Originally Posted by MILD THUNDER

One thing I like about large blowers, is they come alive at the higher RPM range, where the small blowers, like the 177's and 250's, start falling off. This is a good thing for outdrives. A small 177 blower, can make LOTS of torque at low speeds. Would be my blower of choice if I was building a tow rig stump puller. They will actually make more power up to, about 4500RPM, than the larger blowers. But, we are talking boats. Having the consistent WOT power maker, where it doesnt get heat soaked and drop power on long runs, or provide a superheated air temp in the manifold, promoting detonation, is the way to go.

Heres an article where they tested a 177 blower, vs an 871 blower, on a 489CI Chevy. Keep in mind this engine made 550HP in N/A form.

The only drawback is that this blower, while conveniently small, is also a bit undersized for the displacement of a stroked big-block. The out-of-the-box pulleys only made 2 psi boost, gaining 82 hp and 70 lb-ft over zero boost. We ordered a 2.85-inch blower pulley (PN 6790, $71) and used it with the stock 6.00-inch crank pulley to make 3 psi at peak. We later tried a 7.00-inch crank pulley for a blower-drive ratio of 2.46:1 and made a peak of 5 psi, good for 749 lb-ft and 700 hp, but the blower had its tongue hanging out. The belt was starting to slip and the case was getting very hot, causing extreme power dropoff in back-to-back pulls.

So 3 psi was about the limit of the blower on this engine. Not that we're complaining about a simple 660 hp and nearly 700 lb-ft.



You see where they said the power dropped off from back to back pulls on the dyno? Now imagine a WOT run across the lake for miles. HEAT. Here is what happened when they bolted the 8-71 on .

In the first test, in an attempt to match the low boost levels of the mini blower, we gave the 8-71 a 63-tooth blower pulley and a 47-tooth crank pulley for a drive ratio of 0.75:1 (25-percent underdriven) and achieved peak boost of 4.8 psi. That was good for 717 hp at 6,200 rpm and 674 lb-ft at 4,500 rpm. That's an increase of 56 hp, but note that we lost 24 lb-ft, even with extra boost. Since air inlet temps were not increased, the only answer is that it just plain eats more power to spin the larger blower. More evidence of that: We gained 1.8 peak boost, but only picked up 56 hp, or 31 hp per pound of boost. With the mini blower, going from 2 psi to 3 psi picked up 30 hp. The 8-71 doesn't gain a torque advantage until 5,100 rpm, when the smaller blower is probably starting to heat up.

That's interesting stuff, especially considering that the 8-71 displaces 436 ci versus the mini blower's 177 ci, which is why the big blower can spin so much slower yet achieve the same boost. At 6,000 engine rpm, our 8-71 was only spinning 4,500 rpm, where the mini blower was cranking a whopping 12,600 rpm. Perhaps that's why the big blower works better up top. But it makes a really compelling argument for the mini blower at low rpm and low boost.

The Glory Run
You didn't think we'd stop at 4.8 psi boost, did you? With a little guessing and gambling, we figured that the cast-crank, stock-block engine would probably stay reliable to around 750 hp, especially since we didn't think we'd have to lean on the blower too hard to do that. The more you crank up the boost, the greater the load you put on the crank snout. With a casting and a single keyway, we weren't thrilled about trying to stuff 8-plus psi into this thing. But we felt pretty good about 6.4 psi, which was delivered with a 63-tooth blower pulley and a 52-tooth crank pulley for a ratio of 0.83:1 (17-percent underdriven). That gave us a nice 766 hp at 6,200 rpm and 726 lb-ft peaking at 4,600 rpm. And, of course, the 8-71 was now in its glory, killing the mini blower at every point in the curve.


So, you might read that and say, the 8-71 at 5lbs only made 17HP more, than the 177 at 5lbs. However, that was a dyno pull for probably 10 seconds. Hold the 177 setup wide open for say 30 seconds, and you'll prob see that gap widen to 50HP or more. Also, at 5psi, the 177 was about done. With the 8-71, the option to go to 6psi was there, and now you have 66HP more, and still a much cooler air charge. Adding 66HP, is probably 2-4mph on your typical setup. My particular boat, gained 5mph, going from a 250 B&M, to a 420 B&M making 6psi. Not to mention the larger blower offers better fuel distribution, lower air temps, and option to really crank up the power. Had they had a forged crank, and turned the boost to 8psi, the HP would have exceeded 800 easily. Not possible with the 177.

Originally Posted by TGM

That's actually quite interesting, so for a boat applications you would want a bigger blower pulling less boost so it will maintain that constant band of horsepower. I'm glad I made this post though, looks like the wrap may get postponed for some engine work this winter. Where can you pick up a 525 cam at?

Originally Posted by 4bus

My old 177s on my 500hp did just that, I would do WOT runs one direction, back off, make a turn, and blast again and I could feel the loss in HP. Stop and let them cool down and they were back to norm. This was most noticeable on hot summer days.

On a side note.....did I read correctly in the "glory run" portion of the article they thought the cast crank was good to about 750hp? Did polsmoker write it? I smell green paint!

Originally Posted by TGM

Where can you pick up a 525 cam at?