425 vs. 500

[Soup DeVille]

This might be better in the garage, but oh well.

Anyways, I found out today that the 500 I was planning on swapping into the Caddy needs a complete rebuild, which adds a couple of grand to my overall budget no matter how I look at it, but also presents me with an interesting option.

You see, currently the 425 in there runs OK, but its paltry 180HP output is simply unacceptable, so if I wanted to keep that, I'd be building it as well.

Building up either engine would be close to exactly the same cost with maybe the 425 being a couple hundred more expensive, but here's the problem:

A decent built 500 will produce about 475 HP and 550 lb-ft of torque and get about 9-12 MPG. The 425 might (and because almost nobody builds this, it's a big might) produce 400 HP and 475 lb-ft, but at least theoretically could get 14-15 MPG  .

I understand neither of those mileage numbers are spectacular, but if I intend to actually use this car often (and I have no tolerance for trailer or garage queens at all  ), the extra mileage could make it feasible for longer trips.

So, what should I do? Go for the known HP maker and enjoy hige torque and horrible gas mileage, or take a chance on a motor that everybody ignores and wonder about the results in the chance it might suit my needs better?

[sandertheshark]

There's too many stupid-fast Cadillacs with modded 500s.  Do the 425, see what happens.

[Soup DeVille]

There's too many stupid-fast Cadillacs with modded 500s.  Do the 425, see what happens.

That's the way I'm leaning I think.

[The Pirate]

Are there any other advantages to a 500, especially with regards to how robust the block is?  If not, I'd go the 425 route as well.

[the Teuton]

How well do superchargers work with the 425?

[Soup DeVille]

Are there any other advantages to a 500, especially with regards to how robust the block is?  If not, I'd go the 425 route as well.

The biggest advantage is that people know about them and I'll be able to properly set one up with little experimentation. The 500 also weighs about 100 pounds more, but considering the vehicle it's going into, I doubt that'll mean that much. The 500 block and bottom end have been proven reliable to over 600 HP, and I'm not aiming that high. The 425 is based on the same casting but lightened in a lot of areas, and people disagree on how strong it actually is: again because so many just go with the 500.

[Soup DeVille]

How well do superchargers work with the 425?

Good question, and I don't know. Again there have been 500s built to nearly 1000 HP on superchargers or turbos, and the 425 would use the same plumbing as those do. Perhaps there is some turbo/super potential ina 425, but the only way to fit a supercharger on one involves slicing up the hood, and I really want to keep the car somewhat low key.

[GoCougs]

The 500 is such the superior engine in just about every way; block, recip assembly, etc., I'd don't see the value in the 425 at all.

I'd forget about mileage if it were me. Any moderately modded V8 will get atrocious mileage by modern car standards.

[Soup DeVille]

The 500 is such the superior engine in just about every way; block, recip assembly, etc., I'd don't see the value in the 425 at all.

I'd forget about mileage if it were me. Any moderately modded V8 will get atrocious mileage by modern car standards.

Valid points, but I should clarify a few things about my intentions:

If I were to build the 425, the recip ass. would be replaced using forged Olds rods and a crank from a 472. The intake manifold will be from a 500, and shorty headers used.

The gas mileage isn't as much a financial concern as one of range- and while I know neither of them will win awards from Al Gore, one is potentially better than the other.

Right now I'm uncertain as to what I want to do, and I need to get the ball rolling one way or the other.

[omicron]

I cannot possibly choose.

[Raghavan]

I'd go with the 425, assuming reliability in the long run is the same for both motors.

[Soup DeVille]

I cannot possibly choose.

Well, you were one of the people that I was hoping to hear an opinion from...

[omicron]

Well, you were one of the people that I was hoping to hear an opinion from...

I'd imagine there are few things more impressive than opening one's bonnet with a flourish and having children gasp at all five hundred of your cubic inches.

Of course, any V8 is a good V8. I'd throw a leg over either.

