Edelbrock LT1 Performance Package - The Equalizer
Edelbrock Performer LT1 head and cam package delivers a serious wallop at affordable prices
From the January, 2009 issue of Popular Hot Rodding
By Johnny Hunkins
Photography by Al Balsden, Johnny Hunkins
In the last decade, aftermarket giant Edelbrock has become a savior of sorts to legions of fans. Yes, their mainline products for popular engine families like the small-block Chevy remain the great value they always were, but to many gearheads who worship at the altar of lesser engine families like Pontiac, AMC or the Ford FE, Vic and his elves have rained down a cornucopia of specialized products with clock-like regularity. All this wealth of horsepower--often for forgotten powerplants--has leveled the playing field with the small-block Chevys of the world. It's fair to say the big "E" in Edelbrock could also stand for "Equalizer," and that's just what Edelbrock has done again with their LT1 Performer combo.
For the most part, the LT1 is a small-block Chevy, but unfortunately, all bets are off when it comes to activities above the fire deck. Reverse-flow cooling, Opti-spark ignition, and a Gen IE manifold bolt pattern all conspire to make LT1 induction about as common as Ford Y-block parts. A few manufacturers have made an attempt at LT1 induction (most notably AFR), but they are, by and large, modified production LT1 parts or LT4 parts. In short, LT1 owners have had to live at the fringes just like Pontiac or Oldsmobile lovers.Prior to the Performer LT1 heads and cam, the weapon of choice for LT1 owners on a budget has been the LT4 swap. For about $2,500, you can buy all the parts needed to convert your LT1 over to LT4 spec. (The LT4 was the one-year-only 1996 Corvette mill rated at "only" 330hp. It came in all 6-speed equipped Corvettes in 1996.)
Comparison of the Performer LT1 combo to the LT4 swap (including LT4 Hot Cam) is inevitable. From a cost standpoint, it's almost a dead heat with a small advantage going to Edelbrock. From a power standpoint, the LT4 heads and intake with a Hot Cam is going to take a slight advantage, but only if the computer's fuel calibration is maximized. Ironically, the Performer LT1 ports and cam profile are not as radical as the LT4, so your stock computer calibration (as we found out) will work just fine without any tuning. Not so for the LT4 with the Hot Cam. Advantage: Performer LT1.
Based on our experience, we'd have to say the Edelbrock versus LT4 is a close battle. The important thing is that LT1 fans now have a choice. Like the factory-designed LT4 bits, the Edelbrock parts are top notch and fit to your production block and intake with factory precision. The outward appearance of the Performer LT1 heads are so stock-appearing that Edelbrock didn't even bother getting a CARB exemption because it's technically a factory replacement. That is, a factory replacement that happens to make as much as 46 horsepower over the stock heads!
Unlike the LT4 swap (heads, cam, a different intake manifold and higher ratio 1.6 roller rockers) the Edelbrock Performer LT1 system lets you keep your stock intake manifold and rocker arms. You can upgrade your rockers with the Edelbrock heads if you want, but the Performer LT1 cam and valve springs are engineered together to provide plenty of lift and flow.
Edelbrock's cam is an interesting piece. It specs out on paper as being larger than the popular LT4 Hot Cam, but that's a little deceiving. Because most LT4 Hot Cams are installed with taller self-guided 1.6 ratio roller rockers (which came standard on the LT4 in 1996), the Hot Cam ends up being about the same size as the Edelbrock cam in practice. The Edelbrock bumpstick achieves its lift and duration specs with a stock 1.5:1 rocker arm, which is exactly how we installed it in our '94 Z28 test vehicle. This makes the Edelbrock cam cheaper and easier to install with no downside to power. So if you're in the market for just a cam and can only afford to buy the valve springs and not rocker arms, this is a good one to consider. If you're planning on running your LT1 on the street, make note of the fact that the Performer LT1 cam is not street-legal and could raise a few eyebrows come inspection time. As an alternative, Crane Cams offers a Powermax 2050 cam (formerly Compucam 2050) which is 50-state legal (CARB E.O. No. D-225-55, part No. 104241) and specs out to 280 degrees advertised duration and 218 degrees at .050-inch lift. Valve lift with a 1.5:1 ratio rocker is .498 inch and the Powermax is ground on a 116 degree lobe separation angle.
