Frankenmiata Dyno Secrets Revealed!


Ten races after we built it, the Frankenmiata’s original engine was finally dead. Well, dead-ish. It was still running, and didn’t seem all that far down on power, but it was burning oil at an alarming rate. The engine consumed a massive two quarts of oil during its last tank of gas. That should be considered fair warning. If we were damn fools enough to run it again, we deserved the inevitable catastrophic failure.

But how could we fix it? Spending money on LeMons repairs is possible only two ways. Sneakery, and sympathy. We’re incredibly bad at being sneaky (see the Weber incident here), so we usually rely on sympathy. Sympathy works like this: You show Jay Lamm your busted ass car, ask him to decide how much its worth in its current condition, and hope he says something less than $500. Whatever the gap is, that’s what you have to work with. Problem is, with a streak of podium finishes, there was no way our car would be valued at less than $500, no matter how much oil it was burning. We didn’t even bother to ask. Instead, we decided to fix it for free.

frankenmiata small-nose damaged crank

Early 1.6 Miata engines are notorious for crank nose damage. The nose of the crank is very small, and the woodruff key that aligns the timing chain sprocket and crank pulley is too short. Given the right kind of high-rpm abuse, the woodruff key will start to walk up the groove until its only engaging about a quarter inch of crank nose.  With that little engagement, the pulley will rotate, rounding out the groove on its way. 

When this happens to a perfectly healthy engine, its value drops to nearly zero. There is no easy fix for a damaged crank nose. The crankshaft has to be replaced, and most people consider that a big job. Luckily, we are not most people.

After scouring and for a few weeks, we found a 146,000 mile engine with crank nose damage. The owner was just looking for offers. We offered $0.

That didn’t work, but finally, after a short negotiation, we got the engine for $50. 

Since our engine still had a perfectly healthy crank, it was simply a matter of swapping cranks and dropping the engine in. The bearings in both engines looked fine, so we just left the bearings in our new engine, double-checked the bearing clearances with plastigauge, and bolted it together. What about gaskets and other nickle and dime crap? There was none. We pulled the manifolds to look down the ports and make sure things looked clean, but both intake and exhaust manifold gaskets are metal and reusable. We pulled the valve cover to confirm cleanliness up top too, but that rubber gasket also gets to be re-used. The oil pan and oil pump are sealed with silicone by the factory. And the front and rear main seals? They came with the crank from the old engine. The only gasket we ended up buying was a thermostat housing gasket that cost $1.

Despite being filthy on the outside, our new $50 engine was remarkably clean on the inside. The bearings were perfect and we were able to re-use them without fear.

cash receiptSo, in the end we were $51 in the hole. Time to get creative. LeMons rules let you sell parts of your car to recoup expenses, and we had 5 engines worth of hardware we could sell. We sold off a valve cover, an intake manifold, a throttle body, and finally closed the gap by selling the old block, a few damaged cranks, and a warped cylinder head or two as scrap metal. In the end, we were $13 ahead.

Proving these kinds of cash transactions to the judges can be difficult, but we made a solid effort by taking pictures of the transactions. Sure, we could have faked it, but even that would have at least shown the kind of initiative the judges generally respect.

Before we could sweat the judging, we had to test the engine. We had high hopes that a fresh (146,000 mile) engine would make more power than our old one, but after a quick warmup, dyno chart #8 showed we were down a bit of power everywhere. 

new engine, wrong gear

And that’s where it sat for a week, until we realized we tested the old engine in 4th gear and the new one in 3rd gear. Oops. After testing in 4th gear, Dyno Chart #9 showed the two engines were nearly identical!

new engine, correct gear



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