Holley 800 Baseline Tune? bbc - Chevelle Tech
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post #1 of 9 (permalink) Old Mar 10th, 16, 8:51 PM Thread Starter
 
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Holley 800 Baseline Tune? bbc

Hello all

I bought a used 4780-2 Holley 800 DP on craigslist recently to use on my 454.
It was supposedly setup to run on a sbc bracket car.
Its current specs:
Jets 72/86
PV 5.5/blocked
Squirter 37/37
50cc pump with yellow pump cam #643 in front with screw in hole position #1 and #466 Orange 30cc in the rear with screw in position #2.
All 4 throttle blades have been drilled.

I would like to rebuild this carb (my first time-I'm a newb) to use on my mostly street 454, but am unsure what if anything I would need to change.

I have read that I should use the 30cc pump on the primary side and put the 50cc on the rear. Is this a good idea?
What pump cams should I start with?
What other parts should I change..jets, squirters, PV etc?

My specs are 454, large oval closed chamber heads, flat tops, comp 294S cam with matching springs, crane energizer roller rockers, stock hei, pro comp rpm air gap style intake, turbo 350 w/3000 stall, and 12bolt posi w/ 3:73 gears

thanks for any/all help
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post #2 of 9 (permalink) Old Mar 10th, 16, 9:03 PM
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Re: Holley 800 Baseline Tune? bbc

That's an old carb, likely late-70's to early-80's. I'd check all of the gasket mating surfaces with a straight edge to make sure they aren't warped.

Since you are starting from scratch I'd put the carb back to OE specs and use that as a baseline. When you purchase a rebuild kit, consider a Trick Kit.

Steve R
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post #3 of 9 (permalink) Old Mar 10th, 16, 9:57 PM Thread Starter
 
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Re: Holley 800 Baseline Tune? bbc

thanks for the info..yep I will defiantly be checking for any warpage.
I found most of the stock specs for the carb, but found nothing on pump cams.
the yellow #643 cam seems to be for a 4500 style carb..maybe try a brown cam instead for the 50cc?
what about screw positions in the cam?

thanks
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post #4 of 9 (permalink) Old Mar 11th, 16, 12:19 AM
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Re: Holley 800 Baseline Tune? bbc

Catalog says a 4780-2 has 70/85 jets and .031 pump shooters and 30cc pumps front & rear, so you're pretty close.
The 50cc pump kits come with both a brown and yellow cam, so the yellow should be OK, but swapping to the brown won't hurt to be sure. See kit 20-11. I think it's the same yellow cam that is used for 4500 Dominators. #20-81

The position 2 is generally used for engines that idle above 1000 rpm.

I am not sure of the thinking that says 50cc pumps are better on the rear. Holley either used 2x 30cc pumps, 2x 50cc pumps or a 50cc front/30cc rear. I do not know of any Holley carb that comes with a 30cc front/50cc rear.
It's my understanding that the longer opening duration of the primaries requires a larger volume of fuel so the pump shot lasts all the way to WOT. (ie: The primaries have already opened 40 before the secondaries begin).

Set your floats and read up on how to set your idle speed and mixtures. Plenty of good Holley books out there.
But, make sure your ignition timing is where it needs to be first.

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post #5 of 9 (permalink) Old Mar 11th, 16, 9:05 AM
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Re: Holley 800 Baseline Tune? bbc

The carb is pretty close. Why don't you run it first and see how it does? Your modification may help or hurt and you have no way of knowing if you haven't tried the carb.

The 4780-1-2 came from Holley with front 30cc and back 50cc. The 4780 is and excellent carb, better response than the 4781 and will et very close but mph will be slower than the 4781.
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post #6 of 9 (permalink) Old Mar 11th, 16, 10:13 AM
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Dennis
 
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Re: Holley 800 Baseline Tune? bbc

On a used carb I like to dig a little deeper, make sure none of the air bleeds have been drill or if they have at least know what they are, you never know who has drilled out power valve channels restrictors ( pvcr)or the air bleeds.

If you rebuild it make sure EVERY passage is clear and verify, after cleaning and compressed air, I'll use a can of carb cleaner and spray into every hole and verify it comes out the other end, for a newbe this is a good excise so you learn the passsages and maybe pick up a little how the carb functions. Of course use a straight edge to make sure things are flat, I have come across many base plates where the corners are warped from over tighten carb nuts, some I have been able to sand(on flat glass) or file flat( big flat bastard) if not to bad, some have been cracked and need replaced.

Normally the 50cc is in the rear and most generally a 30cc pump in the front is all that's needed, no need to squirt anymore fuel than needed.

Hope some of this helps.


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pics of projects and whatever.
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post #7 of 9 (permalink) Old Mar 11th, 16, 2:28 PM Thread Starter
 
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Re: Holley 800 Baseline Tune? bbc

thanks for the info.

I don't see any obvious tool marks..how can I tell if anything has been drilled out?

Would this kit be ok to use or should I spring for a Holley, AED, or Quickfuel kit?
JEGS Performance Products 150260, JEGS Carburetor Rebuild Kits | JEGS Performance Products

Also what would be good to soak the carb in? maybe lacquer thinner? I've read some people say pine sol works good?
I've heard chemdip use to be the best but has been neutered to pass environmental laws..maybe this is only in California? (I'm in Indiana)

On another forum I had some pics posted and someone said it looked like I have a 50cc pump arm on a 30cc pump..Is that the part circled in the first pic or the part with the arrow pointing to it in the second pic?
Should I change this?

thanks
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post #8 of 9 (permalink) Old Mar 11th, 16, 4:15 PM
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Re: Holley 800 Baseline Tune? bbc

Quote:
Originally Posted by BlackoutSteve View Post
I am not sure of the thinking that says 50cc pumps are better on the rear. Holley either used 2x 30cc pumps, 2x 50cc pumps or a 50cc front/30cc rear. I do not know of any Holley carb that comes with a 30cc front/50cc rear.
It's my understanding that the longer opening duration of the primaries requires a larger volume of fuel so the pump shot lasts all the way to WOT. (ie: The primaries have already opened 40 before the secondaries begin).
Quote:
Originally Posted by sleeper View Post
The 4780-1-2 came from Holley with front 30cc and back 50cc.
I stand corrected.. Looking a little deeper I see that some carbs had the 50cc on the rear. Most of the 850s actually..
I'd like to know what the reasoning is behind the 30cc/50cc and 50cc/30cc arrangements.

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post #9 of 9 (permalink) Old Mar 12th, 16, 1:27 PM
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Re: Holley 800 Baseline Tune? bbc

Call BLP for the kit, have them swap the following. Use .128 N&S, teflon N&S gaskets, green pump cams for both. 76/84 jets will get you in the ballpark, jet for best track performance from there. Invest in a wideband gauge if you want to really dial it in.

Mark Whitener

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