Seems like you gotta have one if the pump is making 14 psi or more and you're running a carb.

But I read that some mechanical pumps that push out 8 psi are required to use one.

But then some say "no"....

Alright, what's the truth here? Could I run 8 psi to a carb w/o a regulator without messing up the carb? How much psi can I go before a regulator becomes necessary?

On a Holley you can. I run the Carter Mech 172 pump. It puts out 8 psi at idle and I have no problems adjusting the floats. I wouldn't go higher than that though. On a Q-jet however, that much pressure may be an issue. I think they require about 6-7 psi.

This 130 gph 7.5-9 psi Holley pump for example:

http://store.summitracing.com/partdetail.asp?autofilter=1∂=HLY%2D12%2D454%2D20&N=700+4294925239+4294839053+4294891547+4294908216+ 4294840134+4294891680+4294891117+115&autoview=sku (http://store.summitracing.com/partdetail.asp?autofilter=1&part=HLY%2D12%2D454%2D20&N=700+4294925239+4294839053+4294891547+4294908216+ 4294840134+4294891680+4294891117+115&autoview=sku)

says directly at the bottom:

A fuel pressure regulator is required for 130 gph versionsSo it sounds as if they're saying if it pushes 130 gph or more a regulator is mandatory. Although isn't it the output pressure that dictates the need for a regulator?

I'm cosidering this pump for my 402 bbc that sees 6000 rpm + action. And yes it is topped with a 750 CFM Holley dual feed.

Of course under the "suggested parts" tab shows no regulator....maybe Summit has their heads up their ass? :p

The flow doesn't matter. You need a regulator if the shutoff pressure is higher than what the needle and seat can handle at idle. 8 PSI on a Holley should be ok. On an Edelbrock it is too high I am told.

If you go to the Holley website and search the different carbs,you will find installation instructions for all.They each list the recommended fuel pressure.For 750,770,800,and 850, 4-7 pounds is recommended. Tons of good information there.
http://www.holley.com/data/Products/Technical/199R7923-2.pdf
http://www.holley.com/TechService/Library.asp

Thanx Ken.

I just went thru my Holley's owners manual and it says 5-7 PSI. But no less than 4.

An issue I am having is my Carter 120 gph pump is rated from 5.5 PSI to 6.5 PSI....but at high rpms (5500) the pressure drops dramaticly to less than 3.

Not sure how good this pump is but it flows as much as the one I have at a higher pressure rating:http://store.summitracing.com/partdetail.asp?autofilter=1&part=CRT%2DM4889&N=700+4294925239+4294839053+4294891547+4294908216+ 4294840134+4294891680+4294891494+4294782820+115&autoview=sku

Perhaps that pump would be adequate for my needs? If anyone would like to comment on it I'd appreciate it.

For what its worth,I have 8.5 pounds of pressure running into my holley 750 with no regulator and theres no sign of flooding issues.Im using the 130 g.p.h. holley mechanical pump and they say regulator is required.I wanted to try it first without doing the extra plumbing for regulator.I fired it up without regulator and its been running that way for 2 years now at 8.5 psi with absolutely no signs of excessive fuel problems.

For what its worth,I have 8.5 pounds of pressure running into my holley 750 with no regulator and theres no sign of flooding issues.Im using the 130 g.p.h. holley mechanical pump and they say regulator is required.I wanted to try it first without doing the extra plumbing for regulator.I fired it up without regulator and its been running that way for 2 years now at 8.5 psi with absolutely no signs of excessive fuel problems.

Is this the pump you have? http://store.summitracing.com/partdetail.asp?autofilter=1&part=HLY%2D12%2D454%2D13&N=700+4294925239+4294839053+4294891547+4294908216+ 4294840134+4294891680+4294891546+4294782684+115&autoview=sku

Yes,that is correct Dawg.That is the pump I am using.

Another great mech pump for a BBC is the Carter M61045. Contact Tom Baird on this site. Username mc71454. He sells them every now and then and should be able to get you a good deal on one. It does have a -10 AN fitting on it. You will need a reducer. No big deal though.

Thanks I ended up getting the Holley 12-454-13. My pressure gauge shows a 9 psi reading. Guess I oughta install a pressure regulator?

If it aint flooding,leave it alone.Like I said in my earlier post,I have 8.5 psi with no regulator and its been like that for 2 years.It seems the holley carbs aint as sensitive to flooding issues as the other brands out there.

Rat

I'm not sure if it's flooding but it does seem to run a little richer than it used to, and I can't keep it running long enough to get out and verify if the bowls are overfilling or if they're only filling to the bottom of the sight hole like they're suppose to.

Just my opinion, but I wouldn't run over 7# without a regulator. It's putting a lot on the needle/seat to run it that high. A regulator isn't that expensive.

Another great mech pump for a BBC is the Carter M61045. Contact Tom Baird on this site. Username mc71454. He sells them every now and then and should be able to get you a good deal on one. It does have a -10 AN fitting on it. You will need a reducer. No big deal though.

Thanks for the Plug Jim, How are You? :thumbsup:

The Carter setup works...PERIOD !!! Without the need for a regulator..

After you try everything else, get a Carter 130, 150, 170 or a 172....:yes:

The size of the needle 'n' seat will affect how much fuel pressure it can hold. A large-diameter needle won't hold the pressure that a small diameter one will.

It's a simple matter of pressure X surface area = force. Fuel level in the bowl is a matter of balancing the force closing the needle valve (supplied by the float) with the force opening the needle valve (supplied by the fuel pump). At some point, a large needle combined with enough fuel pressure results in too much force opening the needle, and the float can't close it.

Just use the carter setup with NO REGULATOR. if it doesnt require one. dont use one, since its a restriction designed to have a high input pressure.

I use one becuase my pump puts out 24psi, i didnt use one when i had a carter.

BTW, using more fuel pressure then is "required" is not a good thing, i shoot for 6.5lbs, though there are needle/seat and float assemblies designed for 5lbs of pressure.

Less pressure, the less the fuel in the bowl is disturbed.

I happen to already have the Holley 12-454-13 pump installed. My fuel pressure gauge shows a 9 psi reading.

I'm going to install a regulator. I hope to use the EAR-916166ERL swivel fitting to adapt the 6 AN fitting of my HLY-34-150 line to the HLY-12-803 fuel pressure regulator. I just hope theres no interference with install with an RPM intake.