roots 871 boost levels

I have bds 871 stage 4 that i have had on self for about 6 or 7 years years, recently started using it. its making 18# boost at 40% overdrive. is this what it should be? would it need to be restripped because sitting so long? about OD does air become to hot to make more power.

thanks for the help!

 

Not enough information to compute.

 

18lbs @ 40% od. the blower needs to be overhauled it should be putting out mid 24-28lbs boost with a 500 inch engine. ref. bds book as a guide.

 

I have a std helix 8-71 @ 25 % on a 440 Chevy, it makes 25 lbs of boost

 

Seems like you got a healthy blower Brian

 

Our Littlefield, billet rotor, K8, high-helix, front discharge 8's made 18 psi at 43% over.

Certainly heads, cid, gages, fuel and cams can vary psi readings.

 

Booooost

bought a K-ll 6-71 from Mert, on a 477 chev makes 36lbs at 53% over 8300 engine rpm. went 6.49 219.45 in a 2025 lb front motor car

 

sorry didn't know what info to list.
540" 11.5:1
big chief 18*
indy cast intake
bottom blower open, no plates, no pies, no ice cream

fixed below typo:
about WHAT OD does air become to hot to make more power.

thanks

 

Again, it depends on combos. You WANT your air to be 170'ish degrees. no colder than 150. Can you have someone measure the intake manifold temp on the return road? aka as soon as you make a pass and come to stop?

Generally, rotor speed should be below 13000RPM, commonly works out to 35-40 over depending on how are you buzz the motor.

 

It all depends on the blower. Typically 40-50% is about it, unless you're doing a screw blower.

Really though, you've got too small of a blower for the combination, which is why you're spinning it so hard to get boost out of it.

Step up the blower size, slow down the drive, and watch the motor come alive.

 

I run a Kobelco K-9 8-71, front discharge, hi-helix, on a 511 ci hemi with Walt Austin heads. I regularly spin it at 63 over and it makes 38lbs of boost in the 1/8th mile. I just recently changed to spinning it at 70 over and now she makes 40-41lbs of boost in the eigth mile and the car picked up about .03-.04 on the average. This all with a blower that hasn't been restripped in about 40 runs.

 

Big difference with a BDS and Kobelco... It's like comparing a pinto to a porsche.

 

This is the first I've heard a statement like that.
Please educate us on why 150° is better than cooler.

 

Methanol evaporates at 148*. If you keep the intake too cold, the fuel will puddle, and turn back into liquid. If you are able to keep it warmer, it will help stabilze your tuneup and keep the methanol suspended, providing a truer A/F ratio.

When too cold, the with a known A/F, the motor will 'look' lean, because the fuel isn't burning well. So you add more fuel, well, it is colder now, so the problem is worse. It is a nasty circle.

Does that help? I can't tell, it seems like i'm mumbling.....

 

Do you mean condensates? Evaporation is turning from liquid to gas.

If high school physics are remembered correctly, atmospheric pressure also comes into play as to what temperature condensation occurs.

I also find it hard to believe, with the amount of air/fuel that is being moved, and the rate it's being moved at, that there would be a chance for fuel to puddle at 35-40 PSI, at 8000+ RPM. Especially after being beaten by blower rotors, then injected 1-2" from the valve.

 

One of the things that hurt the Whipperator vs PSI was average (notice I said average) intake manifold temp was:

W=140-145

PSI= 96-99

Sorry Greg.

BTW: Jirka Kaplin's 6:71 produces 43# = 6.39

 

Bob, thank you for the information. I was relaying what i've read. I guess i hadn't thought the process thru.

Thanks again.

 

70 over???? How high do you spin the motor?

 

About 8300 at the shift points. I never get above 7100 in high as I only run the 1/8th mile.

 

You Guys & Dolls do realize this is the INTERNET and theres a lot of bull s#!t being thrown around, the old saying " don't believe nothing of what you hear and half of what you see " should be taken into consideration when getting info on the net. be carefull out there!
P/S You giveing out the bull s#!t info, The KARMA will bite YOU on the A$$!!!!