351M Fuel
Freshman User
Joined: Mar 2007
Posts: 34
Likes: 0
From: Jacksonville
I have a quick question , can running to high pressure to the carb cuase a higher fuel consumption with out any gain in performance? The reason I ask is I checked the pressure at my carb and found I was running about 9lbs. I put a holley regulator on it and dropped it to 5lbs, I was only getting about 7-9 miles to the gal (7.5 to 8 on the freeway and about 8-9 in town). As you can see I was getting worse mileage on the freeway which does not sound right.
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Hotshot
Joined: Apr 2006
Posts: 11,794
Likes: 0
From: Kansas City, KS
How fast were you driving on the freeway? I have the same issue. Much better mileage if I take the backroads to work at 55-60 mph. On the freeway, running 70ish, I can watch the gas gauge fall!!
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Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
Excessive fuel pressure can blow open the inlet valve on some carbs. Many mechanical fuel pumps do not regulate the fuel pressure very well at higher RPM. The result is a constant flooding of the carb at higher speed, and poor fuel mileage. Also plugs can become fouled, and the idle will suffer when you come to a stop after a sustained run at high RPM.
9 lbs fuel pressure is certainly excessive. Most carbs want no more than 5 lbs.
9 lbs fuel pressure is certainly excessive. Most carbs want no more than 5 lbs.
Freshman User
Joined: Mar 2007
Posts: 34
Likes: 0
From: Jacksonville
Yea, I put an electric fuel pump on my truck after the clev ate 3 mechanical pumps in a row. The electric pump puts out 4-9lbs but is not adjustable at the pump. So I just put the regulator on it and so far as I can tell it seems to be doing better, I'll have to watch it over the next few tanks of gas to see how it does and post the results.
New User
Joined: Jan 2007
Posts: 18
Likes: 0
if you run high octane fuel with stock motors you cause detonation of the fuel and burn up valves and pistons so if you were going to run a higher octane fuel i would advance you timing to increase your compression ratio to help prevent detonation.
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
There are no benefits from premium fuel even with advanced timing on the 351M or 400. Been there done that and the fuel does not detonate. Your fuel mileage and power will decrease, -a total waste of $$.
Last edited by Torque1st; Apr 9, 2007 at 12:47 AM.