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Turbo Inline Six Engine - What's Your Problem?

Turbo Inline SIX
Jacob Potts, Mercer, PA: Here's something you may not hear too often. I'm seriously considering turbocharging one of GM's Turbo-Thrift 250ci L-6 engines for an early '70s Nova. I love the small-block V-8, but I'm looking to try something different - a turbo inline six. Would you please give me some information about the engine, including the exhaust runner size and if it is able to endure forced induction with whatever machine work is required? Also, are there any bottom/top-end kit parts available in the aftermarket? Your help will be greatly appreciated.

Jeff Smith: We did a little digging and discovered a guy by the name of Tom Lowe who is a member of Inliners International and has been building and driving a turbo inline six 292ci Chevy for several years. I spoke with Lowe, a fellow Iowan, and discovered he has close to 30 years of experience building these turbo inline six Chevys. You can see some of his handiwork on his website, 12bolt.com, since he repairs, builds, and sells Chevy 12-bolt rearends. But he also has massaged an interesting inline Chevy head modification that we'll get to in a minute.

The most critical component for the turbo application is a cast-iron exhaust manifold to mount the turbo. Lowe uses a T-4 turbo combined with a cast-in-place exhaust manifold built by a Brazilian company called SPA Turbo. The manifold places the turbocharger in the center and includes a built-in wastegate mount. The manifold is not light at 30 pounds, but it is durable. Lowe imports this manifold and sells it for $450.

Lowe runs a T-4 62-1 Turbonetics turbocharger on his 292ci six and is currently pushing 11 psi and still running the engine on pump gas. He says his 3,700-pound car and driver combination has run as quick as 13.8 at 99.9 mph at Cedar Falls Raceway in Cedar Falls, Iowa, with a 700-R4 automatic shifting at 4,800 rpm. Lowe has also built his own intercooler for the car and controls fuel with a Holley Commander 950 EFI system and feeds air through a stock 5.3L LS engine throttle body. With 42-lb/hr fuel injectors, the little six gets decent gas mileage. Of course, you could use a carbureted intake manifold mounted with a blow-through carburetor and go that route, which should be less expensive. If you do, we'd suggest talking to the guys at Quick Fuel carburetors. We have had great success with their blow-through carburetors on several occasions. They will probably suggest a relatively small-cfm Quick Fuel carb with annular discharge boosters. We recommend you follow their suggestions if you decide to try a blow-through carbureted application.

Lowe also has some suggestions for cylinder heads that work well on inline Chevys. The production inline-six-cylinder head uses a common intake port for two cylinders, which isn't very efficient from a performance standpoint. Compounding the issue is a head bolt boss that runs directly through the center of the intake port. Lowe suggests removing this boss using a reciprocating saw and then dressing the finished cut to improve cylinder head flow. That will then require an Allen head bolt conversion that he also sells. This alone will improve intake flow, but Lowe has created a Hi-Flow lump port kit that takes this initial modification much further.

The lump is a simple cast-aluminum insert that fits in the floor of the intake port and drastically improves airflow in all common port inline Chevy six- cylinder heads. The installation process isn't difficult, but it does require some machine work that might be better left to a professional machine shop. Or Lowe can perform the installation for you for a reasonable price. He has also created a how-to video online on YouTube. Search premium lump port Chevy inline-six 230 on the web and you can see the installation of one of these lump port kits. According to Lowe, the kit-along with a slightly larger intake valve-can drastically improve intake port flow. At 0.400 inch of valve lift, Lowe measured 164 cfm for the stock head, and with a larger 1.84-inch intake valve and the lump kit installed, the flow jumped to 208 cfm, a 26 percent increase in flow. The lump kit is available from Lowe's Autowerks website. We'd also suggest adding a set of forged pistons to the engine just to dial in a little insurance against detonation damage with the turbocharger.

More Info
Autowerks
Dysart, IA
319/476-2172
12bolt.com

Quick Fuel Technology
Bowling Green, KY
270/793-0900
quickfueltechnology.com

CC Quickies
Just For Old Time's Sake
Here's a vintage, '05 On the Rack shot pulled from the archives. It features crowd favorite Holly Weber tightly clad in a fine Detroit Muscle shirt. Ah, the good ol' days.

