just wanted to say that i am very surprised that chevy would have such a low profile aluminum stock manifold on a bb 427 / 390. no wonder the car's power is released with a high rise intake and runs so much better ..(had one put on a 68 bb back in 1968 /my first car...I remember that that car use to "scream" down the road.)
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Re: 1969 bb intake manifold
marc----
GM used the ultra low profile manifolds on 68-72 Corvette big blocks for ONE reason only----that reason was hood clearance. Even with the extra clearance provided with the 68-72 big block hood and "drop-down" air cleaners, there is minimal clearance between the hood and the air cleaner. Not enough, even, for the use of an insulating mat between the hood and the air cleaner.
Personally, though, I don't think that there's any huge difference in power between the ultra low profile manifolds and higher-rise, STOCK types. There's a little, but not a huge amount.
The 66-67 big block manifolds were of a somewhat higher rise design than the 68-69. However, the horsepower ratings were the same.In Appreciation of John Hinckley -
Re: 1969 bb intake manifold
marc----
GM used the ultra low profile manifolds on 68-72 Corvette big blocks for ONE reason only----that reason was hood clearance. Even with the extra clearance provided with the 68-72 big block hood and "drop-down" air cleaners, there is minimal clearance between the hood and the air cleaner. Not enough, even, for the use of an insulating mat between the hood and the air cleaner.
Personally, though, I don't think that there's any huge difference in power between the ultra low profile manifolds and higher-rise, STOCK types. There's a little, but not a huge amount.
The 66-67 big block manifolds were of a somewhat higher rise design than the 68-69. However, the horsepower ratings were the same.In Appreciation of John HinckleyComment
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Re: 1969 bb intake manifold
The intake passages were dropped down 2 inches into the block valley, to allow the beautiful sculpted hood, and alleviate the need for the L88 style hood, which unfortunately somewhat interupts the lines of these beautiful bodied cars. I personally like that hood and wish I had an L88!
The resultant lowering of the intake passages make a somewhat sharper turn, which in turn hurt the top end slighly on these motors. L71, L89, LS6 versus L72, L88 & '67 L71.
However the improved ZL1 head and subsequent changing of the L88 to use this head, middle of '69 has several improvments and reports to flow 15% more than the closed chamber previous design used on '67, '68, & first half of '69 L88 & L89 aluminum head.
I had a LS6 rebuilt to factory specifications, with only a ten thousanths overbore necessary, as the only deviation. It dynoed and calculated to 493 horsepower in this configuration.
I agree with Joe's assertion, that probably some horsepower is lost at the top end, with the low rise design.Comment
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Re: 1969 bb intake manifold
The intake passages were dropped down 2 inches into the block valley, to allow the beautiful sculpted hood, and alleviate the need for the L88 style hood, which unfortunately somewhat interupts the lines of these beautiful bodied cars. I personally like that hood and wish I had an L88!
The resultant lowering of the intake passages make a somewhat sharper turn, which in turn hurt the top end slighly on these motors. L71, L89, LS6 versus L72, L88 & '67 L71.
However the improved ZL1 head and subsequent changing of the L88 to use this head, middle of '69 has several improvments and reports to flow 15% more than the closed chamber previous design used on '67, '68, & first half of '69 L88 & L89 aluminum head.
I had a LS6 rebuilt to factory specifications, with only a ten thousanths overbore necessary, as the only deviation. It dynoed and calculated to 493 horsepower in this configuration.
I agree with Joe's assertion, that probably some horsepower is lost at the top end, with the low rise design.Comment
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