pontiac 326 vs Olds 455

[xxGriffonxx]

Alright here is my prediciment. I have a 1966 pontiac lemans. In the car right now is a 326. Also in my possesion i have a Olds 455 rocket out of a 72 ninety eight. the 326 sort of runs. and the 455 does run. I would like to have a 455 in this car. Reading up about pontiac engines i have come across the information that all pontiac V8 blocks from 301-455 are exactly the same dimensions but just bored to different specs. So theoretically my 326 can be bored to a 455. Either way i will have one of the engines rebuilt to a higher compresson engine. Because of money i dont know if i should keep the 326 and bore it to 455 ci and get rid of the need to modifythe car to put the olds engine in.. on the otherhand i could have the olds 455 rebuilt and would have to modify the car to allow this swap.. I would like to have between 400-500hp and over 500 ft lbs torque. For which ever engine i decide to rebuild i will get a larger comp cam, eldebrock rpm heads, headers, larger 4 barrel carb, msd ignition, higher flowing fuel pump,etc. I have aproximatley 4-5 thousand to spend on an engine.. The olds 455 also has a th350 transmission that i believe will also fit on the 326 being a BOP thing. So should i go the route of extreme boring the 326to a 455 and rebuilding from that or should i rebuild the olds 455 and have to make modifications to make the engine fit in my pontiac..
(i do not have the power steering pump for the olds motor or the mounting bracket that holds the alternator and powersteering to the engine)

[maxwedge]

Hold on here our resident Pontiac expert MrPbody will kick in , BTW I don't believe a 326 will go out to 455., Walls too thin, plus this requires crank rods and pistons, but he will know.

[xxGriffonxx]

Ive read seceral threads on the web saying the 326 all the way through the 455 has the same block. so i just figured a 326 could potentially be bored to a 455. but im no expert or anything

[xxGriffonxx]

Oh and i was also planning on getting a fresh pair of rods and pistons and anew crank as well either way. I wanted to up the compression on which ever one i go with. the 326 is the lower compression version and the olds 455 is a 72 block so the compression is lower then previous years

[MagicRat]

The 326 is the same externally to to other Pontiac blocks, but the actual casting is different. The 455 has larger cylinder wall castings to accomodate the larger bore size. So, no, the 326 cannot be overbored to 455 diameter

(BTW, the 455 also has a longer stroke. But the 455 crank has larger journals than a 326, so it will not drop in.)

If you are going to sink all the money for a rebuild and engine swap into this, look for a decent Pontiac 400 engine.

It is the best choice for a relatively light car such as yours because it builds revs faster and will move your car better, when properly set up. The 455 will build more torque, but is slower revving and is, ideally better suited for a heavier car than yours.

The Olds engine swap would require some work on the engine mounts and accessories to get it to fit and work properly. And as you say, '72 Olds engines were not the best due to low compression ratios.

BTW you could probably sell your 326 and 455 engines for a few dollars, and spend the bucks on the 400.

[MrPbody]

Sorry I missed this one...

MagicRat pretty much got it right. If you're going to put a Pontiac V8 together today, before you even buy a part, get Jim Hand's book "How To Build Max-perormrnace Pontiac V8s", published by SA DEsigns. Understanding how a "different" approach to performnace is required to extract what the Pontiac is capable of is MOST important.

Again, as said, it is the external dimensions of the blocks that are the same. Internally, the bores and strokes vary widely, to go from 287 CID (in '55) to 455 CID (in '70). And no, a 326 doesn't have the "wall thickness" to be bored far enough to make it worthwhile.

The 400 block is considered the "best", particularly those made for the '70-'75 model years. 5 mounting holes on each side is the "easy" way to identify them. Stroker kits to make them as large as 501 CID are available. The 400 block is superior to the 421/428/455 block due to the smaller diameter main journals. That additional 1/4" of "hole' in the large journal blocks is the weakest part. No Olds engine is as capable of BIG power as the 400 Pontiac. We've had many over 750 HP in racers that live for many years. Aftermarket blocks raise that potential to well over 1,200. All the current aftermarket blocks are available in the 3" main version only.

Jim

[bcdons@gmail.com]

correct me if I'm wrong but the pontiac 326 389 and 421 are the same block and I agree the 455 is not

[xxGriffonxx]

The 326,350,389,400,421,428, and 455 are all the same size externally.

[MrPbody]

Bore size and main journal size varies across the "range". Early engines had 2 5/8" mains (287, 316, 347), then 3" (350, 370, 389, 400), and finally 3.25" (421, 428 and 455). Bores from 3.5" to 4.150". Aftermarket blocks are capable of 4.410" bores.

NONE of the blocks are actually "the same", but share bore spacing, deck height and rod length, and are therefore, "interchangeable" within certain limits. Mounting provisions, starter placement and bell housing patterns differ from era to era. Head bolt pattern remained constant.

Jim