Cool is Cool?
Willie Pretorius, Germiston, South Africa: My son and I have replica Cobras that we built ourselves. Mine is equipped with a Ford 351W motor and speed equipment, while my son's is a Chevy 350 powered with equivalent Chevy speed parts. The cooling system works fine with the temperatures on the open road at 197 degrees F and 221 F in town. We are trying to lower the temperatures by correcting the timing and air/fuel settings with information obtained in your magazines. However, I have found some discrepancies:

Hot Rod, Jan. '00 ("Boiled Rat"): "Lean mixtures and too much advance can increase running temperatures." Car Craft, Jan. '00 ("Too Hot"): "More timing improves low-speed cooling, and a rich mixture can make an engine run hot." Car Craft, Jan. '07 ("Corrosive Nature"): "When the engine cools, the coolant is drawn back into the radiator." Chevy High Performance, Apr. '06 ("Pressure-Type Radiator Caps"): "As the engine cools down, the vacuum serves to permit air into the radiator." Car Craft, Nov. '03 ("Radiator Caps"): "Coolant is purged into the overflow tank, though it will not be drawn back when the system cools."

What adjustments must be used if the engine runs hot? Advance or retard ignition? Lean out or increase mixture on Holley 600-cfm carb (lean-counterclockwise, richer-clockwise)? Must air or liquid be sucked back into the radiator when the engine is stopped and cools?

Finally, we bought two Stant radiator caps rated 16 pounds with red pressure relieve levers. One has vented printed on top, and the relieve valve hangs loose at the bottom. The other relieve valve needs force to pull it down, and it doesn't have vented printed on it. What is the difference?

Jeff Smith: To make this more confusing, Willie, most of the above statements are true-but more information is necessary to make them totally accurate. Let's take them one at a time. The statement "lean mixtures and too much advance can cause an engine to run hot" is only partly true. In my experience, a lean mixture with very light load (highway cruising in your car) will not make an engine run hot. Because the engine is only making 20 hp, there are really no problems here. If the engine runs too lean, it will usually surge and exhibit poor light-throttle acceleration, but it shouldn't necessarily run hot. However, retarded timing is guaranteed to make an engine run hot. This is because the late start of combustion exposes more of the cylinder wall to heat that transfers to the cooling system. Excessive vacuum advance could contribute to an engine running hotter (although this is less likely) since the engine is working against cylinder pressure. Usually, overadvanced timing will be felt as a surge as the engine is struggling to overcome the start of combustion before the piston gets to top dead center (TDC). This not only kills mileage but can contribute to making the engine work harder. More often, the engine may run hot because of insufficient timing at part-throttle.

A good place to start with timing for most performance engines would be 12 to 14 degrees initial timing with 20 to 22 degrees of mechanical advance all in by 2,600 to 2,800 rpm. Then it is important to also use vacuum advance that will kick up the timing at part-throttle another 10 to 14 degrees. This may put the part-throttle timing at cruise rpm at 44 to 46 degrees BTDC-and the engine may want that much timing to optimize part-throttle performance. It's also possible that the engine won't require nearly that much timing. That tends to be the case with later-model cylinder heads with good combustion chambers, which generally don't need as much timing as older cylinder heads. The only way to know is to experiment and determine the best overall timing.

As for tuning the idle mixture screws, unless carburetors operate differently in the Southern Hemisphere, your adjustments are backward. The majority (but not all-we'll deal with that in a moment) of Holley carburetor idle mixture screws are adjusted the same way. To lean the circuit, turn the idle mixture screws clockwise (as if tightening). Conversely, to richen the mixture, turn the idle mixture screws counterclockwise. The exceptions are a few emissions-style Holley carbs whose idle circuits are backward (which means the idle mixture screws are turned clockwise to richen the mixture), but these carburetors are relatively rare.

Before you start the engine, fully seat both idle mixture screws then turn them counterclockwise 11/2 turns out. Then start the engine and normalize the temperature. Tuning feedback is always good, so connect a low-speed tachometer or a vacuum gauge (or both). Turn both idle mixture screws in about an eighth turn and watch the engine speed or vacuum. If either or both increase, continue in this direction until idle speed or vacuum tops out or drops off. Always adjust both screws the same amount and then return the screws to the best position. If the initial turn-in hurts the idle speed, reverse the direction until you achieve maximum idle speed and/or vacuum.

