dainjarouz

iTrader: (4)

Thanks MSCA...do you know if Acura TL last generation are DI?

JohnEnglish

Here's a picture of the intake valves from a 2006 VW GLI with 100K on it.

majin ssj eric

Hmm, this doesn't matter at all to somebody like me who leases for 3 years then gets a new car...

Btw, I haven't heard any horror stories about our IS350 and its DI....

JohnEnglish

Here's a guy with 28K on his motor and he has a catch can.



That's becuase the Lexus/Toyota 2GR-FSE uses a "dual" injection system. At low RPMs it uses a regular port injection system. As RPMs increase the direct injection system takes over until it's running at 100% direct injection. You don't get the carbon build up becuase the valves are washed by the port injection system used at low RPMs. The Audi/VW engine is 100% direct injection all the time so its valves are never washed.

MSCA

iTrader: (3)

dainjarouz, I'm pretty sure that the last gen TL was not DI.

majin ssj eric, leasing a car for 3 years doesn't mean you shouldn't be concerned. I've heard that some of the Audi guys begin feeling reduced performance (due to excessive carbon build-up) in less than 30K miles.

JohnEnglish, I didn't know Lexus was already using a dual injection system. Hmmm....maybe you are right when you said that both port and direct injectors may be the way to deal with the carbon problems. Anyway, I found a good article on the Lexus system here:

http://www.sae.org/automag/techbrief...1-114-1-17.pdf

Mike

iTrader: (1)

Dingdingding. We have a winner!

Yet another reason why the VQ is no longer on Ward's 10 best

goomba

yea at the cost of reliability.

goomba

LOL lets just say I was seriously overdriving the car. Thats what happens when you are a noob and driving a car that has a limit way over your head.

JohnEnglish

The Lexus system uses port injectors at low RPMs becuase a DI injection system can't atomize the fuel enough for a clean burn. DI only really works well at high RPM. Using this port injection system has the added advantage of washing the valves too.

The Audi system uses a "flap" to reduce the size of the intake port at low RPMs which has the side effect of increasing air velocity. This allows for the fuel to atomize properly when it's injected by the DI system. However, it doesn't have the advantage of getting the valves washed.

Here are some drawings of how the Audi system works. You can see at low RPMs you're getting faster air flow than you would normally due to the "flap" reduce the intake runner size.

JohnEnglish

Not only that but at a lot of personal expense and time and voiding your warranty.

Mike

iTrader: (1)

This, is absolutely key. However, it would appear most of the members who have already taken the plunge have alternate means of transportation.

My DI knowledge is limited to what I've read, as I've yet to work on a DI car, but where is this "low rpm disadvantage" threshold? My recent experience with a TDI has me totally jazzed, and the car had some serious pull at anything over 1400 RPMs. It is DI, and I would imagine it uses the "flap" to increase air velocity.

One of the oft discussed uses of DI is being able to do a lean burn, but that is typically at over 2400 RPMs or so, which happens to be "cruising" RPMs on most DI engines (any Audi, Lexus IS, etc.) However, this does depend on low swirl/tumble inside the cylinder.

I wonder how an integrated velocity stack would operate on a diesel...

As opposed to the twitchybutt™? The look on your face when the rear got a little loose over lost hill is pricesless

Our lap times weren't two far apart... OT: I'll be at Chuckwalla Friday and WSIR Sunday.

cvt

i do not have any extended knowledge on DI engines either...this is good stuff. keep it comming guys. would audi benifit by still using the 'flap' and having some sort of 'dual' injection as provided by lexus so you get both a clean burn and higher air velocity?

JohnEnglish

There's no specific "cut off" RPM for DI. It depends on piston speed, engine load, combustion chamber design. Generally speaking DI doesn't work as well in situations where the engine is under load and the pistons are moving slowly (i.e. inital acceleration from a stop).

The Lexus engine can vary the DI-Port Injection ratio depending on a number of factors so it's not like at X,XXX RPM it'll always be 30% Port Injection and 70% DI. It'll vary the ratio depending on engine load, piston speed, and other variables.

You're right, the flap increases velocity, and therefore tumble. Since the flap effectively reduces the size of the intake runner the air coming in is now trying to move throuth a smaller space, therefore it has to increase in velocity.