I see quite a number of high hp claims from various tuners using 700, 800, and 800+hp packages. It's though to tell if these claims are using pump gas (91 Octane) or all race gas. What is the upper limits of power (6TT can make on pump gas? Is building up the engine internals necessary for pump gas?
Thx

 

Probably around 650-675

No internals needed till about 700-750. This is a stout motor.

 

I have heard that 700+hp is the limits of the stock internals/rods. I guess my question is....can you actually make 700+hp reliably on pump gas? Don't mind going through upgrading the internals if I can make that much power on pump gas.

 

In short the answer is no: You will not make big power w/ this platform if you are limited to 91 craptane gas.

The key to making big power is safely running boost w/ out detonation.

I can safely run a max of 1.1 bars on 93 and would be risking engine failure if I tried to run 1 bar at 91....I probably could only run .9 and be completely safe. I have pretty much everything you can have on a stock block 996 motor (GT 30's, fuel system etc.). Now, if I run race gas thing change. On a 50/50 mix of C 16 and pump fuel, or say 104-109 unleaded I can safely run 1.3 bars. On pure C 16 I can run 1.5 bars.

My car makes 35 more rwhp for each .1 bars, so the difference between 1.5 and .9 is 210 rwhp (675 hp vs 465).

If you only run **** gas my advice is to go w/ a big block american V 8. However a new option is meth although I want to see some other people run it for a while before I try it.

The above is why I live in Tx and not CA (where I was originally born).

 

On one of my previous 996 TT X50's, I ran the EVOMS IV kit on 91 Octane and it ran 1.2bar all day. There wasn't any detonation/pinging at all. Are you saying .9 bar because of the big turbos you're using on your GT2?

 

Yes, the smaller turbos pose less risk and of make less power. I know what car you are talking about. It is a steal! Buy it, and get a drum of C 16. It is arguably the fastest 996 on the board, the only reason its verified 60-130 is slower than mine is that I am a better driver than its former owner.

 

dr is texas still in the union??? if not the speed limit may go and the smog laws ?? i'll be movin in if i can get a visa from calie

 

I think there is more to this than how much max HP you can make, you also have to consider how much power (hp and tq) can be made and where in the rpm band.

I am close to the limits of the internals because of tq in the lower rpm's, this is the limitation of the factory rods and wrist pins.

 

I will let you know within a week or two....

My K24 91 octane Dyno is below.

 

Ari: I've been wanting to see a dyno sheet on what is essentially the Stage I figures on an X50 running a flash with the wastegate springs....I was expecting something close to 525, and this seems reasonable. I see you go a bit rich between 70-80...that must be when you first hit your WOT in second?....but you're back to pretty close to stoich after that. I would like to see some rpm in the chart.

Do you feel this is pretty representative of the performance curves for the tunes offered by the various folks like EPL, UMW, GIAC etc? (using 91 octane as a baseline)

 

The runs were all in 4th gear in RWD mode. Unfortunately the facility didn't know where to pickup an RPM signal so no torque or RPM curve. Sounds kinda silly actually since they could just plug into the OBDII port.

Either way the car had the following mods but was otherwise a totally stock X50 car.

GIAC "pump" 91 octane flash, EVO intake, Billet diverters, Remus Exhaust, Speed Gallery upgraded wastegates. The boost went 1.2 - 1.1 - 1.2. I put about 15K totally trouble free miles on the car after that (except blew two MAFs until I installd the evo waffle fix in the intake).

Here is dyno Video: http://members.dslextreme.com/users/...Dyno%20Run.wmv

I don't think K24 cars make more than 550-560 Crank HP on a good day. Competition and owner pride has pushed that to 600HP...

I'd bet you get similar numbers with your similar setup.

 

Hey all,

I'm new to the Porsche community, but I'm not new to car building. I'm an engineer by schooling, and have built many turbo cars and assisted in countless others. Hopefully this post will be helpful to some.

