Stuff It
What is volumetric efficiency, and how do you determine it? Is there an equation?
Paul Jones
Cambridge, MA
Volumetric efficiency (VE) is expressed as the percentage of the amount of air actually used by the engine compared to the volume of the cylinder. According to John Lawlor’s Auto Math (HP Books, 1991), the formula for total air capacity in an engine is rpm times displacement (ci) then divided by 3,456 to get the cubic feet per minute (cfm). For a 302ci small-block Ford at 4,000 rpm, this is 349.5 cfm [(4,000 x 302) ÷ 3,456 = 349.5], the theoretical amount of air that would fill all eight cylinders at 100 percent. Most street engines don’t fill the cylinders completely, which means they operate at less than 100-percent volumetric efficiency. Let’s say the airflow at 4,000 rpm on this engine measured 300 cfm. The formula for this would be the actual cfm divided by the theoretical cfm times 100, which equals the volumetric efficiency. Dividing 300 by 349 cfm and multiplying it by 100 equals 85.9 percent volumetric efficiency. This is actually better than most street engines, which operate at 75- to 80-percent VE at peak torque. Maximum volumetric efficiency usually occurs at peak torque. Superchargers stuff more air into an engine than it would use in a normally aspirated state. Therefore, supercharged engines create VE curves well in excess of 100 percent. It’s also possible to build a normally aspirated engine that fills the cylin-ders well in excess of 100 percent VE. The more air you can cram into those cylinders, the more horsepower the engine will make.
Dyno-mite
I’ve just taken delivery of a new (actually rebuilt) VW engine for my Riot. It’s a Type I built to 2,110 cc. The engine builder says it should be good for about 150 hp. The engine now has 94mm pistons and cylinders, ported and polished 42x37mm valved heads, an 82mm wedge-mated/ counter-balanced crank, hydraulic lifters, and an Engle cam, all of which are balanced and blueprinted. Now, 150 hp is the number I’m after, but how can I tell for sure what the actual power output is once I put the engine in the car?
Jim Selouis
Farmersville, MO
A lot goes into establishing what the true horsepower is for any engine in any given application. The use of a dynamometer is really the only way to establish a fairly accurate measurement of true horsepower. First of all, there is a big difference between horsepower measured on a bench dyno and horsepower measured at the rear wheels of the car. On the bench, an engine can be set up to run at its optimum. This is a good thing when it comes to dialing in an unloaded engine. On a bench, variables come into play from any number of directions, such as the carburetion, exhaust system, fuel type, atmospheric conditions, and so forth. Even the viscosity of the oil can have a slight effect on the output. If your engine was dyno-tested using your exact carbs, exhaust system, ignition, and everything else that’s going to be connected to it in your car, your builder possibly could have worked the engine up to 150 hp on the bench with the rating taken at the flywheel. If the engine was put together with the right combination of parts, 150 hp is obtainable.
Be prepared—once you hook the engine to the transaxle, the ball game changes. You see, there’s this thing called parasitic drag that’s made up of all kinds of things that can alter the actual output of an engine—the transaxle itself, the wheel and tire size, the wheel bearings, the half-shaft bearings, the airflow through the engine compartment, the gear and bearing lash, the brake drag, the tire pressure, and anything else you can think of that could impose drag on an engine. There’s really no way of determining an exact horse-power output because of these variables. Your engine may be 150 hp outside the car, but it could really be about 120 hp inside the car at the rear wheels. All in all, this is still healthy for a VW, and in your light-weight car, you shouldn’t be disappointed. When all is said and done, there is no 100-percent accurate way to get an absolute horse- power reading.
Our suggestion would be to install the engine and tune it as well as possible. Then call around to some speed shops to find a rolling dynamometer and set up the car. Spend some time fine-tuning the setup to get your maximum horsepower at the rear wheels. Then, if you want more, you can fine-tune each of the components that create parasitic drag to squeeze out every ounce of horsepower possible. The whole process of dyno-tuning is fascinating, so be careful; it could become an obsession.
Light My Fiero
I’ve been reading Kit Car for only a little while, but I enjoy it a lot. I know the question of boosting the power of a Fiero has been asked a thousand times, but I was wondering what I could do to give myself a little extra horsepower without going broke; I can’t afford to rebuild or replace my engine right now. I also want to know—for future reference—how much should it cost to turbo- charge my 2.8? I have catalogs from a couple of your regular advertisers, and the turbo kits seem to cost about $3,000-$4,000 depending on the amount of horsepower they say they’ll deliver. Is horsepower-per-dollar a cost-efficient way to increase power?
