421 bellhousing
Thread Starter
Le Mans Master
Joined: Aug 2010
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From: Bussey, IA
403 bellhousing
403 bellhousing is correct for a 1968 Coupe 327 with a Muncie 4 speed (with 153 tooth flywheel)?
Last edited by Giddy-up Go; Jul 27, 2025 at 09:41 PM. Reason: Error in number
Drifting
Joined: Jun 2025
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I cannot address specifics of 1968 327 clutch/flywheel/starter etc; Because I have not had my hands on a 68 with a 327 so I cannot KNOW.
But, in general, 153 tooth flywheels work with straight across OE starter bolt pattern (Not staggered, Not diagonal)
While 168 tooth flywheels work with diagonal aka staggered OE starter bolt pattern (Not straight-across).
And, to be clear; ALL OE starters bolt to block and do Not bolt to bellhousing.
There are a relatively Few blocks which have two sets/pairs of holes in a single discrete line; which can accommodate a straight across starter bolt pattern but also a 168 tooth flywheel.
* seems you edited/changed your question while I was editing /clarifying my reply
But, in general, 153 tooth flywheels work with straight across OE starter bolt pattern (Not staggered, Not diagonal)
While 168 tooth flywheels work with diagonal aka staggered OE starter bolt pattern (Not straight-across).
And, to be clear; ALL OE starters bolt to block and do Not bolt to bellhousing.
There are a relatively Few blocks which have two sets/pairs of holes in a single discrete line; which can accommodate a straight across starter bolt pattern but also a 168 tooth flywheel.
* seems you edited/changed your question while I was editing /clarifying my reply
Last edited by Rebelyell; Jul 27, 2025 at 09:56 PM.
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,094
Likes: 4,449
From: Marlton NJ
That would be the smaller 10.5" clutch that was used on SBs until 68.
11" was used afterward, with the other starter, flywheel and bellhousing
They changed that when the 350 came out, with it's extra torque.
In 68 only the 350 SB got the bigger flywheel setup. My SS Camaro had it.
11" was used afterward, with the other starter, flywheel and bellhousing
They changed that when the 350 came out, with it's extra torque.
In 68 only the 350 SB got the bigger flywheel setup. My SS Camaro had it.
Race Director
Joined: Oct 2000
Posts: 12,682
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From: Shamong, NJ
As you can see from the Parts Book page 69L88 posted, the "403" casting was also made wearing the casting number 3840383. I think the "403" is more common bellhousing. In fact, in 45 years of dealing in parts I don't recall ever having a "383" casting, but if you come across one cast "383" it will work with your 153 tooth flywheel.
That would be the smaller 10.5" clutch that was used on SBs until 68.
11" was used afterward, with the other starter, flywheel and bellhousing
They changed that when the 350 came out, with it's extra torque.
In 68 only the 350 SB got the bigger flywheel setup. My SS Camaro had it.
11" was used afterward, with the other starter, flywheel and bellhousing
They changed that when the 350 came out, with it's extra torque.
In 68 only the 350 SB got the bigger flywheel setup. My SS Camaro had it.
Again, I don't know why the change was made, especially when you consider the smaller flywheel will allow the engine rev a little freer, but it doesn't appear to me the torque rating had anything to do with it?
Thread Starter
Le Mans Master
Joined: Aug 2010
Posts: 8,519
Likes: 505
From: Bussey, IA
Yes, the "403" is the bellhousing you need if you're using the 153 tooth, 12" diameter flywheel, but wasn't this all discussed and answered in your post from about a week ago?
As you can see from the Parts Book page 69L88 posted, the "403" casting was also made wearing the casting number 3840383. I think the "403" is more common bellhousing. In fact, in 45 years of dealing in parts I don't recall ever having a "383" casting, but if you come across one cast "383" it will work with your 153 tooth flywheel.
I don't know exactly why GM went to the 11" clutch (14" dia. 168 tooth flywheel) in 68, but I don't think it had anything to do with the amount of torque a standard 350 produced. The smaller 12" flywheel, 10 1/2" clutch combination was what Chevrolet used behind some of their strongest engines, including the 1965 L-78 396/425 (415 ft lb torque), the 67-69 427 L-88 (460 ft lb "advertised" torque) and the 70-72 LT-1 (380 ft lb,of torque. the same as the standard 69-70 LM-1/L-48 4bbl 350).
Again, I don't know why the change was made, especially when you consider the smaller flywheel will allow the engine rev a little freer, but it doesn't appear to me the torque rating had anything to do with it?
As you can see from the Parts Book page 69L88 posted, the "403" casting was also made wearing the casting number 3840383. I think the "403" is more common bellhousing. In fact, in 45 years of dealing in parts I don't recall ever having a "383" casting, but if you come across one cast "383" it will work with your 153 tooth flywheel.
I don't know exactly why GM went to the 11" clutch (14" dia. 168 tooth flywheel) in 68, but I don't think it had anything to do with the amount of torque a standard 350 produced. The smaller 12" flywheel, 10 1/2" clutch combination was what Chevrolet used behind some of their strongest engines, including the 1965 L-78 396/425 (415 ft lb torque), the 67-69 427 L-88 (460 ft lb "advertised" torque) and the 70-72 LT-1 (380 ft lb,of torque. the same as the standard 69-70 LM-1/L-48 4bbl 350).
Again, I don't know why the change was made, especially when you consider the smaller flywheel will allow the engine rev a little freer, but it doesn't appear to me the torque rating had anything to do with it?
