5.7 Timing Troubles

[Map63Vette]

Looking for some advice into setting up the timing on my 5.7. I've been fighting a nasty cut and bog on full throttle hits ever since I got the engine in the car. At first I thought it may have been a carb problem, but I tried all the accelerator pump settings and some different step up springs (it's a Carter Comp AFB 625 cfm) with no noticeable change at all. Before dumping the money into a new carb I figured I'd try to mess with the timing and see if it made a difference. I'm running the MSD 6 Hemi timing box with an Indy Mod Man single plane intake. I'm running the stock MAP sensor that came with the engine when I got it.

I hooked up my laptop to watch the values real time (rpm, degrees of timing, and MAP sensor) and at cruise I'm running between 5 and 6 psi (absolute pressure, so around 10-12 in Hg vacuum if my conversion is correct), and on a full throttle hit I was getting around 12.6 psi. The stock MSD timing curves have a mechanical advance that builds to around 26 degrees of timing or so around 3000 I think and then a slight taper after that. The vacuum curve starts at 10 degrees up to 6 psi and from there it starts cutting the timing and even goes so far as to go negative around 10 psi. That being said, on a full throttle hit the car was losing 17 degrees of timing on the stock map, which I figured may have something to do with the cut and bog. I changed it so that it would just cut to zero (like a normal vacuum advance) at 12.5 psi, and the full throttle issue seemed to go away. However, a few hours later I took the car out again to cruise a bit, but the issue is back.

Long story short, is anyone out there running a carb setup with the MSD box that has had similar issues? Any advice on what I might try to do to fix the problem? I tried unplugging the MAP sensor entirely to remove the vacuum advance and it seemed to fix the problem, so I'm fairly sure the issue is in the timing curve, but I'm not sure how to go about fixing it. I cut the vacuum advance by around 4 degrees across the board and upped the mechanical curve by 2 degrees to keep roughly the same overall timing and the car feels like a rocket now with the extra mechanical timing, but I don't know how far I want to push it on plain gas since I want to keep street drivability.

 

[hemijoejr]

Looking for some advice into setting up the timing on my 5.7. I've been fighting a nasty cut and bog on full throttle hits ever since I got the engine in the car. At first I thought it may have been a carb problem, but I tried all the accelerator pump settings and some different step up springs (it's a Carter Comp AFB 625 cfm) with no noticeable change at all. Before dumping the money into a new carb I figured I'd try to mess with the timing and see if it made a difference. I'm running the MSD 6 Hemi timing box with an Indy Mod Man single plane intake. I'm running the stock MAP sensor that came with the engine when I got it.

I hooked up my laptop to watch the values real time (rpm, degrees of timing, and MAP sensor) and at cruise I'm running between 5 and 6 psi (absolute pressure, so around 10-12 in Hg vacuum if my conversion is correct), and on a full throttle hit I was getting around 12.6 psi. The stock MSD timing curves have a mechanical advance that builds to around 26 degrees of timing or so around 3000 I think and then a slight taper after that. The vacuum curve starts at 10 degrees up to 6 psi and from there it starts cutting the timing and even goes so far as to go negative around 10 psi. That being said, on a full throttle hit the car was losing 17 degrees of timing on the stock map, which I figured may have something to do with the cut and bog. I changed it so that it would just cut to zero (like a normal vacuum advance) at 12.5 psi, and the full throttle issue seemed to go away. However, a few hours later I took the car out again to cruise a bit, but the issue is back.

Long story short, is anyone out there running a carb setup with the MSD box that has had similar issues? Any advice on what I might try to do to fix the problem? I tried unplugging the MAP sensor entirely to remove the vacuum advance and it seemed to fix the problem, so I'm fairly sure the issue is in the timing curve, but I'm not sure how to go about fixing it. I cut the vacuum advance by around 4 degrees across the board and upped the mechanical curve by 2 degrees to keep roughly the same overall timing and the car feels like a rocket now with the extra mechanical timing, but I don't know how far I want to push it on plain gas since I want to keep street drivability.

If you would like, I can send you my program file and you could try it. I have no bog at all but also have no vaccume advance. Just as an experiment to see if it fixes your problem. Let me know!! If you want it send me a PM with your email address.

