Man you guys are a tough crowd!
First, you might be best served by having a shop line hone your main caps and turn your crank. That way you will not be prone to spinning a rod bearing like I did Saturday night. Beat up a bunch of Chevys on the way. The car ran acceptable oil pressure so we drove it home. Guys FORD is built TOUGH!. I did the same thing with a 500 HP Cleveland engine. Drove it for two weeks with a spun bearing, and it still did no extra damage.
Second, I really don't care at all if you guys are using 2" pipes, 2 1/4" pipes, 2.5" pipes, 3" pipes or 4" pipes. Hell why not run the engine without pipes at all?
Because back pressure is needed for the engine to develop torque.
When we dyno an engine, we specifically pull out a header with a minimum of 4 to 6 inches of straight shot off the head. WHY? Because any bend adds back pressure and back pressure reduces horsepower reading. Everyone is looking for the HP figures on a dyno run. It is only guys like me that pour over the torque readings. WHY? Because I like to win, and HP is calculated. TORQUE is measured. It takes torque to move your beast down the street or down the quarter mile.
Back to headers, small blocks usually like 1 5/8 primary tubes and 2.5 or 3 inch collectors. A stroker engine will like 1 3/4 to 1 7/8 primary tubes and 3-4 inch collectors. So will most big blocks. A 641 HP engine I saw was running 2" primaries and 4" collectors. They were after 7 second quarter mile times. Eight seconds will be the gas only times.
If back pressure doesn't matter, then why not run 2 1/2 inch primaries and 4 inch pipes all the way????
Come on guys! You need to know the fundamentals, then you race and learn what works, then you use engineering to improve the margin of victory.
We tune the headers and the pipes to get the backpressure right for where we aim the peak torque point of the engine, and to get the broadest torque curve possible over the usable RPM range.
I have seen some great engines run really slow times and they could never figure it out. They saw a dyno report that showed they picked up 10 horse power by going to 3" tubes. Well they did pick up 10 horsepower at 6,000 RPM. But they lost 20 foot pounds of torque from 2,500 to 4,500 RPM and lost 36 foot pounds or torque from 4,500 to 6,500 RPM. So they ended up with an engine that sings at 6k but has to go from 600 RPM to 6,000 RPM just to enjoy the magic. Hope they use a 5,500 RPM Stall converter and 5.67 gears to get them there really really fast.
An internal combustion engine is basically just a big air pump. The more air it pumps the more HP it is able to make. So WHY does intake runner shape, diameter, and length make a difference on a fuel injected car?
Why did TFS go to a 90mm MAS on their improved intake system? Because they had big *** ports but could not pull enough air through the MAS. Now they are kickin butt.
Remember guys, the intake runners, the heads, the swirl, the quench, the compression, the air fuel mixture, the ignition timing, the exhaust ports, the primary tubes, the collectors, and the exhaust tube size all work together, or they slow you down. It is the total system approach that goes into making a great engine. Remember that as you spend your money.
It all fits into a total package that equals performance. God I am beginning to sound like Vic Edelbrock!!!!
