so hving problems finding a cartech, so i was wandering what other fmu's you guys are running and as well what ratio. btw ditched the turbo back to stock (except bolt ons) and got a m45 with the 2.7 pulley. ive searched and havnt got a clear answer yet. flame on!
I mean I could find the unit but not a clear answer about what ratio to use
thanx ordered the begi, reman unit for cheap! thanx for the link again
the ratio is depenent on boost and f/press.say you're going with 8psi and boost f/press @80psi minus rail f/press from 80psi say [40psi] leaves you w/40psi. divide that by boost,you get 5:1
thanx c2s and pete for helping me understand this
you ditched the turbo for a supercharger???? the horror!!!!!!
lose the fmu and get an actual tune.. an fmu is not a tune. it just exponentially rasies fuel pressure dependent on boost pressure so there is no real accuracy to the afr.
JOE L wrote: an fmu...just exponentially rasies fuel pressure dependent on boost pressure so there is no real accuracy to the afr.
I must take exception with this statement. On low boost applications, FMU's obtain
quite precise AFR's. Fuel pressure is no less efficient a deteminant of fuel delivered than is injector pulse width.
While a 2-bar operating system and PCM tuning can offer more overall tunability (providing one has the vehicle, knowledge and tools to use such), not every application needs that degree of options. Under ten PSI of boost, and using 93-octane fuel, an FMU is a wonderfully simple and easy-to-use option.
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
im sorry. 2 turbo's and lack of tuning options i was done with it, car sat for like 3yrs and im tired of it sitting in the garage so i wanted a lil bit more reliable. i plan on swaping wire harness and pcm/ecu's but dont know when im trying to get rid of a few high priced items but times are tuff and i dont want to give this stuff away. therefore hptuners is still far away right now
Bill Hahn Jr. wrote:JOE L wrote: an fmu...just exponentially rasies fuel pressure dependent on boost pressure so there is no real accuracy to the afr.
I must take exception with this statement. On low boost applications, FMU's obtain quite precise AFR's. Fuel pressure is no less efficient a deteminant of fuel delivered than is injector pulse width.
While a 2-bar operating system and PCM tuning can offer more overall tunability (providing one has the vehicle, knowledge and tools to use such), not every application needs that degree of options. Under ten PSI of boost, and using 93-octane fuel, an FMU is a wonderfully simple and easy-to-use option.
thats very disappointing to see this posted by you. fmu's are not precise. they just exponentially dump fuel. only a certain rpm and boost range are the afr's accurate. the rest of the rpm and boost range they just over fuel the engine. they get the job done on low boost applications such as 6 psi or less but i would never use one with 10 psi boost as fuel rail pressure is tremendous. theres more to tuning than fuel so an fmu is not a tune. its a cheap way to boost and richen your afr's to allow your engine to survive boost but there is no tuneability. your engine will always run rich and produce less power than a professionally tuned engine. fmu's were great in the early to mid 90's as there was no other option. this is 2010 people. fmu's should not be used. instead of an fmu go ahead and replace your stock fuel pressure regulator with a 1:1 boost referenece fuel pressure regulator and get a professional tune.
boosting a n/a vehicle is not cheap. its constant maintenence and investment as n/a engines werent designed for boost. so expect some expense down the road. skimping on a quality tune will lower reliability and cause engine damage. if you want cheap boost by a used stock boosted car because there is no such thing as cheap boost.
JOE L wrote:Bill Hahn Jr. wrote:JOE L wrote: an fmu...just exponentially rasies fuel pressure dependent on boost pressure so there is no real accuracy to the afr.
I must take exception with this statement. On low boost applications, FMU's obtain quite precise AFR's. Fuel pressure is no less efficient a deteminant of fuel delivered than is injector pulse width.
While a 2-bar operating system and PCM tuning can offer more overall tunability (providing one has the vehicle, knowledge and tools to use such), not every application needs that degree of options. Under ten PSI of boost, and using 93-octane fuel, an FMU is a wonderfully simple and easy-to-use option.
