Shaun@SG

Is there anyone (UL perhaps?) who can share in detail why the S2K engine is able to rev so high? What are the factors? Component mass/strength? Rod ratio? Precision tolerances? I'm building a project 1.8T engine in the not too distant future and having it rev to 8000 instead of 6500 would be nice.

Also, why isn't the new RX8 rotary engine able to rev higher than 9000rpm? Shouldn't it be able to do well in excess of that considering it doesn't experience the high inertial stresses that normal engines undergo when it's pistons are at T and B DC? What limits rotary engine RPM?

TIA

Phantom3jt

I thought the RX8 prototype reved to 10 grand but im not sure.. I've heard thats one downfall of the rx8, should but isnt revin past 9grand.

The reason the S2k can rev to 9 grand is, low friction piston's well balanced valvetrain etc..

jlmille5

There are prototype wankels that rev to 26k and have excellent emissions and gas mileage. I am sure if that was a priority Mazda could have made it happen. I am assuming that they are holding out till the price of technology is the most profitable, just like every new technology.

Hams2000

One limiting factor would be fuel.... If you rev to high you could make your injectors go static. I could see that this would be a definate limitation on a rotary, if one of the only few. On the S, a good, light, and balanced rotating assembly helps alot. The bottom-end is said to be stable to about 12K where the valvetrain is not quite up to par. Titanium valves, springs, retainers, along with a higher spring rate will cure this issue and allow the S to rev much higher.

If you're looking to up the Revs on the 1.8T.... I would definately consider having the bottom-end balanced and running Ti valvetrain parts, along with stronger springs. Also, you might consider that the 1.8T is capable of revving that high to begin with, but the factory set it's rev-limit down because it's stock head design cant make power above 6000. and it's pointless to rev past 6500. You might have to run more aggresive cams at the expense of that great torque the 1.8T makes out of the box.

Just some things to consider.

Chris

Bieg

Some of the reasons The F20C engine can rev to 9000 rpms are;

very light but very strong pistons and rods. The pistons are a "Slipper" design (very shallow except 90 degrees to the wrist pin to prevent rocking in the bore). The pistons, rods and crank are all forged for strength.

Roller valve train. Hollow Cams to lighten weight and deliver oil to the valve springs which would fail from hystereis (sp?) fatigue (like when you bend a wire coat hanger) without the added cooling. Valve springs and bearing materials are by-products of the Honda CART Race engine.

Very good breathing characteristics by good head, cam, intake and exhaust design to take advantage of 9000 rpm redline.

Great attention paid to lowering friction in all parts of the engine.

Girdled (die-cast aluminum) main bearing carrier for extra strength and rigidity to keep crank from wipping about at speed.

There are a million more little details but the above list is a good start.

ultimate lurker

You can rev any engine really high with strong internal parts. The only question is, how long will it last? - and by that, I don't just mean actual breakage, but general wear and tear.

There are several key things to consider in being able to rev an engine to (relatively) high rpms.

1. Stroke - how long is the crank's stroke? The longer the stroke, the higher the piston speed for any given rpm. Even more importantly, it means that piston accelerations are higher (accelerations are where the problems are, high velocity in and of itself doesn't matter).

2. Rod ratio - what is the ratio of rod length to stroke? The larger the rod ratio (longer rod), the less sidewall loading you place on the cylinder bore. Typically you won't see rod ratios much under 1.5 on modern engines. Most I4 engines are in the sub 1.7 range. 1.75:1 is considered to be a near "ideal" (whatever that means) ratio for a balanced engine approach (rod weight, sidewall loading, packaging considerations, etc.). An endurance racing engine might be designed with a ratio over 2:1. The F20C ratio is in excess of 1.8:1, which is quite high for a production I4 engine, especially of 2.0 liters displacement (the old B16B 1.6 liter had a higher rod ratio, but was much smaller.

3. Valve train - you've got to have strong enough springs, retainers, etc. You also want as little weight as possible. There are drawbacks, however, as higher rate springs sap more power and can cause more cam and valve seat wear, etc. The general nature of the valvetrain design can play a role too. Valvetrains using direct actuation (usually a shim and bucket on top of the valve with the cam acting directly on the valve) are best as they keep valvetrain mass to a minimum. If you're going to have followers/rockers, they need to be light, stiff, etc. Some engines (like SOHC 16 valve motors) use large curved followers that weigh a lot. This hurts the ability to rev safely.

