Platato,
Here's what I've done so far with my L81 a bit at a time (no access to a dyno so it's all seat of the pants stuff):
Davies high O/P coil, performance ignition module & Moroso leads: started & ran noticeably better, but it probably had clapped out old leads on, so I couldn't say if they are worth fitting in place of a good stock system.
Crane CompuCam 2040, .440/.454 210/216 @ 0.50 lift & matching valve springs: BIG improvement in mid range power, but seemed to lose a bit at the bottom end (or maybe it just felt that way due to the extra power higher up?). A definate must do, but there are more radical cams that can be fitted eg, 2050. Something I'm careful about is to keep good fuel economy, so I've gone for a very mild build.
180 stat: runs cooler, didn't notice any power improvement (but I didn't expect to).
Performer intake: engine felt "cleaner/crisper" in pick up.
Lifter valley oil baffle plate: Improvements due to a cooler intake charge? Beats me, but it will hold the lifters in their bores if it ever drops a pushrod etc. A peace of mind thing really.
MAD dual exhausts with Monza "mufflers": very dramatic improvement throughout entire power range. The exhaust system is probably the cheapest power increase you can do. Economy also improved.
Hypertech thermothingy chip: contrary to what I've heard about these chips (Hypercrap, etc), I was impressed. Nothing dramatic, but low end power was increased (see cam above).
K&N filter: no noticed increase in power but I always use K&N's on my vehicles for ease of maintanance.
No emmisions systems: done (badly) by previous owner (Bubba).
Fitted bushes in carb to repair worn primary shaft bores: well worth doing if the carb is worn - acts like a new carb now.
Cloyes true double roller timing set: for peace of mind.
Comp Cams 1.52 roller tipped rockers: fitted same time as cam so don't know about power increase, but I like the fact that the rollers roll over the valve stem thus imparting less sideways force. And the ratios are more accurate than the stock rockers.
Set initial timing to 11*BTDC (from the 6*BTDC stock): noticed a small improvement, especially low down. Exhaust note sounds more aggresive & the idle is more regular
Dynomax Ceramic coated headers with 1 5/8" primaries into 3" collectors. O2 sensor in the reducers. Also made true dual 2 1/2" exhaust system (I've just junked the stock x-member & fitted a custom one): Power improvements? Very hard to say as I also fitted a TH200-4r transmission which has lower gear ratios. Making the exhausts was a real pain but is worth it. With no x-member to worry about the limiting factor is the drivers floor pan. I've got 4" of ground clearance at this point & it does ground out on speed humps & very rough roads
I also fitted an "H" pipe in the system (just behind the x-member). Supposedly this will give up to 8HP increase in power (yeah, right!), but I did it to quieten the exhaust down - with Monzas the noise was extreme at WOT & the "H" has mellowed it down a lot (still loud though). It's also stopped the popping & banging that occured on shut down (the MAD system didn't have any air leaks, it seems to be a problem with unbalanced exhaust systems).
Oh yes, if you fit Headers then fit a heat shield to the starter (or get a mini one). I cooked mine which isn't funny with an auto!
None of the above caused the computer any problems. The cam opens and closes the valves very quickly which helps to keep a high manifold vacuum at idle, which is what the computer needs to work correctly. If a cam causes a low vacuum at idle then the confuser thinks that you are giving it a bit of throttle & richens the mixture. This will cause emission problems & a bog when you do use some throttle (so I've been told). Choose the cam carefully if you aim to keep the computer.
In theory an earlier X-member will allow you to run true duals, but something to check is if the lower drivers floor pan (due to the electric seat) will prevent the pipe going through the hole in the x-member. You could cut a section out of the stock x-member & weld a plate over the cutout to give room for a pipe.
No mods were required to the computer due to the exhaust system change as the primaries are controlled by the computer, based on the O2 reading ie. it's self adjusting. The secondaries work in the same way as non computer controlled Q-jets so could argueably need slight richening. I didn't find that I needed to with the MAD system & the secondaries mixture still seems OK with Headers on (further testing is required
).
The L81 doesn't have roller rockers as std. I wouldn't bother with the expense of full roller rockers, but roller tipped are worth looking at.
HP & torque- haven't a clue! More than stock though.
Everything I've read says that the L81 was the same in California as everywhere else (or was only auto offered in California?).
What I'm missing is some decent Heads. Most of the mods I've done require decent heads to give the full benefit. The cam also requires the CR to be raised from the paltry 8.2:1 (or whatever it is) to 9:1 or a bit higher. Driving the Vette I can feel that something is holding it back a bit. The power is there, but it's just locked away (strangled). It's hard to describe, but it feels like every emission controlled engine from that era that I've played with. I'm convinced that a set of decent flowing heads with smaller chambers will really wake the engine up
At the moment it's far better than when I got it, but the quest for more horses is addictive - be careful.
Hope some of this helps,
Paul
