Replacing a Gen 2 small block (LT-1) with a Gen 1 small block in a 4th Generation F-body for street use

Howdy folks. After years of talking about it, I am finally doing the swap. I am dropping a 475hp (estimated) EFI 383 gen 1 small block in my 1994 Firebird Formula. This will be a journal of the whole process, starting with some history and specs of the car and engine. All of the photos I gather along the way are being dumped here until I organize them better.

The Ride

I got the car in about 1998 or so. The back end was crushed pretty bad, and it had an automatic transmission. A year or so after I got it, the trans died, so I decided to convert it to a 6 speed manual. Some months after that I finally got to doing the body work. I cut out all of the bad sheet metal, straightened out the crushed inner wheel well, and welded on a new factory GM quarter panel. There are some photos of that project in my photo gallery HERE

The Plant
I built a 383 small block Chevy engine about 12 years ago for a vette I used to have (and never really finished). It's been sitting on an engine stand for many years waiting for a home. The 383 small block is one of the most popular engine displacements that GM never produced. They finally got the idea recently with a few of the current gen 3 small block displacements, including the 6.2L LS3. The 383 is achieved using a 3.75" stroke 400 crankshaft in a 4.030" bore 350 engine block. The popular choice is to use the long 350 rod (5.7"), instead of the 400's 5.565" rod. Using the 5.7" rod requires custom pistons with a raised wrist pin location, but these are so common, they are pretty much the same price as stock pistons these days. It also requires some minor notching of the engine block, to clear the throw of the rod's bottom end. This is all standard stuff at any speed oriented machine shop. The most important specs/parts are as listed:

  • 383 long rod (5.7") short block with Keith Black Hypereutectic pistons
  • Air Flow Research Aluminium 190cc Intake port volume CNC ported heads
  • Isky hydraulic roller cam with AFR rev kit and dual coil valve springs
  • Accel SuperRam EFI system with custom reduced height plenum for use with 4th Gen F bodies
  • Stainless Steel 1.5 ratio roller rocker arms
  • BBK 58mm throttle body
  • 26lb/hr fuel injectors
  • Programmable DFI engine controller


The Plan
The 4th generation camaros/firebirds (F-bodies) were completely redesigned from all other previous generations, based heavily on the space now available from the new short lived LT-1 gen 2 small block. This engine uses a gear driven reverse flow water pump, a distributor mounted just underneath the water pump, and a very low rise short runner intake manifold. GM went from one extreme to the other with the long runner L98 to the short runner LT-1 in 1991. I think they finally got it all right later on with the all new gen 3 aluminium engines, but in my opinion, they never found a happy medium in the power band department until then. Thanks to the late, great John Lingenfelter for giving us the SuperRam intake manifold, based of the L98 TPI manifold. He cut runner length in half and doubled the plenum size, which made for a perfect street power band. It makes great low end/mid range torque and still winds out to 6500+.

The differences between the LT-1 and the gen 1 small block make for some issues trying to put my engine in the 1994 Firebird. My first concern was the distributor. The engine sits way back under the cowl, so the whole back half of the engine is covered by the cowl. I was relieved to find that there is actually plenty of room for the distributor in the engine bay. The only problem is that the distributor has to be in the engine when I put the engine in. Once the engine is sitting in place, the distributor wont be able to be removed. Also, if the distributor ever fails, I'll have to pull the engine out to replace it. I bought a nice aftermarket billet aluminium performance oriented distributor, so hopefully that wont happen any time soon.

The next issue is the cooling system. Since the LT-1 water pump is driven off of the cam, there is no pulley. Space is so tight under the hood, that in order to retain all my desired street stuff (power steering, A/C, etc), I figured my best chance was to keep everything as close to stock as possible. In order to use the stock pulleys/accessories, I am using a CSR-901H electric water pump. These pumps are highly recommended for street use, and will also give me a few extra ponies. I don't have the pump yet, but I mocked up the brackets on the 383 and it looks like its going to work. Yay!