Mark Weinberg
Halifax, Nova Scotia
Canada
Before you begin modifying any engine for more power, make sure the engine is healthy. Adding power to a tired motor will only hasten its demise. Your options with the 2.8 are limited. Hypertech (901/382-8888) makes a Power Chip for this motor that improves throttle response (and shifting in the automatic), but not power output. K&N makes a replace-ment air filter that is an improvement over regular paper filters but not enough for you to feel the difference. About the only hop-up parts on the market are cams from Crane (904/ 258-6174). The Compucam 2020 (PN 254112) is for the automatic and gives improved torque, but no more power. Compucam 2030 (PN 254122) is for the manual box and gives more power above 2,500 rpm. Neither one is a radical bumpstick and each should be right at home in a street machine. The retail price is around $160.
Another reasonable mod is to punch your existing 2.8 out to 3.1 with a stroker kit. One is sold by PISA (602/376-1550) for $1,000 for the automatic or $1,200 for the manual. This includes timing gears and chain, an adjustable fuel pressure regulator (pre-set), a regulator adjustment tool, a new balanced flywheel or flexplate, a performance crankshaft, rod and main bearings, six hypereutetic pistons with chrome-moly rings, and instructions. It’s balanced, but you’ll need to have the rods balanced too. Be aware that you’ll need to buy gaskets and other parts and perhaps have some machine work done. This kit ups power from the stock 140 hp to 165 hp. With a hotter cam, also available from PISA, you can get up to 190-210hp. If you’re on a budget, this makes more sense than a turbo kit since you’ll want to rebuild your stock engine before subjecting it to the stresses of a turbo anyway.
Later, you can turbo or supercharge your 3.1 for even more beans. A V-8 swap will, however, produce comparable power with more tracta-bility and quicker response with the drawback of a little added weight. If you’re a techie and understand the theory behind turbocharging and engine management, turbos are great. If you just want more punch, you should have a V-8.
Porsche or Mazda?
I recently purchased a kit car called the Aquila, based on a ’72 VW Beetle. Will you find out when, where, by whom, and roughly how many of these kits were built, including the prices in kit and turnkey forms? Can you tell me what inspired this kit? One last question: Would you prefer a Porsche 911 flat six or Mazda rotary as a potential powerplant?
Ciprian Coman
Chicago, IL
The Aquila was built by American Fibre Craft in Cupertino, California, in the ’80s. Check out the Aquila info "Air-Cooled All Stars" in the Mar. ’98 issue of Kit Car. We have no idea how many were built, but they’re not particularly rare, as kits go. We suggest Mazda power for price reasons, but the 911 will be an easier swap since you won’t have to improvise a cooling system. The purchase price and maintenance costs will be high. Expect to pay $1,500 or more for a tired, used unit and $2,300-$7,500 (exchange) for a rebuilt 911, depending on size and model. Adapters for the Mazda swap are available from Kennedy Engineered Products (805/272-1147), which can give advice on adding a cooling system. The company also makes adapters to bolt a 911 to the VW tranny (it can take about 120 hp before you need to beef it up). You can also adapt the five-speed 911 gearbox to the VW IRS chassis—not the swing axle—but a simpler and cheaper solution would be to use a modified VW engine with a big-bore kit and maybe fuel injection or a turbo. As much as 275 street horsepower is not out of the question. Call the VW experts at CB Performance (800/274-8337 or 209/733-8222 in CA) and see what they recommend.
Blown Away
I have a Cobra replica powered by a ’93 5.0 engine from a Mustang LX. To take full advantage of the car’s potential, I’ve added 3.55:1 rear gears, a K&N filter, smaller pulleys, 1.72 roller rockers with appropriate shims, and some loud—but enjoyable—exhaust refinements. Next, I want to add a 6-pound Powerdyne supercharger kit, but I’m worried about running boost with the ’93 cast hypereutectic pistons.
Ray Godman
Marietta, GA
We spoke with the folks at Powerdyne about your proposed blower installation, and they insist that you’ll run into no trouble with 6 pounds of boost with the stock spark plugs and injectors. The experience of the staff of our sister magazine 5.0 Mustang & Super Fords has confirmed the claim, as they’ve seen 5.0s running 11 pounds of boost. What should concern you is your fuel supply; you don’t want to run into a lean situation that kills those cast pistons. The Powerdyne—and all other supercharger kits on the market—comes with an FMU (fuel-management unit) that takes care of raising the fuel pressure to adequate levels. An additional adjustable fuel-pressure regulator is unnecessary. Your stock injectors will work just fine with the 6-pound setup, but we suggest that you have your injectors professionally cleaned before the installation. Set your timing to stock (10 degrees) and re-advance to the optimum setting.
