BLOW ME!

Discussion in 'Big Block Cadillacs' started by 48Austin, Jan 1, 2020.

  1. 48Austin

    48Austin Safty First! Then pull the trigger!

    Joined:
    Oct 14, 2017
    Messages:
    464
    Likes Received:
    254
    Location:
    Over here
    What vehicle(s) do you drive?:
    1964 Commercial, 1948 Austin, 58 Pan
    Anybody have experience with Roots type blowers on the Big Cad? Have an 8:71. And have been told and read that this is the smallest to go with. Should I dump it and go bigger?
    Women are 50/50 are on size.;)
     
  2. Cadillac Kid 1

    Cadillac Kid 1 Well-Known Member

    Joined:
    Jun 18, 2008
    Messages:
    1,111
    Likes Received:
    225
    Location:
    San Antonio Texas
    you could try a 16-71, but I think you might need a bit moor room under the hood. Seriously what are you trying to do?
    Greg Surfas
     
  3. gordon

    gordon New Member

    Joined:
    Jan 12, 2017
    Messages:
    21
    Likes Received:
    8
    Standard roots blowers come in several sizes. based on old diesel applications. The numbers have been adopted for sizing purposes to this day. A 6-71 has a rotor and case length of 15 inches and displaces 410 to 430 cu in per revolution of the rotors. If it is a non stripped /sealed blower of standard dia. use 411 to due calculations. Use 426-430 for the stripped race version. 8-71 / 16" 440-470 cu in. 10-71 /17" 470-490 cu in, 12-71/ 18" 490-520 cu in. 14-71 19" 520-550 cu in. Later tonight I will put of some easy calcs for figuring overdrive vs. boost etc. Got to get to work.
     
  4. gordon

    gordon New Member

    Joined:
    Jan 12, 2017
    Messages:
    21
    Likes Received:
    8
    Here are some more tidbits for the brain if you want to put a roots blower on an American V8 . Or any other IC engine. Just easier to paint the pictures with what most on here are familiar with. The minute you bolt the blower on quit thinking so much about actual displacement of your engine. Think in terms of blower displacement x drive ratio. Could be under driven ( small pulley on bottom, bigger on top) , Could be over driven (small pulley on top , bigger one on bottom) , or could be 1 to 1 (driven same speed as crank rpm). If a 6-71 is considered to displace 411 cu in per revolution of the blower and it is on top of a 500 caddy with 1 to 1 drive ratio then you caddy thinks it is actually 822 cu in. It takes two revolutions of the crank to make the 500 inches of the Cad engine but the blower is displacing 411 cu in every revolution . So two revolutions of the engine equal 500 inches with the blower packing 411 cu in of air twice in the same amount of time. Now you have a 822 cu in Cad! Not really due to pumping losses, heating of the inlet charge, and restrictions from the valve timing and ports. If we lived in a perfect world that 6-71 on top of a 500 inch cad would still make boost. Around 9lbs. of manifold pressure. So looking at this , if all you had was a 6-71 and not a sexy 8-71 or even bigger you would still have a boosted 500 inch torque monster. You could still make that same 9 lbs of manifold pressure with an 8-71 but at an under driven ratio so that the blower is turning slower than the crank. This relationship (ratio)between the rpm of the blower and the rpm of the crankshaft does not change . From Idle to redline the rpm differential stays the same. For all those on here that already know this stuff just ignore this post, for those that are toying with the idea of a blown cad combo I hope this tweaks you enough to wrap you head around the potential of a Roots blower . I don't drive one on the street anymore, but my race car is a blower car and I have spent most of my adult life around these things. Feel free to ask me stuff . I will do my best to answer or point you to the answer. Hope I did not bore most of you.
     
    Darius and Red98422 like this.
  5. 48Austin

    48Austin Safty First! Then pull the trigger!

    Joined:
    Oct 14, 2017
    Messages:
    464
    Likes Received:
    254
    Location:
    Over here
    What vehicle(s) do you drive?:
    1964 Commercial, 1948 Austin, 58 Pan
    But isn't a belt driven parts destroyer making boost whether under driven or over driven? Or running 1 to 1? Still trying to stuff in more than what fits.:rolleyes:

    I know D. I may have came up with a bunch more as I was typing.;):whistle:
     
  6. Red98422

    Red98422 Active Member

    Joined:
    Jun 6, 2018
    Messages:
    367
    Likes Received:
    194
    Location:
    Washington state
    That is fantastic information for me at least. I fully intend to go with a turbo for my big caddy. However it’s info like this that I was never expecting to learn about that keep the hobby interesting.
     
