FMU Question.
04-25-2005, 08:56 AM
#11
0.0 BAR
Join Date: Feb 2003
Posts: 0
Re: FMU Question.
Carbs aren't designed for high pressure. Some tolerate ~15 psi base pressure, but that's about it.
You want to get a 1:1 FMU, several places make them, to allow the fuel pressure to overcome intake manifold pressure as it rises under boost. What are you doing to seal the carb up so it doesn't leak? Did you build a carb box, or seal the shafts, etc? Do you have brass or filled floats?
You can also run a stock mechanical fuel pump with the top drilled out to fit a nipple, and boost referrenced. Worked for Sitar's 680whp with slicks spinning on the dyno rollers junkyard 351W build. He also used an EFI fuel pump and a Hobbs switch to spray a little extra fuel into the carb throat at 4+ psig. www.toohighpsi.com has the writeup.
Got anymore details on your setup? If I don't know it, I can provide an intro to someone who has hands on experience.
You want to get a 1:1 FMU, several places make them, to allow the fuel pressure to overcome intake manifold pressure as it rises under boost. What are you doing to seal the carb up so it doesn't leak? Did you build a carb box, or seal the shafts, etc? Do you have brass or filled floats?
You can also run a stock mechanical fuel pump with the top drilled out to fit a nipple, and boost referrenced. Worked for Sitar's 680whp with slicks spinning on the dyno rollers junkyard 351W build. He also used an EFI fuel pump and a Hobbs switch to spray a little extra fuel into the carb throat at 4+ psig. www.toohighpsi.com has the writeup.
Got anymore details on your setup? If I don't know it, I can provide an intro to someone who has hands on experience.
04-25-2005, 01:34 PM
#12
1.0 BAR
Thread Starter
Join Date: Apr 2005
Posts: 375
Re: FMU Question.
Well made some progress. The smoke problem has gone away totally.
The turbo is working really well too. Its poping my waste gate if bliped in Neutral. Something that dosent happen on the first car we did. THere the engine has to be in gear / underload to see any kind of boost.
This got me thinking maybe my hybrid exhaust hosuing is too small. And it would choke top end flow. So did a few 2nd and 3d gear pulls. WIth the Gtech RR hooked up. She is pulling clean to 7500 RPM (Stock is 6500). Stock rubber is 155 now runing 175 and shes shreding even these.
Buttttttt :P
Sometimes she will start jerking like crazy. / Fuel starvation.
Ok so why is the first car working fine and this one not. First doubt the DIY FMU.
So replace all the hoses with see thru tubes.
1. Fuel pump to FMU
2. FMU return line
3. FMU to Carb
4. FMU to Extra dial a jet / adjustable power jet
5. FMU to Carb
6. Carbs orignal return line
Take off the hood and take it for a spin.
No boost. Fuel is returning thru FMU return line and carb return line.
As boost climbs fuel in the return line starts to slow down. At 14 PSI the FMU fuel return line is totally dry.
Cant see any of the carb tubes.
What info do you need. The only thing Ive not mentioned above is that I have something called Adjustable powerjet / dial a jet hooked up. THe FMU out is has a T one goes to this extra jet the other to the carb. THe adjustable jet is setup so that no boost = no flow. As boost croses 4psi and starts to climb it flows a little.
How did we achive this. Just close and then back off a fraction.
We havent done anything to seal the carbs. THe shafts have inbuilt rubber seals from the company. I couldnt belive it either but the thing works fine. With no leaks what so ever.
So fine in fact. That we have been out racing cars with much larger engine capacites and many fancy toys like fancy cams, ecus, and others toys that cost more than our car.
Ive allready posted pics from our first install. Anyway they are here.
http://www.eindiancompanies.com/turbo/
And of the Drag race http://www.eindiancompanies.com/drag/
See esteem vs Baleno
Pics of my own setup Ill post in a day or two.
Everywhere I see the refrence to you need a 1:1 FMU what is this.
Is this diffirent from a Vortech type setup. If so can you provide some more info.
Or on how it works so I can build one or buy one.
The turbo is working really well too. Its poping my waste gate if bliped in Neutral. Something that dosent happen on the first car we did. THere the engine has to be in gear / underload to see any kind of boost.
This got me thinking maybe my hybrid exhaust hosuing is too small. And it would choke top end flow. So did a few 2nd and 3d gear pulls. WIth the Gtech RR hooked up. She is pulling clean to 7500 RPM (Stock is 6500). Stock rubber is 155 now runing 175 and shes shreding even these.
