Yep. That I have. So based on the marking it looks like i have the 389 325HP, Turbo 400, 1X4. i found two instances of this here (engine is stamped 9778789 ) there are two instances of that here: https://www.thepartsplaceinc.com/data-sheets/PontiacEngineCodes.pdf. One says low compression and one doesn’t, but they both say 325HP, so that might be a mistake. the 1x2 shows 256 HP and i doubt if a 4 barrel takes you from 256-325HP. There is also E185 stamped on engine. not sure what that means.
i thought it was called a hydromatic not a turbo 400. but the 325 HP 389 is the higher compression one according to other websites.
The transmission was called the Turbo-Hydramatic 400 (TH400).
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Doh. makes sense
thank you
i really appreciate all the input i get. im learning alot. i took this bonnville from a beat down hoopty to a solid runner and alot is from input from guys like you all on here. you can hardly find someonr willing to sneeze on an old car for less than $500 these days.
The 4 bbl engine has a higher compression ratio (10.75:1), bigger valves and a hotter cam. That is how it gets to 338 hp… which is the number I found.
I am thinking that “valve clicking” you hear is spark knock, not the valves. A 10.75 compression ratio with iron heads should be fed ethanol free premium AND an octane booster! Better yet, add 5 gallons of 105 octance leaded race gas to every tankful.
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Or, if you have a small air field nearby you can purchase 100 octane avgas.
Tester
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I do! 92 ethanol free plus booster! i don’t know where to find the super duper. i think there’s a race track way up north that had it. so i found it. check it out:
it goes
8:6:1
10:5:1
10.75.1 (that’s the tripower rochester 3 2 barrel carbs.
i have the 10.5.1.
i haven’t heard of spark knock. i’ll look it up. thank you!
What’s the age, mileage, and condition of the engine in question here?
I’ve had several late-60’s GM engines with +10.0:1 compression. Some were in such fine condition that I still had to retard the timing by 4 degrees even when running premium and some that were tired enough that they ran fine on 87 octane.
If this is an original engine that’s never been opened up and is burning some oil and compression is 150psi, regular gas should be fine. I would also suggest that any pinging may be caused by tired springs on the flyweights in the distributor, causing the timing to over advance.
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that’s good info but the distributor is new. its got 100k. it runs really good and seems strong. i take back what i said about it burning oil. i thought it might be, but now that im sure of oil level in dip stick, then oil level basically hasn’t moved in a year. i initially thought i could be 2 qts low, which would have meant heavy burn. you get a little puff of smoke once in awhile when starting but nothing serious.
When did you last adjust your points and timing?
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About a year ago. I just got my second full tank of 92 ethanol free plus octane boost, and it seems alot better. i think spark knock is most likely whats going on. i need to drive it until its fully hot to really be sure, just now i just went up the block and back but its cold. i did my water pump recently and i wonder if im running hot, which can make the knock worse. but also i think another timing adjustment probably is worth doing. thank you for that input.
At 100K+ miles, your timing chain could be stretched, I’d check it by putting a breaker bar and socket on the crank bolt and with the dist cap removed, turn the crank CW and then CCW and back CW to see about how much it moves in degrees…
Also the outer ring of the harmonic balancer may have slipped a little, bring the engine up to TDC #1 cylinder and look closely at the timing marks to make sure you are at 0 degrees (TDC) on the balancer…
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