Custom short runner cobra intake

[BHAM]

Working on my cobra intake, full port job on lower, port matched to my ported gt40 heads. The upper was cut in half and ported. I removed 2.5 inches of runner and rewelded it back together. Opened the inlet to 75 mm to match my throttle body. I think this oem cobra will suprise alot of people. I took the blower off and am going na with stock modded parts. Looking at making 325-330 rwhp. To many people say it can't be done, guess I will prove them wrong!!!!

[BHAM]

Inlet opening

[BHAM]

Oem

[BHAM]

Almost done, have to resize the cobra plaque and install it

[thesource]

It can be done and was done years ago. I'm pretty sure it was Mike Andrews that use to have one on his car back in the 90's.

[BHAM]

It can be done and was done years ago. I'm pretty sure it was Mike Andrews that use to have one on his car back in the 90's.

Cool, was it all worked over factory parts?

[Sonic Blue 85]

So I gess you cut the intake with a band saw? It would have been better to shorten the runners on the inside with a die grinder, basicaly cutting out the division between the runners. Doing that way would have given you a much larger plennum, which is one of the things that those intakes need, along with shortening the crossover. I still say you took too much off of the runners and you needed to go into the plennum and improve the flow into the end runners. Trust me it would have been better to cut the plennum off, than to cut through the runners.

[thesource]

Cool, was it all worked over factory parts?

As far back as this was, I don't remember. I was a teenager back then. I do remember his teal Cobra was fast as hell for a street car back then at Alamo Dragway. I think his intake had the box cut down as well as the runners. It was a tiny upper or atleast it seemed like it back then.

[65mustangscott]

i love budget builds like this. are you tryin to run stock cam as well. It reminds me back in the day when muscle mustangs would try to do stuff like this.

[TurboGen1]

Mike's had the end cut off and Extremely ported and as was said cut the runners shorter and then welded a sheetmetal plenum on the end. I am sure I have pics of it somewhere. If I remember right he got that intake back when he got the Skunk(Black white stripe coupe).

[BHAM]

So I gess you cut the intake with a band saw? It would have been better to shorten the runners on the inside with a die grinder, basicaly cutting out the division between the runners. Doing that way would have given you a much larger plennum, which is one of the things that those intakes need, along with shortening the crossover. I still say you took too much off of the runners and you needed to go into the plennum and improve the flow into the end runners. Trust me it would have been better to cut the plennum off, than to cut through the runners.

Hopefully your tune can still make up for my short commings.....

[BHAM]

i love budget builds like this. are you tryin to run stock cam as well. It reminds me back in the day when muscle mustangs would try to do stuff like this.

No I chose an aftermarket cam, I couldn't locate an 87-88 sd cam

[1BigBad4d]

I will have a speed density cam shortly if you want it. Just for kicks I guess. You can hv it if you want to try to see what it does.

[BHAM]

I will have a speed density cam shortly if you want it. Just for kicks I guess. You can hv it if you want to try to see what it does.

I sure could use it

[msd]

All this talk about Mike's Intake and still no pics...



Also, yes, as it has been said, for this modification to really work you really need to open up the plenum.

I hope this helps.

msd

[JCP281]

What is the benefit of shortening the runners? I would think shortening em would not give the air a chance to become laminar into the head?

[Sonic Blue 85]

All this talk about Mike's Intake and still no pics...

[qimg]http://www.motorsportsdigest.com/MA_Intake1.jpg[/qimg]

Also, yes, as it has been said, for this modification to really work you really need to open up the plenum.

I hope this helps.

msd

I knew it had a sheet metal extension for the plennum, I was talking with someone about his intake. The cross over and plennum are two of the biggest problems with a stock Cobra upper, both are too small to maintain atmosphereric pressure in the plennum for an engine that can potentialy move a lot of air. Basicaly they are both too small, so at WOT with an engine that can move a lot of air below a stock Cobra upper, you will start to see it pull a vacuum, which means the air density is dropping, so no matter how good the heads and the runners in the intake are, the air in the plennum will have slightly lower to possibly noticeably lower air density that the air on the out side of the engine. So the whole ram effect of a long runner intake is killed. Cobra or GT-40 intakes usualy make more hp and torgue than most all of the other aftermarket intakes up untill the point the plennum pressure starts to drop, Cobra or GT-40 manifolds on most 5.0 combos are done making power by 5200 to 5300 after that they fall off quickly.

