750 or 830 cfm Quick Fuel Carb

[EBSTANG]

Unless you have your heart set on a new carb I would tune what you have.

You already know from your dyno pulls that the A/F ratio is good at wide open throttle. It sounds like it is rich every where else though. A different carb will not automatically fix this. It will just require a different tune.

The QF carbs are somewhat notorious for rich part throttle. Its a bit of work but that can be fixed by playing with the ifr/iab combo and possibly adding a transition slot restrictor.

Also a 79 main jet may be a bit large for best lean cruise. Do you have a wideband?

I don't know what a wideband is...

Wideband O2 sensor. With it you can measure the AFR of the exahust and help adjusting the carb to run the ideal ratio.

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Ohhh...if I get this carb I was thinking of welding in a bung for that in my exhaust.  Didn't know it was called wideband...could easily be confused with broadband   lollerz

 

[4Vforever]

As I said previously and as others have as well, why not just have your carb built to suit. Annular boosters are good and are usually used on circuit racers running carbs, especially on tight tracks. Your carb can be converted to annular boosters or look into these mini annular booster like I'm going to try for street duties , here's the link   http://www.ebay.com/itm/Holley-QFT-AED-CCS-2300-4150-2-4-BBL-Mini-Annual-Booster-160-12-Hole-/171350913785?hash=item27e54f72f9:g:hO0AAOxyjzNRGBLQ&vxp=mtr

If a new carb is what you really want, then as I said earlier it depends on what you want from the engine and its use. If you want it just as a pure street car then a 750 would be fine, but on engines like these I prefer them to have more CFM and an 850 is what I'd be recommending. One of my main reasons for this though is nobody just sticks with what they have and go about upgrading, so it's better to have a carb capable of taking the upgraded mods later on and tuning it to suit the engine now, then spending more money on carbs as well when upgrading. If you want it tuned for street duties then you must be prepared to loose some of the overall power to get it. Another decision is a throttle body with a choke tower or one with the better flowing HP style throttle body. As I said also, the people that drive on the street and race, mostly will have a different tune for the track and tune it there accordingly. I've also known of others that have a totally different carb and even distributors they bolt on at the track for racing then bolt the street ones back on when the night is over. Also if you contact Quick Fuel you can have any carb built the way you want, black diamond with annular boosters in whatever throttle body configuration you want.

As for widebands, I was given some of the best advice ever regarding them by one of the best builders and racers in the country I worked for. I was one of those people trying to get it spot on and it would drive me crazy not being able to get it exactly where I wanted it. So one day I asked him how he goes about it and his answer actually surprised me. He said sell it to somebody else and tune it to the plugs as the plugs don't lie. He'd been down the exact same path trying to get A/F ratios perfect and in the end said to himself, why. If the engine is running right and is burning properly at peak RPM then it must be right. He also said after going back to doing it that way his times were in fact better. Obviously a street engine different, but when it's a high performance street engine of course there's going to be richness somewhere if you're chasing ultimate power from it. So I've never used one since. I personally know of a 406 SBC that's had that many different people (some very well known in the industry) and a heap of different carbs or different mods on it trying all types of ways of tuning it that the best it's ever ran is when I tuned it by the plugs. Of course it's going to be rich somewhere, but he says it runs great and it's now even using less fuel than it's ever had. To say he's pissed at spending all that money on widebands, different and modifying carbs and many different experts and dynos would be the biggest understatement ever. After I tuned the engine and he had it going for a few weeks he actually rang me to apologise for not listening to me at the start. Thing is I'm not a tuner, I'm a machinist/engine builder by trade. It's one of the reasons I'm not really into chassis dyno BS, just engine dyno as a base just after when the engine has been built.   

So as I said as pure street engine and no further mods going to be done, then go for a 750, but if some strip action or upgrades in the future, then the 850 makes sense now. Either way the carb is going to need to be properly tuned to suit your application.

