From a cost per horsepower standpoint, the Edelbrock heads are a great investment, especia
Michael Rasmussen; Massaprqua, NY: I have a 454 big-block from a Chevy truck in my Chevelle. I just purchased the Edelbrock Performer RPM 60459 heads, an 800-cfm carb, and an Air-Gap manifold. I wanted to step up to a hydraulic roller cam, and I heard a roller cam from a Mark VI block can be used as long as my block has provisions for the thrust plate and a Mark VI timing chain is used. I read the online story on your test of the oval-port big-block heads. I'm wondering if I should build that engine or go with a 496-or-larger short-block? I noticed the cam part number you listed was for a Ford. Everything I read about the XE274HR-12 cam says it's for a Ford. Any suggestions would be great. I love the mag and look forward to it every month.
Jeff Smith: The story on our 496ci big-block oval-port head test in the Mar. '08 issue was a very successful evaluation of all the oval-port big-block heads that were available at the time, including a stock set of peanut-port iron castings, Brodix, Dart, Edelbrock, and TFS oval-port heads. We were surprised by the power we made with these heads, and the Brodix castings made the most peak power at 597 hp at 5,600 rpm and a solid 626 lb-ft of torque at 4,000 rpm. The Dart and TFS heads were right there as well, within 2 hp at the peak with the same torque, so the results were a push among the Brodix, Dart, and TFS castings. The Edelbrock heads were down slightly at 582 hp at 5,600 through 6,000 and torque at 618 lb-ft at 3,900 rpm. As we pointed out in the story, the Edelbrock heads were within 2.5 percent of the peak power, which isn't very much, but more important, they were the least expensive of all the heads we tested with the exception of the stock iron castings. As for the incorrect cam card information, that was a weird deal where the wrong cam card ended up in our cam box and we just copied the information without double-checking. The actual cam we used was an XR276HR with 224/230 and 0.510 lift with a 110-degree lobe-separation angle that ironically has less lift than the Ford cam. When you consider that even with the softest aftermarket heads we made 582 hp and 618 lb-ft of torque with a cast-crank, 10:1-compression 496 Rat motor with a very mild hydraulic roller cam, that's pretty stout.
To get to your question, Michael, the hydraulic roller cams for the Mark VI blocks will interchange with the earlier blocks, but you will need to prevent the cam from moving. Flat-tappet cams employ tapered lobes to prevent the cam from moving in the block. By design, roller cams cannot use this feature, which means you need to use some kind of limiter to prevent the cam from moving forward in the block as engine rpm increases. The Mark VI blocks use a camshaft thrust plate to locate the cam, while your older Mark IV engine does not. The least expensive approach would be to add a cam thrust plate as you suggested-along with the Mark VI-style single roller timing set. This allows plenty of room for the timing set under the cover. The plate will require minor drilling and tapping and is best done with the engine disassembled, although if you are careful, it could be accomplished if you take measures to keep all the drill and tap shavings out of the engine.
Another slick addition for your Rat would be these Dart adjustable 3/8-inch pushrod guidep
As we mentioned in the original oval-port head test, if you want to run a similar Comp hydraulic roller cam in your 454, the Edelbrock heads are shipped with valvesprings intended to be used with a flat-tappet camshaft. In our test, we wanted to make sure the valve-springs were all the same for each cylinder head, so we swapped them for a set of Comp 933-16 hydraulic roller valve-springs. The 933 Comp springs offer 220 pounds of load with the valve on the seat and 490 pounds at 0.600-inch lift. Frankly, since the Edelbrock heads continue to increase flow through 0.600-inch lift, you might consider a cam with more lift to take advantage of the heads' potential. Comp does have a single-pattern 280HR Magnum hydraulic roller that specs out at 224/224 degrees of duration at 0.050 with 0.566-inch valve lift for both intake and exhaust with a 110-degree lobe-separation angle. This will pump the lift closer to 0.600-inch lift, and then you might also consider a set of 1.8:1 roller rockers that would push the lift just below 0.600-inch lift. Anytime you increase the rocker ratio, you accelerate the valves more aggressively, which tends to make the springs work harder. The reality about valve float is that the first place the spring loses control of the valve is on the closing side as the valve approaches the seat. The intake valve is the heaviest of the two valves, so any loss of control will happen to the intake first. When the intake bounces off the seat during closing, it effectively increases cam duration, which isn't really what you want. Every time the valve bounces, it also allows cylinder pressure to escape back into the intake port instead of being captured to make cylinder pressure. If allowed to continue, this valve bounce will kill power and also tend to reduce the effectiveness of the springs. One way to help the springs is to use a lighter retainer. When we did that story in 2008, we used the Comp titanium retainers, as they were the only real alternative to steel. However, Comp has since come up with a series of tool-steel retainers that are not only nearly as light as the titanium pieces, but much less expensive. The stock steel retainers weigh 35 grams, while the titanium retainers only weigh 18 grams. The tool-steel retainers (PN 1732-16) weigh roughly 21 grams but only cost $153.95 from Summit Racing as opposed to $300.00 for the titanium pieces. You'll also need lash cap-style keepers (PN 611-16, $21.95, Summit Racing) in case you need to use lash caps (PN 621-16, $33.95, Summit Racing). This adds up to another $200.00, but now you'll have a bulletproof and lightweight valvetrain, which is a good thing when it comes to Rat motors since they tend to be somewhat abusive on valvetrain parts.
