After picking up 53 rear-wheel horsepower and 30 lb-ft of torque with a Crane cam and Airflow Research 195cc cylinder head swap on our 383-powered Corvette project car (Super Chevy, November ’13), we were driving on Cloud Nine. These upgrades were a huge improvement on the street, but we had a feeling the little 383 had more to offer.
We were speaking with Tony Mamo from AFR during the head test, and he told us that although we had been using a very good dual-plane intake (Weiand Stealth), he was confident his company’s TX-series single plane manifold would be a perfect addition for our street-only application. We decided to call his bluff, so to speak, and did a full test on AFR’s new Titan polymer intake line to see just how well these single planes stacked up against our dual plane.
The Titan TX-series uses a polymer base, with your choice of single-plane uppers—a taller race version (TXR) or lower street application (TXS). The uppers can be swapped without unbolting the base from the heads, making for a quick, neat changeover. The other plus is the composite upper/lower combo weighed in at only 7 lbs—half the weight of our current intake. And after multiple dyno pulls the intake was much cooler than its aluminum counterpart.
Back when we did the head and cam swap, we noticed that the shaft in our factory tach-drive distributor was getting rather wobbly. It could be wiggled a good eighth of an inch back and forth. This was evident in the street drivability, where the engine idle speed would hunt, and there would be occasional run-on when we switched off the ignition.
Another issue, which had been present since we bought the car, was the drive gear for the factory mechanical tach was chewed up. One of the car’s previous owners epoxied over it and we were forced to use an aftermarket electric tachometer rather than the factory piece. The new MSD Pro Billet tach drive distributor and matching 6AL digital ignition controller would hopefully cure both of these ailments.
To make sure the car was running to the best of its ability, we swapped in the new distributor and controller first, established a new baseline, then tried out the manifolds. Read on!
1. Here is the Titan TXR (tall version) paired with the base and how the unit looks fully assembled. It’s made from a composite plastic that is much lighter than aluminum. All mounting holes are fitted with metal inserts, as well as the coolant ports. Its made to accept any square bore carburetor or EFI system. There are cast in bosses for nitrous plumbing, and it uses rubber Viton gaskets to seal just like the LS platform.
2. Here is the lower portion of the Titan manifold system. It is used to seal up the valley and also plumb the cooling ports. This part, once installed, can stay in place allowing you to swap out different runners depending on your needs. It has dual distributor hold downs, mounting boss for some factory alternator brackets, and metal compression limiters at the mounting points to prevent you from over tightening the hardware and damaging the piece.
3. Here is a side by side to show you the difference between the TXR on the left and TXS on the right. Both are a single plane design, and have a 3,000-8,000 rpm operating range. In testing both made more power and torque than our existing dual-plane aluminum intake. The TXR height comes in at 5.50-inch, while the TXS is 4.58-inch, compared to the Stealth’s height of 4.73.
4. Both intake spiders feature a 4150 style carb flange and threaded inserts. By the time you read this AFR will have a dual plane upper as well.
5. Here is our configuration before we ripped into anything. A 383 stroker with AFR 195cc Eliminator Street heads, Crane 0.558 lift 238/242 duration, 110 lobe center cam, Weiand Stealth dual plane intake and Holley HP 750 cfm carb. This combo made 344hp and 368lb-ft of torque to the rear wheels, but was showing signs of a faulty ignition system. So before we get into the intake test we are going to cure the ignition system woes.
6. The engine was brought up to TDC on number one cylinder, then the old Magna-Pulse distributor was plucked from the back of the motor.
7a. The distributor shaft was a mess, wobbly as hell. All that slop had our timing jumping all over the place, and even made the vehicle hard to start when warm.
7b. Another issue with this old unit was the tach drive. Apparently at some point it failed, and instead of fixing it properly one of the previous owners “fixed” it by epoxying over the distributor’s tach gear.
8. MSD’s Pro-Billet Tach Drive distributor with vacuum advance (Part No. 8572) was the perfect choice for our Vette. This beauty features an accurate magnetic pick-up, oversized shaft, vacuum advance, and a billet aluminum housing. It has an adjustable mechanical advance assembly that allows us to custom tailor our timing curve. The tach drive assembly is compact enough to clear the firewall, can be repositioned, and has a grease fitting for easy lubrication. When installing the new distributor, be sure to add MSD’s rubber O-rings at the bottom of the shaft. These improve oil distribution to the lifters over the factory design. Greg Lovell of Antivenom High Performance (Seffner, Fla.) handled the installation, and marked the rotor and distributor placement so the new one could go in as close to the old one as possible. Greg was spot on, as the new distributor dropped all the way in and even engaged the oil pump without having to bump the starter.
