Loving the 390 HOLLEY!

[Doc Bob]

Finally cracked the shits with the 350 HOLLEY yesterday.
A simple combination with good fuel economy and reasonable power......but could not overcome the flat spot off idle
Put up with it for a while, but not good when you have the old vintage caravan on the back and you try and pull onto the highway
at 2000 rpm slipping the clutch to try and overcome the bog.
Got to the point where the Missus was a bit hesitant to drive it in case it stalled pulling out at an intersection.......especially with the kids in the car

So grabbed an old THOMAS CAIN 4 BBL intake and stole one of the 390 HOLLEY'S off the Gemini"s 4x2 Tunnel Ram.
Manifold was not 100% so I to Helicoiled the carb stud threads, drilled and tapped a point for the brake vacuum line and gave the whole shebang a good acid dip & robowash.

I fitted the 390 out with 585 metric jets and a 7.5 power valve.........though may change that once I do a vacuum test.
Set the mixture screws, throttle stops, float heights and cleaned out the emulsion tube ports. (390's only run single tubes in the front barrels Never knew that!)
Fabricated an alloy accelerator cable bracket and all went in quite straight forward.

OMG WOW
Turned it over and once the fuel hit the bowls she fired straight into life, and even though dead cold, idled like a dream.
Gave it a few stabs on the pedal while cold to see what would happen.........NO FLAT SPOT!

Took it for a quick blatt down the highway and was amazed by the throttle response, smoothness and power compared to the 350.
I keep hearing stories of blokes going to 4 Barrel's on their 6's and either having an absolute epiphany, or lots of trouble!
The trick is to picking the right carb and getting it tuned to your engine, I'm real happy this combination seems to suit the current engine/driveline.
Anyrate............I'm a happy little camper and would recommend that anyone toying with the idea of running the same set-up to give it a go.
Really makes a big difference, will just wait and see how the fuel economy side of things work out.

All the best.........Bob.

[basic.green]

good to here was thinking the same i have 450 on now but i think i will go to the 390

[Doc Bob]

Yeah, the whole idea of the 390 was that it's primary butterflies and venturie's are a lot smaller than the 350's
which gives much stronger vacuum and throttle response down low, but still has a good set of Vac Secondaries
for when the going gets tough!

The 450/465's have the basic same primaries as the 350's, so would not really make any difference for what I was trying to achieve.

Have a play around......got nothing to lose!

All the best......Bob.

[Harv]

Cool.

You're right Bob - the 350 Holleys have got 1 3/16" venturis, which reduce down to 1 2/16" with venturi resrictors fitted (assuming you use the off-the-shelf restrictors). The 390 has 1 1/16" primaries... should act like it had a double set of restrictors in it (good bottom end response), but still have the top end once the secondaries open up.

Cheers,
Harv.

[Doc Bob]

Cool.

You're right Bob - the 350 Holleys have got 1 3/16" venturis, which reduce down to 1 2/16" with venturi resrictors fitted (assuming you use the off-the-shelf restrictors). The 390 has 1 1/16" primaries... should act like it had a double set of restrictors in it (good bottom end response), but still have the top end once the secondaries open up.

Cheers,
Harv.

Spot on there Harv, that's why I fully researched the 390 specs before spending all that time getting it all to fit
Looks like you've done a fair bit of research there yourself

[Mick]

that's why i like 4 barrels on a holden 6, years ago i had an EH wagon it had twin SUs could get it to go good down low and shit up top or the other way around couldn't get a midle ground, a mate said stick this on 465 on a 4 barrel manifold if i didn't know better i'de swear the engine had been changed good allround and better down low and up top than the SUs

[Harv]

The 4-barrel carb on a red motor is a neat trick.

At low throttle with the secondaries shut you are only running on the primaries. As Doc points out above, the primaries are smaller than the corresponding 2-barrel, so you get nice crisp throttle response (better than say a 350 cfm 2-barrel). Running vac secondaries is the key here - they stay shut until the engine needs the fuel. Mech secondaries will open up too early if you have a heavy right foot, giving too much venturi area and boggy response (i.e. a mech secondary 4-barrel would behave like a 2-barrel if the driver mooshed the go pedal).