As for movement of coolant after the engine is stopped, both statements are correct if applied to the proper installation. If you have a radiator with a pressure cap that dumps to the ground, then when the engine is turned off, the radiator may push a little coolant out the overflow onto the ground. When the engine cools, pressure drops and any liquid that was pushed out of the system will create a void that will be replaced with outside air pulled in past the cap. If a tube is plumbed to either an overflow or purge tank, any coolant pushed out of the radiator when the engine is hot will collect in the tank. After the engine cools and the system pressure drops, that coolant is generally pulled back into the radiator-assuming the overflow tank line is plumbed into the bottom of the tank or there's a tube that extends to the bottom of the tank. This is the proper way to build a cooling system, and all new cars are set up this way. A purge tank is necessary if the radiator cap is lower than some portion of the engine. A low radiator cap makes it difficult to fill the system, requiring a purge tank located at the highest point of the cooling system. This allows the system to eventually purge the air into the purge tank. The reference in the Nov. '03 Car Craft discussed a bad radiator cap that would not allow the coolant back in. We're assuming here that the cap works correctly. One thing mentioned in that story that is not correct is the suggestion to use distilled water. The distillation process strips electrons from the water. When used alone, distilled water will immediately pull electrons from the softest metals in the cooling system-zinc, magnesium, or aluminum-which is not what you want. The best water to use is either softened or reverse osmosis filtered.

As for your question on the Stant caps, the difference is probably between an overflow system and the older-style vented system. Look for two rubber sealing gaskets on the nonvented cap. The normal seal on the very bottom is what seals the radiator pressure and is relieved only when the pressure exceeds the rating on the cap. The second seal will be located directly underneath the cap and is designed to seal the cap for use with overflow systems. The vented cap probably does not have this second seal under the cap and allows overflow out the tube where it is dumped on the ground.

For what it's worth, many car crafters become upset by coolant temperatures that approach 220 degrees F at low speeds. While high, this is not an excessive temperature as long as the system is not venting steam, pushing coolant out the overflow, or audibly detonating. This high temperature isn't necessarily harmful to the engine, although you would not want to run the engine at maximum power and rpm at this temperature since it could easily detonate. But at low engine speeds with mild throttle openings, 220 degrees F is not an excessive temperature.

CC Quickies
Ted Toki showed us the ballpoint pen test to quickly identify good big-blocks in the junkyard or at the swap meet. If the pen doesn't fit between the bores, it is a 454 or a 396 that can be made into a 454.

Dread Revival
Gary Tetu, Scottsdale, AZ: I really enjoy reading Car Craft, but an article titled "Disco Dread" in your June '09 issue prompted me into action. The article broke with your unwritten rule to avoid the Corvette with: "The best deal in performance cars on the planet-the C4 Corvette." Your article basically promoted finding an early-year C4 for less than $5,000 and then replacing the original engine with an LS engine. I loved it.

I went looking for a low-buck C4. What I found were lots of serious problems attached to each car. Each $3,000, $4,000, or even $5,000 C4 needed bodywork, paint, a new interior, and mechanical repairs. When I added up all these items, it didn't leave any money for a performance engine.

Then I came across a torch red '96 Corvette with the LT4 engine, ZF six-speed trans, and just 41,000 miles on the clock. The car had been very well cared for, so all the mechanicals were in tip-top shape. I feel the LT4 has close to the same performance as a stock LS1 engine.

I paid $13,700 for the car and did not have the fun of all the busted knuckles rebuilding the car. But I think I came out ahead by going for the newer car with the LT4 engine and six-speed. You guys were right-the C4 is the best deal in performance cars on the planet.

Jeff Smith: Sounds like you found a winner, Gary. If I can be so bold, how about a suggestion to tune up the LT1/LT4 motor? I recently ran across a company called EFI Connection that offers a great upgrade for this engine's Achilles heel-the OptiSpark ignition. As you probably know, the LT1/LT4 drives the distributor off the front of the cam with the plug wires coming off the front of the motor. While the concept was good-improved ignition timing accuracy using optical pickups-moisture captured inside the housing caused all kinds of grief, especially for the '92 to '94 versions. Plus, when you have to replace the module (around $90) or the cap and rotor ($280), it quickly gets expensive.

