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Discussion Starter #1
A buddy of mine is putting together some roots setups for his 42 Fountain. Pump gas builds. He is looking at either a pair of std helix littlefield 10-71's, or a pair of 8-71 hi helix. He was told hi helix 8-71's are the way to go. He wants to run 10-12lbs of boost. Blower shop intercoolers. 8:1 522CI engines. I think he might be pushing the envelope a bit on pump gas with the idea of 12lbs? :confused:
 

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A buddy of mine is putting together some roots setups for his 42 Fountain. Pump gas builds. He is looking at either a pair of std helix littlefield 10-71's, or a pair of 8-71 hi helix. He was told hi helix 8-71's are the way to go. He wants to run 10-12lbs of boost. Blower shop intercoolers. 8:1 522CI engines. I think he might be pushing the envelope a bit on pump gas with the idea of 12lbs? :confused:
You can run pump gas with 10-12lbs of boost in a boat with 8:1 no problem
 

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Discussion Starter #5
He is right in the range where you weigh the pros and cons.
I understand the builder suggesting the 8s, but if the price is right on the 10s.......

The 8 is lighter and cheaper, and the 10 isn't going to make a single HP more at that blower speed.
If he goes with the 10's he found he'd save quite a bit of money. His concern is he doesn't think they will make the power as the hi helix 8-71's his buddy recommended. I am unfamiliar with the hi helix stuff. His buddy said "hands down the hi helix is the way to go" for his application.

I can't see there being a big difference in air temp or power output between the two, but thought I'd ask here. I know you guys are well versed with these blowers.
 

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Sorry to get off topic but how is 12lbs ok on pump gas in a heavy boat ??
I have never heard that before even at 8-1 comp .....even innercooled.
 

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Discussion Starter #10
So it's ok to run that much boost on pump gas in an offshore style boat?
My advice to my buddy was keep the boost around 9-10 psi and let it live a long time. He's low compression, but I feel his cam is a bit too conservative to be running that boost level with the $hit gas we have around here. With offshore boats you can't pull a bunch of timing bc on long runs the exhaust temps get to hot.

He is trying every different Avenue to find a way to safely run 12 lbs of boost. I don't think the answer is exchanging the std 10-71 s for high helix 8's but that's why I posted this. I'd be putting my money towards better heads and cam combo vs trying to make power with boost.
 

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Discussion Starter #12
at 8 to 1, I wouldn't want to take it passed 8 psi without an innercooler, with an innercooler, maybe 10.
12 you are walking a tight rope I wouldn't want to try in a offshore deal.
I agree GN. I been trying to tell him that. He talks with a lot of race car guys, and sometimes those guys don't understand how hard an offshore engine is worked. Its not on the gas for 10 seconds then let off. More like on the gas for 10 minutes, then let off. Out of all my buddies with SUCCESSFUL blown offshore engines, the norm is between 6-10psi depending on the setup. Others have tried more boost, but it usually doesn't end up good. With that being said, his engine setup is 522CI. Lunati double cut blower cranks, Oliver rods, JE pistons with upgraded pins, Dart blocks. Edelbrock Marine performer RPM Rect ports :)eh:) and a 242/248 112LSA hyd roller. He also has another pair of 252/262 115LSA cams on the shelf. He wants to make 1000HP at minimum at 6000RPM on pump.
 

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My advice to my buddy was keep the boost around 9-10 psi and let it live a long time. He's low compression, but I feel his cam is a bit too conservative to be running that boost level with the $hit gas we have around here. With offshore boats you can't pull a bunch of timing bc on long runs the exhaust temps get to hot.

He is trying every different Avenue to find a way to safely run 12 lbs of boost. I don't think the answer is exchanging the std 10-71 s for high helix 8's but that's why I posted this. I'd be putting my money towards better heads and cam combo vs trying to make power with boost.
OK, maybe I'm missing something not having a lot of experience with blown gas, but IMHO, 10 lbs boost is the same HP regardless of if it comes from a B&M 144 or a high helix, double throwdown 16-71. There may be a bit of HP difference due to heating the inlet charge by paddling the hell out of the air with a tiny blower, but boost is boost or am I missing something?
Personally, I agree with the idea make the motor a better air pump with heads/cam whatever if you need to keep the boost down. And at 12,000 lbs, we're talking about a ship, not a boat :D

Edited to add that if I wanted that HP level at that RPM, i'd be looking at going to a 632 with a decent head package. Normally, I don't like a 4.75" stroke but at that RPM level, it wouldn't bother me... Put 8 lbs on top of that motor and 1k HP should be a cake walk at 6k RPM...
 

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Discussion Starter #14
Yea, I just can't see there being a big difference in power output or air temp change between a standard 10-71 or 8-71 high helix. I always thought the high helix worked better at high rpm. I never played with a delta opening blower. How is the fuel distribution on them?
 

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Yea, I just can't see there being a big difference in power output or air temp change between a standard 10-71 or 8-71 high helix. I always thought the high helix worked better at high rpm. I never played with a delta opening blower. How is the fuel distribution on them?
I don't care for the delta opening if it has an inner cooler.
The extra working length of the hi helix adds to the leakage, but the shorter rotor of the 8 verses the 10 kind of cancels them out. The higher speed of the 8 will add a very small amount of heat over the 10, but slower speed of the 10 will increase the leakage. Like I said, its pros verses cons.
I still like the 8 when you consider the weight, and the cost, so long as the cost of the hi helix doesn't out run the cost of the 10 by too much. If the price of the 10s is a killer deal, I would go with the 10s.

