355 tuning questions

[rollinon35s]

Ok so my brother and I freshened the motor up in my 84 k20 a couple years ago and though it ran like a scalded dog with 33" tires it seems since I went to 35's and made some motor "improvements" it don't have that same snap it had.

Build is like this 350 4 bolt block bored .030,
4 relief flat top Pistons
Stock crank and rods
Comp cams 12-239-3 extreme 4x4 series
World products torquer 2 heads 170cc runners, 67cc chambers
Weiand speed warrior intake
Edelbrock 1406 carb
Hei distributor from skip white performance
Hooker headers with thrush welded mufflers and full length tail pipes

700r4 trans with upgraded governor springs mild converter (1500-2000) I believe

4.10 gearing and 35" tires

Obviously this is a big heavy truck so I don't expect a dragster but it seems like every since I went to this carb and intake set up it lost a lot of torque. What do you guys recommend to get the most of this engine?

 

[Rusty Nail]

Hi was reading your specs and immediately blamed the carburetor.
Why?
It's TOO SMALL.
I HATE Edelbrock, to be fair. Those carbs are junk.
Big assed truck is gonna want legendary HOLLEY equipped tune-ability. The Primary shot will be crucial.
Think HOLLEY. Think bigger than 600. If you know someone good with carbs, it would be well worth any meager cash spent to have it tuned, unless you are up to it.
I have ZERO experience with a speed warrior intake ,but there is a Weiand on my SS.

I looked it up and made note that is has an exhaust crossover. More information is necessary. Was this intake manifold one of the "improvements"?
We're the exhaust crossover blocked? How was the gasket arrangement. Nice heads, they don't have a crossover, do they? See what I'm getting at here? Stand by.

I find no evidence of that and assume those heads as part of the original rebuild .
I'm at the carburetor.

What carb got replaced with that measly 600? A q-jet could have been a 795 in '84..?

 

[bucket]

What carb/intake did you run before?

 

[bucket]

I was reading your specs and immediately blamed the carburetor.
Why?
It's TOO SMALL.
I HATE Edelbrock, to be fair. Those carbs are junk.
Big assed truck is gonna want legendary HOLLEY equipped tune-ability. The Primary shot will be crucial.
Think HOLLEY. Think bigger than 600. If you know someone good with carbs, it would be well worth any meager cash spent to have it tuned, unless you are up to it.
I have ZERO experience with a speed warrior intake ,but there is a Weiand on my SS.

I don't like Eddy carbs either, but the CFM rating shouldn't be to blame here. A dinky carb that is too small should not decrease low end power.

 

[Georgeb]

I don't like Eddy carbs either, but the CFM rating shouldn't be to blame here. A dinky carb that is too small should not decrease low end power.

I agree 600 cfm should be fine. I would blame it on the setup and tuning of the carb first.

 

[Rusty Nail]

IMO - 600 cfm will not "get the most out of that engine". I'm not talking smack but dude would have WAY better luck with an out of the box 750! 750 q-jet for the win!
600 is inadequate...unless good gas mileage is the intent, but I didn't read it that way.
He's got great components otherwise, it SHOULD run like a scalded dog!

More information is necessary.

 

[rich weyand]

Edelbrocks are set up from the factory for low-vacuum engines, and they are also set up rich because most people don't tune them and rich is less bad than lean.

Use the 8" step-up springs from the spring kit: http://www.summitracing.com/parts/edl-1464?seid=srese1&gclid=CMrexO32ucoCFYJEaQod0hIMNg

Next, adjust the floats per the instructions. They are ALWAYS off new-in-box.

You'll need the gasket to close it back up: http://www.summitracing.com/parts/edl-1499

Set the accelerator pump to the closest-in hole on the arm to get the biggest shot, because a high-vacuum engine will suck a lot of air when the throttle opens.

Connect the vacuum can to the DRIVERS side vacuum port and cap off the passenger side port.

What vacuum can are you running? What base timing are you set at?

Are you running the Edelbrock stock jets and rods?

 

[rich weyand]

IMO - 600 cfm will not "get the most out of that engine". I'm not talking smack but dude would have WAY better luck with an out of the box 750! 750 q-jet for the win!
600 is inadequate...unless good gas mileage is the intent, but I didn't read it that way.
He's got great components otherwise, it SHOULD run like a scalded dog!

More information is necessary.

A 355 at 5000 rpm with an unattainable 1.0 volumetric efficiency will pump 500 cfm. He's not using all the carb that's on there unless he's revving higher than that.

 

[Rusty Nail]

5 grand? Lulz, my grandma revs harder than that!
Image bet dude here is much closer to valve float WITH Torquer SR heads! Gotta be getting near 7 grand...6800? He's leaving power on the table running a 1406.

