On the top of the main block. Next to each cylinder bore hole. GM stamped a letter code as to the bore size of that cylinder. The 403 was Olds first use of Siamese cylinder blocks. ( No water could pass between the adjoining cylinders.) They may have been concerned about cylinder expansion. I don't know. Chevy did the Siamese design with their small block 400 at the same time as Olds did. Chevy also had a big block 400. That didn't have the Siamese cylinders. Bob Dunahugh
Interesting note on the 403 piston bore size
- Thread starter Bob Dunahugh
- Start date
Interesting. Did they make any effort to select pistons for fit?
Someone I used to know worked for olds in the late 60s early 70s said they had an in house 'Blueprinting" effort on certain engines on a separate
line
THe chevy SB 400s [esp the 70 4bolt mains ] are popular in the Hi po world- Ive runa few but they tend to overheat
Didnt know the 403s were siamesed bore. Dont really hear about overheating problems with them. Different cooling flow?
--
76 Glenbrook
Someone I used to know worked for olds in the late 60s early 70s said they had an in house 'Blueprinting" effort on certain engines on a separate
line
THe chevy SB 400s [esp the 70 4bolt mains ] are popular in the Hi po world- Ive runa few but they tend to overheat
Didnt know the 403s were siamesed bore. Dont really hear about overheating problems with them. Different cooling flow?
--
76 Glenbrook
403s were big blocks. The fender badges said "400" to really confuse you at the parts counter.
--
John Lebetski
Woodstock, IL
77 Eleganza II
--
John Lebetski
Woodstock, IL
77 Eleganza II
To be clear I'm talking 403 Chevy BB. 403 Olds considered SB.
--
John Lebetski
Woodstock, IL
77 Eleganza II
--
John Lebetski
Woodstock, IL
77 Eleganza II
Not seen the 403 large block chev, what did it fit when? Many many 400 small blocks because Back When, one class of racing allowed the 350 with a
4BBL but limited the 400 to a two BBL. The move was to get the huge two bbl fitted to some trucks, which will flow 600cfm or so. And eat the 350 on
a dirt track.
--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
4BBL but limited the 400 to a two BBL. The move was to get the huge two bbl fitted to some trucks, which will flow 600cfm or so. And eat the 350 on
a dirt track.
--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
> On the top of the main block. Next to each cylinder bore hole. GM stamped a letter code as to the bore size of that cylinder. The 403 was Olds
> first use of Siamese cylinder blocks. ( No water could pass between the adjoining cylinders.) They may have been concerned about cylinder
> expansion. I don't know. Chevy did the Siamese design with their small block 400 at the same time as Olds did. Chevy also had a big block 400. That
> didn't have the Siamese cylinders. Bob Dunahugh
Of the three 455 blocks I have recently looked at, all three had some bore size marks on the desk. If you can dig into the GM paperwork, it is not
too hard to find out what they mean. In later years, they went to stamping the bore on the oil pan rail of the block.
All of the major (and so not so major have done Siamese bore (liners) over the years. All with varying degrees of success. The Chevy SB400 is a
great example of one of the lessor successes. Kind of like their 502. Great for boats that run 50~100 hrs a year.
Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
> first use of Siamese cylinder blocks. ( No water could pass between the adjoining cylinders.) They may have been concerned about cylinder
> expansion. I don't know. Chevy did the Siamese design with their small block 400 at the same time as Olds did. Chevy also had a big block 400. That
> didn't have the Siamese cylinders. Bob Dunahugh
Of the three 455 blocks I have recently looked at, all three had some bore size marks on the desk. If you can dig into the GM paperwork, it is not
too hard to find out what they mean. In later years, they went to stamping the bore on the oil pan rail of the block.
All of the major (and so not so major have done Siamese bore (liners) over the years. All with varying degrees of success. The Chevy SB400 is a
great example of one of the lessor successes. Kind of like their 502. Great for boats that run 50~100 hrs a year.
Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
Hi Johnny, you saw a 403 bb Chevy on the engine stand in the barn. It came out in 1970, it is a .30 over 396. Was still called a 396 in Camaro's and
Chevelles but in trucks and Monte Carlos was called a 400. The 70 - 71 4 bolt main 400 small block had 2 bbl carbs then in73 the 400 went to 2 bolt
mains and4 bbl q-jets.
> Not seen the 403 large block chev, what did it fit when? Many many 400 small blocks because Back When, one class of racing allowed the 350 with a
> 4BBL but limited the 400 to a two BBL. The move was to get the huge two bbl fitted to some trucks, which will flow 600cfm or so. And eat the 350
> on a dirt track.
>
> --johnny
--
C. Boyd
76 Crestmont
East Tennessee
Chevelles but in trucks and Monte Carlos was called a 400. The 70 - 71 4 bolt main 400 small block had 2 bbl carbs then in73 the 400 went to 2 bolt
mains and4 bbl q-jets.
