penjaja

What do think of the validity of this article? opinions?

http://www.hondastyle.com/news/wmprint.php?ArtID=33

Do think the combo the author suggested would work?

ricodemus

interesting, since I already have a b16 and was looking for a b18c to get some more torque. I had always read not to bore past 84mm on a b16, but maybe that was without sleeving. This guy seems completely theoretical though.

92sleepR

Pure gold

I have actually been following this subject for some time. It's not an easy area of study and there is a lot of off-the-cuff "my sisters boyfriends uncle did this" kind of information out there that isn't very usefull, grossly oversimplified, or just plain wrong.

I have compliled all three articles here. I recommend to anyone who want's to really get an understanding of how Honda motors tick to clip this to a file and study it. If you ever decide to build an engine, or even more importantly, have someone build one for you, it's worthwhile knowing.

Sorry for the size

Honda Engine Building

What is LS/VTEC?

A quick tutorial for anyone who doesn't already know.
LS/VTEC is using a B18A or B18B block (referred to as an LS block, even though it was found in the RS, LS, and GS) and mating it with any of the DOHC VTEC heads- the B16A, B17A, or B18C. The principle is to use the larger displacement of the LS block (READ: higher torque) and mate it with the high end power of VTEC. I'm also sure you've heard of CR-VTEC, which is a very similar idea. It uses the B20Z block of the CR-V (NOT the B20A of the Prelude Si, for reasons that will become obvious later) to achieve the same effect, only on a grander scale. What you end up with is an engine commonly referred to as a "Frankenstein" setup, and it's all the rage these days

Why would Honda do that?

So why in the world would Honda put us in such a situation- having to build these incredible motors all by ourselves? Why would they knowingly decrease displacement and torque in a car being manufactured to be faster than its lower-trimmed breathen?
Look at it, too, from a manufacturing standpoint- Honda is already making the higher displacement B18A and B blocks (blocks are identical, only difference was in the head), so why go to the extra time and expense of developing and manufacturing a separate block, especially if it will decrease output?
The answer is easy: R/S. (ratio)

What is R/S?

R/S is the abbreviation for rod to stroke ratio. It is the ratio of the length of the connecting rod to the length of the piston stroke, or the distance the piston travels from the top to the bottom of its stroke. As the ratio gets lower, the amount of stress on engine internals increases exponentially, killing long-term reliability. The higher the number is, the slower the piston is traveling, killing power output.
The ideal R/S is 1.75:1 (Three cheers for the B16A, at a near-perfect 1.74:1!).

Why a low R/S is bad for reliability

A low R/S means the rod will be closer to a horizontal angle on its upstroke. This means that more of its force will be pushing the piston horizontally, rather than vertically. What does this mean for your engine? Two things.

1. There will be more stress on the sides and in the center of the rod, rather than on its ends, leaving the rod more vulnerable to breaking. Picture a straw. This is no special straw, just an ordinary drinking straw. Is it going to be easier to bend this straw by applying pressure onto its ends, or at its center? Now think of your poor connecting rods..

2. There will be more stress on your cylinder walls. Once again, the rod is pushing the piston at a more horizontal angle- right into your cylinder walls, rather than up and through them. The risk here is double: A. Putting that piston right through the cylinder wall. B. The cylinder wall will actually flex under the pressure, causing the shape to turn from a circle to an oval or oblong shape. This causes the loss of the seal created by the piston rings. What happens? A small amount of oil could slip past into the combustion chamber. Bad things happen from here: The oil gets combusted, leaving nasty carbon deposits in your combustion chamber and exhaust ports- not a good thing for flow or valve sealing.

It's also important to note that as the RPMs increase, so does the amount of stress on your engine's internals.

What is power, exactly, and how do Hondas make it?

Warning: Once you see this, you will never look at horsepower and torque readings the same again, especially after you think about it.

P= (TR)/5252

P= power, in horsepower
T= torque, measured in lb/ft
R= Engine speed, in RPMs

Therefore:

Horsepower= (torque x RPMs) / 5252

Try it- pull out a dyno and see what you get.

So from this, we can conclude that if we increase torque or engine speed, we will get more power, right?

Remember that, it's important...

