Hi all
I have been condering some way of using the exhaust heat to decrease warm-up time for a while. There are some interesting ideas here
However, I have always subscribed to K.I.S.S. (Keep it simple, stupid), and have a couple of ideas I would like to float.
The first is something I have seen on many (mostly older) cars, and wondered if it would be worth it on a more modern vehicle. There was a cowelling around the exhaust, and the intake air was drawn in through that, henced pre-warmed by the exhaust heat. I know this was mainly to improve cold-running ability, but it seems a very simple method of warming up quicker.
The other idea is an extension of this, but would only work well in a car with a full grill block. Do the same with a cowel around the exaust manifold, but use a fan to circulate air accross it inside the (pretty much sealed) engine compartment. This would quickly raise the engine bay temparatures, which would at least help warm up (albeit probably not by that much). The fan can be turned off at any point, which would effectively break the thermal link between the exhaust and engine bay.
This second idea could be further enhanced by using an oil cooler in the path of the heated air, hence tranferring more of the exhaust heat directly to the engine, and by adding fins to the exhaust manifold (which would probably require the cowel to be insulated so as not to degrade warm-running performance).
As I said, I am not sure how effective these methods would be, but they are certainly simple. If they would work they would be cost- and effort-effective methods.