Wednesday, August 3, 2022


Engine 2021: knock knock?

Me: Who's there?

Engine 2021: Your connecting rods!

Me: %@#*! $#!^!!!!!

Some car jokes are funny. Automotive "knock knock" jokes are not... But if you're gonna race a heavily modified car it's a risk. Unfortunately, in this case I was caught between the intersection of Road Racing and Autocross... 

The engine had been newly built in 2020 to support 9250 rpm redline and use 14:1 compression, this had involved special valves, Ferrea roller rockers, lightened crank, Carillo rods, Cosworth pistons, and an externally driven oil pump system. This system was a half step between the traditional wet sump and a dry sump system. Basically it ran a pump off the crank that sucked oil out of the back of the pan which had had the drain plug replaced with an AN fitting. 

The engine was delivered in the spring of 2020... when covid was at its worst. During this period I was not very motivated because no racing was being held for the foreseeable future, and even when the first events were opening up I didn't want to attend because I and my wife have contact with vulnerable individuals. So, once things seemed to be turning around I got motivated again, but I had to go slow and be careful because the car had been apart so long. In the end I managed to get the car running again for 2 events at the end of the 2020 season. Both events turned out to be extremely tight, low speed courses. One so much so that my co-driver decided the course just wasn't fun and didn't bother with the last run.

These events showed that re-assembly went well and there were no major issues on that front, but also failed to really stress the car. It's possible that speeds on these two courses never exceeded 55mph. So when I put the car away at the end of 2020 it seemed like all was well. Unfortunately this was not true. 

The oiling solution had been supplied by Dynamic Racing Solutions who built the engine, and they claim they had used it successfully on two track cars. They are stand up folks who have a solid reputation on Lotus Talk forums, and field mid pack or better cars for professional TC Series races, so I don't doubt that this is true. But as road racers are often amusingly keen to point out autocross is not road racing. 

Road racing has hard stops no doubt, and they pull plenty of sideways G's too... but the transitions between those actions are smoother and less violent most of the time. Also road racers rarely hit the rev limiter or shift as soon as they do. Autocrossers do so regularly, and may ride the limiter, because we just don't have time to be shifting up and then back down unless there's a LOT of rev limiter. For anything less than about 1.5-2 seconds of rev limiter shifting is slower for autocross.

First event 2021 had a much more typical course. It was clockwise and the run through the small runway was mostly the type of sweeping transitions my car excels at. Because of my massive tires and big wing/splitter, after the initial slalom I found I was able to just keep the pedal down, and I touched the rev limiter just before the braking zone. I stabbed the brakes bled just enough speed and had an absolutely fabulous run through the sweeper onto the main run way, exiting hard on the gas. THIS was what I had built the car for and it took off like a rocket and quickly found the rev limiter again, this time for something close to the 2 seconds that would suggest maybe shifting is profitable. I managed appropriate braking for entering the slalom after the faster section...

Up until this point I was in Nirvana. Somehow I had more or less nailed the course so far on my first run and everything felt just GREAT. I can still remember that joy. It was that good. 

I entered the slalom with maybe just a tiny bit too much speed for the hard back side entry, but still basically it went well, and soon I went to add more speed... But then, the bottom fell out of my world. The car lagged and slowed rather than accelerated. I was momentarily confused. It felt like fuel starve, I wondered if I'd forgotten fuel. But soon it was clear something was wrong. 

I limped back to grid with the car actually threatening to stall on me at one point but then seeming to smooth out a bit about the time I got to the finish... I coasted back gently and talked it over with my co-driver. I decided to take it back to the trailer, hook up the computer and see what I could see. As I pulled out of my grid slot I heard a "clack clack clack" sound that I had never heard before. I quickly found it to be repeatable any time I pushed the engine to 2krpm, I quickly realized that it could pretty much only be one thing. I coasted up to the trailer ramp and shut it off. Friends helped me push it onto the trailer. 

My new engine had rod knock.

Data from the ECU showed that the clanking of the rods triggered the engine knock protection, and this very likely prevented me from throwing a rod through the side of the block entirely. If such a thing had happened on the exhaust side of the block, fire and total loss would have been possible. Hooray for good knock sensors and sensible ECU protection routines provided by Cohesion Motorsports!

The combination of working fine in slow courses, and failing bearings after hard brake / turn / accel / limiter pointed straight at the oiling system. Removing the pan I found that though 3/4 of the baffling had been retained there were some gaps where the 4th side had been removed probably allowing some oil to escape along the sides. Then I went back and watched one of my earlier videos and right at the end after the stop into the finish I heard a now way too familiar sound... 

Just a brief second of rod knock sound there and at low speed, probably nearly harmless as such aside from some minor wear acceleration, but a harbinger of the disaster to come. Not having heard it before I didn't recognize it in 2020. 

As described above, I would have broke hard and then accelerated to 9250 rpm immediately, so that knock would have arrived just as I got to around 8-9krpm... no good. A track car would have been turning, but usually waiting slightly before feeding in the power exiting a turn. Plus the track car would have had a shift point in there to bring the revs back down. What we call a sweeper in Autocross is a crazy sharp hairpin on a track. The oil would have sloshed forward, and then immediately leftwards with the motor working hard/fast to redline without oil and without pause.

My brand new race engine that only lasted for about 20 minutes... not funny at all.