Thread: Identical l67 engines, very different power levels. Why?

I've been driving a lot of l67 cars lately, trying to replace my Durango that somebody totaled for me. Does anybody know why some of these engines pull like a freight train, and others seem just plain weak? I have my suspicions, but don't want to mention them until the jury is in. I'm hoping it's as simple as I think it is. The engines have all been stock, and running smoothly. No apparent issues with them.
Thanks, Gas.

Gearing.

Fuel.

Maintenance.

Weather.

Factory freak.

Cat clog percentage.

Fuel, and Maintenance.

The cars I'm looking at don't seem to have been beaten on. I've been in quite a few of those lately, and rejected them all out of hand. Stuff not fixed, loose suspensions, rattling couplers, ragged out interiors and exteriors......... I'm down to 2 (well, 3, but one is a little more than I want to spend) that all seem to have been well taken care of. Several of you have mentioned my suspicion of low octane fuel. The engines seemed to run smoothly with no apparent problems, just an amazing lack of power. I've read that the pcm can pull up to 15 degrees of timing, with each degree worth 2 or 3 horsepower. A 240 horse engine (on premium) run next to a 200 or so horsepower engine (on 87 octane) in the same weight car will seem to be much stronger. This made me think of something else. I need to take my ratchet and plug wrench to see if the plugs are messed up from detonation. Or anything else for that matter.
If there's carbon in there causing KR, how can I get it out? I've heard a water mist will do it, or maybe seafoam, but I'm not sure.

Originally Posted by machinegunsquid

Sparkplugs, the obvious answer!

Pull 1 or 2 plugs on each motor, and see how they look. Old worn out plugs, or misgapped will make a huge difference in power, especially if they are experiencing blowout.

Just a thought.

2nd would be fuel/cat conditions.

If you could, get an Aeroforce scan gauge, and go ahead and hook the powerwire to an add-a-fuse, so you can hook it up/take it off in a matter of seconds, so you can
A: pull any SES codes
B: Check knock
C: know much more about the condition of the engine


Plus, if you're going after an L67, you'll want an Aeroforce anyways =]

This is a great idea, especially for a "new-to-you" car that you don't know the history on. We wouldn't want to chip a piston now would we

Metal fatigues over time so it stands to reason that it may be weak then fail regardless of conditions at time of failure.

The more responses I get, the more questions I have. Tuning - is there software for a laptop? If it was fairly inexpensive, I could get it right away, otherwise I might have to wait until I start modding. I'd rather have the gauge as far as looks and the idea of always having it with me. It seems that the laptop software might be more powerful, though.
Can I run seafoam through the s/c? I can't see any other way, but I'm new to these cars and don't know if there are any ports under it.
How involved is changing the lim gasket? I know the blower would need to come off, which means the fuel rails and lots of vacuum lines plus their fittings which will automatically break. Any idea of the cost involved? Any mods or other regular maintenance I should do while it's that far apart? Valve cover gaskets, vacuum line and fitting replacement, maybe some small coolant hoses, plugs and wires.... anything I'm not thinking of?

I would wait to mod it until you get everything up to par. Start with a good solid base then go from there or you will only be compunding issues by installing mods. That's just asking for more trouble in my opinion.


Yes, there is tuning software out there. IIRC it runs around the $350+ area.

You can get Seafoam into the motor using one of the vac lines coming off the brake booster.


There are write-ups on how to change the LIM gaskets. Get the new gaskets from GM as they are the aluminum ones, not plastic like stock.

As far as other things to replace while the LIM is off: Fuel injector o-rings, valve cover bolt grommets, PCV valve, fuel filter, air filter. Then also clean the MAF and the entire throttle body inside and out. Lots of carbon buildup on the TB by now. If you take your time removing the fuel lines and whatnotc and they won't break (or less of a chance). Just don't flex them too hard as they are nylon and can crack/break. Just remove them from the fuel rail and leave them be.

Once you get it running 100% then take a read through the "Safely modding your 3800" thread to get info on how/what to mod to make sure you don't have to find another longblock

I should have clarified this part. I only meant small mods that could support later mods, in the same fashion as removing the u-bend. No real power gain by itself, but it helps with later mods. I don't know if there will be any similar things to do while the top is off, and I don't want to have to take it apart twice.
I've read through the "safely modding" thread and learned quite a bit. That thread stopped me from buying a pulley right away. I'll do all the supporting things first + a tune (maybe) and see what I've got. If I still want more, then I'll consider going further. I read in one of the threads that you can get into the 13s at sea level without a pulley. Don't know if it's true or not, but it goes to show there's a lot pf power already in these engines without really adding anything to them.