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Dialing in the 850 brawler on my 383 - afr, 4 corner, jetting and PV q's

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Hi there- finally got the wideband hooked up.. car is still very rich-

383 11:1 comp 288HR holley 850 DP brawler

currently idle afr is around 13.5-14. I have a manifold vac gauge hooked up - when i dial in the pass rear screw all the way in the vac starts to rise indicating im on the right path - so are the rear jets too rich?

I have a jet kit here-

hooking up tach now - its idling pretty low all things considered- not even sure what PV came with it so I have a 3.5 here im going to install since I have around 10 inches vac..

Im presuming I need to dial the carb in first then the PV- correct?
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Main jetting has absolutely nothing to do with idle rich or lean.

Typical performance engine will not like being set to idle at highest possible vacuum via the mixture screws....it will then be too lean heading into transition as the throttle is opened.
Adjusting for highest vacuum and leaving at that setting is pretty much just a stock engine thing.

When you make idle mixture adjustments, make all 4 corners the same before judging the vacuum reading....you need to adjust them all in similar increments a little at a time.
Once you reach highest vacuum reading, then back them all out richer by 1/16 to 1/4 turn, letting the engine behavior under load guide you.

If idle or transition needs adjustment beyond what the mixture screws will provide, then it needs different idle feed restrictors or idle air bleeds.

Main jetting is for adjusting 2500-3000 rpm and up cruise and for WOT, with WOT help being added by the Power Valve Channel Restrictions.
I tune WOT jetting with main jets to find peak HP(dragstrip MPH), then to make it more fuel mileage friendly in a street application increase Power Valve Channel Restriction sizes while reducing main jet to get your mileage.
 

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Discussion Starter · #3 · (Edited)
understood re jets and idle etc.. ok i wont use the vac gauge then.. now I have all 4 corners around 3/4 turn out-

for some reason the wideband quit showing me numbers, im wondering if the exhaust gasket started drawing in air, the 02 sensor was welded after the 3 bolt flange, i might move it up to the main collector to before it was extended where the flange connects.

eric didnt u send me a link to the tuning steps of the 4 corner in a prev thread? ill have to look it up- would a higher vac PV open at higher vac and offer better cruise economy?

Ill have to address the afr issue before anything else.. prob weld another bung into the exhaust
 

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550 RPM idle is a characteristic of a factory grocery getter cam, certainly nothing that requires a carb with 4 corner idle.

Four corner idle is used for engines running big cams so that to achieve the needed idle speed the primaries are so far open they are using up the transition circuit.

If you’re not getting AFR readings either there is a failure of gauge, sensor or wiring or the sensor is too far from the engine, unless this is a heated sensor they depend of very hot exhaust gasses to operate. If you can’t keep them really hot you get no reading. An over rich mixture tends to burn hot in the exhaust system as that’s where the excess fuel is being burnt so it is likely that as you leaned out the idle the temps in the exhaust plumbing went under what initializes the sensor to function. Long tube headers can be a pain in this regard as the collector is a pretty good distance from the exhaust port and all that surface area of primaries and collector are bleeding temperature like crazy at idle.

First thing that crosses my question machine is what is the cam, compression, and exhaust system?

Bogie
 

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Discussion Starter · #6 ·
Hi bogie, tha ks.. all info in first post. First step is to pull carb and very transfer slot, then work from there.. might be in a situation with open transfers and too rich ... how a vic jr on and 850dp and comp 288hr can idle so low must be sth wrong, right?
 

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Hi bogie, tha ks.. all info in first post. First step is to pull carb and very transfer slot, then work from there.. might be in a situation with open transfers and too rich ... how a vic jr on and 850dp and comp 288hr can idle so low must be sth wrong, right?
I guess that depends on how your doing this. Just sitting in the garage messing around I supposed you could get a 550 idle but it isn’t a quality you’d take out on the street. On the other hand especially if this engine attached to an auto gear box it isn’t going to be happy with that in gear. So I really don’t know what you 550 revs means. I run the HOT cam it will idle at 700-750 in gear it doesn’t like less out on the street. I guess the other possibility is the cam you bought ain’t the cam you got.

