Hey Oldsmobrothers and sisters,
I've been looking into options for more power for my '71 Supreme.

1. Rebuild my original motor - possibly the most expensive option (pistons, valve train, etc.)

2. Buy a small block that needs freshening but already has all the fun internal goodies - already have an amazing deal thanks to one of our members.

3. Find a good 455 with J heads and wait until I find C heads - I was close on this one but the heads got away. Ain't no such thing as a 455 around here with decent heads, at least not at a reasonable price.

4. I found a '67 425 "D" casting with C heads. Very good price but it doesn't turn over. The question I can't find an answer to is the compression ratio on this motor. It's out of a '67 Delta 88 and has a 4bbl intake which "appears" to be original. I know the Toro motors were 10.5:1 but some of the others were 10.25 as well. And of course there's the dreaded 9:1 which I would like to avoid.

Mark says he can set me up with the cam and lifters (the funky angle thing). The casting number is 389244D if that helps.

Lastly; the 425 DOES NOT turn over by hand (it's on a stand) and has been sitting (possibly outside) for ten years. He wants $300.00, could maybe get it for $250

Thoughts?

Hope your all having a good summer!

 

425s are great engines, with a shorter stroke and longer rods than a 455. The shorter stroke provides faster revving potential. The flex plate will be the early design so you'll need one of those since the bolt pattern on your current one won't line up with the 425 crank.

I think the 2bbl engines were 9:1 and the 4bbl versions were 10.25:1 compression ratio.

 

Right, I read that about the flex plate so I checked the pics and it's there. Woot! Sounds like it all comes down to whether or not that's the original intake.
How about the fact that's it's seized (or at least won't turn over by hand)? Should that be a deal breaker?

 

Apples to apples on it's own, this isn't exactly the entire story, as I've said many times.
There are a few factors that effect quick revving as much or more than stroke length;
1) Weight of the internal parts
2) Compression
3) Head/Intake flow etc.

Think of it this way. If any given set of heads are marginal with a 455 then they're less marginal with less than 455c.i., how ever much that may be.
What the longer rod ratio WILL do however is enhance head flow because of piston speed and that fact that it sits at the top for a few more degrees of rotation. But all else being equal a longer rod will raise the peak torque and hp curves as well. That may be why guys say the 425 will wind up higher. That is an over simplification but the rod length does influence that.
Nonetheless the 400/425 are good options, if for nothing else than their better cranks.

Hope this helps.

 

Scrap motors bring about $.20 a pound in Illinois right now . Multiply by 650 pounds and that's about $130 .
I wouldn't offer too much more for a "siezed" engine . That's all it may be worth .

 

Thanks Mark, I appreciate the info. Do the raised curves sacrifice the low end grunt that 455 owners always brag, I mean talk about?

 

I think of it as the 455 has so much low end torque that it's hard to contain, so having a bit less low end torque and more high end potential is a win.

As for the revving thing, physics says a shorter stroke will spin faster, with all other things being equal (weight of pistons, rods, etc). I've seen this demonstrated at the local Museum of Science, where they have some wheels with weights on arms extending from the center. Move the weights inwards and the wheel spins faster; move the weights outward and the wheel spins slower. But as said, for a direct comparison the weights have to be the same.

 

That 425 may be junk, prob needs total rebuild. It may be cheaper to rebuild that 350.

 

Think figure skater? They pull their arms in and they become a blur, yeah?
So are we agreed that the 455, with the proper heads, has significantly more torque than the 425? Honestly, I'd like to try out some "hard to contain" torque for once.

Oh dude, a total rebuild is just assumed. My question is, and this is where my experience comes up short, if it won't turn over by hand, does that usually mean internals are welded together or it has broken rods, etc. If that's likely the case, then I'll pass.

I think where I go over budget is finding brackets and other unexpecteds making the swap form small block to big block.

 

You never know whats inside a stuck engine. I bought a 67 Toro for the engine that was seized. 99 bucks for it all. Pulled a head to find no piston, a rod thru the block and a bent crank.... The c heads and misc parts were all I got. If water got into the engine it could be pretty bad inside and costs will go up to assess everything and do rust removal. Some parts may not be usable.

 

Hmm, I didn't think about water. That wouldn't be good. Is it bad form to ask to remove a head and/or the pan before handing over my hard earned dough?

I should mention I'm not sold on this idea anyway. My CO buddy is still my best bet for power. It's a small block, 0.30 over, 9.9 CR, and he offered to go through it with me before I freshen it up.

Also, there's a reasonably priced 455 that's local. He claims it's a recent rebuild but I'd go through it anyway. Drawback, it has J heads.

 

How much power is lost with the J heads and how will that affect your intended driving style with the power? Heads can always be swapped at a later date as well, of course.

 

My understanding is that the J heads are the worst big block heads made by Oldsmobile and should be avoided. But I have no personal experience.

 

The J heads have a terrible exhaust side but the 455 will still have big torque. You will need a pretty big cam with iron heads and pump gas with 9.9 to 1. Is that Copper's 350? You increased your stall, correctl? You have 3.73 gears? The 425 will need bored oversize probably at the minimum but who knows till you crack it open.

 

Not really, there are ways to get most if not all of that back.
For the record, there's no guarantee that a longer stroke will automatically give you more torque. Here's just one of many examples;

And wasn't the Buick 455 the torque king in the muscle car era as well? What was the bore and stroke on that vs the Olds 455? Hmmm......

I could go on and on but you get the idea. Thanks.

 

If you can't find a good core--and rebuilding is probably how you will end up--come to the OCA Nationals where there will be 425 and 455s available if you set it up in advance.

 

Thanks for all the comments and suggestions but I'm afraid this thread may be moot. The guy with the 425 went silent so it probably sold.

Yeah, 307, it's Copper's motor and he's making me a very good deal on it so unless someone shows up at my door with a free 455 I'll probably go that route.

@Run: The nationals are a bit far for me this year but I do have a local friend that's going. Maybe I could talk him into looking for me. I'm not sure what you mean by setting it up in advance. Are the OCA Nationals "wares" advertised somewhere?

 

"Are the OCA Nationals "wares" advertised somewhere?"

Not that I know about. In the case of engines or short blocks, due to size and weight, it is better to set up such sales in advance because a seller is less likely to bring one along just hoping it might sell.

In the Western mindset, anything over 3000 miles is far to go to the Nationals. In 2010 I went only 2950 miles to get to Sturbridge, MA.

 

Understood. Thanks Run.