Engine and Transmission Tech

I wonder if this is the proper place for A/C related questions? Well I suppose Curtis will have to move it if not.

So my immediate concern has to do with compressors and in particular, selecting the most compact and powerful unit that can be stuffed under the hood. If you've followed my 340 thread you know why power is desired, if not, let's just say I want to be as cool as is humanly possible. So then it seems the Sanden is a popular choice. Their SD7H15 model has a displacement of about 9-1/2 cu.in. which seems to be close to the upper limit of what is available. (York compressors were available in 6, 8, and 10) The Harrison R4 which is short, fat, and should fit well in front of the cylinder head is 10 cu.in. Is anyone familiar enough with these things to suggest any other alternatives? Thx.

Jim

Jim, Word on the street is "Vintage Air" makes their own. It appears very compact and I've seen it on several hi-end cars. Don,t know the cu. inches. Cabin cooling or............ Good Speed, roverman

Their site was helpful. But their tech email address bounced my letter. Still writing it out helped define the system and I'll copy the important part of it here:
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I’m working on a dual evaporator system to go in a V8-MGB. The main evaporator is 13”x 8”x 3” and application was BMW. This evaporator is housed between an Eaton M-112 blower and the intake manifold feeding a Buick 340 cid V8. The secondary evaporator will be an in-dash unit, dimensions and configuration yet to be determined. The condenser can have up to approx. 460 sq.in. of surface area with roughly 16”x 28” dimensions. Each evaporator will have an individual TXV and solenoid valve, the TXV on the main evaporator has a 2-1/2 ton rating and superheat of 3. I’m thinking I need to go with the biggest compressor I can fit on the engine for this rig, the R4 would fit nicely in front of the cylinder head but I can probably go outboard if I need to in order to fit a larger unit such as the A6. (12+ cu.in.)

Operationally the main evaporator will be switched in by solenoid on demand under boosted conditions and will be operational for only seconds at a time so it is critical to dump as much Freon into the unit as possible initially. The secondary will also be switched by solenoid, most likely in an “OR” configuration. For this reason it appears a smaller compressor and an accumulator of some sort might be made to work. The secondary evaporator will be operated to deliver cool air into a cockpit with the top down under most conditions and a custom unit having a cooling capacity compatible with the main unit will need to be designed. However, the main unit will be operating under elevated temperatures (from ambient up to approximately as much as 200 degrees F over ambient) and will therefore function more efficiently in terms of evaporating the coolant, so sizing gets a little more complicated and fitting the secondary behind the dash will be a challenge. This unit will also get a solenoid and TXV, specifications yet undetermined.

What I need, is to work out the best choices for compressor, condenser, and secondary evaporator/TXV combo. So I have a couple of questions I hope you can answer.

First off, will the 2-1/2 ton TXV (4 seasons # 38882) of the primary evaporator be capable of passing at least the full output of a 12 cu.in. compressor, assuming the superheat remains elevated, and would it be capable of also in addition to that, emptying a reservoir of reasonable size over a 10-15 second period? If so, how large could that reservoir be?

Secondly, given the above, roughly how large would the secondary evaporator have to be and what TXV specs would be needed in order to handle the full output of the compressor without risk of overpressure and compressor stall? I realize that a high pressure cutoff could band-aid the system if need be but would rather avoid that, but on the other hand, refilling the reservoir would be an advantage. I can also incorporate electronic controls for compressor management if it comes to that but would prefer to size the system and charge it so that the pump inlet pressure drops enough to limit pump output as the reservoir reaches full capacity. In other words, starve the pump somewhat to limit head pressure under normal cabin air conditions while maintaining a full reservoir, and then under boost, shut off cabin air and flood the intercooler with the accumulated fluid while maximizing pump output.
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This is the operational theory at present. I anticipate removal of the stock (modified) heater box and possible modification of the firewall to get a large enough evaporator in there, but that can come after the car is roadworthy if needed. So now I need to see if there is an A6 mount for the 340 or 300 which will work for my application.

Jim

Jim, I know precious little about the finite details of AC other than , hot-in, cold-out. Less efficient system , but simpler would be using the cabin ac.'d air directed via flapper door into air inlet of motor,(pre-cooler). Either way, I would want to cold-soak, the inlet tract, while staging, prior to "launch". Cool ideas for the hot set-up. roverman.

Right-on Roverman! I figure to work for about a 15 second dump and hit it just before launch. Did you ever take a small propane bottle and a coat hanger, point it down and let 'er rip? Freezes bumblebees instantly! (and they ain't too happy when they wake up!) Gets you about a 1ft diameter frost zone. That's similar to what I'm going for here. Enough to normally freeze up the core right away but as the revs climb, the and the boost comes up it will make enough heat to melt off any ice that happens to form, and in a few seconds it's all over. Once boost drops off the pump will start to refill the accumulator. For street driving just tie it to boost levels and kick it in whenever there is positive pressure, or even a certain vacuum level.

Years ago a Magnuson engineer I talked to figured a small air/water IC could drop charge temps 50-70 degrees (I have his notes) and I expect this one has a good bit more potential than that, although possibly more airflow resistance too.

Found out I have a stock compressor mount that fits the 340. I might be able to use that with an A6.

Jim

Annnnd....did anyone metion NOX as combustion enhancing/charge cooling medium? Can't ya just smellit? Not the laughing stuff- the schredded tires? Power to the people,roverman.

Art, if I don't have enough 'power under the curve' with this one,... well then NOx might be the answer, but I do believe it'll be enough for awhile. Just have to wait and see what the boost level is, IIRC the drive is 6-3/4" and driven is 2.8" (not positive on that one but close). That means big speed on the blower, in fact a bit more than on my 215 which ran 16psi. Blower is bigger too, 112 vs 90. But I'm occasionally math challenged. How that works out with 340 vs 215? Should be less but exactly how much less I don't know. Somewhere north of half I suppose. I figure on an easy 300hp.

Jim

Jim, Yeah RWHP. Don't know what your charge air temp on previous build was , but this new set-up should be waay denser, crammed with chilled hp. Sounds like the bigger problem will be puttin it to the ground. Your 3.85" stroke isn't going to like alot of rpm. Got good rods? Plenty of rear tires? roverman.

Art, check out the 340 thread for build details. Scat 7" rods, light Venolia slugs, it'll rock-n-roll. Figure about a 7K redline. Tires are 315/35-17 iirc and the same IRS that is in the MGB-Roadmaster but with better gears and posi. Butchaknowwhat? I WANT to be able to light 'em up!

Jim