V8 Engine design mystery. [Any engine experts out there?]
Discussion
My car has a V8 engine.
On the front of the engine there is a plastic cam-belt cover which covers most of the 7 foot long(!) rubber cam-belt. The cover is not sealed to atmosphere.
At the highest point of this cover, on either side where it covers the end of the cam-shaft housings, there is a 1" hole which connects directly to the cold air intake for the engine [pre-filter].
My question is why?
Why would would you deliberately want to draw warm air in from this part of the engine into the cold air intake?
I've seen many theories but no real definitive answers.
One theory suggests its to draw ozone gas away from the rubber belt - but this can only apply to the later engine design which had the distributors mounted on the ends of the cam-shafts. The original 1979 engine still had the vent holes but the distributor was mounted elsewhere. And even if this was the case shurely the designers could have come up with a better design than disrupting the cold air intake?
Has anyone seen this feature on any other engines or can explain whats going on?
Thanks.
On the front of the engine there is a plastic cam-belt cover which covers most of the 7 foot long(!) rubber cam-belt. The cover is not sealed to atmosphere.
At the highest point of this cover, on either side where it covers the end of the cam-shaft housings, there is a 1" hole which connects directly to the cold air intake for the engine [pre-filter].
My question is why?
Why would would you deliberately want to draw warm air in from this part of the engine into the cold air intake?
I've seen many theories but no real definitive answers.
One theory suggests its to draw ozone gas away from the rubber belt - but this can only apply to the later engine design which had the distributors mounted on the ends of the cam-shafts. The original 1979 engine still had the vent holes but the distributor was mounted elsewhere. And even if this was the case shurely the designers could have come up with a better design than disrupting the cold air intake?
Has anyone seen this feature on any other engines or can explain whats going on?
Thanks.
Is it that simple?
I thought that engine manufactures went great lengths to ensure engine air intake was cold, turbo inter-coolers for example. Why would you then just suck in hot air past the front of the engine just because it was a convenient way of cooling the cam-belt? Wouldn't a small fan mounted on one of the pulleys be a more efficient method of cooling the belt? Have you seen this method used on any other engines? Please qualify your statement.
Thanks.
I thought that engine manufactures went great lengths to ensure engine air intake was cold, turbo inter-coolers for example. Why would you then just suck in hot air past the front of the engine just because it was a convenient way of cooling the cam-belt? Wouldn't a small fan mounted on one of the pulleys be a more efficient method of cooling the belt? Have you seen this method used on any other engines? Please qualify your statement.
Thanks.
I have no definitive answer but I would suggest by far the most likely reason is to provide some air circulation to remove any oil vapour contaminated air from around the belt which can otherwise lead to faster belt degradation. It sure as hell isn't to get warm air into the engine which is always done from an exhaust manifold shroud if necessary for cold start purposes on carburetor engines. You'd get damn all heating effect from the air inside a cambelt cover.
I also doubt it's anything to do with keeping the belt cool which again it would make little difference to although there might be a very small consequential additional benefit from that.
A very small amount of oil vapour tends to pass out through crank and camshaft seals, especially when the engine is at high mileage and with some piston ring blowby and high crankcase pressure. Oil contamination is seriously degrading to high tensile rubber components like timing belts. I can see how a negative pressure flow system driven by the induction vacuum would be of considerable benefit here in removing any accumulated vapour and helping dry out any actual oil leaks or spills. It isn't something I've seen before on "shopping" cars but I guess with a belt that long driving so much stuff every little helps to prolong belt life and avoid warranty claims.
I also doubt it's anything to do with keeping the belt cool which again it would make little difference to although there might be a very small consequential additional benefit from that.
A very small amount of oil vapour tends to pass out through crank and camshaft seals, especially when the engine is at high mileage and with some piston ring blowby and high crankcase pressure. Oil contamination is seriously degrading to high tensile rubber components like timing belts. I can see how a negative pressure flow system driven by the induction vacuum would be of considerable benefit here in removing any accumulated vapour and helping dry out any actual oil leaks or spills. It isn't something I've seen before on "shopping" cars but I guess with a belt that long driving so much stuff every little helps to prolong belt life and avoid warranty claims.
It was used on the flat 6 engines of the era (twin distributor 911's). These allegedly suffered from distributor belt failure due to the aforementioned ozone gases, early examples were retro fitted with vent pipes to cure the problem. Both 928 and 944 models have a similar arrangement, this was subsequently blanked off on later 944's, presumably because it does eff all! I haven't come across another cambelt car with a similar vent arrangement.
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