so someone tell me why you can't swap the intakes between cars and trucks with the mod motors ? i just found a 99 expedition for one of my kids , and when i popped the hood it had a rather interesting high rise aluminum intake , and in my old mind i kept thinking about how on my old carbed motors , they were desireable for higher rpm use motors . yet here and abroad im told that too swap them on these lil devils causes them to become dogs ............

 

The high rpm those engines ran at with the big intakes usually had a large open plenum and usually took a lot of tuning to get them right Chrysler had those really long across the engine intakes way back when and the first ones had the individual runners going almost to the carb base. They had ungodly torque at low rpm and were very impressive but for some reason didn't work well at high rpm. They then modified the intake runners to be individual for only about 1/3 to 1/2 the length from the ports and started working a lot better. If you look at the intakes for the current NASCAR and top gas drag cars they have large open plenum intakes, not long individual runners like our current production engines. That big intake would be good for low to mid range torque, from what I've seen. The only intakes that look a little like ours is the ones being run in the Trans-Am type races with dual plenums and MAFs that I think are given to a few teams by Rousch or Ford. They look a bit like the plastic intakes on the later Ford Freestar vans but the vans only have 1 MAF. A really neat intake system was/is being used on the Rover SUVs, its a or more 3 piece intake and the middle has different lengths of velocity stacks in the center section which is the plenum, very nice engineering from the look of it.

 

On an EFI engine. Longer runners mean more torque. Short runners = higher rpm hp.
This is why the Mustang intakes have shorter runners than a truck does.

 

ok i think i got it now , so really in essence the modern intake is kinda the opposite of what i know / knew .... but for the life of me can't see where that longer runner intake making more torque would make my 3900 pound 'bird a dog . hades it should help it !!!!!

 

Just another one of Ford's better ideas.

 

Cross-section and runner volume. Try breathing through a soda straw,then try the same thing with a coffee stirrer straw-you'll understand then.
JL

 

The science currently being used by the "new breed" engine engineers is really involved. I have a little experience with Rick Wilson who builds intakes for many of the top NASCAR teams and other high rollers and they compute the volume of the intake plenum, each runner, valve size and other factors of the engine and it's use. Then they take a production intake and cut it into pieces and using a CNC mill they port the manifold to exact dimensions for the intended use and then weld it back together, put their name on it and glass bead it. From the outside it looks like it was cast that way.
That was the way they were doing it a bit more than 10 years ago. Very impressive, the amount of work and care they put into these manifolds. They get a TON of money for each one of them too.

 

If you are talking about two valve motors, do not swap an early intake onto a later PI engine or vice versa. There will be a port/intake mismatch.

As far as runner volume and length. Long, small tube runners increase gas speed which allows the momentum of the charge to pack more fuel/air into the cylinder as the piston slows down. This helps low speed torque. The small diameter of the tube that helps the low speed torque does not allow the higher flow necessary for high RPM power. It's a compromise, you can enhance low speed torque or high end horsepower.

There are many Mercedes engines that use computer controlled flaps in a set of intake runners to vary the runner length for the load/RPM conditions. It is quite effective and makes a torquey engine out of what would otherwise be a high RPM engine. MB can do this because they sell expen$ive cars and this is an expensive system. It is not something that you would expect to see on a vehicle that is built on a budget such as our beloved Fords.

 

There are many Mercedes engines that use computer controlled flaps in a set of intake runners to vary the runner length for the load/RPM conditions. It is quite effective and makes a torquey engine out of what would otherwise be a high RPM engine. MB can do this because they sell expen$ive cars and this is an expensive system. It is not something that you would expect to see on a vehicle that is built on a budget such as our beloved Fords. <!-- / message --><!-- sig -->
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Doc


Ford does use a similar systen on the higher end vehicles. The Mark VIIIs use vacuum operated butterflies in the intake to improve airflow above 3000-3200 rpm on the 93 to 96 models and the 97 & 98s use electronics. It works just like the secondaries coming in on a well tuned Holley Carburetor. My Navigator has a similar system with the 5.4 DOHC engine. On the Marks it's called the IMRC system on the Navigator its the intake tuning valve. I'm not sure that they both serve the exactly same function but it looks like it might.