All these parts could easily be used on your existing 454 instead of going to a 496. What you'll give up with the smaller engine is both torque and horsepower. We can estimate the power by merely taking the existing power of our test engine at 582 and dividing by the displacement of 496 to get a 1.17hp/ci figure. We then multiply by 454 and come up with 533 hp. This might be a touch low since piston friction will be less with the 454's shorter 4.00-inch stroke, so 550 hp isn't out of the question even with your Edelbrock RPM dual-plane, since that's what we used on our test engine. Plus, with the bigger cam and more lift, you might actually get up into the 575hp range. Torque will also be reduced with the smaller 454 with the numbers crunching out to 565 lb-ft. This is still great power and more than enough to spin the tires or if you hook it up with a 3,700-pound car and a 3.55:1 rear gear to run low 11s at 120 mph without too much trouble. Sounds like a lot of fun, doesn't it?
Using beehive springs on a set of iron Vortec small-block Chevy heads is a quick way to in
Rod Walker; Boone, IA: I am a longtime subscriber from your old hometown of Boone, Iowa. I graduated in the class of 1975 from Jefferson with your ex-wife, Susan. I've run the machine shop at Arnold Motor Supply in Boone for the last 16 years. It's a one-man shop with some pretty nice equipment. We
do a little bit of everything, from all-aluminum FE motors to 500ci Olds and numerous drag, circle track, truck pulling, and street performance engines. I'm getting ready to redo a street rod deal-a '55 International pickup with the engine and trans out of an '85 TPI Corvette. It's been on the street for a couple of years now and the customer wants more power. He's looking for around 450 hp and a nasty idle. The truck is tubbed with a 3.90 gear, a short-block, hugger headers, and air conditioning. Joe Busch's shop built the truck for this guy, and it's pretty nice. We will freshen the engine, and we're thinking about upgrading the heads, intake, cam, and converter. What can you recommend? Thanks and keep up the good work-your magazine is the best!
Jeff Smith: First off, when I get a tech question from my hometown, it's almost a given that I'll answer it! Boone, Iowa, is also the home of the IMCA Nationals at the Boone Speedway. My friend Blake Hanel and I used to sneak into the pits at the track back when we were in junior high school in the late '60s. To get to your question, Rod, an '85 TPI engine is going to be tough to push up to 450 hp with the existing TPI manifold. Those intakes were originally intended to be used only on a 5.0L engine-back in the '80s the internal GM mindset was aimed at eliminating the V8, and they thought the 5.0L 305 was as big as they ever wanted to go. Things have sure changed for the better for GM performance enthusiasts in the ensuing 25 years, haven't they? You might seriously consider a conversion to a later-model iron-block 6.0L LQ4 LS-style engine as opposed to attempting to make power from a TPI engine. We'll look at the 6.0L LQ4 truck engine alternative, then compare that engine with the mods it will take to make equivalent power from the original TPI motor.