Propane Power
I have a question which I’ve never seen addressed. How much boost—turbo or supercharger—could be used with propane as fuel instead of gasoline?
John Doud
Grangerland, TX
Propane has many advantages for high-performance vehicles. It’s clean-burning and eliminates fuel distribution problems such as vapor lock. For turbo installations, the propane advantage is its octane rating of about 105, which beats even high-buck racing gas. In order to avoid detona-tion, which will destroy an engine, a good rule of thumb is to raise the octane rating of your fuel by one point for each pound of boost. For instance, if you’re using gas with an octane rating of 88 and you add a turbo with 6 pounds of boost, you’ll need at least 94-octane premium gas to avoid detonation. With propane, you could use 16 pounds of boost. One downside to propane is that it doesn’t lubricate well or cool combustion chambers as does gas, so to combat rapid wear, late-model heads with hardened seats and valves are needed.
Porsche Parts
I’m still lusting over the GT40 Mk. II. The Porsche 944 looks to be the best donor car for this kit. Which of the 944 variations (944, Cabriolet, and Turbo) has the strongest tranny, with the lowest final drive (long gears)? Does somebody make a V-8 adapter, a bellhousing, and a pilot shaft? How’s the reliability of solid halfshaft/upper control arm drive systems such as the Corvettes, Jags, and ’65-and-up Corvairs? I’d like to know what you think about a 944 donor for mid-engine cars.
Les Dewald
Chattanooga, TN
The last time we looked at GT40 replicas (Mar. ’97), most of them used modified Porsche 911 or 914 transaxles. That’s because those transaxles are already configured for an engine with a conventional clutch assembly, and adapters are available to bolt up to the Ford V-8. They’re also strong (particularly the 911/930 models) and can take the power of a hot V-8.
Renegade Hybrids (866/498-2421) converts all types of 911 trannys to longer final-drive gears and reverses the ring-and-pinion so that they can be used in mid-engine applications. Although not cheap, they’re stronger and less expensive than fabricating a bell-housing and clutch assembly for the 924/944 transaxles. The 944, 944S, and 924S (924 body with 944 running gear) had 3.89:1 final drives. The 944 Turbo had taller 3.83:1 gears.
As for solid upper halfshaft/upper control arm suspension, the Vette and Jag systems are strong enough, but basically inferior to an adjustable double wishbone system as used on GT40 kits. In our opinion, the 944 is not a suitable donor car for a GT40 replica. The transaxle isn’t usable without a lot of custom fabrication, and the suspension (MacPherson strut/ semitrailing arms) would not work in a GT40 replica. Some applicable transaxles are the Porsche 911 units, the Z-F tranny (as used in the Pantera), and the Renault 30, which is popular in European GT40 kits, but hard to find here.
Have a Belt
Where can I get seatbelts to fit a kit car? Junkyards won’t sell me used belts, and I don’t want to have to explain what I need to a new-car dealer.
Ted Evanston
Chicago, IL
In many states, it’s illegal to sell used belts. Try Juliano’s Interior Products (860/872-1932) for new ones. It sells retractable three-point shoulder harness assemblies, retractable seatbelts, and anchors in many colors to go with your kit car or hot rod. Also ask about the company’s power-window kits, brake lights, and steering wheels. You may want to try Jamex (702/ 857-4888) as well, which sells a retractable, three-point, racing harness–style system.
More Fiero Four Fire
I have an ’87 Fiero five-speed, four-cylinder. I am looking for a simple (more hp) four-cylinder transplant. Would a 2.2 four-cylinder OHV GM bolt in easily? If not, are there others?
Ken Cummings
Wilmington, NC
You must have missed our in-depth Fiero engine swap article ("More Power," July ’98). The best four-cylinder swap is the Oldsmobile Quad 4. It was a 2.3 engine with 150-185 hp, depending on year and model, and is an easy swap (buy an engine and transmission together, so the ratios will be correct). The first 150hp models came out in 1987, with the H.O. (180hp) following in 1990. These had different intake manifolds, cast-iron exhaust manifolds, better oiling, higher compression, and different cams and computer profiles. The Getrag five-speed used on the H.O. versions had closer-ratio gear-sets and a 3.6:1 final drive. The fastest version was used in the Olds Achieva SCX. It had 185 hp with 3.94:1 gears. In 1996, the Quad 4 was replaced with the 2.4 Twin Cam, which had two counter-rotating countershafts to make it run more smoothly—wimps were complaining that it was too noisy!. The power dropped to 150 hp, so don’t bother unless you get one real cheap. American Custom Engineering (970/259-4156) makes conversion kits for the most popular Fiero repower options.
