Along with 4-5-6 emulsions...
750 vs 850 vs 950 Holley
- Thread starter skrews
- Start date
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Along with 4-5-6 emulsions...
yellow rose
Overnight Sensation
I'm using just two emulsion holes right now, but I may need to add a small hole to clean up the top end just a bit.
nm9stheham
Well-Known Member
FWIW.... That is 'for real' useful engineering, that has been going on for over 60 years, at least. Weber had a lot of different emulsion tube patterns for their performance carbs by the 60's... the DCOE sidedrafts that I messed with in the early 80's had at least 10 different emulsion tube patterns to choose from. Changing them makes a big difference in how the carb mixes the mains AFR up through the RPM range. See here and the old emulsion tube page that shows 14 different ones:
TheSamba.com :: Performance/Engines/Transmissions - View topic - Emulsion Tube Break Down.. F-7's/F-11's
I find it encouraging that the American hot rod market carbs finally caught up to this idea.
yellow rose
Overnight Sensation
I have dicked with emulsion more that I care to admit and I can say I've never seen more that 2 emulsion holes have a benefit, unless you need to trim the fuel curve in a specific area. I may add a .022 hole in the bottom to clean up a rich spot at WOT.
nm9stheham
Well-Known Member
I would expect that if anyone worked with some Webers, and started changing choke sizes (yes, the main venturi's are changeable) and such, and put them on 10-20 competely different engines types, then the different emulsion tube designs get really necessary. And the one-carb-throat-per-cylinder setups, with no common plenum, may make them even more necessary. I can remember changing between 2 quite different tubes, and the fuel curve, as judged from driving, ear, and plugs, was also quite different; it sure cleaned up a dead mid-range bog.
Krooser
Building Chinese Free Engines since 1959...
I know the feeling.... My advice to the younguns is get your stuff done by age 55...
LAMO! Danm true!
I myself feel like I got about to the half way mark on that. I’m not yet 55, but, I’m not getting anymore experimental play time in. I have the parts but not the cash to throw away on the toys. I’ll save that for later.
I can retire in 3 years. Everything will be good. Not great, but good enough to continue playing around.
Luck wasn’t exactly in my side. Just danm glad bad luck wasn’t pestering me to much.
The higher locations allows air to get on the other side of the IFR when manifold vac is low enough.
Does seem that way. I've seen a few of these builders occassionaly post explanations. Maybe I'll find them and start a thread just on that.
One use of a high idle position is providing a shot of extra fuel from the idle up-well. When the throttle is opened wide flow changes direction and goes from the idle upwell into the mainwell. This seems to be the reason secondary metering plates have the restriction up high. Maybe you have a situation where that extra shot is just what is needed. Mark Whitner's mentioned this, and Tuner explains it in post #23 here: Secondary metering plate vs Secondary Metering Block?
edit: Mark mentions it here, but in reference to the emulsion well.
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I like pictures.
Possible idle feed restriction locations are marked as follows:
H High position (at the junction with the air bleed passage)
P Below the plug in the metering block.
L Low position.
Fuel is shown at bowl level. That is, engine not running.
When the manifold vacuum is pulling pretty steady, even with the High position, the fuel will move up the well and through the restriction.
But when the pressure difference is strongly pulsing, the fuel in the well may easily drop back to the bowl level.
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Whooah buddy....you can't just throw out cold hard facts that disrupt the "bigger is always better" crowd, LOL!
For some reason whenever I tell folks that I run a home built "750" Holley I get SOOOO much crap from the bigger is better folks (sure I would love a bigger carb, but I don't want to drop $1000 for a few hundredths of a second)....Kudos to you sir.
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I hear ya. Always a gaggle of “know it all you don’t know **** don’t you read the internet and car rags!”
I suspect the blade angle was goofy on the 950. Maybe opening too far?
My 950 flows 1011cfm after adjusting blade opening...
skrews
Well-Known Member
I checked that with a machinist square. 90° dead nuts on all.
I understand. But you will find they flow better when the throttle blade is arked over the shaft about 7° or so. Depending upon the shaft width, of coarse.
Do the primaries and secondaries separately. vary throttle opening and watch the manometer.
Do the primaries and secondaries separately. vary throttle opening and watch the manometer.
skrews
Well-Known Member
What are the venturi and base plate bore diameters of your 950? Is it an HP Holley or different brand carb? Part #?