Several years ago, we bought a junkyard iron-block 6.0L engine and installed a GM Performance Parts carbureted intake, a Holley 750 carb, an MSD spark box to run the distributorless ignition, headers, and a mild GM Performance Parts HOT cam (219/228 at 0.050 with 0.525-inch valve lift and a 112-degree lobe-separation angle). The stock LQ4 engine with the carbureted intake and headers made an outstanding 425 hp and 439 lb-ft of torque. Let's emphasize this right here: 425 hp with just an intake and headers! Once we added the camshaft, the power jumped to 483 hp at 6,000 rpm and 450 lb-ft at 5,000 rpm. The total investment if you purchased a used engine and everything new might be roughly $3,500 or less depending on how much of this stuff was used parts. Of course, you could also retain the OE EFI, swap to an LS6-style intake, and have to do a little HPTuners software investment for tuning for the cam, but this is outstanding power in an engine that would be incredibly reliable and powerful. Plus, you're working with 21st century technology. An even simpler version would be a new LS3 crate engine from GMPP, but the cost would be substantially higher with roughly the same power.
Used TPI parts are cheap these days. Look for us to dive into this whole budget market wit
Now let's take a look at the TPI motor. As an '85 vintage piece, it's probably still a two-piece rear main seal engine (one-piece rear main seals arrived in 1986), which also means this is a flat-tappet camshaft engine. While neither of these aspects limits the power potential, the multipiece rear main seal and pan gasket assembly are leakers in the best of times. But the real cork in a performance application is the TPI manifold. You didn't mention if the engine was still EFI controlled, but I'll hazard a guess that it still is the case. The quickest way to add power is with a combination of cylinder heads and camshaft. Assuming there is a budget consideration, we'll fall back on the classic Vortec iron head as an inexpensive way to improve power. The stock Vortec head is limited in application with a combination of the small, 64cc combustion chamber and its stock valvespring. Since you are going to rebuild the engine anyway, you could choose an inexpensive hypereutectic piston such as Speed-Pro's ZW423NP30 dished piston that will create a 9:1 compression ratio with the 64cc chamber. You could then raise that compression with a slightly thinner head gasket.
The Vortec heads will also require a different valvespring. Since machine work isn't difficult for you, the best approach is to machine the heads to reduce both the height and diameter of the valveguide boss to accommodate all kinds of decent performance springs. Those who may not want to machine or can't afford this work (which really isn't expensive) could also go to a beehive-style spring like the Comp 26915. This beehive's inside diameter is large enough to fit over the Vortec guide boss while still offering enough retainer-to-seal clearance for a 0.470-inch-lift camshaft. The beehives are not cheap springs, and you will also have to purchase new retainers and keepers to complete the swap.
Before we get into the camshaft, let's complete our induction system. If you go with the Vortec heads, the stock TPI base won't work. Edelbrock makes a Vortec TPI base (PN 3817, $469.95, Summit Racing) that will allow you to retain the TPI configuration. But add high-flow runners and a 52mm throttle-body and you've got around $1,200.00 wrapped up in this arrangement. An alternative might be the Tuned Port Induction Specialties (TPIS) Mini-Ram, which is a short runner manifold similar to an LT-1 intake. TPIS offers this manifold with a Vortec or Fast Burn head base, and the cost is $895.00, but you still need to purchase a fuel rail kit, which is another $360.00-so you're right back at $1,250.00. All these parts will help make your 450 hp, but the cost gets a bit excessive. This kind of research points out why moving to the iron 6.0L engine is more attractive.
Another option for the standard small-block is to add a set of small-block heads like AFR, Brodix, or Edelbrock cylinder heads and then go with a strong carbureted intake or a single-plane EFI manifold that would retain the EFI. We have had great experience with an ACCEL single-plane EFI manifold with the fuel rails (PN 74139, $489.95) using a four-barrel 4150-style throttle-body. This manifold will also require bigger injectors than stock TPI stuff, and those can run around $400.00. You can make more than 600 hp with this manifold. We've made as much as 570 hp with our 420ci small-block with a very conservative mechanical roller cam and an ancient set of AFR 195 heads.
Given the dollar per horsepower of all this Gen I EFI stuff, it begins to make any LS engine look very attractive. One alternative is finding used TPI parts on eBay for much less, which is a great option. I'm not sure if I've made things clearer or just muddied the waters, but at least you have tons of options.
