if you've got the $$$$$$$$$$$$, do a high compression (10.5:1 or higher) turbo setup with lower boost. you'll have a buttload of low end torque, & a larger turbo will spool up as fast as a small one, without the high rpm flow restrictions & heat that small turbo's have.

that downside of this is that you have to make sure it is tuned correctly, however, with the new AEM EMS & Hondata systems, its not as hard as it used to be

 

One interesting thing of note is to look at the pistons DSMers upgrade to. Stock is 7.8:1 or 8.5:1 depending on generation, and almost everyone upgrades to either the stock 8.5:1 2nd gen pistons or to a forged piston somewhere between 8:1 and 9:1. On a very very rare occasion 9.5:1 is used but certainly no higher.

Lower compression does require higher boost, yes, but you're still flowing relatively the same amount of air. DSMers have found that tuning lots of boost is easier that tuning small amounts of boost. If you think about it, it does make sense. Say 10.5:1 plus 5 psi nets you the same airflow and power as 8.5:1 plus 20 psi. This may or may not be true, I'm guessing based on what I've seen in action. Anyway, with the 10.5:1 + 5 psi, say you wanted to increase boost for even more power. If you're good and your setup is smooth, you'd be able to increase boost in 1 psi increments. So now say you have 10.5:1 + 6 psi which is about equal to, say, 8.5:1 + 23 psi, but say that's too much air flow, what if you wanted a little less? Running 5-1/2 psi is pretty damn tough. On the flip-side, though, 8.5:1 + 21 psi would be a smaller (and more feasible) step.

I sure hope that makes, I'm not quite awake yet but it makes sense to me.

And if you want more bottom end power, turbos aren't for you.

 

You have a good point in that more boost is easier to tune, but a trubo that makes that kinda boost and is reliable is not cheap. A 6lb SMALL turbo like a t3 or t4 or a t3/4 hybrid is a great little turbo that you can get 6lbs out of and not have much tuning issues on an all stock motor. I think thats what this guy is probably gonna do is use a small turbo on a stock block. With a T3/4 hybrid he could easily get 40-60hp out it with an air to air intercooler. 6lbs on a stock block isnt that hard on it, 20+lbs and i dont care how small the turbo is and how little CFM it makes, your gonna have to rebuild the bottom end for sure and probably the top end to be safe. For the cost of just the rebuild im sure he could locate a good small turbo setup that makes less than 10lbs of boost.

 

There are no 6lb or 20lb turbos, that's not how turbos are rated. If you put a turbo sized for a B16 @ 6 psi onto a Viper, do you really think it'll produce 6 psi for the Viper? Come on. Turbos are rated in cubic feet per minute (CFM), and CFM dicates boost pressure. If a turbo kit says the included turbo will provide 6 psi, that means the turbo will flow enough air on the given motor to produce 6 psi of positive pressure in the intake manifold.

Surf to:
http://www.turbofast.com.au/TFcompB.html

Since I have the information handy I'll once again use a B16 as my example.

Bore: 3.189 inches
Stroke: 3.047 inches
VE: 100% (to keep the math simple)

10.5:1 + 1 psi = 11.15:1 boosted compression ratio
10.5:1 + 2 psi = 11.79:1 boosted compression ratio
10.5:1 + 3 psi = 12.43:1 boosted compression ratio
10.5:1 + 4 psi = 13.08:1 boosted compression ratio
10.5:1 + 5 psi = 13.73:1 boosted compression ratio
10.5:1 + 6 psi = 14.38:1 boosted compression ratio
10.5:1 + 7 psi = 15.02:1 boosted compression ratio

8.5:1 + 10 psi = 13.60:1 boosted compression ratio
8.5:1 + 11 psi = 14.11:1 boosted compression ratio
8.5:1 + 12 psi = 14.62:1 boosted compression ratio
8.5:1 + 13 psi = 15.13:1 boosted compression ratio

After doing these calculations I see that I was off by a fair amount, my apologies. But my point still stands that 8.5:1 + 10 psi requires very nearly the same amount of air as the 10.5:1 + 5 psi. Not only that, but the effective compression ratio inside the cylinders and therefore the pressure felt by your headgasket and cylinder walls is nearly the same. (off by a very very small amount.)

