TC- Do you really feel that the belt is slippng that much? Or just a guess? If belt was not slipping than the boost at the compressor would be greater? With resistance in system being greater. Correct?

Keep it comming.

tomcat..
i get it, with my twin, naturally aspirated, 350's...but how can we put it into layman's terms...so ALL enthusiasts can apply that knowledge...my buddy has a 24' Outlaw with a 454 Mag...can we help him?
C

Turbojack - I'm just being conservative and guessing that there is some belt slippage. If there is no slippage, then compressor RPM is higher and that higher RPM curve is going to cross the system resistance curve at an operating point with slightly higher discharge pressure and CFM. The resistance curve of the system does not change, you're just forcing a little more air through the system, so discharge pressure has to be higher.

CG - High flow flame arresters, bigger carbs, high rise intakes, ported cylinder heads, big valves, big cams, better exhaust...in other words, the whole high performance engine industry, is aimed at reducing the system resistance that the air moving device (piston and cylinder) have to work against. What the average enthusiast can learn from our discussion is how to decipher some of the claims made for some of these products.

For example, if I tell you that a certain flame arrester flows 33% more air than your stock flame arrester, what does this mean, and how will it help? First of all, I assume that this claim means that the flame arrester flows 33% more air at a given pressure. Sounds great, but it doesn't mean that the engine is going to get 33% more air because the flame arrester is only one of many components in the intake pathway that present resistance to air flow. It's the total resistance that counts, since that is what the piston and cylinder is working against.

So if the flame arrester is only a small part of the total resistance, even a large improvement in its ability to flow air will not make much of a reduction in the total system resistance. This is why it's common to hear of people changing a single component and seeing no change in performance.

If reducing system resistance is so good, how do you do it?

There are two ways to reduce system resistance so that the compressor will flow more air at the same compressor RPM. The first way is to change cylinder heads, cams and exhaust so that the engine breathes better. If you have ever looked closely at Procharger's specs you would see that the HP500 kits take less boost to achieve the same HP as the stock 502 kit. That's because the engine breathes better to begin with. But one of the main attractions of supercharger kits is not having to go into the engine. So what can you do with the supercharger kit components to reduce their contribution to total system resistance?

First of all we have to know how much of the total system resistance comes from the supercharger kit components as opposed to the engine. In the post above we calculated for the Vortech kit that the compressor was delivering 1100 CFM @ 10 psi, but intake manifold pressure was only 7 psi. So the ducting, elbows, carb box and carb had a combined resistance or pressure loss of 3 psi. There's not a lot you can do to the carb to reduce it's resistance, and you need the pressure drop through the venturis to pull the fuel, so that leaves the carb box, elbows and ducting.

I have written a little spreadsheet computer program that calculates the resistance or pressure losses in these components. The key things are the cross-sectional area of the component (and therefore the air velocity through that component), and the loss coefficient for that type of component. I made educated guesses for the losses and then revised them slightly based on Vortech, Spearco and my own flow bench data.

Here's how the losses at 1100 CFM stack up:

Duct - 0.073
Elbow - 0.418
Elbow - 0.418
Box - 0.783
Carb - 1.259

Total - 2.951 psi (~3 psi as noted above)

I happen to have spent a lot of time developing a new compressor to carb arrangement for my improved intercooler setup. Here's how the losses at 1100 CFM look for the improved setup (no intercooler):

Duct - 0.049
Plenum - 0.865
Box - 0.019
Carb - 1.259

Total - 2.192 psi

The improved arrangement has 0.759 psi less resistance. We haven't changed the engine so 7 psi in the intake manifold will still push 1100 CFM of air through the engine. But the compressor doesn't have to work as hard to get that air to the intake manifold.

The compressor discharge pressure only has to be

(7 + 2.192) = 9.192 psi,

not 10 psi, to move 1100 CFM through the system.

No change was made in the carb; all this improvement occurs between the compressor and the carb. The key was to get away from the small cross-sectional area of the duct and into the large cross-sectional area of the plenum as soon as possible.

Now we can draw the new system resistance curve on the compressor map. We find the 1100 CFM line and mark it's intersection with the new pressure ratio.

