vristang

Exhaust back pressure will hurt efficiency PERIOD.

Larger diameter exhaust ports affect the power level the same as intake size.

You must select the intake and exhaust sizes (both diameter and length) to match the anticipated power and RPM ranges.

3" exhaust may be too big, but you aren't loosing power due to a lack of back pressure.


If there is a power loss, it is because the motor is not capable of making power where the new larger exhaust wants to make power.
It would be a problem of balance.

Here is how it really works...
A pulse of high pressure exhaust travels down the primary and into the collector.
When the high pressure pulse hits the collector, its velocity creates a low pressure wave that runs the length of the other 3 primaries. A vacuum (of sorts) is created on the other primaries.
Essentially, the high velocity gasses SUCK on the other 3 primary tubes.
Length and diameter of the primary tube will have a MAJOR impact on the velocity of the pressure wave when it hits the collector.
Also, the length of the primaries will have an impact on the timing of the low pressure waves. If the pressure wave never fully develops before the next exhaust pulse, then there is no increase in efficiency.


It isn't that a smaller exhaust is better for power on the 302,
However, it is that the exhaust must be properly sized for the intent of the engine.

One book that can help ones understanding in this area (and several others actually) is...
Four-Stroke Performance Tuning by A. Graham Bell
this book provides equations that will help your understanding of how things are actually happening in the exhaust.
There are other books that cover this subject, but this is a great book for enthusiasts, who may not have engineering degrees.



jason

klapdout

+1 on reading A. Graham Bell's books, ive read,Four-Stroke Performance Tuning in Theory and Practice, and Forced Induction Performance Tuning

very good books, both can be found at amazon =D

also, what other books are you talking about, id like to find some info on them

95gt302

i think your right ive been told forever that the biggest u want to u want 2 1/2 at the biggest

LTnone

A. Graham Bell...like the telephone dude? [8D]

vristang

All I can figure is that his parents had a strange sense of humor.

Kinda like Johnny Cash ... A Boy Named Sue.



Here is my complete book list.
I tried to keep it down to just the ones that I thought were REALLY good.
I'm not sure how the formatting will come out here though?


Automotive Reading List

My personal comments are in BLUE.

Mustang Specific (not worth full price if you frequent Stangnet, The Corral, SBFTech, or Mustang Forums; but still fun reads)
How to Tune & Modify Your Ford 5.0-Liter Mustang by Turner
5.0L Ford Dyno Tests by Holdener
Mustang Performance Handbook by Sessler
Ford V-8s On A Budget by Monroe
The Official Ford Mustang 5.0 Technical Reference & Performance Handbook by Kirschenbaum
Ford Engine Parts Interchange by Reid
Mustang 5.0 Performance Projects by Huw Evans
This text has fairly extensive write-ups on the basic bolt-ons; Tuneup, headers, underdrive pullies, mid pipe, Intake, pulling the motor, MAF conversion, supercharger/nitrous,

Engine Building & Re-Building
How To Rebuild Small-Block Ford Engines by Monroe
The Step-By-Step Guide to Engine Blueprinting by Voegelin
I used both of these heavily while building my first motor.
How to Rebuild the Small – Block Ford by Reid
I just purchased this one, and haven't read it all the way through yet.


Math/Calculations
Automotive Math Handbook by Aird
Auto Math Handbook by Lawlor
Great for ETs, Gear Calculations/Speeds, Volumetric Efficiency, Carb sizing, Braking, Cg, etc. Probably only need one or the other.

General Performance
Bosch Automotive Handbook Published by SAE with various authors
Numerous Professional Automotive Engineers write on a variety of topics. If you could only purchase one book I would recommend this one. It covers every automotive system, in theory and application, such as Material Properties, chassis design, and aerodynamics. Some developing technologies as well such as Hybrid powertrains. Mathematical definitions are given as well as written definitions. May only be available from SAE, and they update every couple of years. I think the 6th edition is current.
Four-Stroke Performance Tuning by A. Graham Bell
One of my favorites, I just keep going back to it. I especially like the chapters on cooling/oiling systems and cam design. Formulas are given in many chapters, as the book is intended as a "how to" for the technically knowledgable. Not just theory, but practical application for street and race use. Some chapters are very similar to Bell's Boost book described below, so one or the other may be sufficient.
Performance Tuning in Theory & Practice by A. Graham Bell
It is an older and out of date version of the book above, but has some detailed info on points distributors and carbs. Very detailed info. You will have to search for it though, I believe the last publishing date was in the '80s.

