Street build, specifics listed: '79 350 ($600) or 403 ($600)

[Rob]

Hey everyone.

After two years of gradual upgrades to the appearance of my '88 Cutlass Classic, I finally have the time (and some extra cash) to focus on performance.

What I have now:

• Stock 307, with a nearly perfectly tuned quadrajet carb running on the computer. Gets 29mpg imperial on the highway and takes about 29 seconds to go 0-60.
• Stock TH-2004R. Lockup works.
• 7.5 rear end with 2.56 gears. No posi.
• True duals, 2.5" pipes. No cats. Dynomax super turbo mufflers.
• 215/70 tires on 14x6 chrome rally wheels

Planned upgrades:

• 8.5" rear with 3.42 gears from a Grand National - $350 (no joke)
• Headers

I've come across two candidates for the motor swap and would like to know what you think. Both are running and do not smoke, burn oil, etc.

1. A complete '79 350 rocket, out of a Delta 88. The motor was rebuilt 30,000 miles ago, top and bottom. 3A heads. Unfortunately, the seller has no receipt or build list of what went into it. Assuming it's a stock rebuild, $600 seems like a very good price.

2. A complete stock 403 with only 60,000 miles on it. 4A heads. Never rebuilt. From a late 70s sedan, can't remember which. Currently in a GMC truck. Took it for a drive. Starts easily, runs smooth. Seller was trying to sell the motor and the turbo 400 for $1500 (not a chance), but told me he'll let the motor go for $600.

What I want:

• Mid to low 14s in the quarter mile
• Gobs of power between 40mph and 80mph ... willing to sacrifice "launch" for this.
• Try to retain fuel economy as much as possible. 23-25mpg imperial on the highway shouldn't be a problem, given that I reuse the existing carb ... I want to keep the computer in order to retain converter lockup. The rest of the emissions junk can go.
• Car burns 87 octane (preferably). 91 is all that's readily available, so no more than that.
• Money is a factor as always, but I'm willing to spend money to do the job right. After buying either motor, I'm willing to spend $1000 in rebuild/upgrades.

This car is a daily driver, not a racecar. I'm not interested in high performance add ons that kill "street" driveability and gas mileage (ie: radical cams).

Given the price and potential of these two motors, which seems best able to meet those priorities?

I've already anticipated your first suggestion for either motor ... I have access to:

1. #5 heads for a 350 rocket - $200
2. Steel crank for a small block - $250
3. Big block B, C, or E heads - $150

Don't forget, 91 octane tops. Where does that leave me for compression?

I know you guys get (rightfully) annoyed when someone says "350 vs 403 vs 455" without any explanation, so I hope I've listed everything that is important.

Also posted this in Oldspower ... both of these forums have taught me a great deal over the past 2 years! Thanks to everyone.

 

[G-Body_Vet]

Re: Street build, specifics listed: '79 350 ($600) or 403 ($

I vote 7 or 7A heads on the 403. I think you might be pushing the envelope on octane requirements though. Stock 403's are around 8.0 to 1 CR. Those heads should put you near 9.5 without milling

I'm not an Olds guru, but I thought the "rocket" engines were usually referred to as the older "gold" blocks.

I never take anyone's word on a rebuild without papers either. IMO, street cars can make the most of more cubes/more torque.

 

[CHRIS.O]

Re: Street build, specifics listed: '79 350 ($600) or 403 ($

403 hands down. If you are wanting max power with no mods then having 53 more cubic inches is the way to go. As far as mileage, I really dont think either is gonna give you 23-25mpg. A 403 with an intake and headers would get you going how you want. They are both about the same hp stock but the 403 has 45ftlb more torque. Anything you do to a 350 you can do to a 403 and make more power. Goodluck.

 

[dogsht]

Re: Street build, specifics listed: '79 350 ($600) or 403 ($

Of the two for your goals.. the 403. The Olds did not have the best combustion chamber & head design but with a good quench of around 40 thousands (may require a block deck and or head milling) maybe a lil chamber polish, and proper cam for it (as well as a lil higher lock up stall converter & decent gear to take advantage of the cam) an honest measured calculated 10.0-1 should work fine on 91 octave without pulling timing.

Fwiw more compression up to the point of detonation is more & better efficiency. Better power on the same or less fuel.

 

[Rob]

Re: Street build, specifics listed: '79 350 ($600) or 403 ($

I was leaning towards the 403 myself. I don't trust a 350 rebuild with no receipt, and I know those are the worst of the Olds 350 motors.

The only thing I'm concerned about is making the 403 work with the computer. I'm not concerned with emissions at all, as testing is slack up here in Canada. But I do want to make sure the air/fuel mixture is normal, and the lockup works. If the computer is not happy it'll send out a code, and this will make the lockup converter to refuse to engage, ruining gas mileage and causing additional wear on the transmission.

So basically, how do I ensure the 403 will work well with the computer? Compression should be kept around 9 to 1 and the cam should be very close to stock ... anything else?