Anyone seen Cobra Jet heads with these mods?

[simonlegree]

I inherited these heads on a 428 wanna be 390 and I've never seen these modifications. What really throws me is the intrusion into the combustion chamber with steel plugs run through the lower exhaust manifold bolt holes. The heads resemble medium riser combustion chambers, have CJ intakes and Med riser exhaust valves. There is light porting and surfacing on both the cylinder side and exhaust manifold side. The heads have all new valves, springs, retainers, keepers , and guides. Someone has done lots of work here and I would like to get some opinions on whether these are useable or crap. Will they work on a street 428? Thanks for your opinions guys.
regards
Steve Legree
 

[Chrisss31]

I think I read about a mod like that once.  If I remember correctly, it was used somehow to bleed off compression during a tech inspection.  The bolt (possibly with a hole in it) is hidden under the header.  A small leak will bleed off compression at cranking speed but won't matter much when the engine is screaming.

[TomP]

I think they scooped enough out of the chambers to uncover the exhaust holes and it wasn't a tech cheating thing. If so they wouldn't have made the chambers larger.  Might have been done to lower the compression ratio. The bigger exhaust may have been done to restore sunken valves rather than improve flow. The porting would be for flow though.
 People do weird stuff. I had a set of C8OE-N CJ heads that had hardened seats all around with standard 390 sized valves. The machine shop didn't think they could get bigger seats past each other.

[Stangman]

Awfully hard to loosen those header bolts even if they are only 8 per side like I used to have. The bottom bolts suck.

[Katz427]

I saw a similar setup, but it was originally done to cheat the cylinder displacement checker. As I remember the original was developed by P&G , a company that developed special automotive tools. They became quite popular during the late 60's and early 70's when displacement cheating was quite rampant. The original idea was for NASCAR, and a certain "blue" car that was rumoured to have engines from Chrysler engineering, that were larger than 426.
Speedway still sells a "displacement" checker.
A historical note, I spent many a long night waiting for the track payout, while cars were protested and checked. Became a regular routine. Wasted youth.

[TomP]

The ones I had were Tunnel Ports and had a much smaller hole drill through and no plugs. The header bolts were probably just loosened to make the air leak past when the displacement was checked. A 3/8" hole would make a ten cubic inch and draw a lot of suspicion, a 1/16" hole could make your 480 into a 427 for the inspectors.

[Katz427]

You're right Tom! A considerably smaller hole. An old NASCAR mechanic told me that when the rules allowed a smaller engine, with less weight, it became popular. I believe it was  the 1968 or 69 season.

[Chrisss31]

I stand corrected.  I believe it was to cheat displacement not compression.

[427mach1]

Anyone think the corners of the plug hole would create hot-spots for pre-ignition?

[machoneman]

I stand corrected.  I believe it was to cheat displacement not compression.

Yep. A way to cheat on the engine's actual CID. Heck, another was to have larger bores on 7 cylinders, leaving the one the tech guys most often checked at the std. bore.  And the heck with some engine imbalance too!

[70tp]

I’ve got a pair of tunnel ports that have the holes also.   Was told that it was to beat the p&g pump test