Big ish cam carbed 5.3 timing and jet advice sought.
01-25-2014, 03:15 PM
#1
Big ish cam carbed 5.3 timing and jet advice sought. I'm dialing in a little closer to a good state of tune for my mustang but I still need to do some tweaking to get the drivability and power where it needs to be.
Here's my setup
92 fox mustang
3.73 gears (soon to be 3.27)
Th400 2800 stall
2800lbs
Aluminum 5.3
Comp thumpr cam 219-233@.050 109lsa
241heads
Performer rpm intake
Holley 670 street avenger
Mid length headers 2.5" exhaust
So far my changes to the carb have been minor. Mostly in an effort to eliminate a off idle dead spot. Successfully I might add.
I'm running pill #4 in the box
I've changed to a 3.5 power valve and upped the primary jets to 69's from 65
I've done the obligatory idle tweaking and am pulling appx 12-13" at idle out of gear at 1100rpm
It's doing better but the idle is still weak dropping the rpm all the way down into the 600rpm range in gear. My thought is I need more timing and hope to find an out of date enough computer to talk to this box soon. How much baseline timing do y'all think would be a good starting point to strengthen the idle as well as any educated guesses as to a good secondary jet size to start tuning from. (71 currently)
Here's my setup
92 fox mustang
3.73 gears (soon to be 3.27)
Th400 2800 stall
2800lbs
Aluminum 5.3
Comp thumpr cam 219-233@.050 109lsa
241heads
Performer rpm intake
Holley 670 street avenger
Mid length headers 2.5" exhaust
So far my changes to the carb have been minor. Mostly in an effort to eliminate a off idle dead spot. Successfully I might add.
I'm running pill #4 in the box
I've changed to a 3.5 power valve and upped the primary jets to 69's from 65
I've done the obligatory idle tweaking and am pulling appx 12-13" at idle out of gear at 1100rpm
It's doing better but the idle is still weak dropping the rpm all the way down into the 600rpm range in gear. My thought is I need more timing and hope to find an out of date enough computer to talk to this box soon. How much baseline timing do y'all think would be a good starting point to strengthen the idle as well as any educated guesses as to a good secondary jet size to start tuning from. (71 currently)
01-30-2014, 02:48 PM
#4
Teching In
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Hi, just FYI holley recommends setting the ideal with the car in gear. Also I had a similar problem with my mustang dropping alot of rpm once I put the car in gear. Turned out the torque convert adverticed (2800rpm stall) foot break 1900rpm-2000rpm 11.5 size was way to tight, and dragging the engine down at low speeds. Just some food for thought.
01-30-2014, 06:02 PM
#5
I think figured out how to get my car to idle like it needs to with a little fiddling.
What I did was start the timing at 15 degrees. From there it ramps up to 32 from 5-600 rpm then it tapers off to 22 at 1000-1100 and goes up to 30 from there on out.
What this does is it has the car idling in neutral at a fairly low advance (1100rpm) but when I put it into gear (700rpm) it goes back up to a fairly high advance as the rpm drops which tries to kick the RPM back up limiting the drop in rpm by quite a bit to only 300rpm or so
What I did was start the timing at 15 degrees. From there it ramps up to 32 from 5-600 rpm then it tapers off to 22 at 1000-1100 and goes up to 30 from there on out.
What this does is it has the car idling in neutral at a fairly low advance (1100rpm) but when I put it into gear (700rpm) it goes back up to a fairly high advance as the rpm drops which tries to kick the RPM back up limiting the drop in rpm by quite a bit to only 300rpm or so
01-30-2014, 06:50 PM
#6
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You should have no problem idling that engine at 750-800 in gear or not. My 234/250 .521/.629 112 idles at 850 in my untouched 6.0. I found the vac trick to not work and I set my idle with a wideband and lower timing. I also changed the ifr's in the carb to allow for the 4 corner idle screws to be out further but thats cuz I was pulling my hair out.
Set your t-slots to show .040" (mine Re actually closer to .020") set your 4 corner screws to 3/4 turns from closed, then set your timing at idle between 18 & 22* then adjust from there. Change one thing at a time, sometimes I had to drastically change it to see exactly how it affected the engine. Soon enough youll have it running good, then fiddle to perfection. Your pv has no effect on idle unless its torn so worry about that later. Get your idle and light throttle figured out then work on wot and then pump shot.
Set your t-slots to show .040" (mine Re actually closer to .020") set your 4 corner screws to 3/4 turns from closed, then set your timing at idle between 18 & 22* then adjust from there. Change one thing at a time, sometimes I had to drastically change it to see exactly how it affected the engine. Soon enough youll have it running good, then fiddle to perfection. Your pv has no effect on idle unless its torn so worry about that later. Get your idle and light throttle figured out then work on wot and then pump shot.
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01-30-2014, 07:24 PM
#13
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The thumper cams are designed for sound and have lousy vacuum. 20 degs of timing helps and about 13.6 -+ Afr.
You might even be better off plugging the power valve and up the primary jets 4 numbers to compensate.
You might even be better off plugging the power valve and up the primary jets 4 numbers to compensate.
01-30-2014, 07:32 PM
#15
I agree the vac is low, but OMG this thing has teh ballz! In spite of this my power brakes still feel just like they did with the 2.3 surprisingly.