 

[Map63Vette]

That would be nice, I'll shoot you a PM. You're running the dual quad Edelbrock intake aren't you? Just out of curiosity, does it not have any provisions for a MAP sensor or are you just running without one? What sort of worries and impresses me at this point is that the MSD box comes with a tune that they claim is for premium fuel (best around here is 91), but I've been running it on plain 87 for a tank or two now with no noticeable issues. It even took the 2 degree base timing bump fine as far as I can tell, though I'm trying to keep a close ear out.

 

[myduster360]

Timing reduction for Tip in is normal. Its to prevent knock directly after the trottle snaps open. Generally too much tip in retard won't cause a bog.

Be aware that the stock timing is pretty low near idle and 14psia. Its common for tip-in retard to pull the timing negative.

If you're only gettting 12.5psia at WOT, then your MAP sensor isn't reading right or Kansas has some pretty high mountains that no one knows about. WOT MAP should be very close to ambient pressure (usually between 14.0-14.7). Besides a bad MAP sensor or connection, a restrictive air cleaner/filter can cause a drop in WOT pressure.

For reference, here's an older thread where I posted the stock max WOT timing. http://www.forabodiesonly.com/mopar/showthread.php?t=127947


Do you have any way to measure your A/F?
It would be very interesting to know what your carb is actually doing.

 

[Map63Vette]

Yeah, I thought the pressure seemed a little off. I know I have a pretty small air filter on it right now because of hood clearance issues (saving up for a fiberglass with built in scoop), but when I've had it off entirely I never noticed a very significant change. I really wouldn't think it would be too small of a carb to cause that much restriction, at least I would hope not. I do have the stock O2 sensors that came with the engine that I'm currently using to plug the bungs in the TTI headers. I was going to try to wire them up to a volt meter and see what I could get out of them for at least some indication rich or lean.

 

[swifter]

I'm watching this close,i posted threads about the same problem a few months back,I had one of the best tuners in Wisconsin working on this issue and came out a head scratcher,Hemijoe offered me the same ,My hiccup went away after putting a quick fuel carb on with mechanical secondary's and they increased the jets because I was way lean--Steve

 

[hemijoejr]

Yeah, I thought the pressure seemed a little off. I know I have a pretty small air filter on it right now because of hood clearance issues (saving up for a fiberglass with built in scoop), but when I've had it off entirely I never noticed a very significant change. I really wouldn't think it would be too small of a carb to cause that much restriction, at least I would hope not. I do have the stock O2 sensors that came with the engine that I'm currently using to plug the bungs in the TTI headers. I was going to try to wire them up to a volt meter and see what I could get out of them for at least some indication rich or lean.

Give the timing curve a shot I just sent it to you. Maybe it will work maby it won't but atleast it's easy to change. Let me know how you make out!!
Joe

 

[Map63Vette]

I'm watching this close,i posted threads about the same problem a few months back,I had one of the best tuners in Wisconsin working on this issue and came out a head scratcher,Hemijoe offered me the same ,My hiccup went away after putting a quick fuel carb on with mechanical secondary's and they increased the jets because I was way lean--Steve

Yeah, I'm fighting a carb change about as hard as I can. I just really don't want to sink $300 into a carb to find out it doesn't fix the problem. I don't know anyone around here either that has something close to what I need, so I can't really test out another one. I think there are several fixes to the same problem, but I'm not sure what will make it perform best. If I pull the MAP sensor entirely so there isn't any vacuum advance it pretty much gets rid of the problem with only a very very slight studder that's almost unnoticeable, but I may lose some engine efficiency while cruising (which is mostly what the car will see in it's life). It's just always really disappointing to slam the gas to show off to someone and have the thing fall on its face.

 

[Map63Vette]

Being the engineering I am, I think I've come up with a reasonable theory for why I might be having some of the issues. The Indy intake is a single plane design with a pretty large plenum. My thoughts are that on the initial throttle hit the engine is pulling whatever mixture is in the plenum without necessarily pulling any new air through the carb right away. That being said, I don't think the carb can richen up all the mixture in the plenum in time with the accelerator pump because it's just too much volume to work with. On a fuel injected engine (which I'm guessing the MSD is probably tuned out of the box for), it can instantly richen up the mixture because the injectors are right at the intake ports, so it can handle the ignition cut. Worst case it seems to run fine without the vacuum advance, so I can do that for now. I think a double pumper may fix the problem, but I think I'm going to try to get the O2 sensors working first to see just how off my current carb might be. I'll give HemiJoe's map a try here in a little bit, looks like a fun curve, lol.

