Intake Runners

[Bill Blue]

While messing around trying to make my intake, I noticed I misjudged the size of tube needed to duplicate the ovaled intake ports. Initially, I figured 1 5/8" O.D. tube would do it. But I was looking at the OD of the tube filling the ID of the port. So I tired smashing a 1 3/4" piece of tubing, also too small. Looks like it would take 2" tubing to equal the port cross section. I had a moment of slight panic, so I hit the internet. Seems the 1 1/2" I.D. (1 5/8" O.D.) tubing should give max torque increase at about 4,500 rpm. A 1 7/8" ID tube makes max torque at 7,000!

Ford specs the 2.3 with max hp at 5250 and torque at 3750. Any ideas why Ford would put this manifold on this engine and put it in a truck? As near as I can tell, this manifold is used only on the 2.3 in the Ranger. Seems like a total mismatch.

It appears my runner length will give max torque in the low 2,000's. I'm thinking this will make a great street engine. Not street race, but street drive. Will these smaller runners have that much power loss in the upper rpm range?

Bill

 

[RootesRacer]

I'll tell you a bit of a secret.

Its IMO not a good idea to put an engines intake/exhaust resonant point into the "cruise" region of the map becuase it increases the VE down there to the extent that it increases the peak torque down there, but high VE means high pumping losses at light throttle.

BTW, its the area of the port you need to be concerned with, not the size of tubing it takes to fill it.

I'd go with runners just larger than the inlet port area and let the cam determine the torque curve.

 

[Bill Blue]

I'll tell you a bit of a secret.

Its IMO not a good idea to put an engines intake/exhaust resonant point into the "cruise" region of the map becuase it increases the VE down there to the extent that it increases the peak torque down there, but high VE means high pumping losses at light throttle.

BTW, its the area of the port you need to be concerned with, not the size of tubing it takes to fill it.

I'd go with runners just larger than the inlet port area and let the cam determine the torque curve.

High pumping losses mean reduced economy, right? How much of a hit do you think I'll be taking? Speaking of resonance points, which is the most important factor, diameter or length? To put it another way, what do you think will be the outcome of my setup, a diameter resonating at 4,500 and length at 2,000?

My intent was to try to copy the area of the port, but their shape is too complex for me to determine mathematically, so I tried to match them by squishing tubing to match, but screwed it up. Well, truth be told, I was not using tubing, but lengths of paper fit into the intake opening. In addition, given the purpose of the flaps, I said screw it, I'll go with smaller runners as this is not going to be a high speed engine and I cannot duplicate the flaps or their control. I really want an engine that operates well at low speed. In any event, the intake is what it is mostly due the requirements to fit the engine and my foul ups. It was not until the past few days I realized I'd missed it that much.

I'm finding all this tuning to be interesting, but very confusing. I found a site that said a four valve street engine should have intake runners the diameter of an intake valve. In this instance, that would be 1 3/8"! Compare that to the stock Ford, which must be 2". Quite a difference, given the fact the Ford is in a truck.

I understand the cam determines the torque curve, intake and exhaust just move things around a little. But it seems to me you are saying the added benefits of a modified torque curve due to intake is not worth the effort. Any particular reason for that? Keep in mind this is a street engine that will never see more than 6,500 rpm, maybe even as low as 6,000.

Bill