Suggestions for a cold air intake

[Belgian1979vette]

Compared to a fine mesh type filter over the stacks. I would have assume those took out more flow, but apparently not.

Could be that it still needs some tuning. I roughed it in with the autotune feature and i'm not sure how accurate it is after a couple of runs. The numbers in the VE table are not exactly VE's but a fall in those numbers means that it needs less fuel and less fuel means less air is entering.

However it didn't run to bad and the fuel map seemed to smooth out some. Strange.

That was a below 3600 rpm, which is not exactly high rpm in this combo.
The most noticable is a drop around the 2300 rpm mark.

PS : remember the stack is tapered, actual throttle body diameter is 50 mm.

 

[Richard454]

Nice...I am looking at doing something similar to yours.

Although I also like this design- however,they didn't fit against the hood openings for some reason???





hoodcar

airbox

hood


My set up-

DSCN4590

 

[Belgian1979vette]

The hoods on our cars are very curved in design, also on the inside. Very difficult to fit anything against it + the engine vibrates etc. I don't think that would be a good idea.

Looks like your stacks have a regular dcoe bolt pattern, you could mount your box on the throttle bodies and mount the stacks on the baseplate of the box. A lot easier like that. I couldn't do that on mine, had to mount the box of the bellmouths.

Anyway, at least I have some decent filtration now.

Need to see how it's going to turn out when really going on power. Hopefully it supplies the engine with ample air, otherwise this whole deal would have been an unnecessary problem.

 

[Richard454]

Well- GM did it -just used a large-flexible rubber gaskets...I didn't say it would be easy!!!

Yes it is DCOE flanges- and my trumpets are separable from the base- so I have some options. Haven't figured which way to go yet.

IIRC on 3" pipe- a 90° bend has the same effect as a 7½ foot straight pipe... a 45° is about 4 ft...and 180° is like 12 ft of straight pipe!!! And when you double the air speed, quadruple the loss.

On the other hand- rule of thumb on an average V-8 (300hp) is 1 hp for every 10° drop in intake air temp. That works out to about 1% for 30 degrees.

So a less restrictive flow or cooler intake? That is the real question...

Wanna really blow your mind- here's how BMW tuned the velocity stacks and the plenum-

Richard

 

[Belgian1979vette]

I'm currently thinking about connecting the 2 plenums by a crossover tube effectively doubling the plenum volume and filter surface.

 

[Stroker-427]

OK, I did some calculations.....

Following 4 different configurations with the only difference in the tune of the plenum and his feeding pipe.

Your intake have fized runners (of course) that are tuned in the range of 7000 to 7500 RPM in the third armonic.
12 inches are pretty short for a runner of 50mm ID. (this is tipical for crossrun manifolds).

So we need to tune the plenum in order to have a RAM effect in the range of 4000-5500 RPM (you choose).

It is not easy to notice (may I'm wrong) but it looks that the mouth of the trumpets are veri close tu the roof of the plenum.
This distance should be at least the same of the mouth diameter.

In the following file you have 4000-4500-5000-5500 RPM plenum tune

 

[Belgian1979vette]

OK, I did some calculations.....

Following 4 different configurations with the only difference in the tune of the plenum and his feeding pipe.

Your intake have fized runners (of course) that are tuned in the range of 7000 to 7500 RPM in the third armonic.
12 inches are pretty short for a runner of 50mm ID. (this is tipical for crossrun manifolds).

So we need to tune the plenum in order to have a RAM effect in the range of 4000-5500 RPM (you choose).

It is not easy to notice (may I'm wrong) but it looks that the mouth of the trumpets are veri close tu the roof of the plenum.
This distance should be at least the same of the mouth diameter.

In the following file you have 4000-4500-5000-5500 RPM plenum tune

maximum torque rpm was around 5000-5500.

You could be right on the lid being too close to the mouth. The hood clearance causes issues here. Have to take a look at it. Maybe I could weld in one half of a pipe to have a larger opening in that area, but it will remain a close fit.

 

[Belgian1979vette]

I'm going to have to make some changes to the right airbox, as the front outside corner of the box slightly rubs the hood in that area.

How much clearance is actually needed to account for engine movement ?

Left side has more than enough. Guess this has to do with the engine offset, making the valve cover sitting under the flat sides of engine in that location.

 

[Stroker-427]

You have to take in consideration the counter rotation of the engine under load (unless you have rigid nounts).

For the shrouding of the mouths a nice solution can be a small curve downward of the stacks (if there is room to do it).

To verify if this will be a concern..... test the VE without the cover lids !!

 

[Belgian1979vette]

You have to take in consideration the counter rotation of the engine under load (unless you have rigid nounts).

For the shrouding of the mouths a nice solution can be a small curve downward of the stacks (if there is room to do it).

To verify if this will be a concern..... test the VE without the cover lids !!

No there is no room under the stacks. They are too close to the valve cover.

How much movement can the engine actually make ? I can modify the box (again ) and might be able to get that corner around 1/2" lower but that is the maximum I can get it.

 

[Stroker-427]

It really depends on the engine mounts.... I have urethane ones and are very rigid.

....maybe1/2 inch ???

 

[Belgian1979vette]

I had to cut the left box open and weld in a piece of round pipe section (3.5") to make it lower. Seems to have worked perfectly. At the thightest spot I have 1/2" clearance now.

Meanwhile have been busy tuning her this weekend. A lot of quirks to get out of the system, but it's gradually coming along.

Ran her up to 6400 rpm this sunday after hitting what looked like a sort of revlimiter at 5000rpm.

Seems that my maximum torque point is 5700 rpm, which gives a real VE of around 94%. I would have hoped to get to 100% but I guess the boxes, long tubes and filters do restrict it somewhat.
Anyway, if I reach 7000 rpm minimum with around 85% VE I would have reached my power goal of close to or at 500 Hp it seems.

At 5700 rpm I'm getting around 435 hp. For a small 347 ci I think this is respectable.

Because of the hassle in getting cold air, I'm only 10-15°F below the temps I was seeing without the airbox. At least it's filtered decently now.