Originally Posted by hstuners.com

February 01, 2002 - 23:00
The LS/VTEC and B18C Alternative
by 2ndGenTeg


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?