[thesource]

Damn I didn't remember it being that big. It seemed like you you pull the driver side valve cover off with no issues.

[Sonic Blue 85]

What is the benefit of shortening the runners? I would think shortening em would not give the air a chance to become laminar into the head?

The reason for shortening the runners is the shorter it is, the less restrictive it is, but at the same time you loose ram effect, the more you shorten a runner. By shortening up a long runner is will not be as restrictive at higher rpms, so at higher rpms the power does not fall off as quickly. Many carb intakes use short runners and to reduce restriction to make hp. The long runners used in many EFI intakes take advantage of ram effect to increase hp. With a properly designed long runner intake with good ram effect, you can make more power earlier than you can with a short runner manifold such as a carb manifold. Most of the time shortening a long runner intake hurts power through most of the power band, produces less power at the peak, but raises the point of peak power and the power does not fall as quickly as the longer runner. If properly designed, a manifold with shorter runners can make more peak power, but there are a lot of complex formulas for figuring proper runner lenght and cross sectional area and tapper. I designed a built a sheet metal intake years ago, after a lot of reading and reasearch, I found there is lot more to manifold design than what you would think.

[JCP281]

The reason for shortening the runners is the shorter it is, the less restrictive it is, but at the same time you loose ram effect, the more you shorten a runner. By shortening up a long runner is will not be as restrictive at higher rpms, so at higher rpms the power does not fall off as quickly. Many carb intakes use short runners and to reduce restriction to make hp. The long runners used in many EFI intakes take advantage of ram effect to increase hp. With a properly designed long runner intake with good ram effect, you can make more power earlier than you can with a short runner manifold such as a carb manifold. Most of the time shortening a long runner intake hurts power through most of the power band, produces less power at the peak, but raises the point of peak power and the power does not fall as quickly as the longer runner. If properly designed, a manifold with shorter runners can make more peak power, but there are a lot of complex formulas for figuring proper runner lenght and cross sectional area and tapper. I designed a built a sheet metal intake years ago, after a lot of reading and reasearch, I found there is lot more to manifold design than what you would think.

Well yea, you gotta have a decent working knowledge of fluid dynamics to be able to effectively design most things on the motor. I bet I could find the formulas in a dynamics book I have lol.

Interesting explanation. My thinking was correct for the efi part; kinda weird how a carb effects so much.. but I guess thats what happens when your spraying 2 different fluids at the same time.

[Sonic Blue 85]

It's not that the carb determines the runner design, that's just the way most are done. There are two main basic thereories on how to make power with the intake. There are many thereories on on runner shape, cross sectional area, bends/ turns, port velocity, tapper, plenum vollume, plennum height, runner opening,ect, but most all manifolds use either a short low restriction or a high ram long runner design. Most carb applications choose the short runner thereory. There have been long runner carb manifolds, the reasons for not using long runners with carbs is the fact the fuel in mixed with the air at the beginning of the manifold in a carb application and so with some long runner designs you can have some fuel dropping out of the air and puddling, which can cause many problems. If you installed a Webber side draft carb where the throttle body goes on a fox body style manifold you would wind up with a lot of fuel in the plennum. So you would have problems with the cylinders not getting the fuel they need at times, then other times they may get drowned with fuel, not to mention fuel leaking out of the intake and the potential for serious back fires. Dodge actualy useds a long runner cross ram intake in '64 on the 413 Max Wedge engine, the runners for each bank went across the top of the engine to the opposite side past the opposite side valve cover, so the carbs were actualy sitting out past each valve cover basicaly above the exhaust manifolds. That engine with that manifold was supposed to be one strong running engine. Another place where longer runners are used with carbs is tunnel rams. So bacialy the second reason you do not see many carb manifolds with long runners is making a manifold that will fit under a hood of a car with an air cleaner on the carb or carbs, another reason is cost. Fuel injection gives manifold designers much more freedom when designing manifolds that will make torque, horse power and still fit under a stock hood. Truthfully if power was the main factor in the design of a manifold, it would be possible to make a manifold that would easily make a lot more power than most of the manifolds available today, but about the only place such a manifold could be used would be on a engine dyno, it would not fit under the hood of a car.