Whats the biggest difference between...

[Slacker]

Hoping someone could tell me the big difference from a B&m 177 or 250 from a 6-71. Why would you run a 177 instead of a 671? Any pros or cons? About the same price (depends where getting from). I know the 671,871`s are popular but i dont see many 177`s or so around. Any help would be appreciated.
Thanks .....CT

[TIMINATOR]

The wannabe blowers heat the air a lot more, and have durability problems. If you have a bigblock get the 8-71, with any decent heads and cam you'll need it. TIMINATOR

[Slacker]

Thanx

[Craig]

The wannabe blowers heat the air a lot more, and have durability problems. If you have a bigblock get the 8-71, with any decent heads and cam you'll need it. TIMINATOR
I have a 420 with about 150 hours, never had a problem. 878 horsepower. But if I had to start again, I would go with the 8-71.

[RumRunner]

Actually boost is boost. 5 pounds of boost regardless of the size of blower will generate the same amount of heat. A smaller blower spinning faster will accelerate better than a larger blower spinning slower. It's a matter of getting something that is going to be effiecent on your combination. On a 454 a 250 Blower producing the same amount of boost (same power) as a 6:71 will give you smoother throttle response, and better acceleration.

[Craig]

So you're suggesting that if I put a 174 blower on my 509 and spun it fast enough to produce 5 pounds of boost, the blower outlet air temp would be the same as the air exiting a 10-71 on the same engine spinning to make 5 pounds of boost? I think the blowers efficiency would effect the air temp on the smaller blower?

[Infomaniac]

Actually boost is boost. 5 pounds of boost regardless of the size of blower will generate the same amount of heat.
I'm really surprised to hear that from you man.
I don't have time for a long drawn out debate but I strongly disagree.

[Havasu Hangin']

I'm really surprised to hear that from you man.
I don't have time for a long drawn out debate but I strongly disagree.
Let me take a shot, Info:
The heat from compressing the air may be the same...
...but the heat from the rotor friction spinning faster will be greater?

[RumRunner]

Boost is boost, when air is compressed in an engine to produce additional pressure it generates heat. It will take the same amount of compression regardless of the size of the supercharger to make this boost, which means that the temperature increase going from atmospheric pressure to say 6lbs of boost on a specific would be the same regardless of blower size. Now yes the smaller blower will have to work harder (spin faster) to generate the same amount of boost, which will intern create some more heat. From all of the tests that I have seen measuring inlet, and outlet differences they will be negligible in most applications as long as you’re within the efficiency range of your Super Charger.
Craig,
In your example no, the answer would be no. The smaller blower would run much hotter outlet temperatures since it would be too small for your application. Now at 5 lbs of boost on an engine of that size a 10:71 would probably be too large, and inefficient. Where as a 6:71 would probably give you better acceleration since it would be spinning faster, but wouldn’t loose out at the limited RPM of most Marine Engines. The only advantage to a 10 in that case would be for the mines bigger than yours factor.
You have to size what you’re using to work as a complete package.
Infomaniac,
I'd love to hear your reasoning.

[superdave013]

Slacker, how much boost are you trying to make? How are you going to use the boat? Are you going to cruise it around and lake race every now and then? Or are you planning on going down to blyth and sawing off some of the big hitters?
Rumrunner must deal mostly with I/O's with that low RPM thinking.
With my 461" with an 8-71 (re-stripped every race) I would spin it at 35% over to get 30 pounds of boost @ 8,000 RPM. The discharge temps (with out looking at my old notes) was around 350+ degrees above the intercooler and a right around 100 degrees in the intake. That's Lake Ming water early in the season. I have to think that if I could have ran a larger blower like a 14-71 I could have spun it much slower to make the same boost with less discharge temps. I guess the key phrase in his post is: "From all of the tests that I have seen measuring inlet, and outlet differences they will be negligible in most applications as long as you’re within the efficiency range of your Super Charger." I must have been outside that window.
That's another rant I had when I was shopping for a blower. I deal with industrial fans, blowers and pumps all the time. I always get a fan curve or a pump curve. That's how you select them and know how much HP you need to turn them. When I asked Gean Mooneyham and Mert Littlefield for the blower curves they both looked at me like I was crazy. They had some half ass charts but no real graph showing the performance based on Air Flow @ 70*, (blower) RPM, static pressure and HP. I know on an industrial blower getting on the wrong side of the curve is not good at all.
I bet there alot of guys running thier superchagers on the wrong side of it's performance curve.

[RumRunner]

SuperDave,
You are 100% correct IMO. Based on the size of the blowers Slacker was talking about I was assuming a cruiser not a drag type application. You'll be hard pressed to get actually flow charts on Superchargers from what I've seen. It all goes based upon someone expierence.

