The engine compartment in Gordon Bishop’s Rat-powered AMC joins a pair of large aluminum t
Joe Wahrer; Lima, OH: Greetings, I am a vocational teacher at the Allen Correctional Institution in Lima, Ohio. A student saw your feature on Gordon Bishop's '65 AMC Rambler in the Nov. '10 issue ("AMC It Go," pg. 68). Can you tell us where we could learn more about the carb hat/turbo setup? You are talking about some serious plumbing with taking the compressor side clear to the back seat and then forward to the carburetor. What are the benefits? Tell Mike Yoksich he caused a stir here. Awesome job, Car Craft! Keep up the good work.
Jeff Smith: Turbocharging has finally come into its own for car crafters and we're seeing hair dryers show up in all kinds of different race and street cars. Gordon Bishop's AMC you mention is a wild 8-second drag car with twin 80mm turbochargers designed by Bullseye Power in Muskegon, Michigan. Creating 26 psi of boost (which is almost two atmospheres of pressure), these turbos make a massive amount of heat. Even on a drag car, they spike the inlet air temperature coming out of the compressor side of the turbocharger to somewhere between 220 and 250 degrees F. Hot air entering the engine is less dense than it would be at the same pressure if the air was cooler. The ideal situation to make more power is a combination of high pressure and low temperature. Achieving this ideal situation requires cooling the air after it exits the turbochargers. Many drag racers prefer air-to-water intercoolers because they are more efficient. This system is basically a large tank in which ice water is pumped through a radiator. A large container, which in Bishop's car is located right behind the driver, is built around the radiator and plumbed to the turbocharger outlets. The hot, pressurized air from the "cool" side of the turbos blows through the radiator, which reduces the temperature but also creates a slight restriction or pressure loss. Then the cool air is ducted back to the engine and directed through the carburetor hat and into the engine. While a pressure loss might seem counterproductive, there is still a major net power gain because of the dramatic reduction in charge temperature. Our pal Kurt Urban has tons of experience with drag race turbos and he says that with a good intercooler using ice water, at the starting line you can see discharge temperatures into the engine as low as 50 to 60 degrees! At the end of the run, the inlet air temperature will rise to maybe 120 degrees. While this temperature seems high, it is still a reduction of 125 degrees or more, which is a major increase in density. The key is to create the lowest discharge temperature across the intercooler for the least amount of pressure loss. Urban says a pressure drop of 3 psi or less is a good goal. He also says the key to these systems is ensuring the pump system can produce a high rate of water flow. Intercooler efficiency is based largely on how quickly the system can circulate the ice water.
Returning from the intercooler, the upper tube is connected to the carburetor hat. The duc
When designing a system like this, you also have to take into consideration the overall cost in terms of efficiency for performance. Besides building the entire system with ducting running between the engine compartment and the back seat–located intercooler, the designer also has to account for the added weight. That's why the intercooler is behind the driver and the intercooler tank is on the driver side in the trunk alongside the fuel tank. All this adds weight that the car must then accelerate down the track. The aluminum ducting, the intercooler, the pump, and the water (which weighs 8 pounds per gallon) could easily account for 50 to 75 pounds or more of added weight. This weight may not be worth the trouble if the boost level is perhaps 10 or 12 psi because the power gain from the cooler charge temperature is not enough to overcome the weight penalty. With lower boost levels, a less complicated system would be a stand-alone air-to-air intercooler that just uses incoming air to reduce the discharge temperature. While lighter and requiring less plumbing, air-to-air intercoolers are not as efficient in terms of reducing the discharge temperature. As is the case with most things in life, there are no free rides, except maybe running E85 or straight methanol, which do a great job of cooling the charge temperature based on their latent heat of vaporization—but that's another story.
The Edelbrock 290cc “roval” heads for the big-block Chevy represented the best dollar-per-
John Lubinsky; via CarCraft.com: I have a '69 Chevelle SS with a 454-inch Chevy big-block that has been bored 0.030 inch over. It has a stock crank that has been turned 0.010/0.010 on the journals and reconditioned stock rods with ARP bolts. The pistons are TRW L2465 forged domed. All this has been balanced for smooth operation. The cast-iron heads were ported and gasket-matched. The block has been decked and the heads have been shaved to 115 cc to achieve a compression ratio of 10.25:1. The camshaft is a hydraulic flat-tappet Lunati special-purpose grind with 225/235 degrees of duration at 0.050-inch tappet lift using stock rocker arms. The intake is a Weiand Stealth with a Barry Grant 750-cfm Speed Demon carburetor. Hooker Super Comp headers reduced to 2.50-inch exhaust flowing through Flowmaster 40-series mufflers and 2.25-inch tailpipes. The engine has about 15,000 miles on it. This combination has a lot of power, and I am assuming it produces more than 400 hp. But you know how it is—I want more power. This car is a weekend warrior and I usually feed it 110-octane race gas.
