Holley 6-Pac Jet Kit Compatability Question

[cwestra]

Does anyone know if the Holley jets in the kit below will work with my original Holley 340 6-Pack carbs?


Holley Jet assortment kit 64-99 jet Barry Grant 36-181

[Changin Gears]

Only your center carb has jets, so it will work with it.  Outboards have metering plates.

[gkring]

I don't see a link or picture, but all holley jets should work in your center carb. The end carbs use metering plates and you would have to convert them over to use jets. For the center carb you may even need jets a few sizes smaller than the 64 that comes in that kit.

[cwestra]

I just pulled the jets from the center carb.  Stamping says 61.  Anyone know if this was standard size from factory?  Seems small but maybe not for a small block.

Also, the jet plate on the rear appears to be staggered, with diameters measuring approx. .086" on R, and .071" on L.  According to jet conversion chart, this should be close to #77 and #69, respectively.  Was this stock?  Were they staggered from factory?

I want to dial in my carbs correctly for the engine (stock with Lunatti #60402 cam).  Just wondering how close I might be with the above configuration.

[Chryco Psycho]

61 is the correct stock jet
 I would Talk to Promax , they have a kit to replace the metering plates with a plate that takes the std holley jets

[Moparal]

I just bought a promax jet plate kit at the indy swap meet 2 weekends ago. I talked with the guys at the display for a while about jetting my carbs. They suggested to me that I run a 3.5 to 4.5 power valve. #78 jets in the front carb and # 86 jets in the rear carb and # 64 in the center carb.  I have a 499 cube engine. They had said that stock jet plates were around #76 for the front and back plates.

On the other hand, I have an old Direct connection performance up grade kit in there right now, they used to sell over the counter at the dealerships in the 70's for racing.  It came with #69 jets for the center carb, and bigger hole outboard jet plates in the outboards.  This kit really woke my car up and added some big changes to the performance of my engine tune. I am just now saving up to buy the throttle plate that promax offers to adjust the rear carb while still installed. 

Once I have the throttle plate I will start tuning the engine more at the track. Promax also suggested the light springs in the vacuum pods which are the yellow springs.  I can tell you the direct connection performance kit really works well on my carbs, and am excited about trying out the promax stuff to see if it makes a difference.

Going by the holley jet to drill size chart that promax gave me, it says that #78 jets in the front carb would be an  .0870  thou drill bit size and the rear jet #86 would be a  0.100 rear drill bit size.

I'm not sure if any of this info will help you. I'm just passing along the info I know and the kit I have tried out.

[cwestra]

61 is the correct stock jet
 I would Talk to Promax , they have a kit to replace the metering plates with a plate that takes the std holley jets

Thanks, CP.  I'll give them a call tomorrow.

[cwestra]

I just bought a promax jet plate kit at the indy swap meet 2 weekends ago. I talked with the guys at the display for a while about jetting my carbs. They suggested to me that I run a 3.5 to 4.5 power valve. #78 jets in the front carb and # 86 jets in the rear carb and # 64 in the center carb.  I have a 499 cube engine. They had said that stock jet plates were around #76 for the front and back plates.

On the other hand, I have an old Direct connection performance up grade kit in there right now, they used to sell over the counter at the dealerships in the 70's for racing.  It came with #69 jets for the center carb, and bigger hole outboard jet plates in the outboards.  This kit really woke my car up and added some big changes to the performance of my engine tune. I am just now saving up to buy the throttle plate that promax offers to adjust the rear carb while still installed. 

Once I have the throttle plate I will start tuning the engine more at the track. Promax also suggested the light springs in the vacuum pods which are the yellow springs.  I can tell you the direct connection performance kit really works well on my carbs, and am excited about trying out the promax stuff to see if it makes a difference.

Going by the holley jet to drill size chart that promax gave me, it says that #78 jets in the front carb would be an  .0870  thou drill bit size and the rear jet #86 would be a  0.100 rear drill bit size.

I'm not sure if any of this info will help you. I'm just passing along the info I know and the kit I have tried out.

Thanks, Al.  I really appreciate these details.  Even though your engine is larger cube and probably likes the bigger jetting than mine would, I get the feeling, based on your account, that mine could be dialed in better than the stock settings it currently has, particularily since I have gone to a larger cam.  I'd like to be more of an "expert" on these carbs than I am right now.  I have a feeling that's almost a natural progression for anyone owning a car with a set-up like this.

