Roots Blower Sizing
10-24-2014, 09:47 AM
#41
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I think what Black Baja was trying to say, was that when using too small of a blower for the application, the best bet is to raise the static/dynamic compression a bit. Since the small blower is only capable of so much, getting the compression up a tad, helps the engine make more power on "motor" so to speak.
I agree.
10-24-2014, 10:48 AM
#42
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You guys got the point. I posted my previous comment because I see often where guys try to demand to much out of a smaller blower and the result is a time bomb. With a roots blower there is no indication of detonation unless you stay on top of the plug readings. I just thinks its better to slow the blower down and bring the compression up a little for longevity reasons. Not trying to take away from Joes thread I think it's a great thread. But if your a guy like me sometimes the 8-71 just isn't in the finances and the 250 blower in the swap shop will have to do. Open check book that's a different story. Me I would go past the roots to a screw and it wouldn't begin with a W.
10-24-2014, 11:36 AM
#43
You guys got the point. I posted my previous comment because I see often where guys try to demand to much out of a smaller blower and the result is a time bomb. With a roots blower there is no indication of detonation unless you stay on top of the plug readings. I just thinks its better to slow the blower down and bring the compression up a little for longevity reasons. Not trying to take away from Joes thread I think it's a great thread. But if your a guy like me sometimes the 8-71 just isn't in the finances and the 250 blower in the swap shop will have to do. Open check book that's a different story. Me I would go past the roots to a screw and it wouldn't begin with a W.
My guess is going from an 8-71 at 10% over, to a 10-71 at 1:1, is simply not gonna be as drastic of a temperature reduction, as going from a blower thats 80% over, and then to 1:1.
Some guys have made good dyno numbers using a 250 blower, or 256 blower. Only thing that needs to be considered, is the dyno pull doesnt last long. Hold that little blower at 10000+ rpm for 30 seconds, a minute, on a steady state dyno test, and watch the numbers start to fall off as the blower simply gets HOT.
In some recent testing, a non intercooled 10-71 on the dyno was showing around 130-135* air temps in the intake. The other build, also using a 10-71, but had a blower shop intercooler fed by cold well water on the dyno. At full pull, it was around 112-115* temp in the manifold.
Some things that I wondered about when chewing on that data. The first 1071 was a tight blower. The rotors were stripped on the outside, as well as the inside. At idle, it was heating up a bit on the dyno. Up to around 140-150*. Once the pull was made, and fresh air was introduced, the temps dropped substantially.
Now, the looser 10-71, stripped only on the outside of the rotors, (and I think a bit worn in), with NO water to the intercooler, idled around 125-128*. When I turned the water feed to the intercooler at idle, waited a while watching the air temp, it only dropped about 3 or 4 degrees at idle.
So I am not sure the data was comparable. Its been said that a tighter blower will produce more boost (which the stage 3 blower sure did), they also produce more heat. Both setups had about the same temperature drop from the idle temp, to the wot temp, which was about 10-15*. The absolute only thing i can conclude from a 10-71 at 3% underdriven, idling 20 degrees hotter, than a 15% over 10-71 (with no water thru the core), is blower clearances.
Looking back, I think the intercooled setup, should have dropped more than it did. I mean we were pumping probably 55* water thru the core. With 128* air temp with no water at idle, and only dropped to around 124* when the water was turned on, I was kinda dissapointed.
What we did notice on the intercooled setup, the IAT temp didnt change really at all, whether the blower was at 3% over, or 20% over, or going from 6lbs of boost to 10lbs of boost.
All I can conclude from any of that, is that the non intercooled deal making 8lbs of boost, compared to the intercooled setup making 8lbs of boost, had a difference of about 15-20 degrees. Whether that cooler temp was from the intercooler doing its job, or the looser blower simply not making as much heat, i dont know. From a power standpoint, I could see that making a difference of about, well, 15-20hp. In a 40ft offshore boat, thats about 1mph. Personally, at this point, until further proof, I'd rather spend 3000-4000 bucks elsewhere, on those 2 builds. I dont think going from 135* IAT's to 112* IAT's, is gonna tuck you in at night and allow you to run cheaper gas, more timing, etc. Now, on those mini blowers making gobs of heat, the intercooler may indeed do a whole lot more at reducing the temps. I cant say without data. And nobody ever produces real data when it comes to marine intercoolers.
