Both the Vega and the HT4100-series Caddy engines were outright disasters. Both had iron heads on aluminum blocks. I'm not sure there's cause-and-effect though. Both engine blocks were flimsy weak-ass disasters no matter what heads were bolted to them.
I'm intrigued by the idea that heads run hotter than blocks--so making them out of low-expansion iron instead of high-expansion aluminum would seem to have advantages.
Wild Guess: There's less problem with gasket failure with an iron head on an aluminum block than the other way around--gasket surface smoothness being equal.
But I've never done this, so what do I know?
Cast heads on alloy block?
Moderator: Team
Re: Cast heads on alloy block?
With the notorious weak Cleveland block we never had a platform that would hold it altogether. So I thought with new alloy give it a whirl. However CGI is coming also so could wait for that. The old p/s guys were pushing the hp past where I am but they had new blocks. I talked to one 70's pro stock racer and he said they never had much trouble with blocks. They're biggest issue was valves! Until trw came out with titanium!
Re: Cast heads on alloy block?
The vegas problem was the new at the time liner less block cylinder seal was an issue dont recall head gasket issues much.
Re: Cast heads on alloy block?
The problem with the Vega was that the radiator was a minimalist joke and if the coolant
got even a bit low, the engine fried. Later, in true GM fashion they put a sensor on the rad.
Back in those days, the Japanese stuff was all 4 banger and some had aluminum heads
and iron blocks. Overheat them and the head warped and on many of them, especially
OHC types machining the head was not an option, so the wreckers seemed to be full
of low mileage Japanese engines with no head. The Vega had the reverse, of course,
and if you look at the head it is tall on one side and I'm guessing a hell of a lot stiffer
than the block, so when overheating happened the block deck warped. It also was
among the first to use the 390 alloy high silicon block idea and everybody latched onto
the idea that that was the problem and they would dump the iron plated pistons and
bore the block for liners. They sold a piston, ring and liner package like they had for
diesels.
GM ran away from the 390 alloy idea, which was then picked up by Benz and Porsche
who never seemed to have a problem with it. I remember talking to the performance
engine shop owner who did all the GM warranty block work in western Canada and he
said he had never seen a failure of the high silicon/iron plated piston idea.
I got a Vega nearly free because everyone knew they were junk and after fixing up the
various back-alley "repairs" inflicted on it I drove the crap out of it for years. It even survived
my then wife's outrageous abuses and was passed onto my sister who commuted 100
miles a day on the freeway. Best beater I ever had. The engine used oil and one day I
was bitching about that to a auto wrecker buddy. That night he banged on the door and
dropped an HEI distributor into my hands. Never used oil after I switched it from points.
Go figure.
got even a bit low, the engine fried. Later, in true GM fashion they put a sensor on the rad.
Back in those days, the Japanese stuff was all 4 banger and some had aluminum heads
and iron blocks. Overheat them and the head warped and on many of them, especially
OHC types machining the head was not an option, so the wreckers seemed to be full
of low mileage Japanese engines with no head. The Vega had the reverse, of course,
and if you look at the head it is tall on one side and I'm guessing a hell of a lot stiffer
than the block, so when overheating happened the block deck warped. It also was
among the first to use the 390 alloy high silicon block idea and everybody latched onto
the idea that that was the problem and they would dump the iron plated pistons and
bore the block for liners. They sold a piston, ring and liner package like they had for
diesels.
GM ran away from the 390 alloy idea, which was then picked up by Benz and Porsche
who never seemed to have a problem with it. I remember talking to the performance
engine shop owner who did all the GM warranty block work in western Canada and he
said he had never seen a failure of the high silicon/iron plated piston idea.
I got a Vega nearly free because everyone knew they were junk and after fixing up the
various back-alley "repairs" inflicted on it I drove the crap out of it for years. It even survived
my then wife's outrageous abuses and was passed onto my sister who commuted 100
miles a day on the freeway. Best beater I ever had. The engine used oil and one day I
was bitching about that to a auto wrecker buddy. That night he banged on the door and
dropped an HEI distributor into my hands. Never used oil after I switched it from points.
Go figure.