cam change

[Sensei]

I'm thinking of changing my cam to a Comp Cams 260H. I've heard that on some Vettes with air conditioning you have to take out the a/c condenser (discharge the system). Am I going to need to do that with my '81? Also, what is the general consensus on putting in a new timing set (chain and sprockets)? My engine is basically stock and in good shape with 95k miles. Would I be fine with just the cam and lifters? Any other "heads up" tips from someone who has done this would also be appreciated. Thanks and God bless...

 

[GerryLP]

Sensei,

When I replaced the cam the first time, my A/C system was not charged, so I see your concern. I believe that the law (Federal, perhaps?) requires the capturing of the refrigerant agent. So check around for price quotes on this.

Unfortunately, with the condenser out of the way, it is easier to remove the old cam and install the new one. On the positive side, once you're done with the swap, you'll be able to service it with FR-12 which replaces R-12.

I had the L81 computer running when the 268H was installed, and it behaved much like an L82 engine. A subtle overlap at idle, good idle manifold pressure, and it pulled strong with a very flat torque curve. However, I also had Aluminum Edelbrock Performer heads with 64cc chambers which also bumped up the compression ratio (CR).

The 260H is also a good bump stick, but consider researching other brands for a similar cam with more lift or ask CompCams to customize one for you. The 8.2 CR in the cylinders has to be kept for as long as possible and let go as quickly as possible. A total of 0.440" lift (when using 1.52 rockers) is a good lift, but consider finding one with a bit more (i.e. 0.484" on both intake and exhaust called a single pattern cam) or perhaps with the exhaust cam keeping the exhaust valve open slightly longer (what is normally refered as a dual pattern cam).

Just remember that one single modification to the engine won't work a miracle resurection of the L81 engine (remember that the computer is programmed to keep the engine in a particular profile). With the L81 engine, forget about horse power, and go after torque. The computer knows nothing about the torque.

GerryLP:cool

 

[black_81_vette]

doing a cam swap will require removing the condenser and to make your life eisier take a paint marker outline where the hinges are and pull the hood too.I ts not that bad get a couple buddies to help with the hood,its not heavy but two guys undoing the bolts and one to hold the hood makes sure nothing stupid happens.Also if you can get away with it ditch the feedback carb and distributor the dist with the ecm only gives about 26 degrees advance wich sucks.That and a cam change and you wont belive its the same car!!

 

[Sensei]

When I said "basically stock", I meant no major mods. Here is a little more detail. EGR, AIR and cat are gone, dual 2.5" exhaust with shorty headers and turbo mufflers. MSD 6a ignition. I will be adding an edelbrock performer manifold with the cam. It has the stock Q-jet but secondaries have been opened up and have slightly richer rods. Stock computer, distributor, heads, pistons etc. I have already converted the AC to R-134 and after much adjusting and tweaking it is COLD! I would rather not disturb it, although it sounds like removing the condenser is going to be unavoidable. I drive the car every day and am not a hot-rodder. I am just looking for some respectable umph from the throttle and better fuel economy. Thanks for all the info so far...

 

[Jack]

Your OE cam PROBABLY makes ABOUT .390"/.410" valve lift @ 0.050" duration ABOUT 190*/202* with OE 1.5:1 RAR.

With 1.6:1 RAR that same cam makes ABOUT .416"/.437" vl w/ ABOUT 191*/203* dur ... new 1.6 stamped rockers for ABOUT $60 and ABOUT 2 hours time ... cheap & easy if that'll satisfy you. If/when you open the timing cover on your 95K motor ... do change the timing set. Dump the ECM, Get a rebuilt HEI distributor w/vac can (from local parts house ... cheap, they sell without cap, coil) ... dump the ignition module & wire to your MSD6 ... just the dist will help your oomf & econ.
JACK:gap

 

[Rudzvetz]

You'll be happy with the 260H, especially along with the rest of the mods you have. You do need to pull the condenser and the hood, so your A/C will need to be recharged. You should also do your timing set since you are there and it's relatively cheap. You can remove and reinstall the timing cover without dropping the oil pan by trimming the "ears" off where the pan seal goes in, but I would recommend lowering the pan, less chance of leaks that way. Once you get it all done you'll really like the change. OH, and when you get done throw a vacuum gauge on the fitting on top of the intake manifold to verify that you don't have any vacuum leaks. I've fixed more cars with E4ME's that had vacuum leaks and the owners blamed the carb and ECM than I can even remember. Good luck.


-Justin

 

[Sensei]

Thanks for the help!