One of ? L89 Nova for sale at Russo and Steele

[kwhizz]

After doing some research on the Piston/Head combo's.....Putting 074 heads on a L78 short block would yield approx 9.5 to 1 compression.....doesn't make any sense why the factory would do that in a High Performance application......there was also concerns about the posibility of the closed chamber piston dome hitting the 074 head in the exhaust valve area, even though the chamber was larger ..... Some hit....some didn't......so.....Why would GM put High Performance Aluminum Heads and lower the compression ratio by 1.5 points........Seems more likely that the heads were added at some time in the cars early life by someone who didnt know the difference..



Ken

[Charley Lillard]

Isn't that what they did with the 71 LS6 ?

[69SSZL1]

No, the 1971 LS-6 had a special piston used only in that application. It had valve reliefs and a special dome. The 9:1 compression was not a problem due to the larger 454 ci.

[Charley Lillard]

But the end result was about the same compression ratio. I'm just pointing out that GM could have done something like what we have here.

[Rixls6]

But why would GM put 842's on a 70 Chevelle with the L89 option, yet use the 074 for a Nova???

[kwhizz]

[ QUOTE ]
But the end result was about the same compression ratio. I'm just pointing out that GM could have done something like what we have here.

[/ QUOTE ]

11.0 to 1 with 842's and 9.5 with the 074's....and a possibility of the Domes on the Stock L-78 Pistons hitting the Combustion Chamber in the Exhaust valve area....the Closed Chamber had a straight sidewall next to the exhaust valve which shrouded it......the open has a much larger chamber, but to unshroud the valve, they open up that area, but tapered it and that's where possible contact would occur.........I'll see if I can find that 3 page Wiki-article later and post it..........Bottom line......GM "Never" made a piston for a 396 or 402 block to work with the 074 head...........I think Dave didn't do enough research about the head situation before deciding they were Factory installed on this size engine.....the 074's were only used on larger displacement engines where GM made pistons for that application.....

Been down this road.....when I was building the Gold Nova into a L-89 clone....the first set of heads I bought were 074's because I didn't know any better.....The Engine builder then informed me about the compression issue and Piston un-availability.......Sold them and bought the 842's from a member here......Got an education...Again.....The Heads are the "Value" to this car as he states.....Yet.....Everthing seems to indicate that some just installed them at some time in the cars past....
Look .......Don't want to be a "Jerk" here.....But, Dave is presenting the car as "Factory"......Yet, for all the knowledge that is here about knowing the smallest detail about the correct color of brake line clips, etc...A pass is given to a Engine combination that was "Never" a RPO is Amazing to me...........It just go's to show the "Respect" that everyone has for Brian's opinion....but...If Dave provided the "Documentation" and Brian and Klutt accepted that as Gosphel.....Well??...
Again........It's up to Dave to do a "Verified" Documented History of the car to prove it's pedigree to a potential new owner......The Heads are the Problem.....I know that the car had Issues and doubts in Judging at a couple of shows......?????? Wonder Why??

Ken

[ron67]

[ QUOTE ]


11.0 to 1 with 842's and 9.5 with the 074's....and a possibility of the Domes on the Stock L-78 Pistons hitting the Combustion Chamber in the Exhaust valve area....the Closed Chamber had a straight sidewall next to the exhaust valve which shrouded it......the open has a much larger chamber, but to unshroud the valve, they open up that area, but tapered it and that's where possible contact would occur........

[/ QUOTE ]


Can't pull the wool over his eyes!

[kwhizz]

I learned everything I know from Sammy........