I have 88 5.0 motor in my 53 f100. I took it to the exhaust shop and had them come off my center dump headers with 2.5 pipe for a couple of feet then stepped it down to 2in and then stepped it down to 1.5 over the axle and out the back. I like the pea shooter sound now, but it seemed like the truck had way more "raw fury" with just the headers and a couple of feet of straight pipe. Is this setup choking the motor or what? also switched from efi to carb.

 

Open (uncorked) headers do give that feeling! But, no, I don't think the 1.5 inch pipes are really choking a 302 engine down- heck, in the 60's the duel 1.5 inch tailpipes were considered the "performance" setup of the day!

 

Actually,the hotter the exhaust temp,the better the evacuation.Smaller tips keep ex. temps up.

 

Cool, thanks guys. I was about to cut the last stepdown off.

 

You really believe that 1.5" exhaust was considered to be a performance setup?

To the OP, yes, the smaller pipe is going to be more of a restriction.

 

I agree , you don't want to restrick the exhaust on a 302 , they do much better with a free flowing exhaust... Lew

 

Well, math tells us a 1.5" pipe is only 56% as big as a 2" pipe and 36% as big as a 2.5" pipe. Dual 1.5" pipes will flow less than a single 2.25" exhaust. So depending on what kind of 302 we're talking about you're probably choking it a bit.

Should be no worries with straight 2" duals. The Boss 429 came with 2.25" inch duals...

 

Nothing fancy, fresh rebuild, 650 edelbrock carb, performer intake, hei, headers. It will still do a nasty burnout though. I realize I need some back pressure, but I may have a little too much?

 

Backpressure is a total myth,there is no need for any restriction.While hot exhaust temps help to increase flow,a shorter more open exhaust will improve performance.If you need to exit the rear,an X pipe setup will help greatly.X pipes will force flow,working on the pattern of the exhaust push.When one cylinder fires it fills the tube w/exhaust gas,the next cylinder fires,it pushes it along down the line,and so on http://www.pypesexhaust.com/xpipes.html Check this stuff out,lots of toys I'd like for my 289.

 

People always talk about backpressure but what they're really talking about is exhaust system flow capacity. In a pipe system the maximum flow volume is determined by the smallest section, and it doesn't matter where this small section is in the chain the effects are the same. For optimum low rpm TQ the exhaust should be a bit on the small side, but if you want max HP at 6000rpm it needs to be big. There are tradeoffs though, everyone knows a small system will be restrictive at high rpm, but a big system will also hurt low rpm TQ.. and it's because there is no exhaust velocity to help evacuate the cylinders at low rpms. The big trick is sizing the system to work best for your particular application. A stock headed 302 really doesn't move a lot of air so a dual 2.25" or single 2.5" system is well matched, go slightly smaller if you never rev the motor or slightly larger if you spend all your time at redline.

 

shorter more free exhaust will increase high RPM power cause it can get the exhaust gases out faster. but longer smaller(to a point) exhaust will increase exhaust scavenging and help low RPm torque. and since in my experience the 302 likes to work at high RPMs then i would say your exhaust is too small.

 

......"as-built" purpose of the truck..RIGHT?...

What is the truck really gonna be used for "most" of the time?

Oh yea...HEADERS?...What type?...primary-tube size?...

...then there is that..."what muffler ya runnin'?" thing...

Smithies are nice...been around forever too...



See...the thing about back-pressure is...

...stochiometric ratio!

stoichiometry;
in chemistry, the determination of the proportions in which elements or
compounds react with one another.

The rules followed in the determination of stoichiometric relationships
are based on the laws of conservation of mass and and the law of combining weights or volumes.
See also equivalent weight.

Here is where the term originated from...

The word stoichiometry derives from two Greek words:
Stoichiometry deals with calculations about the masses
(sometimes volumes) of reactants and products involved
in a chemical reaction.

Jeremias Benjaim Richter (1762-1807) was the first to lay down the principles of stoichiometry.

It is a very mathematical part of chemistry, so IF ya REALLY want to get into it...

...be prepared for LOTS of calculator use.

In 1792 he wrote: "Die stöchyometrie (Stöchyometria) ist die
Wissenschaft die quantitativen oder
Massenverhältnisse zu messen, in welchen die chymischen
Elemente gegen einander stehen."

Translated:
"Stoichiometry is the science of measuring the quantitative
proportions or mass ratios in which chemical elements stand
to one another."


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Just thought it might help...

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The purpose of the truck is light cruising and to try and run down anybody that brings a hot car around the neighborhood. It has block huggar headers and no mufflers. I still might just cut off the last stepdown. But I do like the peashooter sound!