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Tech Question
steve whelan, High Wycombe, Australia, 71 Dodge Challenger 318
HI Rick,
I have just bought a 71 Challenger- it is virtually unmolested
since the day it was birthed at Hamtramck, except that it has a replacement
318, which is all black and has a date coded intake manifold of about 1979
and other pollution control devices, plus stickers on the rocker covers etc,
so i know its a newer engine. The car has not been touched since it left the
States. I did a compression test (as per service manual) and was blown away
(almost literally) by how much compression it had. The lowest on 2 cyl was
205psi and the highest was 225 psi! Mostly around 210-215 for the rest. I
know my gauge is correct as I have used it recently on an 8.5:1 360, which
gave around 115-125. SO what's happening with this massive compression? To
all outward appearances it's a stocko engine- 2 barrel factory Holley,
greasy engine, sick TF904 etc. This comp suggests a C.R. of around 12.5:1 !
Any ideas? I have not driven the car since I had it trucked over from
interstate, but it starts easily and idles normally. Any numbers I can
check- maybe its a 318 Magnum? I have no idea why the comp would be so high.
Thanks, Steve
Steve, static / cranking compression tests don't really mean much except as a cylinder-to-cylinder comparison. The camshaft timing has a profound affect on cranking compression - the milder the cam, the greater gauge's reading. So does cranking RPM, amount of oil on rings, etc.
The only real way to know for sure is to yank a head and measure, look for domed pistons, shaved heads, etc. Or drive it on pump gas and you'll soon know!
A block casting date newer than late 1991 might indicate a Magnum shortblock. but the 1979 manifold could NOT be bolted to Magnum neags.
Rick
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