Interference engine- Which are and which are not?

My guess is ALL modern (post 50's) are interference

 

Agreed.

 

My guess would be that several non-high-performance engines are not intereference. The differentiator may be hemisperical combustion chamber designs? A lot of modern cars have dished pistons and these may not be so tight?
A 4 Cyl Chrysler that we had broke a belt and nothing hit. Can't recall specifics, but have heard of other folks "spitting" a belt and not having to replace valves.

Mark

 

I don't get why the valves are going deeper into the cylinder than the spark plugs. I mean, you want the spark plug to go in as deep as possible because the more central the spark, the better the burn.

And we know that pistons don't hit the spark plugs.

Yet valves go into the cylinder further than spark plugs?!

Makes no sense. Split the valves each in half if you have to...that alone would cut their travel down into the cylinder by half...preventing the entire interference problem.

...which doesn't seem to be a problem on electro-timing (no cams), single cams, and push rod engines...just dual overhead (each bank) cam engines.

 

Picture the compression stroke. The piston is "very close" to the head at TDC compressing the mixture and in a sense the spark plug is at center of the mixture. Now picture the intake stroke the valves have to open enough to allow a sufficent amount of air and fuel to flow into the cyl. For disscussion sake lets say the intake valve has to open a 1/2 inch to allow enough air and fuel to get into the cyl. that 1/2 inch is way to much compared to distance at TDC. Same goes for the Exhaust valves they have to open enough to let the exhaust flow out. Maybe someone else can explain that better but Hope that helps. Regards, Vern

 

Picture a wide gate on a fence in your back yard. It could open inward into your yard, or outward into your neighbor's yard.

You could cut the gate in half, put hinges on both ends, and those two gates would only open half the distance into your yard or your neighbor's. You'd still have the same width opening.

Right now, interference engines have valves that act as that one wide gate. Moreover, that gate opens inward toward our pistons...and it is only hyper-critical timing that prevents our pistons from ramming those valves.

But it doesn't have to be that way. You could easily make the valves travel only half as far towards the pistones while still having the same wide gate opening (by cutting the valves in half and hinging each side).

Or you could just have the same valves open *away* from the pistons.

Or you could have valves that slid horizontally to make the same wide opening. Or they could spin open like a screw.

Why have them open inward, towards the pistons, with a catastrophic crash only prevented by a properly timed and tensioned rubber cam belt or two!

It only saves a couple of bucks to use that old design that risks our engines with every RPM. That's not being innovative.

 

Many of the valve arrangements you mention have already been tried - especially in 2 stroke engines. And I can only assume that the currently most popular setup of poppet valves that open inwardly are the most efficient for flowing gas into the cylinder.

 

The valve take up pretty much every spec of space there is in the head and open the minimum distance to get enough flow, there juet is no way to open them less. In your cut the gate example, that is basically what they did when they went to 4V heads.

 

With all due respect, and I'm a Ferrari guy saying this, the Corvette's 500 hp engine is hardly low compression or low efficiency...it probably gets better gas mileage than any of our F-cars...

...and it's non-interference.

I broke the belt on my 1995 Vette and still *drove* that beast to the dealership for a new one.

One Corvette engine, the ZR-1, even had dual overhead cams.

It's embarassing. Here we are in Ferraris but it's the Corvette guys who have heads up displays and bulletproof, non-interference, mondo horsepower engines that get great gas mileage.

Heck, Cadillac now has a car with carbon fiber wheels (and aftermarket companies are making them for the Corvette already).

You know, the last time that Ferrari got comfy, it took a Ferrari racer to personally knock off Enzo's drum brakes...personally install disc brakes...and then show up all of the other Ferrari racers who had the crappy old technology drum brakes.

Is Schumacher really going to let Ferrari get away with using nothing but old tech??

How many Ferrari's even have cruise control?!

Consider how long it has taken Ferrari just to put tire pressure monitors in our wheels...something that I had back on my 1995 Vette.

Ferrari should be *leading* the technology curve, not following.

We've got great looking cars...many of which go fast...but that's somewhat akin to being the pretty bimbo at college rather than the rocket scientist.

We need high tech.

 

As far as I know NO small block chevy is non-interference and they don't have timing belts. They have a timing chain, and if it breaks the engine will smash valves and quite...but since it's a chain, they don't break. The worst I've ever seem is the chain get streched and sprockets worn to the point that it jumps a tooth of 2 and then runs very very bad.

The belt you broke was undoubtedly the serpentine belt, and you could nurse your ferrai along a bit with that belt broken as well if you so chose.

The 4 cam vette motor they made a couple years had belts I think and I'm not positive, I'd need to check, but I think the F1 cars do in fact use belts.

A belt is very efficient and will make more HP than a chain and is also significantly lighter, especially when you consider the extra castings and seals to keep the chain lubed.

 

You broke a belt in your Corvette and drove it to the dealer?? I can tell by your questions and responses that you need a course in automotives 101. With the web telling you everything you ever wanted to know start doing some research on interference engines such as OVC and also pushrod motors. Corvette is a conventional PRM . Also if you need criuse in your Fcar then you need to buy a chevy.