  7. gordon

    gordon New Member

    Joined:
    Jan 12, 2017
    Messages:
    21
    Likes Received:
    8
    Forget boost, boost is air that did not get into the combustion chamber. You can have all the boost showing on your gauge you want . Just wasted energy. I am not a great word smith, I do better in the garage , couple of glasses of single malt and some good music in the back ground. Even for you turbo guys boost is what you are not getting . On a supercharged engine the Blower is now the dictator of power up until it can't get any more air fuel mix into the combustion chambers. It starts getting constipated. Sits there straining to pack more in and just ends up making super heated air and fuel mix. Not good. Inlet manifold charge temps can go to the moon. I have seen 300* inlet temps on poorly set up Alky combos. Gas is even worse due to being not as good on the Latent heat of evaporation rating. Pour gas on your hand and hold in front of a fan , feel the cooling effect, now do it with rubbing alcohol (not poisonous like methanol) notice it gets down right cold. Many times you will run better with less over drive on the blower since it is moving a cooler charge.Or not beating to death as hard in trying to push it into the cyls. As air is heated it becomes less dense (molecules are farther apart ) . When it comes to artificially aspirated engines inlet charge density is key. Now back to the question of making boost weather it is under driven or over driven. Only when the blower displaces more air per revolution than what the engine displaces per revolution. It is simple math. Cad is 250 cu in per revolution ,Blower (6-71 )displaces 410 if it is not stripped inside spin it about 40% under driven and you won't see boost. When the displacements match no pressure difference. Remember we are also surrounded constantly by atmosphere at 14.7psi pressure. If you go with a turbo I would set it up for between .5to .75 atmospheres of manifold pressure ( indicate 7 to 10lbs. on the gauge). Then put more money into charge cooling units. Buy modern ball bearing style turbo assemblies not plain brg. You already have 500 cubes. Going back to my cave for now.
     
    Darius and Red98422 like this.
  8. 48Austin

    48Austin Safty First! Then pull the trigger!

    Joined:
    Oct 14, 2017
    Messages:
    464
    Likes Received:
    254
    Location:
    Over here
    What vehicle(s) do you drive?:
    1964 Commercial, 1948 Austin, 58 Pan
    What do mean by stripped? Rotor seals?
    I want ALL my blowers to be stripped or semi stripped;).
    Mine has Teflon seals. Dyer said that it looked like it was just done. And didn't look like there was much time on it after retiming and seals. Also what you are saying is with 1to1 pullies I'm looking at over 1000 ci.
     
  9. gordon

    gordon New Member

    Joined:
    Jan 12, 2017
    Messages:
    21
    Likes Received:
    8
    Usually blowers for the street are not stripped (teflon in one groove and nylatron in second groove ,one black one white) due to excessive heat generated. My race blower is stripped to seal the rotors to the case walls and to each other while turning. Make max boost available. These blowers when fresh take quite a bit of force just to turn with a long pull bar or 18" ratchet when fresh. If it is worn down on the rotor strips , easy to spin by hand ,theoretically you could run it on the street but the risk of loosing a strip due to high heat on a long run and having it go into engine is not cool in my book. Is your blower an 8-71? Use 440 cu in per rev for your calcs. 500 Cad , 8-71, direct drive ratio, 12 PSI (+- 1.5) manifold pressure . Hope you have no more than 8.5:1 static compression and good rods and pistons. Cam timing makes a big difference on cyl pressure with these . Its all in the combination not just one item that will make it or break it. Keep total ign timing down around 28* to 30* . Have big supply of fuel (volume not pressure) feeding the dual carbs on top . When you put your boot to it , the demand for fuel volume is a butt load.
     
  10. Red98422

    Red98422 Active Member

    Joined:
    Jun 6, 2018
    Messages:
    367
    Likes Received:
    194
    Location:
    Washington state
    You are exactly correct, as some younger folks get too caught up on “I’m pushing 20psi” where the name of the game needs to be about efficiency. It is in fact airflow that is the most important in my opinion (CFM). As a younger(ish) man myself I’m glad there are folks like yourself and others still out there teaching and speaking correctly about such subjects. Honestly thank you for taking time for these posts on roots blowers.

    Charge cooling becomes insanely important for anything running on the street blown or boosted. I’m a fan of chemical cooling personally (water meth or straight meth). That however isn’t the most realistic setup for the street

    I love the mechanical simplicity of blowers as long as I’m not the one that has to tune the carbs. However the initial cost to play the game is just a bit too much for me. As far as turbos are concerned, there are litteraly thousands of different sizes, setups ect. Which can be either awesome or overwhelming depending on your viewpoint.

    We could go even further into the weeds if we start to talk about centrifugal blowers :D which is a whole nother ball of wax (cliff notes, not as good as a roots, or as efficient as a turbo imo)

    Btw I’m more of a bourbon man myself :cool:
     
    Darius likes this.
  11. gordon

    gordon New Member

    Joined:
    Jan 12, 2017
    Messages:
    21
    Likes Received:
    8
    Bourbon is good, just finished bottle of Buffalo trace. Very easy going down. Maybe too easy.
     
    Red98422 likes this.
  12. Red98422

    Red98422 Active Member

    Joined:
    Jun 6, 2018
    Messages:
    367
    Likes Received:
    194
    Location:
    Washington state
    That’s a fantastic bourbon, absolutely underrated by most.
     
