Is rebuilding the engine necessary?

[Foxcraft]

Hey all!

First post here. I recently bought my dream car, 1976 Pontiac Firebird Trans Am with a 455 engine. The prior owner kept it mainly at stock and appears to have only added a Fitech fuel injection system and duel exhaust. I am wanting to upgrade the engine but see a lot of posts stating that the engine needs to be rebuilt first before upgrades are added or it wouldnt be able to handle the upgrades. Is this actually true? Yes, the engine is old but it appears to be in great shape. Is it more of a better safe than sorry situation?

Thanks!

[Frosty]

HI Foxcraft! Welcome to FP and the madness. What a great looking car! Thanks for sharing the pics. We love pics around here!

The 455 is a very stout motor. The question becomes what are you thinking about doing to the car or the motor?

If the car has a lot of miles on it (over 100k) then it might need benefit from some freshening up the engine and transmission.

If this is a low mileage motor, unless we are trying to add a power adder, then it should be fine - unless you envision some sort of strenuous duty in it's future. Examples could be autocross or drag racing.

If you think this is going to be just a street cruiser / cross country / Hot Rod Power Tour car, then only fix what needs to be fixed due to age, neglect, or wear n tear. A tune up, new oil/filter, new tranny fluid/filter, shocks. tires, flush and fill the radiator, etc. should be done to keep things current.

[Foxcraft]

Hey Frosty,

I do believe the engine is over 100k. This car had a one time owner and the guy who previously had it just got old. I think he was in his late 80s. I had all of the fluids replaced recently and tuned the fuel injection. The goal is to have this as a street car to go out on joy rides.  

[B52bombardier1]

Hello,

  And welcome to the group.  Great looking Firebird there!!

 

  Check the oil pressure with an actual pressure gauge while cranking the motor.  Autometer makes a great little gauge for this plus adapters for short money.  Then tell us the number.

  Check compression within each cylinder while cranking the engine with the throttle valve held open.  Disable the ignition within the distributor first.  My ragged bottom number here is 100 PSI in each cylinder but I'd like to see 170 PSI in each cylinder.   There's also some experimentation here by spraying small amounts of oil through each spark plug hole to tell if the cylinder leakage is at the piston rings or in the intake / exhaust valves.

A cylinder leak down test can also be performed.

Do the spark plugs look oily, sooty or wet?

Basically, there are things you can do or have done by a truly competent and trustworthy automotive shop that can help to inform your decision on a rebuild.   A complete engine rebuild around here is $3000 USD so please don't make this decision lightly.

 

Rick

 

 

[Foxcraft]

Hey sorry for the no reply. A lot has happened to our other cars that I had to take care of so the trans am got placed at the end of the list. 

[Frosty]

On 12/28/2023 at 1:59 PM, Foxcraft said:

Hey Frosty,

I do believe the engine is over 100k. This car had a one time owner and the guy who previously had it just got old. I think he was in his late 80s. I had all of the fluids replaced recently and tuned the fuel injection. The goal is to have this as a street car to go out on joy rides.  

Assuming the car has not been abused in any serious way (hey it's Trans Am after all), then basic preventative and proactive maintenance such as oil changes, radiator flush -n fills, tune ups, etc. will do you well.

I would encourage you to replace every rubber vacuum and rubber fuel line in the car as a safety precaution. If the hose is original, it was installed when ethanol fuels were not available. Today's modern ethanol fuels breaks down old hoses from the inside out. Time, grime, and UV light wears then down from the outside. Today's modern hose is design to handle ethanol fuels and prevent break downs or worse, a vehicle fire.

[Frosty]

One more thing - some people may disagree with this but since I got it straight from the late John Sawruk, the Pontiac Historian, I will carry the message forward. Unless the motor has been rebuilt by a professional engine builder with tighter than stock tolerances, do not use synthetic oil in your engine. The tolerances of your engine as compared to a modern LS or LT motor are night and day. The modern engines can take advantage of the synthetic oil's properties, your Pontiac really can not. So run conventional 10W30 or 10W40 in your car.

[TWO LANE BLACK TOP]

Have been away for awhile...Now I'm back...

Something that No one has mentioned...

The best way to guage the health of the rotating assembly (rods..Mains..wrist pins..piston slap etc..) Is to get someone to get in the driver's seat and start the engine...Once the engine is at operating temperature have them put it in gear...Have them hold the brakes really tight so the car can't move...Manually from under the hood at the carburetor/throttle body gradually open the throttle just enough to load the engine up... Just  to the point that everything is tight (drive line...And straining hard against the brakes) Hold it for 30 seconds or so...Then quickly let off the throttle...If you hear a slight knock or internal rattle when quickly unloading the engine...(you will have to listen carefully/closely) to pick up on it...That is a 100% sure fire sign that the rod/main bearings  clearances are getting  loose... And the bottom end and will need to be freshened  up...Sometime in the near future

Alot of people will do a top end rebuild (cylinder heads/valve grind...valve guides and springs...etc..Which is all well and good...the down side is...When everything is new and tight at the top... the  bottom end can/will develop a new rattle/knock... Because with everything being tight at the top...Any existing looser bearing clearances... in the rotating assembly will be amplified....along with worn bores and loose/worn pistons/wrist pins...etc.

TLBT

Edited January 14 by TWO LANE BLACK TOP