Tuning with jets, Power valves and an O2 guage

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Kern Dog

Kern Dog

Build your car to handle.
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Time for tuning!
Now that I have the car up and running, I'm trying to tune it. I installed an AEM wideband guage and have a bunch of jets, power valves and accelerator pump cams.


Here is a recap. 440 based 493 with Edelbrock heads, RPM intake, 2" TTI headers and 10.7 compression. Lunati solid lifter cam with 261*/271* @ .050 556./.578 lift INT/EXH. MP electronic ignition with chrome ECU New wires and plugs. Barry Grant Speed Demon 850 VS carb w/o choke. 85/93 jets stock with 6.5 Power Valve.

I broke in the cam last week. The engine ran hot during the first 15 minutes of run time, so I shut down and let it cool. The same thing happened on the second run. Fuel was boiling in the line which was partlt due to having no fan shroud along with the engine running lean. I have since fabbed up a fan shroud.

Today I installed an AEM brand wideband Air/Fuel guage. It has an oxygen sensor mounted in the RH header, 6" forward of the collector flange. I mounted the guage in a panel I put in place of the ashtray.
 
The first readings I got were with the carb jetted to 86/94 with a 6.5 power valve. The idle mixture screws were 1.25 turns out. the IN GEAR A/F reading was 15.0 +/-.
After backing the screws out to 2 turns total, the numbers bounced between 14.0 and 15.0, but it pegs the guage to the LEAN side when I lightly power brake the engine.

TEST 2:
Since the idle vacuum was now around 5" in gear, I switched to a 3.5 power valve. Idle mixture screws now at 1.25 to achieve best vacuum and A/F #s of 14.5 to 14.9 in Park. In gear idling, it went past the limits of the guage, 17.0 +.

Test #3:
I switched the primary jets to 88s. The idle #s in Park were still in the same range as above, but the IN GEAR #s dropped to the 15.5 to 16.0 range. It seems to me that since the A/F numbers improved (Got richer) with larger jets, I'm heading in the right direction. It just seems that #88 jets seem pretty big already.
 
A 500 -ish RB ,with that can timing NEEDS FUEL. Borrow,beg a 850 Holley/Demon double pumper.
 
I don't even think a 950 quick fuel would be too much, how bout you Tim?
 
I have a 499 stroked/bored 400 with similar cam.
I run an Holley 850 DP, and yes that combo wants fuel.

I too opted to run a wideband and after reading some articles about some engines can idle/transition well as lean as 14:1 there is no way with a carb setup that's going to happen.

I now idle just above 13:1, had to increase my pump shots ( to cover that initial lean condition when getting on the gas ) dropped my PV's ( running front & rear for street driving ) and I would have to check my notes on jetting.

Also, what's you timing set at?
You are going to want ( someone back me up on this? ) more initial timing than a standard big block.
I currently run 20 degrees initial 38 total mech. adv. only no vacc.
 
here are my pennies worth. when you had the 6.5pv it was open at idle then you put in a 3.5pv and it stayed closed. this would be the reason it was way lean and you have the needles to closed. to get it richer at idle open the needles more, about a half turn or so. this will help in the transition from idle to cruise also.
the secondary blades should just be open enough to barely uncover the transition slot. the adjustment screw is under the plate.
pump cam tuning, grab the linkage and open it as quick as you can, if it stumbles go up on nozzle size until it doesn't. now hit the street, stop and in first gear pedal to the floor as fast as you can, if it stumbles go up in nozzle size until it stops.
 
I pulled the 850 and bolted on a Holley 750 from one of my other cars. The idle vacuum went up both in park and in gear.
The Air/Fuel readings were better as well.
Idle @ 1100 in park : 13.8 to 14.2
Idle @ 850 in gear: 14.2 to 14.6
Pwr brake: 13.8 to 14.5
This shows that the 750 actually stays within tuning range while under a load. The 850 went totally lean when a load was applied.
I wonder if there is something lodged in a passage inside the 850?
 
Gotta be something wrong with the 850 I would think. But what do I know? lol
 
I agree. There is something screwed up inside. I don't know what the hell happened. Either something slowly degraded or I messed it up when I changed jets and the PV. Bad gasket blocking a passage?
I changed the cam to avoid detonation and now it is worse.
I blame no one. This is a tuning issue. The '509 cam was too small for the engine anyway. I have wanted an excuse to try a different cam for a couple of years.
Its hard to know if the 850 was slowly getting worse when I had the 509 cam. It was getting worse and was pinging more.
Months ago I talked with Dwayne Porter. He thought the car could be made to run better with some tuning. I should have listened and installed this wideband A/F guage back then.

