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Old 04-29-2005, 06:11 PM
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Question about intake manifold distrobution for Nitrous experts...

Hello guys, I am in the process of a futile effort to get big power out of a V6, and have questions about intake manifolds, and their flow balance to each cylinder in nitrous applications.

I have a 3.8 supercahrged V6 in a 1990 Thunderchicken supercoupe.
I currently have a 75HP shot on a dry setup of nitrous. I have converted the system to a wet kit, with a fogger nozzle, but not quite done, as one of the solenoids went bad, and haven't gotten a chance to replace it yet.

In the near future, I am going to be running a modified bottom end with home ported heads, and a little bigger cam. The shortblock has been outfitted with eagle H-beam conn rods, and custom forged pistons, and I've already got all the bolt-ons waiting to for the new engine (75mm TB,76mm MAF, 42lb injectors, SC overdive pulley, EEC tuner device for tuning, etc etc).

There are guys that have sucessfully run 100-125 HP shots of N2O in these engines, but some of them may have completely custom made intake manifolds, or modified their intake manifolds in ways that they probably don't care to share the details of.

There is a modification to the intake manifold that some have done which increases the volume of the intake manifold, which is suppose to help out on the top end. I donnot know however, if any of the folks running this modified intake use N2O...

The stock intake manifold pictured below shows the location of what some have called an "air divider" which some say was placed there to direct flow (which I can't understand how it would be a probelm in a blown application, as it woud be under pressure). Other have said that this triangle was put there for structural support, and some even think it could just have been put there to somehow aid in the manufacturing proceess??? I do not know what its purpose is, but some say that its removal, and the increased volume helps out in higher RPMs....



The details of the midfication are discussed in the "howto" here:
https://www.mn12performance.com/mn12...ake-howto.html

I have been warned that this modification would change the balance of of flow between cylinders, which may not be bad in a fuel injected and blown application where the fuel isn't deliverd until the injectors... But could become an issue if uneven nitrous/fuel mixture is introduced in unbalaned portions between cylinders.

My first thought is that there has to be plenty of V8 intakes that aren't particularly well balanced, running 200+HP shots of the juice...

I would think that distrobution would have to be particularly bad in a 4 cylinder or straight 6, not that I am aware of anyone using N2O with a straight six, but I'm sure someone is (aren't some of those ricer types running a straight 6?). I would imagine that if N2O is OK on a unbalanced 4-6 cylinder intake, it would have to work OK on this one...

Does anyone have any input on wether this is a bad idea or not?

Thanks guys!

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Old 04-29-2005, 07:47 PM
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I`ll just say this. Size plays a big role in intakes, as does runner lenth. Long runners aide low end torque at the expense of high end power, short runners do the opposite. Adding volume to runner sizes decreases velocity, which is important for low to mid rpm power. when the engine gets to high RPM velocity becomes less important since the engine is creating it`s own to a degree. Keep in mind also there is never a perfect balance between runners or equal distribution, and there likely never will be.
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Old 04-29-2005, 07:47 PM
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I would look more to the tubing going to the intake as it crimps tight and comes really close to the drivers exhaust manifold after the intercooler. By using a larger diameter pipe routed away from the exhaust and heat wrapped you will get not only more total air flow but also a cooler, denser charge which would be much better than removing that little divider... and as far as the nitrous/distribution question in the pic you will see bosses at each port. These would be great for a multiport nitrous system and fix your distribution worries.
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Old 04-29-2005, 08:53 PM
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Thanks for the input guys, but there are no runners in the intake, its just an open "box with windows" the reason the intake is crimped, and concave, is because the blower barely fits under the hood, and I believe it was this was made concave like that for clearance reasons alone...

I have also wondered about lowering the flooor of the blower to create a little more volume, but this would make the floor lower than the bottoms of the ports. Not sure if this is a good idea or not.

As for low end, the car has plenty, as a matter of fact, it had 315 ft-lbs of tourque from the factory, and with my current bolt-ons, the probelm will be keeping the tires planted...

The accounts I've read say that there was no noticable reduction in low end, but then again no-one has done just this mod at one time either...

I will have to look again, but I've read where forced unduction intake should be 1.8x the swept volume of a cylinder, and this intake is no-where near this one.

Most of the guys making big power with these engines do have modified, or custon intakes, becasue it is a well known restriction in the engine.

I know I want a little more volume, but I want to make sure I do it right...

As for the blower tube right next to the exhaust manifold, yeah we know it is not good, as well as the crimp.... I am going with headers, and will wrap those, and the lower intercooler tube with header wrap.

Of course I like the idea of multiport nitrous, but I'm trying to keep a stock look here...

Thanks guys!
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Old 04-29-2005, 09:01 PM
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My brother has owned 3 SC's and i have oned of those engines in a 5.0 'stang.

You want more volume? why not space the blower up and raise the roof of the intake. Also, the biggest restriction in the intake tract is where the throttle body enters the blower on the backside. It can be ported considerably.

http://www.sccoa.com
http://www.sccoa.com/forums/
http://www.sccoa.com/forums/showthread.php?t=29150

Last edited by NXS; 04-29-2005 at 09:07 PM.
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Old 04-30-2005, 12:16 AM
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[QUOTE=NXS]My brother has owned 3 SC's and i have oned of those engines in a 5.0 'stang.

You want more volume? why not space the blower up and raise the roof of the intake. Also, the biggest restriction in the intake tract is where the throttle body enters the blower on the backside. It can be ported considerably.

[QUOTE]

Yep that is my normal board, and those mods are already in the plan, among others... I have a spare inlet, intake manifold and blower, return plenum, heads, etc... I finished up my BS degree this past week, and plan to get busy with the brand new aluminum spool gun mig welder down at the local Army auto hobby shop.

I have already verified that this welder will weld on the intake manifold, but I'm gonna bolt it to the heads when I do any more welding on the intake, hopefully I won't warp it... I am new to wleding!

I've seen the raising of the roof, and the complete new opening in the rear of the manifold with a custom aluminum return plenum. But the raised roof almost requires an aftermarket hood, and I already have to use the raised supercharger top, so not much room for raising the roof.... I want to keep the hood stock, in fact I just sold an aftermarket ram air hood from another tbird SC...

This one is the 35th anniversary model, and the only mods I wasnt visible is the exhaust, and the enlarged supercharger, (but it will also appear stock.) The nitrous is pretty well hidden, and the only irreversable mod to the car is the holes in the trunk for the blue bottle
I've acutally kept the original exhaust in case I want to put it back to stock in the future...

The roof is also contoured, and would be much more difficult to weld on. On the bottom, I could loose the splash sheild, and use the flat casting groves on the bottom and weld a plate right to that...

I am curious if the floor of the intake being lower than the ports would be a problem?

Does anyone think the lack of the "air divider" triangle in there would be bad for the N2O though???

The attached pics show the ideas for lowering the bottom of the intake manifold... I cut along the protruding casting lines, and weld a plate to it.

Thanks for the input guys!!!
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Last edited by sizemoremk; 04-30-2005 at 12:24 AM.
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