Power Adders
Maximum Boost Designing, Testing and Installing Turbocharger Systems by Corky Bell
Have not read yet, but this is one of the most recognized books on practical design of turbo setups, both carb and efi.Forced Induction Performance Tuning A Practical Guide To Supercharging and Turbocharging by A. Graham Bell
Again, one of my favorites. This is a Boost specific version of the Four Stroke book listed above. Maybe one or the other would be sufficient.

EEC-IV Specific
Ford Fuel Injection & Electronic Engine Control How to Understand, Service and Modify by Probst
If you are serious about taking care of your Mustang yourself this book is a must read, no debate. All of the theory on how the computer works is described in an easy to understand way. The diagnostic sections are worth more than their weight in gold.

Repair and Maintenance
Mustang Car Shop Manual Published by Ford Service Publications
This is tougher to find as it is only available from Ford/the publisher. It will be year specific, for example my text is for my year of Mustang. It is fairly expensive too, if I remember correctly. Only covers Body/Chassis Electrical/Powertrain.Haynes or Chiltons for your year/application
Both have their advantages/disadvantages. I recently found some old, outdated Chiltons in a used book store, which had some good info on fuel economy, reading vac gauges, and color pics for reading plugs. Very sweet deal for six bucks.

Sic5OohSC

on a stock car I have experience that less back pressure loses low end power. Plus isnt free flowing exhaust bad for your valves. All I will say is if he went to "Nascar School" I sure in the hell wouldnt want him in my pit if he has that kind of degree and doesnt have a working posi unit

vristang

Most of the REALLY smart car guys I have met, have had POS cars.

For some reason these guys tend to look at every cars 'potential' rather than what it is.

If you guys ever saw my 4 cyl., you would probably ban me [:@]


Just food for thought.

TOOT

2.5" into a 3" tip is as big as I would go. And in my opinion 3" from the headers back will effect performance, back pressure is needed.

88BlueGT

From what I have thought for the past 5 years is that you needed backpressure. And is he saying that you should run smaller pipes with a turbo and bigger NA? If so, punch him in the head because hes retarted. Talk to anyone with a turbo car and they will tell you, with exhaust on a turbo car, the bigger the better! I was reading on turbomustangs.com that they had a 2.5' exhaust on it, swapped it for a three inch and gained like 50rwhp off of it! I think hes wrong......

mustangfxbdy

your right twisted

its the exact opposite of what his buddies saying. i have delt with turbos for a long time. and have friends who cars i still work on that have turbo cars.

So
coming from the supra world bigger exhaust on a turbo set up is what you want. but you can go too big on exhaust on a turbo setup(depending on the size of the turbo). the only reason you would even want back pressure on a turbo is for less turbo lag but that is not enough reason not too put a decent size exhaust on it. because once the turbo spools up the faster you can get the air in and out of the engine the better therefore you want the best flow in and out. if i had a turbo setup on a stang the smallest exhaust i would want is 3". crap i ran that on the supras 3.0L engine and it responded well put 2.5 exhaust on the supra and seen a power lost because you would get less air traveling through the engine.

the engine is a big air pump and a turbo just increases the air in and out. the turbo can keep enough air coming in to compensate for all the air going out through bigger exhaust but an n/a cant keep enough air coming in to compensate for all the air going out through bigger exhaust... so back pressure kind of hurts you on a turbo setup but like i said before even then you can go too big. but ive seen people with a big enough turbo running 4" exhaust on there supra and it helps alot.

now if you have a n/a engine and you have too big of exhaust and you cant get enough air in your killing your horsepower but mainly torque and low end power is what your hurting. nascar engines are setup for top end horsepower not low end. surely he knows that since he went to NASCAR school. I wouldnt want him in my pits or building my engines.( so if he plans on racing anyone by drag racing and they had the same setup with 2.5 exhaust hes going to learn his lesson and i dont think hes going to be racing his car on the nascar tracks so why build it for top end.) I want alot of low end power and some top end

my opinion unless its a 247 stroker or something thats turboed or bad a%% supercharger 3" is too big. i wouldnt go no bigger than 2.5" but i also wouldnt go any smaller.

nascar engines are built alot different than a 302 with ported e7 heads and if your friend doesnt realize that then [:-]...