To install the Quad 4, you will need to modify the subframe mounts and fabricate a right-hand motor mount. The wiring harness should be matched up with the Fiero harness, and the speedo-meter must be modified to work with the new tranny-speed takeoff. A replace-ment torque link is needed to connect the top of the cam carrier to the chassis. You can spend from $3,500 to $3,800 for the conversion kit and engine/ gearbox if you shop in most wrecking yards. You could do better by looking for running gear in self-service wrecking yards, with set prices for engines. Some-times engines and transmissions are as cheap as $500—if you know what you are looking for and don’t mind getting greasy. Four-cylinder engines are not in high demand these days. Always buy the engine, transmission, computer, and wiring harness as a complete unit because visually similar parts from other cars may not work at all.
TOPLESS Z
Is anyone producing kits to convertibalize a 240Z anymore? I read your article on Origin’s kit for the Z car and was interested in its method for modification. I have tried to contact the company without any results. It seems to have gone out of business. I have checked all my old copies of your magazine with articles on this subject, but have found no current companies in busi-ness. There is a place on the Internet that shows using a shortened rear hatch as the trunk lid. If no kits are available, I will probably use the metal-construction method. I am also interested in knowing if anyone is producing a hardtop for a Z. It gets real wet up here in the Northwest.
Wil Hodges
Bellingham, WA
We imagine the place on the Internet you are referring to is www.ztherapy.com, Scott Bruning’s Web site. Bruning has developed one of the best ways to chop the top on a Z. It involves the use of a modified Triumph TR-7 convertible top. Bruning says to cut down the rear strut towers by 2 inches so the top has room to lie flat and flush with the trunk. He sections the 2 inches out of the strut tube below the spring perch and slips front strut inserts into this assembly. He says it does not change the spring rate of the suspension. To help you on your way, Bruning sells videos on a variety of Datsun Z subjects—including top removal. He can be contacted at 208/587-0869. He has also worked out a slick convertible top conversion for the Alpha/Rhino/ Velo Rossa/Thunder Ranch/Stable-type 250 GTO Ferrari replicas that are based on the Datsun Z-car chassis. His latest venture is rebuilding Datsun/SU carburetors to better-than-new status. Owners of other Datsun-based kits such as Spartans and Z-Vettes might want to give him a call.
SCRATCH BUILDER
I had just picked up your May ’99 issue and was not expecting anything out of the ordinary, just good technical columns and some nice kits. Then I got to the Northstar Fiero installation. What a jewel! Ever since seeing the first Northstar Fiero I have wanted to do the same thing to my ’86 SE. Your article has helped me to see more of what is involved and gave me the ability to call Design One to ask further questions and buy the engine and kit. I bought my Fiero solely for creating my dream car after reading your magazine more then seven years ago. I want to do a Northstar install, interior makeover, brake and suspension upgrade, and a rebody. I couldn’t find a kit body that was everything I wanted, so I did a few doodles and made a clay scale model over a Fiero model. How realistic is it for someone without body experience to make their own kit? I have seen ads for books that deal with this. How complete are these books, and can I achieve great looks doing it myself? Is there a firm that will build a rebody for you?
Robert Serrano
Albuquerque, NM
Sounds like you’re on the way to a really great car! The Northstar Fiero is one of the all-time best swaps—kind of like a Ford V-8 into an AC chassis. As for making your own body, we would not recommend you try this for your first kit effort. It’s difficult, messy, time-consuming, and expensive. No book is a substitute for hands-on experience, although you will probably learn something from each of them.
There are several options you might consider. See if there is a kit out there that has the basic lines you want. Then, go to work customizing it. Change the headlights and the tail treatment, add or subtract side vents and spoilers, and so on. We have seen some customized kits that were scarcely recognizable because they were so heavily modified, yet they did not require engineering and fabricating door openings, hinges, windshield installa-tions, body mounts, and the hundreds of other considera-tions that a one-off body would have required. Since you’re familiar with working with clay, you could try out your ideas on the body before you begin.
