need help with 1969 427 decoding..

[69hurstSC]

the restoration on our 69 SS 427 impala is underway. the block is #'s matching with the VIN. i know that there were 2 horsepower offerings on the SS 69 impala, 390 and 425. on the back of the block its cast the words "hi perf" and "conv". whats the signifigance of this? what are the main differences between the 390hp and 425hp? i can get hard #'s off intake, exhaust manifolds, heads if needed.

wes

[SuperNovaSS]

The suffix code on the front of the intake will tell you. The 390HP has a cast intake, oval port heads and 2 bolt main caps. The 425 has an aluminum intake, holley carb, rectangular port heads and 4 bolt main caps.


Jason

[SS427]

Actually there were three. Even though the 335 hp version is not listed as being available in the SS, I have all the documents for a '69 SS427 Impala including POP from a green/green car I found in Andover Auto Parts in 1981. I would never have believed it had I not found this car myself. Harry E. in Cedar, MN (owns the red/black top '68 SS427 Custom Coupe) currently owns the engine from this car.

Keep us abreast of your progress. Any photos?
Rick

[Bill Pritchard]

Sounds cool! Photos and/or more details would be welcome

[TimG]

I believe the casting states "hi perf" and "pass". This means 427 in two or four bolt configuration and not a truck engine. The two and four bolt were cast the same way and configured differently with two and four bolt mains and a larger oil plug for oil cooling on the four bolt blocks.

[69hurstSC]

so the "hi perf" has no relation to the hp of this 427 (335,390,425hp)? also, is there specific reasoning for stamping "pass" (assuming this means passanger) vs "conv" (again, assuming this stands for convertible) on the block?
we have all the casting #'s written down and i'll get them on here for you guys soon!

[TimG]

Correct, all the blocks were "born" the same way and machined differently.

[JHS]

Another difference between the 390 and 425hp is that the latter has a solid lifter configuration. Does the car still have the emmissions sticker on the rad support? It will denote the hp rating of the engine, I believe.

[nuch_ss396]

The 425hp version ( SHP ) will have the external oil cooling
plumbing provision just above the oil filter mounting boss.
The SHP version uses a Holley 4-bbl along with deep groove
pulleys. You should be able to get any/all of these numbers
and post them here. Guaranteed someone here will know
what you have in the Impala.

Steve

[nuch_ss396]

Oh Wes,
One other thing. As someone already mentioned, the
Hi-Perf/Pass notations on the block really don't tell
much at all. That practice was used on-an-off over the
complete development cycle of the Mark IV engines.

Steve