Trying to get an idea of what jets folks are running on their holley annular carbs. I was reading an article where some carb shop took a 950 HP, put annular boosters in it, and rejetted to 68's. That seems REAL lean to me and wanted to see if anyone had any real world experience on how lean you can go with a holley 850 annular carb.

thanks
Dean

A lot has to do with your engine set up, tranny, gear ratio and what you use the car for. I run a 80511 830cfm (F)84,(R)84 6.5,6.5 (I get 10" at idle) 4150HP, which is a stock setup, and works great with no plug fouling on a 10.5:1 460ci BBC. The carb sits on an Edelbrock RPM Air Gap. Cam is the Old CB288R-10 to a M21 and 3.31's. I've plugged the 1/8" holes in the throttle plates with peened brass bolts and seat the Idle air on the secondaries. I don't drag race. I get excellent throttle response from an 800 rpm idle right through the rpm range for a Road Warrior. Gotta love them annular boosters for throttle response.

I imagine Drag Race is another story and altitude of the track would be an important factor. That 68 sounds like a typo to me unless their running something out of the ordinary.

Within 4 numbers of stock jetting or you have the wrong size carb.
No 950 is available with annulars according to my catalog, so if a 1000 cfm (which I have) has 84/88 from factory, I'd expect a 950 to want somewhere around 80-82/84-86.

68s sound super lean even with huge manifold vacuum.
Did this modified 950 have super small air bleeds fitted to require such a small main jet?

Dean,
I'm not sure if this would support the articl or not, but I had a turbo charged ford 347 with a holley 750 (annular boosters) and it was setup for blow thru. I only had 68 in the front and 76 or 74 in the rear. and even with that jetting i was at 10.0 :1 AFR WOT.

The article didn't say if it changed air bleeds or not. You are also correct that the 950HP doesn't come with annular boosters. The article was using the 950HP in an experiment. I just thought that going down 10-12 jet sizes was extreme and was wondering if anyone had any real world experience in how far down from stock you could jet an 850 annular without going too lean.

Men, correct me if I'm wrong but,,,,(has anyone ever said anything WRONG here without being corrected?:D)
But I think 'annular boosters' is an oxymoron. No such thing. The boosters are eliminated from above the venturi and fuel is presented to the airstream from the sides of the bores. Worth at least 50cfm. Kinda the way my new FI works;:thumbsup:
http://epitomesrebuild.com/images/313.jpg

Dean, when taking a 950 carb with down leg boosters and replacing them with annular boosters you decrease the flow of the carb. Annular boosters are bigger and therefore more restrictive so the carb flows less air and needs less fuel.

Annular boosters also are know for creating a very strong signal which further reduces the required jet size. Similar flowing carbs with different style boosters may have entirely different jet requirements.

Another thing that effects jet size (independent of booster type) is the size of the main bleeds. The main bleed works opposite of a main jet -- smaller bleed = richer mixture.

My opinion ;) if you want an annular booster carb buy and annular booster carb.

Eric! What's an annular booster???!
Holley uses the term 'annular discharge' as I recall.

Eric,
I already have an 850 annular carb. I currently run 76 jets square in it. Even if someone changed the air bleeds, I just find it really hard to believe that you could drop the jets down to 68 and still run correctly. The reason I posed the question is to see how far down someone has jetted without doing any damage.

thanks
Dean

Dean, when taking a 950 carb with down leg boosters and replacing them with annular boosters you decrease the flow of the carb. Annular boosters are bigger and therefore more restrictive so the carb flows less air and needs less fuel.

Annular boosters also are know for creating a very strong signal which further reduces the required jet size. Similar flowing carbs with different style boosters may have entirely different jet requirements.

The Holley HP1000 R80513 (downleg) and Holley HP1000 R80514 (annular) both have the same venturi diameter and throttle bore diameter as each other. They are also jetted 84/84 & 84/88 respectively. (Yes, that's a larger secondary jet in the annular.)
So what you're saying may be true, I think the CFM ratings and tuning differences are negligible. :)

68 in a 950 is just way-lean. I doubt the boosters have anything to do with that jet choice. Even an 830 annular uses 78/78 stock.