10-24-2014, 01:49 PM
#44
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Joe in your blower / innercooler comparison did they have the same carbs on them? I have often wondered how much of a difference it would be in intake temps when playing around with carb size. I've always thought that air moving through a smaller oriface would heat up more than a larger... Does the tighter blower need less throttle opening to idle and run at lower rpms than the looser one therefore creating the heat? I don't know I'm just thinking out loud with stuff that lingers in my head. I've always tried to look at things from every angle possible. If I could hit the lottery I would have a couple dynos in my back yard and play on the dyno all day. Atleast during the cold months.
10-24-2014, 01:58 PM
#45
The blower that ran cooler , had twin 1050 carbs 4150 style. The other setup had twin 850 4150 carbs.
The tighter blower made 8lbs of boost on a 540ci at 3% underdriven. The looser blower, took around 15% overdrive to make 8lbs on a 522ci but did have the intercooler in the mix.
I do get where you were going with the carb size vs air temp. I should have mentioned that in the carb sizing post but didnt want to get too deep on how simply a larger carb/throttle body can possibly reduce the temps. I personally have no data to support that but some big time engine builders have witnessed that scenerio
The tighter blower made 8lbs of boost on a 540ci at 3% underdriven. The looser blower, took around 15% overdrive to make 8lbs on a 522ci but did have the intercooler in the mix.
I do get where you were going with the carb size vs air temp. I should have mentioned that in the carb sizing post but didnt want to get too deep on how simply a larger carb/throttle body can possibly reduce the temps. I personally have no data to support that but some big time engine builders have witnessed that scenerio
10-24-2014, 05:38 PM
#46
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I think what Black Baja was trying to say, was that when using too small of a blower for the application, the best bet is to raise the static/dynamic compression a bit. Since the small blower is only capable of so much, getting the compression up a tad, helps the engine make more power on "motor" so to speak.
Lets say you have a stock 525sc. What you have there is a 454, that made a whopping 1.15HP per ci. Thats hardly impressive, as today we can make that number easily without a blower and be marine reliable. Turning the boost up, to make more power on a stock 525sc, was of little gain. Becuase the blower spinning so fast simply superheated the air. You could never add 150+HP to a 525sc with pulley swaps and a chiller, without seriously redesigning the entire engine package, if you wanted to keep the 177.
Now, lets say you take a 525sc engine, but want to make more power out of it, but keep the same small blower. If you were to raise the static compression from 7:6:1, to around 8.5:1, camshaft upgrade, maybe a cylinder head upgrade, now you can pick up 50,75,100, or more hp, but at the same, or even less boost than stock. Simply because its making more power on "Motor".
Now lets talk about a 600sc merc. That had a 420 B&M blower, 7% underdriven. It also was low 7.6:1 or whatever compression. I know of guys who simply took that stock merc engine, added a superchiller, and cranked the boost up to 9-10psi, and picked up tremendous power without touching the engine internals. Simply because the larger blower was capable of making 9-10psi without extreme overdriving and took advantage of that low static compression.
Lets say you have a stock 525sc. What you have there is a 454, that made a whopping 1.15HP per ci. Thats hardly impressive, as today we can make that number easily without a blower and be marine reliable. Turning the boost up, to make more power on a stock 525sc, was of little gain. Becuase the blower spinning so fast simply superheated the air. You could never add 150+HP to a 525sc with pulley swaps and a chiller, without seriously redesigning the entire engine package, if you wanted to keep the 177.
Now, lets say you take a 525sc engine, but want to make more power out of it, but keep the same small blower. If you were to raise the static compression from 7:6:1, to around 8.5:1, camshaft upgrade, maybe a cylinder head upgrade, now you can pick up 50,75,100, or more hp, but at the same, or even less boost than stock. Simply because its making more power on "Motor".
Now lets talk about a 600sc merc. That had a 420 B&M blower, 7% underdriven. It also was low 7.6:1 or whatever compression. I know of guys who simply took that stock merc engine, added a superchiller, and cranked the boost up to 9-10psi, and picked up tremendous power without touching the engine internals. Simply because the larger blower was capable of making 9-10psi without extreme overdriving and took advantage of that low static compression.
10-24-2014, 07:19 PM
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