After looking at that Holley 870 carb on the Summit site, I looked at the 950 carburetors. CRAP those are expensive! The Summit racing CFM calculator shows this: 493 engine with a 6200 rpm max needs 751 CFM for a street car and 972 cfm for a strip car. Maybe the 870 would be a good choice since I don't plan to race the car. If ever, I may make a few passes to get an idea of the cars potential.
 
I decided to change the jets in the 850, now I'm up to #90s. With the carb off, I decided to check the idle air bleeds. It turns out they were PLUGGED! After a few seconds, each one cleared out and carb cleaner poured through the idle transfer slots! There are 8 air bleeds. The outer 4 exit into the idle transfer slots. The inner 4 must exit into the metering blocks or somewhere else because they flowed, but I couldn't see where.
With the bigger jets and clean air bleeds, the car responded well. The A/F numbers improved!

Idle in park: 13.0 to 13.8
Idle in gear: 12.8 to 13.5
Power brake: 12.0 to 12.9
Great news! Now I'll try some #89 jets and fiddle with the idle mixture screws. I may be able to road test tomorrow!
 
I'm not a fan of the Demons - but I was going to suggest a rebuild and good cleaning/inspection. They are super-susceptable to crap in the passages. Carb size doesn't matter for you - yet. Also - the main jets should have nothing to do with the idle air mix. They will as soon as the throttle plates cover the tranfer slots - but at idle they should not. What is your initial timing setting? What rpm is it idling at?
 
I have the initial timing set at 19* with a total of 33 degrees. I have it idling at 1000 rpms. I've heard to set the initial at a point where I get the highest manifold vacuum, but that seems odd to me. What if I run it up to 25 degrees? Wouldn't it be hard to crank over then? Of course if I set it to 25 degrees initial, I'd have to modify the distributor to limit it to 33-34 degrees total. I guess I'll need to learn how to do that!
 
Get a assortment of pump cams for off idle issues. Also make sure your rear throttle blades are adjusted properly. Any time you make a timing change the carb is going to need to be retuned. Power valve and jets don't come into play till after the transition period.
Aaron
 
Frankenduster said:
I have the initial timing set at 19* with a total of 33 degrees. I have it idling at 1000 rpms. I've heard to set the initial at a point where I get the highest manifold vacuum, but that seems odd to me. What if I run it up to 25 degrees? Wouldn't it be hard to crank over then? Of course if I set it to 25 degrees initial, I'd have to modify the distributor to limit it to 33-34 degrees total. I guess I'll need to learn how to do that!
Click to expand...

The old saying is every engine is different, and yeah you will begin to slow the starter at some point, BUT I have even locked the timing out at full advance once and was able to crank over hot.
Sounds to me that you must be close, I like to look at vacuum & RPM ( when it stops climbing with advance )
I have a Mopar dizzy with a fully adjustable advance

Sounds like you got the carb figured out :cheers:
 
BB73Challenger said:
Sounds like you got the carb figured out :cheers:
Click to expand...

I wish that I did.
Yesterday the #90 jets and clean air bleeds resulted in a change of the A/F numbers. Today I road tested it and it ran PIG rich under a load. It went below 11.0 at part throttle.... then it was starting to detonate again.
What !!?? How is it possible to be rich AND detonate at only 33 degrees? I've read that all it takes is for one cylinder to run lean for the engine to detonate. If the 850 has a defect that feeds the left bank, it wouldn't show on the A/F guage. This A/F guage only came with ONE 02 sensor. My exhaust system has no H or X pipe, so each side is isolated from the other. If Cyls 1357 have any lean issues, maybe the engine detonates as a result?
I swapped the #88 jets back in. The #90 jets were obviously too much. Now with the #88s, it idles clean in Park. In gear it goes up to 16.0+/-. On the road it still runs in the 11.5 to 12.5 range.
I'm wondering if the carb needs to be chucked.
Tomorrow I'm going to road test the car with the Holley 750. I had it on the engine yesterday to see what A/F numbers it would make, but I didn't road test it. My thoughts are that if the car runs okay and does not detonate, that tells me that the Demon carb is to blame. If the car still knocks with the Holley, I'll have to look elsewhere.
 
what's do you have for your actual fuel system set up? You never,posted anything, in that department. That information, may hold the key.
 
