482/496 FEs with 850 Carb Question?

[gsharapa]

For those of you running 482/496 FE (600HP up) with 850 Quickfuel or Holley carb I'd be interested in knowing what primary and secondary jets you are running and power valve in the primary and do you have one in the secondary?

I'm running 496 with a Quickfuel 850 and had it dynoed at the crank and then again on the chassis dyno but as you know those always focus on the WOT and I have a lean condition on the primaries say entering on an expressway on ramp in second or third running up to around 3-4,000 rpm and not into the secondaries. The QF came with 76 primaries and 84 secondaries with a 4.5 power value in the primaries. Taking the carb apart I have 70s in the primaries and 80s in the secondaries however they are holley jets and it appears QF may be a bit different. I'm back up to 74s in primaries and 82s in secondaries (QF jets) now an almost eliminated issue but thought I'd like to hear what everyone else is running.

[Hotfingrs]

I've got a 482 with an 850 Quick Fuel. Mine is the Q series with AN boosters. The weather right now is in single digits, and all my info is in the garage. I know when I had it on the dyno doing A/F we had to pull jets out of both ends, then fine tuned the fuel curve with air bleed adjustment. I'm pretty sure the drag race 850 came with bigger jets than you have listed... I'm thinking 92 and 84....and we ended up pulling 5 or 6 out.

[gsharapa]

Thanks for your response. You may be right as I looked it up at Summit and looking at Quickfuel's site it looks like the primaries were 78 and secondaries 84s. I do have the RQ850 Drag Carb. If it warms up in the next couple weeks and you get in the garage appreciate knowing your setup. Thanks.........

Race-Q-Series Specifications
Part # CFM Pri. Sec. Idle Inter. Hi Speed Jet Jet Bleed Bleed Bleed
RQ-750 750 74 82 .073" .036"
RQ-750-AN 750 70 82 .070" .033"
RQ-850 850 78 84 .070" .033"RQ-850-AN 850 76 84 .070" .033"
RQ-950 950 80 86 .070" .032"
RQ-950-AN 950 78 84 .073" .032"
RQ-1050 1050 86 94 .070" .028"
RQ-1050-AN 1050 84 90 .073" .033"
RQ-1050-3 1050 88 96 .061" .053" .038"
RQ-1050-3AN 1050 86 92 .063" .051" .038"
36-

[Hotfingrs]

Gary,

Here's a shot of the dyno sheet showing carb changes.....

start with May 2013 baseline and go down.....

[gsharapa]

Jack,

So your May 2013 baseline was my carb's stock settings.

If I look at your last pull, they went to 71 prim/78 sec, kept idle air bleeds at 70but went to 40 high speed air bleed in the front and 33 rear and assume the front PV was still 4.5 at 38 total timing? Do you know what the A/F readings were at the low end 3,000 and WOT? Also, are you using Quickfuel jets or Holley jets? Assume it made it's best WOT power on that last pull........

Interesting the two where setup pretty close as off the dyno mine was 70/80s (holley jets) with the 70/33 air bleeds (idle/high speed), 4.5 pv at 40 degress. It appears to be too lean on the low end around 3,000-4,000 and I lowered my high speed air bleed down to 28 and made it much better than raised the primary jet (Quickfuel jet now) to 74 and secondary to 82 and seems to be close. I did determine last night that my power valve is blown but would think that would make it richer not lean down low.

[Hotfingrs]

Final air bleeds were 70/40 33 are the squirters... Using holley jets. I can't remember what low rpm A/F was but WOT stayed in the 12.7-12.9 range, which is right on the edge of where you would want it.

If I remember right we didn't pick up any power, or negligible, going from 35-38 timing, and the last test W/O air cleaner netted about 3 horse.

[Hotfingrs]

Forgot to mention that in the last run, without the air cleaner, the A/F went lean.

[gsharapa]

Jack,

Thanks for all your inf/insite. I have QF 74/82 main jets and 70/28 air bleeds in it now and have some 75 and 76s QFs coming in. The only thing I can come up with, is it appears there is a difference between QF and Holley jets. Talking to Quickfuel, they say the Holley jets will work but flow is very different so a #70 Holley jet is not really flowing the same fuel as a #70 Quickfuel, thinking it takes a higher # QF jet to flow what a Holley jet does. It's interesting just looking at the jets with the naked eye the Holley's hole looks larger comparing the same #jets. I came up with a hole size chart on all the Holley jets but can't seem to find a similar chart from Quickfuel. Probably will take so drill bits and see what is the difference between them is. Since mine ended up with Holley jets (70/80) I probably should of tweaked it up to 71 or 72 Holley main jets in the primary vs switching back to the QF jets and trying to dial it in....

