Fuel System }{ LT1-LT4 specific

[Fire67]

Im building toward a target of 650rwhp, which is approximately 765hp flywheel.
According to the calculations I did last night, this requires 72lb/hr injectors and at least 96gph fuel pump.

I've got quite a few questions regarding the actual setup, but most depend on answers to other questions so I'd like to ask them one at a time. Then once everyone has shared thoughts and knowledge, I'll move on to the next question.

So my first question is about line size. Most of the pumps I see that will flow the required fuel have a -10an outlet... Assuming thats the minimum size that needs to get to the rails... Are the stock metal tubes on the rails big enough to flow this amount of fuel? Or do I need to cut them off and adapt AN fittings to the rails?

[1bad2k2ta]

fire67 said:

Im building toward a target of 650rwhp, which is approximately 765hp flywheel.
According to the calculations I did last night, this requires 72lb/hr injectors and at least 96gph fuel pump.

I've got quite a few questions regarding the actual setup, but most depend on answers to other questions so I'd like to ask them one at a time. Then once everyone has shared thoughts and knowledge, I'll move on to the next question.

So my first question is about line size. Most of the pumps I see that will flow the required fuel have a -10an outlet... Assuming thats the minimum size that needs to get to the rails... Are the stock metal tubes on the rails big enough to flow this amount of fuel? Or do I need to cut them off and adapt AN fittings to the rails?

I am at 650 rwhp. I have 65 lb/hr Mototron high impedence injectors. Not sure what the duty cycle is, but my tuner says I still have room to do the 109 octane race tune (looking for 700+ rwhp) and not be any higher than 80% duty cycle.
Fuel system is -10 from the fitting in the 98 model metal gas tank to billet high flow fuel filter, to a Bosch 420lph pump w/-10 inlet and -8 outlet feeding a pair of LS1Speed high flow billet fuel rails. Not sure about the LT1 rails, but the LS1s are iffy at 650 rwhp. Definitely don't want to go lean on the top end w/FI. Exit side goes through the LS1Speed billet boost referenced fuel regulator, then back to tank (-6 I think). LS1Speed claims to have run 750 rwhp without leaning out with this setup.

Having said all that, I have bad news. I blew a head gasket over the weekend and found out last night when it overheated due to no coolant. So, I have to determine why the gasket blew. Was it tuning, or was the fuel system inadequate and it went lean on the top? I think the fuel system is good. I may have warped the heads a little back in the summer when I was breaking it in. It hit 250 a couple of times sitting in traffic. However, it made about 15, or so WOT passes with out any issues I am aware of, other than toasing my clutch pressure plate from hot lapping it. Once I get 'em off, I will have 'em checked for trueness and machined if necessary.

[Fire67]

When doing fuel calcs for a S.C.'d LS1, what kind of BSFC number do you use. I found with my stock motor setup that the fuel calcs where a little low for injector size if I used anything other than .06-BSFC. Im thinking that because the LT1's are less efficient, they need more fuel than an LS1 at similar power levels. Going on my experience with the stock motor under boost, I need 72's to be on the safe side.

I think the Bosch 420 lph pump would be more than sufficient. Im not too sure how I should be understanding the affect of line size on the flow... But if -8an is the outlet size than it must be sufficient.
So maybe that Speed inc. fuel system (which Im assuming you run by the description) would be perfect... Just with bigger injectors.

So can anyone tell me a close fractional equivalent to -08an? Just to determine an optimum inlet size to the rails

1bad2kta-
Does your system Y before the rails or just run from one to the other?
Im thinking I might be able to modify my stock rails by replacing the inlet and outlet fittings (the smallest diameter in the rail assembly is on the quick connect fittings) to save money over buying new rails.
Also would it be possible to get a picture of the fittings going to your tank?

[1bad2k2ta]

fire67 said:

When doing fuel calcs for a S.C.'d LS1, what kind of BSFC number do you use. I found with my stock motor setup that the fuel calcs where a little low for injector size if I used anything other than .06-BSFC. Im thinking that because the LT1's are less efficient, they need more fuel than an LS1 at similar power levels. Going on my experience with the stock motor under boost, I need 72's to be on the safe side.

I think the Bosch 420 lph pump would be more than sufficient. Im not too sure how I should be understanding the affect of line size on the flow... But if -8an is the outlet size than it must be sufficient.
So maybe that Speed inc. fuel system (which Im assuming you run by the description) would be perfect... Just with bigger injectors.

So can anyone tell me a close fractional equivalent to -08an? Just to determine an optimum inlet size to the rails

1bad2kta-
Does your system Y before the rails or just run from one to the other?
Im thinking I might be able to modify my stock rails by replacing the inlet and outlet fittings (the smallest diameter in the rail assembly is on the quick connect fittings) to save money over buying new rails.
Also would it be possible to get a picture of the fittings going to your tank?

Yes, I bought the whole system from Speed, Inc.

I think these are the calculators I used when spec'ing the motor: www.fbody.com/calc.htm

I looked at .55 and .60 BSFC, but also used higher pressure than the 43lbs these calcs are designed for.

