Another Mopar Off My Bucket List - Barracuda Fastback
After having been offered advice from Joe on the FAST efi setup I decided to start from scratch and make certain everything was set correctly on our 383. I wanted to be sure that I knew exactly where everything was set before making any new adjustments.
I started out by verifying TDC and rechecked the phase on the rotor. - Even if we were to go without it later, at least I'd be satisfied that I'd had it set correctly according to FAST's tech.
The obvious things that should never be taken for granted such as firing order, distributor play, good grounds, fuel pressure, etc... came next. So far everything was spot on accurate. No carbon tracking in the distributor cap, proper battery voltage, - I couldn't find anything wrong.
The car was difficult to fire and it had a tendency to pop back through the throttle body. In the back of my head a little voice kept telling me it sure seems like a timing issue. - But that voice has been telling me that for quite awhile. I'd always assumed that the FAST ECU was screwing with it and I could never be sure where the heck it was at when things were being controlled by a temperamental computer.
When we'd sent the original (non-Sportsman edition) ECU back to FAST we were pretty sure there was a problem with it. Surely the new one would have cured any problem we had. We had a new MSD Digital6+ control box too and it shouldn't be the root cause of issues now. Man, I really was banging my head against the wall.
Then it occurred to me that when we got the new ECU back from FAST we also decided to make other changes to the motor. - We'd added a set of tti headers and the aluminum Edelbrock heads with new adjustable chromoly rocker arms from COMP Cams along with matching lifters & pushrods. The headers were unlikely to have had an adverse affect on timing but incorrect valve lash could be a factor.
The decision to install the heads was spur of the moment. We'd discovered that the flow numbers weren't good enough for the horsepower goals we had for the proposer 512 build but knew they'd be a decent improvement over the stock heads that were on the Roadrunner. I'm used to slapping the stock Mopar rocker shafts on and not worrying about adjusting lash. My last experience setting lash was on a small block Chevy almost 30 years ago.
I have read several different ways to adjust lash and I've talked to a number of guys that disagree on what the best procedure is. Nonetheless, I knew I had to re-check the setting I had.
Given the behavior of the engine I felt it likely that the arms had too much of a load on them. My guess was that the valves were opening a little too early and causing the backfire.
Neither the heads nor the block had been shaved. We had gone with stock length pushrods. I figured it would all bolt up easy. We checked for proper alignment of the rockers to the valves. It all looked good. The only thing that seemed odd to me was that we weren't able to back off the adjusters on the rocker arms far enough to get excessive play. Like a dummy, I figured that was normal.
We haven't bent or broken any parts but I'm afraid that we've had the valves opening early. With the lack of sufficient starting clearance when adjusting the valves, (I had NO up & down movement on the pushrods) I made my adjustment by tightening further until I was able to feel less ease of rotation. Because we're running a hydraulic cam I'm thinking I'd forced just enough oil out of the lifters when I bolted the rocker shafts down to allow the pushrods to spin but already had too much load on them.
After removing the plugs, plug wires, and valve covers I decided to take off the cooling fan too. - That way I could rotate the motor without having to crawl underneath the car and I could watch my dial indicator to make certain the cam lobes were precisely where I wanted them before making any new adjustments.
I may not have it done yet, but I have confirmed that the valves were adjusted too tight. Now I've got to try to figure out how to solve this. Even with the adjusters backed out all the way, there's too much of a load. I'm thinking about shimming the shafts. I'll have to determine how much I need first. If this doesn't work I'll probably install the stock rocker arms/pushrods.
View attachment IMG_6601.jpg
View attachment IMG_6602.jpg
View attachment IMG_6603.jpg
View attachment IMG_6604.jpg
After having been offered advice from Joe on the FAST efi setup I decided to start from scratch and make certain everything was set correctly on our 383. I wanted to be sure that I knew exactly where everything was set before making any new adjustments.
I started out by verifying TDC and rechecked the phase on the rotor. - Even if we were to go without it later, at least I'd be satisfied that I'd had it set correctly according to FAST's tech.
The obvious things that should never be taken for granted such as firing order, distributor play, good grounds, fuel pressure, etc... came next. So far everything was spot on accurate. No carbon tracking in the distributor cap, proper battery voltage, - I couldn't find anything wrong.
The car was difficult to fire and it had a tendency to pop back through the throttle body. In the back of my head a little voice kept telling me it sure seems like a timing issue. - But that voice has been telling me that for quite awhile. I'd always assumed that the FAST ECU was screwing with it and I could never be sure where the heck it was at when things were being controlled by a temperamental computer.
When we'd sent the original (non-Sportsman edition) ECU back to FAST we were pretty sure there was a problem with it. Surely the new one would have cured any problem we had. We had a new MSD Digital6+ control box too and it shouldn't be the root cause of issues now. Man, I really was banging my head against the wall.
Then it occurred to me that when we got the new ECU back from FAST we also decided to make other changes to the motor. - We'd added a set of tti headers and the aluminum Edelbrock heads with new adjustable chromoly rocker arms from COMP Cams along with matching lifters & pushrods. The headers were unlikely to have had an adverse affect on timing but incorrect valve lash could be a factor.
The decision to install the heads was spur of the moment. We'd discovered that the flow numbers weren't good enough for the horsepower goals we had for the proposer 512 build but knew they'd be a decent improvement over the stock heads that were on the Roadrunner. I'm used to slapping the stock Mopar rocker shafts on and not worrying about adjusting lash. My last experience setting lash was on a small block Chevy almost 30 years ago.
I have read several different ways to adjust lash and I've talked to a number of guys that disagree on what the best procedure is. Nonetheless, I knew I had to re-check the setting I had.
Given the behavior of the engine I felt it likely that the arms had too much of a load on them. My guess was that the valves were opening a little too early and causing the backfire.
Neither the heads nor the block had been shaved. We had gone with stock length pushrods. I figured it would all bolt up easy. We checked for proper alignment of the rockers to the valves. It all looked good. The only thing that seemed odd to me was that we weren't able to back off the adjusters on the rocker arms far enough to get excessive play. Like a dummy, I figured that was normal.
We haven't bent or broken any parts but I'm afraid that we've had the valves opening early. With the lack of sufficient starting clearance when adjusting the valves, (I had NO up & down movement on the pushrods) I made my adjustment by tightening further until I was able to feel less ease of rotation. Because we're running a hydraulic cam I'm thinking I'd forced just enough oil out of the lifters when I bolted the rocker shafts down to allow the pushrods to spin but already had too much load on them.
After removing the plugs, plug wires, and valve covers I decided to take off the cooling fan too. - That way I could rotate the motor without having to crawl underneath the car and I could watch my dial indicator to make certain the cam lobes were precisely where I wanted them before making any new adjustments.
I may not have it done yet, but I have confirmed that the valves were adjusted too tight. Now I've got to try to figure out how to solve this. Even with the adjusters backed out all the way, there's too much of a load. I'm thinking about shimming the shafts. I'll have to determine how much I need first. If this doesn't work I'll probably install the stock rocker arms/pushrods.
View attachment IMG_6601.jpg
View attachment IMG_6602.jpg
View attachment IMG_6603.jpg
View attachment IMG_6604.jpg