I still haven't see any info on this, and I have been waiting for a while to see what the results would be. Since there isn't a TT kit out yet, the only system with boost that we can look at is the procharger. Cause of the increased area for air of the plenum, it has been said that the plenum actually decreases the boost pressure seen by the engine.

For instance, with the procharger, the 7psi pulley would actually produce less boost cause of the presence of the plenum. But because of the greater volume of air in general, does the plenum make more power when used under boost??

Also, if this were a turbo setup, with a boost controller, would it affect the setting of the boost??? I mean, for instance, if you set your boost at 7psi with the controller of a normal TT kit, with the plenum, wouldn't your engine see less boost?? And how can you make your controller accurate to what the engine is seeing?? Or I might be off where the boost is measured for this controller, lol. Correct me if I am off on this.

Basically, is the plenum worth anything to boosted cars.

 

On the supercharger its a pulley controlling the boost. On the turbo it will be some sort of actuator or wastegate controlling the boost. If I was to guess, the wastegate would try to maintain what ever boost your try to hold due to the fact that it won't dump air till the spring rate reads 7psi. If not the easy fix is to run a boost controller. Now if you are planning on running the ATI with the crawford make sure you have it tuned with a wideband o2. I have heard the two combination have a tendency to run the car extremely lean and upgraded injectors might be a must. just my .02

 

Yes the a plenum is worth power to FI cars as well as NA. I am by no means an expert on FI but here is my understanding. We all know that a motor is an air pump. It will make more power by getting more air through it as long as the fuel is sufficient to keep the car from leaning out. Anyways, getting more air in and out the motor is volume. I don't think a motor truly makes power with BOOST but with the effect of boost, more air VOLUME. I think that 7 psi, for instance, is the boost the supercharger is putting out rather than what the motor may or may not see. Therefore, it is pumping the same amount of air but the plenum will help it flow more, more smoothly, and more evenly to the cylinders. The motor will not need as much boost applied to pump the same volume of air. The same goes for exhaust, headers aren't going to decrease power because they more effectively flow air away from the motor. They will increase power because of that very reason.

 

Actually, potato, it is the boost that the cylinder will see. Boost is just air under a certain pressure. This air under pressure has to become part of the air/fuel mixture for it to make more power.

 

Whatever your def of boost is, the engine makes power only off the effect of it. Volume is increased so then is power. My path may be off, but I think the truth is the same.

 

crawford plenum + procharger makes the compressor work less hard to produce power. same applies for headers and exhaust systems.

 

yea the basic difference in turbo and SC is this
SC- boost is set by the pulley. that is why you see such things as 7psi pulleys, or 9 psi pulleys ect.

the turbo runs off a wastegate. this is controlled by a vacuum line. now these vacuum lines typically run all over the engine (at least on the MR23SGTE. what one line sees is what they all see. it is a closed system when the wastegate is closed. that is why when you have a vacuum leak (blown hose) the car runs like poop. mike is correct, the super charger will nothave to work as hard. just like on turbo cars adding intake/plenum/exhaust/headers you will see your "stock" boost increase, regardless if you change your boost settings. for example a stock mr2with these mods will generally see an increase of 2-4 psi

 

Along these lines, I'd like to clarify how an electronic boost controller on a turbo system works.

You basically have an electronic controller of some sort (whether it's aftermarket or the factory ECU) watching a boost sensor. This sensor is typically installed at the intake manifold or somewhere just prior to it. That boost controller is also controlling the wastegate on the turbo, which determines how much boost the turbo will make. So if you set the boost controller to do 7 psi, the controller will close the wastegate on the turbo until the boost sensor shows 7 psi. It doesn't matter how much boost is being made down at the turbo or anywhere else along the entire intake tract. The boost controller is only watching boost wherever that boost sensor is installed, and it will control the wastegate so that the programmed boost is seen at that sensor.

For example, say you install a larger intercooler in between your turbo and intake manifold. This larger intercooler might cause a 1 psi drop in pressure between its inlet and outlet. (Not uncommon.) The boost controller doesn't know this. All it cares about it that there is 7 psi showing at the boost sensor, which is usually after the intercooler somewhere. So the boost controller will make the turbo spin faster to achieve that 7 psi, while there might actually be 8 or more psi down at the turbo, prior to the intercooler.