Now how do Hondas make power? Our tiny little 1.6-1.8L engines aren't exactly oozing spare displacement and creating gobs of torque, are they? Hondas make power through revving, and revving high. So why does everyone place so much emphasis on creating torque? It's because all these bolt-ons you see advertised won't raise your redline, but they will increase torque. There's nothing wrong with squeezing every last ounce of torque out of your engine- you should. But trying to get torque from more displacement in a Honda is like trying to fill a swimming pool using a squirt gun. You'll never get enough for it to be useful.

B Series, by the numbers

Let's take a closer look at the B series engine blocks.

In the B18 blocks, Honda increases displacement by using a larger crank and increasing stroke (the B20Z also has a slightly larger bore, which is bad for reasons I won't go into here). This, of course, lowers the R/S, since the rod length remains (almost) the same.

B16A:
Rod length: 134 mm
Stroke: 77 mm
R/S: 1.74:1
Displacement: 1587.12 cc

B17A:
rod length: 131.87 mm
Stroke: 81.4 mm
R/S: 1.62:1
Displacement: 1677.81 cc

B18A-B; B20B-Z:
Rod length: 137mm
Stroke: 89mm
R/S: 1.54:1
Displacement: 1834.47 cc

B18C:
Rod length: 137.9 mm
Stroke: 87.2 mm
R/S: 1.58:1
Displacement: 1797.36 cc

B20A (Older Prelude Si)
Rod length: 141.7-142.75 mm
Stroke: 95 mm
R/S: 1.49-1.50:1
Displacement: 1958.14-2056.03 cc

Now you see two things: Why the B20A is widely regarded as a not-so-great engine, and why Honda decreased the displacement from the B18A-B to the B18C. Honda decreased the displacement in the B18C by decreasing the stroke, improving the R/S. This allows the B18C to rev higher, and (Hey!) increase output.

Making sense? I bet you can see where this is going. But wait, there's plenty more...

How VTEC works, and why it lives at high RPMs

A quick crash course for anyone unfamiliar with VTEC:

VTEC stands for Variable Valve Timing and Electronic Lift Control. The premise is that at low RPMs and at idle, a less aggressive cam grind is necessary to prevent "loping." Ever hear a pro drag car staging up at the gates? Sounds like it's about to stall. It's because he's running aggressive camshafts, and since the cam is spinning more slowly at idle, the intake valve is still open after combustion has completed. That's what causes loping. At higher RPMs, a more aggressive grind is desirable. The idea is that you want to cram as much air and fuel mixture (A/F) into that combustion chamber as possible, so that when it's ignited you get as grandiose an explosion as possible. So what is good at low RPMs is bad for high RPMs. So what do you do?

If you're Honda, you invent VTEC. What VTEC does is simply to employ different cam grinds at different RPMs. A less aggressive grind at low RPMs for a smooth idle and low to mid range power, and a more aggressive grind up high to produce that high end pop. At a strategically placed "VTEC crossover point," the camshaft switches grind from the less aggressive to the more aggressive.

What determines this point? Hours and hours dyno testing and tuning. If it is set too low, the more aggressive grind will kick in early, bogging down the engine (think "loping" at 3500 RPM). Too high, and the engine is missing out on valuable time it could be spending with the VTEC engaged. So all those fools who spent $400 on a VTEC timer running stock camshafts just so they could get their VTEC to kick in earlier- they're idiots. They just cost themselves a ton of midrange power. The stock crossover point is optimized for stock camshafts.

So when is a VTEC timer necessary? Easy- when you're no longer running stock camshafts.

If you want big power all motor, you go with one of the big players in the cam game- Toda Spec B and C, or Jun Stage 2 and 3, and you accept no substitutes. All (or at least 95%) of the 225+ all motor whp B18s are running these camshafts.

How does this relate to VTEC crossover point? Well, the VTEC grinds on these cams are so aggressive, that the VTEC point needs to be moved up- way up- usually to 6500-7000 RPM. These cams will also make power to 9500+ RPM (READ: Built motor). Run these in conjunction with high compression pistons (at least 10.5:1), and you'll have yourself an all motor wonder. And this, friends, is where torque in Hondas comes from.
Why it doesn't all fit together
So here's what we've learned:

· The LS/VTEC suffers from a bad R/S, due to the fact that it utilizes an LS block with a R/S of 1.54:1.
· A bad R/S is bad for the engine, especially at high RPMs
· Hondas make power through revving, and high power through revving higher, high compression, and aggressive camshafts

Because of its R/S ratio, it is not recommended that you rev an LS/VTEC past 6750 RPM on stock internals- the redline of a stock B18A-B. With a fairly built bottom end, it is still not recommended that you rev an LS/VTEC past 7800 RPM.

