above: getting down to the finish line: installing the clutch assembly.
Most of our motorcar interests are focused around the auto racing legends of the sixtiesthe Shelby Cobra, the Daytona Coupe, the Porsche 550 Spyder and the Ford GT40 to mention a select few.
It has always been a challenge for me to possess a car that is street legal and fun to take to cruise nights, yet faithful to the theme of a vintage race car. That bar has been raised even higher with the growing popularity of 'Open Track' days, driving schools and club racing events. That leads me to the premise of my latest build: how does one take a replica from any given manufacturer and build a street-legal driving machine that retains its true vintage persona but also be competitive on a weekend excursion to the local road race circuit?
For this project I chose a GT40 from Race Car Replicas in Detroit. All of the things we did to make this project a dual-purpose street/ track car can be done by anyone to most any replica with a little thought up front given to the end goal. This is an enormous project to tackle so I thought it would be best to discuss it in phases. In this article I'll share with you the complexity of the engine build.
After you order your car there is usually some lagtime before it's delivered. We took advantage of this hiatus to build the powerplant that will propel our race car down the front straight at Road America and to the local cruise night when we get back home. It's relatively easy to build a 13.0:1 compression engine to run at 7,000 rpms on a race track burning 110 octane fuel -OR- an engine that cruises at 1,800 rpms all day long and idles comfortably at each traffic light. It's another endeavour altogether to build a powerplant than will excel at both!
With all these formidable factors in mind I headed to Greenville, Illinois to visit "Lumpy" Loughary and Jim at Performance Motorsports Systems. Lumpy has an unsurpassed reputation for building high-performance race engines for clients across the country, largely because his engines produce smooth power and torque across the range and have proven to be extraordinarily durable. Simply put, they win races, and they hold together.
I went into Lumpy's office, poured a cup of coffee, sat down and explained the plan. He was up for the challenge. We spent the next couple of hours talking about compromise, what I could live with in order to achieve something else. This engine would have to be built much different than the street engines I had in my other cars if I was going to be competitive on the track. But it couldn't be an all-out high-compression race engine if I wanted to cruise around town with my boys. We started with the big picture then worked our way down to the nitty gritty.
For this engine, weight is critical and space is tight. Lumpy chose an aluminum dry-sump Ford SVO 302 block with an 8.7" deck height. This will enable us to use a very lightweight 302 rotating assembly and still hit our cubic inch goal of 380. The rotating assembly begins with a billet Scat Ultra Light crank, then we added Oliver Ultra Light billet connecting rods and custom Diamond pistons.
With all the parts in hand and the machine work completed, every tolerance was checked and the short block was assembled. The second major components were the heads. An engine is essentially an air pump and the heads dictate how much air the engine can potentially flow. To give us great airflow within the range of our cam, we chose SVO Robert Yates racing heads. These heads are outfitted with Jesel shaft rockers and titanium valves, locks and retainers. We're installing spray bars in the valve covers to keep it all cool.
The cam selection is one of the most important decisions of your build. It will decide how the air flows through your heads. We're using a custom grind from Competition Cams along with their solid roller lifters. When you run the Dynatek EFI, your cam grind demands some special consideration. I've always heard that it's best to keep your overlap under 25° and your duration under 240° at 0.050 with a lobe separation of 110° or higher.
When it comes to Weber carburetors, it's a love/hate relationship. They are very difficult to get just right. That is why I choose the Dynatek's "Weber-look-alike" EFI setup. It has the authentic look of Weber carburetors with the ease of tuning on your laptop. With the Dynatek system I was able to precisely tune the A/F ratio to maximize the horsepower and the reliability of the engine. An intake that fits an 8.7" deck 302 with Yates racing heads is not exactly an-off-the shelf item. Lumpy asked the folks at Price Motorsports to help. They built a custom 3-piece intake just for our setup. With the fuel injection in place we built the linkage and plumbed the fuel lines.
The dry-sump oil system was next. This is essential on a serious road-race car. The system is made up of a 4-stage Weaver pump, a Peterson oil tank, a custom Aviad dry-sump pan, a abundance of AN fittings and two kilometers of steel breaded line (at least that is what is seems like). This will give us ultimate control of our oiling system and perhaps a few additional horses!
Keeping with the lightweight theme we used a McLeod Magnum Force dual-disk clutch. This setup combined with our very light rotating assembly will yield a very fast-revving engine. We dropped in an MSD Pro Billet distributor, and made the final checks before it went to the dyno room for some final test and tune.
In the dyno room weren't looking for our peak horsepower but instead a flat torque curve and a smooth climb in horsepower all the way to 7,000 rpm where it starts to peak. It was awe-inspiring to see firsthand how spontaneously the engine revs up.
When the dust settled on the engine build, Lumpy had done more than I had expected when I first approached him with this challenge. He and his crew built a high-revving road race engine that can run on pump gas. It is extremely lightweight and has the decidedly vintage GT40 look and persona. It can run safely to 8,500 rpm but has a strong midrange to pull hard out of the corners. It idles smoothly and starts effortlessly. It is all you would want in an all-out race engine and calm enough to run to the Dairy Queen.