Superchargers can't do this. Boost is controlled by the fixed diameter of the pulley. So if you were to put that bigger intercooler between your supercharger and intake manifold, the supercharger obviously could not compensate by increasing boost, which means you will actually see less boost at the intake manifold. You'd have to decrease the size of the supercharger pulley to compensate. (You might not even need to compensate, though, since the cooler air from the better intercooler might actually make more power than the 1 psi you lost.)

But anyway, this doesn't really answer the questions about the Crawford plenum, but I saw a lot of people talking about boost control and such, and I figured I'd throw this in just for reference.

 

paulo has plenum and s/c. He got 7psi no matter what plenum he used. We first tuned the car w/o the plenum and then with it after s/c break in.

 

I believe that the more volume you have between your turbine and your pistons then the more time it will take to build pressure. This applies to both superchargers and turbo chargers.

For instance, pretend I have a pump that can build up 35 psi of pressure. It doesn't matter if I fill up a tractor tire or a bicycle tire. I'll still reach 35 psi in both tires. All that changes is how long it will take to fill each volume.

Similarly, an increase in volume typically means more surface area due to all the plumbing. The surface area can increase the heat loss of the compressed air. If you decrease the temperature of a gas, the pressure will decrease too. Take this concept to the extreme and you have an intercooler.

Finally, restriction within the plumbing can reduce flow rate. The pistons are sucking away pressure all the time. If the pistons exceed the flow rate of the turbine and plumbing, then the pressure will begin to drop. So you want to reduce all restriction from the turbine to the cylinders to get the maximum possible flow rate.

Also, building up high pressures on a boost gauge does not necessarily mean you're getting lots of air into the cylinders. There could be restrictions such as an inefficient plenum restricting flow.

So basically, you're trying to balance these different characteristics to flow the most air at a temperature you can safely use for combustion.

My guess is that the increase of flow to the front cylinders provided by the Crawford plenum outweighs its increase in flow volume (lag) or cooling effect (pressure drop due to temperature drop).

--
Jeff

 

when you guys dynoed the car was it running on the lean side and were you able to keep like say a 12.2:1 a/f ratio. I have only heard that the injectors reach over 85% pulse rate with the SC alone. So I thought by adding the plenium it may not have enough fuel and would start running lean at redline

 

And to add to spazpilot's post, bottom line, did the Crawford plenum show more power on the car that you guys have that has both the plenum and the SC???

BTW, nice post, jreiter. That cleared that subject up, and it gives more reason to think that a turbo will make alot more HP with a new plenum. Only thing to watch of course, is running lean.

 

The car would not run right at anything lower than 12.5:1 We got maximum power, more constant timing, more constant A/F, smooth power band running A/F around 12.7. We think this was due to the injectors. They were not meant for this and should be replaced with any thing more than this setup . . .well its our opinion they need to be changed for this application too. The only time it ran smooth around and below 12.5 was when we fired the 35 wet shot (it needed the extra fuel)! The FMU just could not solve the fuel problem. By the way, when the intercooler sprayer was fired with nitrous (and the nitrous went into the air filter) the HP went to 417 and A/F to low 13’s. Very light pinging occurred.

The plenum did show gains, what I don’t remember. It was maybe 5 or so.

 

So Vandy, are you saying that the SCed car put out around 5 more rwhp with the Crawford plenum, than without?? Can you find out the rwhp increase for us, please??

 

Any more info on this???

Bumping for info.

 

ya ya I'm intrested too

-non

 

paulo has all th dyno sheets but I know it was around 5. The curve was more impressive at all rpms.

 

If you think about it, the Crawford Plenum should help a N/A car much more than a boosted car because of the increase in air flow. With a boosted car the pressure is forcing the air in thus eliminating some of the original issues with the stock plenum restricting air flow. The major benefit one should she with the Crawford Plenum on a boosted engine is the more even allocation of air to the cylinders which should not account for as much power as air flow, but should allow for a safer environment to increase the amount of boost the engine can handle given the proper fuel management. I other words, the Crawford Plenum should increase the HP potential of a boosted engine under the right conditions. The small HP gains mentioned do not suprise me, but I still think the Plenum, along with some headers, high flow cats and true duel exhaust is worth it if for a boosted engine if you really plan on making some serious HP.