 

[EBSTANG]

As I said previously and as others have as well, why not just have your carb built to suit. Annular boosters are good and are usually used on circuit racers running carbs, especially on tight tracks. Your carb can be converted to annular boosters or look into these mini annular booster like I'm going to try for street duties , here's the link   http://www.ebay.com/itm/Holley-QFT-AED-CCS-2300-4150-2-4-BBL-Mini-Annual-Booster-160-12-Hole-/171350913785?hash=item27e54f72f9:g:hO0AAOxyjzNRGBLQ&vxp=mtr

If a new carb is what you really want, then as I said earlier it depends on what you want from the engine and its use. If you want it just as a pure street car then a 750 would be fine, but on engines like these I prefer them to have more CFM and an 850 is what I'd be recommending. One of my main reasons for this though is nobody just sticks with what they have and go about upgrading, so it's better to have a carb capable of taking the upgraded mods later on and tuning it to suit the engine now, then spending more money on carbs as well when upgrading. If you want it tuned for street duties then you must be prepared to loose some of the overall power to get it. Another decision is a throttle body with a choke tower or one with the better flowing HP style throttle body. As I said also, the people that drive on the street and race, mostly will have a different tune for the track and tune it there accordingly. I've also known of others that have a totally different carb and even distributors they bolt on at the track for racing then bolt the street ones back on when the night is over. Also if you contact Quick Fuel you can have any carb built the way you want, black diamond with annular boosters in whatever throttle body configuration you want.

As for widebands, I was given some of the best advice ever regarding them by one of the best builders and racers in the country I worked for. I was one of those people trying to get it spot on and it would drive me crazy not being able to get it exactly where I wanted it. So one day I asked him how he goes about it and his answer actually surprised me. He said sell it to somebody else and tune it to the plugs as the plugs don't lie. He'd been down the exact same path trying to get A/F ratios perfect and in the end said to himself, why. If the engine is running right and is burning properly at peak RPM then it must be right. He also said after going back to doing it that way his times were in fact better. Obviously a street engine different, but when it's a high performance street engine of course there's going to be richness somewhere if you're chasing ultimate power from it. So I've never used one since. I personally know of a 406 SBC that's had that many different people (some very well known in the industry) and a heap of different carbs or different mods on it trying all types of ways of tuning it that the best it's ever ran is when I tuned it by the plugs. Of course it's going to be rich somewhere, but he says it runs great and it's now even using less fuel than it's ever had. To say he's pissed at spending all that money on widebands, different and modifying carbs and many different experts and dynos would be the biggest understatement ever. After I tuned the engine and he had it going for a few weeks he actually rang me to apologise for not listening to me at the start. Thing is I'm not a tuner, I'm a machinist/engine builder by trade. It's one of the reasons I'm not really into chassis dyno BS, just engine dyno as a base just after when the engine has been built.   

So as I said as pure street engine and no further mods going to be done, then go for a 750, but if some strip action or upgrades in the future, then the 850 makes sense now. Either way the carb is going to need to be properly tuned to suit your application.

Thanks for taking the time for that answer.  If I was going to keep the Holley 850 and have it tuned for my application, I would have to send it out to a tuner who would have to add all the air bleeds and other modifications so that it could be done properly.  Living in the suburbs of Philadelphia in the Northeast corridor of the United States, NOTHING is cheap. (unless you do it and are capable of doing it yourself) This is why I was leaning towards the Quick Fuel, as I stated earlier. Either way I most certainly will be looking at the plugs more than I ever did before as my engine builder just taught me, last week, much of what you just stated.  I find it interesting and by picking brains, that is how I've learned what I know today. I again thank you and know your words have not fallen upon deaf ears! Istill think it may be cheaper to buy the QFT carb and sell my Holley as labor costs are so high here.

 

[Stanglover]

I would just like to ditto EBSTANG's reply to 4Vforever's excellent explanation above. He has responded to several of my questions with clarity and yes, from people like him and many others, I have learned so much over the last 2 years. I for one, have a much better understanding of the mysteries of carburation and so much more.

Thank you for passing on your experience.

Geoff.

 

[4Vforever]

If you're needing to do your carb from scratch with adjustable air bleeds and multi stage emulsion and going to billet metering blocks and throttle plates, then going the Quick Fuel route is probably the best and cheapest way around it. Plus the Quick fuels are all aluminium construction as well which is not only lighter, but helps with fuel temperatures as well. As you stated you can sell your carb to help offset the costs. While I'm a huge fan of Quick Fuels, I'm an even bigger fan of a carb that works properly and does its job properly. In fact carb technology keeps changing so much lately it's Interesting keeping up with it all. I've actually just been having experience with a couple different types of Holley's lately that have really piqued my interests back to Holley, but for the money Quick Fuels are hard to pass up on.

