I’ve been writing this little ditty for quite a while now, but as I had to do once several years ago, I need to shake the trees. The inventory of quality letters is dwindling, and I need your help. If you’re thinking of a question, but you’ve been hesitant to email it, pull the trigger and send it on. Thanks!
Where’d His Power Go?
I have a 406 engine that has Dart Iron Eagle heads (2.05/1.94 valves, 64cc combustion chambers, 200cc runners), Edelbrock Victor Jr. intake, Wiseco forged dish pistons, Eagle 4340 5.7 rods and crank, Quick fuel Q Series 750 carb, and an MSD 6AL with 3 Step to retard timing for a 300 shot of nitrous. This set up is in a 1982 Cutlass that is street driven. I have a TH350 transmission and 3.73 rear gear behind the engine. My problem is the car generally runs low 12s in the quarter-mile, but now it will only run high 12s, and I don’t know what the problem is. I had a compression and leak down test done, as well as having the carb rebuilt. I also checked the plugs and wires, and everything is OK. Finally, I checked the timing, which is locked out at 36 degrees. The mark moved when I revved the engine up, which it is not supposed to do. I asked a friend about it, and he said my cam could be moving. Does that sound right to you? Would I lose power like that? The loss seems to be mainly on the bottom end.
Lastly, I’d like to know which style of rod is better, H-beam or I-beam? What are the pros and cons of either one compared to the other?
Winter Garden, FL
When one of my cars does a slow down, I run through a pretty straightforward list of diagnostics. You don’t mention feeling a miss or a layover, so I’m guessing the decreased performance isn’t really perceivable going down the track. You also don’t mention whether this is with spray or not, but I’m guessing with the stated e.t.’s, we’re talking about all-motor runs.
I’m guessing the slow down has been going on for a while, so one of my first checks of cutting the oil filter apart to look for a spun bearing probably isn’t going to be applicable, but I’d still do so. Next is get the valve covers off and check lash, then compression and leak down. When nothing shows up there, I check wide-open throttle and timing. After that, I move to fuel potentials, like fuel pressure and volume. You don’t mention if you’re using an electric pump, but assuming you are, make sure you can pump a gallon in 20 seconds. Hopefully, you have a regulator that you can see going down track.
As for locked out timing moving when you rev it, with a timing chain and a distributor, ie: no crank trigger, the timing is going to retard a few degrees. My NHRA Stockers retard at least 2 degrees when I hold the rpm up to around 4,000. If this is the sort of movement you are experiencing, I’d say that’s completely normal. You say you checked the plugs and wires, but I would simply replace all of the normal ignition tune up parts, ie: cap, rotor, plugs, wires. I sincerely doubt it’s the coil or ignition box.
Potentially, you don’t have a motor problem; it could transmission or converter related. Is it consistent? Is the slow down getting progressively worse?
Regarding your question on connecting rods, I don’t think there is any cut and dry answer; it all depends on your application as to which configuration is the proper choice. Here is a link to a pretty decent tutorial on the subject from our friends at Summit Racing: www.youtube.com/watch?v=fszNIRbS8yw.