[BillsCamino]

Anyone know for sure what configuration the stock factory pistons are in a 1970 Chevelle L65 350/250hp 2 bbl engine?
Are they a 5-6cc four eyebrow flat top OR a dish style 12cc piston?
What is the factory compression ratio on this year engine? I'm thinking 9.0 to 1...
Need to know before I pull the stock heads...thinking about replacing them with a fresh pair of Vortecs and a GM crate 350/330hp hyd flat tappet cam I have
(Lift: .435” Intake / .460” exhaust; Duration @ .050”: 212 deg. Intake / 222 deg; LSA 112.5) on hand but don't want to bump the CR too high.
Adding the Vortecs and this cam should effectively duplicate the GM 350 HO 330hp engine, I would think.

 

[Motorvation]

Flat tops, IIRC. Compression was 9.0 to 1 by virtue of 76 cc heads. 10.25 to 1 had 64 cc heads. 2 barrel engines had 441 heads and 4bbl had 186 heads back then. I ran a 70 Nova in AHRA I/O. .390/.410 lift cam, too. Huh, the things you think you can recall....

Steve O.

 

[BillsCamino]

10.25 CR...bummer.
I'm thinking that's too much for the mild cam I'm using.
Thanks for the info!! :thumbsup:

 

[novadude]

That 10.25 CR is for zero deck height, and "blueprint" specs. Actual assembly line engines were probably a bit lower (like most '60s GM published CRs).

If you are not cutting the block and you are using 0.039" gaskets, your CR will likely be more like ~9.7:1. That would probably be just fine with the efficient Vortec chambers, and the 112.5 LSA / 109 ICL 350 HO cam. Sounds like a pretty good combo, actually.

L65 definitely had 4-eyebrow pistons, so I would guess they are 5-6 cc like you said. I have a '69 L65 apart in my garage now (441 heads and flat-tops - just like '70).

 

[BillsCamino]

Yeah, if I use a .039" gasket and assuming a .025" deck height, I calculate a 9.65 CR but my quench (.064") is a little too large for my taste.
Although this isn't a max effort engine project. Main concern is reliability and running cool on 87 octane.
But, only needing 32-34 degrees of total timing with the Vortecs will help...

 

[VORTECPRO]

Flattop piston, 441 heads.

 

[BillsCamino]

Y'all are correct...I replaced the valve cover gaskets on this engine today...I believe the first time these covers were ever off!!
The heads are -441 castings.