BLOWER SIZE?

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eliminator18

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« on: August 28, 2019, 03:36:01 PM »
LOOKING TO ADD A ROOTS BLOWER TO MY 454 OVER THE WINTER BREAK. CAN SOMEONE THAT RUNS ONE IN THERE JETBOAT GIVE ME SOME INSIGHT. LOOKING AT GETTING A 10-71, BUT HAVE BEEN TOLD THAT AN 8-71 WITH INTERCOOLER WOULD BE BETTER. WHAT ARE YOUR THOUGHTS
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Grimpala

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« Reply #1 on: August 28, 2019, 04:15:26 PM »
What are you current motor specs?

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eliminator18

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« Reply #2 on: August 28, 2019, 04:29:23 PM »
454 .031 over with eagle rods trw pistons with worked 781 heads with comp xm flat tap cam. Iím planning on getting a whole new rotating assembly and aluminum heads and new camshaft as well


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eliminator#1

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« Reply #3 on: August 28, 2019, 09:40:45 PM »
As big as possible


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Grimpala

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« Reply #4 on: August 29, 2019, 06:24:22 AM »
454 .031 over with eagle rods trw pistons with worked 781 heads with comp xm flat tap cam. Iím planning on getting a whole new rotating assembly and aluminum heads and new camshaft as well


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So what are the new motor specs?
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« Reply #5 on: August 29, 2019, 08:07:49 AM »
Here are a couple thoughts:

First, how much power are you looking to make?

You can achieve a really scary ride with a legit 6-71, stripped and clearanced for gasoline.  In a discussion with Littlefield Superchargers, when i picked up my GMC 6-71 a couple weeks ago, it should be producing right around 19 PSI at my current 10.9% overdriven.  Years ago, in a conversation with Mert Littlefield, bigger blowers have longer rotors, have more internal leakage because of the longer sealing surfaces, and more rotor twist.  Combine that with more internal friction and additional weight, in a location that is not jet boat friendly.  The point is, how much do you really need?

Positive displacement blowers produce a lot of bottom end torque, something that jet boats don't utilize very well, until  the impeller is fully loaded.  You will really want to stick with an A cut stainless impeller.  A smaller cut impeller might get you more top speed, but you will blow the pump dry on the hit.  Yes, an inducer will help.

Build your engine for peak power in accordance with the impeller charts.  However, you don't want the engine to make peak power at 7500 if the impeller is going to stall it at 6000.

The additional weight of a blower has already been mentioned here and in other posts.  I have not had the opportunity to verify the weight of my 6, but when about to lift it into the truck, I was told, "It's only 60 pounds!"  It didn't feel that heavy.  Each size jump, 6 to 8, 8 to 10... adds an inch of length to the case and rotors.  I don't see a significant difference there.  What I can say is that a TBS 10-71, carb adapter, and twin Dominators feels HEAVY!

I'm not entirely sold on the cost/benefit ratio of the current intercoolers available for roots superchargers.  Don't get me wrong, there are a lot of benefits to intercooling.  Before I jump off that bridge, I am going to investigate Intake Air Temperatures (IAT) further.  The harder you overdrive the blower, the more heat it will put heat into the IAT.  Again, it comes back to how much do you really need?

I have been researching quite a bit about my own build.  My findings are:
* Dart Big M standard deck block, 4.500-4.550 bore
* 4.0" stroke crankshaft.  Longer strokes just add unwanted bottom end torque.
* Optimize the pistons for ring pack and pin height.
* Make the connecting rod length fit the block, pistons, and crankshaft.
* As with any engine, the best flowing heads are beneficial.  I'm looking at the Brodix Dragon Slayer 320.
* Porting is not beneficial in a supercharged application until you really start pushing your limits.  If you have to do a lot of porting, you are starting with the wrong heads.

Some things I feel are vital:
* A double keyway crank
* 4130 double keyway hub, so it doesn't split
* .187 or better yet .200 wall thickness wrist pins.
* I would not skimp on valves.  I would strongly recommend Inconel exhaust valves.

Building an OE engine, I suggest:
* Bore the block the absolute minimum necessary to clean up.  Overboring allows too much flex in the cylinders.
* Same with decking the block.

Cheers,

Joe
"I want to roll with my brother Joe" - Joe Bateman - January 29, 1950 ~ November 27, 2013

eliminator18

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« Reply #6 on: August 29, 2019, 09:16:25 AM »
Thanks for the info! I really appreciate it


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K-034

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« Reply #7 on: August 29, 2019, 01:26:06 PM »
I would stick with an 8-71 thatís the biggest you can go on a Chevy without using a stand off drive for the distributor,


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eliminator18

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« Reply #8 on: August 29, 2019, 02:46:41 PM »
Thanks for the info!


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« Reply #9 on: August 29, 2019, 05:46:30 PM »
I would stick with an 8-71 thatís the biggest you can go on a Chevy without using a stand off drive for the distributor,


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Do you guys run intercoolers?
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K-034

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« Reply #10 on: August 30, 2019, 05:04:53 AM »
Do you guys run intercoolers?



Not on Alcohol we donít. Intercooler would clear standard distributer or a Mersh  high rise intake, for what he is running I would run a 8 spin it slow and not even deal with a intercooler. That would be the easiest. Just my opinion


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08chevyguy

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« Reply #11 on: August 30, 2019, 02:59:42 PM »


Not on Alcohol we donít. Intercooler would clear standard distributer or a Mersh  high rise intake, for what he is running I would run a 8 spin it slow and not even deal with a intercooler. That would be the easiest. Just my opinion


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Works for me pretty good

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rivrrts429

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« Reply #12 on: August 31, 2019, 08:50:49 AM »
I ran a Littlefield 1071 with intercooler, 23% overdriven, on AvGas. With intercooler the 1071 cleared distributor with no issues.


K-034

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« Reply #13 on: September 03, 2019, 04:46:19 AM »
We run a PSI 110% over driven on alcohol with no issues either


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« Reply #14 on: September 08, 2019, 11:51:35 PM »
Unless you are going for the specific look of a Roots blower, I would strongly recommend a centrifugal, they are much better suited to the power curve requirements of a jet boat.
"I want to roll with my brother Joe" - Joe Bateman - January 29, 1950 ~ November 27, 2013

 


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