My system does not "y", it goes straight from the pump to the rear of the passenger side fuel rail. Sorry, no pics at this time. Will not be able to get the car in the air for at least 2 weeks (my guy's wife just had a baby), and everything is hidden behind a heat shield.

Not sure about the -an to sae conversion. I will see what I can find. Just as a guess, I would say -8 an = ~3/8", but don't hold me to it. I would bet Alex or Aaron could probably tell you, but I will look.

[Fire67]

I was able to find a table on the web that had "approximate" i.d.'s of the different AN lines... The metal quick connect fittings on my stock rails have an inside diameter thats closer to -06an so I will definitely have to figure out how to get around it. The fittings are pressed into the rails which have about 5/8"-3/4" inside diameter. So I think the rail size will be fine if I can replace the fittings with something bigger.
I may even just buy the kit from Speed Inc., it just depends on the funds available after I get the motor together.
Im still really interested in where and how the fittings attach to the tank, and since this project is gonna be in the works for at least a month, please get me a pic whenever you can... If its too much of a pain in the butt, dont worry about it. I'll try and talk speed inc into getting me a pic somehow.
The fuel pressure is definitely the difference in our calcs. I didnt even think of it, but with the flow of that pump, I probably wont need 72# injectors.

[1bad2k2ta]

We used a bulkhead fitting for the metal tank. We put it in the bottom, right-rear corner of the tank. If I had it to do over again, I think I would go ahead and sump it in the center and put the bulkhead in there. As it is now, when it gets down to a 1/4 tank, or so, and I go around a right hand turn, the pump will suck air. It is not a problem as long as you remember not to get on it, but now when I get below a 1/2 tank, I start thinking about filling up.

[94m6hardtopz]

BSFC also depends on what fuel you are going to run.

[Fire67]

94m6hardtopz said:

BSFC also depends on what fuel you are going to run.

I knew that, just not sure which way it goes.. Care to elaborate?

I ended up buying a 383 shortblock with a long list of nice stuff. I wanted to build it myself, but I was too afraid of messing something up.
Were going for 8.7-9.0:1 compression to be able to run around 15psi.
With the intercooling and compression, pump gas shouldnt be a problem for me.

[Fire67]

Well since the site has been down Ive done quite a bit of homework and started modding my fuel rails to support the flow needed.

Those are -08an fittings welded onto the ends.

The cross-over tube from factory got replaced with this aluminum tube, I was planning on plugging these ports to run the system in parallel. But I didnt have any aluminum stock laying around and this tube fit the holes perfectly. I am plumbing two return ports to the regulator from each end of the rails, so the crossover has pretty much just become a balance tube at most.
I have since gotten some bar stock and fabbed some plugs for the ends of the rails which have been welded in as well. Once my 90* 3/8 to -8an fittings show I'll get them welded in to the rails and post up newer pics.

Ive pretty much decided to run an Aeromotive Eliminator pump with the matching regulator and filter.
I know its gonna cost more, but no other company seems to be able to prove what they claim.

1bad2kta:
I found out that the bosch 420 pump actually only flows like 300-350lph at 45psi... Much less at higher pressures.
Maybe that can be linked back to your blown head gasket?

[1bad2k2ta]

fire67 said:

Ive pretty much decided to run an Aeromotive Eliminator pump with the matching regulator and filter.
I know its gonna cost more, but no other company seems to be able to prove what they claim.

1bad2kta:
I found out that the bosch 420 pump actually only flows like 300-350lph at 45psi... Much less at higher pressures.
Maybe that can be linked back to your blown head gasket?

I will definitely look into it. When the heads come off we will check for any hints of detonation and head warpage. Hopefully the car will be picked up today and be running again this weekend.

[Fire67]

On my stock motor, the only sign of detonation it ever had to show was the melted head gasket. Look for the cylinder that melted the head gasket, then check it really good for detonation signs.
Hope everything goes well, I know how it can be without your car. Im goin on 4weeks now without my baby... Only a week or two for the new motor to arrive, Im getting so anxious

[94m6hardtopz]

fire67 said:

94m6hardtopz said:

BSFC also depends on what fuel you are going to run.

I knew that, just not sure which way it goes.. Care to elaborate?

I ended up buying a 383 shortblock with a long list of nice stuff. I wanted to build it myself, but I was too afraid of messing something up.
Were going for 8.7-9.0:1 compression to be able to run around 15psi.
With the intercooling and compression, pump gas shouldnt be a problem for me.

if your BSFC with pump gas is .6, with 117 leaded it would be closer to .5 and maybe into the .4 area with an intercooler. the compression of the stock lt1 is so high that even with an intercooler, it takes a lot of pump gas. my old mustang made over 500rwhp out of 30lb injectors at 60psi fp with vp c12 with my intercooled turbo kit. the a/f was at 12:1. that calculated out to about .4 BSFC.

[Fire67]

I see where your getting at... And that brings up an interesting point. The stock motor was definitely at .6 according calculations. With lower compression on my 383 it could possibly be a lower BSFC??
If thats the case, I should be extremely safe with my fuel system... Its going to be close, maybe 50hp over with my figuring a .6 BSFC. If I can garauntee my fuel pumps with 13.5v, it'd be about 75hp worth on the safe side.