 

[Noohki]

I don't know if I'm on the right track or not but I'll share what I've done.

The first thing I noticed is that under MSD Graphview, the timing was being retarded under part throttle instead of advancing. I called MSD tech support and was told the MAP curve that was sent with the HEMI 6 controller was designed to pull timing using nitrous.

I then modified my MAP curve to try to match it as best as I could with the 5.7 stock timing curve posted on http://www.forabodiesonly.com/mopar/showthread.php?t=127947.

Now the engine runs a lot better but I know I have a lot of tuning to do yet.

The first snapshot is of the MAP curve that was shipped with my HEMI 6 and the second is my mod.

Maybe some of you could share your MAP curve to help the rest of us.

 

[Map63Vette]

Yeah, I've sort of read both ways regarding vacuum advance (pulling or adding timing). I'll have to see about giving that a try though. It crossed my mind at one point, but I didn't really have an idea where to start with the curve. I did find that the air filter was a pretty big issue for me though. Tried HemiJoe's map and it pretty much ran the same. Let the engine sit and idle with the computer plugged in and the MAP was showing around 4-5 psi. Pulled the air cleaner off and it went up to 6 psi and you could hear the engine surge. Ran it around the block with the cleaner off and there's just a small little stumble now, no big cut and shudder like it was doing.

 

[hemijoejr]

Yeah, I've sort of read both ways regarding vacuum advance (pulling or adding timing). I'll have to see about giving that a try though. It crossed my mind at one point, but I didn't really have an idea where to start with the curve. I did find that the air filter was a pretty big issue for me though. Tried HemiJoe's map and it pretty much ran the same. Let the engine sit and idle with the computer plugged in and the MAP was showing around 4-5 psi. Pulled the air cleaner off and it went up to 6 psi and you could hear the engine surge. Ran it around the block with the cleaner off and there's just a small little stumble now, no big cut and shudder like it was doing.

Sorry it didn't work. It was quick and easy so it was worth a shot. That air cleaner deal you got there dosn't sound to good. I have never tried to watch the MAP and run the engine with the air cleaner off. I have always run my car at the track with it off. I'm going to have to pay atention next time to vaccume readings just for curiosity.

 

[Map63Vette]

Yeah, I had a pretty good feeling that my air cleaner was way too small. It's just a little 6 inch one because that's all I could get under the hood right now. I figured any air filter was better than none for now to drive it on the street. I just measured the clearance with putty today and I only have between and 1/8 and a 1/4 of an inch. I was thinking about a drop base cleaner, but I dont' think I'd have the room on the front because of the slope of the hood. Trying to sell all my spare parts around the house in a hurry to fund a new fiberglass one, lol.

 

[hemijoejr]

Yeah, I had a pretty good feeling that my air cleaner was way too small. It's just a little 6 inch one because that's all I could get under the hood right now. I figured any air filter was better than none for now to drive it on the street. I just measured the clearance with putty today and I only have between and 1/8 and a 1/4 of an inch. I was thinking about a drop base cleaner, but I dont' think I'd have the room on the front because of the slope of the hood. Trying to sell all my spare parts around the house in a hurry to fund a new fiberglass one, lol.

Different manufacturers make an offset drop base air cleaner to clear an HEI. You could run it "backwards" to move the majority of the air cleaner to the back of the engine. Maybe it would work? Thank god I have the hood scoop on mine. I had a small block with a 6pak setup on it when it was put together 15 years ago. The 6 pak air cleaner was tall and the top used to slightly fit into the scoop. The hemi is even taller with the eddy intake and the 2nd gen air cleaner. I had to cut more out of the hood to make it fit and wasn't sure if it was going to go. The side of the chrome dome air cleaner is actualy visible from outside of the car with the hood closed!! The Mod Man wasn't available when I built my engine. I had to put my name on a waiting list to get one of the first Eddy dual quads. Do you remember the dimentions of the Mod Man. I know you have the single 4bbl top but the measurements should be the same with exception of the carb placement. I was looking to go faster and with the RPMs I'm running I could use a single plane. Sorry to hyjack your thread!!!! Just looking for some info.

