Started from scratch with the Edelbrock, advice needed...

SnoMan,

The Edelbrock 1406 is in fact an enhanced version of what we used to call a Carter AFB (back in the dark ages), almost identical, and I bet some of the old gaskets would still interchange. The Quadrajet was a very different animal. The only similarities I can see is the vacuum operated metering rods, all else is very different.

Right out of high school I ended up in a Delco factory training school (they used to train their techs, back then) and was one of the first in the state (Oklahoma) to be certified to work on that beast (Quadrajet) and what a beast it was in the first iteration. It improved magnificently over the years.

All this carb talk does take us back some, doesn't it??

George

Well... I have a set of the .095" jets... I'm going to put them in tomorrow and play with my existing meterings rods (I have 3 sets). If I get time I will pick up another set for experimentation.

I laid all the metering rod and jet combos out in a spreadsheet, and after running a few formulas to determine the flow area (area of the jet's hole minus the area of the metering rod) I was able to sort them in a logical order.

Needless to say, after that, I have little respect for Edelbrock's calibration chart.

Honestly though... I think the one thing that would help more than anything would be an O2 sensor and a fuel/air meter. At least then I could actually see what was happening, and when and where in the RPM and vacuum ranges.

You're not confusing me... I've learned a lot about carbs in the last year or so, and I keep my nose in the manual and constantly read websites to try and get a little more insight into what's going on.

Basically, I still think it all comes back to a carb that's not calibrated for that engine, with that cam, with that kind of (low) vacuum. I just need to find that balance.

~jp

SnoMan wrote:

Oh yes... I know it well, LOL...

I'd like to print up a few hundred copies of the PDF manual--to use as fire-starting material.

Actually, the main thing that's not being addressed here is the cruise mode. The springs are advertised as bringing out Power Mode at a certain vacuum pressure, but nothing is mentioned about when the cruise mode comes into play.

Is it 10" Hg??? 8"? 6"?? The carb obviously does not go from idle circuit to full-on power mode.

I need to figure that part out. Then I can play with rods, jets, and springs according to find the balance I'm searching for.

The funniest part of the whole thing is...I've literally cost myself in the thousands of dollars with everything I've been through (some self-inflicted) with the truck. But in a sick way I like it, LOL... I'm forcing myself to learn so much about all aspects of it and I love it!

FYI, the exact link for the manual is here:

Had it bookmarked on both the home PC's as well as the work PC for some time now ;-)

Also emailed Edelbrock, and I'm still waiting to hear back.

Thanks...

~jp

George wrote:

You are 100% correct here. BTW with your current came you want it to start in enrichen around 8 or 9 inches or so and that fact that the opwer vale is felt it tell me that you might be a little lean in mid range and as you richen up jet or metering rods you sometimes need to size down power valve.You migh also try have power valve come in at maybe 4.5 too. I agree that a A/F sensor would help a lot here. I had it down to such a science that I used to run once size in summer months and two size larger in winter months to keep it at peak performance. Trust me it is worth the effort to get it right and ift is very important to watch your plugs too and be prepared to change the heat range of them if you want best possible performance.

----------------- The SnoMan

The A/F meter will be the next serious purchase.

Then I gotta get a bung put in the exhaust manifold...that'll be fun--not.

I may end up trying to find a set of '87-up manifolds and go ahead and swap them out. That way I'll be set up for the O2 sensor from the get-go, and it'll probably make the future TBI swap that much less involved.

Either way, I need it running good enough so I can start reconnecting the emission control equip to get it titled in GA. I'm still running TN tags (don't have emissions in TN) and as much as I hate to consider myself anything but a Tennessean, I've been here longer than the law would prefer without becoming a "proper" citizen.

~jp

SnoMan wrote:

The best factory exhaust manifold ever made for a SB were made in the

60's and early 70's and they were wheat we called the old "Ram Horn" style and they flowed well. They came in two sizes 2 ich and 2.5 inch dump but I am not sure if they would fit/work in your application. Granted, they would not have a O2 sensor port but you could add one to the pipe right beow manifold. . On the air fuel sensor probe. You could drill a hole in exhasut manifold and then tap it to take a bolt or plug so that you can seal it when done.

----------------- The SnoMan

Does it need to be in the manifold for best results, or can it be downwind a ways?

Just trying to make this easier.

~jp

SnoMan wrote:

Also, is the standard GM O2 sensor a narrow band or wide band?

~jp

SnoMan wrote:

Too large or too small of a carb?

Mine's a 600cfm and you think more would be better???

I'm geared at 3.73 with 31" tires...

~jp

Shep wrote:

Eh...looks like I'll be spending the big $$$ for the wide-band sensor and gauge.

The narrow-band gauge shows "lean, stoich, and rich" but that's it. I want hard numbers to look at. Otherwise it's as useless to me as temperature gauges that show a scale with "H" and "C" on either end.

~jp

Shep wrote:

600CFM is about right but 3.73 are not the best with that cam and it would run a lot better with a 4.10 as it would get it on the cam quicker and make better use of improved RPM range.

----------------- The SnoMan

Yeah, but...I just had the rear axle rebuilt 7 or 8 months ago. I don't want to do that again. I kind of consider the 3.73 a bit more ideal than the 3.08's I had, or 4.10's. Just seems like a good compromise between economy and power.

And I don't want to have to rev it up to get moving.

This why I keep coming back to swapping the cam for something better suited to my truck.

~jp

SnoMan wrote:

Jon, do have have 1 and 7/16 primarys or 1 and 11/16 primarys. the 1st is

Not sure... I never measured it. I just know what was on the box, which was the model #1406 -- 600cfm, electric choke, vacuum secondaries.

And it had the combo of parts that the 1406 comes with -- .098" jets, .075"x.047" metering rods, 4" Hg springs...

~jp

Shep wrote:

Shep,

I am with you on this one. I too raced, both strip, many years, and street (young and dumb) and I never had a carb setup (single or multiple carb) this sensitive. Used AFB's, Rochesters, and Holley's and never had this kind of problem. I keep thinking that Jon is actually battling something that as of yet hasn't been put into the equation. I keep reading these posts and can't put my finger on it, but I keep trying.

There is just too much change (mixture) taking place with each change (jetting and rods) being done. What else can be in this equation?

With mechanical advance only the engine should perform great, just not economical.

I am, for now, just stumped.

George

Yes you are at a cross road, deeper gears for current cam and different cam better matched to your gearing.

----------------- The SnoMan

I wholeheartedly agree. However I'm going to try to make due.

I did finally talk to Edelbrock's tech support folks. They answered the question that has been bugging me: At what vacuum level do the rods pop up into Cruise Mode?

They said with my 4" springs, that the onset of Cruise mode should happen around 8" Hg of vacuum.

This pretty much coincides with what I have been observing on the vacuum gauge. While driving down the road, the lean spot is basically between 5" and 8" of vacuum. At 5", it isn't great, but it's really noticable around 5.5"-8".

Oh well... Gonna try to pick up a couple of sets of metering rods on the way home. Gonna get a set with the .068" cruise step. That should take it almost all the way back to stock cruise settings, even with my current jets (which are smaller than stock).

If this doesn't work, I'm going to go ahead and start cam shopping. Will I need to remove the heads to do that, or just the intake, rockers/rods/lifters, and any and everything else from the front of the truck?

~jp

SnoMan wrote: