710 L20B With A Holley 4Barrel and Chevy HEI Ignition

[jozefaz]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[jozefaz]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Any questions?

 

[datzenmike]

The secondaries are supposed to dump into the far driver's side of the plenum and the primaries to the pass side closest to the valve cover. This is why it's called a Dual Port. The primary and secondaries are supposed to be separate in action and the intake is divided this way.

 

You can see the shape is different with the primaries to the top and the secondaries to the bottom.

 

I never understood if this style of intake really makes a difference but it sure works for mounting a 4bbl. Does it bog with that much carb?

[banzai510(hainz)]

Dude Im digging this wagon.

some Rota RB and lowered would look good.

just buff out the paint

white is a great color

 

Might need to cam it to get that carb to work better

 

i think i would junk that smog pump(weight)

[hobbes_the_cat]

Yeah I'm very curious if it has decent street manners. Is your motor stock otherwise? I have heard a lot of guys bash the idea of a 4bbl on an l20b. If yours runs good maybe I should be lookin for a 4bbl mani!

[datzenmike]

You can run dual side drafts which is a sort of horizontal 4bbl. An L20B only needs just over 200 cfm. I think the Hitachi is 240cfm (or so) the 32/36 is 270 and they will bog a bit. Didn't Holly make a 300cfm 4bbl?

[Eagle_Adam]

what radiator is that? 

[banzai510(hainz)]

holly 390 was the common carb for the Carpi V6s back in the day

I asusme this is 2barrel and other 2 are vaccume 2ndaries So kinda like a 38/38 till the vaccume 2ndary kicks in.

 

Kinda hard to get air to make a 90deg bend thru that manifold after a certain point

 

but get us know.

[toyota1515]

Am i missing something here? 4 barrel carb is a cool setup no doubt about it, But where is the HEI system? i only see a ignition module from a GM HEI Dizzy, but the ignition still a OEM style Electronic pick up coil system :/ anyway awesome wagon here a good set of wheels and tires and a little lowered and you got the perfect cruiser!

[DanielC]

But where is the HEI system? i only see a ignition module from a GM HEI Dizzy, but the ignition still a OEM style Electronic pick up coil system

That is the GM HEI system.  The only thing, GM mounts the  module under the distributor cap.

[ProjectFeint]

Looks like a blast to drive!

[Brad's 510]

I put on of those 4 bbl manifolds on a L20B with a Holley 390 carb. The owner didn't want to deal with the side-drafts any more. It was very drivable, had good top-end. The motor was 11:1 compression, a lot of head work, nice cam profile. The motor had more power with the side-drafts but its' drivability was nice.

[Z-train]

Yeah I'm very curious if it has decent street manners. Is your motor stock otherwise? I have heard a lot of guys bash the idea of a 4bbl on an l20b. If yours runs good maybe I should be lookin for a 4bbl mani!

I'm one of them. ANd it's not a good idea. A good set of SU's are superior in every measurable way.

 

To the OP,when that pretty yellow Accel HEI module dies on you, go to the boneyard and find a GM with a HEI in it. THe factory module beats all aftermarket ones hands down.

[hobbes_the_cat]

I was just stirring the pot a little when I said I should look for a 4bbl for my car. I'm also pretty confident that a honkin double pumper is not the optimal choice for an L20b, BUT if this guy made his run decent, I say good for him. I'd like to see if it can be done with minimal side effects. 

[datzenmike]

The problem with any carb is that you need air flow through them from a large enough motor or a small motor revved extremely high. The carb is 'sized' to give good response at all RPMs. When you go to a larger capacity carb from a larger motor, your smaller motor has to rev higher to draw the same amount of air to make it work. The secondaries are usually vacuum operated. You need enough air flow to pull them open. If the 4 bbl is too big, they never will. If mechanical secondaries, it still won't have enough air flow past the venturies to suck the gas in and it will bog or have a very bad stutter getting revved until it can.

 

Most stock carbs are a compromise and can benefit from a slightly 'larger' carb to feed it at very high RPMs, usualy at the expense of some poorer low speed drive ability. If larger carbs made more and more power we would all be rumnning 1180 Hollys. 

[toyota1515]

That is the GM HEI system.  The only thing, GM mounts the  module under the distributor cap.

Lol, NO IS NOT, but whatever you want to call it,

A GM HEI system is a self contained ignition/distributor/coil system that do all the work of the separate components in a normal setup, one part out of the system is not to be called a HEI is just a component of it,

 

Just to educate a little and my 2 cents,

Keepthe good work it is an awesome wagon!

[DaveZilla]

Looking closer at the pics installed on the car I see that the secondary fuel inlet on the carb is capped off and the secondary throttle linkage is disconnected as well as the secondary throttle shaft wired shut so he's only running the primary side of the carb, most likely because the carb is way too big for the engine. Being that we can't tell what size this carb is without being able to read the numbers on the choke horn or seeing straight down the venturis, I'm guessing the carb is a 450 or 600 cfm doble pumper, even a 390 double pumper is too much carb for this engine. A 390 vacuum secondary would work once properly jetted and with the right spring in the secondary diaphram so the secondaries don't open up too fast.

To really take advantage of this manifold and carb you'd need a hotter cam that would let the engine rev much higher, a header, and higher compression with some head work, even with that, a 390 vacuum secondary would be all you'd need for the street. Running lower gearing in the rear end also helps a lot with this since you need to let the engine rev to take advantage of the added horsepower on top but at the cost of a lot less low end torque on the bottom end.

Running this manifold with this carb on just the primaries is pretty much just a bandaid fix for over carburating the engine... The rest of the car looks great but that manifold/carb setup is a mis match for the rest of that engine unless it has the internals that can take advantage of this.

[jozefaz]

The following are new within the last 5-15k miles/5 years ( car is a backup and hardly driven):

Engine misc:
Alternator
Voltage regulator
Starter
Belts
Fuel pump

Brakes:
Drums
Shoes
Wheel cylinders
Calipers
Rotors
Pads
Master cylinder
Booster

Cooling system:
Radiator(heavy duty oversized aluminum)
Electric fan conversion
Water pump
Radiator And heater hoses
Thermostat and thermostatic switches

Transmission:
Output shaft seal
Synthetic fluid
Clutch kit
Shifter bushing
Shifter boot and T-handle
Master and slave cylinder

Ignition:
Cap
Rotors
Heavy duty wireset
NGK plugs
HEI electronic ignition module conversion
Electronic distributor conversion (no points)

Exhaust:
Crankcase evacuation system installed(remove PCV)
SSS Tri-y american cast iron header with air injection ports sealed
Flowtech Raptor 2" muffler
Tapped for oxygen sensor in header

Intake:
Headlight 4" funnel intake conversion
Inline high flow air filter
Specter 4" carb hat
Holley 0-4776 carburetor 600cfm DP (currently secondary's are disabled and wired shut for an effective CFM of 300)
Offenhauser 4barrel aluminum intake manifold

[H5WAGON]

holly 390 was the common carb for the Carpi V6s back in the day

I asusme this is 2barrel and other 2 are vaccume 2ndaries So kinda like a 38/38 till the vaccume 2ndary kicks in.

 

Kinda hard to get air to make a 90deg bend thru that manifold after a certain point

 

but get us know.

Had one of these on my white wagon with Ford V6 Capri motor...Before the KA swap.

[jozefaz]

I have work in 10 minutes but ill reply to a few points made off the top of my head.

 

I am ASE certified in :

Parts (P2)

Engine repair

Engine performance

Electrical

Brakes

 

Yes the dual port design works, proven in the modern varitable runner designs of today such as the toyota 4age and the honda Bseries Type-R engines.

Unfortunatly , even with the manifold spacers i had to make to get the intake to clear the exhaust, the secondary fuel bowl would not clear the valve cover.

I had to design a new top plate for the intake to rotate the carb 90 degrees.

The upshot being i now had a direct rod throttle linkage instead the the bell and crank system that always seemed sloppy.

 

Ill address the rest when i have more time...

[datzenmike]

Well this defeats the dual plane manifold running the carb as a 2 bbl sideways. The right side of the carb runs in the small side of the runner and the left in the larger.

[jozefaz]

Yes it does defeat the design being rotated this way. For the CFM needed i only had 3 real choices, a vac sec 390, a NASCAR mech sec 390 ($$$$) and the 600 mech sec.

 

I have done the 390 vac sec on a Toyota 2tc 1600 before and while it had acceptable low rpm characteristics, overall tuning they(tried multiple) seemed to be filled with "gremlins" for lack of a better word. Everything else was all over the board and even with weeks of tuning the carb and checking over the rest of the engine mechanically, never ended up satisfied with the end result. they really are suited for a 4.3 V6 more than a sub 2500-CC engine, and i think thats due to whats actually cast into the internal passageways of the carb body and metering block themselves.

 

NASCAR 390 are in the 600-900$ range and for that cash i would be 3/4 way to Megasquirt fuel injection.

 

i already had the 600DP from clearance at my work so that's what went on.

 

If i converted to side hung bowls instead of center hung, i might be able to put the original top plate back on and utilize the dual port design of the manifold, but to get the usage at higher rpm id have to run the secondaries and then im back to weeks of tuning, and dicking with throttle linkage.

 

and right now the car runs way beter than everyone thinks its should.

 

Idle has a very slight lope at very low rpm's.14:1 +/-0.5 AFR on my wideband (yes i use a wideband for tuning)

Roll on throttle, even from a stop is slightly aggressive but smooth, no lurching  or surging or excessive clutch slipping.12-13:1

Cruise is smooth and shows about 15:1

Romping the throttle to the floor from idle and staying in it she just screams.12:1 AFR

 

Regular shifts no bog , and especially no lift shift WOT feels awesome, but i try to keep that to a minimum, the trans is cherry.

 

If i had to pick a problem with the car and carb combo, it would be simply the fact it cant respond to lugging the motor in the wrong gear like a normal or undersized(stock) carb can.

IF your in 3rd gear at 20 MPH and roll more than halfway into the throttle, it simply just doesn't have the airflow to keep the venturie's going at such a low RPM and the engine goes dead.(50:1 AFR on the wideband) it seriously feels like somebody reached up and flipped the key off. HOWEVER if you just take your foot back out of it, the engine instantly returns to life as if nothing happened.

 

Moral of the story? Don't lug the engine in the wrong gear!!!

 

Ill try to take a video the next day i get a chance when i can recruit a cameraman 

[jozefaz]

Oh and for the 2 other points brought up

 

1. the radiator was a eBay special. the dimensions and spout locations and sizes were correct but the mount was complexly wrong so we had to desolder the stock radiator brackets and use piece of angle iron to adapt them. Not pretty but once its installed you cant tell.

 

2. the Accell Chevy HEI module was a 1$ buy due to the package was damaged in the parts store due to a leaky roof. (Not that i had put a pile of performance parts in a certain spot in the store when i saw the clouds coming or anything... :angel: )

IF/when it ever dies ill be putting in a Delco. The stock modules are always better with borg warner being a close second. i chose the HEI because every single parts store int he world should have one on the shelf so i should never be stranded. i doubt it will ever burn out though because the box IS the heat-sink. we machined the inside pad smooth and used heat-sink compound in between the module and box. barely gets warm to the touch in our 130F summers.

[datzenmike]

Good description.

[jozefaz]

 

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