Newbomb Turk
Well-Known Member
Yes
Lean idle. Rich cruise.
- Thread starter aaronk785
- Start date
-
Yes
Ironmike
Well-Known Member
to continue, measured my T slot orifice and was shocked. The pic shows a 060 and 055 pin gauge in there. so it's .115 or so. Seems pretty friggin big if ya ask me, but who knows.
Since I'm so rich at cruise RPM, what size should I restrict it to? No idea where to begin.
Since I'm so rich at cruise RPM, what size should I restrict it to? No idea where to begin.
Newbomb Turk
Well-Known Member
I start at .070 and tune from there. You may end up smaller. Thinking about it, I think I’d start at .062 as far as you are.
Its big because that is just meant to be a passageway, not a restriction.
The outer passage goes to the idle port and is restricted by the needle valves (idle mix screws).
The inner passage goes to the transfer slot and is restricted by the slot width, depth, and amount exposed to manifold vacuum by the throttle plate position.
Here's a simplified illustration of the relationships without a TSR.
The Transfer Slots Explained
By Tuner,
... The magazine articles tell us the slots obviously deliver more fuel as more of the slot is exposed to the vacuum at the edge of the butterfly and slot is exposed to the manifold vacuum below it. The real deal (which I’ve never seen described in the funnies) is that the portion of slot above the butterfly is air bleed and that below the butterfly is fuel feed. As the throttle blade changes position up and down the slot, the ratio of air bleed to fuel feed changes. As the butterfly opens air bleed is being cut off and fuel feed is being increased.
Usually (almost all Holley’s & clones), the slot and the curb idle adjustment are fed by the same idle jet and air bleed. If the slot is too long there is too much bled air from the slot above the butterfly at idle and small throttle openings. Because so much bled air is getting in the circuit from the slot, less is needed from the IAB for the same size IJ to function correctly at the dead idle. The result of less bleed area at the IAB to get the same size IJ to function at a dead idle is too much fuel when the total t-slot is exposed to the manifold and there’s a stronger vacuum because engine revs are higher. The mixture gets richer as the blade goes up the slot. Ideally, the mixture is richest at the dead idle and then gradually leans as the throttle is opened.
Last edited:
No wonder Holleys run rich. Carter carbs DO run a restriction to the T slot. Carter called it the 'Economizer' [ & patented it ] for obvious reasons. In many TQs I have checked, it varies from 0.046" to about 0.052". Another name for this restriction is the Idle Down Channel. In the Ruggles QJ book, he gives examples of sizing from std engines to fully modified: 0.040" to 0.055".
Newbomb Turk
Well-Known Member
If you were paying sttention…original Holley’s don’t have that long T slot. They generally do not need T slot restriction.
The "economizer" system accomplishes almost the same thing as a t-slot restrictor, but is not a transistion slot restrictor. It is arguably (and I think practically too) a more effective system because of how it works.
Last edited:
Ironmike
Well-Known Member
Man I just hate the thought of drilling into that aluminum body. Chips everywhere!
Also, do I really need to do the secondary too?
Also, do I really need to do the secondary too?
Newbomb Turk
Well-Known Member
Yes, I do them both. It’s real easy to do and you can always pull them out. I doubt you will because you’ll love what they do.
it's possible to shorten the slot itselfs
Note that secondary side are usually higher up but not always.
This guy went on a journey from greenhorn to a carby smarty.
www.tapatalk.com
www.tapatalk.com
And a great thread with for anyone who wants to go through it.
www.tapatalk.com
Note that secondary side are usually higher up but not always.
This guy went on a journey from greenhorn to a carby smarty.
racingfuelsystems-Transfer slot lengths
Is there a list that states what the correct length of transfer slots should be for various popular Holley carbs? Like a 600 VS & 750 VS as well a
www.tapatalk.com
racingfuelsystems-Transition slot areas and why the differences
Had some time to kill today so I measured the transition slots on 3 , 4150 throttle body/base plate assemblies and found they varied widely . F
www.tapatalk.com
And a great thread with for anyone who wants to go through it.
racingfuelsystems-Holley T-slot length difference
Whoa, Sir! Idle/transition of Ø0.040" IFR & Ø0.026" SIAB out back might be wicked responsive and quick and touchy with the mixture screws, but s
www.tapatalk.com
Newbomb Turk
Well-Known Member
As a general rule, I don’t read the bullshit you post.