[BlownBBC]

By stating Boost is boost, you neglect the importance of compressor efficiency.
Since the ideal compression process is impossible to achieve, we need to be more realistic and work with compression processes that involve actual compressors or superchargers to accomplish the compression work. In this sense, you must consider the “efficiency” of the actual compression process relative to the ideal process. This is called the “isentropic efficiency”. An isentropic or ideal process would also be 100% efficient. Actual compressors, therefore operate at efficiencies below this level and the further this process deviates from the ideal, the less efficient it becomes and subsequerntly the greater the temperature rise.

[bigkatboat]

Back in the 80's we did some Marine Blower testing for B&M, while Dick and Mike Landy did their dyno testing. The most outstanding thing about those small two lobe rotor superchargers, was the heat factor. On a factory stock Volvo 290 (5.7 Chevy) the small blower @5 lbs was in the 420 degree (F) range and @ 8 lbs it ran around 550 degrees (F), inlet temps. We water tested at Castaic lake durring 70/75 degree weather. This indicates to me that @8 lbs ONE THIRD OF THE BTU (thermal efficiency) is lost in the intake system. I want the fuel to start it's burn at 100 degrees and finish with a 1500 degree EGT, not start at 550 degrees and end up with a 1550 degree EGT. The small two lobe blowers run at or above 45% OVER crankshaft speed, this along with their 'less efficient design' cause them to over heat the inlet temps. The rotors at those high speeds don't have time to transfer heat to the case walls (fluid transfer as they pass by), and the bearing/ gear temps are way up too. While (drag) racing boats we have found that we could not put 'too big' of a blower on a motor. If boost is 'just boost', all 5 lbs systems equal, why intercool? I would always run the biggest blower I could get, you should too. PS, turbos are even better than blowers.

[superdave013]

You'll be hard pressed to get actually flow charts on Superchargers from what I've seen. It all goes based upon someone expierence.
And that's my rant. Why not? I have the blower curves for 100's of indurstial roots blowers. That just blows me away that the same chart in not included with performance blowers. How the hell does a guy select the right one and the rest of the combination? When a guy just says "you need this" the very first thing I'll ask is why do I need that over something else.
I want to see the f'in data man. Performance blower selection seems to be based on folklore more then hard measure data.
Take a peek at the data that's at everyone's finger tips for turbo selection. Why don't the blower guys have that info?

[RumRunner]

And that's my rant. Why not?
Take a peek at the data that's at everyone's finger tips for turbo selection. Why don't the blower guys have that info?
If I had to venture a guess I'll bet true data doesn't exist. You're dealing with a side of the industry that started rebuilding cores, and then built what they were asked for. I'm sure some of them could give you some statistical numbers vs. something else but true charts you probably won't find. That portion of the industry didn't develope that way.

[JPA]

I have a 420 with about 150 hours, never had a problem. 878 horsepower. But if I had to start again, I would go with the 8-71.
I have a buddy with a 420 mega blower on his 468. I always thought it was an 871,....is is a 671?
Joel

[superdave013]

If I had to venture a guess I'll bet true data doesn't exist. You're dealing with a side of the industry that started rebuilding cores, and then built what they were asked for. I'm sure some of them could give you some statistical numbers vs. something else but true charts you probably won't find. That portion of the industry didn't develope that way.
I do understand it started from GMC cores. But I'm not letting them off the hook that easy. Why would they not test them and graph the results?
It's not like that is a very hard thing to do.
I got a new intercooler and the very first thing I did was hook it up to a fan with a gas burner to up the temp to 400*. I also ws measuring the GHP and temp of the water. I wanted to know not only how much it cooled but what the differential pressure drop was across it. I tried to show the set up to the company that made the cooler but that 1/2 hour drive must have been to much. They had no intrest in real bench test facts. To bad for them because that intercooler's (heat exchanger) performance impressed the guys that design the exchanges here.

[RumRunner]

But, that is what you're dealing with. Most companies aren't going to spend more money to test a product that their current customer base doesn't require them to. If they were looking for new business they might, but most of them can't keep up with their demand.

[superdave013]

I'd want to know just for my own bad self. I think it would be nice to know the performance of what I'm selling.
I have seen some curves on some of the new blower companys. Long after I was in the market. I would think these new players can use that tool to nab some market share.
Hey man, I'll look you up at PRI to put a face with your screen name. I've read your posts on there sites for awhile now. Good to see you made it over here.

