Exhaust question
Thread Starter
|
Senior User
Joined: Dec 2013
Posts: 124
Likes: 0
Exhaust question
76 F100 302 2BBL. I have worked on plenty of motors that wouldnt run right without backpressure. Would of never thought a 302 would do this. I have a major exhaust leak on both sides where the flange meets the mainifold. I was wondering if anybody else has had these issues. I pretty much lost most of my bottom end but once you get it opened up it is fine. Probably putting some shortys on there. I have quit driving it because i hate the sound of a exhaust leak. So has anybody had backpressure issues?
Moderator & parts slinger
Joined: Feb 2007
Posts: 50,146
Likes: 5,783
From: S/W Missouri, Polk county
I would not think a major exhaust leak like you have would affect the motor operation. I have read/heard that motors run better with some back pressure from the exhaust system.
But then how come race cars, mud trucks, pull trucks ect...run open headers just fine??
Does that truck have the "exhaust donuts" in between the exhaust manifold the tailpipe flange joint area?
Or are you leaking from where the exhaust manifold bolts to the head?
Sorry no real help, have you posted this question over in the eng forums?
Small Block V8 (221, 260, 289, 5.0/302, 5.8/351W) - Ford Truck Enthusiasts Forums
But then how come race cars, mud trucks, pull trucks ect...run open headers just fine??
Does that truck have the "exhaust donuts" in between the exhaust manifold the tailpipe flange joint area?
Or are you leaking from where the exhaust manifold bolts to the head?
Sorry no real help, have you posted this question over in the eng forums?
Small Block V8 (221, 260, 289, 5.0/302, 5.8/351W) - Ford Truck Enthusiasts Forums
Thread Starter
|
Senior User
Joined: Dec 2013
Posts: 124
Likes: 0
It doesn't have the donut gaskets. I'm not real sure if it is suppose to. But the studs are bad so the pipe is just pretty much sitting there. There is a spacer like thing on the driver side were there is a huge gap. This is the main reason i planned on getting some headers. I think the reason mud trucks. etc can have open headers is because they are bringing just a much air as they are putting out. With me having a 2bbl i think the engine can't pull air in as fast as it can push it out. A aftermarket intake and 4bbl would eliminate the need for back pressure. That's what i think.
Thread Starter
|
Senior User
Joined: Dec 2013
Posts: 124
Likes: 0
Put the headers on today. haven't had a chance to crank it up though. I ran it with open manifolds and its amazing how much throttle response you gain. Got to take it to the exhaust shop to get them to fit the pipe to the header. They are ford racing headers and i luckily picked them up for $25 from a freind.
Hotshot
Joined: Sep 2012
Posts: 17,708
Likes: 136
From: Calgary
I've always been under the impression that back pressure was needed to help produce low end torque and power until the horse power curve started to take over. Most race applications are based on higher rpms and are usually pretty lame at low rpm. Large big blocks may be the exception to the rule.
Postmaster
Joined: Sep 2013
Posts: 2,595
Likes: 5
From: Pasadena, Ca
I always thought of it as a venturi effect, where a restriction in the exhaust signal causes the flow to increase. Its like siphoning, the fluid on the down slope is actually pulling the fluid on the upslope. Or like a river with a narrowing in the banks, the water runs faster, pulling the water upstream with it.
With a larger engine, you need less of a venturi effect because the flow is faster, and the point of decreased pressure is shorter.
And because of this, its my understanding that you will get more "back pressure" with headers, at lower RPMs because the signal flow is slower and has more space to expand.
But, idk.
With a larger engine, you need less of a venturi effect because the flow is faster, and the point of decreased pressure is shorter.
And because of this, its my understanding that you will get more "back pressure" with headers, at lower RPMs because the signal flow is slower and has more space to expand.
But, idk.
Trending Topics
Elder User
Joined: Jun 2013
Posts: 685
Likes: 2
Flow is king with a carb engine. Most power gains are from getting air in and out of the engine as efficiently as possible. Porting and polishing heads, larger intakes, more open air cleaners, larger exhaust, free flowing headers, larger carbs, super chargers, turbo chargers, X-pipes, H-pipes exc.. It all has to do with getting in more oxygen, and getting it back out( so you can get more in). With more oxygen in the engine you can put more fuel in, which gives more potential for power. Now this is all performance minded, not at all for MPG.
Our engines don't have complex computer systems to tune correctly or tons of emissions crap that might need it. Larger carbs and tuning take care of the air/fuel mixture.
That is my understanding, but I am no engineer.
Our engines don't have complex computer systems to tune correctly or tons of emissions crap that might need it. Larger carbs and tuning take care of the air/fuel mixture.
That is my understanding, but I am no engineer.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Thread Starter
|
Senior User
Joined: Dec 2013
Posts: 124
Likes: 0
I've always been under the impression that back pressure was needed to help produce low end torque and power until the horse power curve started to take over. Most race applications are based on higher rpms and are usually pretty lame at low rpm. Large big blocks may be the exception to the rule.
Postmaster
Joined: Nov 2012
Posts: 2,806
Likes: 8
From: Langley, BC
High performance race engines that will always be up there in the rev range need the highest flow possible, so it's all about getting air in quickly and out even faster.
Ever noticed how a bigger carb, better intake, and headers made you lose bottom end torque? All that back pressure and overall restrictive qualities from the factory manifolds help torque.
Ever noticed how a bigger carb, better intake, and headers made you lose bottom end torque? All that back pressure and overall restrictive qualities from the factory manifolds help torque.
Elder User
Joined: Jun 2013
Posts: 685
Likes: 2
Even on the bottom end I have never seen it drop below factory numbers. Low end torque may gain less than the mid or top range, but its always an improvement over factory. As far as I have seen that is, I am no engine builder or dyno tester.
Postmaster
Joined: Nov 2012
Posts: 2,806
Likes: 8
From: Langley, BC
All depends on how it's built, but yes it is certainly possible. There are too many variables involved though for any one set of rules to be made. My point stands though that high flow exhausts benefit race applications more than they do street applications.
Postmaster
Joined: Sep 2013
Posts: 2,595
Likes: 5
From: Pasadena, Ca
I am definitely unknowledgeable, lol, but what would the dyno report be if you only added headers to a stock setup? That is essentially what the OP has happening. Increasing the space without increasing the output, will get poorer results.