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Adding dual intercoolers and blow through MAF to Vision Function MP62 SC kit



This will chronicle the progression of my project. We'll call this a VF2+

First some background. I have one of the very early VF2 kits. My car has never really ran "perfect" since I installed it. It idles fine, it cruises around just fine. But the 50%-80% throttle position is almost unuseable. When you get to that point you can feel the sudden change in power and air/fuel leans out tremendously. And it seems to get worse as the temperature rises. Right now in this 106*F temps we've had for 2 months straight the car just isn't that great to drive because I have to take such care with the throttle.

In the 2 years I've reinstalled the kit, replaced every sensor related to air and fuel, had the fuel injectors flow tested, changed spark plugs, gotten rid of all the boost leaks, found other issues, but none of it has fixed the problem. So at this point I believe its between the ECU tune or the engine itself. The car ran great before I put the kit on, even dynoed at like 169HP. So I decided I would take the car up to Kansas and have Kold Fire do a custome tune. But if I'm gonna do that I may as well round out a couple more things. I want to get the car running good, but also wanted to push it a little further and safer.

My goal for this is around 300-330 to the wheels.


The first thing was the basics. I still have the stock header and catalyst. I also have an Arqray Twin Can muffler. Thats all being replaced. I ordered a complete system from 2bular with the new 4-1 header, hi-flow cat, and the GT3 muffler (thru diffuser). Since I was getting the whole system at once I asked Jim to put V-band connections all through out. So it should be a very well sealed system.


This will be the more interesting aspect of the upgrade. As we all know the MP62 does get quite a work out on these high powered models. The air starts to get hot fast once you go above 9-10 PSI. Also living here is Texas, the air gets hot enough on its own. So I plan on keeping the side mount air to air that came with the VF. I will then add an additional air to water inline. So the air will come out the supercharger, first go through the air to air, then through the air to water, and then into the engine. I want the air to get as cooled as possible (outside of esoteric and non-practical methods).

My car has the front oil coolers installed, but due to my work schedule I never have time to go to the track. So my car has become the most awesomest commuter ever! So that being said the car is a street car and the engine just doesn't get stressed (which is partly why I think the engine should be ok with the power levels as it will be short bursts here and there). I plan on repurposing the front oil coolers as the heat exchangers for the air to water. This way I dont have to run any additional lines through the car. I dont have to worry about stacking another radiator onto the main radiator. Plus taking the oil cooler lines out of engine duty might actually save my engine from catastrophic failure!

So far my plan is to get the intercooler from Frozen Boost. I narrowed it down between the Type 3 and the Type 19. I have decided on the Type 19 because the shape and the inlet/outlet size are most favorable to other aspects of the project.

Cardboard mockup of Type 3
Frozen Boost Type 3 Mockup in Engine Bay

Cardboard mockup of Type 19
Frozen Boost Type 19 mockup in engine bay

I will use a Bosch OEM pump for the heat exchanger. I'm not sure if 1 will be enough to push the water up the front of the car and back again. I may have to install 2. The hoses are moving pretty horizontal so its not like the pump would have to push the water up a 10 foot incline but its still a pretty far distance.

Blow Through MAF

The blow through MAF is a bit of an unspoken topic. The Subaru and Mustang guys have picked up on it with success, but its still fairly taboo. I do know of at least 2 people that have converted their Lotus to blow through but when I asked about it they did not respond. MAF (Mass Air Flow) measures the volume of air moving through a known area. Just like sticking your hand in a stream of water, it doesn't matter if the water is being pushed passed your hand or being drawn. Your hand will simply feel the volume of water moving past it. So MAF's do not neccasarily care about boost or vacuum. They simply look at the volume of air. Now there are 2 major reasons that keep OEM's from using blow through MAF's. One is that by putting the MAF right after the air filter (draw through MAF), the air is as clean as it will ever be in the system. The PCV system that all modern cars are required to have introduces oil vapor into the intake stream. This causes problems for MAF's because it can cause a build-up on the sensor. A catch can can greatly help this, but catch cans (especially ones that vent to air) are illegal by most emissions laws. The other issue is that MAF's really like a straight pipe before and after. This keeps the turbulance of the air to a minimum and thus the reading more accurate. This can cause packaging issues for alot of cars. If you look at the VF kit though the MAF has a throttle body on one side and a curve on the other. So I think there is room for improvement.

