Too Slow/Q-Jet question

[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.

[Stan Weiss]

Originally Posted by JP1738

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.

ONE gallon in 37 seconds is only 1.62 GPM.


While that is over 550 pounds a hour which should easily support 1000 HP. It don't always work that way.


Stan

[Chipper Chapman]

Originally Posted by JP1738

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.

Your 305 should make in the 350hp area to be average. And a good rule of thumb I've found for supplying fuel to a Q-Jet engine, is to double the volume (or system hp rating) required for your said power level. IE engine makes 350, you need a system capable of 700 feeding it. The q-jet is great but can be quirky.

Also you most likely just have a whole bunch of small small issues adding up to some big losses. Only time and perseverance will fix that

[JP1738]

HOLY **** BATMAN! My heap SET SAIL this past weekend at a Darlington Dragway test session! changing nothing but timing, shift points and an intake manifold from Tim Stickles, I picked up FOUR TENTHS. Granted, it was in 1000 ft of DA and in a 15 mph tail wind, but I cracked off a mind boggling .39 under in the 1/4 mile! Wow wow wow! I'm so happy, proud, and relieved! I'll see you all in Orlando!

I tried my carb, T Stick's carb, and Chad Taylors carb, but mine ended up being the fastest. I think Chad's showed the most potential as it ran really well through the middle but suffered in the 60ft as it was set up for a 2-step but I was foot breaking. Had a little stumble in it when it left but came alive and hauled the mail out the back. Hoping to get a hold of some one this weekend who can help me go through them to see if I can optimize one for my combo!

Thanks all for the advice and well wishes! We did it! We got under! Much appreciated to all!

[KennyAnderson]

Originally Posted by JP1738

HOLY **** BATMAN! My heap SET SAIL this past weekend at a Darlington Dragway test session! changing nothing but timing, shift points and an intake manifold from Tim Stickles, I picked up FOUR TENTHS. Granted, it was in 1000 ft of DA and in a 15 mph tail wind, but I cracked off a mind boggling .39 under in the 1/4 mile! Wow wow wow! I'm so happy, proud, and relieved! I'll see you all in Orlando!

I tried my carb, T Stick's carb, and Chad Taylors carb, but mine ended up being the fastest. I think Chad's showed the most potential as it ran really well through the middle but suffered in the 60ft as it was set up for a 2-step but I was foot breaking. Had a little stumble in it when it left but came alive and hauled the mail out the back. Hoping to get a hold of some one this weekend who can help me go through them to see if I can optimize one for my combo!

Thanks all for the advice and well wishes! We did it! We got under! Much appreciated to all!

Congrats Keeed!!! Look up Mike McDonald while at Orlando. He and Danny Ashley are my go to carb guys and Mike will be there with Kevin Wells. Just got both my carbs freshened up by him and ran the wagon this weekend with good results.

[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.

[JP1738]

Originally Posted by Mark Yacavone

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.

The car has a fuel cell mounted in the spar tire compartment. It's about a 4 gallon cell. Guess I should have specified, apologies.