Eaton based system, they were never designed for that purpose. And that's without considering the factor of parasitic drag. With a small shot of nitrous on top of what I consider to be maximum safe boost on an Eaton (~12 psi, which will shorten it's life span some), possibly you could get to 350-375hp, but then you'd really be pushing the limits of combustion chamber temps and pressure on pump gas IMO. The only real solution to finding such high power levels is intercooling, but again the Eaton blowers are not well suited to high boost applications; their efficiency rapidly drops when forced into high pressure ratio situations. In this case you could also use a Lhysolm compressor, but you'd still need good intercooling to produce high boost numbers with livable intake charge temps. The Lhysolms will hold high pressure ratios much more efficiently than the Eaton, but they cost a good bit more and no kits are available for use.

The turbo B series motors are different beats entirely, capable of pushing high pressure ratios into good intercoolers at nearly any RPM you decide to optimize things for. 25psi of well intercooled boost at 8000-9000 RPM is going to create a TON of horsepower, and this is the type of setup you see on the top runners. Some even run higher RPM potential, or so I've been told (over 10k). Displacement is also a key to most of their setups, you can bet the average front runner with a B18C block is pushing more than 1800cc of displacement. Beyond that, the turbo cams are going to be custom grinds, and it's not true at all that high duration can't work with forced induction. It is true that this will narrow your ppowerband some and as with any motor increased duration means a power curve leaning toward the upper RPM band. But there are many an example of extremely high specific output turbo setups using big duration cams, many of the more radical Supra Turbo setups use HKS 272 duration cams with great success (one of which is pushing around 900hp). It's the same thing as with an NA engine, the optimal efficiency of the motor just shifts to a higher RPM band. I may write more later, but I need to get out of work now and head home. Peace.

[Someguy]

Also keep in mind the sorts of fuels the guys running the really high horse power numbers are using. If we're limiting this to pump gas, then it gets more difficult.

400 hp as a practical limit for a supercharged B18? Hmm.. I seriously doubt the JR supercharger could push enough air for that. Vortech, Paxton, and others certainly make blowers that can flow much more then that, but the practicality of putting one of a 1.8L engine is questionable. So I'd buy that as a rule of thumb.

You do see a lot of Supras with high duration cams that put out very high peak numbers, but I guess it depends on the objective of the car. They tend to be VERY peaky and have a lot more displacement to work with. On a drag strip with slicks it doesn't really matter as much if the car is peaky, since it will only be seeing a small portion of the RPM band though out the entire run. On a road course or the street it becomes much more important. There is nothing more frustrating then falling off your powerband in a tight corner or unexpected situation and watching somebody walk by you. The pipes; they come into tune and they go out of tune.