[bigkatboat]

"JPA", the '420 B&M' is not close to a 6-71 at lower speeds and 'not quite there' at WOT. Even the Weiand (casting) 6-71 does not breath like a GMC 6-71. Mercruiser uses the '420' style blower on their 575 HP. That motor is only getting 5 lbs @ under 2500' altitude, and is only rated @ 575 flywheel HP. The small blowers can give a "boost" to stock motors (Cameros & pick ups) at lower crankshaft speeds, but larger, custom built marine motors breath better than the small blowers do at most all crankshaft speeds. Also, the Merc 575HP has such a small cam that any blower will show boost in that motor. This brings up the other questions as to blower size/ motor size/ blower speed/ cam timing/ power band, and if more boost is helping or hurting the motor. It does "cost something" to turn any blower, is the price too high? Crankshaft load, heat, air/ fuel separation, are all factors that most don't consider when installing a blower. In other words, if the blower added 100HP to the motor, and the inlet heat (tune up) along with the belt load (turning the blower) on the crankshaft cost 75HP, what did you really gain? YES! it's a little faster, but it could be better.

[Slacker]

Thanks guys for all the input. Just trying to do some research, thinking about adding a blower for next season. I just want to have some more speed and of course the whole blower experience etc.. not looking to be the fastest, besides there is always somebody with more time and money. Just something i have always wanted on my boat.What i am gathering is the little blowers will produce more heat than the bigger ones. I know alot will depend on the motor, heads, cam etc... I know bigger is always not better. ----Chris

[Infomaniac]

Infomaniac,
I'd love to hear your reasoning.
My reasoning is...... Looking at a pressure guage connected to the intake manifold reading "boost" the pressure could be from nice relatively cold air delivered by a large supercharger or heat expansion from hot air delivered from an overworked small supercharger. Both might read the same pressure but are not nearly the same. One will make a ton more power than the other even though they register the same pressure.
If you plot a boost curve along with a torque and HP curve. In a poor combination you might see boost go up and power go down. This is due to heat expansion and not to the blower's ability to feed the engine with more than it can breathe.

[RumRunner]

My reasoning is...... Looking at a pressure guage connected to the intake manifold reading "boost" the pressure could be from nice relatively cold air delivered by a large supercharger or heat expansion from hot air delivered from an overworked small supercharger. Both might read the same pressure but are not nearly the same. One will make a ton more power than the other even though they register the same pressure.
If you plot a boost curve along with a torque and HP curve. In a poor combination you might see boost go up and power go down. This is due to heat expansion and not to the blower's ability to feed the engine with more than it can breathe.
Do you have numbers where you'd expect this to happen? The reason I ask I've witnessed an engine make more power (with the same amount of boost) using a smaller supercharger. Never measured the inlet and outlet temp on that specific engine, but the air in the dyno cell was exactly the same for both. I would attribute the additional power to less loss from having to drive the supercharger (even with the additional heat). Granted this was on a 454" with only 5lbs of boost.

[BlownBBC]

Boost measured with a pressure-sensing gauge does not take into consideration temperature of the A/F mixture. The hotter the mixture, the less dense the air/fuel is, the less power the engine will make.
If the temperature goes up a lot when you increase the boost you can end up with fewer pounds of air going into the engine, so you lose power. That's why a Roots blower is bad if you want lots of boost. Screw compressors, like the WhippleCharger and Centrifugal superchargers like the Vortech and ProCharger have good compression efficiency, which translates into more power with the same amount of indicated boost pressure in the gauge
If you truly want to see what’s going on you need to use the Ideal Gas Law (PV=NRT, where P is the absolute pressure (not the gauge pressure), V is the volume, N is related to the number of air molecules, which is an indication of the mass (or pounds) of air, R is a constant number, and T is the absolute temperature.) to measure the mass air flow.

[lucky]

so if i use Two 177's on a custom made tunnel ram type intake( like a whipple does -- where do you think we would end up -- just a silly question - but it might be cool

[Badburn]

I've had good experience with the 177/174 blowers, and an 8-71- both combos producing about 10 lbs of boost.
Anybody got a dyno? I got a motor and all the parts to answer these questions???

[Infomaniac]

so if i use Two 177's on a custom made tunnel ram type intake( like a whipple does -- where do you think we would end up -- just a silly question - but it might be cool
I've thought about doing that myself. But after measuring the 177 and even the 144. They are much larger than a 2.3 or 3.3 Whipple.

[superdave013]

I've thought about doing that myself. But after measuring the 177 and even the 144. They are much larger than a 2.3 or 3.3 Whipple.
I saw a small block with two 6-71 out at the pomona swapmeet. Get this, it was stuffed into some kind of motorcycle!

[lucky]

I've thought about doing that myself. But after measuring the 177 and even the 144. They are much larger than a 2.3 or 3.3 Whipple.
still could do it with efi - or mill some carb adapters ? I know YOU COULD DO IT RON .

[Infomaniac]

Yea I didnt have a machine shop then. LOL
But they are really long and cannot get an assortment of drive lengths.

[lucky]

Yea I didnt have a machine shop then. LOL
But they are really long and cannot get an assortment of drive lengths.
open penium tunnel sheet metal intake with off set mag drive -- You could do like me and put two million into a 10,000 dollar boat :)