[GoCougs]

Valid points, but I should clarify a few things about my intentions:

If I were to build the 425, the recip ass. would be replaced using forged Olds rods and a crank from a 472. The intake manifold will be from a 500, and shorty headers used.

The gas mileage isn't as much a financial concern as one of range- and while I know neither of them will win awards from Al Gore, one is potentially better than the other.

Right now I'm uncertain as to what I want to do, and I need to get the ball rolling one way or the other.

Thinking along the lines of getting the CR up, how about heads and pistons for the 425? In the least stockers for an early '70s 500 should be at or above 9:1.

FWIW, there's a restored first generation Camaro running around my area with a Caddy 500 and TH400.

[Rupert]

What would the range be with each engine?

[omicron]

What would the range be with each engine?

Two metres for the 500; five for the 425.

[TheIntrepid]

Two metres for the 500; five for the 425.

Hell, I only get 260mi city with a 3.5L V6, I can only imagine what would happen with a rebuilt V8 in an old Caddy boat.

[omicron]

Hell, I only get 260mi city with a 3.5L V6, I can only imagine what would happen with a rebuilt V8 in a wonderful example of American engineering.

Wonderful, wonderful things, my dear Trep.

[SVT666]

FWIW, I doubt your mileage with the 425 is that high right now nevermind after modifications.  Your mileage is gonna suck either way, so I would go with the engine who's parts are more in abundance and the engine that is proven to be the power maker.  Go with the 500.....or just buy one of these:



Chevy 502 with 502 HP or this:



Chevy 572 with 720 HP.

[Raza]

I like things that are quirky and offbeat.  If I were you, I'd go with the 425.

But, were I in your position, I'd go the safer route and use the 500.  But I don't know anything about rebuilds.

With the 425 you're assuming a lot, and you're doing a lot of guessing.  You're hoping for 15mpg, hoping for 400bhp, hoping the engine will be reliable.  There's a little too much uncertainty there for me to be comfortable with that decision.

[3.0L V6]

FWIW, I doubt your mileage with the 425 is that high right now nevermind after modifications.  Your mileage is gonna suck either way, so I would go with the engine who's parts are more in abundance and the engine that is proven to be the power maker.  Go with the 500.....or just buy one of these:



Chevy 502 with 502 HP or this:



Chevy 572 with 720 HP.

Blasphemy. Don't put a Chev engine in your Caddy.

I'd say 500, because mileage won't be much better with the 425, and you'll definitely hit the power mark you want easily.

[J86]

ah fuckit, go 425...the process will be that much more entertaining!

[Eye of the Tiger]

500. BiG-0-TORK FTW!

[FoMoJo]

Use the 500 and put in a bigger gas tank.

[TheIntrepid]

Use the 500 and put in a bigger gas tank.

I can't believe no one suggested that one yet. +1

[Eye of the Tiger]

I can't believe no one suggested that one yet. +1

Or just strap some auxiliary gas cans to the roof, because installing a larger gas tank might not be so easy.

[Soup DeVille]

Hell, I only get 260mi city with a 3.5L V6, I can only imagine what would happen with a rebuilt V8 in an old Caddy boat.

That's why they came with 26 gallon tanks (don't make me explain what a gallon is, canuck).

[Soup DeVille]

FWIW, I doubt your mileage with the 425 is that high right now nevermind after modifications.  Your mileage is gonna suck either way, so I would go with the engine who's parts are more in abundance and the engine that is proven to be the power maker.  Go with the 500.....or just buy one of these:

(pics of crate chevies)

Before I tore the car apart, I was getting 18 MPG highway, and that was with the god awful pellet type cat still intact and clogged up with 28 years of soot. 15 is admittedly the high end of the estimates, but not unimaginable.

Well, not only would I not put the 572 Chevy in there unless I absolutely needed 700+ pump gas HP, but I don't want to spend over $4000 on the engine in the first place.

[Eye of the Tiger]

231 V6 Turbo. I bet two of them, inline, would fit under the Caddy's hood.

[Raghavan]

Sell the Caddy and buy an S2000.
You know you want to.