1964 Pontiac Grand Prix Re-rebuild 389 to a 455 HO

So after about 1200 miles on a fresh performance rebuild on my 389 I was driving down the freeway and crash bang boom bam my drive shaft gave out. Such a strong running motor and a pretty penny invested it was a sad evening. After the shop that built it denied all responsibility (of coarse) I thought it's time to go big. So I found a 71 455 HO fresh out of Santa Ana Speed shop. The only thing I'm concerned about is it has 1972 heads and not the smaller chamber 71 HO heads. But I think the flat top Pistons will make up for the difference. So the journey begins. I'm keeping the th400 trans because I love how hard it shifts. I would love an over drive but I'm afraid of change. I have found it gets expensive.
Here is the build shred on the engine.
Speed Pro forged Pistons .030 over
Isky 901280 INTAKE TIMING
DURATION: 280 deg.
OPEN: 32 BEFORE TDC
CLOSE: 68 AFTER BDC
CAM LIFT: .310"
VALVE LIFT: .465"
VALVE LASH: . HOT
. COLD

EXHAUST TIMING
DURATION: 280 deg.
OPEN: 68 BEFORE BDC
CLOSE: 32 AFTER TDC
CAM LIFT: .310"
VALVE LIFT: .465"
VALVE LASH: . HOT
. COLD
Manley Push Rods
PRW Roller Rockers
Performer 21563
Holy 750 DP
72 heads right around 114 combustion chamber but they have been surfaced so I'm thing about 109. Hopefully I don't have to get new heads with smaller combustion chamber. I am going to see how these run first.
Headman Heagers and 3 1/2 in exhaust with headman mufflers.



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Sounds like a good plan but you better find out why the drive shaft failed so it doesn't happen again.

 

What exactly does the driveshaft do to the engine or would that be engine doing to the driveshaft?

Never in a million years , no 2 million years would I call my machinist or any engine builder for that matter and say " hey man, my driveshaft broke - what are you going to do about it?"

I'm not surprised he denied any and all responsibility,

Or do you mean crankshaft ? Please tell me you meant to type crankshaft please please please

I had a really strong pontiac engine that died an untimely death. The harmonic balancer came off with the end of the crankshaft still bolted to it.

 

Maybe too early and have not had my coffee, but I am confused. You shed the drive shaft after an engine rebuild and you are going for a different engine?

Ben

 

Sorry guys must have been up too late. The Crank Shaft Broke.


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Here are some pics.
So I'm going to go check out the crank shaft. They ground it when they rebuilt the engine so I'm going to be looking to see if they chamfered it after the grind like they should. Any other suggestions would be helpful it's nice to have a little bit of ammo in my back pocket instead of nodding my head like like a zombie when any
Mechanic starts talking to me.


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Ok now we can probably help you

 

Damn, takes a bit to grenade a crankshaft at times. Oil pump failure ? Clogged pick up ? Maybe oil pressure gauge line rupture ? Wow. Dig your GP though....nice. I have a 65 GTO waiting in the wings....with an old school 428 HO....which may never live again....unlike your fine ride.

 

A broken crank is usually related to a balance, vibration issue.

 

most of my failures were due to overcutting the crank ( past.060) and not radius on the journal edges as these were rolled and when cut down and not radiused make a high stress point at the counter weights . only had one crank failure not related to that and it was from the caps not put on the right registers ( they pulled the aligment pins ) and it burned it up .

if your block isn't hurt , you can drop a 400 crank in there and make do . unless you know the numbers of the crank to see if its N ,PI or Armasteel ( fancy name for nodule cast iron ) your better off buying a new in the box one and have it sized and checked , as I have seen several rebuilders use the hub cranks ( which are post 75 and grey iron ) in early blocks and they are junk and only good for slow speed motors , thinking all Pontiac cranks are the same and there are more of the junk ones around than the old good ones .