As we just discussed, in order to get any considerable power out of an engine, aggressive camshafts are a must. In order to get any benefit from aggressive camshafts, the ability to rev the engine high is a necessity. How valuable is VTEC if you can only use it for the top 1000 RPM of your powerband?

LS/VTEC is a fad, and I predict that it will be all but a pleasant memory in a few short years. As soon as kids start snapping rods and putting pistons through cylinder walls, they'll realize how important good engine geometry is. Add that to the fact that they're running stock cams (because it's all their engine can safely handle) and getting burned by kids running Todas or Juns, and they'll wish they had just stuck with their trusty B18C.

Never have I said that the LS/VTEC is an awful motor, and that no one in their right mind should build one. LS/VTEC has been hailed as the biggest thing to hit Honda tuning in years. Import Tuner, Super Street, Honda Tuning, and more have praised the ingenious design, marveled at its torque, and even showed you how to construct this beast in the comfort of your own home. Never do they mention its drawbacks or its subsequent limitations. The intention here is not to discourage someone from building an LS/VTEC. Rather, it is intended to give someone considering one of these hybrids some things to keep in mind before diving into the costly process of building an engine.
Like I said, if it was all that great, Honda would have done it in the first place.

Sources/ Influences
Larry at Endyn
"The best engine will be the best series of compromises."

Katman at FF Squad
"So please... Don't steal any of our cars again. Thanks."

Tuan at SHO
"The more you learn about the factors of making power, the more amazed you become at how good the stock engine really is."

In my last article, I wrote about the evils of LS/VTEC- namely the rod stroke ratio and its subsequent limitations. Remember, power is nothing more than the product of torque and RPM. Hondas make power through high RPMs, not torque. LS/VTEC increses torque, but limits the redline. So how do you get the best of both worlds?
Consider this: Johnny Hondaman, looking at installing an LS/VTEC or B18C into his cherished ride. Here are his options:

B18C: 1797cc of displacement 1.58:1 r/s ratio 140-150 hp
LS/VTEC 1834cc of displacement 1.54:1 r/s ratio 155-165 hp(?) (I have yet to see a dyno of a "stock(?)" LS/VTEC- no cams, stock I/H/E, stock internals, etc.)
So what's a guy to do? I have a better idea.

The Alternatives

So now consider these-
For the same price tag as that B18C, you could do this: B16A1 (JDM Integra XSi) Cylinders bored and sleeved to 86 mm Forged rods and pistons, 12.5:1 cr
And have the following results: 1789cc of displacement 1.74:1 r/s ratio 150-160 hp
For the same price as an LS/VTEC, you could do this:
B16A1 Cylinders bored and sleeved to 86 mm Forged rods and pistons, 12.5:1 cr B17A crank
And have the following results: 1891cc of displacement 1.68:1 r/s ratio 180-190 hp
The most expensive part would be the B17A crank. New, I was quoted $977.23 from my local Acura dealer, and I have yet to see one used. However, since the B16A and B17A deck heights are identical, the rods would be shelved parts- no custom machining (cheaper!). Also, most piston manufacturers do make 86mm bore pistons, to any desired compression ratio.
It should also be noted that both of these options would employ the cable tranny found on the B16A1. If your car is already a cable tranny, no problem. However, if yours is a hydro, expect to invest a couple bones in a new tranny (CTR, maybe?).

The Advantages

So what has Johnny gained, really? Why go to the trouble of assembling an engine when you could just buy a B18C or slap a VTEC head on an LS block?
Advantages over both the B18C and LS/VTEC
-For the same price, you already have a built engine, including: forged rods and pistons, sleeved cylinders, and high compression pistons. Comparably built, a B18C or LS/VTEC would be much more expensive; first you would pay for the engine, then pay for the build-up.
-Oversquare engine geometry (bore>stroke). This is another one of those little things that will increase your redline and reduce stress on your engine internals (read: reliability). With the B16A crank, bore/stroke would be 86/77. With the B17A crank, bore/stroke would come to 86/81.4.
-Better rod/stroke ratios. Although you lose 8cc of displacement (so what?), the r/s ratio of the B18C alternative would improve from 1.58:1 to a near perfect 1.74:1. The increase in redline would more than make up for the loss in displacement. In the LS/VTEC alternative, it would improve dramatically from 1.54:1 to 1.68:1.

