adunlap

iTrader: (2)

So what is the point of flow on a turboed car? It's not like being stuck with a blower where your limited (somewhat) to how much air the unit can move. Alot of people put larger intercooler piping, throttlebodies, manifolds just to say they can make an extra 50hp at 15psi where somebody else might have to crank it to 17 to make that number. But it's all just volume of air--moving faster in smaller volume or slower in greater volume. Kinda like electricity. High voltage or high amperage. It's the wattage that matters.
You could argue that greater energy is required to move the air at higher psi which creates more exhaust backpressure, but how much and is it really significant?

I'm just rethinking my bridgeport plans right now. I've heard that bridgeports require more fuel than stock, but that seems to be assumed because most all of these cars run speed density not maf. I think that an air flow meter would say that the same mass of air is being injested for the given HP level.

Just something to think about.

BLUE TII

iTrader: (9)

Your basic assumption that the turbo compressor is not a restriction is incorrect.

The compressor can only move so much air at any given rpm and that is why a 2 rotor or 3 rotor engine make the same peak power if they both use the same turbo. A 3 rotor can just use a larger turbo and have the same lag/boost threshold.

Anyways, if turbo choice is open the point of FLOW is this; if you decide 35psi boost is the most you can run then your car will be slower than another car running 35psi boost with better flow...

Evil Aviator

The Wankel rotary engine tends to be a "high-rpm" engine. Turbos that are designed for a similar-displacement 5500rpm piston engine will not flow enough for an 8000-10000rpm rotary engine.

Turbos also have a flow limit, but it is not usually printed graphically on the compressor map like the surge line, but rather textually. For example, see this T66 compressor map states the turbo has a max flow rate of 72lbs/min:
http://www.turbocharged.com/catalog/compmaps/t66.html
The turbine A/R ratio will also affect the flow rate, but this is more difficult to calculate.

The plumbing between the turbo and engine creates a pressure drop. For example, 0.2psi for the first bend, 0.4psi for the intercooler manifold, 2.0psi for the intercooler core, 0.4 psi for the remaining bends and restrictions, which causes the compressor to operate 2.6psi higher to deliver the desired MAP. This higher operating pressure ratio requires the turbo to rev higher, increasing lag, and also probably putting it into a lower efficiency range which will reduce the density ratio and therefore reduce the power output of the engine. If piping is part of the cause for the pressure drop, then changing to a larger diameter pipe may reduce some of the pressure drop, increasing the performance output. Piping that is too large can also reduce performance, so it is a balancing act that sometimes takes some practice to work out.

I would hope that a bridgeport engine creates more hp than a stock engine. Therefore, it will require more fuel. I don't see how that is so difficult to understand, lol.

Tom93R1

iTrader: (2)

Horsepower is very directly related to the volume of fuel and air, so in two different motors if you can force the same amount of air and fuel into it then you will get the same power. Now think about blowing through a straw or blowing through your mouth. You may be able to generate 2psi of pressure, but its still going to take you some time to blow a lung full of air out through that straw. You will need significantly more pressure to exhale through the straw at the same rate you exhale through your mouth, turbos are the same way.

For example, a stock FD runs 10psi of boost and makes about 220HP at the wheels. We had a car up on the dyno a few weeks ago that is ported and has a bigger turbo, IC, and everything to go with it. It made 340HP at 9psi. Granted with the stock turbos and ports you could get 340, but you would be running 18psi and no way could you do it with stock exhaust and all the intake plumbing. Now you can port that motor, upgrade IC, exhaust, and get 400HP at 18psi still with the stock turbos.

If you want power flow is indeed very important! Personally though, I wouldnt do a bridgeport on a turbo street car. There is no reason, you can get great power through a street port.

adunlap

iTrader: (2)

Ya that was exactly what I was thinking.

j9fd3s

iTrader: (3)

there is a point where you just cant use any more power on the street. depends on where you live, and how hard you drive, and how many tickets you want to live with.

around here, you only NEED about 40hp. so 300 feels like a rocket ship...

if i didnt live in a city where people drive really slow, it would be different