New pressure ratio =

(9.192 psi + 14.7 psi)/14.7 psi = 1.625

The new blue curve drawn through this point is lower than the red curve based on the Vortech magazine test. Since we have not changed the pulley on the compressor, we extend this new curve to the 40,000 RPM line to find the new operating point for the compressor and system.

The new operating point looks to be about 81 lb/min of air flow vs. 79 lb/min, maybe an extra 20 HP on top of 780 HP. Such a small gain isn't worth the effort, but the difference between the two systems changes drastically when you add an intercooler.

Next time, reducing system resistance on an intercooled setup.

Three Steps Forward, Two Steps Back

Something very interesting happens when you add the extra elbows, expansions and contractions to the standard ducting arrangement when you install an intercooler. All of these additional components, including the intercooler core itself, add resistance to air flow between the compressor and the carb. You don't think about this because the effect of cooling the charge air is so beneficial, but it can be calculated and drawn on the compressor map.

The computer spreadsheet, confirmed by flow bench testing says that to push 1100 CFM of air through the standard intercooled setup takes 4.662 psi. So the new compressor discharge pressure is:

7 psi + 4.662 psi = 11.662 psi

The new pressure ratio is:

(14.7 psi + 11.662 psi)/14.7 psi = 1.793

Locating this point on the map and drawing a curve through it we discover that the curve passes through the 40,000 RPM line at less than 1100 CFM. This is our new operating point; about 1040 CFM. The higher resistance has reduced air flow and would probably cost about 40 HP if you tested without running water through the intercooler. Of course running water through the intercooler gets this HP back and more, but to understand the difference between the standard intercooler setup and the improved setup, we compare their resistance to air flow alone.

20hp in a cat mabe = 1 mph.

Did you take in account the larger pulley thus less HP used to run blower? While I am thing of it, do you know how much HP it take to turn a centrifical blower verse say screw or ?? blower?

Now how does our reduced resistance setup fare when we add the intercooler? Because the plenum has already increased the cross-sectional area for air flow to the size of the intercooler, and the modified carb box retains that same cross-sectional area after the intercooler, we really only add the resistance of the core itself.

The computer spreadsheet says to push 1100 CFM worth of air through the low resistance setup takes only 2.319 psi. So the new compressor discharge pressure is:

7 psi + 2.319 psi = 9.319 psi

The new pressure ratio is:

(9.319 psi + 14.7 psi)/14.7 psi = 1.634

Locating this point on the compressor map and drawing a curve through it we find that we have to extend the curve to reach the 40,000 RPM line. Dropping down to the CFM scale we see that we have about 1120 CFM. Compared to the standard intercooler setup we have improved air flow by:

1120/1040 = 7.7%

which is good for about 60 HP.

Now adding water to both intercooler setups will add even more power, but the 60 HP advantage will remain as long as the intercoolers do the same job of heat removal in both cases. There is some cause to believe that the improved intercooler setup may actually work better since air flow is distributed more evenly across the face of the intercooler by the plenum as compared to the ducted intercooler, which tends to concentrate flow in the center of the intercooler. But that isn't something we can figure out on a compressor map.

Next time, what happens when you turn on the water?

Turbojack - All comparisons are being made at a compressor RPM of 40,000 so I am ignoring differences in HP to drive the blower. I don't know how much HP a centrifugal compressor needs to move this much air. I'm guessing around 50 HP.

When you look at Vortech's data and see how much HP was made with how many lb/min of air, and assume a BSFC of 0.5, there's always less HP than the air flow would suggest. The difference is the HP to drive the blower, but without BSFC numbers at each point, it's just a guess how much.

The best way to measure this would be on the test bench when they're making a compressor map by spinning the compressor with an electric motor. Measure the amps and you've got it.

I'm trying to be conservative on my estimates of improved air flow and HP. What I learned on the flow bench with a crude mockup suggested that it was worth pursuing. The next test with the real thing will be the crucial one. As you know I'm hoping for an overall improvement of 10% more HP, but we'll see.

Also considering the midrange boost levels and the slightly lower by about 50% boost/pressure ratio, it looks that the V7 YS blower is a little small and you need a larger blower and move the working area into the most efficient island. By moving into the more efficient areas of the blower you will also pick up HP.

Vortech's web site doesn't have the curve for the V-4 J or X trim. These might fit the application better. I might have the curves somewhere, I'll check.