403 Olds engine

PetChemMan · December 15th, 2005, 08:31 PM

Circa 1979, a 403 CID engine was available in the full sized Olds cars. What was the origin of that engine? Was it an enlarged 350 ?

Oldsmaniac · December 18th, 2005, 06:40 PM

The 403 is based on the 350 or should I say on the small block Olds but has siameesed cylinder walls meaning there arent any cooling passages between cylinders.....cooling problems can be had with the slightest of overbore on the 403....the stroke is longer as well compared to a 350.....

jdorour · January 3rd, 2006, 11:36 PM

The 403 CI engine is a low deck (small block) introduced in 1977 to replace the 455 as the top of the line Olds engine. The 403 does not have siemesed cylinders and has the same 3.385 inch stroke as the 260, 307, 330 and 350 engines.
The 403 was used in the entire Olds line as well as Buick, Motorhomes and The Pontiac TransAm.
It has "windowed" main webs that cause the bottom end to flex when under extreme loads but the engine is fine for street use. You can really wake a 403 up with a set of big block heads and a good cam.

Oldsmaniac · January 4th, 2006, 03:31 PM

Ok, I stand corrected on the stroke issue with the 403....On 442.com they state that the 403 does have siamesed cylinders a few times in their FAQ's....and I thought I indeed saw that with my own eyes on the disassembled 403 thats in my brother's garage....

jdorour · January 5th, 2006, 10:59 AM

I could be wrong. I was going on memory. I have not had a 403 apart in a long time. It could have siamessed cylinders.

texasred · February 21st, 2006, 07:07 PM

Yes, it has siamesed cylinder walls. But, as I've said before, I wouldn't trust the 442-dot-bomb FAQ for tech info without a second independant source.

C.J.

March 1st, 2006, 11:23 AM

I have a 403 in my 19ft. Sunkisst jetboat. I was thinking of changing it over to a 455 but need info on a few things first. Is the bell housing and mounting the same? Is the engine mounts the same? Exhaust manifold same? Anyone have info or a link to basic engine specs for horsepower and rpm?

jdorour · March 1st, 2006, 11:47 AM

The bellhousing, flywheel, and engine mounts are the same.
The 403 uses small port small block heads and manifolds. The 455 uses the large port heads and manifolds. However, the bolt pattern is the same. If you install the manifolds from your engine on the 455 heads you will, at best, have a restriction. I think the restriction would be minimal. At worst you will burn the gaskets if you use the small block gasket set and the small block manifolds on the big block heads. This will cause an exhaust leak. The 455 is also a little heavier.

The factory output rating for a 455 will depend on the year and model you choose. They had a high of 400HP & 510LBS/FT (SAE Gross) to a low of something like 180HP & 200LBS/FT (SAE NET) by 1976. But if you paln to build the engine for use in a boat you can get all kinds of power from any 455.

If you build your engine make sure you tell your engine builder/Camshaft MFG that you are puting it in a JET BOAT as the performance requirements are a little different than for a Prop Boat. AND FOR YOUR SAFETY TRY TO USE AS MUCH MARINE SPEC COMPONENTS AS YOU CAN. I grew up on the water in Connecticut and saw a lot of people get hurt from bilge fires.

Have fun
John

March 1st, 2006, 12:05 PM

Thank you for the quick info. jdorour. The 403 installed now is still running, so I'm not changing anything yet. But maybe in the future a 455 or just a slightly pepped up 403. I basically want some more speed with little money and mod's.
As for marine equipment; yes that is important stuff! I was informed that boats must have special marine grade alternator, carb, fuel pump, and fuel lines inorder to help reduce the risk of a fire and/or kabooms!

T1MWV · August 10th, 2008, 05:53 AM

Hi,

I have been searching the net for info on Olds 403 fitted to a boat and see that you have exactly that. I have just bought an engine and am embarking on fitting it but could do with a few pointers if you can help me.

Which marine manifolds fit this engine? What other changes have you made to take it from an automotive engine to run in your boat?

Any help would be greatly appreciated.

Thanks in advance.

Tim

joe_padavano · August 10th, 2008, 11:52 AM

To clarify the info above, the discussion about manifolds was concerned with automotive manifolds. Most marine manifolds I've seen for an Olds will fit both big and small blocks the same. Depending on which ones you have, they should fit both a 403 and 455 just fine.

88 coupe · August 10th, 2008, 11:52 AM

Welcome to the site.

After you check the date on this thread, try RealOldsPower.com.

And consider starting your own thread.

Norm

December 15th, 2005, 08:31 PM	#1 (permalink)
PetChemMan Registered User Join Date: Aug 2004 Posts: 93	Circa 1979, a 403 CID engine was available in the full sized Olds cars. What was the origin of that engine? Was it an enlarged 350 ? __________________ Love those Starfires

January 3rd, 2006, 11:36 PM	#3 (permalink)
jdorour Senior Member Join Date: Feb 2004 Location: Atlanta, GA. Posts: 122	The 403 CI engine is a low deck (small block) introduced in 1977 to replace the 455 as the top of the line Olds engine. The 403 does not have siemesed cylinders and has the same 3.385 inch stroke as the 260, 307, 330 and 350 engines. The 403 was used in the entire Olds line as well as Buick, Motorhomes and The Pontiac TransAm. It has "windowed" main webs that cause the bottom end to flex when under extreme loads but the engine is fine for street use. You can really wake a 403 up with a set of big block heads and a good cam. __________________ 1966 Ninety Eight Convertible - 425 Tri-Carb, Factory Dual Exh, Switch-Pitch THM400, 3.54 Posi. 1966 Catalina Wagon - 421 Tri-Power, M21, 4.11 Saf-T-Trac, 8 Bolt Wheels 1989 IROC-Z - 5.7TPI

