"BIG FOURS"
Lessons Learned from
building a 2.5 liter 914-4

Component selection

Pistons/cylinders.  Although bores as large as 104.5mm are available, 103mm is the more reliable "maximum" and they seem to be available only from one source - European Racing.  Two piston sets are available, hypereutectic and forged.  I chose the former since they are reported to stay rounder when hot and are about $100 cheaper.  Big pistons require case machining and head machining, but the stock cooling tin still fits.

Stroker crankshafts.  Any stroked crank beyond 78mm requires machining of the case beyond that which is required by the larger cylinders.  I've heard of 3087mm engines being built with 90mm cranks and 104.5 cylinders, but I chose a 75mm crank (with the 103mm cylinders.  It displaces 2499cc, just under the 2.5 liter breakpoint between Modified classes in our PCA region's autocrosses).

Camshafts.  I located about a dozen aftermarket cams for 914s, and each producing company seems to have at least one specifically for Big Fours.  I heard from several sources that it's important to use lifters from the same company as the cam comes from.  I'd planned on using the mild performance WebCam 86a (.435" x 290 degrees) and single heavy duty springs, but a WebCam 163 (.500" x 284 degrees) was ordered by mistake and installed with dual springs - the difference is that the 163 makes about 5 more hp according to the DeskTop Dyno software, and I guess I'll just have to live with that. ;-)

Heat management.  Big Fours have a reputation for short lives, and the cause of death is usually related to excessive heat buildup.  The primary sources of heat are engine size (a given in this case), high compression ratios (higher makes more horsepower, but also more heat), and inadequate oil cooling.  I've seen dune buggy racing Type IV's with compression ratios in excess of 10:1, but I chose a conservative target of 8.2 for longevity.  Actually, once the heads were cc'd, the stock length of the cylinders generated a 8.27:1 ratio, and that was close enough for me.  In addition to the stock oil cooler, I added a sandwich plate adapter to feed an external 11"x11" (48 row) oil cooler with an electric fan attached to it, use deep finned aluminum valve covers, and had the "headers" (2.0 heat exchangers with the outsides removed) heat block ceramic coated.  Balancing and a self-chosen but ignition controlled redline of 6200rpm complete the "insurance" package.

Assembly

Problems with parts.  I'm SO glad I found a great engine builder to assemble my 2.5 four!  He caught three potentially fatal problems with the parts included in the "Monster Kit":

1. The connecting rod bearings' outer edge radii are smaller than the mating radii of the stroker crank journals.  As a result, the bearings ride only on their two outer edges unless they are machined with a larger radius so they can sit down in the journal properly.
2. The piston-to-cylinder clearance was only .0015"; my builder has seen piston growth from heat seize engines with clearances this small, so he took mine out to .003" (he runs .004-.005" in his own race engine, but also rebuilds it more frequently than I intend to).
3. The piston rings needed gapping.  As delivered, they overlapped.

European Racing (the supplier of the parts) responded:

1. "We've never had a problem with that."
2. "We run them with .0015-.002" all the time." and
3. "Some assembly required."  (all quotes approximate).

Seriously, though, if they don't believe there is a problem . . . .

The assembler.  My builder was Jerry at NorthWest Connecting Rod (Seattle, WA).  The downside of working with Jerry: He's as anti-electronic-commerce as the Unibomber - no Website, no email, no fax, no credit cards - and his quality reputation (a kind of popularity) results in almost constant interruptions from the phone and "drop-ins."  The upside is that he knows air cooled engines inside out, he's a racer himself with a lot of experience, he assumes nothing (measures everything), and lets the customer decide after providing all the facts and likely outcomes.  His only requirement is that if you pick stuff that's outside what he thinks is right, you don't tell anybody he built the engine ". . . but if you want a grenade, I'll build you one!"

You'd be blessed if you can find a similar professional in your own locale.  NWCR is listed in the 206 area code directory, but to keep his work moving along, please don't call him just to chat or get advice.  His customers thank you.

Installation and Break-in

Pre-installation wrenching.  There are no visible difference between a Big Four and whatever engine you use as a core.  I installed the distributor, oil filter mount, intake/exhaust, engine tin, sensors/senders, and so forth myself in the usual way.  I also attach the heat exchangers (inner tubes only) and intake runners (as in carbs, with clean rags in the tops) prior to drivetrain installation.  At Jerry's recommendation, I used Bosch three-prong sparkplugs and straight 30W oil (Castrol GTX non-synthetic).  I cleaned up the abbreviated cooling tin and sprayed on a coat of black metallic Hammerite since dirt doesn't seem to stick to that stuff, and I "modernized" the oil filler cap and dipstick handle by painting them OSHA yellow.

