Chevelle updates

[VintageMusclecar]

A few weeks ago I managed to find the time to get some work done again on the Chevelle.

When I built the 496 back in 2008, I tried something I'd never done before with the ring package that didn't quite pan out as I'd hoped. After the last drive I decided it was past time to do something about it, so the 496 came back out. (note: this is why I test these things out on my own stuff, not a customers engine)

Side-note: I also REALLY wanted to get that 621 bellhousing out of the car. In it's place will be a Quicktime scattershield and block plate.

The engine came down and was re-honed, and while I was at it I swapped in a set of new custom Autotec pistons to drop the compression down from 11.2-1 to 10.5-1. (The Autotec pistons also feature a much nicer modern ring package) This will give me a bigger tuning "window" so I can see what (if anything) there is to be had with more aggressive tuning.

Everything else remains the same from the previous build, noting the addition of the Stef's oil pan I installed after the engine came off the dyno the first time.

I dropped the engine & peripherals off @ Kammers today, the tentative plan is to test some time next week if/when this heat breaks a little (hoping for Wednesday/Thursday).

I was planning a pretty extensive series of tests this time around, but the situation on the home front dictates otherwise--even with my now abbreviated itinerary, I'm still probably looking at two days on the dyno to cover the bases I can.

Note that I'll be using 100 octane LL Avgas as the baseline fuel.

Here's some of the planned tests (in no particular order):

1) Re-establish a new baseline with the engine as it was last in the car/on the dyno save for the change in pistons/rings and the Stef's oil pan.

2) Header test: The existing headers are Hedmans with a 2" primary and 3" collector. Once the new baseline has been established, I will remove the 3" collectors and install a pair of 3 1/2" Schoenfeld collectors. If time allows, I'm also looking to test with a set of 2 1/8" and 2 1/4" headers if Kammers has suitable pipes available.

3) Lash, timing & Jetting loops: I wanted to do this when I had the engine on the dyno the first time, but we ran out of time to get it done. Depending on the outcome of the timing loop testing, I *may* test between 100 octane LL (Avgas) and premium unleaded pump fuel. If the engine wants 38°-40°+ for total timing, I'm not going to bother as I know it won't tolerate the pump gas with that much timing.

4) Spark plug test between non-projected tip and projected tip. (same heat range NGK's)

5) Carburetor test between the 3418 OEM vacuum secondary 855 cfm carb and a conventional Holley LIST 4781 850 cfm double pumper.

6) Ignition test: The engine will be baselined with the OEM points distributor and coil and will NOT utilize the MSD box on the dyno. Afterwards I will install a MSD billet distributor and we will hook up the 7AL unit on the dyno to see what (if anything) is there.

7) Air cleaner test, with and w/o.

8) Intake manifold test: The engine will be re-baselined with the 163 intake with the cut plenum divider. Afterwards I will install a heavily modified Holley Strip Dominator intake (which is destined for another project to be announced later). Next, I will install my Edelbrock UR2X tunnel ram intake and 4779 750 cfm double pumper carbs.

Some of the other things I'd planned to test if time allowed:

A: Move the cam from a 105° ICL to 109° in an attempt to trade some low/mid power for upper rpm power

B: Oil pan test between the Stef's unit and a Milodon 31188 pan.

C: Rocker arm test between 1.7 and 1.8 ratios

D: Testing the baseline 163 with the cut plenum against a <span style="font-weight: bold"><span style="text-decoration: underline">heavily</span></span> ported 163 I have.

FWIW, this will most likely be the &quot;last hurrah&quot; for the Chevelle, at least while it's in my possession.

I'll post the results in a new thread in my forum and link to it in this thread.