Blow Through Holley 3310
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Blow Through Holley 3310
I've been running a 650 DP on a blow through system (street car), I just changed to a 3310 Holley, boost comes on the carburetor goes rich secondaries do not open, before I tear into it what do guys think? I'm running about 7 lbs of boost that comes in about 2800RPM. the DP was very hard to tune for the street (for me). hence the change.
Re: Blow Through Holley 3310
The only factory turbo car I've ever seen blow through used 'boost secondaries' and a restrictor to open them at a rate the fuel could keep up. Basically similar to vacuum secondaries except the canister opened the secondaries at some top-hat measured boost level when the linkage setup allowed it. Without the restrictor you'd get a massive stumble as the secondaries opened too fast.
Re: Blow Through Holley 3310
Look at the vaccuum secondary diaphram housing where the linkage rod from the diaphram comes out.
That side is exposed to N/A normal ambient air.
(14.7 psi)
But now with blowthru the upper part above the diaphram is pressurized as boost builds.
Thats why the seco daries won't open under boost.
Either that side of the vaccum diaphram needs to be sealed and "boost referenced". or put the VS carb in a sealed blow thru carb box.
with blow thru the RELATIVE pressure DIFFERENTIAL between the upper and below the vaccuum secondary diaphram has been offset by the boost pressure value as boost builds (boost psi)
Put the DP blow thru carb back on and correct the ignition advance curve. Its probabily lazy (not enough initial base timing and too sliw of an advance curve.
Big camshaft may want locked out timing.
Replacing the 650 carb body with a 750hp carb body kit will increase power.
Not easy to seal and boost reference the vaccuum secondary housing where the diaphram rod comes thru
Also I bet the critical venturi vaccuum passage signal tube (small copper tube in passage)that pokes slightly into the venturi (to amplifiy venturi signal) is missing in the 3310 750 VS carb body
A common fault that causes the VS's to open late and less than WOT.. (specific to most non oem/3310-2, -3-4 etc carbs.) If your 3310 does not have down leg style boosters. your carb has this missing copper tube fault
That side is exposed to N/A normal ambient air.
(14.7 psi)
But now with blowthru the upper part above the diaphram is pressurized as boost builds.
Thats why the seco daries won't open under boost.
Either that side of the vaccum diaphram needs to be sealed and "boost referenced". or put the VS carb in a sealed blow thru carb box.
with blow thru the RELATIVE pressure DIFFERENTIAL between the upper and below the vaccuum secondary diaphram has been offset by the boost pressure value as boost builds (boost psi)
Put the DP blow thru carb back on and correct the ignition advance curve. Its probabily lazy (not enough initial base timing and too sliw of an advance curve.
Big camshaft may want locked out timing.
Replacing the 650 carb body with a 750hp carb body kit will increase power.
Not easy to seal and boost reference the vaccuum secondary housing where the diaphram rod comes thru
Also I bet the critical venturi vaccuum passage signal tube (small copper tube in passage)that pokes slightly into the venturi (to amplifiy venturi signal) is missing in the 3310 750 VS carb body
A common fault that causes the VS's to open late and less than WOT.. (specific to most non oem/3310-2, -3-4 etc carbs.) If your 3310 does not have down leg style boosters. your carb has this missing copper tube fault
Last edited by F-BIRD'88 on Sat Nov 27, 2021 8:25 pm, edited 2 times in total.
Re: Blow Through Holley 3310
Getting ghe 650 DP carb to work with good throttle responce is mostly ignition curve tuning and accelerator pump shot tuning (rate/ timing and volume of shot)
If Auto trans a tight low stall torque converter can be troublesome... correct the stall speed choice.
Manual trans is a matter of driving technique.
Once the timing curve and accelorator pumps are set up.
If Auto trans a tight low stall torque converter can be troublesome... correct the stall speed choice.
Manual trans is a matter of driving technique.
Once the timing curve and accelorator pumps are set up.
Last edited by F-BIRD'88 on Sat Nov 27, 2021 9:00 pm, edited 2 times in total.
Re: Blow Through Holley 3310
Vortech and Paxton both have sealed holley carb boxes for blow thru.
https://superchargersonline.com/wp-cont ... -012-4.jpg
When you check the price of the carb box dialing in that double pump blow thru carb for better throttle responce won't seem so painfull.
Here is a potential market segment for a Made in China "offshore" product knock off.
https://superchargersonline.com/wp-cont ... -012-4.jpg
When you check the price of the carb box dialing in that double pump blow thru carb for better throttle responce won't seem so painfull.
Here is a potential market segment for a Made in China "offshore" product knock off.
Re: Blow Through Holley 3310
A low tech DIY alternative to "boost referencing " the vaccuum secondary housing (or using a sealed carb box) to account for the net effective relative pressure DIFFERENTIAL acting (now differently because of boost) on the diaphram under boost would be to add on a spring UNDER the diaphram in the vac secondary housing.
This lower spring in the vac sec housing will change the way the secondarys open under boost.
The length and spring rate of this lower spring required has to be found and optimized by test trial and error.
The 3310 still needs that critical VS signal tube added to the vac sec signal passage that is likely missing.
The available Holley/ProForm VS 750 HP style replacement Vac Sec type carb body upgrade kit may already have this critical VS signal vaccuum tube installed in the carb body.
It is going to be at least as much (OR More) work time and effort and money spent as if you just corrected the tune and setup using the 650 DP blow thru carb.
Dialing in the DP carb correctly will likely work better overall.
This lower spring in the vac sec housing will change the way the secondarys open under boost.
The length and spring rate of this lower spring required has to be found and optimized by test trial and error.
The 3310 still needs that critical VS signal tube added to the vac sec signal passage that is likely missing.
The available Holley/ProForm VS 750 HP style replacement Vac Sec type carb body upgrade kit may already have this critical VS signal vaccuum tube installed in the carb body.
It is going to be at least as much (OR More) work time and effort and money spent as if you just corrected the tune and setup using the 650 DP blow thru carb.
Dialing in the DP carb correctly will likely work better overall.
Re: Blow Through Holley 3310
if you disconnected the secondary linkage on the 650 it’s not much different than a vac secondary with secondaries that won’t open ...
Re: Blow Through Holley 3310
Take the secondary pod apart take out the little check ball and try the spring that comes stock in that pod, if still won't open go to a lighter spring.liqu wrote: ↑Sat Nov 27, 2021 4:40 pm I've been running a 650 DP on a blow through system (street car), I just changed to a 3310 Holley, boost comes on the carburetor goes rich secondaries do not open, before I tear into it what do guys think? I'm running about 7 lbs of boost that comes in about 2800RPM. the DP was very hard to tune for the street (for me). hence the change.