ALFAGTV6.COM

[Greg Gordon]

That's an interesting engine. I guess I never heard of it because we didn't have the 2.0 turbo in the U.S. For that matter we never had the 96' GTV.

I suggest you start a new topic in the performance section and ask about turbos there. Mats or Barry will probably help out. I try to stay out of turbo sizing discussions.

Greg

[q4_fre]

Ok, thanks!

But for the matter of low vs standard compression?

The engine I have been using now have all standard internals, and I want to keep them a little longer.. Should I go for low compression & high boost or standard compression 9,5:1 if using 3l and low boost?

Is it like it just have to go wrong with 10-12 psi on an 9,5:1 engine? Or will maybe the ignition need to be so retarded that I will make more power with lower compression and more boost?

I cant see other than that an 3l standard engine with a little breathing help will make for an fantastic allround strong engine, no such ketchup effect as the low compression engines have?

[q4_fre]

The engine is now running. 3l, 9.5:1 compression, QV cams. Already I am seeing around 11.6psi boost.
Started with an basic map which gave around 10-15degree ignition at 0.8bar. Then the engine would not work at all, feels like you are pressing the brakepedal. Changed the ignition to 20degrees, that suddenly gave wheel spin on 3rd so it seems to me that it need to be somewhat advanced.

But strangely, I have not heard any pinging yet, even on that much boost and so high compression.
The internal wastegate on my turbo will not give less than 0.8bar boost. I can feel that it pulls real good at 0.5bar (~7psi) but as the pressure increases it sort of stops to pull.
Hope that some further tuning will make this better. But so far it seems to me that the 2.7l gave way better performance. Though not that fast on the boost, much better response in the 3l..

[Duk]

The engine is now running. 3l, 9.5:1 compression, QV cams. Already I am seeing around 11.6psi boost.
Started with an basic map which gave around 10-15degree ignition at 0.8bar. Then the engine would not work at all, feels like you are pressing the brakepedal. Changed the ignition to 20degrees, that suddenly gave wheel spin on 3rd so it seems to me that it need to be somewhat advanced.

But strangely, I have not heard any pinging yet, even on that much boost and so high compression.

I'd like to point out that 11.6 psi and a 9.5:1 (static) compresson ratio in a 12 valve motor, is less likely to cause detonation/pinging issues than 11.6 psi and a 9.5:1 (static) compression ratio on a 24 valve engine. Even with the (probably) better combustion chamber deign of the 24v being taken into account.

Plain and simply, a 12 valve (2 valve/cylinder) motor will have less actual mass air flow per induction stroke than a 24 engine (4 valve/cylinder) will achieve at any pressure, atmospheric or above.
The small/poor flowing nature of the factory inlet ports are (probably) helping to keep detonation at bay. Improving the flow of the inlet ports could well result in detonation issues at the same boost pressure.
It is for this reason, and others like bore size, combustion chamber design, camshaft specs. etc. in my opinion (I hope everyone likes my big, fat disclaimers ) that those charts that show boost pressure versus compression ratio (for a given fuel octane), should be used as a guide only.

[Nikoror]

Duk can you provide some more info on the subject of more air -> less likely for detonation to occur. I honestly find it difficult to understand...

the way I understand it: 12v -> flows less -> less flow with xx psi boost -> less hp. however, the smaller amount of air is compressed to the desired pressure, so it is hotter by the same amount as the same boost on a better flowing engine -> hot air+high static cr -> detonation. with this said 12psi and 9.5static on some NA valves should be okay

[Duk]

the way I understand it: 12v -> flows less -> less flow with xx psi boost -> less hp. however, the smaller amount of air is compressed to the desired pressure, so it is hotter by the same amount as the same boost on a better flowing engine -> hot air+high static cr -> detonation. with this said 12psi and 9.5static on some NA valves should be okay

Hi Nikoror. Assuming that you had a mythical 100% effeciant compressor (not likely to happen any time soon ), then all the heat that came from the forced induction would come from the actual compression of the air. Therefor, it wouldn't matter if you were pumping air through a 1" pipe or a 3", the heat associated with forced induction wouldn't be more becuase of a smaller/less flowing orrifice, but the heat that comes from the actual compression of the air (or any gas, for that matter).

On that note, Gregs book on Supercharging provides some excellent facts and figures that would help.

[q4_fre]

Have now tried some more. The same story with more boost. Up on 1bar (14-15psi) now. Low ignition 5-15 degree you can do whatever you want with the fuel, more or less, nothing helps. When you put the pedal down the engine will not pull right, lots of misfiring, bangs and small shakes. But when I raise the ignition to about 20degree it helps. Still not so much to do with fuel, it stays the same. Then I tried to raise to 25-26degrees, around 10.5afr, it starts like the other times, misfiring and shakes suddenly it sort of loosens up and starts to pull real hard. Then I adjusted down the fuel to about 12afr, same story at the start, but when it loosens it pulls really really good. I can put the gears, 2nd, 3rd and halfway through 4th the fuelpump is empty. How is it that it can help with so much ignition?
--I can not hear any pinging in any of the pulls--
Thought that 9.5:1 in compression never would cope with that amount of boost on regular gas (98 octane).
So when it first started I thought of any ways to lower the boost. But now I am just really confused of how this is possible, how can more ignition advance help? I thought it would just make matters worse, but thought, heck, lets try it one or two times..