The EFI Connection alternative is to pull most of the distributor off of the engine and convert to a 24X crank sensor wheel and a cam sensor, all located behind a new aluminum timing cover. EFI Connection builds a custom engine harness to adapt a late-model GM LS1-style ECM that will drive the LS1-style distributorless ignition system with the coils located either on the valve covers or relocated somewhere in the engine compartment. For the LT1/LT4, EFI Con-nection even has a do-it-yourself kit that includes the instructions and all the harness components necessary. To do this, you'll need a GM LS1 computer ($150), the coils, and to figure out a way to mount the coils. Or, EFI Connection can build a complete harness ready to go for $650 (which is a great price) to which you just add the coils and the computer. You will also need to tune the system with a software upgrade through EFILive or HP Tuners. All this could easily run more than $1,100, so it's not cheap. But we're hearing all kinds of good things about this conversion. Another advantage (this doesn't apply to those with six-speed manuals) is the LS computer will also control a 4L60/65E electronic overdrive automatic, which means you don't have to invest in a separate controller that can cost between $800 and $1,000. In that sense, it's like getting an electronic trans controller for free. EFI Con-nection now has a 58X conversion that will use the later computers that can also drive the late-model electronic automatic trans.

I also found a variation of this idea from Delteq that converts the LT1/LT4 engines to a waste spark distributorless ignition using the Cadillac Northstar system. Waste spark systems use four coils with twin output terminals that fire two cylinders simultaneously. This reduces the number of coils needed but fires each coil twice for the entire 720-degree, four-stroke cycle. The Delteq conversion system sells for $694.73. It is less expensive because Delteq uses the OptiSpark sensors to trigger the coils. This would appear to work well because the sensors were rarely the problem in the original OptiSpark.

More Info
Delteq
703/476-3566
delteq.com

EFI Connection
Erie, PA
814/566-0946
eficonnection.com

CC Quickies
El Guapo Lives
Log on to CarCraft.com to see a video of El Guapo making 600 hp on the Westech dyno.

Getting Educated
Charles Jousma, Calumet, MI: I've been working on my own vehicles for the last five and a half years without once bringing a vehicle to a mechanic. At this point, I am the person everyone comes to for diagnostics and to try to get free repairs. I now want to take the Michigan mechanic test, but I realize there are two areas of the test in which I lack knowledge: engine rebuilding and repairs and automatic transmissions. Are there any books you can recommend that will prepare me for these portions of the test? I would like to attend school for this, but I do not have the money or time, and at this point, I have vast amounts of hands-on experience. I love the magazine and enjoy the What's Your Problem? section the most.

Jeff Smith: There is a ton of material out there Charles; it's just a matter of choosing the area you want to concentrate on. Since you're reading Car Craft, we'll assume you are into domestic engines and transmissions. There's a website called boxwrench.net that offers some generic information and books that are accompanied by a very professionally produced DVD. I found a CarTech title called How To Rebuild Any Auto-motive Engine that is 144 pages and comes with a DVD that would probably be a good place to start. This book and three-hour DVD are affordable at $39.95 and might be what you're looking for. As far as automatic transmission information goes, I also found a book on the 4L60E GM automatic overdrive trans, but if you have only limited experience with automatics, I would suggest learning on a more basic transmission like a TH350. These transmissions are easy to find and inexpensive, so you could buy one and go through it without a major expense. I'd recommend the Turbo Hydra-Matic 350 Handbook by Ron Sessions that's sold through HP books. I found it for sale on Amazon.com for less than $20. The TH350 is a relatively simple transmission, and you will be able to learn much more about basic hydraulics and the use and control of planetary gearsets.

I might also suggest looking into taking the Automotive Service Excellence (ASE) series of tests for the automobile and light truck certification (test series A). If you log on to ase.com, there's a wealth of information on all the different tests you can take to become certified in several different areas. For example, the A-series of tests involves roughly 40 to 50 questions that cover the basic area in question, such as engine rebuilding or automatic transmission repair. The least expensive route is to take the paper test, which requires a one-time registration fee of $36, and then each test (there are eight in the A-series) costs $28. Currently, ASE has certified more than 400,000 mechanics since 1972, and the certification lasts for five years. There is also an ASE Master Certification program that covers the entire A-series. This is not an easy test, since the ASE says that only two thirds of the test takers pass. But you do get an ASE shoulder patch and a certificate that can certainly help when looking for a job and commanding a better salary than someone without a certification. It's a great place to start.

