When I assembled my engine, I made a conscious decision to use trumpets without air cleaners. There was no major academic argument behind my decision. I simply liked the look, the sound and the potential extra ponies.
The drawback of coarse is that there is no protection against any solid contaminants that might find their way into the combustion chamber. My reasoning there however was that it would be a simple matter of calculating (or estimating) the increase in the resultant engine abrasion and be prepared to live with the reduction in engine life (as long as no large objects find their way down a trumpet). Based on other people’s experience I estimated about a 4:1 increase in abrasion and was more than happy to live with that since the car would not accumulate too may miles over the years anyway.
Eighteen months and 15,000 km down the track, I now have some interesting experiences to report that I didn’t consider when making my original decision.
I recently had the misfortune to blow an inlet manifold gasket (between the coolant jacket and port number four). This caused an enormous amount of coolant to be pumped directly into one of the chambers, creating a big cloud of steam behind the car. It is probably worthwhile mentioning at this point however that the car had been pinging and backfiring at an ever increasing rate over the past month or so, no amount of tuning of which could rectify the problem. Needless to say, I decided not to drive the car any further until the fault was rectified.
For reasons that were beyond my control and not worth going into here, the car was left at a friend’s farm for one week before I was in a position to be able to trailer it home. A week later (and allowing for the fact that one of the cylinders would still be drinking coolant) I decided to start the engine so that I could drive the car onto the trailer. This turned out not to be as simple as we had assumed. Not only did the engine refuse to start, but it also began to pop and bang and throw large flames out of the left exhaust. After lots of discussion and few ideas we decided to try again a few minutes later. No better. In fact it just got worse with each try. We stopped trying after the exhaust gave a very large bang and continued to burn a flame for a few seconds after we stopped. The car was then put on the trailer by other means and brought home.
Shortly after the car finally arrived home, the inlet manifold was removed (discovering the original gasket problem) as were the heads, in an attempt to locate the cause of the violent misfires. I didn’t know what to expect. Why would it run OK one week earlier and so badly a week later? Expecting to maybe see a burnt valve or even a hole in a piston, I instead saw an engine in reasonably good condition except for a very large (and I mean VERY large) buildup of carbon in all cylinders except cylinder 4.
Since time was a precious commodity for me at the time, I decided to leave the job for a week and sprayed all the cylinder bores with CRC to inhibit any likely corrosion.
Returning to the job a week later I found that the CRC had not only protected engine, but it had also dissolved much of the carbon off the bores and pistons. It had been explained to me in the past that it is generally not a good idea to clean the carbon off the pistons because you invariably leave some crusty bits in and around the rings causing more harm than good. Having inadvertently already started the carbon cleanup I decided to complete the job to clinically clean standards.
Having found no other real issues with the engine, I decided to re-assemble it and try to reproduce the backfiring in my workshop. One re-assembled engine later, the engine was cranked over and it immediately burst into life, smooth as I had ever heard it. Having left it to idle for 15 mins and given it a few good revs, I decided it wasn’t going to fall back to its old problem, so the car was consequently driven out of the garage and down the road… smooth as a baby’s bottom. Even the pinging and popping that had been plaguing me in the past was gone.
Car now fixed, I decided to take it for a long drive with no further signs of the problem.
Conclusion (just my theory):
Seems that there are two types of air contaminants, mineral and organic. The mineral contaminants are probably happy to get sucked in, bounce around the combustion chamber for a while and then leave out of the exhaust. The organic contaminants however enter the combustion chamber burn and stick to whatever they can. This eventually creates a significant carbon buildup which results in an increase in compression ratio, hence the pinging. This buildup however does have its limitations. Eventually it will break loose into relatively large pieces and bounce around the chamber until it occasionally finds an open exhaust valve and temporarily wedges itself into it. At this point we have an open valve at the moment of combustion, so causing the popping.
So what caused the large flames back at the farm I still wondered? Well my final theory is based on the fact that there was very little carbon buildup in cylinder four. This must mean that the carbon had to go somewhere. My guess is that the coolant loosened a very large piece of carbon that eventually managed to hold the exhaust valve open considerably more than the smaller pieces of carbon. This created the situation where a large amount of fuel could be pumped into the exhaust system where it eventually ignited.
I would be happy to hear of anyone else with similar experiences, or even an alternative explanation to the symptoms that I experienced.
Final conclusion: I think I might install some air cleaners on top of the trumpets.
