Intercooler ducting solution

[LoneEagle]

Here is a solution to Intercooler airflow issue. Since I have some experience in this area, thought I could contribute to fixing this problem. First off here’s the baseline with the original OEM configuration:
Rough hood scoop opening: 2.5” x 20” or an area of .35 square feet
Air velocity at 45 mph: 66 feet / sec or 3960 ft / min
Air flow at 45 mph: 1390 cfm

Previous posts have discussed at length the air flow challenges. To overcome these issues, I’ve taken a multipronged approach:
1) Use the two humps in the turtle deck to pack in the biggest fans possible. I tried 7” fans, they were too big. Specs for 6” fans are: 700 cfm / 80 watts / 8 amps each. If you do the math 8 amps & 80 watts doesn’t quite add up but you have to take these kinds of specs with a grain of salt anyway. They cost about $30 each on E-bay. Two of them provide about the same airflow as the OEM hood scoop at 45 mph. I’m thinking I will activate the fans above 50% throttle. Maybe someone has a better suggestion?
2) Since the cockpit is an obvious low pressure area with the windshield, this can be reduced somewhat by adding 4 ball vents to the dash. You need them to cool yourself anyway. These will help feed the fan inlets in an indirect sort of way. If you have them closed because it’s cold outside, the intercooler airflow demand will be less too. Ball vents are 2.75” inch diameter. Four of them provide .165 square feet, about ½ of the hood scoop area. This will certainly help reduce the load on the fans. I know, I know, I could use 8 ball vents, but it sure would make my dash look cheesy, don’t you think? Ball vents are $18 each from Aircraft Spruce & Specialty. The Cat ducting to feed them is pricy at $5.40/foot.
3) Leave all of the vent inlets on the turtle deck and rear quarter panels closed. At the same time be sure to open the exit vents on the rear deck and bumper. This will maximize the low pressure in the engine compartment and the area exiting the intercooler. A further step (which may be overkill) is to place a rubber 1 or 2” air fence on the bottom of the car below the firewall. This is similar to the air dams on the front of many production cars and at the rear of aircraft cowlings.
4) Air is nasty to work with because it’s lazy by nature. It always takes the easy path. So the ducting needs to be fairly tight. This is a challenge, since the engine rocks with varying engine torques. So sealing the ducting tightly where possible is important, but at the intercooler you need a ¾” flexible seal.
5) Finally, no point going to all this work if you don’t feed the air filter cool outside air. I will be tackling that project next.
See the attached pic’s. The geometry of this ducting was, shall I say “challenging”, but with lots of cutting and pasting, came out pretty good. Hand rivet gun and left/right snips are a must. Sheet metal brake is very helpful. Suggest using .025” 6061T6 aluminum. Hopefully this will encourage some of you to give it a go yourself… BTW, the dog legs in the two upright panels are not necessary. I miscalculated the room needed for the fans. Like the air, I’m lazy and didn’t want to start all over with a new piece of aluminum!

[Bob_n_Cincy]

Hey LoneEagle,
Stop over in Cincy and we can go for a spin.
I'm curious to see how your design works out. We have done some air flow testing with surprising results.
Our rear radiator was a fail.
Bob

[LoneEagle]

Thanks for the invite Bob. Are you available Saturday morning? I could drive over. Weather doesn't look to good for flying. I'd love to take a ride in your car. Would help charge me up to finish mine. Progress has been rather slow lately.
Chuck

[ben1272]

I like the fan idea and have been thinking about trying something similar. I have read about folks using SPAL fans (like yours), but mounted right on intercooler. Rather than have throttle trigger their on/off state, why not monitor intercooler temperature and trigger off of it? I would think a simple 12V process meter could be had that would allow you to use a thermocouple screw-clamped to a convenient spot? Also, why duct air from the cabin versus the side vents or the deck vents?

Not criticizing, just want to know your line of thought!

Thanks for sharing your approach!