As wrong as you are and as often as you are wrong there is no reason to read what you post very close or even at all.
Ironmike
Well-Known Member
Hope so... carb all apart, everything I need coming tomorrow from good old McMaster Carr. Think I'll try starting at .065. As you suggested.
Newbomb Turk
Well-Known Member
Ironmike
Well-Known Member
Done. At least it's a start. all four corners starting at .070, since they were so HUGE. I didn't realize once the throttle plate is off, that T slot hole has no communication with the carb body other than the bottom . Easy peasy. blew them out......little brake clean. Nice and tidy. Will keep you all updated.
If by chance .070 is no good, i have 46 more set screws.
If by chance .070 is no good, i have 46 more set screws.
mopowers
Well-Known Member
What size blanks did you buy? 1/8" long?
Newbomb Turk
Well-Known Member
I use 1/8 and 3/16 depending on where they go.
Ironmike
Well-Known Member
10-32, 3/16 long did the trick for me. just tapped 3/16 into the body, so they'd be snug. getting it back together shortly.
Ironmike
Well-Known Member
OK. Time to report results. 77 degrees today, low humidity. Took a nice long ride, got it nice and warm. idles at 1150RPM as usual, 13.5 AFR. Good. I do know big(ish) cams like a bit of rich idle.
Next, cruising on dead level road, 45 MPH around 2800, AFR mid 12's.
65 MPH, 3300 RPM 12.8 to 13.2.
And WOT, at a well known "test hit" spot, always between 12.7 and 13. Perfect there......
So the cruise is much better than before but still too rich. Already swapped in .062 restrictions from the .070 I put in a couple days ago. Hopefully it will respond well.
Also, I'm open to all you guys suggestions, so I ordered a 10 degree bushing for my MSD distrib. Been locked a few years but we'll see how that works out. When I talked to Dana at 4 Seconds Flat and mentioned I'm locked at 35 degrees, she read me the riot act. VERY bright people there.
Weather here looks like sh#t for the next couple days, but I will report back! Me thinks you guys pointed me in the right direction. Even an old dog can learn new tricks.
Next, cruising on dead level road, 45 MPH around 2800, AFR mid 12's.
65 MPH, 3300 RPM 12.8 to 13.2.
And WOT, at a well known "test hit" spot, always between 12.7 and 13. Perfect there......
So the cruise is much better than before but still too rich. Already swapped in .062 restrictions from the .070 I put in a couple days ago. Hopefully it will respond well.
Also, I'm open to all you guys suggestions, so I ordered a 10 degree bushing for my MSD distrib. Been locked a few years but we'll see how that works out. When I talked to Dana at 4 Seconds Flat and mentioned I'm locked at 35 degrees, she read me the riot act. VERY bright people there.
Weather here looks like sh#t for the next couple days, but I will report back! Me thinks you guys pointed me in the right direction. Even an old dog can learn new tricks.
Newbomb Turk
Well-Known Member
Depending on how big your main air bleed is, you could be cruising on the main jet at 2800. If you are on the booster at 2800 then you need to drop the primary main jet to get the cruise AFR where it needs to be.
If you are still on the T slots, I'd drop down to .048ish. If you get on the lean side of it the next time you swap in some brass you can always just pull them back out and open them up a bit. It's easier to drill out one set (if you can) than to keep using new brass to go smaller.
Soooooooooooo...if no one has told you how this works I'll give it a shot.
On a Holley or Holley clone, you need to set your cruise AFR with the T slots at low throttle openings and the primary main jet for higher throttle openings. So you have to sort out if you are cruising on the PMJ or the T slot and tune on one at a time.
To that end, to tune for WOT after you have the T slots and PMJ sorted out you only change the secondary main jet OR the power valve channel restrictors. Once you have the cruise AFR ironed out you never touch the PMJ again.
If for some reason you need to fatten up WOT a bit you open up the PVCR on the primary side and add main jet on the secondary.