So what about the heads? We'll let Edelbrock project engineer, Ulises Gonzalez, tell you in his own words: "We were trying to make a cylinder head that would beat the stock head for a while. We basically took the same port configuration from our E-Tec heads and adapted it to the LT1. We did this in combination with a cleaner chamber design--meaning we removed the tooling lug in the stock LT1 which gets in the way of the flame travel. The ports are optimized for high-speed flow and for optimum swirl. The LT4 is a different head--it's a bigger piece with a port near 195cc. Ours is 170cc, which accelerates the airflow."At 170cc intake port volume, the Edelbrock head isn't as big as it could be, so there will no doubt be some vocal message board heroes who will shout foul. Those folks are missing the point for two reasons: the LT4 head is already serving that part of the market very well, and a larger-than-LT4 head would most certainly require bigger injectors, stronger bottom-end internals and a reprogrammed fuel map. Not bolt-on stuff. "The LT4 will give you more rpm and slightly more power above 5,500 or 6,000 rpm," says Edelbrock's Gonzalez, "but ours will give you optimum power from 2,500 rpm on up. In the next year or so we will be coming out with a 200cc version of this head, which will be comparable to the LT4."
We were literally able to bolt all the Edelbrock stuff on and strap it to the dyno with zero programming and no fuel system upgrades. The package idles fine with a nice lope at 650 rpm and torque is explosive off the line, thanks to good low-speed port velocity and a cam with a relatively tight lobe separation angle. We did connect a wide-band air-fuel ratio monitor to the exhaust during dyno testing and found everything to be well into the super safe zone.Valve sizes on the Performer LT1 are 1.94 inch for the intake (the same as a stock LT1) and 1.55 inch for the exhaust (versus 1.50-inch for stock). Valves have a two-angle 45/30 valve job with a radius under the seat, which gives the Edelbrock a huge flow advantage over the stock single-angle valve job. Valve springs on the assembled heads are plenty stout with 120 lbs. on the seat at a 1.80-inch installed height. By comparison, stock LT1 springs are 85 lbs. at the seat while typical LT4 upgrade springs run around 105 lbs. According to Gonzalez, "Our spring allows you to run the engine another 500 to 1000 rpm more than the stock spring." As we shall see, that translates into some very useable power at the top end--not easy to accomplish on a mill with over 100K on the clock.
Our Edelbrock Performer LT1-equipped...
Our Edelbrock Performer LT1-equipped 350 doesn't have much visual punch to show for it, but there's another 34 rearwheel horsepower lurking under those valve covers. The street price on the assembled heads runs about $520 a piece. The cam is around $250 and the throttle body runs about $310. Edelbrock's own testing showed a 73-hp gain on a healthier LT1 Corvette.
The Performer LT1 intake ports...
The Performer LT1 intake ports are a modest 170cc, but they are perfectly sized for a 350 cubic-inch small-block headed for the street. According to Edelbrock project engineer, Ulises Gonzalez, "The LT1 Performer is pretty much matched to the intake gasket right out of the box. We did this to make it a direct bolt-on. Guys don't really have to grind on it."
The Performer's stock-sized...
The Performer's stock-sized 54cc combustion chambers insure that your LT1 will take full advantage of your LT1's octane-tolerant reverse-flow cooling. With your stock short-block, the factory compression will be maintained at 10.5:1. Unlike the factory chamber, there is no tooling lug to inhibit flame travel.
The exhaust ports measure...
The exhaust ports measure 60cc. The transition to the header is CNC machined and matched to the gasket by Edelbrock (as is the intake port). This operation is easy to perform with Edelbrock's sophisticated manufacturing processes, yet saves end-users hours of hand finishing.
The Edelbrock springs offer...
