This is from the Ford 1.9 CVH engine, may be north America only 1990-1993. We discussed it a few years ago. The fuel rail looks interesting too

Well, I've had a minor disaster. I was welding the plenum and didn't notice that I picked up a stainless filler rod. I'm going to sleep on this one since the more I try to fix it, the worse it gets.

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Take a look at an early to mid 1990s Ford Escort/ Mercury Tracer with base 1.9L SOHC engine. I was initially going to use that intake manifold as a base from which to fabricate.

http://www.ebay.com/itm/91-92-93-94-9 ... -FED-773611-/400987659985

The people who build aftermarket intakes live and die by the peak horsepower numbers. I can't stand peak HP engines because they suck to drive anywhere but onto a dyno. Also, shorter intake runners are easier to fabricate and they package better.

Since I'm going forced induction with a (relatively) big turbo, I'm building the intake for torque and letting the turbo take over up top. A good place to start if you are running the stock cam is to just make them the same length or a little shorter than the stock runners.

Here's another good explanation.

http://www.team-integra.net/forum/blo ... er-size-calculations.html

I've read a couple of books on this topic and there's two main types of induction charging; inertial charging and pressure wave charging.

-Inertial charging you keep making the pipe longer until there's no gain, this type will have a smooth torque curve.
-Pressure wave charging is where pressure waves travelling up and down the intake runner as a result of valve opening and closing are used to increase the pressure at the intake valve just before closing. If this effect is strong the torque curve will wave a wave super imposed on it (assuming it isn't filtered out by curve fitting)

There's a couple of places you can get a rough approximation for pressure wave charging lengths. For peak torque boost due to the intake at ~6000rpm you need a runner length of ~600mm (inlet of the runner to the valve) for the 2nd harmonic. You'll also get a bump at 3000 and 4500 rpm as well due to the other harmonics. (http://www.bgsoflex.com/intakeln.html) There's a quoted range because it assumes values for the other influencing factors.

Inertial charging, as far as I know, appears to be done more empirically unless you have access to some pretty sweet CFD based on real test results or some packages that have simplified the flow equations and tuned them to match actual results. Generally longer is better.

The plennum is the other factor that influences the intake charging. Small plennum reduces the peak in size and rpm value but spreads it over a larger rpm range, the bigger you go the closer you get to individual runners which have the largest but narrowest peak at the highest rpm (assuming all else is equal).

Take all these factors and look at factory/ oem designs and their intended use and you start to get a good feel for what the manifold you want will look like. Optimising it is probably beyond the means of most enthusiasts. Mine will have long runners a smallish plennum to boost low rpm torque before the turbo kicks in.

Quote:How does one determine how long the runners should be? Aftermarket manifolds appear to make them as short as possible for best packaging solution (like how can dual DCOEs fit into the car with air cleaners installed). But longer runners should boost torque? Unequal length runners smooth out the torque curve while equal length runners boost peak power (hence the term "peaky"). Where to start?

Very close to what I've designed! I may be interested in a set, how thick are they? I designed them to be machined from a 25mm thick bar. I'm after lowest profile possible because I want my manifold to wrap up over the rocker cover and leave all the space that side for a turbo exhaust manifold.

Damm thats look good :O :D

You have a a round of thought right up my alley!

Here's what I have mocked up to check for clearances. This is not how it'll end up as the runners would be WAY too short. I'll probably throw a 90` elbow in there and put the rounded part facing up; closer to the hood.

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It's all set up for 1.5 x 0.065 tubing. I actually made a set of the intake flanges in both steel and aluminum.