Once those vac secondaries are open, you have a bloody big carb. The 4-barrel is measured at a different pressure (1.5"Hg) than the 2-barrel (3"Hg). If you convert the measurements, a 390 4-barrel will flow 550cfm (compared to a 350 CFM 2-barrel).

So all up the 390 gives you a smaller carb than the 350 2-barrel for quick takeoff, then slowly opens up to give bigger capacity than a 500 2-barrel once you are flying. Neat trick.

Cheers,
Harv

[mudgroup]

hey harv...
sorry to hijack.. but have been meaning to ask you... your opinion on the 'best' set up for a grey motor.... with a wade 240 (34/74)
currently running twin strommies... and have been putting up with that flat stop on take off...
stu

[Devilrod]

I did the same with my old EK Ute, swapped from a 350 to a straight out of the box Edelbrock 500 4 barrel on a two inch spacer. Great down low and awesome top end and if you could keep your foot out of it great economy too.

[Harv]

Thats a pretty large sized carb DR - double the size of the 350 2-barrel (about 710cfm on the two barrel scale). The primaries are no bigger than the 350 2-barrel (1 3/16"), but the secondaries are big enough to suck a pigeon through (1 9/16" compared to the 390's 1 /16").... no wonder she had plenty of top end What motor was in the ute?

Stu,
Best carb setup is a bit of a trial an error, as each motor responds differently depending on how it has been worked over and the parts used. Would suggest venturi restrictors and 47 main metering jets as a good place to start with the twins.

Cheers,
Harv

[mudgroup]

thanks harv !!

[Devilrod]

Thats a pretty large sized carb DR - double the size of the 350 2-barrel (about 710cfm on the two barrel scale). The primaries are no bigger than the 350 2-barrel (1 3/16"), but the secondaries are big enough to suck a pigeon through (1 9/16" compared to the 390's 1 /16").... no wonder she had plenty of top end What motor was in the ute?

Cheers,
Harv

It had a 202 with a yella terra 149 head, stock bottom end, rods and pistons pacemaker extractors, recurved dizzy to match the small crow cam and 10.7 to 1 compression. It would pull like crazy to 6500 and then I'd grab another gear. It had no trouble redlining it top gear... Gave most v 8's a run for their money till I'd run out of legs. And it ran an EH crash box. Not so good...

The carb was recommended by the guys who built the motor and boy was it fun!

[Doc Bob]

I only done this as a trial and error exercise as I had all the bits laying around the shed and could not tune out that flat spot with the 350.
It did not have restrictors fitted Harv, but I thought why stuff around with the 350 when all the other bits for the 390 were already there!
Engine is 20 thou over 186, stock bottom end/rods/pistons, compression around 9.5 : 1, STD cam, STG. 3 Yella Terra Head and a good set of GENIE extractors.
Though the rest of the exhaust is pretty stock 1.5 inch pipe.
4 speed box and 3.08 diff to finish it all off.

As I said earlier, this 390 gear just seems to suit the combo down too a tee.
Have another brand new 40 thou over 186 engine with modified cam, X oil pump etc. sitting in the shed.
Next step will be to swap all the good gear off the old worn out jigger in the Wagon and fit it up to this engine to drop in it's place.
Will get better exhaust etc. all done at the same time to really take advantage of the modifications.

Will let you know how it all goes

[Doc Bob]

Oh yeah Harv.....a little detail I missed out that just came to me........
That 350 was off a burnout car engine and is fitted with Annular Discharge boosters.
Probably does not help with the whole vacuum signal off idle / part throttle etc.

[Harv]

Interesting... I havn't seen annular boosters on a 350CFM 2-barrel before. Must have been fun to fit. Assume the engine was another red 6? Strange idea for a burnout car as I understood that annulars were for bottom end, and reduced the top end if anything. Must have been a low rpm torque monster rather than a top-end scrreamer.

From what I've heard from 4-barrel's retrofitted with annulars, one of two things happens:
a) better throttle response from the increased vapourisation but slightly lower top end due to the CFM reduction (they be chunky buggers!), or
b) they run like crap because they are oversized/don't work with the manifold etc. Not suprised they were touchy on an inline 6-cylinder manifold... the inlet pulses are relatively erratic compared to an open V8 manifold, so potential for upsetting a touchy booster I guess.

Cheers,
Harv