Installing.  My method of engine installation involves having the car up on jackstands (tires left on) and guiding the engine/transaxle into position on a (service station type) long-frame jack (about $160 from Harbor Freight).  The four bolts go in, the jack comes out, then I add the starter, throttle bodies, linkages (accelerator and shift), and connect the CV joints and all the cables, hoses, etc.

Break-in.  When first spinning the engine to circulate oil (with the coil wire off), the original 2.0 starter turned very slowly - sounded like an almost dead battery.  I bought a new battery (it was six years old, but the new one was no better) and rebuilt starter (again, there was apparently nothing wrong with the original one) before I was persuaded that I needed a Hi-Torque (geared) starter.  That little sucker - it's smaller and almost ten pounds lighter than stock - spins the 2.5 easily.  And with the connection of the coil wire, there was ignition!  The distributor had already been set by eye and the throttle bodies' idle screws were set by feeler gauge.  I had a 2000rpm idle that sounded like two 1250cc Harley Sportsters at a stoplight - definitely "cammy" and definitely air cooled in its noises.  I turned the fuel pressure regulator down to 45psi (it's set at 55psi in an earlier step), balanced the left and right throttle bodies via UniSyn to get an idle around 1000-1100rpm, adjusted the linkage to the now-balanced throttle bodies, adjusted the idle knob of the fuel injection cockpit control to 14.7:1 air/fuel ratio, put the air cleaners on, and then kept a steady 2000rpm for 20 minutes to break in the cam and lifters; afterward, I set the timing to 30degrees of advance at 3500rpm.

On-road tuning.  The cockpit control for the fuel injection has two knobs. The idle mixture knob mentioned above is set in the driveway using a combination of "feel" and, in my case at least, an air-fuel ratio gauge.  The wide open throttle (WOT) knob, on the other hand, must be set in 3rd, 4th, or preferably 5th while your foot holds the go pedal to the floor up to redline.  The initial setting was far too lean; the experience was like running out of fuel above 4000rpm - which it literally was doing.  About two and a half turns clockwise (out of 16 turns total adjustment) brought it in nicely.

First impressions

Performance.  Even in the driveway, it's obvious that it takes way less time for the 2.5 to spin the lightened flywheel from 1000rpm to 4500rpm than for my old but strong 2.0, and each such blip is accompanied by a much more fierce sonic "bark" through the intakes than before (it's like the intake trumpets grew big sharp teeth!).  On the road, I have at least as much usuable rpm range now as before (no need to keep the rpms up to avoid jerkiness), it just "launches" like a frog and accelerates with a relentless fury.  I imagine I could now "burn out" of pre-grid to heat the tires before I get to the timing start - although competitors behind wouldn't much appreciate the sand- and stone-blasting they'd get, so I won't.  I'd say 914 Lite with a 2.5 compared to 914 Lite with a 2.0 is like a Shelby Cobra compared to a Shelby (Dodge) Daytona - it's not at all the same car.  I'll need to increase my accelerator pedal control to avoid power oversteer when I don't want it, and I don't expect it will be as much fun on wet courses, but, oh, those dry days!

Other impressions.  There goes the gas mileage!  I haven't actually calculated the miles-per-gallon, but it seemed to use a lot of gas just in the breaking in exercise.  The grins-per-dollar, on the other hand, is awesome!  Each cold start is accompanied by a cubic-meter-sized puff of oil smoke (probably due to the piston to cylinder clearance chosen for longevity), but it otherwise runs clean.

Cost of the Big Four conversion.  I paid $1200 for the pistons, cylinders, rings, bearings, and connecting rods; about $150 for cam and lifters; and about $1350 for machine work and assembly I couldn't do myself.  Separate from the Big Four itself was the fuel injection upgrade (remapping the ECM and exchanging the 23# injectors for 31# ones), coating the exhaust, purchase of the external oil cooler, fan, and hoses, finned valve covers, and so forth.  Even with all that stuff included, though, the total cost of the Big Four was right at $3000 - a tidy sum, indeed, but not even a start on a "six" conversion from what I've heard.

To do and follow-up.  I need seat time - lots of seat time - before I'm really smooth with this "new" car.  I also intend to take it to a chassis dyno to ensure I've got all that I can out of the injection adjustment.

As always, feel free to see the whole car as it continues to evolve at the 914 Lite specs webpage (see below) or via email - especially if you have or are considering a Big Four yourself.

Mike Nugent
NugentMD@gte.net
Kent, WA
914 Lite full specifications