Hello,

I have an inline 250 that is GN T3 turbo-ed. It runs great and I am in the process of pulling the engine to rebuilt it right. On my list of things to do before I put it back is modify the mechanical fuel pump.

I am wanting to boost reference the pump and don't know where to put the reference fitting. Here is a pic of the fuel pump with the top off. The inlet is on the left and the outlet is on the right. With the top on, it is divided into two different sides. Which side do I reference? I am assuming the outlet side, but don't know for certain. If so, put the fitting where the void is towards the bottom?



Thanks,

Boucher

You need to drill & tap the side that has the hole for atmospheric vent hole from the factory.


MBHD

Yes, you boost reference the other side of the pump.

Some of the Studabaker guys have a good pictures of that as the factory supercharged Studes (R8?) had that.

Thanks for the help. So that we are all on the same page, here are a few more pics. First from the top with cover on and second the bottom. I did notice two small holes on the bottom that are vents? After cleaning it, I noticed fluid running out of them, so I know that they are all the way through.

Now that Boucher has his nipples straightened out.......

Anyone know why his fuel pump has two bolts holding cover on?
Seems they are usually held down by one bolt in the center?
Just wondering.

btw: Is that pivot pin loose?

Thanks
Pete

very funny. as I looked back at that title. I had to laugh.

Yep, in the bottom pic, plug one hole and drill out and tap the other so it can be hooked to your vacuum/boost line.

I have a question on this modification.

If you hook a vacum line to a fitting on FP instead of venting it. Isn't the fuel pump vented into the engine crankcase? The pumps I have looked at are. So the reference line will do no good. Except to suck crankcase air.

The hole in the fuel pump is vented to the atmosphere.(The vent hole is on the outside of the FP)

If the FP diaphram had no vent hole,,,it would not pump/work.

Hooking up a fitting into the vent hole & the other end hooked up to the intake manifold will give you added pressure when your intake manifold sees boosted pressure from a blower or turbo.

MBHD

A 7psi mechanical fuel pump has a tough time putting fuel into a carb under 10 psi of boost. If you reference the back of the diaphragm to the boost pressure you fool the pump into thinking it's still in the real world. Sorta like putting blinders on a horse. The danger is still there he just can't see it. I'll try to dig out one of the Stude pumps I modified for the '54. There was an undrilled boss on the last one in just the right place.

thanks all, I would hate to have nipple confusion.

Tlowe, regarding the mod, I had just taken it for granted that it was just the way it was. Reading up on it at http://www.theturboforums.org they say that mod is only good to about 8psi, after that you need to go electric because the leakage into the crankcase becomes excessive. I don't run a fuel pump at all so I don't know.

http://static.summitracing.com/global/images/instructions/pax-1001839%282%291.pdf
PG. 17

Not sure as to why the pressure would vent into the engine case??? must have had a broken/leaking diaphram?
http://www.theturboforums.com/smf/index.php?


A couple of quotes:
Title: Re: Carter 172 gph boost referenced pump?
Post by: sean on September 30, 2008, 03:06:14 PM

Been running a boost referenced Carter mechanical for several years on a junkyard 5.0 tt combo w/o issue. It isn't a power house, (400-450hp) but it has worked for a low buck 10psi deal. Not sure where the limit of the pump is, have never tried to make more power than what it makes at 10 psi

Title: Re: Carter 172 gph boost referenced pump?
Post by: turbobubba55 on October 06, 2008, 02:50:50 PM

i had several mechanical pumps & the 172 was the best, BUT, it wouldn't keep the bowls full. anything over 7 psi- the diaphragm would stall & not pump fuel. -lots of pressure, but no flow.

Straight 6 200 Ford,did not have good luck:
http://www.theturboforums.com/smf/index.php?topic=78651.25;wap2

& http://www.theturboforums.com/smf/index.php?topic=145912.0

Hmmmm,, think I've seen those pics before



In general,this is just for a low buck low Boost application.
After approx 8-10 psi of boost presssure,need to run an electric FP for higher boost pressure .

MBHD