Next is the SuperRam plenum height. The stock SuperRam is too tall to fit under the cowl. That alone would have been a show stopper for this project, but thanks again to the late, great John Lingenfelter, I now have a prototype reduced height plenum that he made for testing on some 4th gen f cars at his shop in Indiana. I was lucky enough to see one laying around at his shop when I was there for work one time, and bought it off him. As far as I know it was never produced for sale, so I got really lucky here.

Finally, the wiring. I've been doing powertrain electronics engineering at the GM Powertrain dyno labs for many years, which involved many harness designs/builds/modifications so this is the easiest part of the job foe me. I am watching a few old 80's tpi harnesses on eBay that I will modify to interface into the firebirds chassis harness and DFI computer.

So, thats the plan. Now onto the shit...

The Pull 2008-08-13

I pulled the engine and trans out as one. It came out surprisingly easy. These cars are notorious for how packed the engine compartment is. I decided to make life easy on myself by stripping down as much as possible before trying to yank it out. I removed the radiator, entire A/C system, fuel rails, water pump, all the front accessories, and headers and it came right out. My brother has the same type of Firebird, and did a whole engine build too. He pulled the motor separate from the trans, but kept the A/C all in tact. He said it was a major pain in the ass, so I decided to strip it all down and save myself the headaches. After I got the engine out, I had the neighbour tow me down to the car wash. I sprayed the engine compartment down nice and squeaky clean. Now it's time to roll the 383 out of the corner and start tearin into it.

The Problems 2008-09-19

I was hoping to have this project finished by now, but we all know things never go as planned. I never expected to run into a show stopper like I did with this though. One would think I was dealing with Fords here. The LT1 engine block has one additional boss cast into each side of the block for the non standard motor mounts that the F cars use. The LT1 has the typical GM (chevy) 3 holes like every small/big block since 1955, but it also has one extra that no other small blocks have. This photo shows how one of the LT1 motor mounts bolts to my GEN1 small block using 2 of the 3 holes, with the 3rd left open. Click on the image to see it closer, it's probably hard to see here.

I thought long and hard about going ahead with 2 of the three bolts on each side, but in the end I decided to go with this BMR Fabrication tubular K-Member with standard small/big block mounts. There are other benefits to going with this tube K frame, including reduced weight and extra space available for aftermarket headers and exhaust. I am also going with the tubular control arms, and eventually the entire light weight tube front end with aftermarket struts/brakes for about a 100lb weight savings off the front end. I just got the K frame installed today, here is a pic of it in place. Click on this image to see all the pics taken so far of the project from the beginning. Now I'm finally ready to drop the new engine/trans in place. Till next time...

THE END! 2008-11-04
Well, not really, but it's running and driving! I've put about 300 miles on it over the weekend, including 2 trips to Clarkston and back. She hums a precision tune! The main problems right now are the electronics incompatibilities in between the TPI based engine and aftermarket DFI computer and the 4th generation Firebird.

Here is a rundown of all the things that were required to make the SuperRam EFI 383 SBC work:

First and foremost was the motor mount problem as described above. Going with the BMR tube cross member was a great idea. There is so much more room to get to things now, and it's much lighter than the stock bulky cross member.

To wire up the DFI controlled EFI system I started with an 88 TPI MAF based wiring harness. I figured that starting with the correct PCM connectors and injector connectors wired for batch mode firing would be the best starting point for interfacing the DFI controlled 383 to the Firebirds existing electrical system. I strived to be as non intrusive as possible to all the existing wiring, and I succeeded very here in doing this. I enlarged the hole in the firewall on the passenger side, where the 3 connectors enter the interior (The 1994 PCM was under the hood) to fit the PCM connectors and the extra wiring thru. I repinned the PCM connectors and the TPI-to-DFI controller adapter harness that I got with the DFI unit. I completely cannibalized the old LT1 harness in order to modify my TPI harness to fit in place. The main interface points were the C100, C210, C220, and C230 connectors that interface the engine harness to everything from injector power, ignition power, speedo/tach signals, gauge signals, PCM IGN, PCM BATT, fuel pump control, etc. It all came out pretty damn good!

