skrews
Well-Known Member
Word to the wise, don't buy a chinesse cheapo base plate. Get an actual Holley made plate. Ask me how I know.
Holley/Demon Carb stumble
- Thread starter Cudafever
- Start date
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Mattex thanks for them pics and explanation.
Have a much better understanding of the emulsion process. when i asked if them holes were(2 e holes) had fuel or air and i got the comment BOTH......now i understand and agree.
I printed them pic's off for further referencing.
Thanks You!!!!
Have a much better understanding of the emulsion process. when i asked if them holes were(2 e holes) had fuel or air and i got the comment BOTH......now i understand and agree.
I printed them pic's off for further referencing.
Thanks You!!!!
Might not be. This is to go with a 750 proform body?
Not that unusual.
Can extend the short slot with a razor saw or thin file, or chamfer the bottom of the throttle blade. Third option is a bit more work, but clever. Run a set screw in to shorten the slot. That was posted by someone RFS forum.
Holes to no holes will change the whole transfer slot relationship. Not saying good or bad in this case. Just that it will be like starting over as far as setup goes.
That's what it's all about.
We help each other learn.
I took and modified those diagrams from another guy doing the same.
That helped me a little then, and a lot when I came back to it when dealing with blocks made for e-tubes that don't have 'em.
MY base is for a 1-3/4 blades, He is asking if he can install the larger base on to a 750 which as the 1-11/16 blade.
If i understand that right??????
Here's a guy building up carb like yours.
Building a Proform/Qft 750
No details on how it ran - at least in that thread.
If money is tight, might be better off snagging an old 4779 750 DP for 150 or less.
old as in low revision number like -2
Building a Proform/Qft 750
No details on how it ran - at least in that thread.
If money is tight, might be better off snagging an old 4779 750 DP for 150 or less.
old as in low revision number like -2
I don't know!
I thought you were using this with a profrom 750 main body and I noticed they posted this base is a for larger body.
I wish they would just post the dimensions on stuff like this. It would make things a lot easier.
FWIW, Holley's 3310 and 4779 '750's have 1 11/16 " throttles:
His proform main body is a 67100c that is for a 750 aka 1-11/16
My proform main body is a 67107c. altho it is a lot smaller main body then the demon one. it tapers out to the 1-3/4 blade size or bore. Is designed for a 1-3/4 blade that is a 850 to 1050 cfm carb.
If you went up to a 1-3/4 throttle blade base on a 750 main body the blade would hit the main body
Go to post 78 to see the difference between a Mighty Demon 850 main body and a Proform 850 main body.
My proform main body is a 67107c. altho it is a lot smaller main body then the demon one. it tapers out to the 1-3/4 blade size or bore. Is designed for a 1-3/4 blade that is a 850 to 1050 cfm carb.
If you went up to a 1-3/4 throttle blade base on a 750 main body the blade would hit the main body
Go to post 78 to see the difference between a Mighty Demon 850 main body and a Proform 850 main body.
Yup and yup
Got it my bad. mderoy was talking about his 750 and then with the 3310 blocks my brain somehow missed what your proform MB really is.
Good people on that forum.
I'm not on that often because I hate Tapatalk.
Not sure you can still join the forum without being a tapatalk member. But if you do want to join RFS forum, see if you can do it without being a tap-a-t member.
I'm not on that often because I hate Tapatalk.
Not sure you can still join the forum without being a tapatalk member. But if you do want to join RFS forum, see if you can do it without being a tap-a-t member.
PRH
Well-Known Member
It would be nice if somewhere in the specs for that main body they listed the Venturi diameter.
I took a Mighty Demon 850 in on trade towards something at one point.
The guy I got it from also took it in on trade for something.
He never tried to use it but said the guy he got it from couldn’t get it to work right.
Well, I took it all apart........ and it had some super cluster f@£k of a tune in it, so I just set it all up to the specs in the catalog.
Tried in on the dyno...... had to tweak the tune slightly, but it seemed to work fine.
I ended up using it for a dyno carb for the 650-750hp type builds, and I never had to mess with it again after that first tweak.
I ended up selling it after a few years........ I was pretty rich with carbs at the time, and had something else I could use for that type of build......... so it ended up with a new home.
With two normal Holley metering blocks, I think I’d be tempted to try the ootb Proform tune as a baseline with the new main body, and work from there.
I took a Mighty Demon 850 in on trade towards something at one point.
The guy I got it from also took it in on trade for something.
He never tried to use it but said the guy he got it from couldn’t get it to work right.
Well, I took it all apart........ and it had some super cluster f@£k of a tune in it, so I just set it all up to the specs in the catalog.
Tried in on the dyno...... had to tweak the tune slightly, but it seemed to work fine.
I ended up using it for a dyno carb for the 650-750hp type builds, and I never had to mess with it again after that first tweak.
I ended up selling it after a few years........ I was pretty rich with carbs at the time, and had something else I could use for that type of build......... so it ended up with a new home.
With two normal Holley metering blocks, I think I’d be tempted to try the ootb Proform tune as a baseline with the new main body, and work from there.
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PRH
Well-Known Member
With that venturi diameter, I think the Proform tune should be a safe place to start.
The QFT SQ-850, Holley Race Brawler 850, and Proform 850 all come with the same air bleed and jet package.
33/33 hsab, 76/84 jets.
It’s basically the same physical size as the original HP950, which is a much better carb for the application than a MD850....... imo.
The QFT SQ-850, Holley Race Brawler 850, and Proform 850 all come with the same air bleed and jet package.
33/33 hsab, 76/84 jets.