Edelbrock; Torrance, CA
Mr. Gasket (ACCEL)
Tuned Port Induction Specialties (TPIS)
With a set of TFS 215cc aluminum heads and a Comp 282 hydraulic roller cam, our HT 383 eng
Ryan Strohecker; Irmo, SC: I have an '81 GMC truck with a 305 small-block, an SM 465 four-speed transmission, 4.10 gears, and 35.5-inch-tall tires. I'd like to build a high-torque, low-speed engine to power it. I had planned to build a copy of the HT383 using the same cam, Vortec heads, 1.6:1 roller rockers and a dual-plane Air-Gap intake with a Holley 670 truck Avenger carburetor. Due to chassis/drivetrain restrictions, I'm going to be running 1 5/8-inch block hugger headers into 2 1/4-inch pipes that Y into a 3-inch single exhaust. I wish I could fit some long-tube headers and duals, but there just isn't enough room under the truck. I'd really like to do better than the factory HT383 rating, especially on the torque, which I would like to get into the 450 to 475-lb-ft range. I think I could get there with a bump in compression, but I'm unsure about what would happen with such a small cam that I'm sure is designed to build low-speed cylinder pressure. What would happen if I were to try and run 11.5 or 12:1 compression on this engine? I'd do it with a thin head gasket, flat-top pistons, and careful attention to compression height, chamber volumes, and so on. I'm toying with the idea of trying to reverse-cool the engine much like the Gen II LT-1s. If I were to run aluminum heads, reverse-cool the engine, and pay close attention to the ignition timing, do you think I could get there? Any chance I could make this happen on 91-octane gas? Has anyone ever tried to reverse-cool SBCs with any successful results? Could I reach my torque goals with a more conventional compression ratio?
Jeff Smith: These are some great questions, Ryan. It's obvious you read Car Craft and that you've paid attention to some of our tech stories. Most of your plan is right on target. You can certainly get to your goal of 450 to 475 lb-ft of torque with conventional compression. Let's start with a review of the HT383 GM Performance Parts engine. The base configuration is intended for applications like Ryan's truck using a steel crank, hypereutectic pistons, 9.1:1 compression, a mild hydraulic roller that specs at 196/206 degrees of duration at 0.050 with 0.431/0.451-inch lift using a pair of Vortec iron heads and a GMPP dual-plane intake. GMPP rates the engine at 340 hp at 4,500 and 435 lb-ft of torque at 4,000. Several years ago when I was the editor of Chevy High Performance magazine, Ed Taylor and I did an extensive dyno series on this engine. The combination that makes the most sense for your truck is the addition of a GMPP Hot cam kit (PN 24502586, $224.95, Summit Racing) that specs out with 218/228 degrees of duration with 0.492-inch lift using a 1.5:1 rocker ratio. This will require going to beehive springs like the Comp PN 26915 as a quick solution to accommodate the Hot cam's additional lift. With just the addition of the Hot cam and the springs with 1 5/8-inch long-tube headers, this engine made an amazing 486 lb-ft of torque at 4,600 rpm and 416 hp. That is exactly your goal, Ryan, and this was with the HT383's stock 9.1:1 compression.
I do find it odd that you don't have room in a fullsize truck for long-tube headers. Unless your pickup is slammed on the ground, there should be plenty of room for a set. While shorty headers fit much nicer, a longer primary-tube-length header is a major reason our HT383 test was so torquey. When the primary tube length is shortened, torque is the first victim. While I've never done this test, it could cost as much as 20 to 30 lb-ft, especially in the midrange where you will most likely need it. If you must use a shorter header, keep in mind that there are midlength headers available that might fit your truck and at least add a little more primary pipe length compared with the block hugger headers. A 3-inch collector and Y-pipe into a single muffler is also a better configuration.
Compression is a great way to make more power with the rule-of-thumb improvement of a 3 to 4 percent increase in power for every point of compression-let's say from 9:1 to 10:1. The limiting factor here is the 91-octane fuel. With the compression already at 9:1, any increase will improve power, but you're running on the ragged edge of detonation. You might be better off to leave the compression as it is and be more aggressive with the ignition timing. Any attempt at reverse cooling is a waste of effort as well. When GM started with a clean sheet of paper on the new generation of LS engines, the company went back to conventional coolant routing and just moved the thermostat to the inlet side.