So if you don't see exactly what you're after on the QF site like the black diamond with annular boosters, then as I said contact them and they'll give you exactly what you're after. Also other things you'll need to decide on are the body type, choke horn or HP style, if going for a choke electric or manual choke and vacuum or mechanical secondaries. Also as I said earlier if it's just a pure street engine and no further mods are going to be done  than a 750 would be OK, but if any sort of racing or further mods are wanted down the track then an 850 would be the best, as either way it will still need to be tuned. This is why during the design stage of the engine I make sure that's what the customer is after, then before the actual build itself starts I make absolute sure that no other mods are planned down the track before any parts are ordered. I've seen it and heard it where I've done rebuilds, then a few months down the track where their minds have changed and wished they listened to me the first time and built it to handle further upgrades as they're now up for a whole heap of new parts. It's the reason my own personal build is way overkill for its first incarnation. I just want you to pick the right carb for not just your needs now, but in the future as well. 

Just tune by the plugs and keep an eye on them around town driving too. With the extra features of modern carbs like adjustable air bleeds and emulsion, getting a better fuel curve is even more achievable, it just requires more tuning by reading the plugs at different parts of the rev range and dialling in the all the adjustable pieces to suit and even PV's and pump cams can have an impact on this as well.Another thing to make sure of is the ignition curve as it all plays a part in the engines overall tuning parameter. For me though I just tune to what the plugs tell me and has worked for me this way for over 15 years. Let us know what you decide on and keep us informed how it goes and if need be plenty of people on here to help get it right.

 

[Jeff73Mach1]

An 850 would be fine. Jetting is easily adjusted. If you have one, 30-40 bucks in parts should get you in the ballpark. Try going with stock settings of 72 in the primaries, 6.5 power valve in the front, plug the rear power valve and go to 82 jetting in the rear. Put in fresh plugs and run it and then read the plugs and adjust from there. This is all just my opinion.

A 750 will leave power on the table, but that isn't a big deal. It will run better on the street. Under hard use, a undersized carb will lean out at the top end. I love spinning my engine up past 7K and hearing the screaming of women and children, so I stick with a larger carb.

 

[EBSTANG]

What cam specs are you using?

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I found the specs...

Bore 4.030

Stroke 4.000

 

Cam Intake Duration @.050         230.000

Cam Exhaust Duration @.050      236.000

Cam Intake Lobe Lift                   0.340

Cam Exhaust Lobe Lift                0.347

Intake Rocker Ratio                     1.730

Exhaust Rocker Ratio                  1.730

Intake Push Rod                         7.950

Exhaust Push Rod                       7.950

Intake Valve Lift                          0.588

Exhaust Valve Lift                       0.600

Intake Valve Lash                        HYD

Exhaust Valve Lash                     HYD

Intake centerline                          107.000

Lobe Separation                          110.000

 

Compression 10.75:1

 

[EBSTANG]

Do you have the Brake Specific Fuel Consumption (BSFC) numbers from the Dyno Pulls? If so, they would be very helpful in tuning the carb you have, +1 on Tommy K's post. As Tommy said, the jetting sounds like it may be too much. Chuck

EDIT: What 850 do you now have and what style boosters are installed, down leg or down leg with a step?

I don't think I was given the BSFC numbers...I don't know what they are even if I had them.

I have a Model  # 4150 (4781-8 LIST) 850 cfm, double pumper, 4 corner idle carb w/ mechanical secondaries

As I stated earlier I sent this carb to AED and they supposedly tuned it to match my build. (that is what they were told to do) AED sent a sheet which stated they rebuilt with these specs...

Jets Primary-79, Jets Secondary-90, Primary Idle Bleed-.078, Primary High Speed-.028, Secondary Idle Bleed-.070, Secondary  High Speed-.025, Power Valve Primary-4.5, Squirter Primary-.031, Squirter Secondary-.036, Air/Fuel Primary-13.2, Air/Fuel Secondary-13.0

They did a "Wet Flow,"  "Rebuild," and "Test Run."  I don't know what that really means.