This is where it all begins. It looks more like a beautiful sculpture than an engine componentat least it does to some of us! This aluminum block saves us about 94 pounds [±42.6 kg] vs. the iron block. Not a bad start!
With an aluminum block you must make sure the sleeves are completely
seated in the block. A little tap with a big hammer will do the trick every time.
Every new block must be decked, honed, bored and clearanced to match the
specifications of a particular job. Here we're opening up the bores to 4.125".
must be slotted to maximize oil to the mains.
Lumpy used a special PBM-coated/chamfered bearing to clear the rods.
By adding Mallory metal to the crank in strategic locations he was able to zero-balance the crank. This creates a foundation upon which to build an "internally balanced" engine which is more durable. You can see where the tungsten has been added to the crank to assure a smooth-running, well-balanced rotating assembly.
Lumpy chose Oliver billet rods. We traced the H-beam rod in red to demonstrate the difference in size between it and the Oliver billet rod. We would have had to do a lot more grinding on the block to get the H-beam to fit properly. The numbers on the rods are the weights top, bottom and total. All the rods are balanced to ±1/2 grams.
Once each piston and rod is weighed, then they are matched up in sets to achieve the most balanced combination and await final assembly. All the piston/rod weight tolerances must be ±1/2 gram of each other.
We asked Diamond to cut a reverse dome in the piston to perfectly match the combustion chamber in our heads. This dish will allow us to bring the static compression down to 10.7:1. That is at the upper edge for an engine to safely burn 93 octane fuel.
When building a lightweight racing engine, aluminum heads are essential. The Robert Yates heads come in just under 30 lbs. [13.6 kg] complete.
A similar iron head tips the scale at just under 60 lbs. [27.2 kg]that alone
contributes a weight savings of nearly 60 lbs.!
Before you can install the valves, the spring height must be checked and shims installed so that all of the springs are set ±0.005" [±0.127 mm] of each other.
Similarly, the weight of your valvetrain can limit the maximum RPM your engine can sustain. We're using lightweight titanium valves, locks and retainers. Here we're cutting a 3-discrete-angle valve job.
Once you know how tall the springs need to be you can measure your open and closed seat pressures to make sure your springs meet the high-RPM requirements but are within the camshaft specs. We have a closed seat pressure of 248 lbs.
The open seat pressure is 555 lbs. That fits with our build requirements perfectly. We also checked for coil bind at this point too. If everything checks out, you're ready to complete the head assembly.
Lumpy installed a set of Jesel rocker arms. Shaft-mounted rockers are stronger at higher RPMs than standard stud-mounted rockers. The rocker ratio is another way to fine-tune the powerplant. On this engine the intake rocker is 1.8:1 and the exhaust rocker is 1.9:1.
The camshaft was ground by Competition Cams for a valve lift of 0.351" intake and exhaust. With our Jesel rockers, that is a gross lift of 0.631" on the intake valve and 0.666" lift on the exhaust valve. The duration at .050 is 242° intake and exhaust. That is a little low for a race engine with a 4-barrel carburetor but it works well with the Dynatek EFI setup. The cam was installed at 106.5 intake center line. We chose to run a solid roller lifter. In the past, solid roller lifters have lubrication troubles in the low RPM ranges. To solve this challenge we installed Comp Cams pressure-fed roller lifters; they will allow pressurized oil to lubricate the bearings throughout the entire rpm range.
A custom intake was needed for this unique application. Lumpy chose a 3-piece intake that would allow mounting flanges to be bolted to the heads with a belly pan to seal up the lifter galley.
The intake was match-ported to the heads. It is very important that the atomized fuel have an unobstructed path to the combustion chamber.
The Dynatek EFI setup was pre-fitted to the intake to check for any clearance problems. The bottom end is sealed up by an Aviad GT40 pan that was converted to a dry-sump pan just for this project. It is starting to look like a serious race motor at this point!
The dry-sump system (not shown) gave us the opportunity to force oil to places that you would not normally need oil for a street engine. The spray bars in the valve covers is a great example of this. By spaying the valvetrain with oil, it will run cooler and more efficiently.
Another simple thing to do to find a few more horses is to use cog belts and pulleys whenever possible. They require much less energy to turn because they fit much looser than the standard pulley system.
Our clutch package is a Magnum Force dual disk from McLeod. The clutch, pressure plate, and flywheel aggregate a combined weight of just over 11 lbs. [5.0 kg]!
From the top you can see just how small this assembly is compared to the standard clutch/pressure plate setup. The small diameter coupled with the low mass has a profound effect on how rapidly this engine can climb the RPM scale.
Once it is all done it is time to break it in on the dyno. This is the time to do your first level of tuning and make sure everything is functioning properly.
The dry-sump system is important to maintain consistent oil pressure when the car is experiencing lateral "G" forces for more than a few seconds such as you'd experience in a long carousel or a banked turn. If oil is forced away from your oil pickup tube for even a split second, it could result in a spun bearing or worse. The dry-sump system is engineered to prevent that from ever occurring.
So now you have the final producta vintage-looking race engine that will behave well enough for your local cruise night and still retain its menacing, take-no-prisoners performance characteristics on the track.
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