[killaz]

I'd like to point out that 11.6 psi and a 9.5:1 (static) compresson ratio in a 12 valve motor, is less likely to cause detonation/pinging issues than 11.6 psi and a 9.5:1 (static) compression ratio on a 24 valve engine. Even with the (probably) better combustion chamber deign of the 24v being taken into account.

Plain and simply, a 12 valve (2 valve/cylinder) motor will have less actual mass air flow per induction stroke than a 24 engine (4 valve/cylinder) will achieve at any pressure, atmospheric or above.
The small/poor flowing nature of the factory inlet ports are (probably) helping to keep detonation at bay. Improving the flow of the inlet ports could well result in detonation issues at the same boost pressure.
It is for this reason, and others like bore size, combustion chamber design, camshaft specs. etc. in my opinion (I hope everyone likes my big, fat disclaimers ) that those charts that show boost pressure versus compression ratio (for a given fuel octane), should be used as a guide only.

Disregard ignition, fuel and heat, detonations are more associated to poor combustion chamber design. Multi valve heads have the benefit of increased combustion efficiency, therefor it is common to say that they "burn fuel faster" than (in this case) 12v.

24v is decades better design than 12v (no matter; NA or FI).

[Nikoror]

Therefor, it wouldn't matter if you were pumping air through a 1" pipe or a 3", the heat associated with forced induction wouldn't be more becuase of a smaller/less flowing orrifice, but the heat that comes from the actual compression of the air (or any gas, for that matter).

On that note, Gregs book on Supercharging provides some excellent facts and figures that would help.

Hmm... The heat comes from the compression. However, when you pump in a 1" pipe you will have same pressure, but less flow (actual air mass) when you pump in 3" you will have same pressure with more flow (more air mass). So 3" (i.e. 24v) engine will make more power on same boost as it will flow more air.
My question was about the relationship mass air flow -> detonation which you mentioned in your first post.

I don't have Greg's book (yet), but a number of other books related to turbo/superchargers/boost and a few textbooks on Thermodynamics and Fluid Dynamics...

On topic: on the 12v 6cylinder my experience is that it requires a good amount of ignition advance (30ish deg at max torque). Advance power easily outpowers boost power, so if you have to dial ignition back a lot to get no detonation at high boost, you could get LESS hp than with less boost and good ignition timing. A lot of ignition is usually a sign of bad combustion chamber design

[Mats]

Mass flow can be the same but speed will be higher in the small pipe.

[Greg Gordon]

Both DUK's and Nikoror's comments are technically correct, although they are expressing things differently. With all other variables fixed, a 24 valve Alfa V6 will have lower boost than a 12 valver with a given amount of air flowing out of the supercharger. Or you can look at it like this, with the same amount of boost (all other factors constant) there will be more air entering the 24 valver's cylinders. This is exactly what DUK said.

Put yet another way. With a 80 cubic inch supercharger at a 2:1 drive ratio, both engines will be getting about the same weight of air however boost will be lower on the 24 valver. The weight of air will favor the 24 valver because lower boost generally means lower temps.

Boost is essentially a measurement of an intake restriction. So almost anything we do that reduces that restriction will lower the boost. This includes more displacement, more valves, bigger valves, porting, etc.

To further explain this, consider this fact. Supercharger compressor maps are often created by spinning a supercharger blowing into the atmosphere and slowly closing off the outlet via some sort of sliding plate to simulate the restriction of an actual engine. The smaller the outlet hole, the more boost. The same thing is true with our engines. The smaller outlet hose essentially simulates a smaller engine.

I am not going to get into the combustion chamber design discussion.

Greg Gordon,
www.hiperformancestore.com

[Nikoror]

Greg, I think we all agree on what you are saying.

My question was related to:
/quote Duk
Improving the flow of the inlet ports could well result in detonation issues at the same boost pressure.
/unquote

Can anyone explain this?

[Nikoror]

Mass flow can be the same but speed will be higher in the small pipe.

In a laminar world - yes. In an engine... unlikely (specifically with 1" and 3")

[Mats]

Uh, what?
There is no laminar flow anywhere near an otto engine as far as I know. Flow losses in the pipes are not huge if you have nice bends even in quite small diameter pipes unless you go to silly extremes like a 1" pipe that no-one would even use even for a single intake barrell.

[Greg Gordon]

Nikoror:

DUK is saying that at a given boost level if you improve inlet flow, via porting, 4 valve per cylinder heads or whatever more air will enter the cylinder. His point is that more air in the cylinder increases pressure during compression increasing the chance of detonation with all other factors equal.

I think in a perfect world that's a sound theory. Due to combustion chamber variables between the 2 valve per cyl head and the 4 valvers, I am not so sure...


Greg