Cost and weight would be my primary movers here, not the size or type of blower rotor.



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Relative to pump gas, should not be a problem running 12 lbs of boost on 91 with intercooler and aluminum heads as long as timing is held no more then say 30/31 total. I have had Teague and GT roots motors in heavy boats that ran exactly 12 lbs on 91 pump gas. That said, you are a bad tank of gas away from a problem.... I always mixed some av gas in as a precaution. Current Teague motors run great at 12 lbs boost on 91 but they are large 5/8 litre Whipples which are more foregiving vs a roots blower, discharge temps are way lower.

The comment on HP being a constant relative to boost levels, that is not necessarily correct. Different air pumps will produce different HP results due to efficiency and discharge temps. Examples; I have seen a whipple screw type blower produce as much as 100 HP more vs a Roots at the same boost level. Same would hold true for some Centrifugals and certainly turbos, they are much more efficient as compared to a roots style blower. Roots blowers consume huge HP to drive them and their discharge temps are pretty high.

I have no input hi helix vs standard but I bet a call to Mooneyham/BDS answers that question.
 

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.....Different air pumps will produce different HP results due to efficiency and discharge temps. Examples; I have seen a whipple screw type blower produce as much as 100 HP more vs a Roots at the same boost level. Same would hold true for some Centrifugals and certainly turbos, they are much more efficient as compared to a roots style blower. Roots blowers consume huge HP to drive them and their discharge temps are pretty high.......
Wow, news to me!! Thanks :)devil
 

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Relative to pump gas, should not be a problem running 12 lbs of boost on 91 with intercooler and aluminum heads as long as timing is held no more then say 30/31 total. I have had Teague and GT roots motors in heavy boats that ran exactly 12 lbs on 91 pump gas. That said, you are a bad tank of gas away from a problem.... I always mixed some av gas in as a precaution. Current Teague motors run great at 12 lbs boost on 91 but they are large 5/8 litre Whipples which are more foregiving vs a roots blower, discharge temps are way lower.

The comment on HP being a constant relative to boost levels, that is not necessarily correct. Different air pumps will produce different HP results due to efficiency and discharge temps. Examples; I have seen a whipple screw type blower produce as much as 100 HP more vs a Roots at the same boost level. Same would hold true for some Centrifugals and certainly turbos, they are much more efficient as compared to a roots style blower. Roots blowers consume huge HP to drive them and their discharge temps are pretty high.

I have no input hi helix vs standard but I bet a call to Mooneyham/BDS answers that question.
Wow, news to me!! Thanks :)devil
Leaving turbos and centrifs out of this, because there is no real argument that they will make more peak power than either roots or screws.
I always get a lttle chuckle out of the horsepower comparisons between the 2. I really like screws and would love to run one if I could. But the HP they claim is more than a little skewed.

There is pretty much one screw, whether it is a Whipple, Lysholm, or Keene Bell, they are all the same internally.
But when they test a screw against a roots, they test against a off the shelf POS cast rotor stage I roots, usually too small and spin the piss out it.
They ALWAYS test them cubic inch for cubic inch, and the roots is a loser on those grounds. Its not rocker science, the screw functions better at speed than the roots. '

They NEVER test dollar for dollar. They never test the screw against a Littelfield LB20, SIS/Kobelco Superman, or TBS XR, never with 18 strip rotors or hi helix, no retro bottom, front discharge or delta opening. Its always some off the shelf Weiand street blower that NOBODY actually uses.

Spend the money the Whipple costs on a roots, and the HP difference gets a whole lot less.
Like Edlebrock testing a dual dominator Victor Ram against a cast iron 2bbl manifold.



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I don't care for the delta opening if it has an inner cooler.
The extra working length of the hi helix adds to the leakage, but the shorter rotor of the 8 verses the 10 kind of cancels them out. The higher speed of the 8 will add a very small amount of heat over the 10, but slower speed of the 10 will increase the leakage. Like I said, its pros verses cons.
I still like the 8 when you consider the weight, and the cost, so long as the cost of the hi helix doesn't out run the cost of the 10 by too much. If the price of the 10s is a killer deal, I would go with the 10s.

Cost and weight would be my primary movers here, not the size or type of blower rotor.
You still can't have my 10 with the 6x case.
:D
 

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Discussion Starter #20
Wow, news to me!! Thanks :)devil
I can tell you this from my experience. On my 468's, in my 38 Fountain

177 Weiands at 5psi 77mph at 115% overdriven

250 B&M's at 7psi -83mph 70% overdriven

420 B&M's at 6psi=88mph 7% underdriven.

When changing from the 177's to the 250's, nothing in the engines changed at all. Was a bolt on change. The engines were freshened when going from the 250's to the 420's, but same parts were used in the rebuild, cam heads, pistons, etc. Just went from .030 to .060 bore and a fresh cut on the valves. All setups were ran on pump 93 octane with 8.75:1 compression and aluminum heads. Engines never been 'hurt' in any way. No intercoolers were used on any of the setups. My guess is from going to the smaller, highly overdriven blowers, to the larger underdriven blower, the air temps were simply reduced.
 
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