Calling 340 with Holley 650 dp

[PRH]

Wrt lumpy low vacuum cams and the typical Holley 4777 type carb(std 650DP), I’ve found the idle manners are much better after you convert them to 4 corner idle.

-I just had a little flash back…..
I bought my first Holley carb from Super Shops on Watt Ave in Sacramento Ca in like 1980.
It was a 650DP, #4777 for $115.

 

[340inabbody]

Wrt lumpy low vacuum cams and the typical Holley 4777 type carb(std 650DP), I’ve found the idle manners are much better after you convert them to 4 corner idle.

Convert to 4 corner? Are you referring to changing out the rear metering block? Detail's?.

 

[PRH]

I modified the metering block and base plate.

There’s drilling and tapping involved, but the only parts you’ll need are some mixture screws and gaskets.

I just followed some instructions in a book, but I’d be pretty surprised if there isn’t a YT video on doing it now.

Thru the years I’ve probably converted 20-30 2-corner idle carbs to 4-corner.

My current 4777 dyno mule was built from a leftover main body and metering blocks from carbs that had been retrofitted with aftermarket HP style main bodies.
I modified the stock 4777 main body/metering block for 4-corner idle, but since I didn’t have a decent baseplate, I just got one of the Proform units, which are set up to accommodate 4-corner idle, so I didn’t have to mod a stock one.

 

[mopowers]

Not sure if it'll show up or if it'll be readable, but here's and article about 4-corner idle conversions.

The 4777 I had on my 340 was an older version that already had 4-corner idle. I'm pretty sure the older ones came like that. Pretty straight forward to convert though.

 

[PRH]

AFAIK 4777’s, at least the zinc ones, never had 4 corner idle…….and probably still don’t.
In that series of carbs, none had it early on, and at some point in the 90’s the 750’s(4779) and 850’s(4781) got it.

 

[mopowers]

Hmm... The old on I've got must've been converted. Hell, I may have even done it.

 

[Mtrhead]

I have a practically brand new Holly Ultra double pumper $900 carburetor that has four corner idle it is badass but I really don't need it if you want it you can get it for $500 ..also have first edition single plane M1

 

[PRH]

Fresh off the Holley site:

 

[Mtrhead]

Intake is $385

 

[Mattax]

4 corner idle essentially doubles the flow of the idle ports.
That's why I wrote that was a route that may be useful if the vacuum at idle in gear can't be improved.

 

[340inabbody]

4 corner idle essentially doubles the flow of the idle ports.
That's why I wrote that was a route that may be useful if the vacuum at idle in gear can't be improved.

Thanks Mattax I am going to try the modification. I just need to find some clear instructions/information on how to do it. Sounds like a good learning experience to me.

I think I found it…. This guy has taught me a bunch of stuff . He’s good.

 

[340inabbody]

Quick question while I have you guys here. I have a brand new pro-form 750 sitting in a box. It’s a really nice carb. Questions is it too much carb for my 340? Would I be wasting my time trying it?

 

[crackedback]

If the 340 is warmed up a 750 is usually fine on them.

Something I have on the 4 corner subject

 

[340six]

What primary and secondary jet sizes are you guys running assuming non stroked 340 motors with a Holley 650dp.

I am starting my tuning in earnest and I am currently running the stock 67 primaries and 73 secondaries. I believe I need to move up and am curious as to what you guys are running.

I know I know all our engines are different and that matters I know. BUT I am alone tuning without much history, friends etc to bounce questions or ideas off of. I want to gather jets that I can play with so just looking to see what you guys are using to look at the range of jets being used.

Thanks for taking the time to read and help out!

View attachment 1716462382

My 4777 had 67 and 73 ran fine on my 340 little rich but ran fine. Still have it. Pulled it for 3310. Fir better street. Pulled that and put 750 AFB added electric choke and hooked up A/'C never went back to holley 4bbl again. Did go with a sizpack

 

[340six]

Wrt lumpy low vacuum cams and the typical Holley 4777 type carb(std 650DP), I’ve found the idle manners are much better after you convert them to 4 corner idle.

-I just had a little flash back…..
I bought my first Holley carb from Super Shops on Watt Ave in Sacramento Ca in like 1980.
It was a 650DP, #4777 for $115.

Got mine From Jake's Speed Shop in New Orleans that Holley #4777 650 DP was on my 340 with a street dominated. Ran welll real well. The TQ plastic started to leak so did Holley Street Dom and #4777 was a great combo. But 3310 gave better fuel milage and worked well with A/C and even put electric choke

 

[Mattax]

Thanks Mattax I am going to try the modification. I just need to find some clear instructions/information on how to do it. Sounds like a good learning experience to me.

I think I found it…. This guy has taught me a bunch of stuff . He’s good.