Buttttttt :P
Sometimes she will start jerking like crazy. / Fuel starvation.
Ok so why is the first car working fine and this one not. First doubt the DIY FMU.
So replace all the hoses with see thru tubes.
1. Fuel pump to FMU
2. FMU return line
3. FMU to Carb
4. FMU to Extra dial a jet / adjustable power jet
5. FMU to Carb
6. Carbs orignal return line
Take off the hood and take it for a spin.
No boost. Fuel is returning thru FMU return line and carb return line.
As boost climbs fuel in the return line starts to slow down. At 14 PSI the FMU fuel return line is totally dry.
Cant see any of the carb tubes.
What info do you need. The only thing Ive not mentioned above is that I have something called Adjustable powerjet / dial a jet hooked up. THe FMU out is has a T one goes to this extra jet the other to the carb. THe adjustable jet is setup so that no boost = no flow. As boost croses 4psi and starts to climb it flows a little.
How did we achive this. Just close and then back off a fraction.
We havent done anything to seal the carbs. THe shafts have inbuilt rubber seals from the company. I couldnt belive it either but the thing works fine. With no leaks what so ever.
So fine in fact. That we have been out racing cars with much larger engine capacites and many fancy toys like fancy cams, ecus, and others toys that cost more than our car.
Ive allready posted pics from our first install. Anyway they are here.
http://www.eindiancompanies.com/turbo/
And of the Drag race http://www.eindiancompanies.com/drag/
See esteem vs Baleno
Pics of my own setup Ill post in a day or two.
Everywhere I see the refrence to you need a 1:1 FMU what is this.
Is this diffirent from a Vortech type setup. If so can you provide some more info.
Or on how it works so I can build one or buy one.
04-27-2005, 12:43 PM
#13
0.0 BAR
Join Date: Feb 2003
Posts: 0
Re: FMU Question.
1:1 FMU is equivalent to a factory fuel injected car's stock fuel pressure regulator. I know you can get them out of Summit's catalog.
Normal FMUs work to raise pressure by blocking fuel return to the tank. With a low pressure carby setup, that might not work so hot because the stock pump can only push out so much. At low boost I can see a possibility of the bowl being overfilled and the fuel return being dry, and at high boost I can see where the stock pump totally can't keep up and it runs out of fuel. Just a mental picture and maybe not anything you have going on.
Check toohighpsi.com and see how Sitar modified the stock 351W truck fuel pump, I really think doing that to your fuel system is what you need to do, then fiddle with jetting until you're running perfectly.
155/175 tires? What car is this, anyway? I get the feeling it's not the domestic V8 muscle I'm used to seeing with a blow through carb.
Normal FMUs work to raise pressure by blocking fuel return to the tank. With a low pressure carby setup, that might not work so hot because the stock pump can only push out so much. At low boost I can see a possibility of the bowl being overfilled and the fuel return being dry, and at high boost I can see where the stock pump totally can't keep up and it runs out of fuel. Just a mental picture and maybe not anything you have going on.
Check toohighpsi.com and see how Sitar modified the stock 351W truck fuel pump, I really think doing that to your fuel system is what you need to do, then fiddle with jetting until you're running perfectly.
155/175 tires? What car is this, anyway? I get the feeling it's not the domestic V8 muscle I'm used to seeing with a blow through carb.
06-03-2005, 12:30 PM
#14
1.0 BAR
Thread Starter
Join Date: Apr 2005
Posts: 375
Re: FMU Question.
As allready mentioned at the start of this post we are using a EFI fuel pump that was puting out 65 PSI when we installed it.
Most of the replies seem to be by passing this aspect.
Also I still havent understood what a 1:1 FMU is. Is it something that boosts the fuel flow by 1:1 i.e. for every increase in boost it would boost fuel presure by 1 psi
Anyway I think we are close to dialing it in we still have one hitch but maybe a one way valve will fix it.
Latest test results.
Presure before FMU 30 PSI (THe pump we tested at 65psi has gone down to 30 psi).
Presure at FMU exit with no boost 4 psi. Therefore Carb inlet 4 psi
Boost taken up to 10 PSI at 10 PSI boost. Fuel presure being output by FMU is 9 PSI. This means the engine is at redline. ANd flowing fuel and there is still 9 PSI at the inlet.
