Holley 3310 jetting for 360

[bbeep71]

I have a 66 Cuda with a 360. CompCam 280 Magnum cam and 9.5 compression. The 3310 runs rich(plugs are black) with stock from Holley 3310. The Holley 600 1850 carb on it runs great(plugs not rich) but low on top end power. I would like to run the 3310 for better power. What jets and tuning have you found good on a 3310 setup like this.
Thanks

 

[Dana]

70 pri 76 sec 6.5 pv

 

[69FBCuda]

I have a 66 Cuda with a 360. CompCam 280 Magnum cam and 9.5 compression. The 3310 runs rich(plugs are black) with stock from Holley 3310. The Holley 600 1850 carb on it runs great(plugs not rich) but low on top end power. I would like to run the 3310 for better power. What jets and tuning have you found good on a 3310 setup like this.
Thanks

What is your initial timing and vacuum ?

 

[AJ/FormS]

My streeter runs a little fat with 72/80/10.5PV with alumunum heads@10.9Scr,a 230@.050 cam, TTIs, dual 3s all the way, and fresh cold air, which made a huge difference. My plugs have over 100,000 miles on them and are fired by a big yellow Accell sq top. I run a mechanical pump,a 3/8 line, and a slightly low wet fuel level. Also, I run a minimum coolant temp of 205*F,and a max of 207; my heads like the heat.
You're right,the 1850 was a serious power loss; I modded mine for fuel economy and use it on long trips.

 

[Mattax]

What is your initial timing and vacuum ?

and at what rpm?

What jets are in it now? and which revision 3310 is it? That's the number after the dash. such as 3310-3.
And no I'm not just shooting off theoretical. I ran that cam in my previous 340 both on a dyno and at the track.

 

[318willrun]

Do you have a metering body in the back, or just the front?

 

[bbeep71]

The carb is 3310-11. It has a block in front and plate in back. It is totally stock from Holley. The timing is about 20deg. and vacuum is around 10 in. in drive at around 900rpm. The MP electronic dist. has about 14 mech. all in around 2500rpm. I believe the factory pri. jets are 70 with a sec.plate of 134-21(whatever that is).

 

[Mattax]

The carb is 3310-11. It has a block in front and plate in back. It is totally stock from Holley. The timing is about 20deg. and vacuum is around 10 in. in drive at around 900rpm. The MP electronic dist. has about 14 mech. all in around 2500rpm. I believe the factory pri. jets are 70 with a sec.plate of 134-21(whatever that is).

Mine was a -3. I don't think there were major changes between 3 and 11 but don't know that for sure.
Sec. Plate 134-21. Holley's catalogs shows that as equivalent to jet size 75 but likely it's miswritten and not right. 76 Jet is probably more like it.
Secondary metering plate vs Secondary Metering Block?
Best runs were with 74 primary jets.
However, yes the plugs would get black on the street. I beleive that was almost all due to the 'idle circuit'.
In part, this was addressed when fixing the high idle speed like you have.
We did the old school procedure (described in Urich & Fisher Holley Carburetors and Manifolds)
Drilled small holes in the primary throttle blades close to the idle bleeds. This let the engine run with less throttle opening.
But then off-idle was too lean - the engine would want to die on any uphill.
So we decreased the idle air bleeds by sticking wires in each of the primary idle air bleeds until it ran well. Eventually I had new bleeds made and pressed them in but really there's no need. I've got two carbs now with wires in the air bleeds. Just wrap the wires so they can't move. I'll post pic if you want.

Timing. This is the tricky part for getting the carburation to work right at idle and on the street.
The Chrysler made Mopar Performance distributors are good, whether its the street unit with vac advance or the tach drive unit.
If you have the Mallory made Mopar perfmance distributor, its only OK.
I can walk you through any of them.
Initial timing with that cam and a low comp 360 should be around 16 - 18* BTC. Vacuum advance plugged.
Total mechanical (initial+ mech. adv) should be 32 - 36* between 2600 - 2800 rpm on a Chrysler built distributor.
When using vac advance in this situation, attach to ported source on the carb. Adjust it as described here:
https://www.forabodiesonly.com/mopa...mopar_performance_instruction-png.1715175314/
If using the Mallory built distributor, may have to dial in less vacuum advance because the mechanical curve is too fast.

With the timing curve closer to what the engine wants, it will be easier to cleanup the carburetion.

 

[Mattax]

I bet the 1850 could be tuned for better top end as well.
its good to experiment.

 

[dano]

Wouldn't a larger vacuum secondary carb run leaner than a small one? Floats too high, too much fuel pressure, choke not operating correctly, etc? Over fueling may not be from jet size.

 

[Mattax]

Over fueling may not be from jet size.

True.

Wouldn't a larger vacuum secondary carb run leaner than a small one?

It shouldn't, but it does depend somewhat on the assumptions made when deciding the out of the box calibrations.
The big differences will be at low throttle and at wide throttle near the top of the rpm range.
Low throttle:
A larger venturi will need the engine to be higher in the rpm range before the air is moving fast enough past the booster to start the mains.
That means the car will be on the idle/transition circuit more with a carb that has larger primaries. If so, that means a little more pump shot will also be needed.
However initiation of the mains can be adjusted somewhat with the size of the main air bleeds, the location of a 'kill bleed' and 'emulsion holes'.

Wide Open Throttle:
The smaller carb may be more restrictive at wide open throttle in the mid to top of the rpm range.
For sake of arguement lets assume it is noticibly so. In which case the velocity past the boosters will be higher and therefore pulling stronger on the fuel than in the larger carb.
So if both carbs had same jetting and airbleeds etc, the the smaller carb would be richer and larger carb would be leaner. This is because the volume of air pulled at any given rpm at WOT would be the same.*
In reality, the AFR at wide open throttle can be made into a straight line by using the right size main air bleed to compensate for a tendency to drift lean or rich at the top.

* Argueably the mass air flow could be effected if the restriction is high enough to alter VE, and I don't know what happens then.

 

[crackedback]

Do the easy stuff.

Lower the float level
Make sure fuel isn't dripping from boosters.

 

[69FBCuda]

If you really want to know "when" it is running rich, run it wot then kill it before any significant idle time occurs. Read the plugs before running again.