The Edelbrock springs offer enough pressure to handle all but the most outrageous street cams (about 120 lbs. on the seat). If you need more spring pressure than this, you've probably chosen the wrong head.
Our Edelbrock 52mm throttle...
Our Edelbrock 52mm throttle body (part No. 3809) is more than enough to handle the added breathing of our Performer LT1 heads and cam. Too small a throttle body and flow would be impeded, too large and driveability could be an issue. Edelbrock offers a 58mm air valve, but the 52mm should be plenty for everything short of a stroker motor.
One of the reasons we like...
One of the reasons we like Harv's Auto & Dyno Tune is their high level of organization. You can see how well prepared Sean Baisden was before digging into our Camaro. Everything is all laid out and ready to go. All the minor gaskets, seals and o-rings have been ordered from the local GM dealership and we've stocked up on Royal Purple synthetic motor oil!
Our test mule is a high-mileage '94 Z28 with an automatic transmission. With 125,000 miles of use, it's no spring chicken, but it is representative of what's out there in the $4,000 to $8,000 range. The stock LT1 long-block had no modifications prior to our Performer LT1 install and test, with the exception of Hooker 1 5/8-inch shorty headers, an aftermarket cat-back exhaust system, SLP cold air induction and a Holley throttle body airfoil. For a complete list of all mods done to our mule (including non-engine mods) check out the handy sidebar.
Other than development cars at Edelbrock, Popular Hot Rodding was the first to install the Performer LT1 for media evaluation. They didn't want to mess it up, so they turned to one of the top late-model GM tuners in Southern California--Harv's Auto & Dyno Tune in Whittier. Harv St. Mary and Sean Baisden are no strangers to fuel-injected GM machinery, and LT1s are an old favorite with them. After taking a tour of the shop and seeing the level of work performed there, we were suddenly in our comfort zone. Sean Baisden, who would be doing the work on our Camaro, is the owner of several awesome GM machines, including an 11-second road-raced LT1 Corvette, so they knew they were in good hands.
We should also note that they took the opportunity to change the oxygen sensors over to new Bosch units. Also, Edelbrock specifically specifies Champion RC-12YC plugs, which they complemented with a new set of Bosch spark plug wires. Since they didn't feel like chasing leaks later on, they used a complete gasket set from Mr. Gasket. As a precaution, they also replaced our worn timing set and pushrods with upgraded pieces from Comp Cams. The final piece of the puzzle was a throttle body swap. The factory 48mm air valve was replaced by a larger 52mm unit from Edelbrock. This swap meant eliminating the Holley airfoil because the Edelbrock unit has a cast-in airfoil.
After making a few baseline dyno tests with the stock motor, Baisden spent the next two days pulling down the engine dress, intake manifold, cylinder heads and cam, then installing the new pieces. This can be done over a weekend by the do-it-yourselfer with a well-stocked tool box, but if you don't have much experience with late-model fuel-injected cars, this might be better left to seasoned pros like those at Harv's. Fortunately, you won't have to get into computer reprogramming like most blower kits, turbos or stroker motors, so your angst will be limited to the knuckle-scraping variety.
As much as they wanted to dive into the cylinder heads, they resisted the urge to work them over. Under normal circumstances, it would be a good idea to do a simple bowl job and gasket match on these heads before bolting them on, but they really wanted to see how good they were right out of the box. Obviously, we were excited to fire it up for the first time, and the Performer LT1 heads and cam didn't disappoint.
Once he was finished checking for problems and leaks, Baisden gave the LT1 a good bill of health. A check of the idle vacuum showed 11 inches versus 18 inches for the stock long-block. A quick drive around the block showed that most of what they wanted to know--they had a radically sharp throttle response off idle and a noticeable amount of additional pull through the midrange and top end. Without the R-compound Nittos, there would've been serious rubber laid on Whittier Boulevard! It's a good thing the brakes still worked great with 11 inches of vacuum (a big plus given the plans to add some serious SSBC brakes down the line).