I'll give that a try when I get the 1.45 main body carb on the bench.
skrews,
That's the funny part. The baseplate is an 850 Ebay knock off. (china)
And the body is a ProForm 67108C
But, it didn't flow that overnight... I had buyers remorse with the knock-off. (I wanted to try it, curious) I ended up completely redoing the baseplate, cause it was basically a anodized copy of a OE Holley baseplate (no big deal, I had the parts)
The usual deal, machined the shafts, button screws, and straightened the pump levers.
Then, all I had to do is find the optimum opening angle. This is by default, I do this on every carb. This is how it was shipped:
Gross, huh?
Below is a pic showing my 'stop' for the primaries. 6/32 screw with the top ground down, center of pic.
That's the funny part. The baseplate is an 850 Ebay knock off. (china)
And the body is a ProForm 67108C
But, it didn't flow that overnight... I had buyers remorse with the knock-off. (I wanted to try it, curious) I ended up completely redoing the baseplate, cause it was basically a anodized copy of a OE Holley baseplate (no big deal, I had the parts)
The usual deal, machined the shafts, button screws, and straightened the pump levers.
Then, all I had to do is find the optimum opening angle. This is by default, I do this on every carb. This is how it was shipped:
Gross, huh?
Below is a pic showing my 'stop' for the primaries. 6/32 screw with the top ground down, center of pic.
Also too, Holley throttle blades are oblong, (you probably know that..) but these were not.
If it were not for cam I'm running, this would be a major problem, because they do not seat completely. (a stockish motor would idle too high) I entended to idle off, both pri and sec, so no foul. In the end, it worked out fine.
Note to readers: DONT BUY THE CHEAP EBAY HOLLEY KNOCK OFFS
If it were not for cam I'm running, this would be a major problem, because they do not seat completely. (a stockish motor would idle too high) I entended to idle off, both pri and sec, so no foul. In the end, it worked out fine.
Note to readers: DONT BUY THE CHEAP EBAY HOLLEY KNOCK OFFS
skrews
Well-Known Member
So you're opening the throttle blade to about 7° before 90° ?
I have used the China base plates, and they are poor quality. The last one I used had different length transition slots, and the vacuum port nipples were so crooked they looked as if Ray Charles put them in with his feet. I won't use the China knock off base plates anymore, too many issues to fix for little money saved.
I have used the China base plates, and they are poor quality. The last one I used had different length transition slots, and the vacuum port nipples were so crooked they looked as if Ray Charles put them in with his feet. I won't use the China knock off base plates anymore, too many issues to fix for little money saved.
LOL Exactly..
The 7° figure is approximate, but close. It varies by the area the shaft takes up. Trial n error.
It's kinda fun, really. You never really know what you're going to end up with.
Let me know what you find. Is the SF1020 yours, or borrowed?
I did a 650 a while back for a rules class that had to maintain the OE look. So the air horn had to say on, but the choke valve was removed. Flowed 709 that way, otherwise stock.
I swapped out the OE boosters for AED dog legs, 850 base plate = 792cfm
skrews
Well-Known Member
The bench is at the shop I used to work for.
The QFT/ProForm 1.45 main body carb wound up consisting of one of the aforementioned "fixed" China 1.75 base plates, 3310 primary blocks, and scrounged fuel bowls. So far it has ran the best of any carb to date at the 1/8th mile track. Still has some fuel curve issues to iron out. The best way to describe what its doing is the A/F is chugging back and forth about a little over half a point . Gonna try different main air bleeds next time out.
The QFT/ProForm 1.45 main body carb wound up consisting of one of the aforementioned "fixed" China 1.75 base plates, 3310 primary blocks, and scrounged fuel bowls. So far it has ran the best of any carb to date at the 1/8th mile track. Still has some fuel curve issues to iron out. The best way to describe what its doing is the A/F is chugging back and forth about a little over half a point . Gonna try different main air bleeds next time out.
I have heard of people swapping boosters and pictures coming up 40-50hp on the dyno.
mderoy340
Well-Known Member
Thanks for the info. The Mighty Demon I have came with downlegs, no choke and 1.69 throttle plate.
Can't confirm the power increase, but I did that on a 3310 atop a Weiand Excellorator for a 383..
EGT's were VERY close, cyl to cyl. It actually made more power than a NASCAR 830 Holley.
Once again, the case for bigger is better is blown out of the water yet again.
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