Too Slow/Q-Jet question

[JP1738]

Originally Posted by Mike Pearson

6-6.5 PSI is what I run for fuel pressure. You need minimum 1 gallon of fuel delivery at the carb in less than 30 seconds. I run a Magna Fuel regulator dead head with #8 line from the cell to the carb. Regulator is mounted on the fenderwell I have one of those Chinese summit pumps that is similar to a holley blue pump. I have run 9.90 with my set up. My carb was built by Jim Boburka.

Have not checked flow from my pump, but I'm going to check that today too. Mine is a Holley Blue pump but it's ancient. -6AN line from regulator to carb through an inline filter.

[JP1738]

Originally Posted by a pontiac

You need to try another q-jet for comparison, I thought I had a good one, borrowed another and was 2 tenths quicker. Also, most jet tuning is with secondary rods.

That's the next step, I've got another intake and carb on the way from Tim Stickles to try. Super awesome nice guy willing to loan it to me to try. Said he'd give me an option to buy it if it works out better.

Also I will be running a compression and leakdown test after work today to check the health of the engine. It's got a mediocre ring package similar to circle track setups (that's all I had when I took it to Mark) so the rings should be sealed already. I will bring it up to temperature and cool it down before I perform the tests. Might take a while but at least I'll hopefully be able to rule out the rotating assembly.

[JP1738]

Originally Posted by Cdncarnut

I have 2 spare Q-jets in my trailer, plus the one on the car, built by the 3 major builders, two of whom have now retired.

I have actually had a case where a carb ran great two weeks ago, would not qualify the car.
Yet, the carb which ran like poop 2 weeks earlier, ran the best ET ever.

I also have one which will get my down the track, significantly under the index, every time.

Getting the rods and hanger correct for race day can be a challenge.

There is no easy answer and really no cheap solution.

Well cheap is relative lol, but I'm learning quickly that's a far fetched idea in this class. No big deal, I still think I can be at the track even with a few minor upgrades for less than 13 large.

[Mike Pearson]

Originally Posted by JP1738

Have not checked flow from my pump, but I'm going to check that today too. Mine is a Holley Blue pump but it's ancient. -6AN line from regulator to carb through an inline filter.

All that should work if it’s mechanically in good working order. Check the flow before and after the filter. If the flow is low with the filter you might need to take it off. I do not run a filter and never have. I am real careful to keep my fuel system clean.

[JP1738]

Originally Posted by Mike Jones

What Model is your 1980 Chevrolet?

station wagon 2S 305/180

[Danny Ashley]

[QUOTE=Adger Smith;692814]I'm not a real Q-Jet tuner, but I question the 6.5 lb fuel pressure.
N/S area vs the small float
What do the experts say about that?
I have had Q-Jet customers that are very particular about regulator location and fuel line routing to the carb...
OK What you say Q-Jet experts??[/QUOTE


Quadrajet fuel pressure depends on the needle & seat size. They are available from .110 - .150. The .110 can handle more pressure than the .150. My choice is the .135 for all applications. It has been used in two of my Super Stock customer's cars who have run in the 8 second zone. You can safely run 6 - 6.5 with it but I have fast customers who only do 5 - 5.5. You will have more problems with too much pressure than too little. A well designed fuel system will go a long way in not creating problems you may attribute to the carburetor. Locating the regulator ahead of the carburetor and allowing inertia to work for you is a plus.

[JP1738]

Update on some of the things mentioned yesterday:

-In order by cylinder #, here are the compression and leak down results from last night where compression is first and % leakage at 100 psi of pressure is second. Testing was done while the engine was warm and leak down tests were performed at TDC for each cylinder:
150/94 155/92 145/93 150/94 155/97 146/94 155/96 145/90

-I flowed the fuel line into a 1 gallon bucket and it took 37 seconds to fill it up

-I took the fuel filter apart and checked it for junk. It had very little if any trash in it. It's a very high micron filter so I don't see it as a restriction, so I put it back on the car. I'm not hell bent on having it, I just like the peace of mind

-the regulator is mounted on the fender well and the fuel line runs straight across the engine bay to the carburetor perpendicular to the direction of motion with a -6 line. Given the flow rate I feel comfortable I don't have a fuel delivery issue, but if you disagree please let me know.

-also, I went back and slow-motion watched the in car footage from the runs and at no point during the run does the fuel pressure drop below 6 1/4 pound. This tells me that despite the Gs of acceleration, my pump keeps up/doesn't care about it.

-As I stated yesterday, I've got an intake and carb coming to try, curtesy of Tim Stickles (thanks again man, you're a stud!). I'm anxious to see if/how much better it is than the one I have now. It could be all of the problem or none of it. Just don't know yet.

[MR DERBY CITY]

You can take this for what it’s worth but ONE gallon in 37 seconds is not desirable. I believe you have an issue there considering you are feeding a Q jet . Also, there is a huge difference between VOLUME and PRESSURE.

[JP1738]

Originally Posted by MR DERBY CITY

You can take this for what it’s worth but ONE gallon in 37 seconds is not desirable. I believe you have an issue there considering you are feeding a Q jet . Also, there is a huge difference between VOLUME and PRESSURE.

True but I now have answers to both questions. Pressure never dips and volume is decent. Y'all really think 2GPM isn't enough to feed a 250hp 305? I'm as green as can be when it comes to racing stock and Q-jets but I still find that hard to believe. Maybe I can back-to-back it this weekend with and without the filter and see if it makes a difference. I'll let everyone know one way or the other.

[Mark Yacavone]

Originally Posted by MR DERBY CITY

You can take this for what it’s worth but ONE gallon in 37 seconds is not desirable. I believe you have an issue there considering you are feeding a Q jet . Also, there is a huge difference between VOLUME and PRESSURE.

Also, there's a difference between battery voltage and alternator voltage.
It sounds like you have a stock tank inside the quarter panel.
In that case , you're also fighting inertia and siphon issues.
Fuel cells don't cost much on Ebay. You will need to place it inside a metal box on a wagon though.