DIY OBD-1 Varioram Conversion Step by Step (More or less)
 

Here’s a write-up of my OBD-1 V-ram conversion for those owners of 1994 and 1995 cars who may find it interesting and are adventurous enough to try it. Before I begin, a few notes/disclaimers:

First and foremost, I was fortunate to have the help of a fellow rennlister, Tal K aka “Guards Red.” Tal has performed this conversion on his early Euro spec 95. He patiently answered all of my questions (a fair number of the stupid variety) and provided invaluable insight into the inner workings of the v-ram system. Frankly, without his help, I’d still be out in the garage scratching my head. Rennlist is a great place because of people like Tal. Porsche people are good people.

Thanks to Mike J for pcarworkshop.com. This wonderful resource contains a large number engine pictures which were tremendously helpful.

This is not a small project. One of the greatest challenges is simply gathering all the parts (you’ll be looking at the PET a lot). And it seems (more and more these days) that every part needed is in a warehouse in Germany. This means you will have to wait for parts – this project took me two months to complete. Try to purchase as complete a v-ram as you can. This will minimize a lot of time and $$$ gathering misc parts.

I recommend checking the function of your existing vacuum system before starting this project. The vacuum system in the 993 is all connected (so to speak). Therefore, if you have a vacuum leak under your dash that you never noticed @#$$%^, your v-ram may not function properly and you will spend hours troubleshooting your v-ram connections only to find the problem in the last place you look!

I was able to complete this project using all Porsche parts – including the electronics! However, as they say, your mileage will vary. More on this later.

It’s a really good idea to do this project with the factory workshop manual in hand. The manual contains wiring and vacuum diagrams which are a great help in showing where things go and perhaps, more importantly, how the system works.

Depending on the choices you make in the install (although unlikely) your car may not pass your state’s visual emissions check In other words, you are on your own if you decide to take on this project.

Installation of the v-ram manifold will make your car harder to work on. It really fills the engine bay. And forget trying to impress your friends by revving the engine by grabbing the throttle butterfly under the hood. You’ll never see your throttle cable or butterfly again.

I am really happy with the conversion. It cost me less than $1500 and the result is an engine which is noticeably more responsive at low rpm and part throttle. Full throttle acceleration feels about the same. Engine-wise, the car is now almost identical to Euro OBD-1 cars. For US cars, this is the best of both worlds, the benefit of v-ram without the hassle of OBD-2. Best of all, it’s all Porsche.

Here’s the car with the 95 manifold in place. Start by evacuating the a/c system and disconnect and remove the a/c lines from the compressor and the driver’s side wheel arch connection. I placed plugs on the compressor and chassis a/c lines to avoid contamination.

Remove airbox, mass air flow meter and fresh air blower. At this point you can begin disconnecting the manifold. I took lots of pictures and tried to label all the electrical connections for easier reassembly. Most connectors are either color coded or only reach one plug.

Once the manifold is out, immediately stuff each runner with a clean rag. If you don’t, you risk dropping something into the engine – perhaps without knowing. Of course, if this happens you’ll now have an excuse to do 3.8 Ps and Cs and RS cams…..

At this point, you’ll need to decide whether or not you want to retain cruise control and you SAI system. Both can be relocated and kept if you are so inclined. If you want to keep the cc, you’ll need to buy the later mounting bracket and linkage. I’ll let you all guess what I decided to do with these.

If you do decide to delete the SAI system, be sure to replace the bolts that attach the oil gallery thingy with shorter bolts. If you forget to do this, chances are, you will likely have an oily engine and much more work to do. Getting the SAI tube on the passenger side of the car is somewhat of a PITA. I was able to disconnect it by loosening the fuel injector rail. Others modify a wrench to do the job. Patrick Motorsports makes a nice $14 kit to block the SAI ports.