It’s basically the same physical size as the original HP950, which is a much better carb for the application than a MD850....... imo.
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Found a complete 3310-2 carb on ebay for 50 dollars.(so i now have 2 front metering block off of a 3310) Only it look like it won't be here before the next race.
Will probably just try and tune it with the new throttle base.
I have a question on that.
Do i just drill much smaller holes in the new base plate Butterflies,(after i have installed it and then removed to see how much transfer slot i'm using) or can i tune it out with Idle air bleeds????? Good idea...Bad idea????
Will probably just try and tune it with the new throttle base.
I have a question on that.
Do i just drill much smaller holes in the new base plate Butterflies,(after i have installed it and then removed to see how much transfer slot i'm using) or can i tune it out with Idle air bleeds????? Good idea...Bad idea????
yellow rose
Overnight Sensation
Start with butterflies that don't have holes. Then drill if you need them.
It's a big deal. It's such a big deal that carbs a are now being made with adjustable idle air bleed systems that do the same thing as holes in the butterflies, but it's more adjustable.
PRH
Well-Known Member
Exactly.
And I wouldn’t be too eager to drill them either.
The Demon flows more than 850, the Proform would be pretty close to 850(wet flow).
I’m not sure where I’d even start to look for my notes on my made-from-parts Holley HP950, but with some mildly blended venturi’s iirc it flowed about 865cfm(calculated wet flow...... 92% of dry flow).
I seem to recall the Demon 1.560 venturi carbs being closer to 920cfm(calculated wet).
The Mighty Demon 850, Race Demon 1000, and Race Demon RS 1025 are all the same “size”, and all flow basically the same.
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PRH
Well-Known Member
I was looking through some dyno sheets.......
I have one sheet with a 410, mild solid roller, rpm heads, Victor intake, QF-850 carb.
524tq/538hp....... it’s still quite rich.
I don’t know exactly which QF 850 was used( I do know it wasn’t the SS-850), but on this run the jetting was 74/85.
No air bleed info.
I didn’t run this motor, but it’s richer than I would have preferred it, and I’m sure there was a little power left on the table.
That carb, with those jets, on that motor......... used a TON of fuel...... and the bsfc numbers were not very good.
So....... I’d say it’s going to be pretty easy to get one of these too rich.
Also, if you rewatch that video I posted, the the Holley Brawler ended up with fairly small jets in it(70/80)on that combo.
Granted it’s only 750, but the venturi diameter is very close, so I wouldn’t be expecting a big difference in the jetting requirement.
Like I said, with 74/85 on the 850 here, it was still quite rich.
I have one sheet with a 410, mild solid roller, rpm heads, Victor intake, QF-850 carb.
524tq/538hp....... it’s still quite rich.
I don’t know exactly which QF 850 was used( I do know it wasn’t the SS-850), but on this run the jetting was 74/85.
No air bleed info.
I didn’t run this motor, but it’s richer than I would have preferred it, and I’m sure there was a little power left on the table.
That carb, with those jets, on that motor......... used a TON of fuel...... and the bsfc numbers were not very good.
So....... I’d say it’s going to be pretty easy to get one of these too rich.
Also, if you rewatch that video I posted, the the Holley Brawler ended up with fairly small jets in it(70/80)on that combo.
Granted it’s only 750, but the venturi diameter is very close, so I wouldn’t be expecting a big difference in the jetting requirement.
Like I said, with 74/85 on the 850 here, it was still quite rich.
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I'm going to start with the stock jetting of the Proform main body. I believe, as you guys do, that it will need to go down in jet a lot!!!!
But i'm scared too just drop 4 jet to start with, with all the popping and banging i had before when i did that.
also going to cut up my "removed exhaust system" and see if i can get a colector long enough to get some low speed/idle reading with my o2 meter.
But i'm scared too just drop 4 jet to start with, with all the popping and banging i had before when i did that.
also going to cut up my "removed exhaust system" and see if i can get a colector long enough to get some low speed/idle reading with my o2 meter.
PRH
Well-Known Member
Sounds like with a spare set of float bowls and some hardware you could have two complete carbs.
Then, put the Demon back together how it was last running good, and re-baseline the ET with that carb........then swap on the new Proform bodied carb...... preferably at the track on the same day.
Then, put the Demon back together how it was last running good, and re-baseline the ET with that carb........then swap on the new Proform bodied carb...... preferably at the track on the same day.
What rpm is middle of 2nd ?
yea. You're not the only one that's found a tighter converter can make lots of work. Took a long while to work everything out.
Learned a lot along the way.
I agree with the others.
Do it this way.
Measure the turns in on the idle mix screw to open the throttle blades enough to reveal .010, 020, .030 and .040"
Do the same for the secondary throttles.
Measure how deep the transfer slots are - primary and secondary. Secondary might start higher up. If so, keep that in mind.
Only drill if you can't get the engine to idle at reasonably civil rpm with primary transfer slots in the 0.20 to .030 range and there's problems coming off idle.
Before drilling, try a opening the secondaries a hair more. That's why measuring beforehand helps a ton. You'll know if you've got to open either side up in the .040 range or more to keep it idling - that's going to be no good.
While you're waiting for stuff, go buy the drill sets so you can measure everything.
The restrictions need to be ballpark matched up.
For example, if the IFRs are 0.035 then its unlikely to be a good match with IABs .068
Definately want to know the power valve restrictions before making the jetting decisions.
I assume since you're using a primary block on the secondaries, you will be using a PV plug there. If so - then its just the primary side to be concerned with.
I can tell you what the 3310 blocks were originally - doesn't mean that's what they've got now.
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