Dual sync distributor

[Bobby Fazio]

Originally Posted by buzzinhalfdozen

Bobby, I've never used one of the dual sync set ups....what type of trigger is being used? Are both sensors the same (Hall effect,or VR type) ? Also your EFI controller does it have datalogging? If so does it indicate unusual engine speeds when the issue arises or a big change in injector pulse width? Or do you have other datalogging (racepak Ect.) that may show an unsteady RPM? I would think that if the crank trigger portion of the unit were acting up it would show up on a datalogger as a drop or spike in engine RPM. Joe

Joe,

They are both hall effect sensors in the distributor. Yes the DFI box has datalogging and the RPM curve looks kind of choppy throughout the entire run but I don't know the resolution of the curve. Car sounds strong though up until the mph cones when this miss starts happening. However, yes you see it on the graph, the injector pulse width starts fluctuating at the end, the MAP sensor reads more (or less). In Charlotte it was 97.9kpa the whole run until the traps and it jumps to about 101-102kpa. It is usually 103 on the two step. o2 sensor reads rich at the end as well. I have tried leaning it out/fattening it up but doesn't change anything.

Looking into possible valve float but I have good springs on there because I told Manley I wanted something good up to 7300rpm since I had no clue what I would go through the traps at when I was putting it together. This is only 6500 rpm though..

[buzzinhalfdozen]

You may be onto it there with the valve float as that would definately effect the Map reading. This is a stick car isn't it? does it act up before the gear change or are you shifting prior to this RPM?

[JHeath]

Bobby, what lifters are you running ? Mine used to stutter from 1200' to the finish line @ 6500, I put Sherman lifters in , and the stutter disappeared.

[Bobby Fazio]

They are supposed to be Sherman but I got them used on eBay a few years back.

[Bobby Fazio]

Originally Posted by buzzinhalfdozen

You may be onto it there with the valve float as that would definately effect the Map reading. This is a stick car isn't it? does it act up before the gear change or are you shifting prior to this RPM?

Joe it's an auto but I shift in the 5700 rpm range so it never gets that high until the finish line.

[magnumv8]

Most Oem fuel injection equipped vehicles for more than 20 years use a factory crank trigger while " Crank trigger systems prohibited unless Oem distributorless ignition. " this does not apply since the distributor does not initiate the spark in this case.....if this actually applied (and it doesn't) there would be hundreds of illegal crank trigger equipped vehicles on the track.....




D L Rambo....Stk 1300

Hey Bobby, do you have a bracket type cam your car, or a dwell type stocker cam? There can be a big disconnect between a random Manley tech that does not know the traits of a stocker cam and lobe profiles. An off the shelf street or bracket cam will not need the spring pressure that one of our cams will require. Maybe talk to the guy who ground your cam, and ask him about the RPM and spring your running.

If your search doesn't turn up anything, maybe try shimming up the valve springs and see if it changes where you have the problem.

Originally Posted by Bobby Fazio

Joe,

They are both hall effect sensors in the distributor. Yes the DFI box has datalogging and the RPM curve looks kind of choppy throughout the entire run but I don't know the resolution of the curve. Car sounds strong though up until the mph cones when this miss starts happening. However, yes you see it on the graph, the injector pulse width starts fluctuating at the end, the MAP sensor reads more (or less). In Charlotte it was 97.9kpa the whole run until the traps and it jumps to about 101-102kpa. It is usually 103 on the two step. o2 sensor reads rich at the end as well. I have tried leaning it out/fattening it up but doesn't change anything.

Looking into possible valve float but I have good springs on there because I told Manley I wanted something good up to 7300rpm since I had no clue what I would go through the traps at when I was putting it together. This is only 6500 rpm though..

[Bobby Fazio]

Originally Posted by Todd Hoven

Hey Bobby, do you have a bracket type cam your car, or a dwell type stocker cam? There can be a big disconnect between a random Manley tech that does not know the traits of a stocker cam and lobe profiles. An off the shelf street or bracket cam will not need the spring pressure that one of our cams will require. Maybe talk to the guy who ground your cam, and ask him about the RPM and spring your running.

If your search doesn't turn up anything, maybe try shimming up the valve springs and see if it changes where you have the problem.

Very good point Todd. I just went back to cam grinder emails and found one with his spring recommendation based on 7000rpm and it looks like the Manley spring I went with was actually a little stronger and had a slightly higher rate than what was recommended. I think I need to put in-car camera onboard and let you guys listen to it.

Accel recommended the large cap for the dual sync but that wouldn't clear my fuel rail so I had to use small cap. I have read dual sync can have trouble in the 6200-6500 range so I need to research that more. Either that or I got some bogus lifters. Head starting to spin lol. Thanks for your help.

[Bobby Fazio]

Here is a zoomed graph of RPM (red) and MAP (blue) and you can see at the end there are some gaps in the red RPM line and the MAP also senses the blips. I don't think this is valve float but I don't entirely know what that looks like on a graph.

[buzzinhalfdozen]

Bobby, it's a bit hard for me to see (maybe my screen resolution) but it looks like your MAP starts to really jump just as your RPM trace begins to show gaps. I've never seen a trace where there is an actual gap in it before. However that may be a clue, as an engine misfire will effect the MAP reading, how bout you contact the manufacturer of your data logger and run it by them. This is only my opinion but since the trace has a gap does that indicate there was NO RPM signal recieved? Also does your tach in the car indicate similar issues? Such as jumps or bounces?