I'm saying don't do it unless you need to.
If we knew more about the engine it would be an easier call.
Do at least one iteration of the basics first. Timing, air bypass, more fuel via IFR/IAB (wires down the IAB).
Depending on the improvements, then "poor mans 4 corner" may be the route.
There's lots of tempting rabit holes and this one is promising but do the homework first.

This gets in to productivity. If you're going to spend time and money on a 4 corner, it may be best doing a carb that will do the top end good. IF this engine has good wide open throttle fuel distribution, headers, and can produce peak power at 6000 rpm or above, then a less restrictive carb wll take advantage of this. Find a used 4778 or 4779 or something similar. Doesn't need to be a whole one if you want to put something together. Nothing wrong with learning to drill and tap.

 

[Mattax]

Its funny how certain things become popular.
Right now its 4 corner idles and 3,4,5 emulsion holes.
At one time it was drilling priming throttle plates to let more air in at idle.
Then for a short while that got beat on after Bill Jone's "idle-ease" idea caught on.
They're all useful techniques. The tricky part is figuring out when they best apply.

Funny not so many videos and web articles on how to let more air in at idle. Yet this method was even used on some production carbs.

As far as articles on how to 4 corner. There as at least on thread on Racing Fuel Systems forum - not sure if its photos survived the tapatalk take over. Got to look to be sure there is enough meat in the walls of some of the higher - throttle bodies. -3 and up 3310s for sure are in this catagory.
To do the "poor mans four corner" which is a sharing for the primary idle fuel to the secondary side, need a base with the 'snake channel' in it.

Four corner is also shown in Vizards How to build HP vol 2. That's how I went down that rabbit hole, along with anular boosters. Short version is those rabbit holes where $400 fail but I learned a lot (and spent more money) digging my way out.

 

[Mattax]

Just saw you posted that you have a "750" Pro-form. That is not too big if this is good flowing, high revving set up.
The 650 Holley may be slightly easier to get good idle and off idle.
Map out the Proform and then make its initial calibration more like an old school Holley 4779. Low idle jet, 2 open e-holes, etc.

 

[PRH]

I also have a 4779 dyno mule, that was built from a left over main body that came from another carb that got the Proform main body conversion.

This carb actually got built mostly from new parts(back before all this stuff was crazy $$$).
New stock Holley baseplate and metering blocks, etc.

I had originally intended to do a main body swap on the dyno with it, using the Holley HP main body kit, but in the end I just ended up buying a bunch of QF parts and building another carb out of the Holley HP body.
Of course, about when I did that the Brawler carbs came out and you could buy one of those for about what I had in parts to put mine together.
Carbs have gone up enough in price now to where I’m not “upside down” with mine anymore.

But, back to the 4777 4 corner mod………
With a low vacuum cam, no real downside imo.
If it’s more idle capacity than truly “needed”, there’s no law saying you must have all 4 mixture screws adjusted the same.
When using 4 corner idle carbs on engines that don’t really need it, sometimes I’ll get good results with adjusting the rear screws to something like 1/4-1/2 turn out, and then do the major idle tuning with the front screws.

 

[340inabbody]

Just saw you posted that you have a "750" Pro-form. That is not too big if this is good flowing, high revving set up.
The 650 Holley may be slightly easier to get good idle and off idle.
Map out the Proform and then make its initial calibration more like an old school Holley 4779. Low idle jet, 2 open e-holes, etc.

“2 open e-holes”? What does this mean?

 

[TT5.9mag]

“2 open e-holes”? What does this mean?

Look up “Holley emulsion circuit”

 

[340inabbody]

Look up “Holley emulsion circuit”

OK, I didn’t realize e was short for emulsion. Now, are you talking about adding more emulsion holes or opening them up? This is for mid-high-speed tuning right?
Essentially messing with the whole fuel curve?

 

[crackedback]

4 & 5 emulsions are essentially worthless for most stuff. A good 2 emulsion stack will give a good slope. The old 750-780 vac carbs back in the 60-70's had a two emulsion stack and were VERY good carbs. Go figure. Don't try to fix something that isn't broken. This 4-5 emulsions is a monkey see, monkey do nonsense from manufacturers. If two are good 4 then 5 must be better. IMO, it's a rabbit hole that leads to a tougher to tune carb, now you have 5 holes to F up, LOL.

 

[TT5.9mag]

OK, I didn’t realize e was short for emulsion. Now, are you talking about adding more emulsion holes or opening them up? This is for mid-high-speed tuning right?
Essentially messing with the whole fuel curve?

@Mattax was saying something similar to what @crackedback said above. Most new billet blocks come with a 4-5 hole replaceable emulsion stack. It’s very tunable and you can quickly get carried away chasing a tune up. For almost everything we (300-600hp basic street strip stuff) do a simple 2 hole stack like the original Holley blocks have generates a fairly consistent fuel curve if the MAB and IAB are in range.