JRider

iTrader: (1)

So my new to me motors have nice Blower Shop billet 871s which I believe are stripped high helix with closed/pie shaped discharge. They sit on superchillers. The motors are tall deck 548, talking with the builder they were advertised at over 900 HP. My question is if there is any advantage or disadvantage to switching to BDS 1471 blowers. If you look at the upper pulley it seems to be purty small, wondering if the blowers are undersized? I think it makes 8psi boost with the chillers.

https://www.youtube.com/watch?v=_MX8EOYanzY

cmattj

Done some street cars with BDS 671 and 871(got real tight in clearance)
We would up larger top pulleys and intake heat did go down with similar boost levels just in driving low speeds. I would think fitting a 1471 would be tricky length wise but with your chiller set up I would stay where you are. Awesome set up BTW !!

F-2 Speedy

iTrader: (6)

That's a small displacement for a 1471, that's a huge huffer, jmo

edit: maybe go to a 1071

MILD THUNDER

iTrader: (3)

Pie shaped deltas with carbs or throttle body injection scares me. Fuel distribution sucks as it is with a twisted helix rotor setup, i cant see the delta opening helping that. Im sure it can work fine, but id def be watching individual cylinders fuel tuning .

I dont think the jump from an 871 to a 1071 is worth the effort in most cases. Youre looking at maybe a decrease of 300-400 change in blower rpm at 6000 engine rpm. Unless your overdriving the 871 pretty hard with that chiller (say +20 percent over) , i doubt you'll see much going to the 14-71.

Whats the current pulley ratio on your 8's and how much boost are they making on that setup?

I saw a nice gain in power going from a 250 blower to a 420 blower, but i also cut rotor speed down about 5,000rpm at full throttle.

mike tkach

iTrader: (3)

imo,a 8/71 is a little small for a 540.a 10.71 would be the way i would go.don,t get me wrong,the 8.71 will work,the 548,s i had in my cat had 8.71,s and made 950hp but i had to over drive them more than i really liked to.i did some 523s recently with 10.71 and they made a little over 1000hp.as far as the pie shaped delta opening,my 8.3l whipple,s have that opening and they seem to work alright.EDIT IN.imo the 14.71 is overkill for a low boost [under 15 lbs]540..a set of whipple 4l superchargers would be really nice on those 540s.

cigrocket

iTrader: (3)

Not to mention you can't pull the distributor on the 14-71 because of the length without removing the blower. Kind of a pain in my opinion. I had 10-71 on 509's that made 950HP. I turned them down to make 875HP, very little Boost. They had a chiller. I think you should just stick with the ones you have. You will have plenty of blower to make reliable HP.

MILD THUNDER

iTrader: (3)

Its pretty well known cylinder to cylinder fuel distribution sucks with pie shaped openings when using carburetors or throttle body injection. Lots of guys out there burning stuff down even though their afr meter reads its ok. Problem is couple cylinders are rich on that bank, and couple are lean. The 02 doesnt tell you that. Heck, some blower designs are enough to make one bank of the engine run over a full point leaner or richer. Same concept as the 250 B&M blower with a single carb . They knew the front cylinders starved for fuel with the single carb. They came out with an offset adpater to move the carp closer to the front of the blower. With twin carbs on that blower, fuel distribution was much better. Imo, unless you have 8 o2 sensors, we are kind of guessing.

Dan switched from 871s to 1071s, same boost level, gained zero. He is turning the blower .06 percent slower though now to maintain that boost level. As far as performance gains, he didnt see any i dont believe from just the blower change.

Ive also discussed intake temps with a few friends who have played with this stuff. When going from straight up, to 5 percent, to 10 percent, to 15 percent over, the air temp changes were minute on the larger roots blower stuff. Negligible . Now, take a 177 blower thats 120 percent overdriven making ridiculous detonation inducing heat in the intake manifold charge, and replace that with a larger 1:1 roots and see nice gains. I took a 77mph boat to a 90mph boat , by simply swapping supeechargers, and didnt increase 1 psi of boost on the gauge. Hot air kills power.

My advice, throw an intake temperature gauge on the thing, and see what your temps are. Then go from there.

JRider

iTrader: (1)

According to TBS website the blowers I have are good up to 550ci, so I am probably good. Was kicking it around because I ran across a decent deal on the 1471s. I really need to run this thing and see how I like it. Thanks for the input.

BTW, the whine gives me a boner.

575cat

I think you have t$$ much coin burning a hole in your pocket $$$$$$$$$$$$$$

cigrocket

iTrader: (3)

I would just run the blowers that you have....see how everything runs this season, then when you put it away, take the blowers off, have them freshened up, and re-tefloned. Then you could always change a pulley size. Better to run it for the season, make sure you have no bugs and then play around. Freshened blowers usually add a little HP and efficiency. Good luck, enjoy the boat. I know we need something to talk about because this weather sucks and its cold, but save the coin and enjoy.