Next you will need to address the 3 oil breather hoses from the oil tank. These are different on v-ram cars. I replaced the two larger hoses with the later v-ram hoses (See PET 104-01). The small diameter hose (it looks like a heater hose) I simply shortened and added a junction (this can be found on your old manifold). Adding a junction is important as it is very difficult to get to these hoses once the v-ram manifold is installed. You’ll want to attach these lines to v-ram manifold before you install it.

Next you’ll want to mount the vacuum tank (see pic) in the driver’s side wheel arch. The tank is specific to v-ram cars and is much larger than the 95 coke can sized tank (see PET 107-14). You’ll also want order 2 meters of both large and small diameter vacuum line and the little rubber connectors (I guarantee these will come from Germany). The lines are listed as numbers 29 and 30 in PET 107-14 without part numbers. The part numbers are 900-918-005-40 and 000-043-300-56. Take the larger diameter vacuum hose and run it from the vacuum tank through to the engine compartment through the grommet used by the charcoal canister line. Be careful not to kink the line.

Next, it’s time to address the electronics. NOTE THE FOLLOWING INFORMATION IS BASED ON MY ASSUMPTIONS AND CONJECTURE – YOUR RESULTS MAY VARY. I have always been under the impression that Euro and US car used much different ECUs. Through the process of deduction, I realized that is not really true. Here’s why (bear with me on this).

The US non-vram 993s used 3 different ECUs:

1. Early 95s (no drive block) – Porsche # 993.618.123.02 / Bosch # 0.261.203.163
2. Later 95s w/o Drive Block – Porsche # 993.618.123.03 / Bosch # 0.261.203.674
3. Later 95s with Drive Block – Porsche # 993.618.124.03 / Bosch # 0.261.203.675

* Note: Both 1 and 2 have been superceded by 993.618.123.06 (this is important as we’ll see in a minute).

Tal has an early Euro 95 which came with the (identical to US) 993.618.123.02. (I was always concerned about US/Euro fuel differences but again this is the same ECU for both sides of the pond. Anyway, he purchased from a “tuner” who shall remain nameless a v-ram conversion chip. It would not start his car. He subsequently bought a Euro ECU 993.618.123.11 / Bosch # 0.261.203.678 (non-drive block) which worked perfectly and operated the v-ram. Tal generously sent me the tuner chip to try in my car as I have the later (#2 above) ECU. It started my car right up. Bill Verberg has mentioned that he has had success in adding v-ram with simply a chip change. This led me to theorize that the difference between 1 and 2 above was the hardware to accommodate v-ram. Why else change the part number? And, as noted above the same ECU has superceded both 1 and 2. Further theorizing led me to believe that the difference in the later 95 Euro and US ECUs was just the chip to operate the v-ram. On a hunch I sourced a copy of a chip from Euro ECU 993.618.123.11 / Bosch # 0.261.203.678 from Steve Wong. The chip works perfectly and operates the v-ram. In other words, I essentially converted my 993.618.123.03 to a 993.618.123.11 by changing the chip.

S to review:

If you have number 1 above, you will need a later ECU and chip to operate the v-ram.
If you have number 2 above, a chip from 993.618.123.11 may work.
If you have number 3 above, a chip from 993.618.124.11 may work

Now onto the wiring. NOTE: THE FOLLOWING ASSUMES YOUR CAR HAS THE UPDATE RECALL WIRING HARNESS. For US cars you will need to piggy back to 2 connections in the ECU 55 pin connector. Euro cars without SAI will need to source one connector and piggyback the other. Don’t look for this connector in the 993 section of the PET – it isn’t there. Check out the 964 PET . Both Euro and US cars will need 2 bullet type connectors for the plug which attaches to the engine harness in the engine fuse box. I struggled mightily sourcing these until I realized that Porsche uses a BMW!! connector. The part number is 61 13 1 376 191.