The only other thing needed was to know how much power? With the stock long-block, power peaked at 5,600 rpm and made 249hp at the rear wheels. If that sounds low, keep in mind that this is an automatic trans with a 2,800-rpm stall converter, so there is more than your average amount of driveline loss. Also, all runs were performed in second gear in order to keep the trans from downshifting mid-run. This typically holds power down because parasitic drag is greater in second gear. What's important is the relative increase, not the peak number. With the Performer LT1 heads, cam and throttle body, power peaked at 5,900 rpm and made 283 horsepower. That's a peak-to-peak gain of 34 rear-wheel horsepower.
Better yet is the fact that horsepower was up at all points in the power curve, except at 3,700 rpm where our runs began (it was down 1 hp at that point). Power was up 46hp over the stock heads and cam by 6,000 rpm, but they suspected a lot of that gain was because the old valve springs were worn out. Still, we're guessing there are a lot of high-mileage LT1s out there that could benefit from a better set of heads with fresh valve springs.
As you might expect on a motor with a hard-hitting torque converter (our Precision Industries Vigilante has to be one of the best out there) torque peaked down low at 3,700 rpm for both stock and Edelbrock combos. By 3,800 rpm, however, The Edelbrock Performer LT1 took the torque lead and by 6,000 rpm was up a whopping 40 lb.-ft. Clearly, the Performer LT1 intake port is not too small for a 350-inch LT1! They suspect there is even more power on the table with some rudimentary tuning via LT1 Edit, but we thought it better to let the out-of-the-box numbers do the talking. If some tuning is done later on, it will probably be to raise the idle speed and clean up the emissions for inspection time, but until then, they're just fine with the mule's street manners.We'd have to say the Edelbrock Performer LT1 combo is a homerun. It's relatively simple to install, the American-made parts fit well, the increase in power is in line with the cost of the parts, driveability on the street is excellent and reliability has proven to be good. For those stroker or blower customers wanting even more, keep your eye peeled for some bigger offerings down the road. If this is any indication, we can expect some more great news from Edelbrock.
Most of the first day was...
Most of the first day was spent tearing down the LT1. Here, the radiator, a/c condenser, accessory drive, brackets, intake manifold, cylinder heads, and the timing chain have been removed. The oil pan bolts have been loosened to speed the swap of the cam and timing gear. All gasket surfaces have been thoroughly cleaned to insure effective sealing later on.
Baisden has slathered on liberal...
Baisden has slathered on liberal quantities of Redline assembly lube and is now stabbing the cam into the LT1 short-block. In this shot you can see how helpful it is to have the radiator and condenser removed.
Ten years and 125,000 miles...
Ten years and 125,000 miles have taken its toll on the factory crank timing gear (left). Deep wear marks are evident on all teeth (as well as attendant stretching in the timing chain). The new Comp Cams gear (right) will make valve timing, once again, a precision affair.
Now for the obligatory "line...
Now for the obligatory "line up the dots" timing chain photo. Failure to do so will result in engine not go boom-boom.
Our Opti-spark distributor...
Our Opti-spark distributor had been replaced about 30,000 miles ago and was working fine, so we reused it. These aren't known as real long-life parts (ours could be considered borderline), so it's probably a good idea to replace. Note the splined water pump drive shaft just above the Opti. To prevent future leakage, it's important to insert the shaft with the lip of the new seal flapped to the inside--a seemingly impossible task. You don't want coolant dumping right into that distributor!
We're putting this timing...
We're putting this timing gear photo out of sequence to show you how the gear keyway is referenced to the bump on the balancer hub. That's important to know because the damper is referenced to the bump on the hub, as shown in the next photo.
Kent-Moore tool J-39046 is...
Kent-Moore tool J-39046 is required when removing or installing the balancer hub from the crankshaft on 1992-97 L99/LT1/LT4 engines. Here Baisden shows the alignment bump on the crank hub and crank damper. These must be aligned whenever installing the damper.
We ordered new exhaust gaskets...
We ordered new exhaust gaskets from Mr. Gasket, but we were so impressed with our old Flow Tech gaskets from Holley (part No. 99150AFLT) that we reused them for this installation. The Flow Tech gaskets feature multiple layers of dead-soft aluminum which crush to conform to the shape of the header flange and mounting surface. In the two years since we originally put them on, they have yet to leak and are still going strong.
