What doomed GM's 400 cid small bloc V/8 engine in '78?

[machmeter62]

I think there is a lot of GM "guru" here that will finally answer this question? I was told it was because of the siamese cylinder walls with steam-holes only, that would cause pre-mature failure of the bloc?

If that was true, why did many years later, the bloc become very popular with engine performance builders that could get increased hp from it without any "block-twist?"

I don't remember any recalls for that issue....was it sales people that caused the short production cycle?
LEE

 

[carpenter383]

The 400sbc was made for 10 yrs. 1980 was the last yr.
'70-'72 were 4 bolt mains the rest 2 bolt.
I don't know why they stopped building them, but I'd bet it was something to do with gas mileage and or emissions requirments.
Yes the 400 is very popular in the performance world. Big bore (4-1/8") helps the engine breath and fairly large displacment in a small package. There are aftermarket kits to build a 454 cube sbc!

 

[Pops15]

CAFE (fuel economy) standards.

 

[Raspy]

From what I recall, there were head gasket problems and possible out of round bore problems. These are not necessarily problems associated with individual builders that can install better head gaskets and who may not be as interested in lonevity as much as performanc from a large displacement small block that is light and compact.

The new Cummins 6.7 also has siamese cylinders. And for the same reason of trying to get more displacement from the same bore centers. In the Cummins case, they are turning out to be fine engines, but there has been a lot of speculation that they would be a problem from people remembering the 400 small block.

 

[Egon]

Big bore (4-1/8")

If memory serves me correctly it had to do with regulations on engine bore size.

A lot of other engines disappeared about the same time. When gas and more HP were required 10 cylinders were brought out.???:thumbsup:

 

[om21braz]

I'd guess CAFE and/or reducing amount of large c.i. engines to make way for smaller ones. They kept the 350 & 454, nothing really required in between those two at the time. Got a friend w/ a 1979 Cheyenne lb 4wd with 400 - not too may miles, but all original & not for sale. Nice truck.

 

[rjkobbeman]

The big bore in the same small-block form factor required the "siamese bore". All of the bores in given bank are so close to each other there is no coolant that flows between the bores. This causes heat related issues. Also, the head gasket between these bores is also relatively narrow.

Aside from those issues, the 400 seemed to have a bad rap because it always seemed to be "detuned" from the factory -- never really running to its potential. I'm sure there were exceptions, but the ones I always remember seemed to be poor performing. Considering most of its production run was in a time where smog equipment started to be implemented on production cars... and that was a bad time in auto history. The late 70s and 80s seemed to put out some of the worst cars...

On top of that... if you were after inches, the big blocks had a variety of choices... as long as you could physically fit them in your engine compartment. With all of the options out there, the 400 never really was a great option.

A 400 can be made to scream -- but then you get back to the heat issues I first talked about.

Cracked cylinders where they were "conjoined" was a common problem. Not just inside the cylinder... but also across the head gasket surface. Blowing a head gasket was not uncommon.

 

[wedge40]

How many of these were on tractors?

Wedge

 

[LBrown59]

How many of these were on tractors?

Wedge

:confused2::confused2::confused2::confused2::confused2:

 

[timswi]

It was fuel economy..CAFE, Jimmy Carter (remember him?)...Had a 77 Blazer with a built and dyno'd 406...That thing ran like a stock car....Still does from what I understand.

I'm not sure it would have been all that much better than a similar 350 build though...Kinda like the 305 w 2bbl...What was the point of that? The mileage was oftentimes worse than a 350 w/Q-jet.