So now we've seen the downsides, what are the upside of a blow through MAF? The MAF measures the air volume that passes through it. Any changes in the air volume after that negatively affect the fuel trims. So for instance in the VF the MAF measures air at the filter. It then travels quite a distance before it actually goes into the engine head. There are many points for air leaks. By moving the MAF to nearly infront of the intake manifold now any leak in the intercoolers or supercharger or charge pipes is non-threatening. Only leaks in the intake manifold now affect the tune.

The other feature is more profound. By having the MAF at the intake, the MAF will see the air temperature as it is coming from the outside world. This temperature will then be used to set trims for the fuel and timing. So no matter the heatsoak or the amount of boost the ECU will always see a very steady air temperature. I have verified this with an OBD-2 scanner that allows datalogging. The MAF air temp sensor would read about 2* above ambient and stay there. By moving the MAF after the intercoolers we can now see the actual temp of the air. After its been heated up and then cooled back down. I haven't found much info about it, but it looks like MAF's have an upper limit of about 170-190*F. So another reason for 2 intercoolers....wanna stay within the resolution of the MAF.

By moving the MAF to in front of the intake manifold you also measure the air almost as soon as it goes into the engine. I don't know if this will increase throttle response. The throttle body itself is still a good distance from the engine head, but at least were measuring the air more accuratly. I have noticed on mine that when I stab the throttle very quickly and then release the engine takes a second to respond and then sounds like its bogging a bit. Its not like a good all motor where cracking the throttle gives a nice instaneous and confident rise in RPM's.

So for the MAF, I plan on mounting the air to water (A2W) on top of the engine. The air to air (A2A) will be on the side. Air will exit the supercharger and go into the A2A. The air will then enter the A2W on the drivers side. The charge pipe on the A2W will be 3". This way the MAF will see the same cross sectional as it does in the stock location. This is vital for tuning. The charge pipe will then make a 180* turn on the passanger side and head back towards the drivers side. This should give a nice length of about 14" of straight pipe. The pipe will then make a 90* turn. I will then use a 90* 3" to 2.5" silcone reducer to then connect to the intake manifold. The MAF will be situated in the middle of the straight run of pipe. That will give about 7" of straight length on both sides. Hopefully this will provide plenty of time for the air to set a good laminar and get a good reading.

Now for a visual representation. I am not the best at 3D modeling, but I think you get the general idea here. Its actually not that complicated.

3D Mockup of intercooler piping (view 1)
3D mockup of intercooler piping (View 2)
Currently for VF Stage 2, I believe the pulley is 3.0". I will probably go down to a 2.9 or 2.8 if things are looking optimistic. I don't know who makes them in those sizes so I'll need to investigate. I'm still on the stock engine so the 2.6" or whatever that is out there is too bold for me.

I am most interested at seeing what the intake air temps will be afterwards.


Oil Sandwhich Delete

To repurpose the front oil coolers the sandwhich plate on the oil filter needs to be removed. To do this, Toyota Part 90904-04002 will need to be used. It uses a hex shaped bore to be tightened. (Picture copied from Lotus Talk on this thread)

2ZZ Union to delete oil sandwhich

Proof Of Concept

To see if the blow through MAF concept would even work, I decided to fabricate a aluminum pipe that went from the supercharger outlet that loops around to the manifold intake. Inline with this I will put a MAF housing. It will all be 3" pipe and the silicone couplers will transisition from 3" to 2.5".

I bought this 3" kit from Frozen Boost
aluminum pipe kit

And this 3" MAF housing from ATP Turbo

atp maf housing


Created a simple loop that fed from the outlet of the supercharger to the inlet of the intake manifold. I rotated the elbow on the Vision Function kit 180* and it fit fine.

The system is made from 1 U-bend and 1 J-bend as well as the MAF housing.

MAF Front

You can see the MAF is now on top of the engine. To do this the harness needs to be lengthened considerably. I used 20ga stranded wires and added about 24" of length. Be sure to use heat shrink and solder to make a solid sealed connection. There are 5 wires on the MAF. The 2 Yellow wires are tied to each other so it doesn't matter which one you wire on each end. The Greens however look the same, but are two different signals, so you need to take care to differentiate one on each end of your splice so you don't confuse them. I used a Sharpie and drew a dash on one of the green wires at both ends of the exposed harness.  The blue is by itself. I also put some sleeving over the wires to protect from heat, water, grime, etc.

MAF Wiring

Heres some videos of the experiment. It seems to work very well using the tune that I had to begin with. Responsivness of the engine feels improved. You can see that the MAF actually reads a much more accurate temperature. The idle is a little rough, but I think a tune would make it managable.