The question of "how much power can I make on x octane" is more nuanced than most know. Of course the short answer is: until it detonates. What's detonation? The uncontrolled burning of the air fuel mixture, typically set off by pre-ignition (ignition of the mixture in advance of the spark plug firing), but an engine can detonate from the spark plug firing too. Typically it'll be a combination where a hot spot preignites and the spark plug starts a completing flame front that collides with the preignited front. That said, in most engines you can't hear it detonating. And if you've changed the harmonics of your engine (sometimes hanging different headers can do it.. clutches and flywheels almost always do it), your ECU knock protection is handicapped. So how do you predict where it'll detonate?

There are two things that must first be understood: compressor efficiency and dynamic compression ratio. First, compressor efficiency.

Most people know that bigger turbo = more air flow, and that's true, but most don't understand why it's true. It's true because the larger the turbo, the slower the impeller needs to turn to compress the same amount of air. The slower the turbine, the less heat is generated, and denser air enters your engine.

Although the ideal gas law formula is for static situations, it is still instructive here... Pressure*Volume=constant*moles of gas*temp, or PV=T for our purpose. The volume is constant, so P is proportional to T. As temp increases, so does the pressure. Density = Pressure/Temp. So if the pressure is constant, say 1 bar, the lower temp of the bigger turbos means a higher air density and thus more power.

Ok no more math.

Dynamic compression can be thought of as your cylinder head pressure. A fairly accurate rule of thumb is dynamic compression ratio = static compression ratio + PSIg/3. (Oops, I lied about the math) Thus, for every 3 PSI above atmospheric, the ratio is upped one point.

So how does it all come together? It's a combination of pressure and heat.

The higher the cylinder pressure, the more likely that the fuel charge will ignite. The higher the cylinder temp, the more likely that the fuel charge will ignite. Thus, high pressure + high temp = higher chance of detonating.

This is probably a good place to quickly go over gas octane. The higher the octane, the more stable (i.e. the higher resistance to ignition) the gas. Thus, higher octane is harder to ignite. A very desirable characteristic in a high compression, high temp engine.

Ok, enough of the theoretics.. how does this play in the real world?

Well, generally 91 octane gets away with 13.5:1 dynamic compression. But like I said, it's nuanced. A lot of that depends on the engine generally and the specific engine -- are there natural hot spots in the engine or head pitting in the specific engine? If so, that engine will detonate far earlier than a non-pitted motor. Also, a more efficient turbo (cooler air) can run a little more boost (higher pressure, lower temp).

From what I understand, the factory 996TT is 9.4:1 static. Running the factory .7 bar, that's 12.8:1 dynamic. Thus, .9 bar would give you 13.5:1 and is generally considered safe. Some cars can even run up to 14.5:1. I'm not familiar enough with Porsche yet to give my opinion on their safe amount. Suffice to say, there's a lot of misleading conjecture and uninformed opinions floating around.

Some may be wondering how some cars run more than that seemingly without problems. I would submit to you that most are detonating, but not enough to cause catastrophic failure. Often, they're damaging the rings and pitting the head. The engine begins to wear and never really fails -- it eventually has so much blow-by that it's no longer usable. Additionally, factory ECUs can come to the rescue by changing timing and/or adding fuel (cooling the cylinders).

Notice the one term not mentioned... Horsepower! As you can see, it's largely irrelevant to the threshold detonation question. What it is relevant to is margin for error. Of course the more power that is made, the more fuel that is in the cylinder. Thus, the detonation is that much more violent because it has that much more fuel (energy) available. Detonate one time at 1200 HP and that's most likely all that engine wrote.

It's late at night, so forgive me if some of it was confusing. Hopefully that helps. Bottom line is there is no one answer to "what's the max power at x fuel."

 

Dennis: This is the most concise and layman-friendly explanation of the subject matter I've seen. I'm thankful that I was up till midnight to see this post. You have a great writing style...understandable with good continuity and flow....now if the information is all correct it's a keeper.

Plus rep point to you my man....

 

+1 Ditto...

 

Hey Dennis - +1 on the great write up. Being an engineer (Mech) also I believe you have hit the mark on all your points. To add one thing, on 93 octane the max dynamic compression should go up to about 15 (I am basing this on memory, not actual in the book info) so the boost should go up to about 1.2 bar with no problem. Am I close?