Here is our Scat four-inch...
Here is our Scat four-inch stroker kit that turned our 350 into a 408 (Scat PN 1-40576; $2,358.95, Summit price). This kit features Mahle high-tech pistons and Scat's stroker-friendly rods, which offer far greater internal clearance than most rods. This kit comes complete with rings, and as an option from Scat, can be had as a balanced assembly for $250 extra.
Dyno Testing
We did our dyno testing on T&L's primary dyno in phases. First a "safe and conservative" tune-up was done to act as a provisional baseline. This basically consisted of an ignition setting that was a little retarded, and carb calibration that we anticipated was just a shade too rich, along with a secondary tuned length too short. At this point, we swapped intakes from the two-plane Air-Gap to a single-plane Super Victor to see what it would do. After that the Super Victor was changed out for a Dominator Super Victor to establish what that would do to our 408's power curve. After these exploratory tests, the Air-Gap was reinstalled, and the final detailed tune was done to extract every last ounce of power. Check out the sidebars for the results of our manifold tests. For some applications, you may find it suits you better to go single-plane on one of these powerhouse 408s. Remember, we are on pump gas with a compression ratio of only 10.5:1. Just check the power curves: This street driver cranked out, through the mufflers, a very creditable 551 lb-ft of torque and just a shade over 560 hp. But the best part is the cost: T&L will build you a replica, minus headers, water pump and mufflers, for $7,685, and that includes a video dyno test.
Wet Flow Intake Ports
There's a lot more to these AFR Comp Eliminator heads than meets the eye. Unlike most small-block Chevy heads within this price range, the AFR heads have some very worthwhile performance features not found on other heads. For starters, the valves are a lightweight design that come in at about 15 percent less than you will find on most other heads. Also, the springs on the AFR heads are more like the upgraded springs we see on most of the competition. All this goes to make a better valvetrain package, and it shows in terms of valvetrain control and higher rpm limits. Nevertheless, to the untrained eye, these assets might just pass unnoticed. Pull an intake valve out of the port and what you see in the bowl will most certainly catch your attention. Alongside the guide on the cylinder wall side of the runner is a fuel-shear ramp. The intent is to reduce or eliminate the heavy fuel wash normally seen on the chamber wall immediately adjacent to the spark plug. This wash drastically increases bore wear and negatively impacts power, economy, and emissions.
Two questions need to be asked here: Does the presence of the ramp in the port compromise flow, and does it improve wet flow characteristics as intended? Well, there was not time to run wet flow tests, but we went one step better and removed the heads after testing to check the burn pattern. It proved to be very uniform with no visible signs of fuel wash, so on that score, yes, the ramp apparently works great. As for compromising flow, our dry flow tests indicated that if the ramp did compromise flow, the amount was more than offset by the top-notch wet flow characteristics. From the result achieved on the dyno, we would have to say that the AFR Comp Eliminator looks to be one hot ticket.
Here's the finished short-block....
Here's the finished short-block. Due to the lower piston friction of the Mahle piston/ring assembly, static turning torque was measurably lower than with a more conventional piston/ring assembly.
More Manifold: What's It Worth?
For its displacement, our 408 has not got a particularly big cam, but 408 inches and high-flowing heads make it a deep breather. This combination puts a lot of emphasis on manifold flow capability. Although the air-gap design is a great deal for a two-plane, we asked ourselves what this 408 could do given more intake flow in the form of a single-plane Super Victor. Before looking at the results, remember that this test was done prior to optimizing the timing and exhaust, so the numbers are down on what we achieved in our final round of testing. Nevertheless, the "before" and "after" results are totally indicative of what happens when the air-gap intake is replaced with a Super Victor. A check of the graph curves shows that our 408 was still a low-speed torque monster, but to a lesser degree. A duplicate of our 408 build, but equipped with a Super Victor, can be expected to net better than 575 streetable horsepower.
Let It Eat! It's Dominator Time
Since our 408 responded to the tune of 20 horses when given the better-breathing Super Victor, we speculated that it might just like even more induction flow. Even if it didn't, it would be an interesting experiment to see what effect a lot more intake flow would have on the engine's power curve. To this end, we had the almost ideal intake and carb setup. T&L was in the middle of building a 454 small-block for a customer, and the heads and manifold were already complete. A check of the intake showed it matched the ports of our 408's AFR heads perfectly. The only downside was the port size of the Dominator-equipped manifold for an engine nearly 50 cubes larger, and one that would utilize a race cam instead of a street cam. Knowing that, we decided to go ahead anyway, as the test would still give us a ballpark indication of the pros and cons of using a bigger manifold with a 1,150-cfm Dominator. Another angle was that AED was claiming to have improved the low- and part-throttle driveability of their Dominators to the extent they can be used on much smaller engines than previously thought practical. Here was a test of both power and part-throttle behavior at low speed. Check out the graph, and you'll see power up by as much as 25 horses. The good news is that low-speed manners were as good as the 900-cfm 4150 this AED Dominator replaced.
A point worth noting is that had we spent the time at this point (instead of after the final manifold change) to tune the exhaust, the engine would undoubtedly have topped the 600hp mark by as much as 10 horses. Not bad for an engine that still has street manners.
