396 325hp vs 350 vs 375 - Chevelle Tech
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post #1 of 33 (permalink) Old Apr 14th, 16, 9:24 PM Thread Starter
MJL
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396 325hp vs 350 vs 375

Have a 1969 chevelle SS 396 325 hp, what changes were made to make a 350 hp and also a 375hp?


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post #2 of 33 (permalink) Old Apr 14th, 16, 9:58 PM
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Re: 396 325hp vs 350 vs 375

I am sure the differences are many. Off the top of my head I belive the 325 had a cast crank shaft and the.350 & 375 had a forged crank. The 375 had 4 bolt mains while the other two had 2 bolt mains. I believe the 375 block had a provision for an oil cooler. Also not positive without checking but I think the 375 had square port heads and the 325 had oval port heads. Not sure on the 350.
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post #3 of 33 (permalink) Old Apr 14th, 16, 10:05 PM
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Re: 396 325hp vs 350 vs 375

Ya the 375 hp had forged pistons,large port closed chambered heads,solid lifter camshaft,aluminum intake,just a few i can think of.
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post #4 of 33 (permalink) Old Apr 14th, 16, 11:12 PM Thread Starter
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Re: 396 325hp vs 350 vs 375

Yes, I believe all the things mentioned are true, but does a forged crank versus a cast crank and 4 bolt vs 2 add horsepower or are those things necessary when you have more horsepower?


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post #5 of 33 (permalink) Old Apr 14th, 16, 11:22 PM
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Re: 396 325hp vs 350 vs 375

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Originally Posted by MJL View Post
Yes, I believe all the things mentioned are true, but does a forged crank versus a cast crank and 4 bolt vs 2 add horsepower or are those things necessary when you have more horsepower?


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Forged crank & 4 bolt mains add no power but add strength so the engine can live.
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post #6 of 33 (permalink) Old Apr 15th, 16, 2:47 AM
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Re: 396 325hp vs 350 vs 375

Quote:
Originally Posted by MJL View Post
Have a 1969 chevelle SS 396 325 hp, what changes were made to make a 350 hp and also a 375hp?


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Major difference between a 325 and 350 H.P. was the camshaft.

375 H.P. was considerably different with its solid lifter cam, forged 11 to 1 pistons, rectangular port heads with matching aluminum intake with large Holley carb. All 375 H.P. engines had forged crank and 4 bolt main block.

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post #7 of 33 (permalink) Old Apr 15th, 16, 11:38 AM
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Re: 396 325hp vs 350 vs 375

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Originally Posted by GLHS60 View Post
Major difference between a 325 and 350 H.P. was the camshaft.
That's the way I remember it. Both had Q-Jet carbs and oval-port heads. Same compression.

The 325 hp cam was a real turd. The 350 hp cam wasn't a lot better. The aftermarket had superior grinds even then--although you wouldn't get by with the stock valve springs.

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post #8 of 33 (permalink) Old Apr 15th, 16, 12:10 PM
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Re: 396 325hp vs 350 vs 375

In '67 I am 99% sure the 350 hp had a Holley.

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post #9 of 33 (permalink) Old Apr 15th, 16, 12:51 PM
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Re: 396 325hp vs 350 vs 375

In '66 the 325hp had an anemic hydraulic flat tappet cam and a high rise cast iron intake with a q-jet carb and oval port heads along with 10.25 cast pistons, the 360hp had an anemic hydraulic flat tappet cam and a small holley. I think the 360 could have come with either 2 or 4 bolt mains with a cast crank with 10.25 to 1 cast pistons with oval port heads and the 375hp had 4 bolt mains, a forged crank, forged 11.25 to 1 pistons, rectangle port heads and a solid lifter cam, a aluminum high rise and a 3310 type holley. We didn't realize that the ovals could hold their own at the time against the rectangle heads with a few small changes. Those days, much like these days the factories offered some amazing power with the power of today easily trumping our old stuff.
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Last edited by Stokerboats; Apr 15th, 16 at 2:57 PM.
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post #10 of 33 (permalink) Old Apr 15th, 16, 2:51 PM
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Re: 396 325hp vs 350 vs 375

I have seen a few 396 /325 ad 350 HP with a forged crank. (6223 part number)

I don't know how it was broke down but that's why you can find so many 396-427 forged cranks

the 396 /375 HP was a small bore 427- 425 HP engine

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post #11 of 33 (permalink) Old Apr 15th, 16, 3:23 PM
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Re: 396 325hp vs 350 vs 375