 

Franks Pontiacs has all kinds of cranks I will prob get one from him. That was such a strong motor I was amazed at the torque and so were the big block guys when they caught up. this guy pulled up to me at a light in a 60s C10 and I said what do u have in there a 350? He smiled and shrugged his shoulders like he didn't know and asked if I wanted to race. I said absolutely. Long story short after he caught up to me at the next red light he said damn what do you have in there. I told him and he seemed very upset when he told me he had a 454. Hahaha love it!!


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I had a 71 T/A with a 455 H.O. perfect engine for that big G/P lots of torque

 

You shoulda kept it

 

Pontiac racing has a great history so phenomenal that pontiac and performance were synonymous for many years. However, Pontiac got a reputation for having weak bottom ends because enthusiasts would try to pull off feats equal to the big boys while using grandmas parts and scattering the inferior parts out of the bottom.

Not all pontiac parts are created equal is the point I guess.
With the right parts Pontiacs will thrive on being flogged daily, with the wrong parts Pontiacs will really thrill you once or twice.

 

the bean counters killed the racing aspects as it was suppose to be a cheap luxury line , the motors were designed to make max torque at low rpm, not high rpm and cruise for lots of miles . not like a chevy , and the problem with them is people try to run them like a chevy and blow them up , and even today you have people trying to make them run with chevy mentality and it will not work ( and you have to use parts with chevy designs used in them ) . it took me several years to learn what was what to make one run and to pull the rpms out of them and also to do it with low compression too . ( when I ran SS in the 80's-90's you had to run stock compression , factory rods, factory unported or ground on heads ) try pushing a 3500 pound car into the upper 11's with 7.8 compression and a 400 ( 413 actual ) and stock style rods ( we reworked the cast rods by new rod bolts ( the big weak link ) and blueprinting them and shot peening them so they would hold up to 8000 rpm ) today I can buy eagle rods that are cheaper than doing that and way stronger out of the box , plus I do not have to change them out at the end of every season because of stress ..

and like you said you have to know like every other brand what parts are good for what and there limits and know your part numbers .

 

should have kept both if he could ..
kind of like when my 73 Sd was wrecked , I should have kept the car and parted out what was left . the rods alone today are like gold to a collector or restorer and so were the heads ( block was destroyed unfortunately and not repairable . broke the right side water jacket thru )

 

here you go guys. Let the cause arguments begin!


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I don't think that's from any machine operation

 

Neither do I . I've never broken a Pontiac crank, even in racing.
Something bad wrong there ..with the casting or?

Might as well use the 455 now.
BTW 71 and 72 HO heads have the same size chambers.
72 has the peanut plugs.
All factory and replacement pistons are flat, save for the chamfers that some had.
How did you get the T400 in the Slim Jim tunnel? With a big hammer?

 

The heads are not HO
Yes a big hammer


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I'm thinking the cause was dragging brakes having 3 people in the car with me and doing 75 mph at 4000rpm.


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7M5 heads are still the same size chambers as 197 heads (About 4 cc's difference) Not enough to worry about

 

What..were you in second gear? What gear ratio?

 

Thanks I was kind of worried about that.


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3.64


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Jeez, DP carb...gas mileage must be horrible.
Give that thing a break with the 455 and put about a 3.23 gear and a Qjet on it.

 

I would if I didn't have another car for a cruiser. This is my go fast car. I'm planning on keeping the same gears and putting an 870 street avenger the gears and posi were the best thing I did to this car. It was night and day from the stock gears and non posi rear end. This car will not be in the freeway again that's for sure. I do have the stock gears and they are in great shape if I do change my mind on that.


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I am planning on running the 750 holly that I had in the 389 but the engine was set up to run on dual 500 carters according to the engine shop, so I might need to switch to the 870 down the road. I looked at my cam specs and it calls for a 750 so I guess we will see. I switched from dual quads because all the carb rebuilders had about a 3 month wait list around here. Can't wait that long.


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Not a fan of Holley, especially DP's ...or Carters for that matter.
So, can't help you there.. 66 Tripower would be cool!

 

They look cool but I can barely dial in 1 carb. And I have heard they are for looks. Not to mention people hoard those things and try to sell them for 2500 bucks!!


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