Kurtz

iTrader: (1)

FYI-

http://en.wikipedia.org/wiki/Honda_K_engine#K20

RSX-S- 11:1 compression on both the K20A2 and the K20Z1 engines.

The regular RSX is 11.8:1

And according to this the race kit (for the 11:1 RSX-S) only makes.... 5 lbs of boost. And even that requires changing the injectors and an ECU flash

http://www.intensepower.com/jarargejrsuk.html

lobuxracer

iTrader: (2)

Funny how people think it's not a big deal to get all this stuff to work. If they'd only actually had to make it work, they'd be marveling at anyone even thinking about attempting it.

I have some ideas for ways to do a few things with the 2IS, but the risk of screwing it up just isn't appealing for a DD. I'll play with my Supra, it's my toy anyway.

nabbun

^^^ would you be willing to share some of those ideas? perhaps some of us 250's would like to give things a try . . .

Gaugster

I was pondering one of the many limiting factors about boosting an ISx50 car. In general there is a huge pressure drop that happens when the DI fuel injector is opened and fuel is sent into the combustion chamber. For DI this is done during the compression stroke. So if you had a fuel rail at 10,000psi (Diesel??) and fuel was injected into a chamber that has a lower pressure, you get very good fuel atomization etc…

So the cranking pressure for this engine is around ~200psi when a standard compression test is performed. The amount of pressure will only get larger due to better volumetric efficiency of a running engine. The VE will go way up as boost is added and result in higher ‘psi’ prior to ignition.

So what’s my point – The ISx50 uses two fuel pumps, an electrical type in the tank (Low pressure) and a mechanical pump to boost the pressure higher. However, from reading through the manual, the specification for the fuel pressure is only around 500 – 900psi. Lower than I expected but it probably helps to minimize the ‘ticking’ noise while getting the job done. Maybe I am reading it wrong as well????

So if you take the cylinder volume with the piston at Bottom Dead Center (BDC), place it under 7psi from a turbo or SC, compress it – what would that compression measure???? I have not done the math but I would expect it to be much higher the 200psi. If it is getting close to the fuel pressure of the Direct Injectors, that means less fuel, bad atomization, system malfunction, etc…..

I guess I am saying that it is not just about changing the fuel injector pulses as we will probably need to upgrade the fuel pump(s) as well.

Does anyone know the size of the combustion chamber for the IS250 and/or IS350?

Flaming Enabled

uschardcor

25.42/35.59 cubic inches?

lobuxracer

iTrader: (2)

When you start exceeding 200psi static, you run into fuel octane problems big time. Adding 7 psig means you've raised your base pressure from 14.696 to 21.696 psia, or 32.2%, so you could expect to see ~266 psia (actually more, because there will be an even greater temperature rise from the act of compressing the air which will in turn increases the pressure.) Still, this is peak pressure, and the pressures at which the injector fires will be significantly lower, although typically any pressure increase will reduce the volume of fuel injected and the ultimate flow rate of the injector in service (a common issue with boosted engines anyway). DI does not do what you might expect. It fires multiple times at different degrees of rotation to create a stratified charge effect in the combustion chamber improving efficiency and allowing a leaner overall burn without the problems of attempting to light a very lean mixture without enough fuel near the sparkplug.

Injectors would be the smallest of my worries until we get into 15psig boost. Toyota does a wonderful job of using extra large injectors (most of the time) on their performance platforms.

You can calculate the volume of any combustion chamber if you know the bore, stroke, and compression ratio. There are lots of websites with formulae for doing this, and you can derive it yourself pretty easily - it's simple arithmetic.

Gaugster

Thanks for the input regarding the cranking pressure etc…. The relative calculation is a good way of thinking about it. The 200psi 'rule' has been around for a while so I would guess that a DI engine can handle a little more.

I want to clarify that the combustion chamber that I was referring to is only the volume in the cylinder head minus what ever space is occupied by the piston crown with the piston is at TDC. So if anyone knows that and the compressed gasket thickness please chime in.

This data is usually measured (cc'd) as it can't be calculated directly unless you have a CAD file of the head design. The numbers posted above are just the engine displacement divided by 6. Not what I was after by a long shot.

Just to clarify, DI engines create a stratified mixture where the area around the spark plug is relatively rich in fuel and the rest of the combustion chamber is lean (~20:1 or so but it changes per design etc...) This is done by injecting the fuel into a “sub-chamber” that is designed into the piston crown. Your comments are accurate but I want to explain how the A/F ratio ends up being leaner overall. All this is the opposite of the homogeneous mixture that was the old standard.

There were some good pictures of the internals posted a while back that showed this in some detail. I can only guess this is one of the reasons that these cars have the triple electrode sparkplug and tend to run in a "pseudo choke” mode for longer than I consider normal.

lobuxracer

iTrader: (2)

Size of the combustion chamber is not the volume of the head. As you stated, those numbers are different. I haven't had a 2GR head to measure or I would tell you. The other problem is, production tolerances mean you are not likely to see the exact number the factory claims. More often than not, your measured compression ratio is low by 0.2 to 0.5 because the tolerances are set to stack on the low side, not the high side, especially on engines designed for premium fuel because if it's a little too high, the engine will come back for warranty replacement. A little low, and you just lose a little efficiency (and power potential) but the manufacturer doesn't have to plan on replacing any engines under warranty.

It's the same reason OEM fuel maps always go pig rich at WOT. They'll never replace an engine that goes pig rich, but always replace one that goes lean for any reason.