600-cfm Holley 1850
05-25-2009, 10:43 PM
#1
2nd Gear Member
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Join Date: Jul 2007
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Posts: 322
600-cfm Holley 1850
Hi friends,
What do you think about what is written in this article: http://www.hotrod.com/techarticles/6...ons/index.html
I run this carb, I have a somewhat big camshaft and - even after a successful dyno tuning that increased my peak rwhp by 30 - I am still not 100% happy with the way it drives. Sure I have amazing power when hammering it but my long road trip showed me that launching the car requires reving high and a too light use of the accelerator pedal creates bogs.
I am being difficult but hey, I love that car.
What do you think about what is written in this article: http://www.hotrod.com/techarticles/6...ons/index.html
Because the 1850 is designed with a somewhat lean idle circuit, driveability problems occur when it is used on an engine with a big camshaft and low manifold vacuum because the idle circuit cannot supply sufficient fuel to run at light throttle.
According to Murphy, the best application for this carb a 300- to 400ci engine equipped with stock or mild camshaft timing and 16 to 20 inches of idle manifold vacuum. Ideally, this engine would be in a 3000-pound or heavier car equipped with an automatic transmission and a 3.30:1 or numerically lower gear set. The problem with low manifold vacuum in the 1850 is it requires more idle throttle blade opening, which exposes most of the idle transfer slot to feed sufficient fuel to the engine to keep it running at idle. This often creates an overly rich idle mixture, which leads directly to a lean flat-spot just off-idle. This lean condition often leads to a backfire.
According to Murphy, the best application for this carb a 300- to 400ci engine equipped with stock or mild camshaft timing and 16 to 20 inches of idle manifold vacuum. Ideally, this engine would be in a 3000-pound or heavier car equipped with an automatic transmission and a 3.30:1 or numerically lower gear set. The problem with low manifold vacuum in the 1850 is it requires more idle throttle blade opening, which exposes most of the idle transfer slot to feed sufficient fuel to the engine to keep it running at idle. This often creates an overly rich idle mixture, which leads directly to a lean flat-spot just off-idle. This lean condition often leads to a backfire.
I am being difficult but hey, I love that car.
05-25-2009, 10:54 PM
#2
6th Gear Member
Join Date: Apr 2007
Location: California
Posts: 10,468
It's true.
Idle circuits are the bane of most drivability issues at low rpm and small throttle openings. Much of the fuel comes from the transfer slot, and is regulated by the idle feed restrictors and idle air bleeds. If the bleeds are too big and/or the IFR's too small, then you need more vacuum to draw fuel through the circuit. When the idle circuit is out of whack the idle mixture can't always be set correctly, and the engine will suffer from off idle stumbles or hiccups and low rpm/throttle position cruise issues.
Idle circuits are the bane of most drivability issues at low rpm and small throttle openings. Much of the fuel comes from the transfer slot, and is regulated by the idle feed restrictors and idle air bleeds. If the bleeds are too big and/or the IFR's too small, then you need more vacuum to draw fuel through the circuit. When the idle circuit is out of whack the idle mixture can't always be set correctly, and the engine will suffer from off idle stumbles or hiccups and low rpm/throttle position cruise issues.
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