What to use in my FMU? 10:1 or 8:1

[JJ95GTID]

Greetings all ,

My 5.0L blew a head gasket. Could be a few different things like using the stock fuel system with a 12:1 FMU, no bypass valve, stock heat range spark plugs, etc.

I am using an old school ball drive Paxton GSS that sees 7psi of boost @ 5700rpm.
This is all I ever plan to use with this car.

What I have purchased so far is a 190lph in-tank fuel pump, 24lb injectors and a MAF cal'd for them, and a bypass valve kit.

I want to update the FMU but Vortec list both 10:1 and 8:1 for 24lb injectors.
So, which one would you recommend and why?

BTW, I did email Vortec. They didn't reply.


Other mods are:

Explorer intake
FRPP Y303 heads
1.7:1 roller rockers
BBK E/L headers
Pypes catted X-pipe
Pypes catback
3.73 gears

The times in my sig were running NA with u/d pulleys before the supercharger.

 

[96stangRC]

Honestly, I would not screw around with an FMU. I know they are cheap and work to an extent, but they can be a headache. Do yourself a big favor, sell the 24lb. injectors and the 24lb. calibrated mass-air meter (or get it recalibrated) and pick up a set of at least 42lb. injectors, a correctly calibrated mass-air meter, a 255lph high pressure in-tank pump, and a 255 inline pump as well (T-Rex or similar). Next get the car to a good shop and have it dyno-tuned to make sure you have a safe air-fuel ratio. Another handy thing to have in a blown car is a wideband to verify your air-fuel ratio at all times to let you know if your car ever runs lean due to a pump failure or other problem. AEM makes a very nice wideband for around $300. I know all of this seems expensive and it is, but when dealing with a boosted car it is 100% necessary in my opinion and will save you many headaches down the road as well as money in the long run by preventing serious damage. You've already come this far to have a H/C/I blown car, finish it right. Just my opinion on this subject as I have seen what can happen when people put blowers on cars without an adequate fuel system and tuning.

 

[HGFireHazard]

I don't have any experience with the FMU or the discs, so I can't comment on that. I can, however, also support some of the items mentioned above.

If you can afford to upgrade your injectors, MAF and fuel pump, it would be greatly to your benefit. A HP 255 fuel pump is all you need, so don't bother with the t-rex or any other in-line pump. I am currently using both and the t-rex has caused me several problems, including being stuck on the side of the road. A pump as mentioned above will support you to and above 500 hp and has plenty of pressure for that 7 psi you mentioned.

If you can't afford all of that and a tune, I bet someone else can recommend what disc to use.

 

[PUNISHER RACING]

THROW AWAY THE FMU OR EBAY THAT SUCKER AND GET SOME 36 LB INJECTORS I AM USING CAPS BECAUSE I AM STRESSING THE POINT , TO DITCH THE F M U !!!!!

 

[Stanger007]

I agree fully on the tune. More to the point on your question, however:

How about a cheap wideband (Innovate LC-1, PLX m300) then start rich and work your way leaner with the disks?

Wes

 

[final5-0]

Greetings all ,

My 5.0L blew a head gasket. Could be a few different things like using the stock fuel system with a 12:1 FMU, no bypass valve, stock heat range spark plugs, etc.

I am using an old school ball drive Paxton GSS that sees 7psi of boost @ 5700rpm.
This is all I ever plan to use with this car.

What I have purchased so far is a 190lph in-tank fuel pump, 24lb injectors and a MAF cal'd for them, and a bypass valve kit.

I want to update the FMU but Vortec list both 10:1 and 8:1 for 24lb injectors.
So, which one would you recommend and why?

BTW, I did email Vortec. They didn't reply.


Other mods are:

Explorer intake
FRPP Y303 heads
1.7:1 roller rockers
BBK E/L headers
Pypes catted X-pipe
Pypes catback
3.73 gears

The times in my sig were running NA with u/d pulleys before the supercharger.

Hello Joe

Just in case you don't know

When you see FMU ratios of 12:1, 8:1, etc, the whole focus is on raising
the fuel pressure to fatten up the mixture under boost.

The first number in the ratio represents the amount of raised pressure.

