Is 4,5 psi ok with q-jets needle and seat? Can i run this regulator? http://www.summitracing.com/parts/hly-12-842/overview/ Peace, Kacper.
I used to think that 6 or maybe 7 psi was all the Q-jet could handle, but Cliff posted that he has seen them handle 10-11 psi. http://www.v8buick.com/showthread.p...acceleration&p=2088866&highlight=#post2088866
What is the carburetor part number? What diameter needle/seat assembly is being used? What size float?.....Cliff
7041305 this is carb, looks like replacement made in seventies. I am goin with small needle/seat, float standard phenolic for this carb. Peace, Kacper.
That would be correct, service replacement, and it will have the early hinge pin location and large float. For high performance work, max fuel inlet size would be .135". Absolute maximum fuel pressure 6psi, 4-5 would be better.....Cliff
I was thinking of 4,5 psi, that's the smallest preassure that return style regulators can be set to. I noticed that with 0.135 inlet those earlier q-jets are wet, they have very high float setting. I was thinking of 0,125 or even 0.110 and 4,5 maybe 5 Psi. How does it sound? Peace, Kacper.
Depends on the power level. Very difficult to keep up with big power using a tiny fuel inlet seat and low fuel pressure. A .125" seat and 4-5 psi may be OK for a 350 with 250-300hp, but it will NOT keep up with a 455 making over 400hp, in most cases, unless the fuel delivery system is superb. I would use the high flow .135" seat, float at 3/16", and at least 5psi fuel pressure for most applications, especially if the fuel system is stock with a mechanical fuel pump. Keep in mind when reading this that the early Q-jets with the large float and rear hinge pin location are what gave q-jets a bad reputation as a performance carburetor. Later designs are far superior, and can handle large fuel inlet seats, high fuel pressure, and keep up with big power levels. I have customers making over 700hp and running into the 9's with them, with zero issues anyplace for fuel delivery.......Cliff
Cliff, i am using this carb on a 425 Nailhead witch will never see anything beyond 400 hp. I will be happy when it will make its advertised 360. Guess 0,125 needle will be good with 4,5 psi for now. Peace , Kacper.
According to TA performance (which is a highly reputable Buick specialization parts manufacturer and vendor), their Street/Strip mechanical fuel pumps put out 8 PSI and 80 GPM max and are "safe for all carburetors including Quadrajet and Carter AFB/Edelbrock Performer." Stock Stage 1 replacement pump good to 450 HP Street/Strip pumps good to 500 HP Replacement Nailhead pump good to 500 HP This is according to TA. They recommend anything over 500 HP use electric or mechanical/electric hybrid.
Gary, Jim Weise has been using this pump for many years on some high power builds, http://www.cvproducts.com/ProdDet.aspx?PN=SPIN-MP-2509 It makes 8-9 psi, and according to Jim, "it can supply enough fuel for anything you care to put a licence plate on":laugh: Jim puts a Buick arm on it. It is pricey, but according to the webpage above, it is good to 850 HP. I like the simplicity of a mechanical pump. I am feeding it with a Robb Mc 1/2" pick up and -8 push lok hose. Despite getting a defective one from the manufacturer (gasket put on backwards), it is performing flawlessly now on the engine in my signature. Jim assures me that my Q-jet (he is modifying it now) will work just fine with this pump.
High output mechanical pumps are limited in flow potential by the lines feeding them. For big power levels that will see drag racing with good traction, we still use and recommend a sumped tank or fuel cell, and 1/2" or 8An lines/fittings everyplace. Keep in mind when reading this that a stock 3/8" steel line is only 5/16" inside diameter BEFORE you put bends in it! A 69 or later Buick Q-jet will be fine with 8-9psi fuel pressure. We use a lot of 71-74 Buick 455 center sections when the application requires an early style divorced choke carburetor, as they are the only early units with the larger primary bores......Cliff