I plan to talk to Promax today or tomorrow to discuss my set-up and what they recommend.

A couple of questions for you, though.

1)  What does the vacuum pod do and what affect does a change in spring rate have on performance?  It seems to have a damping effect on the rate of closure of the throttle plates when actuating in hand.

2)  And you mentioned the 3.5 or 4.5 on the power valve.  I can't see a number on mine that looks like that.  Where would this be located?

3)  As I mentioned, my outboard plates have staggered jets drilled.  You mention a difference between front and rear on yours but not about staggering right and left.  I assume, then, that yours are not staggered within the carb.  Any idea why they would have been from the factory?

By the way, I understand you wanting to replace the base plate on the rear carb.  What a pain having to pull the carb everytime you want to make a 3 second adjustment to the idle mix.  I'm guessing when they originally decided to place 3 2bbl's on these cars, the only practical option was to use the base plate from a stand-alone 2 bbl., where direct access to the mixture screws was not a problem.

Thanks for your assistance.

[Moparal]

I had heard of some people staggering jets on the stock 6pk intakes from left to right. I specificly asked Promax about this area and they kept says no....front and back stagger. They were tuning I believe a 470 cube on the dyno for a test engine.

The yellow springs allow the outboard carbs to open quicker and eliminate the bog in the throttle response.

The stock power valve is around a 6.5 I believe.   Cars with less vacuum useing bigger cams need a smaller number power valve that is measured at the intake when Ideling in gear.

[Supercuda]

Th most important thing in all this, is to remember that it is still a 4160 carb. The secondaries have been separated and doubled, but it still has all the same circuitry and tuning response of a 4V setup. It has more airflow capability and some fuel distribution issues due to the carb placement, but it is essentially just a blown-apart 4160. Staggering the jetting from side to side is due to the dual-plane intake design; it sometimes will run better if tuned in this way. All setups are unique, and require specific tuning. Many will run better if the jetting is staggered front to rear, for similar reasons of intake design. Reading the plugs (for ALL cylinders) will help with tuning decisions; so also will some 0-60 jaunts against a stopwatch. Allowing the secondaries to open more quickly is almost always a good idea; most are set too conservatively from the start. Just remember that you can open them too quickly, as well.

[Moparal]

One noticeable thing I have seen in comparison to the outboard carbs being basicly the same as a 4160 is

On the outboard 6pk mopar carbs, you have air mixture screws, kinda like some 4 barrel holley 4 corner ideling screws. Then on the corvette 2300 6pk outboard carbs, there is no mixture screws, so there is to some extent some internal differences.  Also the promax plates have scew in bigger air bleed screws.


When I mash the gas pedal, I want all 3 carbs to open up as soon as possible.  Useing the holley spring kit correct weight, the correct size power valve, and propper jets will taylor the carbs opening and fuel distribution.  Also the stock squirter is a 28, You will most likely have to step up a bit to like a #31 squirter to help keep the bog out at throttle transition when the outboard carbs start to open

[Supercuda]

Like I said; simple, 4160 tuning procedures. The idle mixture screws were added to achieve better idle fuel trim. Almost never adjusted after they left the factory (by the regular guys, anyway), they made a huge difference in idle and transition. Yo do want the secondaries open quickly, but there is always a limit; I have crossed this line once, and it's just as disappointing as having the secondaries open late.

[cwestra]

I talked a bit with Promax today, but unfortunately, all they were able to tell me is that it was a guessing game trying to dial in the carbs and there wasn't much they could do unless I dyno'd the engine.  And I am way too nervous to put it on a dyno.

My plan, now, is to buy a couple of jet sizes larger than the #61's currently in there, get some of the yellow vacuum pod springs, and identify the power valve currently in my car now.  Then, with my current set-up, dial in the adjustments (float, idle mixture, idle speed, timing, etc...) and take it out on the street to set a baseline for performance.  Then I'll try adjusting for optimization.  Thanks for all the insight from everyone. 

[Supercuda]

Since you have two secondary carbs, you need two of the Holley spring assortments. You might want to experiment with other springs, as well; but the yellows are where we all usually wind up. Most of this kind of tuning is trial and error; just be careful, and change only one thing at a time. Start with basic fuel metering changes, then worry about your secondary tip-in.

[Chryco Psycho]

as the secondaries are connected together you can also experiment with 1 lighter & 1 heavier spring to give a different combined spring rate as well ,so you can half step between the spring rates