9. To support the distributor and give us the best spark possible, we picked up one of MSD’s new Digital 6AL Ignition Control boxes, part no. 6425. The box looks fairly similar to the old 6AL, but MSD has made a ton of changes. On the outside it’s thinner, has better wiring hook ups, and the rev limiter was moved to the front of the box for easy access to the two rotary dials. Inside the circuits are updated with efficient components that help the ignition produce more power while drawing less current.
10. Even though we had been using another brand ignition box, we wanted to match the MSD distributor to its box. This made wiring the new distributor a plug-and-play operation.
11. You set the rev limiter with two screws under a flap on the top of the box. The one closest to the edge is thousands, the one to its right in hundreds. We set our limit to 6200, since we don’t plan on revving this engine any higher than that.
12. To mount the box we drilled two holes and attached it to the block-off-plate for the car’s heater. This allows us to quickly remove the box to reset the rev limiter if we need to, since we are putting it into a very tight engine compartment.
13. The new box was mounted to the firewall in the passenger side inner fender behind the fender gills. It’s out of the way and hard to notice. We were already using MSD’ 8.5mm Super Conductor wires and a factory-style cap, so we reused the low-mileage cap and wires rather than switching to HEI-style wires and cap that came with the new distributor. We will probably switch at the next tune-up. For the tach, all you need to do is plug the factory tach drive cable into the distributor and tighten the coupler.
14. Once everything was connected, the car was running a whole lot smoother, and there was no dieseling when we shut it off. The car would hold a nice low rpm idle, and didn’t stall when we turned the A/C on—another problem with the original 92,000-mile distributor—plus the factory mechanical tach came to life! Note actual peak torque was 370, not the 383 figure shown. The 383 number is an unexplained spike in the graph.
15. Now the new distributor, along with everything else hooked to the manifold, was taken off so we could remove it. All the intake ports were plugged with rags, the valley covered, then the surface areas were cleaned of the old gasket material.
16. The upper and lower parts of the intake install with reusable rubber gaskets. The intake comes with all the hardware and gaskets you need, including a tube of RTV sealant.
17. We had to plug three of the coolant crossover holes, since we were only using one line on our old school application. We needed a smaller nipple for the coolant line.
18. A 1/4-inch bead of the supplied RTV sealant was applied to the china walls, and at each corner of the heads. There are a few more areas that need a dab or two of this sealant, but that is all mapped out in AFR’s instructions.
19. The lower piece is installed and tightened to 25 lb-ft.
20. Then the seals were installed into the upper portion of the intake.
21. Since we knew it wouldn’t fit under the stock LT-1 hood, we tried the TXR race series upper first. It’s a full inch taller than the street design. This gives the fuel a straighter, longer shot into the intake ports for improved horsepower and torque. It is mated to the lower section with the provided hardware.
22. All the other items were reinstalled without any drama. The engine was warmed up and timed before we made our initial pull on the dyno. After making a few pulls, we were confident she gave all she had. We shut down and swapped out the runners.
23. The TXS upper was pretty easy to change since it splits from the lower. All we needed to swap over was the carb. The distributor and cooling stuff stayed in place. We did have to move the heater hose because the intake is lower than old Stealth manifold, and was interfering with the fuel line, but that was the only small issue. One thing to note was the manifold’s temp: Even after multiple dyno pulls the manifold was fairly cool to the touch, not something you can say about the aluminum piece. Since the TXS is lower than the Stealth intake, we were curious to see how it would do.
24. We had a baseline of 344hp and 368 lb-ft of torque before we added the new ignition, That got us to 350hp and 370tq. The TXR (race) put down 380 hp and 378 lb-ft, adding a whopping 30 hp to the rear tires. Torque was up 8 lb-ft. The TXR bested the Stealth dual plane across the entire rpm range. The TXS was down less than 4 peak hp and 6 lb-ft to the Titan TXR, but up 26 hp and 2 lb-ft to the Stealth at peak. Torque-wise, the Stealth has it below 4,000 rpm, but after that the TXS pulls ahead.
25. All in all, no matter which Titan intake you choose, either is a great option. Had we more hood clearance, we’d have definitely used the race upper, even on the street. The only drawback looks to be the price, which is $581 at Summit Racing, making them expensive in the SBC realm for a carbureted intake. There’s no difference in price between the street and race versions.