80804-1 850 Ultra XP Tuning

[80427]

Not sure if I made a mistake but I decided to buy a new Holley for my 520 BBC in my 70 Chevelle instead of piecing one together.

The engine specs are 4.35 bore X 4.375 stroke, 10.5 to 1, AFR 265 heads, Performer RPM Howards Hyd roller-243/249, 296/302, .640/.640, 112 LSA camshaft, 4 speed, 3.55 rear gears 275/60-15 rear tires.

This is absolutely a cruiser/driver and really is only as big as it is because the parts were cheap/available but does allow me some flexibility with taller than normal gears in the future. currently idles at 12in/hg with 30 degrees (vac + intial) 34 total right now (has a little rattle at wot but might be due to a little leanness at WOT). May look at increasing the idle timing but need a better starter first. Cruising down the road it is 17+in/hg at 70+mph.

It started with this calibration
ist 80804-1
PMJ-84 SMJ-84
PMAB-.033 SMAB- .033
PIFR-.036H SIFR-.036H
PIAB-.066 SIAB-.066
PPV# 4.5 SPV# 4.5
PPVRC-.069 SPVRC-.069
PE1 .029 SE1 .029
PE2 .029 SE2 .029
PE3 .029 SE3 .029
PE4 Plug SE4 Plug
PE5 .029 SE5 .029
Kill Bleeds-.012 P&S

Is is currently
List 80804-1
PMJ-76 SMJ-92 With extensions
PMAB- .029 SMAB- .029
PIFR-.029L SIFR-.029L
PIAB-.066 SIAB-.066
PPV# 6.5 SPV# Plug
PPVRC-.069 SPVRC-.069
PE1 .029 SE1 .029
PE2 Plug SE2 Plug
PE3 Plug SE3 Plug
PE4 .029 SE4 .029
PE5 Plug SE5 Plug
Kill Bleeds-.012 P&S

I currently have the secondaries unhooked to tune the primary circuit. At low speeds the af is 11/12s. Cruising at 70 the af 13-14 I am looking to move to .027 Ifr but this seems to be getting pretty small and I maybe I should be opening the IABs. Worried about creating more circuit overlap if the air bleeds are increased. It seems to be getting crisper as I lean it out more. I am looking at a 8.5 pv just because the cruising vac is so high.

Thanks for all the help

[rgalajda]

I don’t know if this will help

David Vizard quote
“Vacuum draws fuel from the float bowl through the idle jet ( IFR) . It then communicates with a passage that goes from the idle air corrector jet ( IAB ) to the idle mixture adjustment screw.
In the passage , air from the IAB and fuel mix to form an emulsion . In addition to air from the IAB , air is also drawn in through the transition slot. This, at idle , is above the butterfly where it experiences typical air pressure. The idle mixture screw , when appropriately adjusted, meters sufficient fuel emulsion into the intake airstream to meet the idle needs.
As the throttle opens beyond the idle position , the butterfly begins to uncover the transition slot. The slot then begins to experience the intake manifold vacuum . As a result the slot progressively stops drawing in extra air and instead discharges extra fuel emulsion from the idle circuit to meet the needs of the extra incoming air from opening the throttle.”

I assume your looking to improve low speed / part throttle AFR.
My understanding is that the idle system / transition slot fuel continues through out the cruise to wot. One only needs to adjust the idle mixture screws to see the AFR change at low speed and cruise.
Therefore increasing the IAB slightly could not affect circuit overlap. MAB sizing could effect the earlier start up of the mains , effecting overlap of the circuits.
Some guys use a transition slot restrictor . I wonder what size your transition slot is? Length and width.

[Right hand drive]

[rgalajda]

High Speed Air Bleed 28
Idle Air Bleed Size 70
Marine Use No
Material Aluminum
Model Brawler Street 850
Primary Main Jet 78
Primary Power Valve 6.5
Primary Pump Nozzle Size 33;35
Primary Venturii Size 1.570"
Product Type Carburetor
Secondaries Mechanical
Secondary Main Jet 86
Secondary Venturii Size 1.570"
Supercharged Application No
Throttle Bore 1.75 inch
Warranty Limited 90 Day
UPC 090127009123
Part Number BR-67314

So this is what you get in street version 850. Notice the 78 PMJ, and I bet this would be on the rich side cruise AFR
10 sizes on IAB may be a little drastic

[80427]

I knew it was a $1000 saddle for my $100 horse but I didn't have time to modify a 4781(and actually this is my first NEW carb) I have built a few but they were always used. It is a pretty nice carb and I am getting it tuned in but I was getting small on the ifr and I wondered if I should check. I don't see a reason I can't go to .070 from .066 on the iab. That should move me more into the .031-033 size that seems closer to what I have used in the past.

I have tried it at WOT briefly and it is a bit lean but my plan was to get the idle and primary main circuit A/F reasonably close and then work on the power valve restrictors. Then reconnect the secondary and just tune the secondary jetting at WOT. I typically go to the dyno but it is easier to tune the drivability by recording what I see driving to and from work. It might not be the best carb for what I am doing but I knew I would have to work on whatever I built for this car.

This car will go to the track a few times and may even go on a drag week in a slow class. Never the less, it is more about driving and comfort than MAX hp or it would have been a rectangle port, single plane, solid roller with a dominator. It now has AC and will likely get OD.

Thanks for all your help guys. It is great to find a website were people help, not just suggest we all get fuel injection

[FC-Pilot]

Oh, I still love and recommend fuel injection. Just not “that” type of injection. LOL. That is why I am here as well. I love the technical, not the “monkey see monkey do” mentality. I have been racing with Stack injectors for over 20 years and plan on it for another 20 if I have my way. As seen here,I use a hat every now and again.

Keep working with your carb and report back so we all can learn from what you have done.

Paul

[Right hand drive]

[80427]

List 80804-1
PMJ-76 SMJ-92 With extensions
PMAB- .029 SMAB- .029
PIFR-.030L SIFR-.030L
PIAB-.070 SIAB-.070
PPV# 8.5 SPV# Plug
PPVRC-.077 SPVRC-.077
PE1 .029 SE1 .029
PE2 Plug SE2 Plug
PE3 Plug SE3 Plug
PE4 .029 SE4 .029
PE5 Plug SE5 Plug
Kill Bleeds-.012 P&S

So this is where I am at. At low speed idle the a/f has maybe changed from 11 to 11.5 at low speeds. I am pretty sure the idle circuit is still effecting the a/f at highway cruising because the vac is 17in/hg at 70mph with minimal throttle. I had a 74 jet in it and the a/f at cruise was leaner and it progressed to very lean even with the pv open. I suspect that I need to idle feed restrictor to lean the idle so I can jet it richer on the main circuit. I may try a big idle air bleed to see if I am just maybe too small yet but I doubt it.

So, I am guessing I am on track to add a idle slot restrictor. Not sure where to start.
With 2 small children it takes a lot of time to iron all this out.

On a side note the pvrc is .077, I must have forgot to record it.

[80427]

I think since it is quick I will try a .079 IAB over lunch because I can do it as a quick mod. At least that will tell me where I need to go.

[Right hand drive]

Idle circuit definitely engaged at highway speeds/rpm. Try the .079” iab and note results. Then put .070” iab back in and try .025” mab and note results replicating previous drive test. Those two tests should give an indication of how much transition is contributing and how much mains is contributing. This will determine what circuit to focus on next.