The oil pump drive gear is...
The oil pump drive gear is basically the bottom half of a distributor. Since there is no typical distributor shaft on an LT1 but the oil system architecture is still the same as the Gen 1 small-block, this little piece remains. Don't forget to put it back in!
Time for the LT1 Performer...
Time for the LT1 Performer cylinder heads--which we took right out of the box and dropped right on the short-block. Note how the Mr. Gasket intake gaskets have convenient tabs that hold them into place while your intake manifold tries to do the watusi on them. The LT1-specific head gaskets are Mr. Gasket part No. 5715.
Baisden has dropped the new...
Baisden has dropped the new Comp pushrods in and is now finger tightening the rocker arms in place with the factory nuts. He'll crank down on them later.
It's easier to bolt on your...
It's easier to bolt on your LT1 intake already assembled with the throttle body, injectors, fuel rails and sensors attached. To spruce things up, Harv's completely disassembled the intake, cleaned it, then spray painted it with fresh aluminum paint. Now it looks new again. We probably should've flowed and cleaned our old injectors while we were at it, but we rationalized that we were trying to duplicate a worse-case scenario. Yeah, that's the ticket...
The best thing about re-using...
The best thing about re-using stock rocker arms is that it takes zero finesse. Just crank 'em on and forget about 'em!
Bosch supplied the world's...
Bosch supplied the world's first high-voltage ignition system in 1902 and has continued to supply superior wire sets for nearly 100 years. Bosch plug wires feature stainless steel Mag winding, a 100 percent pure silicone jacket, and a Kevlar reinforced core for maximum voltage, and a hotter, more powerful spark. Bosch is also a leader in oxygen sensor technology. It's a good idea to change your oxygen sensors every 50,000 miles and we were overdue.
We ordered our Comp Cams High-Tech...
We ordered our Comp Cams High-Tech pushrods (part No. 7940-16) prior to getting our Edelbrock Performer LT1 heads. These are the stock 7.200-inch length in a 5/16-inch diameter. After receiving our heads, the directions recommended .100-inch longer pushrods (Comp 7949-16 according to the instructions). Due to time constraints, we used the 7940-16 pushrods anyway with no problems.
On the dyno, our '94 Camaro...
On the dyno, our '94 Camaro Z28 with Edelbrock Performer LT1 heads, cam and throttle body cranked out 283 hp at 5,900 rpm. That's 34 hp and 300 rpm more than our stock baseline. We've got a really cool mpeg movie of our dyno run on the PHR website. Just click on www.popularhotrodding.com to see and hear it!
"Everything bolted up good...
"Everything bolted up good with no modifications necessary," says Sean Baisden of Harv's Auto & Dyno Tune. "All the components went back on without modification, which is pretty unusual for aftermarket parts. It made good power--the power they said it would make--which again is rare for most companies. I would definitely recommend to somebody looking for another 30 or 40 rearwheel horsepower that they look into the Edelbrock upgrade. It's a near perfect combination. It's also a good basis for additional add-ons. For a stroker, I'd definitely want to port these more or wait 'til the bigger 200cc heads come out."
BASELINE PARTS LIST
Like many 10-year-old Z28 Camaros, ours also had a complement of bolt-on performance parts that it had accumulated over the years. The following parts were already on our test car when our baseline dyno test was performed. Some of the items listed have a direct bearing on the power output to the rear wheels (such as the exhaust and cold-air package) while other items have an impact only on the street or at the track (such as gears, wheels/tires, differential, or shift kit). With the exception of the Holley throttle body airfoil, all the items listed were in place for the dyno test after the installation of the Edelbrock Performer LT1 package. It is worth noting that most people considering the Edelbrock Performer LT1 package will either have similar items or will get them soon. These basic bolt-ons are the low-lying fruit which should be harvested before any additional major mods are completed, and as you can tell, our stock-engine test car was ripe for the head and cam package.
