Building for low revs, part 2: The turbo(s). (long post)

LincolnMarkVII, here is some food for thought:

An intercooler on a normally aspirated engine is going to do zip. If anything it will actually be a heat soak that raises the incoming air. As much as I detest the term, a "cold air intake" (CAI) is going to be the most efficient method of lowering the supply air temperature...., but be very much aware that increasing the length of the induction pipe can have a marked adverse effect on power delivery. Invariably the CAI will have a pod filter attached to it which will allow noise breakout, giving the impression of increased performance.

For every kW of engine power you will be pushing about 1 l/s of air. For every degree drop you want to get using refrigeration you will need 1.213 watts heat rejection per kW engine power. For instance if you have 50kW engine power and you want to drop the incoming air 5°C you will need 303 watts. A thermoelectric cooler (peltier) typically has a COP of about 0.7, so you input power would be about 212 watts (17.6 amps).

Unfortunately this only applies to sensible heat and does not factor in latent heat. So all that mositure in the air must also have an energy loss, without reaching dewpoint. So if you were to say the sensible heat ratio was something like 0.6, the peltier would increase in size to 303/0.6 = 505 watts.

You have to then ask yourself what benefit, say a 5°C drop provides in terms of density. With a turbo charger the intercooler is dropping in the vicinity of 50°C. The increase in the number of oxygen mols per degree at atmospheric pressure is very minor and the deleterious effect of higher ambient temperatures on combustion within normal ambient conditions is minor too, unless you live in a very hot environment (in which case you will probably be more concerned with how hot the cabin temperature is and no desire to be sprinting on the street)

You undoubtedly will be trolling the net for the guff on the ram air systems, some members have recommended. These are a nonsense and can easily be refuted, if not in practice, then theoretically simply by working out the upstream stagnation air pressure of the car travelling at speed.

I mentioned the Peltier for one reason: It's capable of cooling below ambient temperature. In fact, that's why it's not more popular with PC overclockers.. cools below ambient, generates condensation on a poorly-sealed overclocking setup, ruins the motherboard. Anyway, all the radiators in the world can only cool as far as ambient. I was thinking about the possibility of cooling as close to ambient as possible with the radiator (within reason, obviously.. I don't want an engine bay full of radiators) and then giving it that extra chill with a couple of Peltiers. Cooling for a Peltier or set of them can be a heat sink and a fan. I suppose to get into the truly ludicrous, one could even go as far as to have a radiator to cool the hot side of the Peltier(s).. but like I said, engine bay full of radiators: Do not want.

As for a shaker hood.. interesting idea, and I have thought about a shaker in the past.. but the current plan is to make a carbon fiber cowl hood of my own design. Yeah, there's that little problem of me not knowing how to do carbon fiber yet.. (don't worry, I'd want to paint over any carbon fiber body panel I'd use.. I'm not into the "carbon fiber look") but I have awhile yet to solve that. To try to hang onto some of the sleeper look, but gain a little wiggle room for the 250, I'm hoping to make a hood that raises the existing hood lines, and adds a second set of hood lines meant to try and look natural. I never really liked that boxy cowl look. The hood of the new Jag XF is roughly how I imagine it:

http://www.automobilemag.com/reviews/ja ... to_01.html

(I started this before the above was posted)

How about the BA Falcon bulge - it looks very nice:



http://cgi.ebay.com.au/BA-XR8-BOSS-STYL ... dZViewItem

I don't need to go off chasing after info on ram air setups. I'm aware of what's out there that could be adapted to my use, if I were really interested in using it. Now I could be wrong.. it's what I'm good at.. but I would imagine I would not get the most benefit out of a ram air system simply because the car would rarely see really high speed for long periods of time. (70+) This will be total around-town toy.. tons of gear-thrashing between 30 and 60 mph, going around corners faster than the car could handle in stock form, etc. If it can handle the occasional jaunt on the Interstate, that's fine.. but I have my Mark VII for road trips, and that's much more comfortable for that sort of thing.

The talk of an IC on a naturally aspirated engine is confusing. Whatever I do to the car, it will have forced induction. Being a once-in-a-lifetime type project, and being that I've always wanted something with forced induction, how can I not? I'm guessing you mentioned it for explanation purposes.


Actually that BA Falcon bulge is closer to what I had in mind as far as the center section.. lines, height, etc.. but I was hoping to step the hood up to where I could tuck a couple gauges under the middle of the cowl if the urge hit me. (although hopefully recessed a little more than people usually do, so they're a bit less obvious to anyone not in the car)


Sorry if that's a little more rambly than usual.. been up since 1 in the morning.

Well if you are talking a turbo, then an intercooler will have many benefits and you don't have to get too clever with one. Properly sizing it for say 80% efficiency will knock a lot of heat out. But there are always tradeoffs because of increased friction and dynamic losses.

When you install an IC you have to increase the operating PR of the turbo to compensate. Your throttle body size will change (increase) because of the increased density. Necessarily there will be an introduced lag while the air compresses and fills the increased volume pre plenum.

TMIC with a shaker might be be very effective, but FMIC is going to give you best temperature drop, but then it's going to have a more pipe and bends introducing losses.