Retaining the stock accessories using the stock accessory bracket required some changes to make things work. First of all, the shortest serpentine belt type crankshaft pulley that I am aware of, is the one used on TPI based corvettes (1985-1991). Even with this pulley, though, the pulley was still 1 inch too far out than the accessory pulleys. I spaced the entire bracket off of the block by one inch using 2 big nuts and one flat washer at each of the 3 mounting locations. This made for perfect alignment. It also made removal of the even side valve cover a breeze. The alternator used to block the valve cover from coming off when it was an inch further back.

Plumbing changes were needed for the electric water pump inlet. The inlet pointed right up too and almost touched the side of the accessory bracket. There was absolutely no room to get a hose on there. I used a bunch of 3/4" threaded plumbing to run the inet down, then forward, thu the middle of the drive belt, then down, then to the passenger side right near the radiator outlet. From there it connects to the radiator via a small 1 3/4 90 degree bent piece of radiator hose. It fits nicely, but if I ever have to change the belt, I will have to remove the bottom radiator hose. One day just for fun I'm gonna go into a jiffy lube and request that I get a new belt with an oil change :)

I upgraded to a Walbro in-tank hi performance fuel pump to satisfy the hi pressure(55-60psi) and higher flow demands of my 383. Thanks to a website I found, mentioned below, It was a total breeze. I decided to cut an access panel in the floor right above the fuel tank. The Racetronix website mentioned below had all the measurements laid out, so it was a simple cut.

The DFI controller has no provisions for vehicle speed, so I scored a couple stand-alone VSS buffer modules from a 1991 S-10 from the local junkyard. The purpose of this module is to convert the analog AC sine wave from the vss sensor into square wave suitable for use with various devices such as ABS, cruise, and the speedometer. The LT-1's PCM has this conditioner circuitry built in, and has conditioned VSS outputs. Unfortunately, the DRAC module didn't completely solve the problem. For some reason, the F-Car version of the T56 trans has a 17 tooth VSS reluctor wheel, instead of the mostly standard 40 tooth reluctor that the automatics, and even the aftermarket version of the T56 has. This 17 tooth reluctor produces a VSS signal to the DRAC that is out of the range of what the DRAC was designed to convert. It's pretty easy to swap the wheels, so I am going to go that route. Once I have the reluctor, it will only be a matter of changing the dip switch settings on the DRAC module to calibrate it to my 2.73 gear ratio, then once again when I switch to the 3.73 gear in a couple of weeks.

The tachometer is a similar story. I believe that the tach expects one pulse per revolution, where right now it is getting 8. That's a pretty simple bit of electronics I need to build (divide-by-8 counter).

So, as of Nov 11th, here's what I have left before I feel she's super long distance road worthy:

  • 3,73 rear end gear swap
  • 40 tooth reluctor swap
  • Correct the tachometer signal
  • Final fuel map and idle system tweaking via calmap. The idle wanders an bit and it runs a bit rich ATM
  • Interior PCM wiring cleanup and routing. The passenger seat and floor is currently a mess of electrical spaghetti
  • Hit the road, jack!

Finally, I would like to mention a couple of the internet resources I used to get the job done. These sites in particular were invaluable resources that I used daily over the course of the 3 months I worked on this car.

http://shbox.com
This site has the contents of almost the entire 93-97 F car GM service manual, most importantly the highly detailed electrical schematics and connector pinouts. I would have had to spend a fortune on a full GM service manual had it not been for this site. I can't thank the owner of this site enough for all of this information. If the owner keeps track of his webserver logs, he will see hundreds of hits from me to the ECM pinouts and Harness connector faces links :)

Racetronix fuel pump install page
I used one and only one thing from this page. It's the first image showing the measurements for the hole to be cut for access to the top of the fuel tank. If it weren't for having those dimensions, I would have never attempted to cut an access panel, and would have went thru the painstaking task of pulling the rear end and exhaust to drop the fuel tank. I had the whole fuel pump swap done in about an hour thanks to that single image. I give that image a 'best gearhead photo of the year' award :)

GM VSSB/DRAC Calibration page
This page has a table of all of the ratios to jumper settings for calibrating a DRAC module for vehicle speed, along with the equation for determining the ratio for any wheel, gear, reluctor tooth count combination.