|Item:||Part No.: |
|SLP cold-air intake package||21014 |
|SLP 3.42:1 ring & pinion w/Zexel heavy-duty diff.||64048A |
|SLP reluctor gear||26029 |
|SLP weld-in subframe connectors||70802 |
|SLP driveshaft loop||65050 |
|SLP 160 degree thermostat||100224 |
|SLP manual fan control switch||63011 |
|SLP LT4 driveshaft||64273 |
|Holley throttle body airfoil||120-140 |
|Dynotech Performance Hi-Pro 4L60E trans||n/a |
|TransGo 4L60E Shift Kit||TRG-4L60E |
|Precision Industries Vigilante torque converter||2800-rpm stall |
|Hooker 1 5/8-inch shorty headers||2062 |
|Corsa cat-back exhaust||14144 |
|Dynomax 3-inch Super Cat||15143 |
|BMR lower rear control arms||TCA002-R |
|BMR LCA relocation brackets||CAB002-R |
|BMR adjustable Panhard bar||PHR002-R |
|BMR adjustable torque arm||TA001-R |
|BMR lowering springs||SP001 |
|Nitto NT555RII Extreme (front)||275/40R17 |
|Nitto NT555R Drag Radial (rear)||315/35R17 |
|Topline Products "Bullett" 17x9 front wheels||1119-7961S |
|Topline Products "Bullett" 17x10.5 rear wheels||1119-7161S |
|THE NEW PARTS |
|Item:||Part No.: |
|Edelbrock Performer LT1 cylinder heads (2)||61909 |
|Edelbrock Performer LT1 camshaft||2108 |
|Edelbrock 52mm throttle body||3809 |
|Bosch spark plug wire set||09753 |
|Bosch oxygen sensors (2)||15703 |
|Champion spark plugs (8)||RC-12YC |
|Comp Cams timing chain set||3206 |
|Comp Cams pushrod set||7940-16 |
|Mr. Gasket LT1 head gasket set||5715|
|Mr. Gasket LT1 intake gasket set||135G|
|Mr. Gasket valve cover gasket set||5867 |
|Mr. Gasket one-piece oil pan gasket||6561 |
|Approximate Parts Cost (mail order):||$2300 |
|Edelbrock Performer LT1 Cam Specs-- Part No. 2108 |
|Advertised Duration||286 degrees (intake & exhaust) |
|Duration @ .050-inch||218 degrees (intake & exhaust) |
|Lift @ Cam:||.350 inch |
|Lift @ Valve:||.525 inch (1.5 rockers) |
|Lobe Separation Angle:||112 degrees |
|LT4 Hot Cam Specs (reference) |
|Advertised Duration||272/281 degrees |
|Duration @ .050-inch||210/228 degrees |
|Lift @ Cam:||.328-inch |
|Lift @ Valve:||.525-inch (1.6 rockers) |
|Lobe Separation Angle:||112 degrees |
|Stock '93 - '95 LT1 Camshaft Specs |
|Duration @ .050-inch||202/207 degrees |
|Lift @ Valve:||.450/.460-inch (1.5 rockers) |
|Lobe Separation Angle:||116 degrees |
|Edelbrock Performer LT1 Heads--Specifications |
|Head Bolt Torque||65 ft.-lbs. (steps of 40, 55 & 70) |
|Rocker Stud Torque||45 ft.-lbs. |
|Combustion Chamber Volume||54cc |
|Deck Thickness||5/8 inch |
|Valve Seats||Hardened ductile iron (compatible with any fuel) |
|Valve Size||1.940-inch intake, 1.550-inch exhaust |
|Valve Spring Diameter||1.450 inches |
|Valve Spring Installed Height||1.800 inches |
|Valve Spring Seat Pressure||120 lbs. seated, 340 lbs. @ .600-inch lift |
|Max Valve Lift||.600 inch |
SWEAT THE DETAILS
There are three versions of LT1 timing covers--ours is the first one. There are also different versions of timing gears, distributors, distributor drives and crankshaft keyways for different years of LT1. You will need to visit your GM parts counterman to sort out this mess because it's too complicated to dive into here, but suffice it to say you will need several specialized seals, o-rings, and gaskets to properly complete your cam swap. We dug up a great web page on rebuilding LT1s and hope it's still there by the time you read this (see www.automotiverebuilder.com/ar/ar99928.htm).
