So, I have this pile of parts in the basement, I need a plan for how I'm going to move from that to a running engine. Let's define some goals:
- Venue. Intent is to have a generally streetable car which can be driven to an autocross or track day event, and driven home. Fuel is 93 pump octane unleaded. It must idle well enough for Friday cruise ins, but not the daily rush hour.
- Durability. I'd like to get 5 to 10 years worth of autocrossing and track events out of this build (depends on miles).
- RPM range. Everything I've read says that a Corvair engine that stays under 6500 RPM will last a long time. To a certain extent, that limits other choices which will affect the overall power level. I'd like it to be drivable on the street at 2000 RPM, and have real power from 3000 - 6000. Maximum shift point of 6500.
- Power level. Let's say I'm trying for 160 to 180 net crank HP. That may not sound like much, but remember that a stock 140 only makes 121 HP net, so a 160 HP net engine is a 30% increase, 180 is 50%.
- Car weight. This is a full interior car, although it has the Yenko rear seat treatment and lighter front seats. Figure 2600 pounds.
- Transaxle. The car is fitted with a '66 4 speed transaxle with 3.55:1 gears.
- Budget. I'm willing to spend for required items, but really trick stuff - custom pistons, fuel injection, etc., are out. Let's say that counting the parts I already have, and allowing zero for my labor, the budget is around $4000 total. If I focus on the base engine, then hopefully I can bolt on other parts as time and money allow.
- Rules. I can't really afford an SCCA SM legal engine, so I'm staying within the SP rules. That means the internals have to match one of the stock or Stinger configurations, within the limits of available parts, and there are many available "bolt on" mods. I'll be building a copy of a Yenko Stage III engine, plus any allowed SP mods.
Parts In Hand.
I've accumulated a fair number of parts already, plus what is available from the 140 I'm replacing and the 140 out of the '66:
- 140 crank, turned .010
- Otto fail safe cam gear
- TRW Clevite 77 bearings
- Clark balanced rod set with ARP bolts
- DALE balancer
- Roller rockers (not really necessary, but I have them)
- HD rocker studs (not really necessary, but I have them)
- Isky springs and retainers
- Offenhauser +2 quart oil pan (add a magnetic drain plug)
- New top cover baffle and Otto fan bearing
I'm not including the external parts like carbs and ignition for now, but bear in mind this is a Rochester carb'd engine.
Cylinder heads play a huge role in the performance of the engine. Coupled with the cam, they essentially define how the engine will perform. In many ways, it's best to determine the head specs and cam first, then build the rest of the engine to match, so I've put this section first.
- Base head are '66 140 castings.
- Heads milled to remove step.
- CC combustion chambers for 9.5:1 CR.
- Cleanup ports
- Install slant exhaust tubes with side outlets (mostly for ease of header install).
- Deep seats
- New valves and guides.
To achieve the durability and power I need a good foundation in the shortblock, that is the assembled crankcase and cylinder barrels.
- Select crankcase. A case with studs that have never pulled is vastly preferred. Check cam journals for wear - limit is 1.442", that is .003" clearance on the cam.
- Blueprint (not enlarge) and clean oil system as suggested in performance guides, basically smooth the passages and get any crud out.
- Remove flash and chamfer holes in crankcase to promote drainback to the oil pan.
- Pin crank. Crank gears sometimes will turn on the crank.
- Nitride crank.
- Bearings are new, but check using Plastigauge anyway.
- Select cam to be close as reasonable to Yenko Stage III "short track" cam. These cams were approximately 280 degrees advertised duration and .450" lift. There are several similar grinds available (e.g. Isky 280). Use Source deep dimple lifters.
- Degree cam using an old cam gear modified to slip fit and install Otto Fail Safe gear.
- Install ARP replacement case studs.
- Pistons and rods are Clark's balanced, sized, and ARP bolted with balanced TRW forged pistons. Magnaflux the rod from the damaged cylinder.
- Pistons are TRW forged +.040. Detail the pistons in the oil ring groove.
- Clark's new cylinders
- Convert PCV to modern "cross flow" system.
- Baffle oil pan. I have a system in mind using an Offenhauser deep pan. The Otto parts pan and baffle would be similar.