> Not seen the 403 large block chev, what did it fit when? Many many 400 small blocks because Back When, one class of racing allowed the 350 with a
> 4BBL but limited the 400 to a two BBL. The move was to get the huge two bbl fitted to some trucks, which will flow 600cfm or so. And eat the 350
> on a dirt track.
>
> --johnny
--
C. Boyd
76 Crestmont
East Tennessee
If being picky - a 0.030” over Chevy 396 is a 402!
Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath
>
> Hi Johnny, you saw a 403 bb Chevy on the engine stand in the barn. It came out in 1970, it is a .30 over 396. Was still called a 396 in Camaro's and
> Chevelles but in trucks and Monte Carlos was called a 400. The 70 - 71 4 bolt main 400 small block had 2 bbl carbs then in73 the 400 went to 2 bolt
> mains and4 bbl q-jets.
Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath
>
> Hi Johnny, you saw a 403 bb Chevy on the engine stand in the barn. It came out in 1970, it is a .30 over 396. Was still called a 396 in Camaro's and
> Chevelles but in trucks and Monte Carlos was called a 400. The 70 - 71 4 bolt main 400 small block had 2 bbl carbs then in73 the 400 went to 2 bolt
> mains and4 bbl q-jets.
Main reason siamese cylinders did not work well for Chevy and they did for
OLDS was the metallurgy involved. Olds used high nickel alloy in their
blocks, Chev used graphite (carbon) alloy. One wears well, the other wears
out quickly but is cheaper to cast and machine. All about the benjamins.
Jim Hupy
> If being picky - a 0.030” over Chevy 396 is a 402!
>
> Rob
> Victoria, BC
> 76 Royale - Rear Twins/Dry Bath
>
> > On Aug 31, 2018, at 5:53 PM, Charles Boyd
> >
> > Hi Johnny, you saw a 403 bb Chevy on the engine stand in the barn. It
> came out in 1970, it is a .30 over 396. Was still called a 396 in Camaro's
> and
> > Chevelles but in trucks and Monte Carlos was called a 400. The 70 - 71
> 4 bolt main 400 small block had 2 bbl carbs then in73 the 400 went to 2 bolt
> > mains and4 bbl q-jets.
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
OLDS was the metallurgy involved. Olds used high nickel alloy in their
blocks, Chev used graphite (carbon) alloy. One wears well, the other wears
out quickly but is cheaper to cast and machine. All about the benjamins.
Jim Hupy
> If being picky - a 0.030” over Chevy 396 is a 402!
>
> Rob
> Victoria, BC
> 76 Royale - Rear Twins/Dry Bath
>
> > On Aug 31, 2018, at 5:53 PM, Charles Boyd
> >
> > Hi Johnny, you saw a 403 bb Chevy on the engine stand in the barn. It
> came out in 1970, it is a .30 over 396. Was still called a 396 in Camaro's
> and
> > Chevelles but in trucks and Monte Carlos was called a 400. The 70 - 71
> 4 bolt main 400 small block had 2 bbl carbs then in73 the 400 went to 2 bolt
> > mains and4 bbl q-jets.
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
Chris Tyler. The 403's that I've checked the pistons in. The same letters next to the bore. Matched as to the piston size. Seems that the pistons were matched to the bore. Surprising to me. Never saw the markings that Matt C mentioned on the 455. I've always been into the Chevys. But always felt that Olds built a more dependable engine. Bob Dunahugh
________________________________
From: Bob Dunahugh
Sent: Thursday, August 30, 2018 11:22 PM
To: gmclist
Subject: Interesting note on the 403 piston bore size
On the top of the main block. Next to each cylinder bore hole. GM stamped a letter code as to the bore size of that cylinder. The 403 was Olds first use of Siamese cylinder blocks. ( No water could pass between the adjoining cylinders.) They may have been concerned about cylinder expansion. I don't know. Chevy did the Siamese design with their small block 400 at the same time as Olds did. Chevy also had a big block 400. That didn't have the Siamese cylinders. Bob Dunahugh
________________________________
From: Bob Dunahugh
Sent: Thursday, August 30, 2018 11:22 PM
To: gmclist
Subject: Interesting note on the 403 piston bore size
On the top of the main block. Next to each cylinder bore hole. GM stamped a letter code as to the bore size of that cylinder. The 403 was Olds first use of Siamese cylinder blocks. ( No water could pass between the adjoining cylinders.) They may have been concerned about cylinder expansion. I don't know. Chevy did the Siamese design with their small block 400 at the same time as Olds did. Chevy also had a big block 400. That didn't have the Siamese cylinders. Bob Dunahugh
Rob. Not picky. Just a fact on what went on back then. Never understood why Chevy had a big block, and small block that were both referred to as 400's. Remember. Figures don't lie. But liars can figure. We see this same thing now with ALTERNITIVE FACTS.
Bob Dunahugh
Bob Dunahugh
I was referring to the fact that the 0.030” over 396 BBC is a 402, NOT a 403. The small block 400 is really a 401 (which, if used - would just confuse things even more!).