I now have the funds for aluminum heads and a complete roller cam and valvetrain. I was considering the Edelbrock RPM Performer aluminum heads (PN 60459) and a Comp Cams roller camshaft. My questions are: 1) Will I have any problems with the Edelbrock heads and the pistons I currently have in the engine? 2) Would you recommend different heads than the ones I have chosen? 3) What camshaft would you recommend? 4) Would a hydraulic roller be better than a solid roller? and 5) What kind of distributor gear should I get for my Accel distributor? I would like to break the 500hp mark with a naturally aspirated engine. This is not a daily driver and fuel economy is not a concern. I have subscribed to your magazine for more than 10 years and enjoy reading all of the tech tips and articles you have about making more horsepower. Any help you can provide me will be greatly appreciated.
Jeff Smith: John, I think your Rat plan has plenty of potential, but, as usual, I have some suggestions on how to over-deliver on your 500 hp goal. I think the pistons that are currently in your engine will work just fine. The Edelbrock aluminum heads are a good choice. But rather than the 315cc rectangular-port versions you mentioned, I'd suggest going with the "roval" port Edelbrock version (PN 60479). These heads use roughly a 10 percent smaller intake port volume (290 cc versus 315 cc). The smaller port will deliver a greater mixture velocity and therefore better throttle response. We've tested five oval-port heads, including a set of factory peanut-port heads ("Big-Block Cylinder Head Test," Mar. '08, pg. 30), using a 496ci stroker big-block Chevy. The heads we tested included Brodix, Dart, Edelbrock, and Trick Flow Specialties. AFR now has an oval-port head, but they were not available at the time of our test. Our engine used a Comp hydraulic roller XE276HR with 224/230 degrees of duration at 0.050-inch tappet lift with 0.510-inch lift on both the intake and exhaust. The Brodix heads made the most power with 597 hp at 5,700 rpm and a scorching 626 lb-ft of torque at 4,000 rpm using an Edelbrock RPM Air-Gap dual-plane intake. The engine made this power with 2 1/4-inch open headers along with very cool water temperature and hot oil, so the numbers are a little better than what you would see in your Chevelle. The Edelbrock heads made a little less power than the Brodix castings (582 hp and 618 lb-ft of torque) but are also the least expensive. For the price, they make an excellent purchase. Since your engine is 36 ci smaller, it makes sense to go with a smaller intake port.
To give us an idea how much power your engine could make, let's whip out the calculator. Our 496ci test engine with the Edelbrock heads made 618 lb-ft of torque (1.24 tq/ci) and 582 hp (1.17 hp/ci). The average torque was 582 lb-ft (1.17 average tq/ci) while average horsepower came out to 515 (1.12 avg. hp/ci). Using the peak hp/ci figure of 1.17 and multiplying it by 460ci (454 with 0.030-inch overbore) equals 538 peak hp with a peak torque estimate of 570 lb-ft.
As for a camshaft, I'd suggest using a hydraulic roller. I found a Lunati hydraulic roller cam (PN 60212) that uses 231/239 degrees at 0.050- and 0.600-inch valve lift specs for both the intake and exhaust, with a 110-degree lobe- separation angle (LSA). This has slightly more duration and 0.100 inch more valve lift on the intake (0.090 inch on the exhaust) compared with the flat- tappet version that would surely bump the power. I would also recommend investing in a set of roller rockers. When you get into the 0.600-inch valve-lift range, the slot on the bottom of the stock rockers will probably hit the rocker stud, causing all kinds of damage. Plus, you will have the advantage of a far more accurate rocker ratio than that with stock rockers. As for the distributor gear, most cam companies now design their hydraulic roller camshafts to use a stock-type iron gear, making a bronze gear unnecessary.
I've received several letters from readers who assume that a solid roller street camshaft will deliver superior power over hydraulic roller lifters. We're about to do a dyno test of some new short-travel lifters that appear to be the hot ticket for street engines. We expect these new lifters will deliver virtually the same power curve as a mechanical roller camshaft without the problems associated with the solid roller cams. Aggressive street big-block Chevys seem to be plagued with solid roller lifter failure problems. It appears these problems are related to excessive valvespring pressure combined with long periods of idling that hurts lubrication. Generally, hydraulic roller lifter cams require lower spring pressures and do not seem to suffer the same kind of durability problems. If these new short-travel hydraulic roller lifters can deliver a similar power curve right up to peak horsepower, why would you bother with mechanical rollers? It's worth considering.