Abodybomber said:
what's do you have for your actual fuel system set up? You never,posted anything, in that department. That information, may hold the key.
Click to expand...

Good point.
I have a stock replacement gas tank. 3/8" sender with a 1/4" vent. 3/8" fuel line to Holley mechanical pump PN 12-440-11 rated at 110 GPH. 3/8" line to a clear fuel filter, then to dual feed line. NO return line. It runs consistantly between 5 and 7 psi. at idle but drops a bit during extended RPM operation while stationary.

This setup has been the same since 2002. This engine has been in the car since 2004. I have never noticed a fuel supply issue until the break in of the cam last week.
I've driven this car on several road trips with no fuel issues of any kind. This was with the 509 cam. I have a hard time believing that a cam swap of this manner would increase the demands of a fuel system this much.
 
Does it shut off when you screw the idle mix screwed in all the way?

Not enough initial timing IMO. 19? Turn it up to 24-26 if it will start when hot. The RPM drop is big.
 
Rich will ping just as bad as lean does. in fact, it can be worse. But - remember the O2 will only monitor unburnt oxygen. Lean shows as bad as rich in that regard. If it were me I'd go back to the the mid 80s for jetting and drive the car more. Is there a reason you have to idle it that high? I'd think it would idle cleanly at 800 or so and you will be able to close the throttle enough to get off the mains at idle.
 
The engine stumbles and dies at idle when I turn the idle mixture screws in all the way. I only did that as a test since I was actually able to get the A/F ratio in the proper range with most combinations of jetting & PVs so far.
I have tried setting the timing to 24-25 initial. Idle vacuum only went up to about 11.0 compared to 10.0 with the timing set to 19 initial.
Can somewone tell me what it means when there is a large RPM drop from idle to in gear?
 
Here's another little point to stick away. I haven't kept up on "all the models" of Holley based carbs, but most? of them the PV does not change jetting, except for the vacuum kick in point.

That is the "metering" in the PV is a combo of the additive of the main jets and the FIXED ORIFICES in the metering body. In some cases you need to drill those to get WOT where you want and still have reasonable cruise.

An example.........

http://www.carsandparts.com/Articles/General/Tech/tuning-holley-double-pumpers-part-1

h01-1111ae.jpg


h03-1111ae.jpg
 
I wish I had good news to report.
The 750 seemed to run great. It certainly idles smoother than the 850. I was able to get it to idle at 600 in gear. The 850 wouldn't idle well below 750 or 800. The A/F numbers were within range at all times, but the engine still detonated beyond 3/4 throttle no matter the road speed or rpm. I thought that maybe the spark curve just comes in too fast, so I held it at 3000 while running in 2nd gear, (Knowing all the timin g was fully in) then floored it. It still knocked like any other time past 3/4 throttle.
EVERYTHING that I have done since I got it running has resulted in spark knock. I've tried bigger jets, smaller jets, Bigger PVs, smaller PVs, different timing settings. Different distributors. Different carburetors. Cold engine, warm engine. 80 degree weather, 94 degree weather. I've had the Air/Fuel ratios on both sides of the targeted 13.0 (Under throttle). The only time I was able to floor it without spark knock was on the first drive when I backed it off to 6 degrees initial and 20 total.
I really do not know what to make of this. It truly defies logic. This cam resulted in a reduction of cranking compression but the engine actually detonates MORE.

******************************************************************
Grasping at straws here, but here are the variables that may or may not matter:

* All the gasoline has come from the same station, the same pump. What if their 91 octane wasn't actually 91 octane?
* This time when installing the intake, I only used the tin valley pan without the paper gaskets. There are no vacuum leaks that I can find, but I had paper gaskets on the valley tin before the cam swap.
* The two distributors I have tried have light advance springs. They start increasing advance at 1500 rpm. I have some old OEM RB distributors here that feel harder to the twist than the MP distributors.
Aside from the above, I am totally out of ideas.
 
What kind of spark plugs are you running? How do they read? Are they fouled? I am going through a similar problem with the 383 in my Road Runner. The problem ended up being a vacuum leak in the intake valley pan. Recheck yours carefully. Does your vacuum guage hold steady at idle or is it moving slightly around?
 
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