After building my engine last summer, the 2-3 shift was late (not happening at full throttle). I took it to my tranny guy, and he put a governor for a 350 IROC in it. In drive with the pedal floored, it will shift out of first at 5500 rpm; just where I want it. In second gear, it still won't shift to third with the pedal floored, but if I lift off the pedal just a little, it will shift. This is probably just due to TV cable adjustment, right? The problem now is that from 5000+ in second gear, there is a miss. It doesn't do it in first, and I really haven't had the need to see what it does shifting out of third. The revs will drop about 100-150 rpm, then come back up, then drop down again. Is this just my coil telling me I need a better one, or is it something else? It revs much faster in first, of course, so does it miss in second because the revs are sustained longer. Like I said it didn't do it before he changed the governor, but I don't know what that would have to do with it. The tranny is a 700R4 and the motor used to be an LG4. See my sig for engine mods.

Thanks,

Eric

 

O.K., but where's the signature?

 

My bad, it posted, and then when I edited my post, it must not have shown up. Here it is. My other thought is I think my passenger side header flange gasket is loose. I used copper gaskets, so I just need to tighten it up, but I haven't had time to jack the car up and do it (it isn't really bad, and only makes noise when the car's cold). When the engine misses at high rpm, I don't hear a backfire or anything, but could a possibly leaky collector gasket cause the miss?

Eric

 

TTT

 

No.

Probably valve springs. If so, it's pretty destructive, it's valves bouncing off the seats when they close (probably one or more intakes); take care of it before something breaks.

 

So does that mean I need heavier springs, or are they loose or something? Also, is it just coincidence then that it started doing it after I had that tranny work done?

Thanks,

Eric

 

Yes. Probably. Especially since it probably goes to a higher RPM than it used to, and it makes itself worse over time.

What springs are in it now? What cam is in it? (XE149 doesn't exist)

 

I did run the engine that high before and manually shifted, it just shifts later on its own now. The springs are just stock lift springs. When I ordered my cam and heads, both the cam manufacturer and the place I ordered the heads from told me stock lift springs would be fine. Okay, so I'm an idiot. I was going off of memory, but after looking it up, how's an XE249H sound. It is very similar to the XE250H, but just has wider lobe separation. Duration @0.05" is 206/212, lift is 0.432/0.444, and lobe separation is 112 degrees. Like I said though, if I rev it up in park or even redline it in first gear, it doesn't do it. If it is the valve springs, wouldn't they be popping anytime I rev it up. Also, when it cuts out on me, I don't hear any loud noises. Also, the engine only has 3,000 miles on the rebuild. If you still think it's the valve springs, what kind would you recommend?

Eric

 

The thing about those XE cams, and other modern super-aggressive-profile cams, is that their ramps are FAR steeper than stock cams. Think about how you would get more flow through a valve that's open part of the time. Obviously there are 2 ways; either make the valve bigger, or keep it open farther, longer. To avoid all of the "big cam" problems that go with holding the valves open longer, Comp in particular has developed these ramps that hold the valves into their high-flow lift range for as much of their open time as possible, without raising the total fraction of the time that they're open. They snap the valves open very quickly, and drop them back onto their seat equally fast. Lift numbers alone do not tell the story. Not all cams with the same lift will stress other components equally.

The cam you have is a hydraulic roller, which is even more aggressive in this regard than their flat-tappet cams. Factory roller cams are stupid in alot of ways, not the least of which is that they entirely failed to take any advantage of a roller's capability for fast valve action; they just copied their lame "peanut" designs onto a different blank.

http://www.compcams.com/catalog/056_057.html about the middle of the page

Get rid of the stock valve train. Put a set of the springs Comp recommends on it, which is their part # 981; use the retainers they call out for; and put .090" of shims (you can get them at any machine shop or most real parts stores, not Auto Zone or CSK or any of those) under the exhaust valves, to make up for the factory "rotator" crap that needs to go in the garbage. A set of roller, or at least roller-tip, rockers will make ALOT of difference too, just from getting those lame factory rubber things out of there. You can do all of this work yourself with the heads still on the car.

Look at the lobes in this pic. The cam on the left is a XE roller, the one on the right is a stock cam (it's the L69 cam no less, already one of the most aggressive factory cams there is). Look at how much more rapidly the XE will open the valves than the stock one. That's why you need some real valve springs, instead of the stock garbage.

 

I see what you're saying and it makes sense. This morning though, I let the engine warm up to operating temperature and got after it to listen closer to see if I could hear anything; it ran smoothly and didn't miss a beat. When it misses on me it seems to be after the engine has been running for quite a while. Do the springs weaken more after they get hotter, and is this why it does it only after the engine has been running for a while? Also, the cam is just a flat tappet, not a roller. I've never installed valve springs before. How difficult is it to do?

Thanks,

Eric