[ratuned]

i have been doing some research on this. the opinions seem to be all over the place. holley recommends using the boost referenced carbs. a LOT of people say its not necessary on a roots system. others(mostly boat sites) say no but run a 10.5 pv. i help work on a friends vette with a 454. he runs a tripower on a 671 with 10-1 compression but only has 4#'s of boost max. he has done this for years on many motors and never had a problem. at what point is it absolutely necessary? in my book " street supercharging" they make NO mention of boost ref. but say increase primary jet 10% and sec. 25%. i just spoke to one local carb guy who claims he runs no pv's and just jets up accordingly. he does install 4 corner idle though. i asked if any of the motors load up at idle and he claims he's never had that problem. i understand how and why but the opinions seem to be all over the place. what do you guys think? thanx mike

 

[GRN69CHV]

From what little I know, the carb will always see high vacuum levels because the blower is always sucking in air. The few guys I talked to also run high PV's and get away with it fine.

 

[forcd ind]

i never ran boost ref. on my blower motors(roots), mainly used ones with an opening point based on idle vac., so they were not trying to open at idle.
what it does is just gives an earlier opening point as you go into boost
if you use an lm-1 meter, and see a drastic spike in afr's for an instant, it may cure that
i do run one on my procharger car, as its a little more critical and less forgiving than a roots style-it doesnt hurt to boost ref them though, if you think your having a problem with them opening, this is where an afr ck comes in

 

[ratuned]

it seems that with a procharger boost referencing is considered mandatory because the carb is under pressure. i race with a friend who is about 80+ years old. he runs a 454 in a 67 vette. he rebuilt a 6-71 blower and made a plate for the tripower carbs. the carbs are stock except for slight jet increases. the engine even runs 10-1 compression but has aluminum heads. he also runs stock LS-6 mechanical cam. no msd but just a high performance coil and single point distributer. on a chasis dyno he made a little over 600#'s of torque and 575 hp. car only runs 11.30 at 130 mph. he also uses the carter 172 gph pump and stock 3/8" fuel line. somehow he makes it work. thanx mike

 

[ironhead]

i have been doing some research on this. the opinions seem to be all over the place. holley recommends using the boost referenced carbs. a LOT of people say its not necessary on a roots system. others(mostly boat sites) say no but run a 10.5 pv. i help work on a friends vette with a 454. he runs a tripower on a 671 with 10-1 compression but only has 4#'s of boost max. he has done this for years on many motors and never had a problem. at what point is it absolutely necessary? in my book " street supercharging" they make NO mention of boost ref. but say increase primary jet 10% and sec. 25%. i just spoke to one local carb guy who claims he runs no pv's and just jets up accordingly. he does install 4 corner idle though. i asked if any of the motors load up at idle and he claims he's never had that problem. i understand how and why but the opinions seem to be all over the place. what do you guys think? thanx mike

Boost referanced carbs will deliver better fuel mileage..seeing how you can run a lower PV#.it is possible to have manifold boost and still have high vacuum under the carbs..hence no enrichment from the PV ckt but reqd under boost.The higher 10.5 pv may open under part throttle load/no boost.The referanced 6.5 would not.Any boost seen by the PV is low vacuum and the 6.5 would still open and enrich the mixture.I think the boost referanced carb will result in a cleaner running engine at part throttle and respond to manifold boost when reqd.

 

[norvalwilhelm]

I have been running my blower for going on 8 years now. I hope to make about 1000 horse this summer. I get about 14-15 mpg combination town and open road running.
I STRONGLY believe in intake manifold referenced PV's. I run NO springs on the power valve, NONE.
My power valves get their signal from the intake manifold. I modified brand new holley 850 4 corner idles for this back in 1999.
I run lean, 15-1 on the air/fuel gage and yet when the boost needle crosses into boost the mixture jumps to 13-1.
Power valves referenced off the top of the blower always see vacuum. I run twin boost/vac gages, one above and one below the blower. While the intake is on boost the vacuum under the carbs is good.
I run up to 12 pounds of boost with my 8-71, I run 81's in all 4 corners, lots of timing, 43 degrees and a boost retart computer.
My plugs are white after running the expressway and I keep the motor at about 190 degrees all the time.
Yes I believe in intake manifold/below the blower referenced power valves.

 

[ratuned]

thanx norval, thats some useful info. mike

 

[ratuned]

http://www.hotboat.com/forums/showthread.php?t=58893

thought this might be useful for someone mike