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Question on 6 Pack Vaccuum requirement

Posted By: scrag

Question on 6 Pack Vaccuum requirement - 08/15/13 05:17 PM

I currently have 7" at idle (800 RPM) I have read a lot about 6 pack tuning, I don't think the car is making the power it should that maybe the carbs are not opening when they should (light yellow springs on the outboards) I have a Hydraulic Roller cam and roller upper end. Manual brakes....so the only thing requiring vacuum is the carbs and the PVC. This is a new engine (500 miles on it) manual transmission.....is 7" enough to do the job? I really wanted to stay with the 6 pack....but....
Posted By: Yellow Fever

Re: Question on 6 Pack Vaccuum requirement - 08/15/13 05:45 PM

What motor? 440 or 340 or???? What is your timing at? What size roller cam? Give it as much base timing as it will take and that should help your vacuum some.

http://www.mopar1.us/6barreltips.html
Posted By: Twostick

Re: Question on 6 Pack Vaccuum requirement - 08/15/13 06:07 PM

Manifold vacuum has nothing to do with opening the outboard carbs.

Kevin
Posted By: lewtot184

Re: Question on 6 Pack Vaccuum requirement - 08/15/13 06:29 PM

Quote:

Manifold vacuum has nothing to do with opening the outboard carbs.

Kevin

x2, it's air velocity thru the passenger side center carb venturi. look for a fuel delivery problem.
Posted By: scrag

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 02:41 AM

My post was stupid - apologies. Engine is a 500 CID stroker (based on a 440) cam specs are:
intake exhaust
Duration .050 252 256
Separation 109
Gross Valve lift .573 .567

Timing was set at 38 degrees total. Jets are 84 in the outboards and 66 CL. I have the promax center mixture block, outboard jet plates and the rear carb has the promax base. TTI headers 2 into 3.5. It feels pretty smooth (asked a lot of questions here - thanks for the knowledge base) and was thinking of doing a Dyno tune to get it dialed (pricey) - this is a street car and I could be second guessing myself too..I will recheck the center venture (passenger side) I was thought it was a bit on the rich side - a tad - but I was told that 6 packs tend to do this - again many thanks.
Posted By: superwrench

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 05:38 AM

With any of the yellow springs, those end carbs should come on VERY quick. I went one step up to the purples to take a bit of hit out of the car.I have a Comp XTQ296 cam.....264/270 @ .050 and about the same vacuum reading as you. Stomp the loud peddle.......1.45 60' and HOLD ON. Make sure those end carbs cycle freely... and another thing that might sound stupid......make sure the base gasket is on the right way otherwise the end carbs will NOT open. I've ran into that twice on a couple of customers cars.
As said, engine vacuum has nothing to do with the end carbs opening.
Posted By: hunterstroble

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 05:58 AM

I had a new engine I wass dissapointed with until one day I noticed my throttle cable was only opening up the throttle 75%. Dumb question, is your throttle getting max pull?
Posted By: lokalik

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 02:19 PM

are the diaphrams new? about every other year i have to replace mine, i can tell when its time because the outboards open late ( not at the rpm they should) and the car pulls slow, replace the diaphrams and it really makes a difference.
Posted By: moper

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 02:22 PM

Quote:

Make sure those end carbs cycle freely... and another thing that might sound stupid......make sure the base gasket is on the right way otherwise the end carbs will NOT open. I've ran into that twice on a couple of customers cars.
As said, engine vacuum has nothing to do with the end carbs opening.



x2 - the gaskets can also hold the secondaries open... DAMHIK
Posted By: Mr.Yuck

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 02:58 PM

why do you have the idle so low? I'd think you'd want it a tad higher. I'm running a solid roller, (588) I pull about 8-9 at idle (900-1000rpm) I'm running the stock MP 6-pack, I'm using 70main jets (probably a tad rich) 35 squirters, and purple springs. I'd probably go back to square one, set your timing in full at 36* early 2200rpm, turn you mixture screws all the way in them out a turn and go from there, tweak for best vacuum. You should also make sure your outboards are opening 100% Your build should fly. not sure how the billet blocks work, but it should run fine w/ or w/o them. I adjusted my primary w/o the outboards hooked up. Good luck
Posted By: scrag

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 03:40 PM

I checked the butterflies and gasket - (found that problem early on and as I tighten the carbs down I work the throttle open and close to make sure it is not interfering (thought I had a throttle stick and that was the culprit after junked base plate. I will check actual cable travel - that would be almost funny but I have not done that yet....I will replace the diaphrams too - maybe go to a stiffer spring.
Posted By: superwrench

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 04:45 PM

Even at 1/2 throttle, when the load/venturi signal is right, those end carbs will still give a kick in the Azz with the light springs.If you're not having the feeling that all h&ll is breaking loose, then something is NOT right.
Vacuum hoses to carbs are on right???
Posted By: buildanother

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 04:48 PM

I bought new carbs in around 1998 that had the vacuum passage completey plugged solid between vac pods and venturis of the end barbs. There is a restricted airway there and these had NO air getting through and I also found the out of box performance poor on my 500 cube duster. Opened the airway and the car then ran like it should have. Just saying.
Posted By: lewtot184

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 04:51 PM

check fuel supply, pressure and volume.
Posted By: scrag

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 08:02 PM

Well I took a the vacuum lines off and tested each carb - rear carb works like a champ front carb hisses....diaphragm is toast and it is my fault as I over tightened the cover when I was swapped the springs out....and of course no one in MD has a 135-6 diaphragm. I have one place left to try...thanks for the help. I am also going to spring is lt silver and not yellow btw...

