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Discussion Starter · #1 ·
Hey guys. Sorry if something similar has been posted but I couldn’t find exactly what I was looking for. This is my first builder and am still learning as I go. I have an ‘81 that originally had a 229. I swapped it with a 350. It’s got a rebuilt TH350. First gear gets me to around 25 mph, second to about 45, and I am redlining at just over 65 mph. I am assuming this is due to not swapping the rear end after upgrading the engine? Looking for recommendations on what rear end ratio I should install. The car is an in town driver, not a track car, so it needs to be good for to and from work and short stints on the highway. Thank you for your help!
 

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Discussion Starter · #4 ·
Did you use the 229 tach for the 350?
Tom
No. It originally had the sweep speedometer with no tach. Replaced the instrument cluster with an original tic toc tac and the 1,4,1 gauge set up. The RPMs may not be 100% accurate but you can hear and feel the engine working extremely hard as well so I’m inclined to believe it’s at least in the ballpark.
 

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Did you drive the old combo? Reason I ask is this:
Top gear in all GM trannies (auto or manual) is 1:1 unless it has Overdrive. So if the 229 had a T350 or four speed manual, the cruise rpm in top gear would be the same and it would be singing with both combos.
If so (or you didn’t drive the old combo so you don’t know) your rear gears have been swapped and are really steep. If someone swapped gears (trying to get some pep out of the old bent six) then that would explain it. Jack up the rear and spin the driveshaft while counting the tire rotation (should be vids online detailing it). The only other explanation would be a very loose converter slipping.
Patrick
 

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most all old tachs do not read correctly
need to hookup a temporary tach & see what the difference is
 

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most all old tachs do not read correctly
need to hookup a temporary tach & see what the difference is
I can confirm this. I ended up going to MikesMontes website to order a period correct remanufactured tach and love it. My original was off more as rpm’s increased due to the counter weight behind the dial decomposing.






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If your tach is right and a gear swap is the fix, the sweet spot for a driver in town and on the highway is 2.93, 3.08 and 3.23. A 3.42 and steeper gets a little buzzy on the highway, and numerically lower than 2.93 is a little luggy in town. (For non-OD trans).
First though: you might want to buy a cheap aftermarket tach to verify the rpm. If you have a really accurate rpm number and a close guess on rear gear (from counting rotation) then you can use your math skills to see if there’s a driveline problem like excess slipping from the converter.
Patrick
 

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Discussion Starter · #9 ·
Did you drive the old combo? Reason I ask is this:
Top gear in all GM trannies (auto or manual) is 1:1 unless it has Overdrive. So if the 229 had a T350 or four speed manual, the cruise rpm in top gear would be the same and it would be singing with both combos.
If so (or you didn’t drive the old combo so you don’t know) your rear gears have been swapped and are really steep. If someone swapped gears (trying to get some pep out of the old bent six) then that would explain it. Jack up the rear and spin the driveshaft while counting the tire rotation (should be vids online detailing it). The only other explanation would be a very loose converter slipping.
Patrick
The 229 was totally shot so I never got to drive the old combo to compare. But I have no idea the history before I got it so that’s possible it was changed. I’ll give the rotations a try and see what I find, thanks!
 

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Discussion Starter · #10 ·
I can confirm this. I ended up going to MikesMontes website to order a period correct remanufactured tach and love it. My original was off more as rpm’s increased due to the counter weight behind the dial decomposing.






Sent from my iPhone using Tapatalk
Nice looking set up. I’ll check them out thanks.
 

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Discussion Starter · #11 ·
If your tach is right and a gear swap is the fix, the sweet spot for a driver in town and on the highway is 2.93, 3.08 and 3.23. A 3.42 and steeper gets a little buzzy on the highway, and numerically lower than 2.93 is a little luggy in town. (For non-OD trans).
First though: you might want to buy a cheap aftermarket tach to verify the rpm. If you have a really accurate rpm number and a close guess on rear gear (from counting rotation) then you can use your math skills to see if there’s a driveline problem like excess slipping from the converter.
Patrick
Great info, thanks!
 
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