1. fmu's are not precise. they just exponentially dump fuel.
2. only a certain rpm and boost range are the afr's accurate. the rest of the rpm and boost range they just over fuel the engine.
3. ...there is no tuneability.
4. your engine will always run rich and produce less power than a professionally tuned engine.
I suspect you dont actually understand the true functionality of an FMU, as you've made many inaccurate statements above. I've separated them and numbered them for easy reference.
FMU's are proportionate, in that they add fuel in varying amounts according to changes in boost pressure. You seem to be of the impression that they simply add a fixed amount of fuel no matter what the boost pressure, and that's an incorrect notion.
If anyone would like me to elaborate on these four points, just ask, and I'll be happy to expound.
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
ok, so im goin to lay it down... i know i need to find a 97+ pcm and harness and a couple of other thing to run hptuners.. im ass deep in emanege stuff (i had i hb civic but rolled it) and need to sell cause i have the hp money right there. i am going to do it but i needed to buy some time.. thanx allot bill for not flaming me cause i know its not the 100% way to do it but it will be safer for now. not like i drive everyday now anyways
The only real issue I see with using an FMU (apart from approaching dangerous rail pressures with high boost) is that you assume VE changes as a fixed percentage relative to boost pressure for all RPM's...This is hardly the case, but it's certainly a good enough approximation to maintain desirable AFR's on low boost as Bill mentioned.
Also, I can see how an FMU would be highly desirable with an ALPHA-N fueling scheme during transience (especially on larger turbos). No professional tuner in the world can tune this kind of condition with an ALPHA-N PCM better than an FMU.
I have no signiture
I forgot you said you have a supercharger...
I have no signiture
Whalesac wrote:The only real issue I see with using an FMU (apart from approaching dangerous rail pressures with high boost) is that you assume VE changes as a fixed percentage relative to boost pressure for all RPM's...This is hardly the case, but it's certainly a good enough approximation to maintain desirable AFR's on low boost as Bill mentioned.
Also, I can see how an FMU would be highly desirable with an ALPHA-N fueling scheme during transience (especially on larger turbos). No professional tuner in the world can tune this kind of condition with an ALPHA-N PCM better than an FMU.
Right you are!
High rail pressures can be one drawback of an FMU system, but this is why in most all of our FMU-equipped systems, we also provide larger-than-stock injectors which thus enable us to reduce idel fuel pressures considerably. Doing this expands our range of usable boosted fuel pressures nicely, and allows us to also avoid dangerously high full-boost fuel pressures.
Some are surprised to learn that, within reasonable pressure ratios (less than 2.0:1, or 15 PSI boost), the VE curve stays near identical in the boosted condition as it did normally aspirated. We've seen this time and time again in comparing not only AFR results, but power curves with testing before/after boosted cars (including those FMU equipped). The power curve shape and proportion is identical at the new boosted condition, just (needless to say!) much higher. As such, increased fuel pressure proportionate to boost performs accurate enrichement nicely, with no PCM changes needed.
Why is this? At moderate boost pressures, while the addition of the turbocharger certainly has some small effect on overall VE characteristucs, it's a minor one at these low boost pressures. The major determinants remain camshaft and cylinder head design, and their interaction with the engine's bore and stroke...all constants that, of course, are not altered by the addition of boost. This is also why we typically do not advise head or cam changes on moderately boosted engines, for such changes WILL change VE dramatically, and create the need for major remapping of VE.
And yes, as you note...on a 1-bar ALPHA-N, no amount of PCM tuning can provide propotional boost fueling. The PCM simply cannot read boost, so it cannot scale fuel delivery to accomodate different load conditions or boost pressures. Such cars are perfect candidates for FMU to provide this proportional fueling factor. Should the owner desire, he can also then incorporate PCM tuning to address other factors such as ignition timing, speed limiter, etc,. However, it's important to note that at our standard systems' 8-10 PSI boost, stock ignition curves are suitable when used with 93 octane fuel...so ignition remapping is not even required.
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