More Info
Automotive Service Excellence (ASE)
Leesburg, VA
703/669-6600
ase.com

BoxWrench Media
Venice, CA
866/350-5005
boxwrench.net

CC Quickies
The Disco Nova
Remember the Disco Nova? This short-lived project was a paint and body model for the 2005 redesign of the magazine. How time flies. On the right is former CC Executive Editor Terry McGean, on the left is Hot Rod Editor-in-Chief David Freiburger adding the stripes for the story. We don't know where the car is now.

"Houston, We Have No Ignition"
Bob Marty, via CarCraft.com: I have an electrical problem on a numbers-matching '67 RS/SS Camaro. We completed a show-quality restoration, and it all went well until it was time to start it up. The motor fired right up. However, as soon as the ignition switch was released from start to run, the motor shut down. We checked all wires and connections. With the key in the run position, our Fluke meter showed no voltage at the coil but 12 volts at the resistor wire on the firewall. As I understand, there should be an approximate four-volt drop from firewall plug to the positive side coil. Both front firewall harnesses were new reproductions. We put the original motor harness back on and had the same problem. After many "Wow, that wire is really hot" experiments, I will tell you how we got to where we are now.

First, we eliminated the yellow wire from the starter solenoid to the positive side of the coil. We then replaced the resistor wire at the firewall plug and installed solid wire from the plug to the coil. This gave us 12 volts to the coil all the time. We mistakenly thought we would just need to replace ignition points a little more often. Yeah, right-how about every 300 miles? Currently, we're running a Mallory HEI ignition module in a distributor with a high-voltage coil with 8 ohms of resistance built into the coil. We've driven the car approximately 400 miles since this, and all seems well. This ignition module is designed to run on 12 volts with this specific coil. Can you please help us understand what the heck is going on here?

We used the original coil that was OK before the restoration. Can this problem somehow be related to the ignition switch? We build nice cars, but electrical problems are not our strong points. My two sons, 8-year-old grandson, Hot Rod Tyler, and I would be grateful for any assistance you can offer us. Thanks for your help!

Jeff Smith: You have a lot of things going on here, Bob, so let's take them one at a time. A typical points system cannot operate with a full system voltage of more than 14 volts with the alternator charging. This much voltage (and the attendant current flow) will burn up the points, as you discovered. As you surmised, that's the reason for the GM resistance cable that is in the harness between the firewall plug and the coil. When you tested for voltage at the positive side of the coil with the resistance wire connected to the coil, it's likely that the points were closed. This creates a closed circuit to ground on the negative side and would produce the zero voltage reading at the coil if you were reading voltage off the negative (distributor) side of coil. The wire from the starter solenoid to the coil is a battery voltage source only when the key is in the start mode and was designed to bypass the resistor wire and feed cranking battery voltage to the coil for better starting performance. Eliminating this wire only reduces voltage to the coil during cranking if the inline resistor wire is still used to the coil.

This doesn't fully explain why the car would only run on the start mode. We've seen situations in which a car crafter has wired the ignition switch for an HEI-type distributor off the accessory side of the ignition switch. In this case, the engine will not fire until the key is released from start to run. This is the opposite of what you are experiencing. We have seen ignition switches that have melted connectors on the backside of the switch due to circuit overload because too many circuits were loaded through the hot side of the ignition switch. I would also use your ohm meter to check resistance in the resistor wire. If the reading is zero (or open), the wire is defective. This is unlikely since you have two and they both performed the same.

All factory and most aftermarket electronic ignitions are designed to run on full system voltage at ranges from 12 to 14.5 volts. It sounds like you have converted to an HEI-style distributor that uses full system voltage, which is why your ignition system is working now. This will work fine, and you should not have any more difficulties.

More Info
Actron;
Cleveland OH;
800/228-7667
actron.com

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CarCraft@CarCraft.com
CarCraft.com
Car Craft Mag
831 S. Douglas St.
El Segundo, CA 90245

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