One way to improve combustion efficiency (which equates to both power and fuel efficiency) is to pay particular attention to piston-to-head clearance. This will most often require mocking up the engine with at least the four corners of the engine (cylinders 1, 8, 2, and 7) to measure the distance between the piston tops and the block. The ideal way is to also ensure that the block deck is not just flat but square to the crank. We've seen blocks (especially Rat motors) that are tilted in relationship to the crank. The relationship of the piston to the head includes not just the deck (a 0.005-inch-or-less distance is good) but also the head gasket thickness. If you don't want to go through the expense of this machine work, it's still good to measure so you know how thin a gasket you can get away with. For example, if the pistons average around 0.024 inch down in the hole, you could add a thin Fel-Pro rubber-lined head gasket (PN 1094) that is only 0.015 inch thick. Adding the two dimensions, you end up with a piston-to-head clearance of 0.039 inch, which is about as tight as you'd want to go. The thinner head gasket also reduces the total combustion space volume, which increases compression. The beauty of this approach is that decreasing the piston-to-head also increases what is often called squish or quench. As the piston approaches TDC, the tight portion of the wedge chamber and the piston squish or push the air/fuel mixture out into the deep portion of the chamber, increasing mixture motion, which generally reduces the combustion chamber's tendency toward detonation. This also can mean that the engine needs less timing to make the same power. Less total timing requirements (especially at peak torque where the engine is running at peak volumetric efficiency) means less negative work where the engine has to squeeze against combustion activity and also means less chance of detonation. All this tight quench work creates a situation in which the engine is making more power with less ignition timing-power and efficiency go up with no negatives! This is the reason we go through the effort to blueprint engines rather than just assemble them with whatever clearances are created. So to wrap this up, it appears that with a mild cam and valvespring swap along with maybe a little bump in the static compression ratio you can come very close to achieving your major torque goal. But what would really help is if you can figure out a way to add a set of long-tube headers.
GM Performance Parts
The Corvette/Camaro 6.2L LS3 is one of several current engine packages offered through GM
Ken Swinson; Wailuku, HI: I am a dyed-in-the-wool Chevy fan, particularly the small-block engines. I got totally away from the hot rod scene for many years, mostly because of financial constraints. In my younger years, I did lots of customizing, engine swaps, and engine performance enhancements and owned some very hot cars. My question is this: In numerous articles, the technical writers refer to Chevy engines as LS engines. What is the difference between former Chevy engines and the LS engines? I think this is a question many of your readers would be interested in seeing published.
Jeff Smith: Let's see if we can do this succinctly. The LS series of engines debuted with the '97 Corvette, later in trucks, and now represents the standard for domestic GM pushrod V8 engine performance. This was a clean-sheet-of-paper redesign, so there are few commonalities to the original small-block (Gen I) or even the short-lived Gen II LT1/LT4 engines. The bore spacing, which is the distance between the cylinder bore centerlines is the same at 4.400 inches. The LS engine family actually uses the same hydraulic roller lifter as the earlier production small-blocks, and except for one bolthole, the bellhousing pattern for the LS engine (also called the Gen III/Gen IV) is the same. The original LS1 346ci 5.7L engine was designed as an aluminum engine, so the block was reinforced with deeper block skirts to add strength along with cross-bolted main caps that use a total of six bolts to retain the caps to the block. The gerotor-style oil pump is mounted on the front of the crankshaft to eliminate load on the camshaft, but it now spins at engine speeds so the pump can possibly drain the sump under continuous high-rpm engine operation. The crankshaft flexplate/flywheel pattern is also different compared with either the one- or two-piece rear main seal versions of the Gen I small-block. Using a far more sophisticated fuel injection system, perhaps what really improves efficiency is the distributorless ignition system using a coil-near-plug ignition that employs a separate coil for each cylinder. This single step not only dramatically increases ignition power at high engine speeds, but also creates far more accurate ignition timing, since proper spark advance is now not affected by all the clearances of a spinning distributor, rotor phasing, and other built-in ignition timing inconsistencies that afflict the typical distributor-style ignition system.
The LS series engines also enjoy a far more efficient cylinder head design with intake ports either of a cathedral- or rectangle-port design. The lowliest stock 4.8L head still enjoys a 15-degree valve angle that is far superior to the old small-block 23-degree angle. Along with properly engineered combustion chambers that reduce timing requirements, this effect combined with production compression ratios of more than 10:1 and excellent airflow from the ports all make for a very powerful engine. There are several truck and SUV variations that are built with an iron block, but most performance applications come through as all aluminum, which really adds to the performance advantage. A typical all-aluminum block for a small-block Chevy will reduce engine weight by roughly 50 to 60 pounds but that is a costly upgrade, since most aftermarket Gen I blocks will cost around $4,000.00. For less than that, you can purchase a complete used LS engine that is already all aluminum. The real advantage for the Gen I small-block is that the price for most parts is far less than comparable LS engine pieces. But other than cost, it's hard to beat the late-model engines for performance, efficiency, and weight. That's why you're seeing so many LS engines swapped into older performance cars. It just makes good sense.
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