Again, cruising down the freeway at 70 you are on the booster (which is another way of saying you are on the PMJ) so yo would adjust that and get it correct.
And you have already cleaned up your transition and T slot AFR.
Once you have that sorted out you can go to tuning for WOT. If your cruise AFR is where it should be, you don't touch your T slot restrictors or the PMJ. You change WOT with your PVCR's and the SMJ.
This of course leads to unscrewing the power valve timing issue.
The power valve cold have been named the economizer valve because that's really what it does. It allows us to run a very lean and crisp, clean cruise on the PMJ and then as you get further into the throttle and vacuum starts dropping the power valve opens and adds extra fuel. It really is two small jets behind the power valve. They work like main jets but they only add fuel when manifold vacuum drops below whatever your power valve is rated at.
A 2.5 power valve will open significantly later than an 8.5 for example.
Holley says (and so do many others but they are wrong) to set your power valve opening point at half your idle vacuum. If you have 14 inches of vacuum at idle they'd say use a 6.5 to start. And that's probably not close.
I use about 75% of CRUISE vacuum to start with and tune from there. If you have 18 inches at a cruise then I'd start tuning with a 10.5 because that's all you can get in that range. If I could get a 12.5 I'd start with that.
The thing to remember about the power valve is it tunes two ways.
One is off manifold vacuum (when it opens and shuts as the vacuum goes up and down with load and RPM) and the other is with the restrictors.
The rating (8.5 or 4.5 etc.) sets at what manifold vacuum it opens (which is really the start point that it adds fuel) and those little restrictors control how much fuel you are adding. And any change you make to the PV is always separate from the primary main jet. You can change the opening point (which will add fuel sooner or later) and then change how much fuel you are adding at WOT.
You can find some nice little power gains but more importantly you can trim the fuel curve right up and get EFI like fuel consumption and drivability if you learn to tune.
I hope this makes some sense.
If you are still on the T slots, I'd drop down to .048ish. If you get on the lean side of it the next time you swap in some brass you can always just pull them back out and open them up a bit. It's easier to drill out one set (if you can) than to keep using new brass to go smaller.
Soooooooooooo...if no one has told you how this works I'll give it a shot.
On a Holley or Holley clone, you need to set your cruise AFR with the T slots at low throttle openings and the primary main jet for higher throttle openings. So you have to sort out if you are cruising on the PMJ or the T slot and tune on one at a time.
To that end, to tune for WOT after you have the T slots and PMJ sorted out you only change the secondary main jet OR the power valve channel restrictors. Once you have the cruise AFR ironed out you never touch the PMJ again.
If for some reason you need to fatten up WOT a bit you open up the PVCR on the primary side and add main jet on the secondary.
Again, cruising down the freeway at 70 you are on the booster (which is another way of saying you are on the PMJ) so yo would adjust that and get it correct.
And you have already cleaned up your transition and T slot AFR.
Once you have that sorted out you can go to tuning for WOT. If your cruise AFR is where it should be, you don't touch your T slot restrictors or the PMJ. You change WOT with your PVCR's and the SMJ.
This of course leads to unscrewing the power valve timing issue.
The power valve cold have been named the economizer valve because that's really what it does. It allows us to run a very lean and crisp, clean cruise on the PMJ and then as you get further into the throttle and vacuum starts dropping the power valve opens and adds extra fuel. It really is two small jets behind the power valve. They work like main jets but they only add fuel when manifold vacuum drops below whatever your power valve is rated at.
A 2.5 power valve will open significantly later than an 8.5 for example.
Holley says (and so do many others but they are wrong) to set your power valve opening point at half your idle vacuum. If you have 14 inches of vacuum at idle they'd say use a 6.5 to start. And that's probably not close.
I use about 75% of CRUISE vacuum to start with and tune from there. If you have 18 inches at a cruise then I'd start tuning with a 10.5 because that's all you can get in that range. If I could get a 12.5 I'd start with that.
The thing to remember about the power valve is it tunes two ways.
One is off manifold vacuum (when it opens and shuts as the vacuum goes up and down with load and RPM) and the other is with the restrictors.