The second number in the ratio represents the amount of boost

With a 12:1 disk at 7psi you would see around 84 additional psi

Of course ... the larger inj you select ... the less pressure you would need
thus
You typically would use a lower ratio disk for less fuel supplement

Again ... just in case you didn't know

It has to eventually boil down to this ... No Matter What :Word:

Without a wide band ...
You just don't have anyway to verify you are safe
and
Won't be melting pistons

One last thing that you need to address Joe

Are you certain you are not pegging your maf with that blower

Good Luck Joe

Grady

 

[JJ95GTID]

Yea, I hear you guys on the Wide-band A/F gauge. I already picked out a couple that I like and will get one.

Grady---yes I understand the workings of the FMU----Thanks for laying it out though. Your help is always appreciated.

I am thinking the 190lph pump should be able to flow the fuel at those pressures. But, maybe not. As pressure increases, flow decreases with FMUs.

As for getting it tuned on a dyno that is not likely. There is one shop in town that tunes with SCT hardware but they deal with FWD/AWD tuner cars. Or, I can drive 8 hours to Portland to get it tuned.

With this SC peaking at 7psi I was hoping to get by with the FMU setup.
They gotta work....right? Not like I am running 8-25psi of boost.

 

[Stanger007]

The FMU will work at that low boost, but you leave power and more importantly, safety on the table. Sounds like you are sorta on a low-buck budget. Jumping up to a custom tune will add some parts to your shopping list such as a MAF, injectors and possibly modifying your CAI to accept them. Then the cost of the chip/tune. $++

You know how it goes though, nothing in this hobby that is of good quality is free -- you get what you pay for -- (like my advice haha). Typically quality/performance go hand in hand with cost.

If you are buying a pump, get a 255 high pressure pump. That will keep you going if you decide to up the ante.

Wes

 

[final5-0]

I gotta kinda echo what Wes said

To answer your Q ... Sure they work
but
Like all things ... Considerations need to be known

I've seen two main shocking things said about using FMU's

1) You never want the hose on the FUM to become blown off as it is instant
lean time and you have a very good chance to pop a hg before you even
know something has happened

2) You know they are purely mechanical in operation ... so if one fails by
sticking ... you can pop a hg in an instant as well

I understand about not having much support in your area
so
YOU ... have to take charge

I'd start out with a main focus and priority of researching widebands that
give you the ability to datalog and upload to a laptop.

YOU MUST HAVE HARD DATA :Word:

To be efficient with your self tuning efforts

To bottom line your objective

Start out very fat ... Look at your data ... Lean back in little steps

You just can't leave this kind of stuff to chance

Grady

 

[Black95GTS]

There is no doubt that you are pegging your MAF. 7 PSI is about 1/2 an atmosphere, which is about 50 percent more horsepower from the blower.

Figure you have, on the low end with your mods, 240 RWHP. If you add 50% more, you get to 360, which is about 60HP over what a stock MAF is typically good for.

A new MAF / Injector setup is critical path IMO.

Adam

 

[JJ95GTID]

Black95GTS---I did mention above that I bought a MAF cal'd for the 24lb injectors. It's a black plastic 75mm MAF from Summit. The injectors are FRPP variety that I bought from a buddy who decided to go carb'd with his project.

I know this isn't the preferred method since our cars are load based EEC-IV. Using a Tweecer or some other electronic tuning method to tell the car's brain that the injectors are larger is the best way.

Thanks everyone for the responses so far. Anymore are greatly welcomed.

 

[final5-0]

I know this isn't the preferred method since our cars are load based EEC-IV. Using a Tweecer or some other electronic tuning method to tell the car's brain that the injectors are larger is the best way.

Yes ... Self tune with a pcm interface or Pro Tune with a chip would be best

But ... You work with what you got for the time being.

I did not specify above ... but ... I was talking about the 24# caled meter

I'd use it along with the 24's and see how things go.

Of course ... the wb will be needed to know for sure.

Also ... when you get around to doing WOT tuning with the fuel ratio

It would be a good idea to keep the spark dialed ... way back

Grady

 

[JJ95GTID]

Also ... when you get around to doing WOT tuning with the fuel ratio

It would be a good idea to keep the spark dialed ... way back

Grady

Yep, got the MSD BTM for this already. Thanks