When I finally poked my head under the car with a flashlight, I could see something was amiss in fuel pump land. The "sled" that the main pump rides on was barely hanging on by 2 bolts and there were quite a few zip ties and drips of fuel. I jumpered the pumps at the fuse panel and found that the in-tank pump was DOA and the main pump was on its way out. That explained the grumpy sound that would emanate from under the back seat.
Probable culprit found; now to decide on replacements. I didn't want to touch the pumps again for a long time so I figured I'd better build in capacity for my planned power goals.
I posted this thread asking for recommendations in my particular situation:
http://forums.turbobricks.com/showthread.php?t=224579
I had to make sure the new pumps would work (for a while at least) with the B21F running k-jet.
Time for some math:
Eventual max crank power goal: 400hp
BSFC assumed worst-case: 0.65
Fuel flowrate required = hp x BSFC = 260 lb/hr = 186 L/hr of gasoline.
Fuel pressure required = base pressure + total boost (est) + pumping losses (est)
= 43.5 + 25 + 5 = 73.5 psi
The above was calculated considering the future B230FT making somewhere around 400hp, which gave me a reasonable maximum limit to consider. I know it will take some work to get there!
One of my co-workers gave me a neat old K-Jet booklet from 1979 after he saw my car. On page 4 we learn that the naturally-aspirated k-jet main pump is regulated to 110 L/hr @ 5 bar. So I that gave me a lower end limit to work with. In the beginning of the booklet, we also learn that "your advantage" is "the K-jetronic from Bosch," also that k-jet is "forward-looking!" Swell.
Here's some fuel pump geekery, compiled from a variety of different sources (not my data):
Pumps@13.5V by
Chris Floren, on Flickr
The following is copied from my fuel pump thread:
"I don't know how much trust to put in these curves; the data was taken from many different sources so there may not be a true correspondence between pumps due to variations in test method, test rig setup, instrumentation used, and so on. But it's all I've got for now.
As you can see, the popular Walbros and Bosch options are shown along with the new Deatschwerks in-tank pump and a few options from Aeromotive. The light green line near the top, "Walbro 255 x2 in series" was taken from some testing done by AMS. They were comparing various single pumps to others mounted in parallel, and others in series. Since I want to try the series setup (i.e. stock Volvo layout) for now to keep it simple, that's what I was interested in. I know that two 044s in parallel will give me enough fuel to make one million horsepowers, but I'm being realistic (for now) and saying my car will eventually make 300-400hp at the crank. So looking at the two 255s in series, I saw that the flow stays much more constant as pressure rises when compared to the single 255HP. I was disregarding actual flow values and looking at the slope of the curve...between 40 - 90 psi, the single 255HP loses almost 30 gal/hr whereas the two 255HPs in series only lose 12 to 13 gal/hr.
From there I assumed that since a single 044 apparently can flow very similarly to two 255HPs in series, why not put a 255HP in series with an 044 and bump that curve up even further? I don't know exactly how to calculate the theoretical performance of two pumps in series given the curve for each pump individually, so I didn't want to speculate on what that would look like...just assuming that it should be better than the single 044.
The four single points near the bottom of the graph show what my engine(s) might need in operation. I read somewhere (?) that the stock K-jet system puts out 140 L/hr @ 5bar, so that's represented by the grey X. The other three estimate turbo'd performance with a lot of educated guesses and theoretical calculated boost pressure, all at 6000rpm. Purple diamond is what might happen when I swap in the B230FT running LH2.4 making 300bhp. Teal square uses the same assumptions at 400bhp target. Orange triangle assumes worst-case BSFC of 0.65 for the 400bhp target, so I figured that would be my worst-case fueling requirement. You can't get me lucky charms!
Now I know that all of these points lie well below even what a single 044 can do, but I'm thinking that even with stellar wiring the fuel system will still have some restriction which will increase demand from the pumps to meet the required pressure at the fuel rail. Also, all this data is at 13.5V; I'll have to see what they end up running at voltage-wise but I'd assume it's going to be lower unless my charging system and wiring are phenomenal, which they aren't. Call it a Volvo-Wiring-Safety-Factor (VWSF)."
So the decision was made to go with a Walbro 255HP in-tank, feeding a Bosch 044 main pump, for these reasons:
1) both pumps should fit in the '81 242 with minimal modifications
2) the combination of 255hp in series with the 044 should (I think) help to maintain fuel flow as pressure is increased, i.e. flatten out the total flow-vs-pressure curve to be more consistent than either pump would be by itself.