I ran into a friend the other day and he is in the process of a remote turbo build on a 1992 3.1L camaro. He has a FMU for the fuel requirements but asked me about info on them with speed density. I have little advice for him so i figured id throw some questions out here.
1. With stock injectors, is a FMU capible of supporting 6lbs of boost?
2. What FMU ratio is good? 6:1, 8:1?
3. How much timing should be retarded to compinsate for the turbo setup.
4. Will speed density meter not work well with out a tune of somesort?
This is a cheep build and is only needed for 6lbs of boost. And any info is awsome....i plan another route on a turbo set up soon to come but love learning more about other types of buget builds. Thanks!!

 

An FMU will usually bump the fuel pressure enough to support low boost on an otherwise stock engine. This low boost is usually between 4 and 8 PSIG.

The ratio needed depends on the actual fuel requirements of the engine. This is where adjustable FMUs are nice. If you or your buddy needs one, I have one that bought, but never used myself.

Timing also depends on what the engine wants. Most people start at 2 degrees retard per pound of boost. Again this is where adjustable or even programmable timing controllers are nice.

The Speed density ECM, will just see the engine is at 100% load, or more correctly, 100 KPa when boost is present. The ECM then just uses the cells at this KPa to calculate fuel and spark delivery. The down side to this, is that the engine usually requires more fuel beyond the 100 KPa point, since more air is flowing in. This is where the FMU will work to add more fuel, whether it is enough or not, has to be tested for sure. The other down side is that the ECM thinks the engine will want a lot of timing due to what the ECM sees as the load point. Beyond 100 KPa, the timing will need to be reduced to reduce the possibility of detonation.

The engine will need the exact same requirements for fuel and spark up to and including the engine being delivered air at 100 KPa (atmospheric pressure, what an N/A engine would see at WOT), so the stock ECM will run the engine very much the same way as before the turbo is installed, provided the O2 signal isn't changed drastically, due to location or other possible things that could affect the readings. It is only beyond 100 KPa that the ECM, in stock form, can't compensate. This is why the best way to tune is to tune the ECM to see the added air flow, or in the case of the SD ECM, added manifold pressure.

There is code that can be used to tune the 3.1 SD ECM, but requires some knowledge or at the very least the desire to tune the ECM for proper fuel and spark delivery.

 

Ok , so I understand the FMU and the function of it. How much do you want for the Adjustable FMU and what brand is it? I know the fixed FMU's are roughtly $100 so im guessing the adjustable ones are much more.
Also, say we use a fixed FMU and it meets the fuel requirements of the boost, how exactly do you retard the timing 2 degrees for every pound of boost? So 5 psig would require 0degrees of base timing(since base timing is 10degrees as of now)??? Or are we talking Total Timing?>

We are working on the cheepest, but yet stable 5 or 6psig boost that we can. We would be exstatic with a 180Hp+ outcome, So total cost does matter. The whole exhaust section is fab.ed up already and now he and I are just trying to figure out how to run the boost and not blow the motor sky high.

Also colder plugs and higher octane(93+) will help lower detination...right?? Thanks for the advice!

 

I'll get back to you on a price for the FMU.

The timing retard is off of total timing.

The easiest way to control timing is with something like an MSD 6BTM. BTM = Boost Timing Master. This will allow the timing to be whatever is input to the ignition box, but once boost comes in, it will retard the timing 1 to 3 degrees per pound of boost as set by the control ****.

Higher octane and colder plugs help reduce possibility of pre-ignition, which is the mixture lighting off before the spark is created at the plug. There are other factors that can cause pre-ignition, but higher octane fuels and colder plugs are the easiest things to do to help reduce this possibility without opening the engine.

 

Ok thanks for the info.. Ive seen the boost timing master by MSD your talking about. One last dumb question... what it the total timing on the 3.1L. I know the base is 10* but have no idea what the total is. Thanks again for the help.