The Stag v8 engine got me thinking

[Eric]

The way it was built, designed, etc. and then thinking of the way we do things today.
Why do we still have head gaskets?
With todays cnc multi axis machining, and everything going to boosted small engines, why is there still head gaskets and a separate head?
I'd think, having the cyl banks with heads even if they had to have an separate crank case to bolt to, to keep cost down,would make more sense than having a head gasket that can fail under boost. heck, even n/a they fail.
I understand why it wasn't done at the time they started , as the machining machines were limited and casting had it's limits, but that isn't the case today.
So, why still produce engines with a head that can warp, and gasket that can fail?

What say you?

[nickleone]

They are easier to build with separate head block. Look at the Offy engine for complex assembly procedures. Hot Rod did an article on assembling an Offy engine in the past.
Nick

[silver_bullet]

the tooling would be over complicated and cost prohibitive, otherwise the factories would have done it.... it would be like a surgeon going through your butt to remove your tonsils....

[Gateclyve Photographic]

Gaskets and fasteners are better now. Computers manage the combustion precisely.

However I would not be surprised if we get into an era of super-elevated cylinder pressures (e.g. micro-mills operating with several atmospheres in HCCI or near HCCI) that someone will move the parting line down to improve reliability. .

Note that most modern engines have parameters which are dictated by the installed base of an OEM's tooling and the necessities of mass production. .

I suspect some have evaluated a deep-groove sleeve interface with the head but abandoned it for various technical reasons.

[DanStokes]

Nick hit on the "right" answer. Basically, the Offy engine uses that technology as it was designed in the 20's when head gaskets were a nightmare. It woks great but necessitates a pretty big crankcase as the pistons have to come up thru the bottom to get installed. Not sure how you could make it as anything other than a true hemi (Offy's are) just due to the machining process. Assembly is a trick, too, as what would be the head on any other engine also has to get loaded from the bottom before the pistons so the assembler is reaching up thru the crankcase while a helper catches the valves and installs the springs. We see them at Bonneville and they seems to work really well but they were always race-only engines and therefore are crazy expensive - you could buy a train load of Eco-Tecs for the price of one Offy (I might have exaggerated a tad.....).

Dan

[Gateclyve Photographic]

you could buy a train load of Eco-Tecs for the price of one Offy (I might have exaggerated a tad.....).

Dan

If I'm not mistaken, Jeff Hartman's book Turbocharging Performance Handbook (ISBN-13: 978-0760328057) details the interesting saga of developing the EcoTec to the output levels of the old turbo Offys of the late '60s and early '70s. The Cliff Notes version is that GM spent a lot of dyno time, blew up a lot of engines, and ended up replacing nearly every production part before breaking through the 1,000 horsepower barrier.

That being said,, any number of modern DOHC production engines can be built to crazy power levels with turbocharging. The trade-off is often in durability, which the old Offys had in spades.

The Offy (and to a lesser extent Ford's Indy DOHC V8) initially showed the way. 50+ years later, a few of us are enjoying technology and horsepower that was $25,000 Indy front-row stuff in 1963-65 . . . .

[Thumpin455]

So, a radial engine type of cylinder rather than the typical siamese inline engines. Radials have a jug where the piston goes, it bolts to the crank case kinda like Subaru and air cooled VW engines. Separate jugs cause more issues, primarily cooling and packaging. The Subaru engine is kinda girthy, sorta long, and it takes up lots of space due to the opposed flat four design.

If you have ever rebuilt a Th350, you know about the snap ring at the bottom of the case. Imagine trying to measure the valve seats at the bottom of a Th350 case. Extreme, yes, but it gives you an idea of how it would go. These would probably be throw away engines, if the head was integral with the block. What are you thinking of, a 7" bore with a 2" stroke so you can see the valves easily? Or perhaps a two stroke more like a model airplane engine, with a supercharger to create positive cylinder pressure, and there goes the emissions so it would need to be a clean fuel like hydrogen, CNG, or ethanol to eliminate emissions problems.

Cast iron and cast aluminum is considerably less expensive to produce than billet steel and aluminum. Knowing how the machining works, and having machined all the metals mentioned just now, yes we can machine a single block with the heads, but it will not be anywhere near cheap. You still have to check your parts as you are producing them. Tools wear, thats the boring bars, the tool inserts that actually do the cutting, and things move around with temperature differentials. Cast iron with a +/- tolerance of .0001 is less difficult and pricey than billet aluminum and .000001 tolerances, plus the finish spec required on all the parts.

The entire reason the chevy did not get killed off in 1978 like the better Pontiac engine did is because when you are building a few million v8s, the $.47 more the extra casting mold and machine operations required to give it screw in studs, air gap intake, cam retaining plate, fully machined combustion chambers, milled gasket surfaces rather than as cast like the sbc, ads up to a considerably amount of money. The tighter tolerances of the Pontiac cost a bit more as well, because it slows production time to get the measurements more exacting. Look up the spec for the line bore of the chevy main journals from the factory, its freaking huge to a machinist. We are talking bench grinder size here for someone who has held aircraft tolerance, which is required for a no gasket fit, and often the machinations of some delusional engineer that result in tooling fixtures for every single operation...

From a CNC machinists point of view, it could be a nightmare. Not because we can't do it, but because we would have to lose our asses doing the work to make it profitable. For mechanics its even more of a nightmare trying to rebuild it, unless it has the huge bores and tiny strokes so you can get your hands in there with micrometers... unless you can afford some kind of laser measuring device. See how the costs are going to go up?

[silver_bullet]

Spot on.... It's how the bean counters have killed design.... and, on top of that, this is why GM killed the excitement division altogether....