Power valve question for BB
Le Mans Master
Joined: Mar 1999
Posts: 6,744
Likes: 1
From: delmont pa
Cruise-In I Veteran
Cruise-In II Veteran
Re: Power valve question for BB (467-Ratman)
that stumble was caused by the #65 power valve opening too late,try a #85. the IFR are brass orifices pressed into the metering bodies.
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Re: Power valve question for BB (clem zahrobsky)
DP are set up rich for racing and to lean out for around town driving i would reduce the size of the idle fuel restrictions(IFR),reduce the jet size while enlarging the power valve restrictions the same amount in area. the power valve has nothing to do with idle if the idle transfer slots are set correctly. most BBC need 8.5 power valves to prevent part throttle leanout.
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Re: Power valve question for BB (467-Ratman)
Matt
I am using .025 " in all 4 passages but I am using a 750 dp on not so wild eng, 9.1/1 comp, 220/230 dur cam. I would probably be better with a 650 dp but I had the 750 so I decided to use it. I went from have very little reponse when adj the idle circuits to now I am at about 1/2 to 3/4 turn on each corner and a 1/4 turn on any shows up on the vac gauge. Think Norval is using a .018" wire in all 8 of his idle passages.
Rattman
I would hook a long peice of vac hose up so you can check your vac at cruise and see if you get a stumble before your vac drops below the pv rating when giving it some gas. You may not need to lean out your idle circuts with the 'wire trick' if they are sensitive enough. Your eng is much better suited to a 850 dp than mine is too a 750 dp. I am using a heated O2 sensor also which def helps in the tuning department. I am by no means a tuning guru but offering some things that have helped me. I am still having issues but I think I might not be getting a 100% accurate tdc reading from my tab and balancer cover. I am going to get a tdc locator and see where I am at.
:cheers:
I am using .025 " in all 4 passages but I am using a 750 dp on not so wild eng, 9.1/1 comp, 220/230 dur cam. I would probably be better with a 650 dp but I had the 750 so I decided to use it. I went from have very little reponse when adj the idle circuits to now I am at about 1/2 to 3/4 turn on each corner and a 1/4 turn on any shows up on the vac gauge. Think Norval is using a .018" wire in all 8 of his idle passages.
Rattman
I would hook a long peice of vac hose up so you can check your vac at cruise and see if you get a stumble before your vac drops below the pv rating when giving it some gas. You may not need to lean out your idle circuts with the 'wire trick' if they are sensitive enough. Your eng is much better suited to a 850 dp than mine is too a 750 dp. I am using a heated O2 sensor also which def helps in the tuning department. I am by no means a tuning guru but offering some things that have helped me. I am still having issues but I think I might not be getting a 100% accurate tdc reading from my tab and balancer cover. I am going to get a tdc locator and see where I am at.
:cheers:
Race Director
Joined: Oct 2000
Posts: 15,013
Likes: 79
From: central FL, near the beach.
Re: Power valve question for BB (467-Ratman)
ratman
if you are shifting at ~2500 light throttle i would expect 12-16". if you are shifting at 1200 it might go down quite a bit. i don't drive like that, but my dad does, so it really boils down to driving style. A "lugger" might need a lower PV, most will need a higher PV like clem says.
Nobody but you can give a truely custom tune.
You can copy somebody elses custom tune, that would be one possibility(should be better, but not likely to be best). You could start a new hobby, tuning(i like it, it's fun when things come together)
Or you could buy a carb designed for street use, like the QJET. Some of the new Holleys are calibrated for street use, that is possible also.
Tuning without an A/F meter is like flying a plane blindfolded. An expert can do it, but can anyone else?
if you are shifting at ~2500 light throttle i would expect 12-16". if you are shifting at 1200 it might go down quite a bit. i don't drive like that, but my dad does, so it really boils down to driving style. A "lugger" might need a lower PV, most will need a higher PV like clem says.
Nobody but you can give a truely custom tune.
You can copy somebody elses custom tune, that would be one possibility(should be better, but not likely to be best). You could start a new hobby, tuning(i like it, it's fun when things come together)
Or you could buy a carb designed for street use, like the QJET. Some of the new Holleys are calibrated for street use, that is possible also.
Tuning without an A/F meter is like flying a plane blindfolded. An expert can do it, but can anyone else?