  13. 48Austin

    48Austin Safty First! Then pull the trigger!

    Joined:
    Oct 14, 2017
    Messages:
    464
    Likes Received:
    254
    Location:
    Over here
    What vehicle(s) do you drive?:
    1964 Commercial, 1948 Austin, 58 Pan
    Bourbon? MAGIC!! I in a bottle! Just like "I Dream of Genie".
     
  14. 48Austin

    48Austin Safty First! Then pull the trigger!

    Joined:
    Oct 14, 2017
    Messages:
    464
    Likes Received:
    254
    Location:
    Over here
    What vehicle(s) do you drive?:
    1964 Commercial, 1948 Austin, 58 Pan
    Was thinking 9.5 with E85 and two Predators. If Predator gets back up and running again. If not I have 5 carbs that ain't worth shit.
     
  15. gordon

    gordon New Member

    Joined:
    Jan 12, 2017
    Messages:
    21
    Likes Received:
    8
    I have zero experience with E85 . Most of my experience is with blown alky (Methanol) or a mixture of Alky and Nitro. With Methanol only 10.5 compression and upwards of 40 psi manifold pressure indicated. Easy to tune and easy on parts. Relatively speaking.Some of the guys will try 13 to 1 or a bit more with butt load of boost. but they have to over fuel it to stay out of detonation. 12 to 12.5 can be very competitive with a good ($$$$$) blower. Start adding nitro and compression comes down. by the time you are running 85% or higher the compression is going to be between 6 and 7 to 1 with about 35 psi in manifold ,some times more. With all this stuff it is real easy to get greedy especially when drunk from the power high . The aluminum gods will demand a Sacrifice! Gasoline is kinda like Nitro in that it detonates easy causing damage. Keep the compression down due to the heat generated by the blower. If and when I do another street blower deal be it Twin Carbs or electronic fuel inj. it will use a boost referenced Water/Alky inj to control det. . One more thing I like using klotz Uplon top oil additive in my stuff especially the race car except when it has to pass a fuel check. Start with low boost set up at first to get your cherry popped . The instantaneous down low out put of a blower motor , even at low boost can catch you out. Stop and think, a 500 inch engine seeing 1.5 atmospheres absolute ( about 7.5 psi plus existing 14.7psi) from just above Idle and carry that pressure through 6000 rpm limit of a Cad will get most peoples attention. You can always change pulley sizes later for more giggles . As that woman on TV says "Whats in your Wallet?". Only reason my big cad motor is not getting a roots is I don't want it sticking through the hood of my 53' Stude. and there is not room to do a Potvin style drive for it off the front of the crank. The car will eventually get boost , just not sure what flavor. Studebakers are supposed to have boost!
     
  16. Darius

    Darius Well-Known Member

    Joined:
    Oct 15, 2004
    Messages:
    4,227
    Likes Received:
    709
    Glenlivet 18.
     
    Red98422 likes this.
  17. richie49

    richie49 Active Member

    Joined:
    Nov 19, 2005
    Messages:
    266
    Likes Received:
    67
    Location:
    Pasadena texas
    Darius
    How are you doing? you just had hospital stay didnt you? Hope you doing okay!

    Richarde richie49
     
  18. richie49

    richie49 Active Member

    Joined:
    Nov 19, 2005
    Messages:
    266
    Likes Received:
    67
    Location:
    Pasadena texas
    Opps
    Didnt see the other post about how you were doing there Darius. ,glad your doing good.
    Richard richie49
     
  19. 48Austin

    48Austin Safty First! Then pull the trigger!

    Joined:
    Oct 14, 2017
    Messages:
    464
    Likes Received:
    254
    Location:
    Over here
    What vehicle(s) do you drive?:
    1964 Commercial, 1948 Austin, 58 Pan
    Followed a thread on the HAMB. The guy ran 10.5 comp. with E85. Bbc 4speed in a 53 Austin Somerset gasser. Said he didn't seem to have issues. Don't think I want to try my luck with that ratio. But I don't remember what his drive ratio was. All I know is the car ran mid to low 9's. Still a street car.
    I'm also building a gasser. 90" wheel base, 22, 25 lbs, with blown Cad. I guess I'm getting real stupid in my old age:confused:.
    D how ya doin.
     
    Darius likes this.
  20. Darius

    Darius Well-Known Member

    Joined:
    Oct 15, 2004
    Messages:
    4,227
    Likes Received:
    709
    48 Austin,

    Welcome to the world of "Senior Stupidity"!! Think of it as having an "SS" Cadillac!! o_O

    It has been a week since my surgery and I can verify that recovery does take longer as we age. So far I feel worse than when entering the hospital. That's like your bank account before and after starting a high performance big block Cadillac project.

    bro. "SS" d :D
     
    Red98422 likes this.

Share This Page