Don't forget to reinstall the cam retainer plate before installing the new timing chain. You don't want to discover these leftover parts after you've bolted on the timing cover! Here, the oil pan is loose and connected by only two bolts at the back of the block. This allows the timing cover to be easily installed without pinching or damaging any gaskets. We also took this opportunity to swap in a new Mr. Gasket one-piece oil pan gasket.
It's also advisable to check the water pump drive and bearings for grooves. If there are grooves, there will be leakage and you can only blame yourself for not checking. Be forewarned, however, if you decide to change the water pump drive and drive gear, you can't just knock it into the block with a hammer!
GO WITH THE FLOW
The world of engineering is nothing more than a balancing act of compromises. Any design cannot be all encompassing. Nowhere is this better realized than when examining why the late-model enthusiast should consider the Edelbrock Performer LT1 cylinder over the popular GM LT4 casting.
All too often the finesse of cylinder head design is not realized by the consumer and instead they comparison shop flow numbers alone. Based upon the flow data for the Edelbrock Performer LT1 and stock LT1 and LT4 castings, the latter has the clear advantage. But there is much more going on in a cylinder head then can be documented on a flow bench with a fixed depression. That is where the Edelbrock casting shines.
When it comes to airflow, a cylinder head needs to provide an equilibrium between port velocity and volume. It is all too easy to develop big flow numbers on a test fixture only to have poor velocity and thus low volumetric efficiency and power when bolted to a stock-displacement engine. The qualifier the industry uses for intake port volume is cubic centimeters (cc). This is a liquid measurement of the volume of the port. By itself it can be deceiving since the entire port is what is being measured, including the bowl area. Given the confine of space available in a given application, the port volume can be used as a good qualifier of the expected velocity of the charge. Low volume usually equals high velocity. To this cause Edelbrock's Senior Design Engineer, Ulises Gonzalez, worked very hard to maintain the 170cc volume of the stock GM LT1 design while improving the airflow. In contrast, the GM LT4 casting undeniably flows more air but has a much greater port volume, pouring out at 195cc. At 0.500-inch valve lift, the Edelbrock Performer out-flows the stock LT1 design by nearly seven percent.
Intake flow is critical to power production but the exhaust port is just as important. Edelbrock recognized that more power can be produced if less is consumed evacuating the cylinder on the exhaust stroke or pumping loop. The Edelbrock Performer LT1 has the ability to flow fifteen percent more spent gasses at 0.500-inch lift than the stock design. A more efficient exhaust port creates less pumping losses in the engine and will produce more power for a given volumetric efficiency.
Other features of the Performer LT1 casting that make it a good choice are thicker walls by 0.300 inch for future porting, a thicker deck surface for stability, along with a 54cc combustion chamber and 1.94/1.550-inch valves on the intake and exhaust, respectively. In addition, the Performer bolts right up to the GM intake manifold and does not need extensive rework to align the air path as the raised-port LT4 requires.
If you are looking to upgrade your LT1 cylinder head, undeniably the GM LT4 is an excellent choice. The Edelbrock Performer LT1 offers better port velocity and increased throttle response and low-speed torque which are just the ticket for a stock displacement street/strip car.
With the Performer design fitting right in the middle of the GM castings, maybe the marketing mavens at Edelbrock should have called it the Performer LT2.5!--Ray T. Bohacz
|Cylinder Head Flow Data* |
|Stock LT1 |
|GM LT4 |
|*All flow data is at 28 inches of H2O with a radiused intake and no exhaust extension. |
|Dyno Results- Edelbrock Performer LT1 Cam & Heads |
| ||Torque ||Power |
|RPM ||Stock ||Edelbrock ||Change ||Stock ||Edelbrock ||Change |