Which FMU Is Correct?

[gingerbredman]

I say "mid" boost because, at least to me, 7-8psi is about half of what I'd ever expect to make lol

Anywho, first off I'd like to know why there are some people using an 8:1 fmu and a few using a 12:1 for their stock-block ka-t setups. Lots of people with turbo hondas like to run 12:1 for some reason and the only theory I've come up with is that an 8:1 would have to deliver 'more' fuel than a 12:1 fmu. Well, the honda clowns must think so..

However, I'm 95% sure that a 12:1 would add more fuel, hence 12psi of fuel pressure to every pound of boost, correct? and so forth..

So, would using an 8:1 fmu on a mid-boost setup be the utmost limit? I was planning on using a 10:1 but since everyone seems to like the 8 I figure I should do what works. Now, I'm going to run an atmospheric bov (stuf lol) because as long as it's taken me to simply get a turbo for my project I don't want to risk losing it to flutter, even if it means it won't retain stock driveability. I could afford the extra gas I'd spend, but if I had to break down and buy a frickin turbo I'd be screwed..It'd be temporary until I upgrade injectors and get a good ecu tune. So the point of all this blabber is "Will running an atmosheric bov with and fmu alter the ratio of the disk I'd need?"

Also, I heard one guy mention that using an in-line fuel pump along with the fmu is really good, any word on this? I mean with the hi-pressure in tank fp as well, of course.

You guys are probably gonna tear at me like old people on applesauce but I'm trying to bum my buddy's 370cc's for my project, problem is he won't do anything with his sr.. even after getting smoked by a lifted Caprice...

Enlighten me!

[WDRacing]

Um...your post kinda makes my head fog up a bit. I'd explain everything, but I don't know if you'd understand it

You want to use a 8:1 FMU for no more then 8psi. I'd retard your base timing a couple degree's just to be on the safe side. Anything higher then a 8:1 will make you run really rich.

I'm changing your title because it's awful. Try being descriptive and simple so people will understand what you're saying.

WD

[gingerbredman]

Sorry boss, I'll make sure to try and refine my stuff before I type it down next time. I've just been trying to polish my knowledge and understanding down, I stayed up the other night for hours going over theory's and formula's and such and I was pretty fogged up when I posted.

Thanks for your input btw, appreciated

[oz240red]

Second what WD said.

I was running a 8:1 FMU with a turbo kit set at 7psi. I also dynoed it and it was on the rich side, but after 5500rpms it went a little rich, 12.5

However, I also put a Walbro 255lph instead of the stock fuel pump. That is very recommended if you're using the stock injectors.

The fmu + 7psi + Walbro 255 has been used a lot by other members and I rode like that for 3k miles with no problems. I think it's a great start up options. Just know your limitations so that your engine doesn't suffer too much. If you care about your engine that is, lol.

[nelson8708]

I put 15K on my t25, fmu, walbro setup.

[WDRacing]

I put 15K on my t25, fmu, walbro setup.

Like I've been saying for years, against the popular uninformed opinion of most, the FMU is a fantastic and affordable way to to control the added fuel needed for a low boost set up. It gives repeatable results almost everytime, it's cheap AND reliable. Which makes it somewhat unique since those two words are seldom used together.

WD

[deevietboi]

well, while this post is up i might as well ask some questions

well lets just start by saying im going to be doing a ELCHEAPO turbo setup! my goal is a simple 200-240 hp, just looking for a more enjoyable drive in the SOHC (sense turbo swaps are illegal here its not the route im looking for)

my buddy gave me the whole turbo pieces free from his s13 redstop SR(manifold,turbo,smic and piping, downpipe)

going to be using stock injectors, stock maf, FMU and either a z32 fuelpump+fuelfilter or a walbro

the plan is to run this untill the motor gives(ka24e with 187+K) and sense i live in california and are smog laws are so LAME, i will be removing this turbo when its time to get new tags and smog, then reintall

with a simple setup like that i shouldnt need to mess with the ECU right? just retard the timing a little and im good?

[gingerbredman]

Does the sr manifold fit the ka-e?

Nah like you said retard timing a few degrees and it should be fine, at least through all my searching that's what seems to be the solid answer.

