Re: Edelbrock AFB blow thru modifications- pics - vid

No track times, just a street cruiser, for something easily tuned stick with a holley
way more support and tricks to get them perfect

 

Re: Edelbrock AFB blow thru modifications- pics - vid

Thanks, great information guys.

 

Re: Edelbrock AFB blow thru modifications- pics - vid

Did the fuel bowl vent mod...went sooo damn retarded rich almost did not make it around the block

Removed my air bleed restrictions, jetted down my secondaries from .116 to .098, changed my step down springs from 7" to 4" and it was slightly better but still loaded up bad.

LOL this mod definitely works. Just got to dial it down. Going back out in a couple minutes

 

Re: Edelbrock AFB blow thru modifications- pics - vid

HA sweet! I figured that would fix it for you, I found almost stock jetting worked good. What kind of hat are you running? I found the EV hats block the stock vents with the air divider that's in the hat

 

Re: Edelbrock AFB blow thru modifications- pics - vid

ok...so my main concern/issue was Id go dead lean towards the top of 3rd like clock work, everytime. Basically preventing me to attempt even a 1/8th mile pass, let alone 1/4 mile.

converted to dual feed...actually made it worse. Ended up playing with air bleeds with with .030 mig wire in front and back it helped restore it to previous ways but with slightly better midrange. however still like a damn switch, dead lean in top of 3rd.

So I did the fuel vents. Of course SUPER RICH. rolling coal status to the point where it was everything to clear it up and get it home.

jetted it down. was .086/.116, went to .074/.098s & removed the bleed restrictions. stupid lean, barely ran, did not make it out of the garage. went to .077s & still was not enough. went to .083/.086 & was a little lean on light cruise but WOT was low 10s (before all this I was mid upper 11s). Flipped them around, .086/.083 & its pretty good & I can finally part throttle boost now! But anytime with any turbine speed its dead rich. WOT was upper 12s until lean switch.

Went and talked to a buddy of mine & he suggested removing the gas cap, thinking I was well beyond its venting capabilities. Did not seem to make a difference.

I'm going nuts here. I really do not want to go EFI

 

Re: Edelbrock AFB blow thru modifications- pics - vid

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Heres my set up. The vent lines go into the transition cone with an approximately 20* angle towards each other and trimmed like a merge Ypipe into a common port just about after the BOV port.

Also I forgot to mention the last round I also went to 600cfm primary boosters in attempt to numb the signal to lean out the rich part throttle.

Sometime this weekend I am going to try to rig up a fuel pressure gauge too see if that's an indicator of WTF is going on in top of 3rd.

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Re: Edelbrock AFB blow thru modifications- pics - vid

It might be necessary to play around with the angle of the tubes. What they do is using dynamic pressure as speed and density of air increase in order to increase pressure in the float chambers.

If they face the inlet of the hat directly too much pressure might build up and the mixture will be overly rich. If they are at an angle to the incoming air the speed of air inside the tubes will decrease, and so will the pressure that they build inside the float chambers.

A design where the angle can be adjusted might work best...

Simon

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Re: Edelbrock AFB blow thru modifications- pics - vid

Let it sit for a week to ease my frustration

Changed the wastegate spring was running 11-12psi which felt friggin awesome

Along with some smaller restrictions in the fuel vents and lower boost I can make a clean pull all the way thru 3rd now.

7psi...is dog slow compared to 11-12. Must be out of the compressors happy range.

Im thinking of shortening my fuel vent lines to just inside the plenum and trying again with higher boost

 

Re: Edelbrock AFB blow thru modifications- pics - vid

I Just recently went from 7psi to 12psi and its a crazy difference, glad she is starting to work better for ya

 

Re: Edelbrock AFB blow thru modifications- pics - vid

I shortened the vent lines about 3.5" to reduce their sensitivity. With no other changes it definitely leaned out a bit...light throttle was lean surging, get up on the converter it was fine and WOT was clean all the way thru at low boost with 11~ AFRs. So i removed my restrictors in the lines and it helped the lean surge but I didnt get a chance to try out the rest in town.

