I need to replace the wornout front coil springs on my 67 bird. My motor is a 428 out of a 69 Grand Prix with an aluminum (Edelbrock) intake and a Holley carb and no AC or smog gear. Should I use the springs for a '67 400 w/out AC, a '67 400 w/AC, or go the custom route? Is a '69 428 substantially heavier than a '67 400? Is there a '67 428 spring?

Tough call I don't think there's no real way to be 100% sure I would'nt think a 428 would be that much heavier, if it is you're already liting it up with the alum. intake but just to be sure you may want to go with the coils for the a/c car.I don't know if you've ever replaced coils before but if you hav'nt make sure when you're putting them in that where the coil starts on top that it fits into the groove on the upper arm so that when your done the car will sit right (made that mistake before!!)I always drop the lower ball joint to get mine in.

After thinking about it I would say a 428 would be lighter than a 400. I've been told the pontiac engines are externally the same size. After looking at the 455 in the garage and my 400 and my 350 they do look the same. So with a bigger bore I think it might be lighter... I dont know for sure. But it is something to consider.

you also have to consider if your running 14in. or 15in. tires as you turn and go over bumps ouch.or just the overall stance you are looking for

Detroit Eaton Spring will sell you custom springs specifically for your application. They'll want a detailed account of what you are using, and what you intend to do with it. Then they'll recommend a product.

The 428 should be with in a few pounds of the 400. Not enough to make a noticable difference. So the standard 400 springs should be just right.

And you should have more choice that way... price wise. Just be careful when removing and installing the springs!

Good luck - Brett - 67 Drop Top 455!