a few questions arise ........
I am no expert .. but been around these cars for 40 years....
is the differential the original 10 bolt ? 411 sounds chevy ish we had 390 and 433
yes a gear change is a great way to lower rpm
if you do have a close ratio m 21 going lower than 355 the ratio between 1st gear and
the differntial makes for a chattery clutch and lack luster performance off idle
and starting on a hill ... well ... its not fun ...or easy on clutches...
if its an m20 wide ratio alot better .... for the 336 ratio
355 and close ratio I dont think ever came together in our gto's
closeratio needed a 390 gear to get rpm's up
there is alot of good info here .....
ole pinion should chime in ,,, I havent seen him on in a while .. hopefully hes fine ..
basically you need to know for sure what your first gear ratio is
for starters probably a 325 case close ratio and 390 gears
even wide ratios with the lower first and second gears and 355 wind out pretty good
with the stock 14" tires ..... whats your rpm on the freeway at 60 and tire size ??
is it an aftermarket or original tach .... many original tachs need calibrated and repaired
DO NOT TRUST AN ORIGINAL TACH for accuraccy until you have put a known modern one
hooked up along side to compare on a run around the block.....
these are just my opinions and insight from tinkering on over 100 pontiacs in my auto maintenence life