What size fmu

[mitsocruiser]

I am starting on my turbo journey and I'm trying to figure out what size fmu to use when searching the post you get some different answers I'm just looking to boost 6 to 7 psi I always thought you used a 12/1 but then one thread said 1/1 I found a vortech 10/1 fairly cheap would this work ?? or just stick with the 12/1

 

[1slow97]

12/1 will work for you.... If you are running portfueler or megasquirt 1/1 is what you will need...

 

[cs82685]

A 12:1 is what's usually recommended (as said above, a 1:1 is used for the portfueler or megasquirt)

You should also be fine with a 10:1

Here's a great article on the fmu to use

Project Sleeper Fuel Setup

 

[Car_guy_09]

12:1 if you dont have a wideban.

10:1 if you have a wideban and can make sure its running good.

 

[mitsocruiser]

I had read that 420a sleeper project and it made me wonder which one was right then I read the fuel section and it said with a 255 hp lph walboro pump we would just barely met the fuel requirement for 8 psi of boost . This maid me start to wonder the harm of putting in a 12/1 even if it's over sized it can still only supply as much fuel as the fuel pump can put out correct me if I'm wrong . I'm looking for a basic turbo set up like I said 6-8 psi of boost Im just looking to give it that little push on the low end nothing major for now. I only drive 3 miles round trip to work the car is mostly for weekend fun. I have a nother question if I run low boost wouldn't I be better off with a larger wastegate to help expel that large amount of exhaust and if this is right what sive wastegate to use . Thank for the help in advance !!

 

[dsmdragon]

Well when it comes to wastegates ( depending out internal or external) comen that people use is 35-38mm. that will flow just fine. but most of all you have to worry about is the psi rating on the spring. just so you know 5-6 you should use for everyday driver. and 7-8 when racing, but that's just to keep the engine alive for a longer time. when at this low of boost you don't really have that big of a problem with size of a wastegate.
Oh and with the fuel q? if you buya SFMU youcan tune it for idle. and you can select what fuel disk range you want to use. This is also A good idea if you are using bigger injectors. but on stock injectors use a normal old FMU with 12:1 so you have enough fuel at low rpm's/boost and at high rpm's/boost. But you can not tune with an FMU

 

[mitsocruiser]

What advantage does a sfmu give you isn't a fmu that you can adjust if thats the case wouldn't one of those air bleed valves vortech sells for around thirty bucks do the same thing ?? Another question I have is do you have to replace your fuel pressure regulator to a after market one that is adjustable to help add fuel or is the fmu alone enough ?? One more thing while I'm killing the topic do you have to have a bov with this low of boost and if you have a bov do you have to have a wastegate . I know that together it helps turbo surge but with this low of boost do you have to have both or is one better then the other ??

 

[Locke]

A BOV and wastegate do two seperate things. The wastegate controls maximum boost level, the BOV releases excess boost pressure from the intake when the throttle is closed to prevent/combat compressor surge.

You don't really NEED a BOV at lower boost pressures, but it does ensure the longevity of the turbo. Many of the older turbo Dodge's came from the factory without BOV's. It is recommended to use one, though.

The SFMU allows you to adjust rate of gate and base pressure. A FPR is not needed when using a SFMU. A FMU is unadjustable, and provides a set rate of gain. Using an adjustable FPR with a FMU will not work well, while you can reduce static pressure to idle larger injectors, your rate of gain from the FMU will be stuck too high for bigger injectors. AFPR's are not needed with these basic types of fuel management.

 

[mitsocruiser]

Thanks locke you have been a big help ever since I joined this site time and again. One more question is it worth getting the vortech bleeder valve with a fmu to help in fine adjustments ??

 

[Locke]

I wouldn't bother with it, personally. The 12:1 FMU barely keeps up with 8psi. (the 255HP cannot flow enough fuel at the insane FP's caused by the 12:1) A bleeder will prevent the FMU from seeing actual boost, and will in-turn supply even less fuel.

 

[rstare]

I wouldn't bother with it, personally. The 12:1 FMU barely keeps up with 8psi. (the 255HP cannot flow enough fuel at the insane FP's caused by the 12:1) A bleeder will prevent the FMU from seeing actual boost, and will in-turn supply even less fuel.

Still don't understand how the 255hp can supply enough fuel at 8psi...
53psi from the stock fpr. 12 x 8 = 96 96 + 53 = 149psi
The pump pretty much bottoms out at 140psi.
Chris is the only one who I really know of that actually encountered a problem with this. Alot of people have had this setup for a long time though.... Of course most other people that use this setup don't have a Wideband 02 sensor to really tell.
Here's his (Chris') thread
http://www.dsmtuners.com/forums/420a-engine-management/289811-super-lean-i-need-advice.html

 

[chris712vt]

I'll just throw a little bump into this thread .

+1 to what Ryan said about the 12:1 at 8psi demanding pressures in excess of what the 255 is capable of producing. I had that problem with leaning out on the 12:1.

+1 to the other advice you have already gotten.

I just wanted to throw this out there... I have a BEGi adjustable FMU I don't use that I can sell. Not an SFMU because you can't change the idle/static fuel pressure, but it is better than the standard 12:1 FMU in that you can adjust the gain rate (2:1, 4:1, 6:1, 10:1, 12:1, whatever) by turning a knob. BEGi is Bell Engineering, Corky Bell's company the author of Maximum Boost.

I also will be selling my Vortech SFMU as soon as I get my MSnS installed, hopefully this or next weekend. I won't need my 450cc injectors anymore either.

And I think I have a Turbonetics Delta II wastegate with a 7 or 8psi spring in it somewhere... I may have sold that but if I find it that's available too.

And.... a 2.5" T3 5-bolt downpipe, 2.5" Tsudo N1 catback, T3 with shaft play and blown oil seal, 50 trim with shaft play, etc etc. I keep upgrading and never unloading my old parts, I need go through it all and make a big for sale ad.

Sorry, shameless plug . I figure it could help if you're looking for used parts and didn't find what you need in the classifieds. Yes I know this thread is a couple weeks old too haha.

 

[chris712vt]

wow Ryan... I just looked through that old thread of mine you linked. What a disappointment. Can't wait to redeem myself on my next trip to the dyno. Hopefully double that with a safe AFR.