Input on previous 427 rebuild

[Don W.]

1969 427 390HP Engine Rebuild

I have receipts from a rebuild of my engine and would like to get input on what may have done to the engine as far as modifications and performance changes. Was the compression changed? Also, was it converted to run better on unleaded fuel?

The car was purchased about 3 weeks ago.
The receipts are dated 3/5/87 and show 50,854 miles. The key points are below:
• Flex plate (what is this?) $35
• Harmonic balancer $80
• 260 crane cam $75
• 16 lifters $35
• 8 L2300F X030 Forged Pistons $198
• 50058 oil pump $35
• 52042 oil pump screen $6
• 7208 timing chain & gears $55
• 205-613 030/000 re-ring kit $80
• MS829 PX010 main bearing $20
• SH 6165 Cam Bearing $14
• Freeze plug
• 16 guides $20
• 16 seals $11
• 16 stock rod bolts $28
• 2285 Motor mounts $40
• PC407 water pump $82
• 40534 fuel pump $31
• 180 degree thermostat
• Grind crank $58
• Complete valve job $80
• Surface heads $30
• Bore and hone block $60
• Vat block $40
• R&R pistons and rods and align rods $29
• Resize 8 rods $80
• Magnaflux all metal $40
• Check align bore $20
• Balance complete assembly $90

[Joel Falk]

Re: Input on previous 427 rebuild

A flexplate is the equivalent of the flywheel for an automatic.

L2300F piston is around an 8.5:1 compression with closed chamber, 107cc heads.

The Crane H260 cam has a 260/260 duration, .484/.484 lift, and I believe a 110* lobe separation angle.

I think this is a decent replacement cam for the L36 and would work fine with those pistons.

So it appears to me that the person who rebuilt this engine lowered the compression, ostensibly to run on unleaded gas. It does not look like they had hardened valve seats installed, but these are not really needed anyway in my opinion. Others may disagree on that point.

If the engine runs strong and has good leak-down numbers I would not change a thing.

[Duke W.]

Re: Input on previous 427 rebuild

If the cam is a Crane 103032 it has less duration and more overlap than the OE cam - not one I would recommend for a rebuild. You can look it up on the Crane Web site.

According to references I have your OE head castings are 3931063 and nominal chamber volume is 96.4 cc. The L2300F has a dome and will yield about 10:1 with these heads depending on deck clearance and gasket thickness. As built this piston has a .140" dome with net piston volume of 16.8 cc, but, interestingly, my F-M Speed Pro catalog also lists CRs with the "dome removed", which drops the CR by nearly 1.5 points.

As long as the engine operates detonation free and shows no other problems, I would leave it alone.

My recommendation for L-36/68 restorations is the OE cam, massaged heads, and piston/head gasket combination to achieve a true CR in the range of 9.75-10:1, Premium unleaded fuel required. Hardened valve seats or seat inserts NOT required. All replacement parts Federal Mogul or Dana Corp. OE replacement brands - Sealed Power, Perfect Circle, etc. No aftermarket hot rod parts.

Duke