 

Re: Edelbrock AFB blow thru modifications- pics - vid

My wastegate and fuel pump reference line was Tees off one source nipple on the hat.

So in the midst of all of this I separated them and moved them to back of the hat.

I have a feeling the wastegate bleed might of been an influence on the lean out condition at top of 3rd at WOT

 

Re: Edelbrock AFB blow thru modifications- pics - vid

yup that makes sense, keep at it

 

Re: Edelbrock AFB blow thru modifications- pics - vid

Well ..continued effing around, ordered some more different metering rods and I think I have it about as good as it gets.

Still running 7psi. Every time i go north of that it goes lean top of third. Actually starting to think its ignition. Im going to regap the plugs smaller (right now I think i have em at .035) tomorrow and have a go.

Also going to put restrictions back into the vent lines. Now with the onset of boost...dont matter what rpm after WOT it goes full rich hard for a moment and bogs/loads up the car so it stumbles bad. Hoping the restrictions numb that. If no difference Ill put the 2ndary weight valve back in and see if that smooths it out.

Im going FiTech even if this gets all sorted. Its still a learning experience and I will apply it to my carb tuning regimen for other builds and vehicles

 

Re: Edelbrock AFB blow thru modifications- pics - vid

Your fuel system cant keep up. If it was the carb it would do this in every gear.

Normally if its a plug gap issue it will happen at the heaviest load point which isnt the top of high gear.

 

Re: Edelbrock AFB blow thru modifications- pics - vid

Agreed, probably needle and seat. I've drilled and tapped edelbrock a for .145 n/a for a quadrajet I ordered from Edelbrock. Ran 10.90's on a 600 Edelbrock.

 

Re: Edelbrock AFB blow thru modifications- pics - vid

Ive changed everything i could around. Bigger fuel pump, HF needle and seats, converted to dual feed.

No matter what like a damn switch at 4700rpm at the top of third dead lean.

In previous builds when the fuel was not keeping up I would get a surging and only in third gear when the load is highest. Put a bigger pump in and it always fixed it.

The way its like a switch, and not surging it really seems its an ignition issue.

 

Re: Edelbrock AFB blow thru modifications- pics - vid

So with the timing bumped back up a smidge and the restrictors in the vent lines she is running pretty good at low boost.

Didnt get to mess with the plugs today

 

Re: Edelbrock AFB blow thru modifications- pics - vid

Here is something for you guys to discuss.

I have always struggled with light accel and tip in boost fueling. I swore it was in the needle and messed with that for some time. I went as far as grinding the tips back so they were just inside the jet far enough to pilot them back down correctly and I still dealt with that lean spot.

So, I just stood there staring at the carb and trying to think through it as to why it would go lean. Then, it hit me (I think). What if the light accel/tip in was actually holding the needles down?

I have a small turbo compared to most of you and that could easily amplify my issue. I see my fuel pressure start ticking upward when I still have 5ish in/mg. If there is a vacuum signal under the needle drum thing and 1-2 psi above it, it would hold the needles down and cause a restricted jet. As soon as positive pressure hits my boost gauge, it richens up and drives great.

I am fairly certain this is my cause but cannot come up with a method to prevent it. At one point, I was going to vent the top side of the drum to atmosphere with a short piece of 1/8" copper tube. It seems like that is whats needed but, I am afraid fuel will push up past the needle under boost and blow out the little vent tube.
Thoughts?

 

Re: Edelbrock AFB blow thru modifications- pics - vid

^sounds like you need to do the vent mod. That made such a difference in part throttle availible fuel for me.

I had to jet the carb way back and also trim my vents to reduce their authority somewhat on the fuel curve

 

Re: Edelbrock AFB blow thru modifications- pics - vid

Also play around with different step up springs. That help tunes the primaries fueling. Stiffer spring brings the rods up in power mode sooner meaning more fuel