January 5th, 2006, 10:59 AM	#5 (permalink)
jdorour Senior Member Join Date: Feb 2004 Location: Atlanta, GA. Posts: 122	I could be wrong. I was going on memory. I have not had a 403 apart in a long time. It could have siamessed cylinders. __________________ 1966 Ninety Eight Convertible - 425 Tri-Carb, Factory Dual Exh, Switch-Pitch THM400, 3.54 Posi. 1966 Catalina Wagon - 421 Tri-Power, M21, 4.11 Saf-T-Trac, 8 Bolt Wheels 1989 IROC-Z - 5.7TPI

March 1st, 2006, 11:47 AM	#8 (permalink)
jdorour Senior Member Join Date: Feb 2004 Location: Atlanta, GA. Posts: 122	The bellhousing, flywheel, and engine mounts are the same. The 403 uses small port small block heads and manifolds. The 455 uses the large port heads and manifolds. However, the bolt pattern is the same. If you install the manifolds from your engine on the 455 heads you will, at best, have a restriction. I think the restriction would be minimal. At worst you will burn the gaskets if you use the small block gasket set and the small block manifolds on the big block heads. This will cause an exhaust leak. The 455 is also a little heavier. The factory output rating for a 455 will depend on the year and model you choose. They had a high of 400HP & 510LBS/FT (SAE Gross) to a low of something like 180HP & 200LBS/FT (SAE NET) by 1976. But if you paln to build the engine for use in a boat you can get all kinds of power from any 455. If you build your engine make sure you tell your engine builder/Camshaft MFG that you are puting it in a JET BOAT as the performance requirements are a little different than for a Prop Boat. AND FOR YOUR SAFETY TRY TO USE AS MUCH MARINE SPEC COMPONENTS AS YOU CAN. I grew up on the water in Connecticut and saw a lot of people get hurt from bilge fires. Have fun John __________________ 1966 Ninety Eight Convertible - 425 Tri-Carb, Factory Dual Exh, Switch-Pitch THM400, 3.54 Posi. 1966 Catalina Wagon - 421 Tri-Power, M21, 4.11 Saf-T-Trac, 8 Bolt Wheels 1989 IROC-Z - 5.7TPI

August 10th, 2008, 05:53 AM	#10 (permalink)
T1MWV Junior Member Join Date: Aug 2008 Posts: 1	Olds 403 in a boat Hi, I have been searching the net for info on Olds 403 fitted to a boat and see that you have exactly that. I have just bought an engine and am embarking on fitting it but could do with a few pointers if you can help me. Which marine manifolds fit this engine? What other changes have you made to take it from an automotive engine to run in your boat? Any help would be greatly appreciated. Thanks in advance. Tim

December 18th, 2005, 06:40 PM	#2 (permalink)
Oldsmaniac Registered User Join Date: Oct 2005 Location: NJ Posts: 702	The 403 is based on the 350 or should I say on the small block Olds but has siameesed cylinder walls meaning there arent any cooling passages between cylinders.....cooling problems can be had with the slightest of overbore on the 403....the stroke is longer as well compared to a 350.....

January 4th, 2006, 03:31 PM	#4 (permalink)
Oldsmaniac Registered User Join Date: Oct 2005 Location: NJ Posts: 702	Ok, I stand corrected on the stroke issue with the 403....On 442.com they state that the 403 does have siamesed cylinders a few times in their FAQ's....and I thought I indeed saw that with my own eyes on the disassembled 403 thats in my brother's garage....

February 21st, 2006, 07:07 PM	#6 (permalink)
texasred Tom Servo's Stunt Double Join Date: Apr 2004 Location: San Antonio, Texas Posts: 824	Yes, it has siamesed cylinder walls. But, as I've said before, I wouldn't trust the 442-dot-bomb FAQ for tech info without a second independant source. C.J.

March 1st, 2006, 11:23 AM	#7 (permalink)
Lutzifer Guest Posts: n/a	I have a 403 in my 19ft. Sunkisst jetboat. I was thinking of changing it over to a 455 but need info on a few things first. Is the bell housing and mounting the same? Is the engine mounts the same? Exhaust manifold same? Anyone have info or a link to basic engine specs for horsepower and rpm?

March 1st, 2006, 12:05 PM	#9 (permalink)
Lutzifer Guest Posts: n/a	Thank you for the quick info. jdorour. The 403 installed now is still running, so I'm not changing anything yet. But maybe in the future a 455 or just a slightly pepped up 403. I basically want some more speed with little money and mod's. As for marine equipment; yes that is important stuff! I was informed that boats must have special marine grade alternator, carb, fuel pump, and fuel lines inorder to help reduce the risk of a fire and/or kabooms!

August 10th, 2008, 11:52 AM	#11 (permalink)
joe_padavano Super Moderator Join Date: Mar 2007 Location: Northern VA Posts: 4,395	To clarify the info above, the discussion about manifolds was concerned with automotive manifolds. Most marine manifolds I've seen for an Olds will fit both big and small blocks the same. Depending on which ones you have, they should fit both a 403 and 455 just fine. __________________ Joe Padavano 64 Jetstar 88 Conv 66 442 L-69 Conv 68 W-30 69 H/O 69 442 70 W-30 72 442 84 Custom Cruiser 86 Caprice wagon (w/307 Olds)

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