Which means we can take the boost up to 16 PSI and we would still have 3 PSI at the carb inlet.
Both return lines are kept seprate. i.e. return line from FMU and Return line from the carb.
I have one doubt though. The FMU exit hole is 1.8mm dia. My carb jet dia is say 3mm should I leave it as it is.
What would the effect of changing the FMU exit hole be. i.e. Im thinking of making the exit size larger i.e. match it to my jet size. i.e. 3mm so will the pressure go up or down. Im afraid it will go down.
The problem is when the car starts moving i.e. no boost just starting to move it starts jerking like fuel starvation.
Two problems could be causeing this
1. The line to the FMU is seeing a vacum and pulling shut the FMU killing flow.
2. WHen I turn the Ign on. I can hear the fuel pump whine then there is a click from under the dash and the fuel pump goes off. On the other car the fuel pump never goes off. (We asume the fuel pump starts up again when the engine is runing). But by then its playing catch up. What we did was remove the stock fuel pump and put in the MPFI pump in the same position in the tank. ANd hooked up using the same wires.
Pics of the setup have allready been posted. On another thread.
Most of the replies seem to be by passing this aspect.
Also I still havent understood what a 1:1 FMU is. Is it something that boosts the fuel flow by 1:1 i.e. for every increase in boost it would boost fuel presure by 1 psi
Anyway I think we are close to dialing it in we still have one hitch but maybe a one way valve will fix it.
Latest test results.
Presure before FMU 30 PSI (THe pump we tested at 65psi has gone down to 30 psi).
Presure at FMU exit with no boost 4 psi. Therefore Carb inlet 4 psi
Boost taken up to 10 PSI at 10 PSI boost. Fuel presure being output by FMU is 9 PSI. This means the engine is at redline. ANd flowing fuel and there is still 9 PSI at the inlet.
Which means we can take the boost up to 16 PSI and we would still have 3 PSI at the carb inlet.
Both return lines are kept seprate. i.e. return line from FMU and Return line from the carb.
I have one doubt though. The FMU exit hole is 1.8mm dia. My carb jet dia is say 3mm should I leave it as it is.
What would the effect of changing the FMU exit hole be. i.e. Im thinking of making the exit size larger i.e. match it to my jet size. i.e. 3mm so will the pressure go up or down. Im afraid it will go down.
The problem is when the car starts moving i.e. no boost just starting to move it starts jerking like fuel starvation.
Two problems could be causeing this
1. The line to the FMU is seeing a vacum and pulling shut the FMU killing flow.
2. WHen I turn the Ign on. I can hear the fuel pump whine then there is a click from under the dash and the fuel pump goes off. On the other car the fuel pump never goes off. (We asume the fuel pump starts up again when the engine is runing). But by then its playing catch up. What we did was remove the stock fuel pump and put in the MPFI pump in the same position in the tank. ANd hooked up using the same wires.
Pics of the setup have allready been posted. On another thread.
06-14-2005, 03:03 AM
#15
1.0 BAR
Thread Starter
Join Date: Apr 2005
Posts: 375
Re: FMU Question.
I just thought Id post an update on this.
We solved the problem. What was hapening was when accelrating the line to the FMU would see a strong suction this would pull shut the FMU and stop flow to the carb. What I did was install a one way valve on the FMU signal line. So the FMU would flow its 4 PSI when not under boost and not see vacum but when under boost it would see pressure and allow flow.
Another thing we did was connect the power supply line of the fuel pump direct so now if it the ign is switched on the pump is runing it never cuts out.
THe car is runing fine now.
We took it for a spin and have even sampled 16 PSI boost with no problems.
Im still keen to save up some money and buy a Vortech FMU some day. And am keeping a look out on egay. Just not sure about this 1:1 business and what FMU I should get.
We solved the problem. What was hapening was when accelrating the line to the FMU would see a strong suction this would pull shut the FMU and stop flow to the carb. What I did was install a one way valve on the FMU signal line. So the FMU would flow its 4 PSI when not under boost and not see vacum but when under boost it would see pressure and allow flow.
Another thing we did was connect the power supply line of the fuel pump direct so now if it the ign is switched on the pump is runing it never cuts out.
THe car is runing fine now.
We took it for a spin and have even sampled 16 PSI boost with no problems.
Im still keen to save up some money and buy a Vortech FMU some day. And am keeping a look out on egay. Just not sure about this 1:1 business and what FMU I should get.
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