Itb Installation

Mercedes 2.3-16 ITB Installation: ITB’s will work on a 16V Mercedes and work well. There have been many posts on the pros & cons of ITB’s, a few abortive attempts at group buys, and many pictures of different ITB set-ups but no write up on an installation, problems and solutions. I will try to fill in the gap….. Starting point: A 1986 Euro 2.3-16 with MegaSquirt EFI using a BMW 65mm throttle body, MegaSquirt controlled distributor less EDIS coil-over-plug ignition, Bosch 300cc injectors and a 2 1/4” exhaust system. The quality 16V MS kit as supplied by Silver Cosworth made the conversion easy: the entire Merc injection system (except the intake manifold), the entire Merc ignition system, the ECU, and related wiring were removed and replaced with the MS ECU and wiring loom. A single Volvo electric fan, shroud, & relay mounted behind the radiator and controlled by MS replaced the engine driven and standard electric AC fans. The MS conversion is now 3+ years old and works great: smooth, easily tunable, dead reliable and fast: I have seen 255KPH on the clock. The MS EFI conversion transformed the car and was well worth the cost & effort.

If you are not into ITB’s stop here and just go for MS EFI. Silver Cosworth’s kit makes it almost idiot proof. It’s the best thing you can do for a 16V (or for an 8V).

Starting point for the ITB conversion: 1) a fine running, strong EFI car and 2) good MS knowledge/experience. Jumping into ITB’s without either is dumb and a quick route to frustration and a bad running car, if it runs at all. Trying to do both at once will leave you without usable transport for a long time while you try to figure which of the tuning problems are MS related and which are related to the ITB’s.

There is no quick way around it: do the EFI first, get the car running really well and then think about ITB’s. The ITB’s:

Ex-eBay: an early AMG set of 52mm ITB’s for a 2.5-16V. They were not cheap but they are super rare, made for the 16V engine and eliminated the need to chop a standard 16V intake manifold and adopt after market or E-30 BMW or motorcycle ITB’s. I have never seen another set of the early AMG ITB’s so the chop and adopt route is probably the only way to go unless someone recasts the AMG bodies. The following pix is a cut 16V manifold with welded-on flanges to accept Weber pattern after market ITB’s. A nice solution.

The ex-eBay AMG ITB’s were powder coated and: 1) a 3/8” vacuum port was drilled & installed on each throttle body; 2) each throttle body was drilled and tapped to accept Weber air bleed screws. We built a vacuum manifold out of 3/4” square SS tubing with four 3/8” bungs for ITB vacuum, a small bung vacuum source for MS & the fuel pressure regulator, and a 5/8” bung at the rear for brake servo vacuum.

Two of the 3/8” and the small vacuum bung on the square tubing manifold can be seen in the above pix. The 3/8” vacuum ports on the ITB’s can be seen to the right of the Weber bleed screws. We had a pile of throttle linkage bits left over from old projects and made up linkage and a 1” X 3/16” throttle linkage and fuel rail hold-down bar that fit over the 3/8” ITB vacuum ports.

The above pix shows the throttle linkage bar, linkage, fuel rail and the hose connectors between the ITB body vacuum ports and the vacuum manifold. The Merc 16V oil filter unit interferes with the ITB set-up. The standard 16V intake manifold is skewed slightly forward to clear the unit. It may be possible to get around this on a chop-&-weld ITB conversion but with the AMG bodies the oil filter unit had to go and a remote filter and thermostat unit installed. Thorsten supplied an AMG copy oil filter adopter plate. Perma-Cool supplied the remote filter hardware and the thermostat. The whole “mess” is plumbed with 15bar @200degC rated oil hose. We used normal hose clamp connections for two reasons: space and cost. The hose, clamp fittings & hose barbs are rated way over anticipated duty but are not as pretty as Earl’s costly bits.

The remote oil filter and mounting plate attach to the block using vacant stud bosses. The thermostat unit is strapped to the chassis box section. An after market oil cooler is mounted in front of the radiator. The original AMG plenum would not fit so a fiberglass plenum was made with a large enough “nose” to accept an air filter element and still clear the surroundings. The reservoir on top of the Merc power steering pump interfered with the air intake plenum so the reservoir was removed, a remote PS reservoir adopter plate made and a remote PS reservoir mounted on the fender well next to the ABS unit. All the above took a lot of time: chasing parts, waiting for component delivery, getting friendly and accepted by the machine shop and welder. Everything except the throttle

bodies had to be sourced or fabricated. We are lucky to have a fairly complete home workshop and piles of left over bits from past projects: don’t ever throw anything away. Time was not a factor, the ITB’s would get fitted when they got fitted: we had a fine running fast everyday 16V and a spare engine to trial fit everything and work out mounting problems so it was 18 months after buying the ITB’s before a leaking head gasket provided the opportunity to fit them. With the head off the oil system went right on. The ITB’s went on with the head. TPS mounted & calibrated, fuel lines attached, oil system primed….. it started first turn of the key……

……and ran pretty well, the throttle butterflies needed synchronization and a few throttle spindle/butterfly vacuum leaks sealed with liquid electrical tape. Total head gasket replacement/ITB conversion time: 2 full days. The Result: Going from a single 65mm throttle body to four 52mm ITB’s on a 2300cc engine is a big jump. A lot needed to be changed in MS from the previous single throttle body configuration. This is when MS knowledge and a bit of experience paid off. We changed from Speed Density to Alpha-N, played around with the VE and acceleration enrichment numbers,

made a few test runs adjusting VE using a wide band AFR meter. After a few more hours and runs we had a car that starts instantly, hot or cold, idles rock steady and pulls smoothly from idle to 7000rpm….and goes like hell. Total tuning time: say 4 to 5 hours. ITB’s are known for off-idle stumble but with a good MS VE table and sensible acceleration enrichment numbers there is no stumble. Acceleration (hard or gradual) is seamless and registers a 12.5 - 13 AFR all the way up. Response is instant. Some people may disagree, but MS is a very cost effective, user friendly and flexible EFI system. There is not much it can’t do. The results speak for themselves. The car is very fast and a joy to drive.

The only bitches: 1) with the improved gas flow and efficiency the exhaust note has sharpened so we need to fit another resonator to quiet it and 2) I am retired and need a new project……….I have a spare MS ECU, saw a nice Datsun 510 for sale and know of two Alfa Romeo Montreal V-8’s sitting in a shed. Questions/Comments: e-mail me [email protected] Regards, bobf (Feb. 9, 2007)