You also mentioned using 2 1/4-inch tailpipes. You might want to consider building a minimum of a true 2 1/2-inch exhaust system (a 3-inch system would actually be better). Flowmaster makes a system specifically for your Chevelle that is well designed and fits even with large mufflers. A 3-inch, mandrel-bent system could be worth 10 or more horsepower over a system with 2 1/4-inch tailpipes, especially considering that compression-bent pipes significantly reduce the inside pipe diameter compared with mandrel-bent pipes.
You also mentioned 110-octane race gas with this 10.25:1 compression engine. With the combination of this compression and a longer-duration cam, I think that 93-octane pump gas can handle the effective cylinder pressure. The best way to ensure good combustion is to control the piston- to-head clearance. A tight quench package (a piston-to-head clearance of between 0.038 inch and 0.045 inch) and a decent chamber design with the Edelbrock head should only require between 34 and 38 degrees of total ignition timing for best power. At these timing numbers, even today's 93-octane fuel should have sufficient antiknock capabilities to prevent detonation. Avoiding detonation is the only real reason to use a higher-octane fuel. Higher octane numbers represent the ability of the fuel to prevent or suppress detonation. To put this another way, there are no power advantages to using a 110-octane race gas. Some oxygenated race fuels may produce minor power gains from exotic chemistry, but that hardly justifies the $12 a gallon cost of the fuel. We used 91- octane for our 700hp big-block Chevy dyno test.
Edelbrock; Torrance, CA; 310/781-2222; Edelbrock.com
Flowmaster; Santa Rosa, CA; 800/544-4761; FlowmasterMufflers.com
Lunati; Olive Branch, MS; 662/892-1500; LunatiPower.com
Last Words On Master Cylinder Bore Diameter
Joey Carvalho; Santa Rosa, CA: Excellent job on the magazine. I felt I needed to write after reading about the 7/8-inch-bore Wilwood master cylinder in the Sept. '10 tech column. This master is an excellent product and I continue to use it today in my Torino with front and rear manual disc brakes. However, I hate to say it, but it seems to have longer travel than other master cylinders of the same size. I was using a Ford OEM 7/8-inch master until it started to leak, and I went crazy trying to bleed out what seemed like air after I installed the Wilwood. Yes, my Torino has long pedal travel. Yes, my pedal ratio is correct. And yes, I get 1,250 psi front and 975 psi in the rear. I did try a 1-inch unit but that didn't produce enough pressure. I believe the reason lies in the design of the Wilwood. Bench-bleed it and you will discover that approximately the first 25 percent of the stroke sends fluid to the front circuit only. Push a little more and front and rear fluid is pumped. Installed in the car, you will have more travel than normal until the rear circuit contributes volume. The prop valve is doing its job properly, balancing the pressure to front and rear still. At 200 bucks, I will live with it. Thanks again for the great magazine.
Jeff Smith: We shared your letter with Dustin Burr at Wilwood, and this was the response from one of Wilwood's engineers:
"There is a flaw in the reader's observations. He is basing them on what he sees during bench bleeding. There is no pressure developed during bench bleeding because the system is open. There is a differential in return spring preloads between the front and rear circuits, with the rear being higher by perhaps 5 pounds of force. I don't know the exact figure off hand. That is so the front piston is held in the correct location upon full release of the stroke. Because of this differential, during a bench-bleed stroke, the front spring is collapsing (and pushing out fluid) until its spring load matches the rear, then the rear starts pushing fluid. That may well take 25 percent of the stroke (I have not measured it). That is what the reader is seeing."
Wilwood's Dustin Burr added to this explanation: "Essentially what our engineer is saying is that what you see when bench-bleeding the master cylinder is not the same as what happens when the system is closed and under pressure. Under pressure, the return spring is overcome much quicker and fluid is pressurized at both ports at the same time.
"My two cents on brake pedal travel is that much of this is entirely subjective. Two guys can drive the same car and one will tell you the travel is too long, and the other will tell you the travel is perfect. Both of their opinions are based on the brake lever travel they are accustomed to feeling. So, if the pedal feels like the car you drive every day, you'll probably say the pedal feels good. If it doesn't feel like the car you drive every day, you'll say the pedal doesn't feel good. Drag racers typically use large-bore master cylinders because a very high and hard pedal at the end of the 1,320 is comforting, even though a smaller bore that requires less effort is more effective at stopping the car. Road racers typically go the other direction, with smaller-bore master cylinders that require less effort and are easier to modulate. Neither of those two opinions matters at all to brake function. The purpose of a brake pedal is to create and modulate pressure in the brake system. If the pedal allows you to create enough pressure to operate the brakes and can be manipulated for different stopping levels, then it's doing its job correctly.