If you were to match up an appropriate turbo for a B16 it won't matter if you run high compression or low compression, you'll still need the same air flow. Check out this page on calculation horsepower and air flow requirements:

http://www.turbofast.com.au/tfcalc.html

Notice they never ask for the compression ratio of the motor, it simply isn't required. The engine still has the same displacement, still draws in the same volume of air. Same volume of air, same turbo requirements.

For more information, read this post:
https://www.honda-acura.net/forums/s...316#post333316

 

Very interesting, but i have never heard of a turbo having 100% effeciency. I know you used it to keep the math simple, but it also screws up the #'s a bit. and some turbos have internal ir external wastegates that limit the boost it can make. You can get around that by either removing it or using an external blow off valve sometimes. I know my friend did on his 99 F350 with a power stroke, he cute the line for the wastegate and got 5lbs more boost out of it and is running upwards of 27psi on his truck. I think the Eclipses make like 8-10lbs of boost and are only getting like 50-60hp more than the NA eclipses, but they are totally different engines as well. Its really hard to figure out just how much HP your gonna get either way with out puting the turbo on and doing a dyno pull.

 

Wastegates can be controlled and held shut by boost controllers in order to raise boost levels. Blow off valves have nothing to do with control the level of boost a turbo puts out, and a blow off valve is inductively "external" by definition, unless it's a bypass valve, which gets routed back to the intake piping before the turbo inlet.

 

You guys are missing the point a bit.

Turbos have an effective range where they move the most amount of air with the smallest heat generation. The translation to how many PSI that is depends on the size of the engine.

Now, how does this help to make power? It's a combination of putting more oxygen in the cylinder, keeping the intake charge cool [so that you can go back to the first item of having more oxygen in the cylinder] , and most importantly, raising the peak cylinder pressures during compression.

So far, I haven't mentioned compression ratio at all [current case exlcuded], and that's because for the most part, the info so far on this thread is accurate. So why, then, do most people view a lower compression engine better for boost?

The answer is actually pretty simple. You can only increase the cylinder pressures during compression so much before gasoline spontaneously ignites [detonation, pinging, whatever you want to call it, it's bad]. What happens, then, is that when you boost a high compression engine, the boost makes a larger effect on the peak cylinder pressures than the same boost level on a similar engine with a lower compression ratio. So why, again, do most people view a lower compression engine better for boost?

With a lower compression ratio to deal with, you can inch yourself closer to the maximum cylinder pressure for the given fuel you're using easier than you can with the relatively constrictive range of boost you can deal with on a high compression engine. The downside, again, is that you need a turbo that will operate efficiently to provide the necessary amount of air according to the three guidelines I covered earlier.

Another thing to keep in mind is that anytime you compress air, it gets heated, and since you make your power from the rapid expansion of air in the cylinder, the lower the beginning temperature theorhetically yeilds the greatest change in temperature in the cylinder, which means the fastest/most forceful expansion, which equals power. I take this to mean that if you can compress more air more efficiently and then compress it in the cylinder with the least amount of extra heat generated, the more power you will make. So far, most turbo engine manufacturers/racers agree with this.

In this forum, pretty much anyone that mentions CFM talking about a turbo is likely to be someone that I've told/taught about boost. CFM [cubic feet per minute] is a measure of how much air the compressor will flow efficiently [ie- low temperature increase], and so that is the context it is mentioned, not as a literal definition of how much air the engine will ingest in a cycle, only how much air it can move effectively enough to be useful.

 

:bowdown: Harry, you're a hell of a lot better teacher / explainer than I am.

 

Where where you when this thread first started Haryy, your always the genius that can answer it all, you never fail.

 

I thought I'd sit back and see how far you guys would go before stepping in. I've been doing that on a lot of threads lately if you notice due to my busy schedule.