If this sounds good to any of you, I will be selling this carb once the new one is installed and running good.  It is my impression that the Quick Flow carbs are much easier to tune (cost me less if I am not the tuner) or would be much easier to learn if I decide over the next few years to learn how to tune myself.  The advancements made with new tech in carbs, regarding tuning, and the art of tuning should make this much easier for the hobbyist.  Thoughts...?

If I could get $300-$500 for this rebuilt carb it would certainly offset the cost of the new and someone else would get a perfectly good Holley 850 which may be better suited for their build. My dyno pull video on this site was done with the Holley.

Some additional reading for those who were interested in Chuck's request for..."the Brake Specific Fuel Consumption (BSFC) numbers from the Dyno Pulls?" My BSFC #'s are listed at the end with the other Dyno Data.

Reading a dyno sheet

The data display on the dyno's computer screen can be printed out for your reference. Understanding what each column represents is critical in getting the most from your dyno time.

Most dyno operators will print a form with columns of numbers for the customer or tuner to reference. Reading the dyno sheet is fairly simple if you understand the categories. Dyno printouts come in various different formats but inputs or categories are usually consistent: 

Engine RPM refers to the engine revolutions per minute (RPM) and serves as the reference to which all readings in the same row were taken. 

Torque (either corrected or uncorrected) should be represented in a subsequent column. We prefer to see uncorrected torque and corrected torque in separate columns. This gives a visual indication that everything is recording correctly. If you happen to see a difference between the corrected and uncorrected torque values of more than 50-ft/lbs, there may be a problem that needs to be checked out.

Horsepower isn’t measured by the dyno, but rather the torque and rpm readings are run through a formula to calculate the horsepower. This number reveals much about your engine. Pay attention to where in the RPM range your engine hits peak horsepower and torque. Making component changes like fuel systems or intake manifolds can move your power band up or down in the RPM range. There is a large difference between horsepower numbers from an engine dynamometer and a chassis dynamometer because of the numerous variables that exist in the vehicle’s drivetrain. Chassis dyno horsepower numbers should never be used to verify engine dyno horsepower numbers.

Fuel Flow, displayed in pounds per hour (lbs/hr) can be a very useful means of balancing multiple carburetors on a single engine, or the data can be used to refine electronic or manual fuel injection systems. 

Brake Specific Fuel Consumption (BSFC) refers to how efficient fuel was turned into horsepower. While this data will not tell you if the engine is rich or lean, it will explain how efficient or less than efficient the fuel consumption was as it relates to targets set for type of fuel and output power of the engine.

Mechanical Efficiency (ME%). This reference number is simply brake horsepower divided by indicated horsepower. Used by many engine tuners working on fuel use in their engine programs. Typical stock street engines register 70% to 80% mechanical efficiency. Above 80% of mechanical efficiency indicates an efficient engine. 

Barometric Pressure. This column represents the local barometric pressure at the time of the test. Many engine dynamometers have a weather station that provides the barometric pressure for the location of the dynamometer on that date and time of the test. It is an uncorrected number and displayed as raw data.

Dyno Data

Mustang Dyno, loadable type w/ engine on the stand (horsepower @ the flywheel) 

DEPAC # 54          Tst# 9304             2700 to 6000 RPM

CRATE.CFG           FUEL SG .715       Time 8.5

BARO:29.5           A tmp:87              jet:0

Customer:            Engine: 408          Clev IGN Timing:30

Comments: Timing File:

Manifold: Air Gap

Carb: Holley AED

Spacer: None

Muffler:

Cam Degree:

Header: MME EMC

Air fuel:

RPM                      C TORQ                               C PWR                  BSFC                     OIL P                     WAT T

BAND                    Ft-Lbs                    CHP                       #/HrHP                 PSI                         Deg F

2728                     564.2                    293.0                    0.399                    80.9                      148.4

2800                     572.1                    305.0                    0.4                         81.5                      149.2

2900                     575.6                    317.8                    0.43                      81.4                      49.2