The drawback of coarse is that there is no protection against any solid contaminants that might find their way into the combustion chamber. My reasoning there however was that it would be a simple matter of calculating (or estimating) the increase in the resultant engine abrasion and be prepared to live with the reduction in engine life (as long as no large objects find their way down a trumpet). Based on other people’s experience I estimated about a 4:1 increase in abrasion and was more than happy to live with that since the car would not accumulate too may miles over the years anyway.
Eighteen months and 15,000 km down the track, I now have some interesting experiences to report that I didn’t consider when making my original decision.
I recently had the misfortune to blow an inlet manifold gasket (between the coolant jacket and port number four). This caused an enormous amount of coolant to be pumped directly into one of the chambers, creating a big cloud of steam behind the car. It is probably worthwhile mentioning at this point however that the car had been pinging and backfiring at an ever increasing rate over the past month or so, no amount of tuning of which could rectify the problem. Needless to say, I decided not to drive the car any further until the fault was rectified.
For reasons that were beyond my control and not worth going into here, the car was left at a friend’s farm for one week before I was in a position to be able to trailer it home. A week later (and allowing for the fact that one of the cylinders would still be drinking coolant) I decided to start the engine so that I could drive the car onto the trailer. This turned out not to be as simple as we had assumed. Not only did the engine refuse to start, but it also began to pop and bang and throw large flames out of the left exhaust. After lots of discussion and few ideas we decided to try again a few minutes later. No better. In fact it just got worse with each try. We stopped trying after the exhaust gave a very large bang and continued to burn a flame for a few seconds after we stopped. The car was then put on the trailer by other means and brought home.
Shortly after the car finally arrived home, the inlet manifold was removed (discovering the original gasket problem) as were the heads, in an attempt to locate the cause of the violent misfires. I didn’t know what to expect. Why would it run OK one week earlier and so badly a week later? Expecting to maybe see a burnt valve or even a hole in a piston, I instead saw an engine in reasonably good condition except for a very large (and I mean VERY large) buildup of carbon in all cylinders except cylinder 4.
Since time was a precious commodity for me at the time, I decided to leave the job for a week and sprayed all the cylinder bores with CRC to inhibit any likely corrosion.
Returning to the job a week later I found that the CRC had not only protected engine, but it had also dissolved much of the carbon off the bores and pistons. It had been explained to me in the past that it is generally not a good idea to clean the carbon off the pistons because you invariably leave some crusty bits in and around the rings causing more harm than good. Having inadvertently already started the carbon cleanup I decided to complete the job to clinically clean standards.
Having found no other real issues with the engine, I decided to re-assemble it and try to reproduce the backfiring in my workshop. One re-assembled engine later, the engine was cranked over and it immediately burst into life, smooth as I had ever heard it. Having left it to idle for 15 mins and given it a few good revs, I decided it wasn’t going to fall back to its old problem, so the car was consequently driven out of the garage and down the road… smooth as a baby’s bottom. Even the pinging and popping that had been plaguing me in the past was gone.
Car now fixed, I decided to take it for a long drive with no further signs of the problem.
Conclusion (just my theory):
Seems that there are two types of air contaminants, mineral and organic. The mineral contaminants are probably happy to get sucked in, bounce around the combustion chamber for a while and then leave out of the exhaust. The organic contaminants however enter the combustion chamber burn and stick to whatever they can. This eventually creates a significant carbon buildup which results in an increase in compression ratio, hence the pinging. This buildup however does have its limitations. Eventually it will break loose into relatively large pieces and bounce around the chamber until it occasionally finds an open exhaust valve and temporarily wedges itself into it. At this point we have an open valve at the moment of combustion, so causing the popping.
So what caused the large flames back at the farm I still wondered? Well my final theory is based on the fact that there was very little carbon buildup in cylinder four. This must mean that the carbon had to go somewhere. My guess is that the coolant loosened a very large piece of carbon that eventually managed to hold the exhaust valve open considerably more than the smaller pieces of carbon. This created the situation where a large amount of fuel could be pumped into the exhaust system where it eventually ignited.
I would be happy to hear of anyone else with similar experiences, or even an alternative explanation to the symptoms that I experienced.
Final conclusion: I think I might install some air cleaners on top of the trumpets.
![58887-escapespoon[1].jpg](/data/attachments/3/3825-7c667b2890065ff36e3f78852d1190e8.jpg)
![58888-4651008562[1].jpg](/data/attachments/3/3826-6623ca697c24780171fa5c12c4e748e9.jpg){kind=small}
