milano maroon

I am planning on building a L79 and have a question or two. I want to use the L2166 pistons, 350hp cam, but am considering using an aftermarket head instead of the 2.02/1.60 462s. Problem is the heads I found have a combustion chamber volume (advertised) of 75cc.

So when I plug all the numbers in the calculator, and I am guessing the deck height at 0.025", I end up with a compression ratio of 9.4. I used the following:
bore - 4.024
stroke - 3.250
dome - -5.3cc
gasket - .028
deck - .025 (this is a guess)

I know I can decrease the deck height maybe .015 or .020 and use a thinner gasket but the best I can do with those heads will be 9.8 to 10.0.

What do you guys think? Is it worth the trouble or should I just use my old 2.02 heads? Is 9.4 enough compression for that camshaft?

Heads I found were World Products SR with 2.02/1.60 valves.

Thanks,
Jeff

Scott Marzahl

That kind of defeats the whole purpose of building a L79 with 2166 pistons. YOur bore number should be an even number (.020, .030, .040 etc.) Why the SR heads, the stock heads with a pocket clean up and mild port will be more than sufficient, just do not install hardened seats or will may end up with cracked heads (I found out the hard way). (If you want an alternative aftermarket head, look at a set of Brodix IK180s, they offer a 70cc head or JEGS sells Profiler heads under their house name). Also keep in mind the more milling you do to the heads and/or block may result in needing to mill the intake to fit. Just keep in mind the gas you have available, a lot of west coast only has 91 and 92 premium available. My motor is 10.5:1 running Brodix IK180s milled to 68cc chambers with a LT1 cam and I have no problems so far. I built it on 10.5 simply due to the low 91 octane gas available in California.

Bluestripe67

I did the same as you want except I used my orig. '67 300HP heads. Port matched and cleaned the C chambers. Your lucky to have the larger valve heads...use them. The 350HP cam has a center line overlap that lets some pressure bleed off making it easy to use pump gas. As a mater of fact I can use 89 in my engine. Dennis

milano maroon

Thank you for the comments. You're right Scott, I should have said 4.020 for the bore.

The World Products heads were offered to me at a good price, probably the same cost as what I will have in my 2.02s once they are reworked. But the chamber size just causes too many problems.

I'll shoot for 10.25 to 10.50. Does that sound about right?

Scott Marzahl

Sounds perfect, I'm running 10.25 in my sons motor using l79 cam and it runs fine on 91 fuel.

AZDoug

If you do end up with 9.4 CR, I would run your cam through a dynamic CR calculator and see where you end up. You may want to select a cam with a slightly altered intake closing angle.


I would look at a hyd roller, if you have high flowing heads, you can have shorter duration, but higher lift for good higher RPM flow. For 9.4 CR, I would think a ~218 duration vs the ~221 the L 79 cam has may be better for more low end crispness, but bump your lift to the .480"-.500" range.

Doug

milano maroon

One other questions comes to mind. If my deck height was correct at .025 I could need a head gasket with a compressed thickness of approximately .044" to achieve 10.25 to 1.

Do we worry about quench distance here? I have read on other places that optimum quench distance (deck height plus head gasket thickness) should be around .040. I would be approaching .070.

JohnZ

Deck height for quench for a street engine is nowhere near as critical as some folks would lead you to believe; MEASURE your deck height when you mock it up before buying your head gaskets.

Scott Marzahl

You are probably closer to .030+ if it has never been decked before. Measure it when you tear it down. My hunch is you will be fine with a Mr Gasket 1134G .028" gasket. Be sure to cc your heads and confirm they are 64ccs.

milano maroon

Thank you for the replies.

Donny Brass

My quench is .006 + .015 and it runs OK

larrywalk

Hey Milano, with your location being Los Alamos (elev 7,300 ft!), you should get as much compression as you can - 11:1 or better. With the 2166 pistons; I'd not recommend a 75cc head - it's way too big. Try to see if you can get the chambers to 64 cc or less. Also, with a deck ht of .025", I'd recommend a head gasket of .015". This gets you a nice .040" of quench for best anti-knock. You'll need to tune your carb quite a bit toward the lean side to get best power because of the altitude.

Good luck!

larrywalk

I should add that to tune your carb at that altitude, you will need to reduce the jet areas by about 10%.