Engine technology thread.

[serialk11r]

Oh, I had no idea. I assume they don't run the engine at the very limit for reliability, so I'm speculating on how much headroom they leave. So I realize if you give only like, 3psi boost, that's still a >10% increase in peak absolute temperature (assuming gamma=1.4, not that good of an assumption..but still), which is pretty significant.

[suprachica79]

What needs to be done to lower compression to make an engine more boost-friendly? Ie. if someone where to boost this car, what measures would you take to make sure it is as safe as possible? Does it depend on what type of FI you go with? SC vs. turbo?

[Allch Chcar]

Originally Posted by serialk11r

Well if timing has to be retarded that's not good, as it is essentially reducing compression, so I guess I was asking how much pressure you can run literally without changing anything but the amount of fuel (but not the A/F ratio either).

Originally Posted by suprachica79

What needs to be done to lower compression to make an engine more boost-friendly? Ie. if someone where to boost this car, what measures would you take to make sure it is as safe as possible? Does it depend on what type of FI you go with? SC vs. turbo?

^Look at WoW's previous post.

The power from adding boost more than makes up for the power lost from pulling timing. Plus you can keep the timing advance when off boost. Am I right WoW?

[WingsofWar]

Originally Posted by Allch Chcar

^Look at WoW's previous post.

The power from adding boost more than makes up for the power lost from pulling timing. Plus you can keep the timing advance when off boost. Am I right WoW?

Simplest answer is yes,

If we wanted to build peak performance on and off boost, having an adjustable timing map is the golden ticket.


Here is the shitty part about this whole conversation,
since we are ultimately applying this to the D4-S 2.0 flat-4, which would most likely have a compression ratio ranging anywhere from 12-13.5. This is not because the internal chambers produce that much compression, but due to the fact that the direct injectors themselves inject fuel DURING compression stroke, after port fuel has been injected via, intake stroke.

Here we add boost, no matter how much timing you pull we might be reaching the limits of how much pressure each cylinder can handle even under small boost. There are a few other variables im not to sure of as well...

[serialk11r]

With a fuel like gasoline that doesn't absorb that much heat upon vaporization, yea operating under max power with only direct injectors during compression stroke will increase pressure. But say the A/F ratio is 13:1, then we are adding 1/13 atm pressure, minus whatever the cooling effect is, so it's like adding less than 1 psi "boost"... is that significant? I don't have any context to take it out of, never owned a car :P

[WingsofWar]

Originally Posted by serialk11r

With a fuel like gasoline that doesn't absorb that much heat upon vaporization, yea operating under max power with only direct injectors during compression stroke will increase pressure. But say the A/F ratio is 13:1, then we are adding 1/13 atm pressure, minus whatever the cooling effect is, so it's like adding less than 1 psi "boost"... is that significant? I don't have any context to take it out of, never owned a car :P

Most cars come with a slightly rich fuel mixture from the factory to give the engine longevity. a 13:1 fuel mixture sounds normal operating mixtures for normal driving conditions.

a 13:1 Target AFR under no load no boost idle will probably using port injection or direct injection but not both at the same time. This will probably make the ECU adjust timing more advanced to use that rich mixture for better performance and economy.

a 13:1 Target AFR under Cruse load/ with no boost, (2500rpm) will probably be using both port injection and direct injection. if anything with a slight retard.

1 13:1 Target AFR under WOT, might be looking at a bit too lean of a mixture, and internal pressures could be hitting the limits.

[serialk11r]

Wait I thought cars typically run stoichiometric since running rich too long screws the catalyst? If the engine runs rich at cruise, there is no way it can pass emissions... Rich is under power, to preserve the engine and get the most power out, right?

[WingsofWar]

Originally Posted by serialk11r

Wait I thought cars typically run stoichiometric since running rich too long screws the catalyst? If the engine runs rich at cruise, there is no way it can pass emissions... Rich is under power, to preserve the engine and get the most power out, right?

This is where tuners alike destroy engines when adjusting fuel maps. For a long time there is an illusion going around that a stoich fuel mixture is the best mixture for your engine for performance and reliability. This is not true.

Every engine has a unique temperament, and when it feeds on fuel it has its own preference of peak power and economy. Which is not synonymous with stoichiometric mixtures.

My rx7 has a happy starting fuel mixture of 11.5AFR which you can say..is that particular's engine preference for peak power and economy. 12-12.5-13 is too lean, and below 10 is overly-rich.

Running rich isn't an issue for many parts, running overly-rich can foul up spark plugs and o2 sensors. Running rich isn't bad for emissions. Running overly-rich is. Running lean can bring out the best peak power the engine has to offer, but is also bad at a certain threshold, as it destroys catalysts, damages internals, and puts out very bad NoX.

[Allch Chcar]

Well actually they usually run Stoich MOST of the time on a street engine. But it is only during closed loop operation, which is low load eg <70% load and not past a certain RPM like 4000 or so. Stoich is where the emissions are the least and it also happens to balance power with fuel economy.

But in open loop, it is exactly as WoW said.

I think that should clear up the confusion.

[WingsofWar]

Originally Posted by Allch Chcar

Well actually they usually run Stoich MOST of the time on a street engine. But it is only during closed loop operation, which is low load eg <70% load and not past a certain RPM like 4000 or so. Stoich is where the emissions are the least and it also happens to balance power with fuel economy.

But in open loop, it is exactly as WoW said.

I think that should clear up the confusion.

yikes 4000RPM for closed loop? On my car, my closed loop operation ends at like a guesstimate of 40% throttle, and if im doing highway (50-60mph) speeds at 2500rpm im out of closed loop.

[Farred]

Originally Posted by WingsofWar

Simplest answer is yes,

If we wanted to build peak performance on and off boost, having an adjustable timing map is the golden ticket.


Here is the shitty part about this whole conversation,
since we are ultimately applying this to the D4-S 2.0 flat-4, which would most likely have a compression ratio ranging anywhere from 12-13.5. This is not because the internal chambers produce that much compression, but due to the fact that the direct injectors themselves inject fuel DURING compression stroke, after port fuel has been injected via, intake stroke.

Here we add boost, no matter how much timing you pull we might be reaching the limits of how much pressure each cylinder can handle even under small boost. There are a few other variables im not to sure of as well...

Are you saying you think the frs/brz will have that high of compression?

[suprachica79]

Originally Posted by Farred

Are you saying you think the frs/brz will have that high of compression?

If they are looking to getting ~200hp out of a 2.0l NA i4 then I would think the compression has to be at least 12:1. Which is what worries me about trying to run FI on this engine without some serious internals workup... I wish I would have boosted my 97 acura 2.2cl... compression ratio of 9.2:1, would have been boost city!

[markitect]

Originally Posted by suprachica79

If they are looking to getting ~200hp out of a 2.0l NA i4 then I would think the compression has to be at least 12:1. Which is what worries me about trying to run FI on this engine without some serious internals workup... I wish I would have boosted my 97 acura 2.2cl... compression ratio of 9.2:1, would have been boost city!

The direct injection should make this less of a problem. First because I don't think the compression will need to be that high, and second because DI allows a lot higher compression. Audi's 2.0T has 11.1 compression. Also Mazda has new DI engines coming out soon that run 13:1 compression on regular gas.

So with premium fuel, and 12:1(or lower) compression we should still be able to see at least 8psi of boost.

[madfast]

the ferrari 458 runs 12.5:1 CR. i honestly dont think they will go above that. yes the mazda skyactiv uses 13:1 (US cars) and 14:1 (world) CR but the engine also makes 150 hp. its an economy car tuned engine.