Stick with the 1966 389? Or go with a 400/455?
 

Hi Guys,
Newbie here. As my first post I mentioned I had just purchased a 66 Pontiac Bonneville. It currently has a 389. I would like a beefier engine. What would be the best route to take? I heard some 389s were good motors.
Should I:

Keep the 389 and get a stroker kit?
Or aim for a 400/455 with a stroker kit?


Mike

I would keep the 389. I went down this road with a 64. I changed the 389/4 speed hydro to a 462/th400. the motor had ported 6X heads and a 041 cam. The car ended up being a pain in the ass, it was loud, smelly and sucked gas like crazy. I was always trying to rev it up into the power band that cam was so wrong for a street car with this weight. Frankly it didn't go much faster then when it had the 389. I would put a 068 cam in that 389 and play around with the timing. Keep the points and use it to trigger a CD box like the MSD6AL. Look for a nice 3.08 rear end with a dual quad intake and run two Carter AFBs on it.. Remember its a Bonneville not a GTO..

Thanks for the info! What about the cylinder heads? Keep stock and rebuild them? Or go with aftermarket?

What about a set of 093 heads for a 389?

What kind of compression were you running? Sounds like something may have been off with your tune or combination of parts. A 455 with ported heads and 041 cam should run STRONG from idle to the rev limiter if set up properly

What are you going to do with the car? For cruising, you don't need anything but stock heads. If you are going to regularly see over about 4500 rpm, you might want aftermarket heads or just upgrade what you have. Just remember your budget- too much power and you start breaking things, and then need to upgrade those. If everything else is done on the car and the way you want it- paint, interior, suspension, etc, go for it. But if you start adding power, and the trans isn't upgraded, and the suspension, and the brakes, and if you don't have an unlimited budget, you can easily start down a road where you will never drive your car because you will always be fixing it. The cars came out of the factory with equipment made to handle what power the motor made.

I would like it a street cruiser. Not using it for drag racing. Just street. But would like the torque to be there when needed...

Yes a 389 will do the job well!
There’s a guy in Western Canada, SDPerformance. He would be great to work over your heads. He has a website, he can be difficult to contact, but is worth the effort. The website is SD Perfo

That's great!! I found their website and added it to my favourites so I can contact them later on.
Thanks again!

Go with the 455 for the best street engine if torque is what you’re after.

A bone stock 455 will make you smile, and will be less expensive than a hotrodded 389.

Both engines are great and have their place, but on the street cubic inches gets the job done without the need for ported heads and big cams.

Another thing to be aware of is 1966 389 blocks are not known for their strength and are also known for having very thin cylinder walls, I would avoid building a hot engine using that block.

A big Bonne needs a big engine, you won’t be sorry going with a mild 455. In later years (1969 for example) the 428 became the standard Bonneville power plant while all the other big Pontiacs came with the 400.

No replacement for displacement BUT with that being said the 389 in your Bonneville should at least take a .30 overbore and even without a stroker kit will put a smile on your face if built properly. I had a chance to buy a Mint 66 Bonneville in 2002 back before the car boom. Car was perfect and had power windows and AC the whole 9 yards. I went and drove it and told the man I would be back the next afternoon with cash. The asking price was 5500 bucks. Before I could get there the asshole sold it to a 17 year old kid who drove it for about 2 weeks before hitting a light pole in a grocery store parking lot.

The problem with ‘66 389 blocks is there seems to be a wide variance in cylinder wall thickness. I personally know of two that had cylinder walls of .090 or LESS. If you’re going to use the original block have it ultrasonic tested before boring. A 3” main 4 inch stroke crank along with a .060 overbore will give you a 428 engine. Nothing wrong with the performance of a 428.....A .030 overbore with the same 4 inch stroke crank gives you a 421. The biggest question is how large is your budget. Around here, 455s is scarce while 400s/389s are far more plentiful.

66 389s had thin cylinder walls. Over heated a lot. There were plenty of come backs to the dealers back then.

Usually cheaper to work over your current engine than to buy a new one.

This just sounds like the 462 was comprised of the wrong components for your desired application.

A set of ported 389 heads are going to set you back close to 2k by the time they’re upgraded to screw in studs and guide plates.

A near stock 455 would be cheaper and more street friendly than a 389 with head work and all the valve train components necessary to support a cam that allows the heads to shine.

A stock torque converter works nice with larger displacement engines, a 389 with a big cam will need a higher stall converter.

A big mild engine beats a high-strung smaller engine when it comes to all around street performance and driving pleasure.

Good luck with whatever engine you choose.

Excellent advice:thumbup:

So looks like I’m leaning towards a 455... if I’m going after a used one and rebuilding one properly. Is it just worth it to just end up getting a crate from Butler instead? I’m in Canada, and the 455s are hard to get here along with the parts, so if adding everything up. Would it be easier just to go with a crate from Butler?

Go with whichever builder you trust and can afford.

Any high quality engine build, no matter what the cubic inch displacement, is going to set you back a good amount of dough. You might as well get the all the cubes you can if you’re gonna pay.

Most likely they’re going to set you up with a 400 block with a stroker crank, which is fine. Nothing wrong with building off of a 455 to start with either, but since they’re becoming scarce a 400 based engine is the ‘go to’ these days.

For your needs a set of stock 6X heads will more than fill the bill for what you’re doing, coupled with a mild flat tappet hydraulic cam you can easily make 375 to 400 horsepower. Top it off with a factory iron Quadrajet intake and matching carb, no need for anything fancy or aftermarket. Same for the ignition, a good factory HEI distributor that’s been gone through by a competent distributor builder is more than fine.

Spring for a set of long-branch reproduction exhaust manifolds and you’re all set, free-flowing and solid without the rust out of tubing headers with very close to the same performance.

What I was thinking was if I can find a 400, or 455 block.
Get the block sonic tested, prepped, etc.
Butler stroker kit
Along with a top end package with d port heads..
Thoughts?