 A four-inch-stroke crank will...  A four-inch-stroke crank will gather up the oil and entrain it. To avoid this, a Moroso stroker pan is a must. We're crossing our fingers that everything fits properly inside our Laguna! |  A four-inch-stroke crank will...  A four-inch-stroke crank will gather up the oil and entrain it. To avoid this, a Moroso stroker pan is a must. We're crossing our fingers that everything fits properly inside our Laguna! |  Up front, T&L elected to use...  Up front, T&L elected to use a heavy-duty-finish Como Cams timing cover and a Professional Products damper on our 408. |
 Here, the Comp Endure-X solid...  Here, the Comp Endure-X solid roller lifters are being installed. These are 0.300-inch taller so that the link bars clear the higher lifter bores of the late-model block casting. Improvements in street roller cam profiles-and subsequent longer intervals between maintenance-made us take a hard look at a solid roller cam, and we decided to take the plunge. |  A key component choice was...  A key component choice was the AFR Comp Eliminator heads. These had strong flow characteristics throughout the lift range, and ports that enhanced the mixture quality upon entering the cylinders. The result was a head with excellent combustion properties. |  The AFR Comp Eliminator 210...  The AFR Comp Eliminator 210 is available in combustion chamber volumes of 65cc and 75cc to suite a variety of displacement, fuel octane, and compression ratio needs. |
 Our flow tests of the AFR...  Our flow tests of the AFR Comp Eliminator head showed similar figures to those on AFR's website. In the main, our numbers were slightly less for the intake, and slightly more for the exhaust. |  |  The highly functional AFR...  The highly functional AFR Comp Eliminator chamber shape is clearly seen, but the most unusual feature is the "ramp" in the intake port (yellow arrows). The purpose of this is to act as a fuel shear point so that the large fuel droplets commonly generated from the fuel stream at this point are broken down into a much finer state. After testing, a check of the burn pattern showed these heads to be excellent in this context. |
 The exhaust ports on the AFR...  The exhaust ports on the AFR Comp Eliminators were a cut above the average for flow. This makes these heads good for a nitrous application as well as our 408. |  Our flow tests showed that...  Our flow tests showed that the AFR heads flowed well on the intake (298 cfm at 0.700-inch lift), and very well on the exhaust (225 cfm at 0.700 lift), but strong midrange flow was probably the most significant factor toward making good power. |  ARP bolts were used in all...  ARP bolts were used in all high-stress areas, including those performing the job of clamping the heads to the block. Here we are using ARP's less expensive six-point fasteners. |
 The length of the Comp Magnum...  The length of the Comp Magnum pushrods we used for the 408 was determined by the sweep pattern over the end of the valve. Our Comp Cams Gold rockers had a 1.65:1 ratio, and after lash was factored in, total valve lift was 0.602 inch. |  The intake manifold we selected...  The intake manifold we selected was Edelbrock's highly functional Performer Air-Gap. This provided race-like top-end output along with great low-speed torque and driveability for the street. |  Our selection of an AED-built...  Our selection of an AED-built Holley carb was based on outstanding results on a string of previous engines. This 4150-style carb based on the Holley HP series delivered a wet flow of 900 cfm. |
 The penalty paid for swapping...  The penalty paid for swapping out the two-plane Air-Gap to the single-plane Super Victor was 35 to 40 lb-ft of torque below 4,600 rpm. From there on up, the Super Victor showed its worth. From 5,000 to 6,000 (about the range this engine would be use on the strip), the Super Victor was as good as the two-plane, but climbed to a 20-point advantage by 6,200. This test proves once again just how good Edelbrock's Performer Air-Gap is. |  The Edelbrock Super Victor...  The Edelbrock Super Victor in this "what-if" test was port-matched to the AFR heads and given a rudimentary casting flash cleanup. |  We went with a Performance...  We went with a Performance Distributors HEI for several reasons. They custom build each unit to specifically suit each individual engine, and these distributors have shown great high-rpm spark output and outstanding reliability. When we install our 408, we'll be swapping this one out for a Racing DUI Distributor with Performance Distributor's Instant Timing Knob. This will allow on-the-fly adjustments to base ignition timing for differing fuel quality. We've also ordered that unit with Comp's composite distributor gear for long-life wear. |
 The near cavernous ports of...  The near cavernous ports of the Dominator-style Super Victor intended for another 454-inch small-block can be seen here. Ports with about 10 percent less area would have probably shown even better results than we saw from this borrowed combo. |  This 1050 AED Dominator looked...  This 1050 AED Dominator looked and ran like it was right at home on the Laguna's 408. Idle speed was a smooth, lope-free 850 rpm, and though the dyno is not the best of tests, we saw no signs of any low-speed, part-throttle driveability problems. |  Dominator Carb Test In spite...  Dominator Carb Test
In spite of having runners sized for a 454ci race engine, the AED-Dominator-equipped Super Victor showed its strength well. Below 4,600 rpm, it was down on torque over the smaller-runner 4150-equipped Super Victor. Above 4,600 rpm, it delivered as much as 25 horsepower more. On the strip, the Dominator/Super Victor combo would dominate. It's good to know in advance that there's a lot more left in this engine with an easy swap, should we decide to ditch our practical intentions. |
 Here you can see the step...  Here you can see the step design headers we used on the 408. These headers belong to T&L's dyno, and proved very effective for the rpm range our 408 was to run in. For the Laguna, we will attempt to duplicate these as best as we can with a catalog item, or a custom-built header if necessary. |  |  T&L's "Dyno Doug" Aitken is...  T&L's "Dyno Doug" Aitken is seen here loading our 408 onto T&L's Number One SuperFlow dyno. Note the dyno's big Flowmaster mufflers. Our final results were with these in place. |