Folks,

I have a battle of experts going on. Me, I'm no expert! Since last September's thread by Argentina and Cstryker I have been studying the Holley 4160 ---8007 (390 cfm) and experimenting with modifications. NOT to the extent of Argentina, but I did go to a Holley mfgr school to the battle I need your experience with began.

I am running above-mentioned Holley on the Offy 4bbl intake. My vacuum source for my in-cab and test vacuum gage is a brass tree I put together to feed power brake booster and gage. The two tee tree is in the number six intake runner. Prevously I was running a Eddy 500 cfm and the Eddy's throttle plate fitting provided vac for the gage and power brake.

Well, the Holley factory trainers say ONLY put a vac gage on the litttle bitty full manifold vac pipe that is on the carb; that using a vacuum tap from an intake runner can be WAY off. I have been wondering why my well tuned Holley is giving me 15 inches vac at 750 rpm idle on top of a 3 inch riser, where the Eddy gave me 20 inches at 500 rpm. lCould it be Holley engineers are right? Should I stop using the intake tap?

I know you are saying why not do it and see...it ain't that easy. That darn little pipe is for a hose the size of a vac advance hose. My gage and booster are using 3/8 inch hose. So an adapter would be in order from little hose to bigger. Again, no problem, but is it likely to change anything before wasting time? I am sure the Holley guys here can weigh in. Like I tell my employees, in theory there is no difference between theory and practice, but in practice there often is.

Thanks
rock
'64d100

Try it and see. The adapter and a piece of hose can't be more than $5.

What problem are you atually trying to solve?

_________________
Official Cookie and Mater Tormentor.

Thanks 'zilla,

I figgered a wizard here knew already and it would save me the installation time and minor sum for parts, or show spending both was worthwhile. No problem to solve, I don't think, but a 5 inch vac. differential is curious to me between two basic 4bbls. Runnin a 8.5 power valve; installed quick change spring kit with yellow spring; put on a secondary metering block. Using 25 shooter and 51 and 57 jets and orange cam. No holes drilled in plates.

rock
'64d100

I think the Holley guys are right.........

Also the #6 runner tap for the brake booster doesn't need to be a constant source as the brake booster has a check valve.

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

If there is then the theory is either incomplete or incorrect.

_________________
David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

I can see that maybe there'd be a slight difference between the vacuum port on the carb and a runner at certain speeds, when the runner's tuning causes a standing wave in the runner. But I can't see it being 5" at idle.

If the Holley is giving you 5" less vacuum at idle and timing and everything else are still the same, then the mixture is either a) not as precisely set as the Edelbrock, or b) the fuel distribution isn't as good.

Try the fitting on the carb, but I don't expect any difference. As for using the runner- in general remember that a vacuum gauge doesn't actually introduce any air into the stream like a brake booster or vaccum line for the HVAC doors will, so it won't affect the mixture in and of itself. Putting a vacuum "load" like a booster or the HVAC servos on a runner will lean out that runner, but a gauge won't.

_________________

440..

Thanks a ton. I didn't know there was a chance of air in from a booster...never had one before. Hmmmm, those Holley guys might know what they were talking about! OK, I'm gonna do the change adn report back. I sure don't need number 6 being leaner either so I may take the booster to the throttle base too. And indeed I am still dialing in the Holley whereas the Eddy was in a high state of tune. I am still approaching the transfer slot exposure a couple of thousandths a trial. But I wanted a vac gage reading in which I could have faith. So, do it the factory way! I have faith in my gage because I use a mercury manometer for the testing and match my dash mounted gage from a old piece of lab. apparatus. to the column of mercury.
Thanks again to all!
rock
'64d100

You can place a T fitting in the choke pull off hose (if the Holley has one) and that is a great source for vacuum.

I wish I could post a pic of my BBD. I don't run a choke and I plugged a vacuum gage into the pull off hose and hung the gauge on one of the mounting bolts in a hole on the carb. I do need to mount one inside. I run one on the dash of my van.

_________________
'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

Thanks trucker,

I don't use a choke so could use the choke hose...good idea. Wish I'd a thought of that before. I fired up the lather and turned an adapter to transition from the small vac advance size hose to the 5/16 gage hose . Just a simple stepdown fitting made from 3/4 inch round stock center bored for the vacuum, then moved the gage from the #6 runner to the carb fitting.

I had what I consider a marked change in vac reading. Remember it was reading 15 inches with the manifold tree and I use as precision a gage as you could get. Well upon changing to carb via new adapter, NO ohter changes, I get 18 inches reading. I was able to squeeze another inch out with tuning, up to 19. Now that satisfies me! The Eddy was idling at 19 - 20, so a steady 19 doesn't bother me a bit. So if you ever wondered if you could get a markedly different reading if a booster was in the same line as the gage, well I can! (Now, if I can just get secondaries adjusted so they feel like a 25 hp boost when they kick in...)
rock
'64d100

hey rock

as we talked about, I believe that extra inch of vacuum is waiting to be discovered if you drill them blades. That would allow you to dial in leaner idle without hurting the transfer slot (they take mixture from the same "well" or circuit) and holleys are notoriously rich at idle.

_________________
Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Pulling the 19" at idle with what cam and what RPM? 19" is mighty fine!

_________________
'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick