GASGZLR

I recently switched from an Edelbrock 600 carb to a Holley 650 double pumper. The holley was way too rich out of the box, but I had my car chassis dynoed/ wide band O2 to tune it. Below is a rough pic of what the two different curves looked like. I could not get my Edelbrock A/F steady no matter what jets/rods we tried. As you can see the Holley is near perfect and with only a couple of jet sizes pulled due to elevation (5400 feet). The pump shot was right on too it drops straight down to 12.8 AF and just slightly leans out to 13.2 at 6000 rpm.

My Edelbrock carb ran great and was very reliable and fun, but it was not perfect. The two carbs ended up making the similar peak power with the Holley only beating the Edelbrock by 6 hp, but the midrange torque and HP were higher with the Holley due to the stable fuel curve. Also the added pump in the rear of the Holley cured my off-the-line bog once and for all.

F-BIRD'88

Nice job. So the Edelbrock was way rich above 3000rpm and did not respond to jet and rod changes?

Was the Holley just as rich when you started? out of the box? what jetting did you finally end up with in the holley?

Seems a lot of people have trouble dialing in the Edelbrock 600. The 750cfm carb seems to be a lot less of a hassle to get it right. May have been something wrong inside the 600 to make it not respond to jetting.
I'd look at the air bleeds and remove the venturii clusters and inspect the gaskets and (emulsion) down tubes. Something is up.
One possibility is if the secondary air velocity flap counterweight was the wrong weight and did not allow the air door to open freely based on the engine's airflow requirement @ WOT, the jetting would be rich simular to if the choke was stuck on. Was the choke closing on ya?
something to check.

Just a thought, the high altitude may be affecting the air door calibration. A lighter counter weight may be nessessary to compensate for the lighter(thinner) air acting against it to open the flap.
Even thou at 5400ft elevation there is lots of airflow throu the carb @ WOT,,, BUT>>>> the airflow has less mass (weight), then at sea level and can;t overcome the counter weight keeping the air door from opening as it should.
One way to tell would be to run it without the secondary air door (or just block it open). It should run fine as long as you don;t go from part throttle to WOT quickly.

smoktire

What jets size you got in the holley?

GASGZLR

F-Bird- It did respond to changes in rods and jets. The graph would move around in some places, but it never got straight like the Holley. My pic is where we left it for the best compromise.

smoktire- The Holley A/f was in the 11's out of the box, but the curve was still nice and straight. The stock jets were 67 front, 73 rear. We took 3 sizes out of it, to 64, 70. It made good power there but just to keep the A/F closer to 12.8-9, we put a size back in. Now it is at 65, 71 with an 8.5 power valve. The pump cams are unchanged.

Pablo

iTrader: (1)

The Holley DP is a great carb, I want one.

I have an edelbrock myself, I think your air fuel ratio problems are not because of the carb though. I can post numerous AFR datalogs from my wideband and my edelbrock 1405 setup demonstrating that the only problem I have is lack of pump shot.

I too have a stick (non wc T5) and on the launch and the shifts I get real lean transitions and im at the limit of pump shot tuning (needs more volume, and curved differently.. basically needs secondary squirters) I even drilled out the airvalve aux fuel passage (the restriction isnt the nozzle, its the feed tube under the booster, drilled it from .035 to .045) , I also blocked the airbleed for the aux secondary fuel circuit.

while all this stuff helped immensely I long for fuel injection.. or a cheap dbl pumper

my steady state AFRs are stable and tunable though. I do notice past 5600 rpm or so it starts to curve rich though.. its a bummer.


Id say the edelbrock is best suited to cars that a vac secondary holley are best suited to, automatics... they can be made to work with others but after all in the end its only a carb there is only so much it can be made to adapt to.

Tom 400 CFI

I disagree w/that. I have a 750, and it hasn't responded to my metering rod/jet changes very well at all. I dislike it. Anyone want to trade me for a Holley? It's almost brand new, and would come w/ a jet/metering rod kit, and book. Anyone?

-Tom