-Ben

[LoneEagle]

Temperature rather than throttle can certainly be used to cycle the fans on and off. I chose the front of the fascia humps location because they were the right shape and size. The ducting was simple that way as well. Didn't seem like there was space to mount the fans on top or bottom of intercooler. In regards to inlets, I think the turtle deck openings look to be a little small. The rear quarter openings would probably be ok size wise but the shape and location lead to some fairly complicated ducts.

One thing that may be a concern with the current location is noise levels since the fan are right behind your head. The seat back will provide somewhat of a barrier but may still be noisy. Of course my exhaust won't exactly be quiet with only a 12" long muffler. At high throttle the exhaust will bark pretty good.

That's the trouble with doing a new design. You really don't know till you have hardware and then you are pretty committed. I wish I wasn't having to do this at all, but just wasn't comfortable with the FF solution. Most of the other stuff is just erector set and it moves much faster. Wiring harness is in that category too...

[Sgt.Gator]

I would switch the fans on boost, not temp. Boost will be instant on and off, there will be lag if you do it on temp. If you aren't in boost you don't need the extra flow. Control them with a relay controlled by a boost pressure gauge. Maybe add a delay on them so they stay on for a short while after the boost drops off. The good side is that at low speeds if you nail it the fans kick on to cool the IC charge air before the airflow would naturally occur as speed ramps up.
The bad side is the fans may restrict the airflow at high speeds.

[ben1272]

But I thought the idea was to prevent the TMIC from becoming heat soaked in the hot engine bay? If you wait until boost calls for fan, the air charge will be pushed through a hot intercooler versus a cooler one, had the fans been switched on temp., no? I have zero experience with these sorts of things, so keep that in mind!

[Sgt.Gator]

But I thought the idea was to prevent the TMIC from becoming heat soaked in the hot engine bay? If you wait until boost calls for fan, the air charge will be pushed through a hot intercooler versus a cooler one, had the fans been switched on temp., no? I have zero experience with these sorts of things, so keep that in mind!

Good point. You do both.

[RM1SepEx]

run them all the time to keep temps down. I've been playing with my side mounted AAIC and that is the only way to keep IC temps down

[tmoretta]

Where are you mounting the inlets for the ball vents? Anywhere under front hood or at base of windshield will pick up warm air.

[LoneEagle]

I was going to mount the center vent inlets down low, just below the sheet metal pan under the radiator. I am concerned about mud puddle splash so have to give it some more thought before making a final decision.

Haven't decided on the outer vents. I have the body panels back from paint, so will hang everything again including the rocker panels to see what my options are. Will try to avoid hot air off the radiator.

[FFRSpec72]

My sealed IC and using the side scoop vents lowered my IAT from 140 on grid to 125 on track, I imagine if I could have built up more speed my temps would be lower, it was also 103 out on the track

[LoneEagle]

That's good info Tony and your solution looks to be quite effective.

If we can quantify the results of our design approaches, it makes it easier to compare the effectiveness of various strategies.

It remains to be seen how effective my inlets with fans will be and whether the noise level behind my head will be tolerable. Or more important now that I think about it, how tolerable the noise level will be behind my wife's head!

[GS guy]

Nice ducting. I think the biggest drawbacks, besides long hair getting a quick trim(!), are the "optimistic" CFM ratings of the ebay fans. If you look at anything comparable from Spal or Maradyne, both slightly larger fans at 6.5" or 7", both rated at 6-6.5A, you're getting 300-375CFM max. These small fans just don't put out that much CFM, and I just don't seeing another 2A more than doubling the CFM output! I think realistically you're looking at less than 800 CFM combined, well below the 1400CFM OEM.
Maybe an inner plenum/baffle could be installed directly above the IC fed from a bigger/higher CFM fan mounted horizontally? Use the main plenum as a cold air inlet?
Just throwing out ideas....

[LoneEagle]

Your may be right about the 800 CFM. It would be nice to mount something bigger right on top of the IC. When you look at the clearance height wise, doesn't leave much room to work for the bigger fans. You could cut an opening directly above, but doesn't work too well in the rain. Also the aesthetics considerations...

The dual side inlets may be the best alternative as described in this thread by Tony.