You will need to run two wires from the ECU to the engine fuse box. Remove the driver’s seat, rear shelf and driver’s side rear panel to do this. Porsche has a lovely habit of using a very sticky glue to attach the carpet, so a heat gun is helpful to get under the carpet. I sourced a roll of cloth tape and used the correct gray/white and green/white wires from an old E30 M3 loom I had to maintain a factory appearance. Carefully open the ECU 55 pin connector and splice into the #1 and #32 wires (the locations are numbered but hard to see – you may need a magnifying glass). FYI - #1 is used to control the resonance flap and #32 is used for the SAI. Next remove the engine fuse box cover and find the 21 pin connector. You can remove this connector by sliding the “drawer” to the side (the drawer lacks the connector in place). Connect ECU wire #1 with a BMW bullet connector to #18 in the 21 pin connector. Connect ECU wire #32 with the other BMW bullet connector to #4 in the 21 pin connector.

More wiring pics

It’s now time to assemble ensure your v-ram manifold looks like this (see pic). Note that on the zinc plated “tree” the top connector is for fuel vapor, the middle is for the v-ram, and the bottom is for the brake booster (C2 only). Reference the factory vacuum diagram. Now is a good idea to test each of the actuators (the 3 round things on the manifold) with a vacuum pump. Attach the vacuum pump to each so that they move. Hold vacuum for a few minutes to ensure they don’t leak. You do not want to have to change these once the manifold is installed. Double check everything and don’t forget to attach the oil breather lines.

Solenoid pics

Your next concern will be the throttle cable. Note that the v-ram cars have a different cable, although the 95 cable will work. Most people think that the engine must be dropped a bit to install the manifold and attach the cable. I was able to do both with the engine in place. If you are careful and have some dexterity, you can attach the throttle cable with the manifold half-way installed and by opening the throttle a bit so the cable can reach. Once the manifold is in, you can fine tune adjustment under the car using the adjuster underneath the shift linkage near the transmission. Be careful not to damage the actuators when installing the manifold. It’s a very tight fit with the engine in place.

Next up it’s time to hook everything up. Connect the vacuum lines, oil breather lines, etc. Both Tal and I ran into a problem with the recall wiring harness. There is simply not enough length to attach to all the plugs on the passenger side of the car. This means that we were force to slit the sheathing to separate the wires. Also, the green knock sensor plug will not reach the bracket on the rear runner on the v-ram manifold. I’ve attached two different solutions to this problem. Tal, copied the RS and drilled an tap a hole in the manifold. Being lazy and discovering this issue once the manifold was installed, I mounted the bracket to the “bridge” between the front most runners on the manifold

Next mount the mass air flow sensor (loosely) and the inner air box. For those you 95 owners with no experience with the later style air box (you will need this for the conversion), it is much more of a challenge than what we are used to. Basically you need to mount the mass air flow sensor loosely and mount the inner air box. Then twist the air flow sensor to lock into the box. Then you will need to thread a tool way back into the engine to tighten the mass air flow sensor (my Hazet flexible nut driver was a godsend here). Next the a/c lines. The a/c lines are different although I think Bill Verberg adapted the early lines in his RS replica. I sourced a used set of later lines as they are very expensive new. Note the bracket I used above the fan. Most 95 cars do not have a mounting hole in the fan housing to attach the later style a/c hose bracket. Instead I used one of the brackets off my old lines (see pic). You can use the later style bracket along the driver’s side frame rail and attach with double sided tape (it’s not going anywhere). Finally, install the blower.

Note: I stole the second picture below from Mike J.

Start the car and run it a bit to build vacuum in the system. Turn the car off and then have a helper turn the key on to the second position. You should see all three actuators cycle. This is an indication that the v-ram is operational. Go for a drive and enjoy!

If the system doesn’t cycle ensure you don’t have a vacuum leak and that you’ve connected the system correctly. The factory manuals have a procedure to check. I'll do my best to answer any questions anyone may have.

Here's the end result.....

Holy cow!!! Nice write-up. Thanks for sharing.

WoW! Excellent write up. How much HP did you gain from this conversion and is a dyno run in the near future?


Ken

Excellent work Joe, looks great. The real beauty of it is that it looks totally stock and all the parts can be sourced from Porsche to keep it in fine fettle. Great pictures and a brilliant write up - though you have over played my role!

Best wishes
GR