 

All GT cars need cruise control. Race cars do not need cruise control, GT cars do. It's that whole "grand touring" thing.

I've had a chevy. The Corvette is great. Ferrari is better.

But don't get so caught up in the Ferrari mystique that you let the factory slide into another technology slump. Enzo wouldn't put disc brakes on cars for *years* after all other manufacturers had done so, telling people that if they wanted disc brakes that they should go buy a chevy.

He had to eat crow over that one. Happens to the best of us.

Let me know how your drum brakes work though.

 

Thanks. Good to know.

 

The Corvette ZR-1 engine, called the LT-5, used duplex roller chains to drive the 4 overhead cams. I do not know if this was an interference engine, but then again, chains do not have all the problems belts do.

 

....shows what I know....

 

FWIW, F1 engines use a gear train to actuate the valves. No belt or chain, just gears.

i have had bot no-interference and interference engines: the difference seems to be performance-related. For example, an old 8V VW watercooled motor is non-interference, but the same block, fitted with the 16V head, is interferece. But interestingly, VW shaped the combustion chamber such that only the intake valves will hit the pistons. This is a good thing because the exhaust valves are sodium-filled, but a bad thing because it makes the exhaust port shape non-optimal. Just remembered, I have a pic! See how the exhaust port has to make a 90 degree turn? Bad for flow...
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I remember reading someplace that the F1 engines actually have individual pneumatic valve actuators on every individual valve. I did not think they had belts, cams or gears connected onto the crankshaft to take away valuable horsepower. And at 18,000RPM a normal mechanical (non-desmodromic) valve arrangement would just bounce. Maybe somebody here can confirm my memory, or if I'm getting old...

 

quote Mk e

"A belt is very efficient and will make more HP than a chain"

Surely neither 'make' HP, rather one is more efficient so results in less HP loss than the other?

 

You are kidding right? Have you looked at any of the serious technological advances on a 360 or 430? Just to name a few, how about F-1 transmissions, e-gear diffs, carbon/ceramic brakes..etc.

Don't get me wrong, the Corvette is a fantastic, hig tech car, especially for the money! To say that Ferrari is behind in the technical curve though is just ridiculous. Check the list above. See a pattern yet? All the Ferrari "high-tech" advances have to do with one thing..... Improving Performance.

If you're that embarrased by your Ferrari, sell it and drive a Corvette! Oh, and by the way, the 430 does have chains not belts so there shouldn't be nearly the controversy with them.

 

I'm sure that's not true. They use pneumatic valve spring to close the valves, but normal cams to open them.

I didn't realize they had gone to gear drive though. Honda had a sport bike in the late 80's or early 90's the had gear drive, thye must have lifted it from F1. The hot ticket for small block chevy was to replace the chain with a gear drive, there were several kits available as I recall, but it's bee years since I messed with one....it seems like the factory many had added that to the vette engine too....hmmmI'd have to do a little digging.

 

Sure I should have said " a belt is very efficient and THE ENGINE will make more hp"...., but in math minus a negative and plus a positive are equivalent....it just depends how you choose to write the equation

 

Do the math, guys: compression ratio is a ratio of volume at either end of the stroke. So, if the volume before compression is cyl area (aka pi*(bore^2)/4) times stroke plus "X", and the volume after compression is cyl area times "X", then your compression ratio is 1 + (stroke/"X"). Solve for X, and you find out just how close the cylinder comes to the heads. (Okay, flat cylinder/flat head example, but you get the idea.)

My Japanese cars aren't interference engines. But they're only 8:1 compression .... mechanically. Then they add big honkin' turbochargers to pre-compress the air. Which is one of the reasons the Ferrari is so much nicer to drive: no turbo lag.

There's a new gimmick in the works: cam balls (no, not mouse balls). Spheres on the cam that fit over the "valve" openings, with a cylindrical hole bored through them: when they rotate to the right position, the gasses pass through the hole.

Of course, you now have the issue of sealing the rotating sphere to the valve opening (which may be why the group working this gimmick has no major engine makers supporting them.)

At the start of the power stroke, you have enough pressure (after ignition) in the cylinder to ... well, to push a car. Enough pressure to create your torque on a little crank arm. How much pressure? (Exercise for the student)

And that happens in each cylinder every other rotation -- up to 3500 times a minute, the whole time you're driving. Using that pressure to create the seal works better in the long run than trying to fight it.

And no, you can't keep yourself in your seat in a crash by holding onto the steering wheel, either.

 

once broke a timing belt and bent valves-does that make it a high performance engine??????

 

I'm sure the several trillion (yes, with a T) dollars floating around the auto industry each year hasn't thought about any of this before...

If you're really interested, pick up a book or two. "Great Engines" is a pretty interesting read, it goes through around 20 popular engines of the last century. The Ferrari F1 book has a good section on valvetrains as well.

Getting back though, Ferrari tends to be very consistent through the years regarding their design philosophy. As such, I'd be surprised if any of the engines aren't interference.