If you’re determined to build from scratch, we recommend that you find a local kit car company or an individual who is assembling a kit car and would like some help. This will let you learn about the technology and get some hands-on experience without investing a lot of money. Most, if not all, kit manufacturers we know began assembling kits by other companies before working on their own designs. You could try checking with fiberglass companies about having a one-off body made, but it will probably be prohibitively expensive.
SPEEDSTER SUSPENSION
Kudos for an excellent magazine. Which manufacturers make good-quality-and-value disc brakes for a daily driven Speedster replica? Do we use the same disc brakes for front and rear axles? Who makes a good IRS system for a VW-based Speedster? Please have more articles on Speedsters and the Intermeccanica 356B. I am a loyal subscriber. Thanks again for a great job on "our" magazine.
Mike Moran
Laurel, MD
You have a number of options up front. Depending on which model VW your Speedster is built, you may be able to use the disc brakes that came on ’67-and-up Ghias. You can also buy front disc brake kits from CB Performance (800/274-8337) for both link-pin and ball-joint frontends. The ball-joint kit is for ’66-and-later sedans and Ghias, and it includes rebuilt spindles, calipers, backing plates, and new rotors. The link-pin brake kit is for VW sedans up to ’65, and it includes the brake parts and all that’s needed to adapt them over. If you want to lower your car at the same time, CB sells special disc-brake kits that include dropped spindles as well. The company also sells two rear disc-brake conversion kits. These fit either swing-axle or IRS chassis and come with everything you need, including parking brakes on the street model. The competition version omits the parking brake for less weight, but for the street this is not a good idea. Many states require a working parking brake in order to pass inspection.
The rear suspension on ’69-and-up Beetles and Ghias is already an IRS system. Although this cannot be retrofitted easily onto an earlier chassis, you could probably replace your chassis with an IRS model for less than the price of fabricating a custom IRS system that might or might not work. Or you can modify a swing-axle system for improved performance with an aftermarket camber compensator. The factory Z-bar installed on ’67-and-up Beetles is not enough for a hot kit car. While you’re at it, install a 5/8-inch antisway bar up front and upgrade to performance shocks as well. You can even get adjusters that weld into the front torsion-bar tubes to allow the frontend to be quickly adjusted up or down. Thanks for the kind words. We always keep a lookout for recent developments in the Porsche replica scene.
Axle Folly
I’ve subscribed to your magazine for several years and it has helped me a lot in building my dream car. I have a Cobra with a live axle rearend. My problem is that I received the rearend with slightly bent axles. The flat where the rim bolts on has about 0.007 inch warpage. When I measure it with the disc on, I get 0.045 inch of warp at the edge of the disc. For that reason, it squeaks all the time and the rear brakes do not work well unless I pump the brake pedal twice. How can I fix this problem without having to buy a new set of axles and having them shortened and resplined?
Mr. Beraillon
via e-mail
You have a couple options. If the flanges are merely bent, they could be straightened or machined true by a machine shop with a long lathe that can accommodate your axles. If the axles themselves are bent, you can try taking them to a driveshaft or axle shop (check the Yellow Pages under "Axles"). Some shops can straighten axles using a lathe to check for accuracy. However, be aware that your axles may have several problems and you could spend a fair amount of money trying to repair them.
Rather than buying stock axles and having them resplined, measure your axles and call around to some differential specialists, hot-rod shops, or Cobra kit manufacturers that sell live-axle models. We’re guessing that you have a Ford rearend—either an 8.8- or 9-inch model, both of which are quite common in narrowed form. Dealers may have axles to sell that are already the correct length for less than doing the machine work yourself. If you decide to have new axles resplined, be aware that axle steel is very hard and chews up machine tools like crazy!
Cobra Chassis Specs
I’m thinking about building a Shelby Cobra, but I’d like to build the chassis myself. The only problem is that I can’t find the dimensions or specs anywhere. Do you know where I might be able to find detailed diagrams of the Cobra chassis?
Joe Smith
via e-mail
Cobra Restorers (770/427-0020) sells a complete set of blueprints for the Cobra frame and substructure. They are completely detailed and dimensioned prints of the 427 Cobra including suspension pickup points, differential mounting brackets, and body mounts. The plans do not include A-arms, spindles, or uprights, but Cobra Restorers will sell you those items to complete your kit. The plan set sells for $199.95. But be aware—building a frame is not for amateurs. If you are off much more than ¼ inch front to back, your car will not steer or brake straight. Unless you have racing experience and have access to a surface plate and good welding gear, you’re better off buying a frame.