Can I deck these heads far enough to take my lg4's compression from 8.6:1 to 9.5:1?

Is 9.5:1 safe for 93-94 octane?

How much can i expect to be charged to have these heads decked? average machine shop cost.

 

anybody?

 

Put flat-tops in. Makes a lot more sense.

I'm running 9.7:1 on 85 octane. But, I've got a knock sensor.

 

Check this out: http://www.rbracing-rsr.com/compstaticcalc.html

Assuming .020" steel shim head gasket, .035" deck height (what my 305 measured at), 14cc piston dish, 58cc chambers (probably low), you'd have to reduce the chambers to 50cc to get close to 9.5:1. That's about .040-.045" milling, which would require the intake to be milled as well.

So, you could probably do it, but the "best" way to get there would be to deck the block (for better quench) and flat-tops.

 

I was able to flat mill my 305 heads right downto the valve seat ans spark plug boss. thats as far as you can flat mill these heads. These heads do not angle mill well because of the spark plug placement. My finished chamber size with 1.94x 1.60" valves was 52cc.

That would raise your cr to 9.27:1 from 8.5 using a .015" steel shim gasket.

 

In that case, why not pick up some 601s? They have 52-53 CC chambers STOCK. Angle mill them and you can get them down to 49 cc. I have a pair that have been angle milled and that is what they CC'd. I ran them on a Flattop piston 305 (L69 piston with 6 CC worth of valve reliefs) for a while with a .020" steel shim gasket (3.800" diameter). The block was milled for a .020" deck height. That put the quench at .040" in theory (probably +/- .01"). The intake had to be milled to take up the difference. Compression was at about 11.23:1, but the XE-274 cam kept the cylinder pressures in check. Roughly 210 PSI at cranking speeds. The engine ran fine on 93 octane despite the high compression ratio, it did use a 160* stat, careful timing curve, high stall torque converter, EGR valve, Knock sensor, and rich secondary metering rods.

The stock LE9 305 truck engine that these heads came from had the LG4s 14 CC dished piston, .035" deck height, .020" nominal head gasket w/ 3.800" diameter, and the 53 cc 601 head. That makes 9.27:1 compression, with no changes other than the heads. Mill the heads to get to 49 CC, keep the steel shim gasket, keep your current pistons and you get 9.7:1. Want to keep the compression at 9.5:1, simply unshroud the intake valve slightly get the chamber back to 51 CC. That will give a nominal 9.49:1 compression ratio.

My current engine is .040" over, uses the L69 style Forged piston with 6cc valve reliefs, has a .020" deck height, 58 CC 081 heads angle milled to 55 CC, .020" nominal gasket with a 3.800" diameter. That gives me a 10.33:1 compression ratio, which caused TOO much cylinder pressure with the old 115* lobe seperation angle of the L82 cam that was in it. I added a roller cam with a 110* lobe seperation and more .050" timing to reduce the dynamic compression ratio.

Unless you cam your LG4, don't change the Static Compression ratio as the Dynamic Compression ratio is already pretty high due to the smallish stock cam.

The 601 head was actually cast for the old 267, but was run on the Van/Truck 305s too (Look for one of the ESC trucks) They came with the special RPO LE9 305 which came from GM with a 9.25:1 advertised compression ratio and a knock sensor. The LE9 also came with the 929 cam in it (regular old 350 cam), 800 CFM Q-Jet, Aluminum Intake, Special Advance curve, Monolith style cat, Single In Dual out muffler, and a HP rating of 175 @ 4,500 with 255 ft/lbs @ 2,000. That is nearly as much power as a L69 with more torque, back when the LG4 was making 140 HP and 230 ft/lbs. The 601 will outflow a 416 stock, not sure about ported, but I did get 224/160 out of them when ported, with a 49 cc chamber, an ALMOST vortec style chamber, and better spark plug placement than the 416/081 it is a hard head to beat. I have a buddy that uses them exclusively for circle track racing in a 305 class. Lets say he dominates the competition that uses 416s. Lets also say there is a little undercover ACID porting involved too. The ONLY reason I swapped to the 081 is for the extra bolt hole on the front of the passenger side head to run a serpentine belt setup. The ported 601s are on my Smog DISHED piston 350 in my 1980 Chevy C10.