Helllllo OP?! How much horsepower did you want to NOT MAKE in your 6000 pound truck? I guess it has a handsome surplus then ,yes? You never, ever hold the gas pedal down until it won't rev any higher, do ya?

 

[rich weyand]

If he's revving above 6500, the 1406 will run out of breath. Short of that, no.

 

[rollinon35s]

thanks for all the input fellas, the carb is where i was going to start but wanted others opinions before just tossing more money at the problem. I have come to despise these edelbrock carbs anyhow, for more reasons than one. but rather than waste time bashing carbs i am looking for a solution.
The original build had a set of custom built 305 heads from a local machine shop, it had lots of torque which is what i told the guy i wanted but with the flat tops and the small chamber design of those heads it ping'd and dieseled when trying to shut it down overtime it got hot and humid unless i ran race gas. plus it ran out of power way to early. it also had a performer intake on it at that time with another 1406 carb.
When i bought my new heads i replaced the intake and carb set up as well. Everyone kept telling me the tuning issues were due to the worn out carb and or a possible vacuum leak at the intake from the carb being taken on and off so many times, so i bought a brand new "junk" carb and the weiand intake hoping to resolve the issues.
The new heads breathe way better and i am convinced now from you folks that a better tuned adequate sized quadrajet may really wake this beast up, once it starts seeing the fuel it wants.
I believe total timing is set at 36 degrees at this point if i remember right??

 

[rich weyand]

Any carb you just buy and slap on will run like **** unless you get real lucky. Carbs need to be tuned. Not tuning the carb you have will not be fixed by buying a new carb and not tuning it either. You're just pissing money down a hole, and you will still have an untuned poorly performing carb.

The Edelbrock 1406 carbs need the following:

1) the float heights set. They will be wrong right out of the box.

2) either an air-gap manifold with a thermac air cleaner, or a thermal gasket between the carb and the manifold. The 1406 is sensitive to temperature and needs isolation. This is probably what you were seeing before.

3) the step-up springs adjusted. The step-up springs should be half of the idle vacuum. The 1406 comes with the 5" springs installed. Now, if you have 10" of idle vacuum, that's perfect, but most of us have idle vacuum more like 18" to 20". That's characteristic of an engine tuned for torque rather than horsepower. Mine pulls 18" at idle, so I used the 8" step-up springs and stretched them a bit to get earlier step-up. Without getting the springs right, you will be in the cruise circuit all the time unless you really get your foot in it. The power circuit SHOULD kick in at half the idle vacuum. Running around on the lean cruise circuit all the time will kill any kind of throttle responsiveness and mid-range torque.

4) lean out the power circuit. The Edelbrocks ship rich, because they are tuned for the average hot-rodder type engine, not a high-vacuum torquey truck engine.

5) richen up the cruise circuit. The 1406 is tuned for mileage. This means the cruise circuit is way lean.

6) increase the accelerator pump shot by moving the actuator to the inner hole on the accelerator pump arm. High-vacuum engines need more of an accelerator pump shot because the air rushes in so fast when the throttle is opened.

Now, if you just take an Edelbrock out of the box, and put it on your engine, and hook up the fuel line and throttle cable, you will get ****** performance. Duh. If you do the same with any other carb, guess what? Same thing.

I'm convinced that most people who complain about the Edelbrock carbs have never learned to tune one, or didn't bother. There's a reason the Carter AFB was used on so many cars and hot rods over the years. When properly tuned, they work very well.

 

[rollinon35s]

Ok I get the tuning concept and I agree the carter afb was a good carb when tuned right, that's why I ended up with the edelbrock in the first place. My brother had run carter carbs in the past on his nova and gran prix 1/4 mile street toys. He always had good luck with them back then but something changed when edelbrock took over. I don't mind tuning a carb but I don't like doing it every time I get this truck out for a weekend cruise and that's the stuff I have experienced since buying the 1406. My brother was so determined it was something with my truck that he took the old one rebuilt it and started all over tuning it for his truck after a month or so with fooling with it trying to find consistency he finally tore it off tossed it back on the shelf and installed a quadrajet tuned it to his motor and boom problem solved. The truck runs better than it ever has since his rebuild. His motor is different than mine though so that's why I was asking for some tuning advice as to where to go from here cuz I sure don't want to keep throwing darts in the dark at it if ya know what I mean lol that gets expensive quick.

 

[rich weyand]

I set up my 1406 three-four years back and haven't touched it since. Once a year I clean off the step-up pistons -- when I don't forget.

So I haven't seen consistency problems.

 

[bucket]

All the Eddy carbs I've had are only happy in about a 15-20* temp window. When the weather changes a week later, you need to mess with it again. Well, all but one carb. The too-small Eddy on my crew cab's 454 always seems to run well, it just chokes badly in the upper rpm range.