You got it. Broad torque curve beats peaky hp all the time. Doesn't matter how you get it. That's what made the old Hemi's great vs equivalent Chevy's and Ford's- flatter torque curve with equal hp. Now if I could just afford the new turbo Porsche instead of just get to ride in it or get the new E55.

 

Beautiful write-up. Thank you for taking the time to post all of that, I know it had to take a long time to write it all out.

 

thanks everyone for the good dispute and educational thread.

i guess i am not going to quote any more specific posts to argue because a lot of it is coming down to opinion or arguement left over with no real physical evidence from either approach.

i personally do not agree with the whole heat disadvantage... while turbos generate a lot of heat i find it something that does not cause any problems if dealt with accordingly, such as heat wrap and a fair sized intercooler with fair sized turbochargers.

other than that... i cant think of anything left to argue.

-charles

 

I can live with that... I do think it creates more heat but its nothing you cant deal with... and I dont think its anything thats going to cause problems

-non

 

In my personal opinion heat is a huge concern when dealing with FI. Basically heat will lead to detonation, which will lead to a blown motor. 350z have high compression engines, so basically with boost heat is already a minor issue. Finding ways to control the heat is very time consuming and a huge headache. I know this first hand. Yes, there are ways to control the heat, like colder spark plugs, the gap of the plugs, timing, octane, compression, intercoolers, etc. But, what it all comes down to is tuning. The last thing you want is your inlet temperatures to be to hot, and you start getting detonation. You car will retard timing by itself, because of the knock sensors, and you may even ruin your whole bottom end, if you do not control the heat issues. Remember, heat and lack of fuel are the two main causes of detonation.

 

The turbo will retain more heat in the engine. It's just a fact that turbo restricts the exhaust flow. With less flow comes more heat being left in the engine, it has to go somewhere, the cooling system, spark plug or retained in the cylinder.

A blower does the same thing but not the extent of a turbo, when ever you make more power you will be producing more heat. The percentage of mechanical work produced from combustion is less than 35% so 65% is lost in the form of heat. So as the HP levels increase so does the heat.

With heat comes detonation and pre-ignition problems, this applies to both types of FI but I think more so with a turbo vice a SC. As you can add a header(s) to an engine to reduce the back-pressure and in turn removes the heat quicker. Or use a bigger turbo(s) to flow more but with that comes lag.

Too both forms of FI there are drawbacks.

 

...basically tuning is the key. =)

 

Maybe I'm weird, but on my big turbo cars I liked the lag on the street. I personally like to feel the boost build, it's a great feeling...

I mean if you're drag racing (which I did a lot) you stay out of lag RPMs anyway, and just normal driving it's fun boosting around.

Now on track days it sucks trying to make everything up on the straight aways, but overall for the street turbo is still a good time to me.

My supercharged V8 was fast, but it sucked always being under boost IMO, I liked to be able to tune the turbo more.

However, like I said before, I'd never turbo an NA car again, only build factory turbo cars...

 

I'm confuse when people say the s/c is always under boost? They are vacuum operated, so as long as you are not giving it load then you will not see boost...you will be in vacuum. Can some one help me out on this?

 

Well on a turbo car you can turn the ****, or not gas it, and remain civil. However, on a supercharged car like my Camaro, you are always raising hell no matter what. Even if you're not on the gas the charger always whines and the exhaust is always rumbling...

 

On the ATI setup there is a bypass valve that works on manifold vacuum/boost signal. As long you are not at WOT the bypass is open and venting the boost off. The vacuum pulls the valve open and at WOT-0 vacuum/0 boost it is closed and you build boost and if it's a manual car then between shifts it vents boost like a BOV.

On an old roots type blower I could see it being a pain. I am guessing your Camaro was a 1st or 2nd Gen car, not a fuel injection car.

 

Amen, AgZ-you got it about the by pass valve. The Rootes/Eaton though are a pain to work with this. And they do build intake heat a lot.Plus the damn things were developed for low rpm diesels and dragsters.

 

I think the new Fords (Slobras and Sparkys) have some sort of bypass valve on the Eatons. I wish I had saved the site I read that with the by pass open it only takes .5 hp to turn the blower. I would think that is about the same as the restriction the turbo has on the exhaust flow.

Nothing is free in life and making extra power is always a game of trade offs.

 

Great post, but to inject another view on the TT vr SC list...

"1: More HP with less work from the engine."
On a stock internaled VQ the max Hp is determined by the limits of the engine. The difference between crank load of an sc and the backpressure of a TT are negligible and Hp/work shouldn't be a factor when deciding between the two. Better gas mileage will only be acheived with a TT as long as you stay off the boost, and the SC owners have more control over how much stress they put on the motor with their right foot. When the TT boosts(all at once) it puts much more stress on the motor than linear power SC's. If you must pick a winner in this catagory, I would say SC.

"2: SC systems boost with less control."
As far as driving the car goes...boost on SC's is always there. You control the linear power with your right foot. The most control you have over spool-up is accomplished at the work-bench. In high Hp applications, the tune-for-power aspects of the TT are awesome, but on this application, nearly worthless.

"3: Reliability."
Turbo systems have always been known for complexity, cost to maintain, and unreliability. This is why auto manufactures would rather SC their cars. The 1990's was somewhat of a failed experiment with turbocharging factory cars.

"4: Noise, SC cars make a lot of noise."
True...but...come on, feel the noise...

"5: The ONLY downside from the turbo system is the LAG."
IMHO, turbos are better for Road Racing wher your rpm's are always up and your always on boost.
SCs are better for drag racing where you need power from a stop.
For high powered streetcars, the tuneability and potential of a turbo would get me to look past it's complexity and unreliabilty.
For the Z(which is limited to 400-450Hp by it's rods) I would prefer the power on demand low maintenance SCs.