holley 4 barrel question

[63ronin]

Greetings again...

Ya know, we seem to have gotten off azkyinc's original question. But since he's gone back to the 390, maybe some of this will help.

So at this point my Z is actually running pretty good. Starts up with out problems. Idles fine. Decent accel. No major flat spots. I got my motorcycle carb synch tool out and used it to adjust the pilot screw settings. HUGE improvement in idle and off idle accel. Holley says adjust the pilot screws to max manifold pressure. Damned if that didn't work. Was able to adjust idle after that as well (then re-tweak pilot screws). With that done I switched over to the white cam for the accel pump. The Holley flow curve says the total volume injected is lower than the Orange cam that came stock but more than the black cam I tried. Less flow at bottom part of curve with more flow at the higher part of the curve. Seems to work just fine. Oh... and I'm still running the 49 main jets (stock from factory was 51). Have not tried different squirters yet. According to Holley, my carb came stock with the smallest size available. So it's all up from here. I'll keep tinkering for a while and see what happens.

I even washed the windows today so I can see out of the thing...

Later

[Zedyone_kenobi]

Keep in mind the small squirter does not inject less fuel, it injects fuel over a longer period of time. A larger squirter will dump the same volume of fuel faster.

Happy tuning.

[ozconnection]

Keep in mind the small squirter does not inject less fuel, it injects fuel over a longer period of time. A larger squirter will dump the same volume of fuel faster.

Happy tuning.

Exacto!

[clutchdust]

Agreed, you're cheapest, fastest and best end result is to go with a set of stock SU round top carbs. Have never heard anyone say they have a reliable 4BBL driver.

I know this is an old thread but you've heard it now. I took the SUs off mine years ago and put the Arizona Z and 390 on mine. It took a little bit of tuning (with an O2 sensor) to get right but it starts up as soon as I turn the key, no flat spots and good power.

And as for the comment about no 90* manifold on a straight motor, ever think that most carbureted v8s have two 90* turns?

So if anybody has a 4bbl set up they just can't stand, let me know. They work like a champ.

[LeonV]

And as for the comment about no 90* manifold on a straight motor, ever think that most carbureted v8s have two 90* turns?

Ok. That's not a good thing.

It "works", but it doesn't mean there isn't something better...

[Zedyone_kenobi]

Well, V8's are more of a 45 degree slope... if you want to get picky

[LeonV]

The absolute best you can do in terms of intake design is a straight shot into the valve, especially for a wet runner design such as any carburated manifold.

*These images are not mine.

[ozconnection]

True Leon, I agree with you with what you say. Nice pics too btw.

I like my Arizona manifold because it helps boost throttle response and low rpm torque in my engine. For my streetcar, the two small primary throttles help with fuel economy because they can be jetted that way. The secondaries can be tuned richer for a more powerful top end. The manifold divides the engine cylinders into two groups which allows a unique manifold resonance. This resonance boosts cylinder filling of air/fuel mix at low engine speeds.

The floor of the arizona manifold is 90 degrees to the downward flow of the air/fuel mix coming out of the carb. Most street V8's running a four barrel carb will have a manifold floor that is also at 90 degrees to the flow out of the carb. Whilst not optimal for a RACE motor, its more than acceptable for a STREET motor. Just ask Ford, GM, Chrysler etc. An acceptable compromise, especially when there may be other positive attributes which will sway the decision not to use a race style induction on what is predominantly a street driven car and one that I'm very happy to live with.

[LeonV]

True Leon, I agree with you with what you say. Nice pics too btw.

I like my Arizona manifold because it helps boost throttle response and low rpm torque in my engine. For my streetcar, the two small primary throttles help with fuel economy because they can be jetted that way. The secondaries can be tuned richer for a more powerful top end. The manifold divides the engine cylinders into two groups which allows a unique manifold resonance. This resonance boosts cylinder filling of air/fuel mix at low engine speeds.

The floor of the arizona manifold is 90 degrees to the downward flow of the air/fuel mix coming out of the carb. Most street V8's running a four barrel carb will have a manifold floor that is also at 90 degrees to the flow out of the carb. Whilst not optimal for a RACE motor, its more than acceptable for a STREET motor. Just ask Ford, GM, Chrysler etc. An acceptable compromise, especially when there may be other positive attributes which will sway the decision not to use a race style induction on what is predominantly a street driven car and one that I'm very happy to live with.

Sure, as I've said, it "works". While you may understand the ramifications, others just don't.

However, I'd be surprised if there was much of a positive resonance effect with that manifold. With the runners having different lengths, resonance will happen at various engine speeds when looking at different cylinders. This means that while 2 and 5 are in resonance, 1 and 6 are already past the peak and 3 and 4 are coming up to it. FWIW, you can tune pretty much any system for fuel economy at part-throttle and a powerful top end, it's not unique to 4-barrels.

With that said, I'm hoping my next major project will be a V8 with ITBs. 1UZ looks tasty...

[ozconnection]

The Arizona isn't a bad effort really, the runners may not be all the same length as you've noted but they do 'tune' themselves at a number of different rpm's that way. There is a comparison to exhaust headers here. Tuned length promote high end power at a particular rev range. (ie triple weber individual runner manifold) Interference, by design, don't offer a power peak as such but a spread of power over a somewhat larger and lower rev range. (ie Arizona four barrel manifold)

Race vs street setups.

Agreed, most performance carbs can be tuned to offer the best of both worlds to some degree. I just don't hear too many people tuning their triples for economy!

Having, in effect, two carbs in one body just lends itself so easily for this kind of calibration.

[LeonV]

The Arizona isn't a bad effort really, the runners may not be all the same length as you've noted but they do 'tune' themselves at a number of different rpm's that way. There is a comparison to exhaust headers here. Tuned length promote high end power at a particular rev range. (ie triple weber individual runner manifold) Interference, by design, don't offer a power peak as such but a spread of power over a somewhat larger and lower rev range. (ie Arizona four barrel manifold)

Race vs street setups.

Right, an intake and/or header can be tuned for any rpm you want, length depends on which rpm and harmonic you're shooting for (usually 3rd because of packaging limitations). A longer manifold will be "tuned" at lower rpm and a shorter manifold at higher rpm. The bandwidth and magnitude can be altered by varying taper. This can include built-in taper and/or air horns. In the case of a header, "steps" are also sometimes used.

Having different cylinders hitting resonance at different times is not buying you (as) much.

Agreed, most performance carbs can be tuned to offer the best of both worlds to some degree. I just don't hear too many people tuning their triples for economy!

I am.

Having, in effect, two carbs in one body just lends itself so easily for this kind of calibration.

Most carbs have circuits, which can be tuned individually and somewhat independently (e.g. idle circuit doesn't really affect WOT main circuit). There is no reason that a carb can't maximize mpg and power to its utmost potential, unless something went terribly wrong with that carb's design.

If you're interested, I've made a few somewhat in-depth posts on intake and exhaust runner design:

Intake

Exhaust