"One of the things that plagues many hot rodders is this: Nearly everyone has a late-model car as a daily driver, and nearly all late-model cars are built with vacuum boosters, large-bore master cylinders, and short pedal ratios. This makes for a pedal with little travel but plenty of system pressure due to the vacuum booster. Everyone has become accustomed to that pedal feel and by default assumes it is the "correct" pedal feel of a good brake system. Of course, the problem is that many hot rods and muscle cars don't have enough vacuum to support a booster and rarely enough room for a booster of sufficient size. So they go with a manual brake system, which functions well but feels different from their daily driver. It doesn't feel "correct" to them because their daily driver has been telling them how it should feel for 30 years or so. But isn't that the point of having a hot rod, that everything feels different from your daily driver? Different doesn't mean wrong. No one thinks uncontrollable amounts of power are wrong, they're different—and that's why we build them, right?"
Wilwood; Camarillo, CA; 805/388-1188; Wilwood.com
West Coast Racing Cylinder Heads offers a CNC porting service for existing 6.0L and LS2 he
Big Ports vs. Small Ports
Mike Smith; via CarCraft.com: I decided to do a motor build for my hot rod based on your Late Crate Update series. I called my local GM dealer to order the GMPP L92 CNC heads that are getting such rave reviews (PN 88958698). Imagine my dismay when they told me that those heads have been discontinued. A nationwide parts-dealer search showed none available anywhere, and every online store I have contacted has told me the same sad story—they are unavailable. At this point, I am stuck because I based my engine build budget on these heads. Are you aware of any future plans for GMPP to sell a comparable setup? How can they just discontinue the most cost-efficient head available with no warning? We deserve answers. Thanks in advance and I absolutely love your magazine.
Jeff Smith: While the heads were a very good deal for a CNC-ported cylinder head, there are other solutions. Rather than getting into why the head was discontinued, let's look at what those heads really delivered. In my engine buildup detailed in "The Garage-Built LS Stroker Part II" (Feb. '10, pg. 22), we flow-tested four LS heads, including the stock 6.0L castings, a set of West Coast Racing Cylinder Head CNC-ported 6.0L heads, a set of stock L92s, and the CNC-ported GMPP L92 heads. While the ported L92 heads took the win for the highest flow of all those heads tested, the results need closer inspection. Sure, these heads flowed 337 cfm, but that also occurred at 0.700-inch lift. How many street engines run a 0.700-inch- lift cam? For a street engine, even with the LS engine's power potential, this is akin to using huge 360cc rectangle-port cylinder heads on a 396ci big-block. A smaller, properly sized intake port produces much greater velocity, which will produce more torque in the usable rpm band for a street engine. Many enthusiasts get caught up in maximum flow numbers at peak valve lift. While peak flow numbers make for good bench-racing fodder, it's best to look at the midrange flow numbers of around 0.400 valve lift when considering a street cylinder head. Larger flow numbers in the midrange tend to support excellent midrange torque. Large- port heads tend to deliver impressive peak valve-lift numbers that may or may not be attainable. For example, the L92 heads can deliver some huge flow numbers at 0.700-inch valve lift, but few street engines achieve more than 0.600-inch valve lift, so the flow potential at 0.700-inch valve lift is superfluous.
Generally, a smaller port won't flow as much air as a larger port, but a cathedral-port head that will produce acceptable numbers of around 280 cfm at 0.600-inch lift will produce similar if not better overall power. Why is midrange power important? Because this torque is primarily responsible for accelerating the car down the quarter-mile, while peak horsepower helps create the ultimate trap speed. It's the combination of torque and horsepower that makes the car quick, but because virtually all street cars are under-geared for ultimate quarter-mile acceleration, the engine spends more of its time in and around peak torque as opposed to peak horsepower. So by building an engine with stronger torque in the midrange, you will have a quicker car that also is hammer-flat fun to drive.
