408 tuning with a Wideband sensor

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Bushing works perfectly. Set the initial to 24 and it hits 34 exactly at full advance. Now I was able to get the idle ratio in the mid 14s where it belongs. Only problem I have now is I can't get it to idle below 1000. I have the street idle screw backed all the way out. If I pull on the throttle linkage I can get it to idle down so I may just need a stiffer return spring. I'm seeing around 12 on the meter when cruisng so I'm going to drop the main jets from 71 to 69 and see what happens. My max manifold vacuum is now around 7-8 so I'll switch to the 4.5 PV also.
 
Good size cam with a 4spd.... Mine was 260* @50 it idled right around 1100RPM. So 1000 is in no way out of bounds. Will keep oil splashed up on the cam too.
 
for 5 bucks, I'll take a bushing as well! I dont have a MSD pro billet in use as of now, but I will soon!!
 
Took the car for a ride after swapping the jets to 69 and the PV to 4.5. Getting mid 13s at cruize now. I noticed hesitation during light acceleration on the freeway so I backed the timing off 2 degrees. When I accelerate on the freeway the AFR goes lean to around 16 before richening back up. I'm thinking I need one of 2 things. Either larger pump nozzles or to enlarge the PVCRs. Any thoughts??
 
The ratio looks good when the secondarys are open. On the street it's pretty hard to have them open for long though. The car is severely traction impaired... Haha.
 
What vacuum does it pull on the highway?

You may need a higher number power valve so it opens earlier.

I'd put the timing back to where you had it and tune it there. If it's not pinging under load, run it there.
 
I don't know. Seems to me that the 69 Jet is small. I ran 76's and 84's in the rear on my 750 on my brown car. It was a Demon though. Maybe at light crusing it is ok and as you put your foot to it a bit you are tapping a hair on the secondary's and that is richening it up? Just a thought to toss around. I would almost put the bigger PV back in it and up the main Jet size a bit in to the 72-76 range and see how it acts.

I have a Holley 850DP for the stroker going in the scamp has 80's in the front and 90's in the rear with a 6.5 PV , the guy I bought it from was running it on his 408 Stroker and said it should be pretty close as it is for mine. We will see hopefully soon.

I will be tuning with a Wideband also and this stuff is all new to me using one.
 
Plus I have clutch problems. A oil leak ruined my clutch disc so it won't hold under heavy accelaration. I'm pretty sure it's the oil pan and I'm gonna try to fix it this weekend. Once it's fixed I'll have to replace the clutch disc. The oil leak is the main reason I'm gonna wait until next friday to go to Escondido.
 
Mad Dart said:
I don't know. Seems to me that the 69 Jet is small. I ran 76's and 84's in the rear on my 750 on my brown car. It was a Demon though. Maybe at light crusing it is ok and as you put your foot to it a bit you are tapping a hair on the secondary's and that is richening it up? Just a thought to toss around. I would almost put the bigger PV back in it and up the main Jet size a bit in to the 72-76 range and see how it acts.

I have a Holley 850DP for the stroker going in the scamp has 80's in the front and 90's in the rear with a 6.5 PV , the guy I bought it from was running it on his 408 Stroker and said it should be pretty close as it is for mine. We will see hopefully soon.

I will be tuning with a Wideband also and this stuff is all new to me using one.
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It's pretty light acceleration so I doubt the secondarys are open at all. Maybe the transition circuit is too rich. I should be able to cruise in the mid 14 range no problem.
 
Yeah I was just REACHING for an answer. It seems like you got it pretty close then. I would try what Cracked is talking about....... He know his shizzle really damn good for sure when it comes to tuning issues!!
 
crackedback said:
What vacuum does it pull on the highway?

You may need a higher number power valve so it opens earlier.

I'd put the timing back to where you had it and tune it there. If it's not pinging under load, run it there.
Click to expand...

I'll try to get a vacuum reading while driving this weekend. I backed off the timing because i think it was pinging under load but that may have been caused by the lean condition.
 
Loosenutz said:
I'll try to get a vacuum reading while driving this weekend. I backed off the timing because i think it was pinging under load but that may have been caused by the lean condition.
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Don't fall for selecting using the 2" below in gear or splitting the idle vacuum in half. That's a good starting point, not a set in stone method to get the right one. The vacuum gauge and A/F meter will tell you. You can run a PV that is rated HIGHER than your idle vacuum reading. I do it all the time.

If it's got adjustable air bleeds, you can make some adjustments there.

There is a guy that has done some real extensive a/f tuning and testing over at slowparts... I'll see if I can find a couple of the threads

The meters are great as a tool.
 
Cool read. I am going to read it one more time and then go to sleep so the dendrites in my brain connect the dots and then it is in Photographic Memory! LOL
 
crackedback said:
What vacuum does it pull on the highway?

You may need a higher number power valve so it opens earlier.

I'd put the timing back to where you had it and tune it there. If it's not pinging under load, run it there.
Click to expand...

I did some vacuum measurements today. At idle it pulls between 5-7 depending on whether or not the electric fans are running. Most cruising situations yield around 13. The car is still quite rich at idle = mid 13s. Low RPM cruise (less than 2500 is in the mid 12s. It leans up a little when I get closer to 3000RPM. I'm guessing the mains are starting to come in at that point.
 
Which 750DP do you have? Adjustable air bleeds?

If yes, go up .003-.006 on the idle air bleeds, outers. Readjust you mixture screws and see how the cruise reacts. It should lean it a little.

Usually when the mains start to activate you'll see a decrease in A/F reading. If it's still getting leaner, you're likely still on the IFR/transfer slot circuit.
 
Can't help with the holley, but i have a similar combo, with a 236/242 @0.050, .544 lift, 5 speed, using a large boare TQ. I idle at 850, and cruise at 14.5-15.5 depending on temperature. 18 initial, 34 all in on the timing. WOT is around 12.5. Just keep tinkering. The Wideband A/F was the single best thing I did for tunability. That and a strip kit with jets/metering rods and I can tune it to any AF I want.
 
crackedback said:
Which 750DP do you have? Adjustable air bleeds?

If yes, go up .003-.006 on the idle air bleeds, outers. Readjust you mixture screws and see how the cruise reacts. It should lean it a little.

Usually when the mains start to activate you'll see a decrease in A/F reading. If it's still getting leaner, you're likely still on the IFR/transfer slot circuit.
Click to expand...

Standard Holley. Air bleeds aren't adjustable. I have every drill size available though and could increase them. No going back on that change though.
 
The other is put a smaller idle feed restrictor in the metering blocks
 
I finally fixed the oil leak! Once I replace the clutch disc because it won't hold the stroker's brute force anymore, I'll be able to start tuning under heavy load. Anyone want to buy a slightly used centerforce disc?? I think it would hold up to a mild small block. Which holes are the idle feed restrictors? I've heard of doing this before by inserting a small diameter wire in them to reduce the area.
 
This thread, deems to be stickie+....Please, someone pull the trigger.....
 
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