TPI Intake Conversion - Unleash the Beast

This project started like most, with a little bench racing session discussing the pros and cons of the myriad of intake choices available for the L98 engine found in the third generation F-body. One of the hottest intake topics going around the various internet boards dedicated to the 3rd gen is the use of the LT1 intake. Is it worth it? Can it work? Should I get the Super Ram instead? Which one is best for me?

Well like most, I had heard the pros and cons of each style, some myths and some real. The biggest change one would expect would be a gain of upper end breathing (more HP) at the expense of lower end port velocity (less torque), but just how much? Since I was already using the ACCEL SuperRam base, runners, and plenum I wanted to find out just what was the difference.

I would consider my '88 Camaro like many third gens out there cruising the boulevard; mildly-to-heavily-modified on a budget (if you can use those words in the same statement).

The car started out life as a 305 TBI dog, which I converted to port fuel injection about 5 years ago when I installed a larger 379. To facilitate the swap I used a programmable Haltech E6GM ECM, which is a speed density system. A programmable ECM is not required, but to maximize the potential of any electronic fuel injection system, the ability to change the fueling and timing parameters is key. There are many products and DIY websites available to help in this area if you are inclined enough to learn to do this yourself.

I had been running the SuperRam system for the better part of three years with no real complaints. The cam is a holdover from the days when the car served daily driver duties. Compression ratio sits about 9.3:1, which is a little on the low side for normally-aspirated fuel injection, but just right for throwing 9 to 12 psi of intercooled air in the near future.

To get the swap rolling I enlisted the help of some fellow F-body enthusiasts cruising the southeast thirdgen board (www.sethirdgen.org).

Steve Phillips offered up some spare stainless braided fuel lines and fittings, while Rob Faulkner drilled and tapped the fuel rails to accept the AN6 to NPT adapter fittings. Fellow board member John Millican (of www.lt1intake.com) modified the intake that I supplied. These modifications can be accomplished at home and John has some instructions available on his website, or you can pay John to do them for you for a more complete turnkey package.

These modifications involve adding the distributor hole and spacer, modifying the intake-to-head bolt pattern, and coolant crossover. The factory LT1 intake does not have a conventional distributor or coolant flow in the intake. Other items you'll need are the remote mount thermostat housing, fuel lines (and appropriate fittings/adapters), intake gaskets, and miscellaneous vacuum tubing/fittings and coolant hose. The LT1 intake requires the use of a small-cap HEI distributor with a remote-mount coil, which is standard on the '87 to '92 F-body.

It is easiest to start with a complete '94-'97 intake with fuel rails and regulator. Being the difficult type, I started with a '93 intake, which does not have a front fuel crossover and the rear of the rails interfere with the distributor if they are not shortened. After mocking the intake up a few times, I decided to add the front crossover to ensure sufficient fuel to all the injectors as it was going to be difficult to achieve the crossover in the rear. I also opted to use an Aeromotive adjustable fuel pressure regulator and plumb everything from the factory fuel hard lines with AN6 (3/8-inch) braided stainless hose. With the '94 to '97 intake it is possible to use the regulator and fabricate factory-style fuel lines to forego the aftermarket fuel setup.

If you set everything up ahead of time and do some careful planning, the swap is relatively straightforward with very little modification needed at swap time. One area that did need some clearancing was the passenger side accessory bracket in the area of the IAC connector and TPS sensor. A little trial fitting, some work with the air grinder, and the throttle body was bolted in place in no time.

This swap can be performed by the average automotive enthusiast so We haven't gone into great detail in step-by-step instructions here. It's recommended if you don't feel comfortable performing the swap to locate a local shop to do the work.

Make sure when you're done routing the coolant hoses and remote mount thermostat housing that the radiator cap is still the highest point in the system. If this is not done, you'll most likely end up with air trapped in the system, which will lead to cooling problems. The only wiring that needed lengthening was the coolant temp sensor, which gets relocated from the front of the stock/SuperRam base to the remote mount thermostat housing, which is mounted on the driver's side.

We reused the stock upper radiator hose although we had to shorten it a little bit and flip it over to get it to work. The "custom" cold air kit made for the SuperRam intake worked fine with the new intake as well.

To try and level the playing field as much as possible, Tim Gibson at GPS in Beaufort, SC offered the use of his Dynojet and shop services to perform the swap. We arrived early and dyno'd first thing in the morning. Using STD corrected numbers we put down a max of 335 rear-wheel horsepower at 5,000 rpm and 392 rear-wheel torque at 3,800 rpm.

We then proceeded to remove the SuperRam and install the LT1 intake. Craig Skiles pitched in with the actual intake swap and kept us going into the wee hours of the night. The swap was accomplished in one day (one long day) and we strapped the car back down on the rollers to see what kind of changes we saw. After the swap and some wideband O2 tuning, we spun the rollers up to the tune of 343 rear-wheel horsepower at 5,500 rpm and 360 ft-lbs. of torque at 4,600 rpm.