I agree that GM did some very odd stuff at times. I still occasionally come across a Trans Am owner that think their 403 is a Pontiac engine...
Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath
>
> Rob. Not picky. Just a fact on what went on back then. Never understood why Chevy had a big block, and small block that were both referred to as 400's. Remember. Figures don't lie. But liars can figure. We see this same thing now with ALTERNITIVE FACTS.
>
> Bob Dunahugh
I agree that GM did some very odd stuff at times. I still occasionally come across a Trans Am owner that think their 403 is a Pontiac engine...
Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath
>
> Rob. Not picky. Just a fact on what went on back then. Never understood why Chevy had a big block, and small block that were both referred to as 400's. Remember. Figures don't lie. But liars can figure. We see this same thing now with ALTERNITIVE FACTS.
>
> Bob Dunahugh
GM and many other domestic and foreign manufacturers have selectively
fitted pistons into cylinder boxes since the 1940's and perhaps earlier
than that. Production lines being what they are, emphathis has always been
on assembling the most units at the lowest cost.
Is that bad? Depends on who you ask. Automobile manufacturers have
always used offsite suppliers for components that are used to manufacture
their products. Castings, forgings, fasteners, difficult to manufacture
stuff like pistons and rings, it is a big list. Trying to get all those
pieces to fit each other and hold up longer than the warranty period, with
your competition breathing down your neck, has and is challenging. Lots of
steps involved. Same for automotive rebuilders. They have to know many
brands, not just one. Keeps you on your toes. Just ask Dick Paterson.
Jim Hupy
Salem, Or
> I was referring to the fact that the 0.030” over 396 BBC is a 402, NOT a
> 403. The small block 400 is really a 401 (which, if used - would just
> confuse things even more!).
>
> I agree that GM did some very odd stuff at times. I still occasionally
> come across a Trans Am owner that think their 403 is a Pontiac engine...
>
> Rob
> Victoria, BC
> 76 Royale - Rear Twins/Dry Bath
>
> >
> > Rob. Not picky. Just a fact on what went on back then. Never
> understood why Chevy had a big block, and small block that were both
> referred to as 400's. Remember. Figures don't lie. But liars can figure. We
> see this same thing now with ALTERNITIVE FACTS.
> >
> > Bob Dunahugh
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
fitted pistons into cylinder boxes since the 1940's and perhaps earlier
than that. Production lines being what they are, emphathis has always been
on assembling the most units at the lowest cost.
Is that bad? Depends on who you ask. Automobile manufacturers have
always used offsite suppliers for components that are used to manufacture
their products. Castings, forgings, fasteners, difficult to manufacture
stuff like pistons and rings, it is a big list. Trying to get all those
pieces to fit each other and hold up longer than the warranty period, with
your competition breathing down your neck, has and is challenging. Lots of
steps involved. Same for automotive rebuilders. They have to know many
brands, not just one. Keeps you on your toes. Just ask Dick Paterson.
Jim Hupy
Salem, Or
> I was referring to the fact that the 0.030” over 396 BBC is a 402, NOT a
> 403. The small block 400 is really a 401 (which, if used - would just
> confuse things even more!).
>
> I agree that GM did some very odd stuff at times. I still occasionally
> come across a Trans Am owner that think their 403 is a Pontiac engine...
>
> Rob
> Victoria, BC
> 76 Royale - Rear Twins/Dry Bath
>
> >
> > Rob. Not picky. Just a fact on what went on back then. Never
> understood why Chevy had a big block, and small block that were both
> referred to as 400's. Remember. Figures don't lie. But liars can figure. We
> see this same thing now with ALTERNITIVE FACTS.
> >
> > Bob Dunahugh
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
Thanks for the clarification, Chuck. I'm not a gint chev fan - usually want something to outrun them 
Cummins didn't siamese the cylinders in the
Big Cam motors so the could rebuild with liners and new pistons. Unfortunately they came out too close together and would boiled the water between
pairs which led to erosion of the liner steel. Their solution was water filters numbered one to five which related to the amount of chemical in the
filter to lessen the erosion wit5hout eroding the radiator with it according to my long term Cummins/Onan tech. There was a test kit to determine the
amount of the stuff in the coolant, and the proper filter was selected based on the test. Ours made it 22 years that way until one pinholed. OIl in
the water, coolant in the oil, gimme a short block.
--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
Cummins didn't siamese the cylinders in theBig Cam motors so the could rebuild with liners and new pistons. Unfortunately they came out too close together and would boiled the water between
pairs which led to erosion of the liner steel. Their solution was water filters numbered one to five which related to the amount of chemical in the
filter to lessen the erosion wit5hout eroding the radiator with it according to my long term Cummins/Onan tech. There was a test kit to determine the
amount of the stuff in the coolant, and the proper filter was selected based on the test. Ours made it 22 years that way until one pinholed. OIl in
the water, coolant in the oil, gimme a short block.
--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