4. Cams and head - you've got to have cams designed to flow enough air at your target rpms. And your head has to be capable of flowing the air to support the hp target. As Beig stated, you can compromise your low end if you go for a big top end cam, especially if you don't have a system like VTEC. A big head can often reduce flow velocity at low rpms, also hurting bottom end power.

In the case of the 1.8T, the head is designed to flow very, very well at low valve lifts (a benefit, apparently) of the 5 valve design. However, it doesn't do so well at high lifts. While the top experts have gone back and forth over the last decade about whether or not 5 valves or 4 valves are better, but you'll note that most high revving bikes and cars (and even F1 engines maybe) seem to prefer 4 valves/cylinder for whatever reason. You'd probably need to do some serious headwork to get it to really flow up high (although with a turbo, you can just as easily add more boost :-). I don't know what the rod ratio is on the 1.8T, so you'd have to check that. You can't change it by much without a lot of work, but you can change it _some_. The other factor to look at might be the intake manifold and see if its a long or short runner design.

Honda has an advantage in high rpm stuff simply because no one out there seems to be able to design a cylinder head that does so much, so well. Honda heads simply outflow comparable cylinder heads from other manufacturers, and do it without dramatic increases in port size/volume which would seriously reduce velocity and low rpm power. Frankly, having seen the flow results from many production heads, I don't think anyone does it better (for production cars) than Honda. The F20C head, in particular, is a masterpiece.

UL

Shaun@SG

Thanks for the informative replies guys, esp UL.

Crappy thing about a small displacement engine (1.8T) with a low redline (6500) is that it seriously limits power output. We try to get good low end, but that compromises top end. We get a big turbo that supports a high flow rate, but redline limits using that good flow rate. Plus all the cars that come with the 1.8T are kind of heavy. 12's have been done, but 11s and 10s look really hard.

Still, I guess if we wanted we could build out the block and internals and get the head ported. Don't see much problems with pulling the engine apart every three or four years.

I'm fairly certain the 1.8T head flows a good amount. This is from the experiences of 1.8T guys have already run 12s on the entirely stock engine. Here's what CTC Motorsports had to say about the 1.8T head.... http://www.ctcmotorsports.com/current.php#5

ultimate lurker

Hmm, that's not what I've seen (not that it means it isn't true). A fully developed (and I mean a lot of development) Eclipse head (1st gen) actually flows about as much on the top end as a stock F20C head. The 1.8T head I saw flowed didn't come close to either one. In fact, its high lift flow wasn't even as good as a B-series head IIRC.

The same Eclipse head I mentioned, on a 2.0 liter bottom end, was able to produce 420 whp at about 7000-7500 rpm on pump gas with a little more than 1 bar boost with Motec engine management, which tells you how efficient the engine was.

I would suggest contacting Alaniz Cylinder Head Technologies (www.alaniztechnologies.com) for more info. He has flowed the 5-valve 1.8T head and would probably be willing to share the data with you.

UL

Shaun@SG

Could be AEB vs non AEB flow rates.

Thanks a lot man

Hyper-X

I am so out of sync with the modern VW cars that I wish that I still had my 1st/2nd GTI now so I can keep up with the current technology behind them.

My take on this rev topic of the 1.8T is this... I've always played to the strengths of the car.

Since the 1.8T is boosted, it doesn't need to "rev" very high to gain power. That in itself is a benefit to its design. An N/A engine since it has no device to push air into the intake tract, has to spin to much higher rpms in order to help generate faster air speeds in order to make a lot of power out of a smaller displacement engine. I recall installing race camshafts into unboosted engines that made the idle rough, the car torqueless at lower rpms but made considerable power nearing the red zone.

If VW followed its history of making bombproof engines, I'd look at increasing your airflow through modifying your boost pressure, intake & exhaust tracts all followed by a well-tested ECU/Chip upgrade that can keep things together on pump gas. I used to call Darrell Vittone at Techtonics Tuning almost once a week regarding my Rabbit GTI years ago... try contacting him or Colin and get more info regarding your setup.

I'm not like UL where I can start talking tech like an alien from outer space (j/k UL) but (in theory) if there was a magical button where you could press right now to lift the current rev limit and make it for example 9000 rpms, there's a few more things to consider, like gearing. A car making a lot of its HP and torque higher in the rpm-band, can take advantage of gearing better, so we're talking about a complete re-design of the fundamentals of the existing 1.8T setup to include other major factors besides the engine.

Once again, IMHO I believe you should play to your strengths. Your setup is force-fed, use that to your best advantage.