The Right QJ Inlet Fuel Filter for High Horsepower 455s?

I used to always use the standard 2 inch paper fuel filter for all my 455s until I discovered the Marine Mesh filter that appears to flow much better. But I noted when unpacking one of the mesh filters that there is a note saying this filter is only for the "short" filter housing. So, I did the blow-through test between the paper filter and the mesh filter and the paper filter is less restrictive when installed in the filter housing. Reason? Part of the paper filter is long enough that part of it is exposed out the carb side that fits against spring while the mesh filter fits fairly snug completely inside the housing and held there by the spring.

So, if the paper element is the right one to use, is it adequate for 500+ HP BBB motors? My engine builder said that the motor lost several HP with the paper filter so he removed it for the final runs.

I should mention that I maintain the stock look with the stock steel line going from the fuel pump to the QJ and my only other fuel filter is a large billet filter before the fuel pump. What are you folks using for your High horsepower 455s? Please respond to the poll. No need to respond if your 455 is stock or close to stock. All comments are welcome.

 

Thanks, Larry. I recall you discussing your setup and it's a good one. You may recall that I prefer my setup to remain totally stock looking. (at least from the top as the RobbMC pump is only slightly stock appearing from the top)

 

Wix makes a high flow filter (originally a Motorcraft/Ford design) that fits in the stock inlet. Dave Hemker told me about it; I can’t remember the number but I’ll ask him.
Patrick

 

Thanks. Yes, please do.

 

The marine mesh filter was my go-to for stock-looking jobs back in the day too, including the strangely appropriate 800 cfm q-jet I put on a customer's 454-powered Century CTS ski boat. Went from 49 mph to 55 mph by replacing the small Holley carb with the big q-jet. Happy customer!

Devon

 

I think that the removal helped in your first Q-jet Ray, because the needle and seat were too small, so any reduction in restriction before the needle and seat would help.

With the proper size needle and seat in your new carb here (Ruggles suggests a .140 for anything over 450 HP), then I don't think the paper element is a concern. I know I have dyno tested motors with higher fuel demand than yours in the past, with that filter in place, and we have removed it, and seen no difference in fuel flow lbs/hr.

I will re-run that test with your new carb here. it will be on a motor that should have similar fuel flow requirements to yours.

JW

 

My .149 needle and seat would flood at 8-9 psi. You must have a .140 or smaller Larry. There was an interesting chart in a Thermoquad booklet I have. Showed the different sized needle and seats and the gph flow. The larger needles could outflow the smaller ones while using less pressure to do so. (more volume less pressure needed) The smaller needles could handle more pressure and would get pretty close to flow of larger ones....if the pressure was cranked up.

 

Yes, that's the mesh filter I have and have used in the past. So, if that mesh filter stays inside the long housing while the engine is running it is actually more restrictive than the paper element. The only way the mesh filter is less restrictive is if incoming fuel pressure pushes on the mesh element, overcoming the spring pressure behind it and allowing the back part of the mesh element to pop out of the filter housing. Try it.

 

Wow! Even a Dominator wouldn't be happy with that.....

 

Ya, the Q-jets have a strong float, anyone that has ever bent one to adjust the float level can attest to that. I have personally seen a Q-jet withstand 12psi of fuel pressure, with no issue. Most folks don't know this, but this is exactly what happens when you cap the return on a Stage 1 pump.. that is where I saw it.. I was surprised. I was just fooling around on my run stand one day with a motor, and for some reason capped the return. The fuel pressure reading was an eye opener.

I use a .140 Needle/Seat in just about every Buick carb. It's the best compromise between fuel flow and high pressure capability.

I don't recall if we tried a paper filter in your 600HP combo Larry. As far as the build, it's no different than any other Q-jet I have done over the years. Key is dyno tuning.. anyone building carbs without testing them, is simply playing Russian Roulette. Carbs are made from cast bodies, in which casting issues and pinholes that you can't see can play an issue in how it works, combine that with warping issues and human error, and you can see the need for testing to insure a good result.

I don't build carbs for the general public because of this, and until recently, I had sent customers to various builders for carbs for the engines I was building them. To be honest, while I have all the stuff to plate/color them, the job is kind a loser, unless you do a lot of them. But after several issues with carbs built elsewhere in the last couple years, I have decided that I need to start building them again for my engine customers.

JW

 

Holleys, as a rule, have weak floats.. although you will always find an exception to that, apparently Larry has one. But with dual needle/seat assemblies, the common .118 diameter seat is more than enough to feed just about anything on gasoline. But ya, with a Holley, 6-7 psi is your best bet. Another factor is that observed pressure at idle with a mechanical pump is pulse pressure.. where as from an electric pump it is steady pressure. Steady pressure will always shows needle/seat issues sooner.

JW

 

Your carb was tested on a motor that was on the dyno after yours Larry.. I probably just did not mention that. It's SOP around here.

Contrary to popular belief, most carbs are not that sensitive to the engine sitting underneath it. It's only when you kill the vacuum signal, via a big intake or really long camshaft timing, do you have to start making calibration adjustments.

In your case Larry, I simply tested it on a motor with a single plane intake, and similar camshaft to yours.

I have not sent a carb out without testing since I came across one of those ones that did not work, back in the early 2000's.. I never did figure out what was wrong with that one, my conclusion was it must have had a pinhole leak in an air bleed passage.. it had to be jetted really rich by normal terms, to function correctly.. Had not seen one like that for years, and dozens of Q-jets, till I came across the one recently. that one had to have 80 something primary jets in it, to meter fuel correctly, and all the air bleeds were sized as they should have been. The body parts appeared to be reasonably flat, so I chalked it up to an internal casting issue, and just jetted it up as required. We see this with Holleys too every once in a while.

JW