ultimate lurker

In the August 2001 issue of Racecar Engineering there is an extensive discussion of the new rules in British Touring Car designed to keep costs down and racing competitive.

Among the many changes made are significant changes to the engine spec. Some of the specs are as follows:

1. 2000 cc max displacement
2. Control (everyone uses the same) TB - 60 mm in diameter (this means no individual throttle bodies)
3. Spec ECU (reprogrammable, but everyone uses the same system)
4. 8500 rpm rev limiter
5. Maximum compression ratio of 12:1
6. Maximum valve lift of 12mm
7. Valve head and stem diameters must remain sized the same as the production car the engine is based on
8. Wet sump engine required (no dry sump conversions allowed)

The net result is that one year into the new spec, the engines are producing 270-280 hp. Additionally, competitors are penalized for championship points if they use more than 5 engines (meaning rebuilds, etc.) during the season (15,20 races?). Thus, the engines must be very reliable be able to handle multiple races without rebuilds. This compares to the old dry sump, individual TB, high compression units that produced about 330 hp.

What does this mean for F20C fans? Well, first, look at the restrictions we don't have to play with.

1. Our rev limiter is not limited to 8500 rpm. Thus, we can rev higher and make more power for a given torque output.
2. Our valve lift is not limited. For a high output 2.0 liter 12 mm of lift is not much. The old Prelude VTEC was using almost that much stock and the 220 hp Prelude Type-S had lifts in excess of 12 mm.
3. Our throttle body is already much bigger than the 60mm spec used in BTC. Thus, we don't have the same flow limitations.
4. Our valvetrain is 'free' - we can alter valve sizes (somewhat) and stem diameters. Not to mention that the F20C probably has a _stock_ valve design more advantageous to power than any other production 2.0 liter today.
5. We can run a compression ratio very close (or equal). The JDM 11.7:1 ratio is close enough to call them the same and I know we can run that here in the U.S. (well maybe not in CA with the 91 octane now :-(

So, in the end, we have a very restricted class producing 270-280 hp from the same displacement we have. Our engines, in stock form, already have advantages over these race engines and we can make further modifications to distance ourselves. I have no doubt in my mind that with proper cams, ECU and head tweaks we can exceed 270-280 hp in a street driven and reliable engine.

UL

s2kmtl

yeah! what he said.

rob

josh3io

nice observation. so what gives those engines the 40-50hp gain over ours, as-is? and by making the changes, will our engines need rebuilding multiple times per season?

Silver S2k Guy

I'd bet that most of the 40-50 hp difference all has to do with emmision control crap that our cars are required to have. Also I don't think that by simply removing all the emmisions control devices you could pick up 40-50 hp because our cars were designed to work with these devices. I think you'd need an engine specificly designed for racing with no emmisions controls taken into account to make this kind of power.

Penforhire

In our cars the whole "running-rich" thing bugs me. Isn't that worth a big chunk of the difference? And that means a new ECU (but not just the Mugen), and maybe AFC, that doesn't exist now, right?

BB AP1

Maybe the Apexi power FC would help..

ultimate lurker

In terms of ECU stuff, yes, we seem to run kinda rich, and apparently, like every other Honda, the OEM programming pulls back ignition timing a lot on the top end. This serves two purposes. First, even with questionable fuel, supr high temps or driver abuse the engine will hold together. Second, the power roll-off encourages you to shift before the limiter. If you've ever driven a car where the power keeps growing, it takes a concerted effort to avoid the limiter, especially in lower gears (see SC'd S2K, high output B18C, etc.). Our "hard" rev limiter isn't particularly good for the engine's health.

I plan on picking up a VAFC and harness as soon as my IRS refund comes in July, so I'll be on the dyno documenting results.

In terms of emissions controls, all we really have is the cat and crankcase ventilation. The cat is probably one of the freer flowing units out there and they don't harm power that much (I got 230 hp out of a street driven 1.8VTEC with the factory cat, which is not as good as the S2K cat).

On the reliability front, if you were racing your engine 15-20 times a year in 30 minute sprint racing and with qualifying, you'd probably want to rebuild it, even if it was bone stock. Racing takes a lot out of the engine. Imagine spending 50 hours between 7000 and 9000 rpm. Even with 10 track days a year you wouldn't get to half that number.

I think where the touring car engines have their advantage is in careful ECU mapping, carefully ported heads to maximize flow (for example, a B18C5 Integra TypeR head can pick up15-20% more flow capacity with good porting) and properly profiled cams. With careful blueprinting of the bottom end you have a powerful and reliable engine.

UL

S2kRob

No, I don't think so. It's not so much that the engine is designed to work with the emissions equipment as the ECU is. Those race engines are based on production engines that have just as much emissions equipment as the S2000 when installed in a road car.

TEC II or MOTEC is probably the best solution. Not only is it fully programmable, but they also deliver a much more powerful spark along with other benefits.

lupin

If the BTCC cars are indeed "only" pushing out 280 hp, then Honda did a damn good job in getting 240 hp out of a production street engine.

Although shouldn't the BTCC cars have around 300+ hp??

The 2.5L BMW S14 engine from the '91 DTM had 380 hp. It did have an extra .5 litre, but technology today should be able to offset that. But again, I don't know much about the rules and restrictions.

ultimate lurker

lupin,

Two years ago the BTCC cars were producing 330-340 hp from 2.0 liters, even with the 8500 rpm mandatory limiter.

Last year they went to much tighter restrictions (outlined in my first post) which put some limits on power (and cost) and also bring them more closely in line with our street engine. In fact, as I pointed out, we have some freedom to look for power in areas they don't.

UL