Bogie
 

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eric didnt u send me a link to the tuning steps of the 4 corner in a prev thread? ill have to look it up- would a higher vac PV open at higher vac and offer better cruise economy?
It works exactly opposite of that.
Power valve is held closed by vacuum, as soon as vacuum level drops below the powervalve rating, it opens and provides additional enrichment fuel to the main boosters, since vacuum only drops when you accelerate and need more fuel.
The closer the Power valve rating is to the cruise vacuum reading, the sooner it opens,..... or to put it another way If the valve rating is too close to your cruise vacuum reading, it ends up opening at every little mild acceleration you do, murdering fuel mileage.

how a vic jr on and 850dp and comp 288hr can idle so low must be sth wrong, right?
Nope, everything is fine....as you just demonstrated, the Vic Jr can work at low RPM a lot better than magazine published BS and internet chatter would lead you to believe.
 

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Discussion Starter · #9 ·
eric gotcha thanks - im going to relocate the 02 bung.. I did buy a 3.5 PV, yes my mileage is being murdered literally, and not because this is a thirsty motor, its beyond. 10 mile round trip to long beach and back = between 1/8 and 1/4 tank of gas not kididng..
 

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Personally, Id ignore the AFR gauge at idle and set it for best idle by ear and throttle response around 750-850rpm.
AFR guages are good, but they lie sometimes, epsecially at idle when the burn isn't usually complete anyway. THey are best suited for mid to full throttle while timeslips are best for min jetting.
 

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Discussion Starter · #11 ·
gotcha - im gonna at least try get it hooked up for cruise etc- i do have at least 20 initial to help with the burn.. but something is killing the mileage.. going to try get a o2 in there today or 2moro -

thanks for the tips -
 

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Generally, with a Holley carb, mileage is going to start with figuring out best peak power jetting, then taking main jet back down while increasing Power Valve Channel Restrictors (PCVR's)to make the WOT mix back to what it needs.
Then the main jet is smaller and doesn't murder mileage so bad.

Along with a working and well dialed in vacuum advance.

Does the Brawler carb you have come with replaceable PCVR's in the metering blocks??
 

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I have an Innovate dual wideband, and it says that idle readings aren't reliable... so don't obsess over that.
For cruise, you want it around 14.5 according to everything I've read.
At WOT you want 12.5 for the best power.
I'd assume that in-between cruise and WOT, something in the 13's is probably good.
 

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eric gotcha thanks - im going to relocate the 02 bung.. I did buy a 3.5 PV, yes my mileage is being murdered literally, and not because this is a thirsty motor, its beyond. 10 mile round trip to long beach and back = between 1/8 and 1/4 tank of gas not kididng..
IMHO the 850 is way too big for a 383 unless it is a strip warrior only. I run an 830 on my .030 over 440 with a flat tappet solid lifter cam, crane gold race rockers that is street/strip driven. PV is determined by vac @ idle in gear on an automatic trans, go 1-1 1/2" below that #, manuals are different.
 

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Discussion Starter · #15 ·
I agree - I have a 750 vac seconday on the shelf ... i just bought this at the time cos holley was out of the 750s, and with a 496 on the table this carb would be perfect.

I was initially trying to get max hp on this too - once i reach an acceptable number ill tone it down a little on the carb-

thanks ill forego the idle afr then - need to swap in the 3.5 but swamped at the shop..

IMHO the 850 is way too big for a 383 unless it is a strip warrior only. I run an 830 on my .030 over 440 with a flat tappet solid lifter cam, crane gold race rockers that is street/strip driven. PV is determined by vac @ idle in gear on an automatic trans, go 1-1 1/2" below that #, manuals are different.
 

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I agree - I have a 750 vac seconday on the shelf ... i just bought this at the time cos holley was out of the 750s, and with a 496 on the table this carb would be perfect.

I was initially trying to get max hp on this too - once i reach an acceptable number ill tone it down a little on the carb-

thanks ill forego the idle afr then - need to swap in the 3.5 but swamped at the shop..
 

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Frankly for a street engine the 800cfm Edelbrock AVS-II is perfect with its annular boosters and the ability to play both with jet and metering rod sizes and with the metering rod springs. So you can manage the fuel flow to the venturies very closely and where which metering rod step trips on or off. If you’re a sharp tuner you can do your own springs and mod the steps to making your own metering rods. So if you’re a sharp tuner you can get this thing to function almost like fuel injection.

Bogie
 
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