3000                     582.1                    332.4                    0.49                      81.5                      150.2

3100                     581.5                    343.3                    0.52                      82.6                      149.7

3200                     581.7                    354.5                    0.56                      83.6                      149.7

3300                     587.4                    369.1                    0.59                      84.6                      150.4

3400                     592.0                    383.3                    0.61                      85.4                      150.7

3500                     591.7                    394.3                    0.5                         85.4                      150.7

3600                     589.0                    403.7                    0.4                         86.2                      151

3700                     591.3                    416.6                    0.34                      86.3                      151

3800                     589.5                    426.6                    0.29                      86.3                      151.1

3900                     593.1                    440.5                    0.2                         86.2                      151.9

4000                     598.0                    455.5                    0.3                         85.6                      151.9

4100                     597.9                    466.7                    0.33                      85.4                      151.5

4200                     599.7                    479.6                    0.3                         85.1                      152.3

4300                     597.1                    488.8                    0.34                      85.1                      151.9

4400                     595.3                    498.8                    0.36                      83.8                      151.9

4500                     595.4                    510.2                    0.38                      82.4                      152.7

4600                     588.2                    515.2                    0.39                      81.9                      152.8

4700                     587.3                    525.7                    0.39                      81.6                      152.8

4800                     588.5                    537.8                    0.4                         81.6                      152.8

4900                     584.6                    545.4                    0.4                         81.1                      153

5000                     570.1                    542.8                    0.41                      80.8                      153.4

5100                     565.6                    549.3                    0.42                      80.9                      154

5200                    561.2                    555.8                    0.43                      80.5                      154.2

5300                     554.7                    559.8                    0.43                      80.4                      154.2

5400                     544.7                    559.5                    0.44                      80.1                      153

5500                     536.8                    562.3                    0.44                      80                          154.7

5600                     528.1                    563.2                    0.46                      80.7                      154.9

5700                     521.8                    566.2                    0.48                      81.1                      154.9

5800                     515.3                    569.1                    0.48                      81.1                      155.1

5900                     509.4                    572.2                    0.49                      81.1                      155.1

6000                     500.4                    571.6                    0.49                      81.3                      155.1

 

[turtle5353]

I am running an 850 quick fuel on my 408. FWIW.

 

[EBSTANG]

I am running an 850 quick fuel on my 408.  FWIW.

do you take it to the track?...or just street use?

 

[turtle5353]

Street only. Few burnouts and car shows.

 

[EBSTANG]

Street only. Few burnouts and car shows.

Exactly my use also. I'm getting, from builder, performance garage owner & his mechanics and even QFT themselves, that it is better to under carb a street engine than to over carb. All emphatically keep telling me that the 750 will be perfect for street use but most guys will put on a carb which is too large.

 

[turtle5353]

Street only. Few burnouts and car shows.

Exactly my use also. I'm getting, from builder, performance garage owner & his mechanics and even QFT themselves, that it is better to under carb a street engine than to over carb. All emphatically keep telling me that the 750 will be perfect for street use but most guys will put on a carb which is too large.

I talked to Tnfastback (Ray) about a year ago on the phone. We talked about his carb on his 408 and how mine was acting finicky on the street. He told me his did the same think with his 850, he dropped to a 750 and said its much more street friendly. Maybe you can PM him and ask him about his carb. He has very similar build to yours and mine. I never swapped to a 750 to try it because I already spent a lot of money on the 850 quick fuel.

 

[EBSTANG]

Street only. Few burnouts and car shows.

Exactly my use also. I'm getting, from builder, performance garage owner & his mechanics and even QFT themselves, that it is better to under carb a street engine than to over carb. All emphatically keep telling me that the 750 will be perfect for street use but most guys will put on a carb which is too large.

I talked to Tnfastback (Ray) about a year ago on the phone. We talked about his carb on his 408 and how mine was acting finicky on the street. He told me his did the same think with his 850, he dropped to a 750 and said its much more street friendly. Maybe you can PM him and ask him about his carb. He has very similar build to yours and mine. I never swapped to a 750 to try it because I already spent a lot of money on the 850 quick fuel.

Thanks for the lead, he'll certainly be able to give some hindsight advice. Just what I'm looking for!