We decided to go looking for a pair of cathedral-port heads with equal or better flow compared with the CNC-ported L92 heads. We found a set of Trick Flow Specialties Gen X 225 CNC-ported heads that offer a much smaller intake port (compared with the L92) yet with better flow. While the intake side of the TFS head offered measurable flow increases throughout the valve-lift window, the real difference was on the exhaust side, where at 0.400-inch valve lift, the TFS head flows an astounding 45 cfm more than the stock L92 head. This means you can run a single-pattern cam with the TFS head, while the L92 head requires a cam with as much as 12 to 14 degrees more exhaust duration. This also means the cathedral-port head at the same flow will automatically increase the intake port velocity. The downside of all this better technology is that the TFS CNC- ported heads cost $2,395.95 compared with roughly $1,200 for the stock L92 heads.
As a budget alternative, you could go with a CNC-ported production head. Several companies offer this service. One shop is West Coast Racing Cylinder Heads (WCRCH), which can deliver some impressive flow numbers for an affordable price. If you supply the cores, the WCRCH Stage 2 porting service will deliver a set of heads that flow slightly less than the CNC-ported L92 heads through the midrange valve lift on the intake but offer outstanding exhaust flow all the way through the lift curve with as much as a 21-cfm improvement at 0.400-inch. Again, this better exhaust port means using a single- pattern cam to take advantage of how well the exhaust works. The price for all this is $1,575, which is only a few bucks more than the L92 heads—and the potential for more torque in the middle is excellent. We hope this will get you to start thinking about cathedral-port heads as something more than just low-performance stockers.
West Coast Racing Cylinder Heads; Reseda, CA; 818/705-5454; ProHeads.com
Trick Flow Specialties (TFS); Tallmadge, OH; 330/630-1555; TrickFlow.com
Knute Weber; Reinhold, PA: I am trying to become a performance mechanic/tuner and I was wondering if you could help me. What you would recommend as a school for tuner/performance mechanics? What are good skills to have? Being 16, I am still in school but need to plan. I am considering going to Hennessey's Tuner school, but I was wondering if you would recommend something different? I would like to know all the information possible about becoming a tuner/high performance mechanic, but so far I cannot find the information anywhere! I am not like most other kids who like cars. I have a passion for cars and I have had this passion since I was just 1 year old (there is video of me in my dad's '70 Stage 1 Buick trying to drive and shift his car). Almost everyone in my family owned muscle cars at one point and I am a huge muscle car fan! I have read Car Craft ever since I could read, and I continue to read every issue. I love to expand my knowledge about cars and have learned a lot, but I still need to learn more!
Jeff Smith: You are definitely headed in the right direction, Knute. While experience is one of the best teachers, combine that with a solid technical background and it will not be long before you will be teaching other guys the nuances of tuning. The best recommendation would be to consider expanding your knowledge base beyond just tuning. A solid background in general automotive mechanical knowledge can be extremely useful when diagnosing problems. I did a quick Internet search within Pennsylvania and came up with three schools: Automotive Training Center in Exton, Lincoln Tech in Philadelphia, and Pennco Tech in Bristol. It's also possible that your state may offer junior college vocational/technical schools with an automotive technology focus. While repairing stock vehicles may not be nearly as romantic as tuning a 2,000hp drag car, you really won't be very good at tuning without a solid mechanical knowledge base.
Another approach you may not have considered is aiming higher. Several well-versed tuners I know have a mechanical engineering background that gives them a decided technical advantage. If the math doesn't intimidate you, you might want to give thought to working toward a mechanical engineering degree. I spoke with Mark McPhail, a former GM engineer, and he made a good point that powertrain engineering is in such a state of flux right now that concentrating on tuning might limit you in the future. While internal combustion engines will be around for at least the next 30 years or more, we're already seeing the next big push from the OEs with emphasis on direct injection as opposed to just multipoint fuel injection. The basics of combustion will not change, but it's clear that the way fuel is introduced into the engine is likely to continue to evolve. As an example of how this affects tuning, we hear that direct-injected engines demand a completely different thought process as to how air is inducted into the cylinder, which means tuning might take on a completely different path. Another interesting aspect in regard to future vehicles is the concept of control processing with computers, which will only continue to grow. So a well-versed knowledge of computer processing and writing code and software control will certainly put you near the head of the class of future tuners.
Another related area of expertise is power sources. Fuel seems to be an area that will become increasingly important, and beyond gasoline, there appears to be potential in alternative fuels such as liquefied petroleum gas (LPG), methanol, ethanol (like E85), and possibly other gaseous fuels. Obviously, there are a ton of opportunities worth investigating before you make any decisions. As an enticement for attending a four-year school in mechanical engineering, the Society of Automotive Engineers (SAE) has created a competition for engineering students called the Formula SAE, where students build an open-wheel race car.
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