 

[Map63Vette]

Haha, no problem, The Mod Man was just a cool setup since you could change it up pretty easy without having to do a lot of work. It comes with bosses cast in for injectors (or nitrous) as well, so you can get one that's drilled from Indy or have it drilled by someone later if you want. It measures in at right around 4.5" from the bottom of the intake flange at the head to the top of a top plate. It's probably about another 1/4" or 3/8" to the bottom of the carb since the carb plate is machined on the top of the flange and would bump up the overall height a little. Frankly, you could probably even make your own top plates pretty easy, they're just a big rectangle.

 

[swifter]

This in effect is HELPING all of us with these issues,MSD has "blown me off and offered no help" if I knew how to put my final timing table on here I would do it,Thanks to all of you for posting this,We will all benefit from this,The guy who tuned my car at the dyno kept adding timing and the car just loved it every time the final result was 40 degrees and it freaked him out at first BUT after every pull they pulled plugs from both banks and read them and there was positively NO signs of detonation on the plugs,SO I have a car that runs very strong,yet to take it to the strip but that is coming SOON but in the back of my mind I have to trust the plug reading BECAUSE a good tuner even with a a/f reading will still check the plugs. THANKS GUYS FOR ALL YOUR INPUT I SEE NOW I'M NO LONGER ON A ISLAND BY MYSELF WITH THESE PROBLEMS Steve

 

[Map63Vette]

Well, an update on my side as well. Figured I'd try to make my own little carb hat and remote filter setup since a plenum alone runs $75+. It's pretty goofy looking, but hopefully it will work and I think it came in under $50 all together. While I was at it I checked out my MAP sensor. Plugged into the MSD and pulled from the intake it was only reading 12.8 or so. My parents have a 2004 Ram with the 5.7, so I pulled the MAP from it and tried it out. It read 13.6, which still seems a little low, but I tossed it in the intake anyway and figured I'd give it a shot. Kept the air filter off entirely (didn't have the new setup finished yet), and the car finally seemed to run right. There were no cuts whatsoever on a full throttle hit and only some minor bogging on a higher gear hit at lower speeds with the stock MSD curve (which may have been a low fuel issue since I was almost running it dry apparently). It was almost scary the way it took off on a hit since I was so used to it bogging, lol. Now the problem is finding a new MAP sensor. None of the part stores have them, going to call the dealer tomorrow and hope it's not too expensive. After that I may mess with the timing some and see if any of the other curves I've been messing with work any better.

You may just try to post a picture of your curves Swifter. If you hit the print screen button with the program open you can then paste the picture into MS paint or something and post it that way. I'd be curious to see what you came up with.

 

[myduster360]

While I was at it I checked out my MAP sensor. Plugged into the MSD and pulled from the intake it was only reading 12.8 or so. My parents have a 2004 Ram with the 5.7, so I pulled the MAP from it and tried it out. It read 13.6, which still seems a little low, but I tossed it in the intake anyway and figured I'd give it a shot. Kept the air filter off entirely (didn't have the new setup finished yet), and the car finally seemed to run right. There were no cuts whatsoever on a full throttle hit and only some minor bogging on a higher gear hit at lower speeds with the stock MSD curve (which may have been a low fuel issue since I was almost running it dry apparently). It was almost scary the way it took off on a hit since I was so used to it bogging, lol. Now the problem is finding a new MAP sensor. None of the part stores have them, going to call the dealer tomorrow and hope it's not too expensive. After that I may mess with the timing some and see if any of the other curves I've been messing with work any better.

Glad you're getting it figured out.

13.6psi might be closer to ambient if you've had any severe weather.

 

[Map63Vette]

Yeah, I wish I had a barometer handy to double check. I'm picking up a new sensor today, so I can check that one and see what it says. I wouldn't have thought it would have made that much difference if the sensor just read a little low all the time. Maybe it has a real inconsistent output or something that just has the timing jumping around. The air cleaner had a little to do with it as well since it had a little cut on full throttle even with the good MAP sensor. I'm just hoping this finally fixes it for good, I'm tired of trying to chase down different ways to try to fix it.