Additional advantages over LS/VTEC

-Uses a B17A VTEC crank. The VTEC cranks are far superior to their non-VTEC counter parts, and perform much better at high engine speeds. This is due to (among other things) better lubrication and better rod bearings (although these would more than likely be upgraded, regardless).
-Uses a B17A VTEC block. No more machining, tapping, and drilling the B18A/B block to accomodate VTEC. Much more user and installer friendly, much more reliable.
-1891cc of displacement. Remember how excited everyone was to get an extra 37cc of displacement for their VTEC motor? Well, this is an extra 94cc. Nearly three times the increase, and 57cc more than an LS/VTEC, with all the aforementioned advantages.
Between the superior engine components and geometry, and properly built (and with an adequate valvetrain), I can see this engine spinning to 12K RPM all day without a hitch. There aren't cams out there that could use 12K, but I'll bet you could. And that speaks volumes about the engine.

The Disadvantages

By now, everyone is pretty familiar with my favorite saying: If it was all that great, Honda would have done it in the first place.
-The combustion chambers in the head will have to be machined to accomodate an 86mm bore. While this isn't a huge problem or really especially costly, it does present another problem. It increases the size of the combustion chamber. Combine that with the B16A's or B17A's relatively short stroke, and getting a piston dome high enough to generate a respectable compression ratio starts to look pretty big. This creates two problems.

1: Valve to piston contact becomes an issue with any high dome piston used in conjunction with any high lift/ long duration camshaft. Survival here depends on a good valvetrain and knowing when to say when and not getting too aggressive when choosing a compression ratio. At 12.5:1, it should be safe, and pump gas would still be an option. Good tuning of the valve timing and an experienced engine builder will also help immensely.

2: A high dome piston isn't all it's cracked up to be. Sure, generally the higher you go with compression, the more power you can make. However, once the piston dome becomes too high, you start to run into combustion issues. Think of the combustion wave as it is first ignited in the chamber. With a smaller or flat dome piston, the combustion wave has a much easier, much more direct route across the piston and combustion chamber. The higher the piston dome gets, the more it is in the way of this combustion wave. For these two reasons, I wouldn't go above a 12.5:1 compression ratio with this engine. The piston dome would simply have to be too big to be practical.

-When I first started exploring the possibility of boring the cylinders, I talked to many people who had bored theirs out to 84mm. The first question I asked was why stop there? Why not keep going to 86? 90? Larger? The largest you can bore the stock cylinders is 84mm. Any larger than that, and the cylinder walls become too thin. So what about sleeving? When working with a larger bore application and sleeved cylinders, you can only go so far before from above, the cylinders begin to look like an Audi logo. The achilles heel of the engine has now become the head gasket, and the space between the cylinders. To remedy this, a thicker head gasket is necessary (further increasing our dome height problem), and strong head studs (such as the ARP) to reduce flex.

So What?

This motor has potential. In a serious build (aggressive cams, head work, bolt ons, etc...) and some good tuning, I can see this engine hitting 210-220 hp without too much difficulty. Couple that with its good geometry (less stress on your engine internals- reliability!), and this would far and away be my choice over an LS/VTEC. It does have its weak points, but I believe that with an experienced engine builder by your side, they shouldn't present a problem at all, and are nowhere near as big an obstacle as a bad rod ratio is. If I were starting from scratch, trying to decide what to build, this would be it. Cheaper price tag, better geometry, superior reliability, and more potential. So, Mr. Hondaman, what's it gonna be? [WM]

penjaja

Wow, great reply.
Gave me some things to think about too. I especially agree with the quote by Tuan at SHO
"The more you learn about the factors of making power, the more amazed you become at how good the stock engine really is."
BTW what does SHO stand for?

Thus the question left in my mind now is, is it safe to bore to 86mm on a sleeved block? Has anyone done that? what probs did they encounter?

mafioso102

excellent article. I was going to try ls/vtec, however, a cheaper and more efficient route seems to be cams for me.