Another question, what brand of FMU has pretty good background? I've heard mostly good about Vortech FMUs but they're a little more expensive than the Blox or OBX ones off of Ebay. I've seen some people are using Cartech FMUs and I looked on their site and apparently they are 'adjustable' I've searched some, but couldn't get anything specific..

..and yeah I retract my previous statement about running an atmospheric bov.. I'm going to run it recirculated. My head's been full of CNC stuff here lately

[gingerbredman]

Btw the ka24de they boosted in one issue of Sport Compact mag put down around 225whp iirc and at 7psi. That was with a Holset turbo and I can't quite remember the specs on it, but after doing the math it turned out to be about 12whp per psi of boost. I figure a solid 10whp is reasonable to guesstimate.

I'm thinking about 200-220whp with my setup, I just hope I break the 200whp mark

[C-Kwik]

However, I'm 95% sure that a 12:1 would add more fuel, hence 12psi of fuel pressure to every pound of boost, correct? and so forth..

Yes.

So, would using an 8:1 fmu on a mid-boost setup be the utmost limit? I was planning on using a 10:1 but since everyone seems to like the 8 I figure I should do what works. Now, I'm going to run an atmospheric bov (stuf lol) because as long as it's taken me to simply get a turbo for my project I don't want to risk losing it to flutter, even if it means it won't retain stock driveability. I could afford the extra gas I'd spend, but if I had to break down and buy a frickin turbo I'd be screwed..It'd be temporary until I upgrade injectors and get a good ecu tune. So the point of all this blabber is "Will running an atmosheric bov with and fmu alter the ratio of the disk I'd need?"

Running much over 8 psi on available fuel pumps probably won't do any good. As flow increases, it becomes more difficult to keep the pressure up. At some point, regardless of what FMU ratio you run, the fuel pressure will stop increasing. At this limitation (which will vary with pump size and perhaps condition of the pump), fuel flow will be the same, but the differences seen will be how quickly the system reaches this limit. Higher FMU ratios will run richer sooner but will ultimately lean out as it reaches max flow.

The only real fix is to build a higher pressure system that can keep up with the flow as well. Doing so would likely require a expensive pump with custom work to fit the pump in the tank correctly and possibly increased fuel line sizes. Not to mention as pressures increase you'll be heavily taxing lines and connections. I'm also not sure if too much pressure might affect injector operation either.

Also, I heard one guy mention that using an in-line fuel pump along with the fmu is really good, any word on this? I mean with the hi-pressure in tank fp as well, of course.

An i-tank will be more than adequate for this type of boost. Beyond this, its likely, going with a set of larger injectors along with a piggy-back to control them will not be much more.

You guys are probably gonna tear at me like old people on applesauce but I'm trying to bum my buddy's 370cc's for my project, problem is he won't do anything with his sr.. even after getting smoked by a lifted Caprice...

Not sure what a set of SR injectors are going for these days, but they were pretty cheap when I got a set years ago. But you'll still need a piggy-back, a tuned ECU, or a stand-alone to compensate for the larger injectors...

[carheadman]

im runnin an 8:1 myself with 7psi on a t25, works great, does backfire though

[hpmachine]

I'm seriously thinking about going this route myself. Has anyone here run this setup and watched their air fuel ratio with a wideband while driving? How has the fuel economy reacted?

[WDRacing]

It's usually overly rich when boost comes on. But then recovers pretty well and hangs out in the 11's. It might lean out though depending on the fuel pumps health and type.

WD

[pancho y onions]

Im glad i ran into this. I will be running a begi 7:1 fmu (cartech) with a 255 pump and colder plugs and back up the timing by 2-3 deg. I wont be running no more than 6psi since im running a t3-t4. I belive it should be fine. And yes the cartech FMUs are pretty nice. Some come with onset of gain which lets you adjust it when you want the fmu to basically come on.

[GODCHSR]

... kill me now... How do we change the timing on these cars without hacking the ECU?

[DMan II-40]

I was thinking of getting a MSD BTM, haven't really read alot about it though so I'm not really sure. I have other stuff i want to read about that are more interesting to me right now.