I'm torn between deciding to go with an oldsmobile 403 or a 350 rocket.

Both motors need work, and cost about the same price. I want to replace the 260 that is currently in my oversize car.

Here is the 350
http://kansascity.craigslist.org/pts/1721543940.html

Here is the 403
http://kansascity.craigslist.org/pts/1754065991.html

I guess things that help me decide or which is the better deal for the $. Which is more reliable and cheaper/easier to build
Which is easier to find parts for?

I'm leaning towards the 403, but I don't want to make the wrong decision.

Thanks

 

Well they both need to be torn down and gone through...new parts or not. You just don't know what was or wasn't done to the 403.

I think I'd go for the 350, but still look for some early heads like I posted in the other thread. Again because it will bump the compression up. The #8 heads have the large chamber (78cc) and small dish pistons so it will respond well to the early heads. Now if you need new pistons then you can stick with the heads that are on it and modify your compression with pistons instead.

 

Thanks Randy.

When you say earlier 350 heads, that years specifically?

 

I would go with the 350 if it is more complete. Why buy an engine without good heads, intake manifold, exhaust manifolds, oil pan, valve covers etc.?

 

Between the two i would go with the 350. This engine was will most likely be a low compression smog engine can be checked to see if it has the 8 stamped on the heads and you may wish to replace the heads at a later date to some with higher compression. the 403 had Siamese cylinders and had a problem with over heating between the two also was not the strongest on the bottom end. both would work but the 350 is the easier one to rebuild and has a larger knowledge base as to those who have had them and worked on them.

 

68-72 on the heads. 5,6,7,7A

 

Think the smog heads were used 73-75 number 8 heads

 

Thanks for the reply guys, I just found a complete 350 engine and t-350 trans set up out of a 1969 cutlass, asking $400. Might go that route

 

What trans is in there now?

 

It was actually 73-76. They changed them in 77 when they revamped the 350 with the windowed mains and ½" head bolts.

 

That was a later question I was going to ask. The dealership had very little information about this car, they were not sure on what the transmission or what the motor was in this car. Originally the car had a 330 in it, but was replaced somewhere down the road. I have no clue as if the transmission was replaced or not.

Is there any type of identification number on the transmission?

 

Is it a 3 speed or a 2 speed?

 

Haven't driven it more than from the trailer to the driveway. I'm currently getting the carb rebuilt. Should get it back early next week, so I will drive it around and figure it out

 

Well move the shifter and count the clicks from park. 4 is a 2 speed and 5 is a 3 speed.

 

7a heads have hardened valve seats and allow you to run unleaded with no worries about valve seat wear and eventual valve recession.

 

My vote is the 350. The deal with the trans sounds decent. I agree you should go thru it & make some intelligent upgrades. The 403 is a strong engine but a weak bottom end. You can only get one overbore on it before the cylinder walls become too thin. Throw some good light weight 10:1 pistons in it, have it ballanced, put one of Jim's Halo girdles on it. Then choose the right cam for your application and concentrate on the heads, intake, and carb matched setup. You might want to look into getting a Holley Street Dominator intake for it. I've heard good things about them. I have one I could sell you but I personally haven't tried it. If you contact Jim here he can give you advise on a cam or headwork. He's a good guy & can help you.
http://www.jsmachineoldsmobile.com/home.html
Here's a chart with SB head specs that should help you in your search.
001.jpg
The smaller combustion chamber will yield higher compression ratios but you can also mill the heads. Some engine builders might debate with you about whether or not hardened seats are really necessary. I'm not going to comment but for what it costs to have new seats installed you could probably buy ten cases of lead additive.

 

It moved 4 times so it is a 2 speed, will the tranny included with that 350 work?

 

From what I have seen in the last week the 350 should bolt up in place of the Jetaway you have so that shouldn't be an issue. You'll just need to run a cable for the kickdown to the carb or the pedal.

 

Either way you go, you are going to want heads. I say go with the new parts and the "free" engine stand with the 403. OF COURSE take it apart and look at what is going on, but if the seller is being honest, you are going to come out ahead.

On the subject of overbore: the 403 is standard, if it looks like it will hold at that you have another build in the motor. (Maybe 2 if you're lucky) and that should be lots o'miles and smiles from now.

My uncle had a 403 in a regal, so I am a little biased. I am building one right now. Most parts interchange with the 350.

Good luck making a choice. Either way you'll end up way ahead of the 260. Lot's of ways to go here.

sb

 

This is another good opportunity for a raffle ...whomever guesses which engine you get goes to Vegas...

 

I'd go with the 350/350 setup if it's in good shape. 1969 should have decent pistons in it.

 

well svnt you owe me a new tranny!!! (JK)

I walked in the garage today to find a pool of transmission fluid on the ground
all i did was go from park to L then back

o well, guess that 350, with the T-350 is what i'm getting especially now

 

If you just want a cruiser, both will do fine.
Which one is more complete?
Which one needs more work?
How much power do you want to make?
The only REAL difference between the two is the bore size.
The 403 will give you an easy 40-50 more hp (due to displacement), do you really need or want it?
The 403 will be perfectly fine to around 400hp at the crank, if there is no detonation.
Jim

 

I wonder what happened to cause that? How odd.

 

Just how my luck goes

I'm definitely going to pick up that 350 motor and trans combo next weekend, and rebuild the motor.

 

Well Its finally official.. Saturday I'm going to pick up a 1966 425 olds motor. It was rebuilt 5 years ago but was never started, rebuilt with all new parts,cam, lifters heades redone etc. comes with eldabrock performer intake. It has been stiting for a while.

forsaleitems006.jpg

 

While I do not like things that have been parked and not kept fresh. I do like the 425. Please let us know how things turn out.

 

I plan on tearing into it regardless. Replacing gaskets, re-lube, etc

Don't plan on dropping it for a few months.

 

Nice use of a beer can to keep the motor from rocking in the back of the truck...

 

Great find!
I would check a few things, and change a few things-IF it were me.
Check:
bearing clearances
Oil pump, mods to it.
ring gaps
Compression ratio (what pistons were used)
Camshaft???
Valve size
Correct valve stem tip height!!!!!
Check for correct plugs in oil galleys...

Change?
I'd clean it.
Sell the carb and valve covers, use your 260 valve covers (!), and a q-jet.
Good luck, you're going to love this engine!!!
Jim

 

Thanks for the tips Jim I will go over it very carefully, with a buddy of mine.

My 260 valve covers are blue, What was the factory color of a 1965 425 block and heads and valve covers? I'd like to paint it back to stock

 

It should be a red color, but I don't know the exact color red. Some of the guys are really up on the stock engine colors.

 

Tear it apart,so you know exactly what you have.Great find,& great engine to build.

 

I've always gone with the old tire method myself