Oldguard 7

Pistons may be forged. They look like the L-82 pistons which were forged.

Drawmain

I don't know if they are forged or not in the L83 engines, I've heard both forged and hyper. Does anyone have that information?

terry82

http://forums.corvetteforum.com/c3-t...ston-slap.html

cardo0

Well the NCRS archives say the L83 came with forged piston - same as the L82: http://www.ncrs.org/forums/archive/i...p/t-26448.html. They look very much like a forged piston rather than cast. The stock cast pistons seem to have all kinds of dishes and vlv reliefs and vlv reliefs within dishes. U can allways have the piston to bore measured and maybe just rehone and reuse those pistons - just an idea. Tank it, clean it, rehone and rering it. I think piston to bore clearance with forged pistons can be very generous - something like 0.006" to maybe 0.010" measured with a taper gauge (long 12" feeler gauge).


Wow, pretty amazing how the car continues to run with 3 wiped lopes. But oh that is familer to my engine also.

74 LS4-454

This info also listed in the "sticky" under "I" in WEB SITES which contains all of the L83 specs for 1982.

http://www.corvetteactioncenter.com/.../82engine.html

Drawmain

It was still breaking tires loose, too. I think the block will need to be bored. You can feel a slight ridge inside each bore.

terry82

when I changed my cam it had 3 bad lobes and I did not know it till tear down.

Drawmain

NCRS says forged, Tom's link says cast aluminum. I think they are forged, but it doesn't matter as they have to be replaced due to boring the block anyway. Maybe I should offer them for sale here...

Drawmain

Just heard from the machine shop. The block will be bored .030 over. I'm looking at these pistons, http://www.dssracing.com/E350_p/e350.htm Does anyone have any feedback?

cardo0

DSS pistons are new to me. But u need to measure the chamber of the cyl head first before choosing a piston with a certain dish volume. But a quick look at your compression ratio with your 72cc alum heads and a lets say a 4.166" x 0.039" compressed head gasket and a 5cc crevice vol. Crunching the numbers gives u 8.6 compression ratio with those 5cc dish pistons. Is that what u want?
JFYI 64cc heads with those 5cc pistons gives u 9.3:1 c.r.. Or a 5cc dome with 72cc heads yields 9.5 c.r.. And 64cc heads with +5cc dome = 10.3:1 c.r..

cardo0

Drawmain

I have 72cc heads and I'm using a 4.140 x 0.020 copper gasket, pistons are .025 in the hole, that gives me about .045 squish and I came up with 9.4:1 compression with the 5cc 2 valve relief flat top. Did I read the description wrong?

From the website:

"350 Chevy DSS E Series Forged Piston (For use in 3.48" stroke x 5.700" rod) -5cc Flat Top with two valve reliefs, 1.560" comp hgt, Includes .927" full floating pin with double True Arc pin locks, 5/64 5/64 3/16 ring groove, Approximate Compression Ratio: (58cc Head = 11.15 to 1) (64cc Head = 10.37 to 1) (76cc Head = 9.11 to 1).
MADE IN THE U.S.A."

alconk

Very interesting Marc! How many miles was on that engine?

alconk

Boy I really wanted to do a complete overhaul on mine but the wife was giving me a lot of grief over the $ I had already spent. I did check the bearing and all of them looked great and with so little miles I put on the car I'm sure this should last me for years. However I am checking into replacing the rear gear now. Shhh... she don't know about that yet

Drawmain

Just over 100,000 miles on the engine. It was time.

I won't tell your wife, lol. I had that issue with an earlier Vette. I don't have that issue now, lol.

alconk

Well mine has 94K and still holds above 40 psi oil pressure and just a little under at idle. I have to stop thinking about this or it will drive me nuts. That is that I should have done a complete rebuild....

Drawmain

Well you saw the issues mine had with the cam. Other than that it was in decent shape. You just replaced your cam and heads, if the bottom end was in good shape and you are getting good oil pressure you should be fine. I just wasn't sure what was in mine so I decided to rebuild it so I'd know what was in there.

cardo0

Ok i did the math again and your right. Using your numbers it came out as 9.4:1.

1cc = 0.061in3

Start with the static volumes:

Head = 72cc x 0.061in3/cc = 4.392in3

Gasket = (4.140"/2)x(4.140"/2) x pi x 0.020" = 0.269in3

Piston to deck vol = (4.03"/2)x(4.03"/2) x pi x 0.025" = 0.319in3

Piston dish = 5cc x 0.061in3/cc = 0.305in3

Crevasse vol = 5cc x 0.061in3/cc = 0.305in3

Sum = 5.285in3

Swept vol = (4.03"/2)x(4.03"/2) x pi x 3.48 = 44.389

C.R. = (swept vol+static vol)/static vol = (44.389+5.285)/5.285 = 9.4

Ok so 9.4 it is. But dont u want to be a little closer to 10 with alum heads?

One more thing. Those copper gaskets are good for racing where the heads are removed and replace frequently. But I have seen the tinyest leaks with copper gaskets. Thats a nice trick when using alum heads and producing quench also. Just dont be surprized when u see some tiny coolant bubbles.

Funny those pistons dont have their weight listed. If your reusing your stock rods then u want pistons that weight close to your stock pistons - reduces effort/cost when balancing.

Drawmain

Thanks for the confirmation. You are right about the weights. The machine shop is supposed to call when they confirm whether or not the block has to be bored. I will call the company in the morning to find out the weight of the pistons. Unfortunately, I don't know the weight of the stock pistons... I assume the .030 over pistons will weigh more because they are larger, but in any event we will weigh everything when we balance the assembly.

My goal was to get as close to 9.5:1 as I could. Although 10:1 was obtainable with 64cc heads I'd like to be able to run whatever fuel is available here without worrying about detonation at all. I think going up .5 in compression over stock is good with the relatively small cam I'll be running. My figures with the Lunati cam I've chosen come out to about 7.88 DCR. I think if I went 10:1 CR my DCR would go over 8:1 with my chosen cam. I am aware I'm leaving hp on the table, but my goal is more low and midrange torque with this build and keeping the Crossfire system in place for now. I will be using copper spray as well on the gaskets instead of installing them dry and I think that will help with sealing and avoiding the tiny bubbles. Thanks for weighing in on this, I appreciate any and all help and advice.

Drawmain

Got the engine back from the machine shop. They even primered it for me. Ended up going .030 over on the bores, .010/.010 on the crank. I'm very pleased with their work.

Some progress pics:

In primer:



Driver's side painted:



Passenger side:



We're on the way!

alconk

Very nice!