Monday, July 15, 2013

Time to rebuild a Spec Miata motor!

I've been racing on a low mileage (91k miles), unopened, street motor for the last 3 years.  It dyno'ed 107 RWHP 2 years ago.  Being down on HP in a Spec class means you are at a disadvantage.  My plan had been to practice and get experience on this street motor and then upgrade to a better motor down the line when my skills improved.

At one point, a friend and fellow competitor did a practice session on my car with fresh tires and was able to do a 2:13 at Thunderhill.  He typically lays down 2:08 - 2:10 and better lap times in a 99 with a "pro-built" motor.  That was my target time.  If I could improve up to that time, then my skills would have improved sufficiently to make full use of a pro motor.

I have finally improved enough where I can hit a 2:13 but I still wasn't as consistent as I'd like so I've been holding off.  Until the events of Laguna Seca a couple of weeks ago.....

At Laguna, I made contact with a tire wall when I made a mistake at Turn 4.  When I changed the oil after the event, I found a few metal chunks stuck to my magnetic oil drain plug.  My theory is that the impact shifted something inside the motor.  On a thread on, knowledgeable people speculated that it could be casting flash while other suspected pieces of a thrust bearing.  Either way, having metal bits coming our of your oil is never a good sign...  See pic:

In your typical Spec Miata field, the engine situation typically breaks down as follows:

1. Cheap bastards like me with untouched street or junk yard motors.
2. Decent, unopened street motor bottom ends with a "pro-built" head that has been rebuilt and machined for higher compression with blueprinting at the valve throats and whatnot as the rules allow.  This typically yields 110-116+ RWHP.  Pro built heads are typically $1k - 1,500k.
3. A rebuilt "regional", "pro-built" motor that is a budget rebuild of the bottom end and head and maybe some head work.  This typically seems to yield around 113-118 RWHP.  Rebello offers a package for $2,500 which a few friends run.
4. A full "nationals" "pro-built" motor that gets all kinds of attention, special sauce and special grease.  Pixie dust as well.  This typically seems to yield around 120+ RWHP.  Haag, Rebello, (local shops) and Race Engineering, East Street are the big names here with prices upwards of $5k.

I could have gone to any number of good engine builders but I decided to try and rebuild the original motor that was in the car.  I'm a low budget, weekend racer.  I don't want to piss away a ton of money on a recreational activity.  I'd rather have it in the bank.  Plus I've always wanted to rebuild a motor.  Now I have an excuse!  I know the history of the 180k miles of the original motor that was in the car so I know it was taken care of.  The poor, neglected motor has been whispering at me from the corner of the garage where it lay for the past 3 years asking to make it run again.

So hear goes nothing.  Over the next few weeks and 2 months, I'm going to chronicle my rebuild, take lots of pics and write a few blog posts about my adventure.  Follow along.  Hope you enjoy it.

I'll leave off with a pic of the poor engine on it's dolly.

Suggestions and advice are greatly appreciated so post up or email me.