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the 400 small block

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Iggy
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Post by 76Chevelle2Tone Tue Jan 30, 2024 4:05 pm

At the supermarket a guy pointed at my Malibu and asked what year it was. He then said he had had a Malibu Classic years ago with the 400 engine. I replied that's interesting and you are the first Chevelle owner I've met that had a 400 engine. I also said you should have kept the car. He nodded and said you are so right!

Anyway what is the story about the 400 SBC engine in the G3 cars? I haven't seen people here mention them. I know they were phased out in 76 for Chevelles.
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Post by zucchi Wed Jan 31, 2024 9:49 am

My Monte Carlo came with a 400. It's a small block on the outside but had some interesting engineering done on the inside in order to get that much displacement. The cylinders in the block were siamesed meaning there was no gap between the cylinders for coolant to flow through. The engineers compensated for that by drilling steam holes in the block close to where the cylinders came together and corresponding holes into the cylinder heads. Their crank journals were a different size and the crank was externally balanced. They produced lots of torque because the stroke was so long but that produced such severe rod angles that they couldn't spin very high otherwise a piston could be shot through the side of the block; think of two bicycles, one with long pedals and one with short. It's hard to keep your feet on the long pedals when going really fast.

One thing that used to be done way back was to put a 350 crank into a 400 block which, if memory serves, gives you about 378ci. The other was to put a 400 crank into a 350 block which would give you 383ci. That's where the now popular 383 stoker comes from.
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Post by 76Chevelle2Tone Wed Jan 31, 2024 12:00 pm

Thanks for the info. The design seems rather unusual and seemingly not very popular for Chevelles. It was used though I believe in small trucks for some years. I would wonder about running hot given the design. Was it trouble prone or more reliable than not?
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Post by zucchi Wed Jan 31, 2024 12:23 pm

76Chevelle2Tone wrote:…seemingly not very popular for Chevelles.
I can't comment on its popularity or how many Chevelles were equipped with the 400 from the factory. I speculate it was the best way for Chevrolet to bump up the HP of its SBC during the first few years of the malaise era. I would further speculate that most 2nd, 3rd, etc., owners didn't know they have a 400 and assumed it was a 350. After all, the only way you could tell the difference without taking it appart was to examine the dampener on the front of the crank.

76Chevelle2Tone wrote:I would wonder about running hot given the design. Was it trouble prone or more reliable than not?
I bought my car with ~97k miles. Did a road trip from Monterey CA to Klamath Falls OR and back. I never had any temperature problems or reliability issues with the 400. It behaved like any other small block.
Since the cylinders in the block were siamesed, the block was inherently more rigid which is a plus.
Mine had well over 100k miles before I swapped it for a 350 SBC I built myself.
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Post by Iggy Wed Jan 31, 2024 5:39 pm

I have run several 400 SBC through the years, never had an overheating issue. They got the reputation for overheating when someone would use a 350 head gasket without steam holes. For a small block, they put out really good torque and a lot of folks like to use them to make a 427 small block. I do like the 400 Small Block, however....

Myself, I prefer the BBC once you hit the 400 cubic inch mark - a 396/402 using stock type heads can make a lot more power than a 400 small block. You have to put down some cash for after market heads that flow as well as BBC heads, and mild blending of the BBC head is worth 50HP. Downside is they do weigh 200 pounds more than a small block, but if you have a 454 you will not even notice the weight!
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Post by zucchi Wed Jan 31, 2024 5:46 pm

Iggy wrote:They got the reputation for overheating when someone would use a 350 head gasket without steam holes.
The same can be said when folks would bolt on a pair of camel hump fuelie heads (or any small block heads for that matter) without drilling the steam holes.
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Post by REVINKEVIN / Mr. 600+HP Wed Jan 31, 2024 10:12 pm

Hey.  This link is kind of neat ( https://www.automobile-catalog.com/make/chevrolet_usa/chevelle_malibu_2gen/chevelle_malibu_2gen_coupe/1976.html#gsc.tab=0 )  It shows the engine options for the 76 model year.  The 400 small block was available in the G3 cars for years.  I have had several 400's over the years.  My 86 Silverado has one right now with AFR heads.  The funny thing about the 400 is it's bore size of 4.125.  If you look closely at the advertised flow for aftermarket SBC cylinder heads, most of them are flowed on this bore size to show more CFM.  Its very easy to get around 500 hp with a 400 with aftermarket heads and a good cam now days.  The main thing that people do when rebuilding these into a hotter performer is to get rid of the really short connecting rods.  Anyway, I digress.  Yes, the 400 was an available engine option with your choice of a 2 or 4 barrel carb.
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Post by bracketchev1221 Wed Jan 31, 2024 10:32 pm

Yes as was said, the 400 was a different engine but it was a good engine. There’s lots you can do with them to make hp. They have gotten a bad rap over the years but they can be spun to rpm just like anything else. Put a long connecting rod in it and a light short skirt piston and it’s a 7000 rpm+ engine. The long stroke needs a bigger head port to get the air in.
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Post by g3chevy / Mr Pontiac Wed Jan 31, 2024 11:10 pm

My Laguna was ordered new with a 400 4 barrel and still runs good almost 49 years later with just over 90k miles. Below is the engine decal. Most all these vehicles with this decal came with a 400 in 1975 and 1976 unless it was sold in California. Due to the strict emission laws at the time, the 350 4 barrel was installed instead of the 400. And I believe the 400 was first available for our generation vehicles in 1974 as a 2 barrel option. Love the low end power of these engines.
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Post by 76Chevelle2Tone Thu Feb 01, 2024 5:47 am

Regarding numbers sold what I could find was about 16,500 400 SBC in Monte Carlos per year intially but apparently faded a bit through the mid 70s.  The 400 SBC had a short run in Chevelles I think only between 74 and 76 so doubt many were sold with them; maybe 30K total tops and 15k bottom just guessing. After 1976 it was removed from all car models and limited to trucks.
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Post by relic7680 Wed Feb 07, 2024 11:21 am

The 400 was available in the G3 Malibu/Laguna/El Camino/Sprint '73 thru '76. It soldiered on in light duty trucks thru '80, with exception of the Blazer, which lost it after '79. It was designed to be a high torque, smaller package engine for the larger passenger cars as the big block was being phased out in those markets. Ford's 351M, 400, and the Olds 403 were intended for similar purposes during the era.
I have a 509 casting '74 400 waiting to become a 450hp 406 for my Sprint when the restoration starts.
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