Fuel pressure / Volume requirments, how much needed, can we put this to rest

69 N.O.X. RATT · 01-19-2003, 04:11 PM

Unlike most topics, I have seen a lot of varying opinions on fuel pressure / volume requirments from people who know a lot more than I do. I find it hard to understand the disparage in opinions. I have a friend who does 123.5 in the 1/4 with 3/8 line and a Holley red pump. This is with a dyno confirmed 600+ hp 496 wedge motor. How does he not run out of fuel?

I guess the only way you really know is to run the car. If you are running out of fuel how do you really know, will the car always just nose over like you are hitting the rev limiter, or could it be something as little as the plugs are a little white.

clem zahrobsky · 01-19-2003, 10:01 PM

install a inline fuel pressure gauge and even a big block will make max power with 4/5 # of pressure at WOT as long as you do not have the bronze filters in the carb. if you need more than 2 steps larger jets than the carb came with you need more fuel. also make sure the fuel tank pickup is in the back of the tank:chevy

[Modified by clem zahrobsky, 9:02 PM 1/19/2003]

427Hotrod · 01-20-2003, 01:38 PM

A lot has to do with overcoming G-forces. My 427 ran 123 mph 1/4's too with a mechanical Holley pump and 3/8" lines. Never had an issue...to many folks' surprise. NASCAR guys can run 200 mph and 750 HP with a mechanical pump, but they don't have the launch issues.

I've run the 540 with the same setup too. It feeds it so far to the 615 RWHP stage, but I know it has really got to be on the edge. It pulls hard to 7000 rpm in all gears so far. Haven't had a good run at the track with it and slicks due to those little rear axles issues.....but I suspect it would have had problems during a hard launch.

It is going to be upgraded as I go back together. I guess it still comes back to making a few passes with a gauge hooked up. I know ML67 did some fuel pressure tuning on the chassis dyno with his 540 '67 and several of his buddies. There was a 455 Stage 1 Buick and a 454 Chevelle. They found that the Comp 140 was having a tough time maintaining on the 540 and the Holley electrics were maxed out on the others. But they did pick up measureable power everytime they worked to get pressure back close to the optimum.

There are discussions that the large volume of fuel in a -10 line is hard to overcome on a hard launch. I doubt any of us have anything that launches that hard.

If I was going to the trouble of running lines, I wouldn't use anything smaller than a -8 for sure, preferably a -10 to the front. Maybe a -12 feeding the pump, or at least a -10 out of the tank. I would use -8 to the carb and regulator(s). For nitrous I always use a dedicated pump and line. For most, the stock 3/8" line works well for this.

They don't always just nose over. If they are right on the edge, they kind of act like weak valvesprings....they just don't pull at the top end like they did earlier in the run.

There are many 9-10 second cars running on the old Holley Blue pump and doing well. Anything better than that is good insurance. Don't equate $$ with what you need though. Barry Grants are pricy, but another issue where lots of people complain aout them and their service.

JIM

69 N.O.X. RATT · 01-20-2003, 03:01 PM

Jim, I have my regulator set at 6.5 #'s. Would it be safe to assume that if I am keeping that pressure throughout the run I am ok.

If I ever feel it noseing over or not pulling like it should, I can shut if off and check the plugs right then. If it is not getting enough fuel the plugs should look lean, correct?

This is a subject that has always made me wonder why there are so many opinions, you would think it would be very linear.

norvalwilhelm · 01-20-2003, 04:57 PM

69 N.O.X. RATT. How can you look at a gage under a hard pass? I have 2 holley blue pumps feeding a 1/2 inch stainless line running 15 pounds pressure at the firewall then into a large holley regulator set at 6 pounds. I have all the gages but can not see them once I start a run.
I need a shift light to tell me when to shift, can't see the tac and besides it can't keep up to the motor, can't see the oil pressure gage so have a big red oil pressure light. Have never seen the boost gage under full boost either.
I might be getting too old but a good bigblock like yours under a hard run you don't have time to look at anything, just shift, shift shift.
I have been a passenger in my car while my son drives it and that is the only way to see what's happening.

69 N.O.X. RATT · 01-20-2003, 05:28 PM

I agree Norval, it is enough work just trying to keep up with the tach. luckily I have a volunteer to watch the gauges while I try to keep it in a straight line.

I like how you have the some of the gauges and warning lights where you do. I am going to do something similar when I get the hood cut up to fit. I want to hide a shift light and oil pressure warning light in the hood. I will have to figure out a way to make it work and still be able to open the hood. I do not want the gauges visible from out side the car, unless you look directly down the L-88 cowl.

Les · 01-20-2003, 08:36 PM

RATT,
You pose a worthwhile question. I don't have any data for you but I found Harold Brookshire's(Ultradyne Cams) recent comments interesting. When discussing my cam change to his 276/284 solid flat tappet cam, he said that I'd probably need to upgrade to 1/2" line to provide enough fuel for my relatively mild combo( but that the stock 427 fuel pump would be fine). He suggested that I try it first & look for the car nosing over in 2nd & 3rd gears- if it does, then the change would obviously be in order. I hope that helps a bit rather than adding to the confusion. :cheers:

norvalwilhelm · 01-21-2003, 09:49 AM

My gages are mounted to the firewall and the hood closes over them. It allows me to run 2 fuel pressure gages outside the car but not really outside. Once the hood is closed they are hidden from the outside. I also run a temperature light set at 215. While running really hard across country I blew a fan belt and didn't notice the temp gage because here again you have no time to look at gages.
Gages are great to monitor the engine but useless when really running hard. In the Movie the FAST and the FURIOUS remember when the star was looking at his lap top and punching something in in a 10 second car. NO WAY.

norvalwilhelm · 01-21-2003, 09:51 AM

Found this picture with the hood closed. The hood is dusty.

69 N.O.X. RATT · 01-21-2003, 12:55 PM

The fast and the furiuos was a very stupid movie. I finally watched it last weekend. My girlfriend was laughing watching me wrinkle my nose and complaining at the sound of the those stupid 80 hp fart bombs.

Norval, that is the exact look I am going for. I have the short L-88 hood so I have to mount my gauges a little farther down. Having the gauges hidden in the hood is pretty trick looking.