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Originally Posted by Stokerboats View Post
In '66 the 325hp had an anemic hydraulic flat tappet cam and a high rise cast iron intake with a q-jet carb and oval port heads along with 10.25 cast pistons, the 360hp had an anemic hydraulic flat tappet cam and a small holley. I think the 360 could have come with either 2 or 4 bolt mains with a cast crank with 10.25 to 1 cast pistons with oval port heads and the 375hp had 4 bolt mains, a forged crank, forged 11.25 to 1 pistons, rectangle port heads and a solid lifter cam, a aluminum high rise and a 3310 type holley.
Actually, the vast majority of 325 HP 396 in 1966 Chevelles still used Holley carbs... But for "California" smog (RPO K19), the 325HP version used the Q-jet... Being from California, its probably pretty common to think all the 325s had Q-jets (I know I used to think that)...

In 1966 (1965-1968), ALL 396s (325 HP included) used Forged crankshafts... in 1969 or so, the low perf engines got the cast cranks...


Early 360 HP engines used the 4-bolt "962" engine blocks...

Its kind of amusing when I see either a cats-iron Holley intake or a 360HP-coded 4-bolt block, and the sellers talk about how rare they are, when actually, they are pretty common...


Quote:
Originally Posted by rp930
In '67 I am 99% sure the 350 hp had a Holley.
I think thats correct for many 1967s, they hadn't all gone to Q-jets yet...


For all years, the 375 HP version also had deep groove pulleys and A/C was not available... Due to the deeper grooves, the center-to-center spacing on the grooves also changed, so you can't really switch one pulley, you need to swap the whole set to get them to line up properly...

375HP used an 8" balancer, others used 7".

Different ignition curves (distributors) for each version...

325HP used a closed air cleaner ( single snorkel for 66-69), while the 360/350 HP and 375 HP came with the open element air cleaner.
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post #12 of 33 (permalink) Old Apr 15th, 16, 3:55 PM
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Re: 396 325hp vs 350 vs 375

Just as a note, when you checked the 375 HP option, you really got a whole different animal.

Where as the 325 and 350 versions were quite docile, the 10 extra horses in the 375 made it a real animal, mainly because it made over 375, and in truth was a much more radical engine than the HP rating indicated, especially when combined with the lower rear ended ratios to take advantage of the revving capability.

I have driven well tuned Chevelles in all three HP options, and the difference, (it seemed like), was night and day.

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post #13 of 33 (permalink) Old Apr 15th, 16, 4:06 PM
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Re: 396 325hp vs 350 vs 375

Quote:
Originally Posted by 1966_L78 View Post
Actually, the vast majority of 325 HP 396 in 1966 Chevelles still used Holley carbs... But for "California" smog (RPO K19), the 325HP version used the Q-jet... Being from California, its probably pretty common to think all the 325s had Q-jets (I know I used to think that)...

In 1966 (1965-1968), ALL 396s (325 HP included) used Forged crankshafts... in 1969 or so, the low perf engines got the cast cranks...


Early 360 HP engines used the 4-bolt "962" engine blocks...

Its kind of amusing when I see either a cats-iron Holley intake or a 360HP-coded 4-bolt block, and the sellers talk about how rare they are, when actually, they are pretty common...




I think thats correct for many 1967s, they hadn't all gone to Q-jets yet...


For all years, the 375 HP version also had deep groove pulleys and A/C was not available... Due to the deeper grooves, the center-to-center spacing on the grooves also changed, so you can't really switch one pulley, you need to swap the whole set to get them to line up properly...

375HP used an 8" balancer, others used 7".

Different ignition curves (distributors) for each version...

325HP used a closed air cleaner ( single snorkel for 66-69), while the 360/350 HP and 375 HP came with the open element air cleaner.
Thanks, I bought one new with a holley (360 hp) and "assumed" all the 325's came with Q Jets. I thought all of the pass engines came with cast cranks. I have my current Chevelles original engine here which isn't a 962 but a 961. I'll have to look at the crank and check the number out.

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post #14 of 33 (permalink) Old Apr 15th, 16, 4:12 PM
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Re: 396 325hp vs 350 vs 375

My early 360HP had the 4 bolt , steel crank, oil cooler plugs and a qjet .
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post #15 of 33 (permalink) Old Apr 15th, 16, 4:18 PM
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Re: 396 325hp vs 350 vs 375

Best mod for the 'ole L34 and L35 motors back in the day (even for us guys in the 1980's and 90's) was to install headers and the GM "143" solid lifter camshaft.
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