Tuning my 360 with a wideband.

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bigtooth

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My details:
360 Magnum crate 390 hp
R/T heads
230°/234° @ .050" 0.501"/0.513" Lift 107* lsa
4spd
3.91 gears
Holley 80508s vacuum secondaries
MSD Ignition 25 initial 34 total one light blue spring and one light silver spring
50cc Accerlerator pump, currently playing with squirters to get rid of a slight off idle lean condition when punched
Also, should add, 12" of vacuum at idle and currently a 6.5 PV in in it.

My question:
When I'm cruising on the interstate, around 3k RPM I can't seem to get my a/f raio higher then mid to high 13's but when I
cruise around 2-2.5k rpm its ussually right around mid 14s. Because it went fatter towards the higher rpms I tried to lower my
mains, i've gone from a 71 to a 70 and now down to a 69 with only slight improvement. I don't want to go any lower, because I think i'm
loosing power during acceleration.
I'm not sure what to try next, I was going to try to restrict the IFR's and put the 71's back in but thought i'd try here for some advice also, I know you were able to give loosenutz some great help.
thanks!
 
Off idle make sure the arm is adjusted properly so you get fuel moving as soon as the throttle is cracked open. It may want an entirely different pump cam.

If you need to lower the main jet to get your higher RPM cruise A/F correct, the offset is to enlarge the power valve channel restrictor (PVCR). If the metering block isn't set up for being adjustable, this can get fun.

Map out the A/F's are at every 250-500 rpm while cruising and see where the curve lies. Try to pinpoint where the mains are activating. Sounds like you've done some of this at least to 3K. Try to get readings up to 4K.

The power valve may need to be a higher rated number, see how that reacts using a vacuum gauge to see when the enrichment occurs. Watch for lean spikes as you roll into the throttle.

You can mess around with air bleeds a bit but I like tho use them to fine tune the overall curve, not to make big adjustments like you are dealing with.

I'd do one thing at a time so it doesn't become overwhelming. Paralysis by analysis can hit you with so many different areas to address and all the data. Start at the bottom, idle then off idle, etc. Good luck.
 
right now I've got the brown cam and a 31 shooter, it seems to really want the large initial hump in the cam. I just drove it again and its quite a bit warmer out then this morning. It seemed to bump the a/f ration up quite a bit, so around 2-2.5k its now in the 15.5+ range and in the 3k+ its reading around 14.5. Is the 15.5 safe? I think I understand about what you're saying with the PVCR, got to keep the ratio correct when the vacuum drops.

I have read of putting in an extremely large primary and drive it just to see exactly where they start to come in on the a/f gauge.

Heres another question, do you think, since this is a 100% street car, that it would be worth my while going from an m1 single plane to a dual plane?
 
IMO an Air Gap will run better on that then a M1.

15.5 is pretty lean. Higher than I generally like to tune stuff, usually around 14.5ish . If you can go down a bit on IAB .003ish, that should richen your cruise. You'll have to readjust your idle mix settings.
 
Thanks cracked. My air bleeds and IFRs are not currently adjustable.. its a pretty base model carb. But that's not to say I'm not afraid to drill and tap.

to touch on the intake again, this would be correct for the air gap, correct?
http://www.summitracing.com/parts/edl-7577/overview/

I hate to just throw money at it, but this cars rev limiter is set at 6000 and all my research seems to point towards the air gap for my purpose.

crackedback said:
IMO an Air Gap will run better on that then a M1.

15.5 is pretty lean. Higher than I generally like to tune stuff, usually around 14.5ish . If you can go down a bit on IAB .003ish, that should richen your cruise. You'll have to readjust your idle mix settings.
Click to expand...
 
Yep, that's it for a magnum headed engine. One of the best intakes for a hot SB ever made. I'm not a fan of the M1's

Hard to go smaller on IAB's if they aren't adjustable. A round of abuse from a drill bit and 6-32 bottoming tap will do wonders. :)
 
If you want to try richening the top of the transition/idle with smaller IABs, you don't need to remove 'em. Stick some fine wire in the air bleeds. You can use two seperate wires, but I prefer to use one. Run 'em down under the air cleaner gasket so the stay secure.
 
Mattax said:
If you want to try richening the top of the transition/idle with smaller IABs, you don't need to remove 'em. Stick some fine wire in the air bleeds. You can use two seperate wires, but I prefer to use one. Run 'em down under the air cleaner gasket so the stay secure.
Click to expand...

Yep, that's what I do with IFR's on 950hp carbs.

If the carb has a .036 idle air bleed, find a .014 wire and .018 wire, that would reduce the area to ~.033 and .030. I know some guys that use worn out guitar strings. They range from .008 to .022 depending on brand.
 
I'll say this, I think I'm learning just how much weather has and influence on the a/f mixture, specifically humidity. Its been like 80+% relative humidity in the mornings here, and like 30% in the afternoons, I dropped my idle mixture down a bit and that seemed to help the lower rpm cruise #s come down. So in the AM i'm around 13.5-14 all around, getting a bit richer towards 3500rpm. And right around 14.5 in the afternoon when the air is dryer.
Now, choosing a PV..? I have a 6.5 in there, and vacuum at curise is easily around 15", when I start to open it, the a/f mixture stays at ~14 till the pv starts to open up, should I try the 9.5 PV I have to try to get the mixture richer, sooner, when accelerating?
 
I think you are on track with installing the 9.5 power valve, I have close to the same combination and the power valve change really helped mine...
 
As the load increases, the AFR should be fairly flat to a little leaner. Only when the load gets very high that a richer AFR is needed. If ithe engine feels like its losing power or being held back and then power kicks in when you push the throttle down below 6.5"Hg, then try the 9.5 PV. If its pulling strong until you push the throttle open enough to drop the vac below 6.5, then it slows down briefly, then try a 4.5 or 5.5 PV.

This is one of the harder things to nail down even with a WBO2 and datalogger. A shop with a 4 or 5 gas analyzer and a dyno can figure it out very precisely. But hardly anyone has access to a place like that. So we have to do the best we can with what we got.
 
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