The rating (8.5 or 4.5 etc.) sets at what manifold vacuum it opens (which is really the start point that it adds fuel) and those little restrictors control how much fuel you are adding. And any change you make to the PV is always separate from the primary main jet. You can change the opening point (which will add fuel sooner or later) and then change how much fuel you are adding at WOT.
You can find some nice little power gains but more importantly you can trim the fuel curve right up and get EFI like fuel consumption and drivability if you learn to tune.
I hope this makes some sense.
TT5.9mag
Two atmospheres are better than one
Great post
- Joined
- Dec 31, 2005
- Messages
- 8,525
- Reaction score
- 4,646
They all do.
Ironmike
Well-Known Member
reviving this old thread again! Ordered a 10 degree bushing and a whole new set of springs from 4 Seconds Flat. Played around with the curve for a couple weeks and here's what I got:
My particular engine in MY car absolutely hated every curve I tried. And I tried everything everyone suggested. Made a serious calculated effort, too.
Distrib locked at 35 degrees, the whole damn thing was happier. Started better, idled better, and is faster. Faster from the 2 step, faster from a roll, just plain faster. Don't know why.......I read all the benefits of a curve........but proof is proof. So THAT theory, for me, is put to bed. Period.
My next effort is concerning T slot restrictors. As posted earlier, I went down to .062 all 4 corners and it made a pretty good improvement. I am still a wee bit rich at cruise around 2600 to 3000 RPM and thinking I should go down to somewhere around .050. Does this sound like too much restriction?
Also, Idle and WOT are both exactly where you'd want them, so I don't think it's a jetting issue.
Have done nothing to the emulsion bleeds in the metering blocks. Each block has 4 on both sides. 8 per block. None are blanks. I kinda think that should change, but have no idea what the hell to do with them. They're Voodoo to me.
My particular engine in MY car absolutely hated every curve I tried. And I tried everything everyone suggested. Made a serious calculated effort, too.
Distrib locked at 35 degrees, the whole damn thing was happier. Started better, idled better, and is faster. Faster from the 2 step, faster from a roll, just plain faster. Don't know why.......I read all the benefits of a curve........but proof is proof. So THAT theory, for me, is put to bed. Period.
My next effort is concerning T slot restrictors. As posted earlier, I went down to .062 all 4 corners and it made a pretty good improvement. I am still a wee bit rich at cruise around 2600 to 3000 RPM and thinking I should go down to somewhere around .050. Does this sound like too much restriction?
Also, Idle and WOT are both exactly where you'd want them, so I don't think it's a jetting issue.
Have done nothing to the emulsion bleeds in the metering blocks. Each block has 4 on both sides. 8 per block. None are blanks. I kinda think that should change, but have no idea what the hell to do with them. They're Voodoo to me.
Newbomb Turk
Well-Known Member
reviving this old thread again! Ordered a 10 degree bushing and a whole new set of springs from 4 Seconds Flat. Played around with the curve for a couple weeks and here's what I got:
My particular engine in MY car absolutely hated every curve I tried. And I tried everything everyone suggested. Made a serious calculated effort, too.
Distrib locked at 35 degrees, the whole damn thing was happier. Started better, idled better, and is faster. Faster from the 2 step, faster from a roll, just plain faster. Don't know why.......I read all the benefits of a curve........but proof is proof. So THAT theory, for me, is put to bed. Period.
My next effort is concerning T slot restrictors. As posted earlier, I went down to .062 all 4 corners and it made a pretty good improvement. I am still a wee bit rich at cruise around 2600 to 3000 RPM and thinking I should go down to somewhere around .050. Does this sound like too much restriction?
Also, Idle and WOT are both exactly where you'd want them, so I don't think it's a jetting issue.
Have done nothing to the emulsion bleeds in the metering blocks. Each block has 4 on both sides. 8 per block. None are blanks. I kinda think that should change, but have no idea what the hell to do with them. They're Voodoo to me.
Didn’t you dyno your engine? If so was it locked out then?
It would be rare that your engine would hate a curve.
In fact, do you mind posting your best curve you’ve found? Whatever was the best of the curves?
Edit: if you have 4 open emulsion holes it’s probably too much.
Edit II: what size is your carb and what size is the main air bleed?
-