Fred. I took some pics out of a Holley book for you! ;)

http://img210.imageshack.us/img210/4434/annulardischarge002jf5.th.jpg (http://img210.imageshack.us/my.php?image=annulardischarge002jf5.jpg) http://img210.imageshack.us/img210/7127/annulardischarge001ju5.th.jpg (http://img210.imageshack.us/my.php?image=annulardischarge001ju5.jpg)

Thanks Steve but the web site won't let me have them. And I turned my stuff upside down looking for my Holley book. Must be at my mothers house.

Steve, thanks for sending those snaps to my email. I'd forgotten about that model carb. The annular discharge model that uses no boosters is a whole different animal.

Fred annular boosters just have a bunch of small holes in a circle around the inside of the booster for discharging the fuel. The benefit is supposed to be a better quality mixture. A conventional straight or downleg just has one big hole at the end of the tube. The pics show it better than I can explain.

Steve, there are a lot of different size boosters out there and if two different types are the same diameter and in the same position (downleg vs. straight) then yes I agree the carb could flow the same and have similar jet requirements. If they are in a different spot but the same size the location difference will effect both airflow and booster sensitivity.

That still does not take into account what size high speed bleeds these two HP 1000 carbs you are comparing use. It is very possible that primary and secondary HS bleed sizes are not the same. Again, a smaller bleed has nearly the same effect as a larger jet (and vice-versa for a larger air bleed), except changing bleed size also effects circuit timing and potentially the linearity of the fuel curve.

Lots of fun huh :D

Dean,

I've jetted down to 68 with an 850 down leg booster carb on E85 so I'm sure it could be done on gas with an annular booster -- especially if the high speed bleed was very small (like around .026-.028"). If the PVCR is big enough it won't do any damage at WOT. In my case 68 was dead lean at mid-throttle and 73 was as lean as it would tolerate.

Mid-throttle tends to be the hard spot to tune around with a very small PMJ because the power valve is closed and moderate loads don't do well around and up above 14.7:1 AF ratio. Bottom line, I think it could be done, but it would likely have a cranky lean spot or two . . .

JMO

That still does not take into account what size high speed bleeds these two HP 1000 carbs you are comparing use. It is very possible that primary and secondary HS bleed sizes are not the same. Again, a smaller bleed has nearly the same effect as a larger jet (and vice-versa for a larger air bleed), except changing bleed size also effects circuit timing and potentially the linearity of the fuel curve.

Lots of fun huh :D

Good point Eric, and I don't have that info so I guess I'm now stopped in my tracks! :p :thumbsup:

Thanks Eric. Definitely lots to think about now. Just trying to get mine to be more responsive.

Dean

What's your combo like Dean? (engine, carb tuneup, etc.) I bet there are somethings to try short of swapping boosters.

Dean wanna see my pin drill collection? Yep, even the air bleeds are fine-tuned with their own bleeds. It's the biggest reason I went to EFI.

Eric,
My engine specs are 454, 10:1 compression, Edelbrock large oval RPM intake, hyd roller voodoo 60211 (.575/.575, 221/229 @ .050), Edelbrock oval heads, 100cc chambers (opened up the runners to match the RPM), 850 holley (already has the annular boosters) jetted 76 square with 6.5 power valves, 4-corner idle, 1 3/4 full length headers. Running a Unilite distributor and my timing is set at 14* initial with 24* in the dist. I run a vacuum advance and use manifold vacuum (not looking to go into the merits of manifold or ported vacuum, just stating so you know what I have)

Not sure what size air bleeds I have in the carb, but they are removable, so I can easily change them. This is a VS. I am also running the pink cam, 30cc pump with .031 squirter.

So what size air bleeds and/or jets should I be running?

thanks
Dean

Dean,

I would make a couple changes to start.

For one, I'd plug the rear power valve and jet the rear up from 76 to 86 (you might eventually come back to an 84 if its a hair too rich). You could also gain a little by changing the front power valve from a 6.5" to an 8.5" one. This would help it open earlier, enriching your mixture sooner.

Not sure about the accelerator pump calibration. Might be OK, might need a little more fuel on the first tap of the throttle. It's hard to say . . . is there an off idle hesitation when you nail it?

For now I'd leave the bleeds alone.

I don't care for the manifold vac setup with your mild cam, and would rather see initial at about 18* with 20* in the mech advance curve with ported advance -- but I won't go into that since you are unwilling to change or discuss.

thanks Eric. Now to go buy some parts. I am also shooting you a PM if you don't mind

Dean

Fred,
If I understood what you said, that was funny. Even the air bleeds have air bleeds. :)

Dean