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· Administrator
14,391 Posts
Discussion Starter · #1 ·
Dear Members.

I all ready have the radiator block mod on both my vehicles, and that does help them to warm up quicker on cold days, however the cold air intake temp is an issue, with LB more difficult to obtain and maintain.

I have read the hot air mod posts and other pre heat ideas, and have been thinking about a couple of solutions.

1) Use a small cpu cooler radiator in the air intake system to pre-heat air.
Use warm water from return side of car heater system diverted through this small rad before going back to engine block.

Something like this rad 120mm square should be fairy easy to incorporate into air intake system. Smaller sizes are available.

I would use the return side of the car heater system to avoid too much of an impact on the car heating! This use of warm water rather than hot would also probably put the intake air temp rise into the optimal range. Use of the hot water might be too much heat! This could be controlled by an electronic divert flow valve.

2) Use the above radiator idea, but collect heat in the form of hot water from the exhaust system after the cats. This would require the fabrication of a section of exhaust pipe with an outer low capacity water jacket. Insulated pipes and a small 12v cpu cooler pump would then feed water to the air intake radiator. Replacing the first muffler/exhaust box with a heat exchanger assembly might be the best bet.

Low power 12v 12w pumps are here

I'm now looking at the Insight engine bay and working out were to put the stuff and what to try first. Option 1 is probably the easiest so i'll try that first. I appreciate there is little spare engine heat.

It would be pretty easy to control any pump via a simple electronic stat in the post radiator air intake system to avoid over heat of intake air.

I haven't looked at the fuel supply pipe run yet, but again low temp water say <35C could be used with a heat transfer jacket on the fuel pipe to pre-heat fuel if it is accessible.

I'll keep you posted of course.

Anyone know the air flow in CFM at the air intake at an engine speed of 2500rpm? This would help with intake radiator sizing so as not to restrict air flow too much.

Regards Peter

· Registered
1,325 Posts
If you have a small digital camera, it would be interesting to find out which way the air flows through the large opening in the front wheel well. (The one that the steering rod goes through.)

Most front wheel wells suffer from high pressure caused by the rotating wheel acting like a pump. That's why there are vents on the tops of the fenders of some racing cars--and some modded Porsches.

In the case of the Insight, from the aerodynamic viewpoint it would be nice to be able to seal the front wheel opening underneath, to make the bottom of the car flatter. There are two problems:

1.) As a production car, the Insight has to take into account the possibility of mud, tire chains, etc., to make the car user-friendly. If you don't care about those things, you could make a panel that barely clears the tires and effectively seals the underbody around the front wheels.

2.) But if the cooling system depends on airflow through that opening, that is, if the radiator cooling air exits into the wheel well, sealing that area of the bottom of the car would be bad.

So if you knew which way the air flowed through that big hole, you could decide whether to seal the bottom of the car in that area.

· Premium Member
4,836 Posts
Rick Reece has been a leader in hot air mod design in the past. Looks like your poised to "overtake" him. ;)

His experience (and I would also concur) is that maximum benefit peaks around 110F IAT Intake Ait Temperature as measured by the IAT sensor). My observations for an absolute peak IAT for hyper MPG would be 120F (49C). He rigged one that provided 150F (65C) with _no_ discernible MPG improvement. :shock: The trick is that since ambient so variable that the peak amount heat needed to add to the intake air must relatively large and also be quite variable. It appears that in lower temps (sub 40F (5C)) the rolling resistance of cold tires becomes a more significant factor in hyper MPG. So any hot air mod that has the punch to heat colder air also has a lower "pay back".

A quick CFM calculation for the Insight a 2500 RPM would be:

Displacement 1000cc
Cycle 4

therefore intake volume will = 333.33cc / rev

333.33cc x 2500 RPM = 833,325 cc / min = 83.33 l / min

1 cu/ft = 28.31l

converting = 2.94 CFM / min.

However, since air mass dramatically varies with temperature and pressure (humidity plays a large role in pressure) the amount of heat needed to raise this mass will also be highly variable. Hence the standard units of SCFM (Standard CFM, calculated for a specific temperature and pressure). This unit won't be of help for this application since its air mass and heat transfer efficiency that is significant for this modification.

Kinda reminds me of a story from history where Thomas Edison was unimpressed by a "new" mathematical approach to calculation of an irregular solids volume. While the mathematician was busy doing the calculation Edison simply dropped the object onto a liquid filled graduated cylinder and voilà.

Yup, Edison didn't show the foresight in regard to the potential. And it wasn't until the development of digital computers that it was fully realized. Still a good lesson in perspectives.

And maybe the inverse will also be "true" in some instances. I'm unclear in my mind which perspective will be best suited for further development of this project, having endeavored in it myself. ;) All indications of the theoretical seem to indicate a very low "payback". But a hands on application may prove it wrong :!:

HTH! :)
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