Attached picture 7816612-IMG_0807a.jpg
Posted By: Twostick

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 09:42 PM

That'll do it.

Kevin
Posted By: superwrench

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 09:46 PM

Promax will have them. I don't know whether Mopar Performance still has them or not....I bought 3 of them about 2 years ago.
Yep....those screws don't have to be overtight...the diaphragm will just squish out if they are snugged up too much. DAMHIK.

And yes....put yellow springs in there. The plain ones are a tad stiff.
Posted By: Mr.Yuck

Re: Question on 6 Pack Vaccuum requirement - 08/16/13 10:20 PM

Quote:

Well I took a the vacuum lines off and tested each carb - rear carb works like a champ front carb hisses....diaphragm is toast and it is my fault as I over tightened the cover when I was swapped the springs out....and of course no one in MD has a 135-6 diaphragm. I have one place left to try...thanks for the help. I am also going to spring is lt silver and not yellow btw...



I have one or 2 on my bench... except I'm in SC until Sunday. If you can't find one by then PM me. Advanced Auto has a complete re-build kit however it's like $35
Posted By: 62maxwgn

Re: Question on 6 Pack Vaccuum requirement - 08/17/13 12:50 AM

Have a few !!
Also,put a little grease on the screws,if not the screw can catch and tear the rubber around the hole if the opening is not centered over the hole.

Attached picture 7816868-Picture1027.jpg
Posted By: superwrench

Re: Question on 6 Pack Vaccuum requirement - 08/17/13 01:15 AM

Quote:

Have a few !!
Also,put a little grease on the screws,if not the screw can catch and tear the rubber around the hole if the opening is not centered over the hole.o



Like he says....
Posted By: ThermoQuad

Re: Question on 6 Pack Vaccuum requirement - 08/17/13 02:51 AM

Your initial timing should be 18 and for total try 34. Try heavier secondary springs as well...you might be surprised. If you read the guide it says to start with black springs.

A pcv oil separator - that's a mustang part - makes a difference as well. Oil in the mixture causes detonation at high rpm which is difficult to hear
Posted By: scrag

Re: Question on 6 Pack Vaccuum requirement - 08/18/13 07:58 PM

Thanks Everyone - lots of good info and I am looking for forward to getting the part (due Monday)...I need to to get a couple more....what was the part number for advance? Grease on the screws....sometimes you read something like that and do the face palm - thanks -regarding the springs I will go back to see the color - I know that kick when the secondaries come in is actually a flat spot and a sign for a lighter spring - I was told smooth is the word when it comes to secondary operation....
Posted By: superwrench

Re: Question on 6 Pack Vaccuum requirement - 08/18/13 11:26 PM

I got the purples in my race car.....with the 4600 convertor I don't feel a thing... except brutal toque.....My car will actually slow down with the short yellows. Just keep the initial timing up at 16 or better....you'll love it!!
Posted By: BSB67

Re: Question on 6 Pack Vaccuum requirement - 08/19/13 01:39 AM

Quote:

... I was told smooth is the word when it comes to secondary operation....



You were told wrong. If you are trying to maximize performance, you can only determine the best spring at the track. The springs that generate the lowest et, best mph, may, or may not be smooth on the street. Weight, gear, and converter play a key role in what springs are best, and whether or not there will be a sag when they come-in on the street.
Posted By: lewtot184

Re: Question on 6 Pack Vaccuum requirement - 08/19/13 02:25 AM

Quote:

Quote:

... I was told smooth is the word when it comes to secondary operation....



You were told wrong. If you are trying to maximize performance, you can only determine the best spring at the track. The springs that generate the lowest et, best mph, may, or may not be smooth on the street. Weight, gear, and converter play a key role in what springs are best, and whether or not there will be a sag when they come-in on the street.

what BSB67 says is fact. as far as the short yellows slowing a car down; the short yellows actually have a slower opening rate than the long yellows. this is per holley's info. i don't know why they even marketed them. i use purples for street use but yellows go quicker. from a standing start you won't feel any soggy spots, like from a kickdown, with softer springs. anything heavier than purples is worthless.
Posted By: scrag

Re: Question on 6 Pack Vaccuum requirement - 08/24/13 09:50 PM

Many thanks to all - here is an update - I went with the short yellow springs when I replaced the diaphragm.....I am really stoked as the neck snap is back as is the smile. Thanks!
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