boosted_D

iTrader: (1)

Kinda long post, sorry, but needed to understand my reasoning!

So let me start by saying, I understand fmu's are a dated technology that are obsolete with modern tuning capabilities.

That being said, fmu's still have a place even in the Honda world. Example: my friend intends to boost his 99 civic ex (d16y8) on 6 psi from a small .42/.48, we live in NY and the inspection standards here are stringent on obd2 cars, if it won't scan with no codes, you don't pass inspection, period.

This is a logical reason to have a small boost set up, and want to keep the car obd2 with the stock ecu, so there are no problems at inspection time.
( I have to swap my injectors, and ecu back to stock, pull a charge pipe, and put 100 miles on my car to get it to pass inspection, and its a pain in the butt he doesn't want to deal with)

So....fmu and map check valve it is.

Trying to understand fuel consumption needs based on things like this calculator:
http://witchhunter.com/injectorcalc1.php

And this post:
https://honda-tech.com/forums/honda-civic-del-sol-1992-2000-1/%5Bfaq%5D-what-you-need-know-about-fuel-setup-1521170/

I'm trying to understand actual fuel needs for a set up like this.

My math (which could be completely wrong, as I'm no expert at this kind of thing, hence the reason for this post)

A bsfc of roughly .60 will achieve a safe AFR without being overkill.

Everyone recommends a 12:1 fmu for some reason, which at 6 psi would make fuel pressure 115 psi

Well 240cc injectors at 115 psi will flow 394 cc/min. This is way too much fuel for a roughly 160 whp set up, and obviously the pressure is too high, it would be nice to keep it below 100 psi.

For a bsfc of .60 on a 170 whp motor (aiming a bit high to be safe, really should be 160 whp or less)You would need about 315cc/min maximum flow.

To archive 315 cc flow on 240cc injectors, the pressure needs to be 76 psi.

A 6:1 ratio fmu would raise pressure to 80 psi, giving a total flow rate of 330cc. This seems like more than enough fuel, making the 12:1 fmu entirely overkill.

Does anyone with fuel system knowledge follow my reasoning here? Does it make any sense? Please tell me if I'm way off base!

TheShodan

iTrader: (14)

Heh. A lot of people won't answer this one because they weren't driving when these FMUs were still popular.

I have to be totally honest, I won't be able to help with your actual calculations, but when we used the FMUs with the 240cc injectors, we used 10:1 FMUs for anything lower than about 10psi for a turbo 51lbs/min or less, like a 57 trim. Wound up being just fine. You're going to get a lot of fuel pressure at the line anyway, that's the whole point of FMUs when they were used as they were a rising rate regulator. But it was only once you got into positive pressure.. It just so happened that Honda B-series fuel lines could take that increased pressure.. To a point.

OneBadTurboCRV

You can do calculations all day long, but as we know the real world dictates what the results will be. The rising rate isn't THAT exact of a science unfortunately, but they can work. I would personally start with an 8:1 and go from there. If you can't do it with technology, be prepared to buy different shim kits to "tune" it. Don't expect an exact AFR curve that is flat, there will most likely be blips one way or another. Worst case and typical tuning practices would tell you to start with more and back off to less. 10:1 would most likely be the logical compromise.

Either way, to plot it out correct on paper you would need to do calculations for every PSI to get an idea of what the curve will be. Rich tapering lean or lean tapering rich... very rarely will you see a nice curve.

Also, this is still the "accepted" way for some "older" cars.

boosted_D

iTrader: (1)

Thanks guys, I just wanted some confirmation that 12:1 was excessive.

I know you want a richer AFR because timing won't be tuned. 6:1 may be a bit lean to be on the safe side, I just can't decide if 10:1 or 8:1 is the better choice.

Shodan, what pump were you commonly using with similar set ups?

I will retard timing at the distributor, not sure how much it is adjustable at the distrib. Or how far I should take it.

OneBadTurboCRV

You can get away with a Walbro 255 standard pressure and not throw codes. At least this has been my experience. There are only two counties left in Indiana that require emissions testing and it is strictly OBD2 port. The car could be filling up the "Clean Air Check Station" with black/blue smoke, but hey, as long as it passes the readiness test - no problem. What I am getting at is we see these types of builds still from time to time.

Retarding the distributor much more than 2-4* you will experience drivability problems - mainly down lower in the RPM range. Bucking when the clutch is let out and things of that sort. There is a huge downside to doing these types of builds, and it comes down to detonation being the biggest problem due to lack of "fine tuning". Too bad Edelbrock discontinued their kits earlier last year... Hell, a lot of support has been dropped for 2000 and earlier when you take the time to actually look around.

Muckman

iTrader: (2)

I disagree with the original premise of the thread that this method is required to pass inspection. Tune via OBD1 but build your car so you can easily swap the OBD2 components back in once a year for inspection. ECU, injectors, Map, cat, O2s. I can swap mine back in under an hour. You can keep the turbo on just keep it out of boost until the readiness monitors are set then pass inspection.

xile6

2 words aem fic.

Fmu r ok but with that high fuel psi its going to be stress on the injectors.

wilham320

iTrader: (1)

AEM FIC or Greddy Emanage (blue or ultimate)... I used Emanage for about 8 years long ago. Much better tuning than you will ever get out of a FMU. You can retard timing in increments with boost, instead of just lowering base timing.

TheShodan

iTrader: (14)

Ironically we were still using OEM fuel pumps. Looking back on that, it wasn't the wisest choice but we didn't know any better back then. I'd use the Walboro 255 regardless.