[Bobcat]

The reason the Quick Fuel jets and the Holley jets are different is because Holley jet flow is determined not just by the hole size but also by the angle of the bevel/taper in the jet . I spent some time looking over a chart that compared Holley hole diameter to actual flow rates a while back and found some jets with the same hole diameter flowed completely different amounts of fuel ( measured in cc ) . If you just drill a straight hole , it won`t flow as much as one that has the bevel/taper in it ... another reason to not just drill out jets .
FWIW , I have a Pro Systems 950 on a dual plane on a Ponds 482 . Primary is 74 and secondary is 84 , Primary PV is 4.5 and no PV in the secondary . I have changed the IAB , pri and sec to 80`s . Keep in mind that I use Holley jets , so this probably won`t be a direct comparison .

[gsharapa]

Thanks for your insight......So do you think Quickfuel jets flow more or less fuel than Holley jets or the difference is insignificant?

[bingo2]

Holley® jets are broached, flowed, and stamped according to flow rate. NEVER drill jets, as this seriously alters flow characteristics. Stamped numbers are reference numbers and DO NOT indicate drill size.

The above is taken directly from the instruction sheet for a Holley DP carburetor.

My experience with QF jets is the number stamped on the jet coincides favorably with a measurement made in thousands of an inch; a jet stamped 70 has a hole size of .070 inch and the entrance and exit openings are coned. The only exception is the exit opening of the Power Valve Restriction, it is not coned.

[gsharapa]

Interesting that might be my issue than. I looked up a Holley Main Jet 72 and it has hole size of .0755 and if a QF 72 is .072 than you would need a 75 or 76 QF jet to be equal to a Holley jet. Get's worse the higher up you go like Holley 82 is .094. I just can't seem to find any hole size charts on QF main jets. Since my engine dyno ended with Holley jets and I was trying to richen the primaries and went to QF jets but it appears I may have actually leaned it out using the QF jets. I'll go back to Holley jets and see the results.

[bingo2]

Correction!!

My statement regarding the jet size is accurate for air bleeds and other restrictions.

I looked at my notes and quickly measured a number 76 QF Main Jet and it measured at .0805.

Sorry if I added to the confusion.

[gsharapa]

No confusion as a Holley 76 is .084 vs the QF of .080 so it appears the QF is still smaller. I sent an email to QF (as they are closed Sat) to see if they have a chart like Holley. I just find it interesting that my dyno results ended with 70/80s Holley Jets at 681HP and A/F at 13.1. I had this small lean condition on the primary's in 2nd/3rd gear at 3,500 or so and started going up in jet size to see if I could eliminate it but used QF jets and it appears I leaned it out, so makes sense. Guess the only way I will know is to go back to the Holley Jets and start with 72/82s and see how it is. The others are also using Holley Jets so maybe that is my issue that I made worse......

[Bobcat]

bingo2 is correct and I wasn`t very clear . For example , a Holley #88 , #89 and #90 jet all have a .104" dia. hole , but all have different flows . Generally , one jet size change is about 5 to 7 % flow change in cc/min. Another example ... a 72 and 73 Holley jet both have a .079" hole , but the #72 flows about 5 % less cc/min than the #73 jet . It`s the chamfer leading into the orifice( hole ) and the orifice together that also determine actual flow . In other words , Holley rates their jets by flow capacity and not hole diameter as it appears that Quick Fuel does .
Are you sure of the orifice size of .0755 on the #72 Holley jet ? My book shows an orifice of .079" for both the 72 and 73 jets . If you based your jet change on the Quick Fuel being the same flow as the Holley , you`re really leaning it out .

[gsharapa]

I looked it up on the Holley site in their product catalog but they show increased hole size as you go up in number...

Holley Performance Products Catalog

[gsharapa]

Well I might of found my problem. I took front bowl off to go back to Holley jets and decided to check the power valve as long as I was in there. It has a 2.5 vs the stock 4.5. I have run as low as 3.5 but thinking the 2.5 it probably wasn't opening at the 3,500 rpm on the primary causing my lean issue. Think I will go back to the stock 4.5 PV and my original Holley jetting or bump the primary to 72 and try it.

[Hotfingrs]

For a reference point, the other carb in my specs post, is a 1000+ CFM 4150 Pro Systems on the 800 horse motor.