As expected peak torque is down and peak HP is up as well as a shift in the curves up in rpm range. However, the torque curve is as flat as a board for the LT1 intake until it starts dropping off about 5,000 rpm.

Both sets of dyno runs reflect a fair amount of wide band dyno tuning, more so on the SuperRam intake as it was run for a couple years as previously mentioned. During the LT1 runs, however, we noticed that the fuel pump was not keeping up and pressure was dropping off at higher rpms. This is odd considering I had never noticed this problem with the SuperRam intake. Even so, the WB O2 sensor on the dyno showed only slightly lean exhaust gasses.

A new Walbro high pressure 255 ltr/hr pump was installed shortly after and another trip to the dyno was made with no appreciable difference in power, so it appears that the loss in fuel pressure wasn't as serious as it might have appeared. However, the bigger Walbro pump will allow for more mods in the near future.

After putting a few miles on the car with the new intake, I can say that driveability is excellent as well as throttle response. At the track on the day following the swap (with the stock fuel pump) the results were very similar to the SuperRam despite the large drop in low end torque, maybe this was a case of too much of a good thing. All that torque wasn't being transferred to the pavement efficiently so it was essentially being wasted at the track. If we look deeper and compare the averages of the curves, they are not far apart. The runs down the strip bare out the differences as the LT1 intake attempts to run down the SR on the top end.

It should be noted that this swap is not emissions-legal unless you install an external EGR valve. It may be possible to modify a system from a stock V-6 3rd gen F-body, which uses an EGR valve mounted to the exhaust manifold.

You can plan on spending anywhere from $200 to $600 for the LT1 intake swap depending on how much of the conversion you plan on doing yourself and what you get the used intake and fuel rails for. The SuperRam (new with an aftermarket base) is close to $1200. However, with some careful internet swapmeet/classifieds shopping you can probably get a complete setup for $700 to $900.

Is one of these the "better" intake? Well that question is up for each individual person to answer on their own. Future plans call for a much bigger roller cam to see where the new intake can take us.

KEEPING COOL

As mentioned in the story, the factory LT1 intake does not have provisions for a thermostat, housing, or coolant crossover between the heads. Because of this, provisions must be made to ensure proper cooling is maintained. One way is to use the remote mount thermostat housing, which I mounted on a bracket I fabricated that bolts under the driver's side STB brace. I used the factory TPI thermostat neck and upper radiator hose, which was flipped over and shortened, to provide return flow back to the radiator. The remote housing needed to be drilled and tapped for four (4) holes: three (3) for the coolant lines and one (1) for the coolant temp sensor, which is factory mounted in the TPI base. The coolant crossover lines were tapped from the rear of the intake instead of the front like the factory to provide more room for the throttle body and associated linkages. I used 1/2 NPT to 3/4-inch nipple fittings on the intake and the housing. The 3rd fitting in the housing should be plumbed back into the factory diverter valve and replaces the stock coolant line that came out of the factory TPI base manifold. It is important when mounting the remote housing and routing the coolant lines that the radiator cap remain at the highest point in the system to avoid getting air trapped in the system during normal operation. Upon initial start up we had to "burp" the system to remove all the trapped air, so keep this in mind to avoid any problems.

GETTING DIZZY

Another major modification needed to mount the factory LT1 intake manifold on a traditional small-block Chevy is a distributor. (unless you configure a distributorless ignition system similar to the Buick GN or current LS1, but that development was beyond this intake swap) This swap requires the use of a small diameter remote mount coil distributor found on '87-up F-bodies as well as some truck applications. Using a stock intake manifold you can fabricate a template out of cardboard or thin sheet aluminum (preferred) to mark the location of the hole. The hole should be drilled out to approximately 1-3/8 inches. The stock GEN I intake is approximately 1/4-of-an-inch higher and slightly angled when compared to the LT1 intake in the distributor mounting area, so a spacer will be required. You can either have this piece machined locally if you are doing the modifications on your own or you can pick one up at www.lt1intake.com ready to mount. Mounting of the distributor is a key step so make sure you measure twice and drill once when performing these tasks.

HEADY ISSUES
To mount the LT1 intake on GEN I cylinder heads, you need to drill the holes in the intake flange to match. To clean up the appearance you can then fill the stock hole in the flange, sand and paint. Another option to look at is to use a set of stock LT1 cylinder heads on the traditional block. Some modifications to the head on the deck surface would be required, as the LT1 cylinder heads are different in this regard. Having said that, as LT1 heads are aluminum, flow fairly decent, and can sometimes be found for less than $300 used, this may be a viable option if you are starting with factory cast iron heads and are working on a budget. I recommend you investigate everything needed for this option prior to laying down your hard earned cash as I have not performed this modification myself.