L31 intake swap-I am actually doing it not a question.

[beardeddummy]

That's the one I was looking at. money is holding me back so I'm just getting a list together. do you think vortec dizzy will work? I'm kinda scared of this the only swap I've done have as been plug and play.

 

[Jrgunn5150]

I've seen one with a Vortec Dizzy in it.

 

[Supercharged111]

Multiport fuel injection doesn't really work like that. With the injectors at the port, the runner's only have to carry air, so making them long, only restricts airflow. Cam choice becomes more important on a short runner engine though.

Runner length absolutely dictates torque curve/peak. Look at the TPI, its midrange is massive. These trucks suffer from a 2200 RPM dip caused by the stock intake, and the LT1 manages to not really have a torque peak. The runners are so short that, when combined with a wide LSA cam, there's no real hump in the middle.

 

[Jrgunn5150]

Runner length absolutely dictates torque curve/peak. Look at the TPI, its midrange is massive. These trucks suffer from a 2200 RPM dip caused by the stock intake, and the LT1 manages to not really have a torque peak. The runners are so short that, when combined with a wide LSA cam, there's no real hump in the middle.

It dictates it through restriction though. Changing one piece of the puzzle will have that effect. Changing the intake, and adding the appropriate cam to go with it, will give you a better engine overall, everytime.

Try adding a cam to the same TPI engine, and it will have almost no effect, or run like poop, because the runner's are so stupid long. Which is why most TPI's are either Carb'ed or running Holley Stealth Ram's now.

 

[Supercharged111]

So you're telling me that the restriction created by the TPI intake creates that huge midrange swell? Please tell me why the 454 Vortec has such long runners that don't help with torque at all as well.

 

[Jrgunn5150]

I'm telling you that forcing an engine to breath through a straw isn't the way to make more power.

And I'm telling you that a 10.5:1 Vortec with a short runner intake and the appropriate cam will make more power EVERYWHERE than stock. As do Stealth Ram equipped TPI engines.

 

[Supercharged111]

http://www.wallaceracing.com/runnertorquecalc.php

http://www.enginebasics.com/Advanced Engine Tuning/Intake Runner Length.html

http://www.eng-tips.com/viewthread.cfm?qid=165529

As you can see, restriction has nothing to do with it. It's reflected pressure waves bouncing back and forth and, at some point, they shoot down when the intake valve is opening. This is the RPM for which the intake is tuned. It's a lot more technical than that, but that's the dumbed down version.

 

[Supercharged111]

I'm telling you that forcing an engine to breath through a straw isn't the way to make more power.

And I'm telling you that a 10.5:1 Vortec with a short runner intake and the appropriate cam will make more power EVERYWHERE than stock. As do Stealth Ram equipped TPI engines.

It's not fair to compare a choked out stock intake to a superior aftermarket offering and use that as the basis for "long runners are bad".

 

[Jrgunn5150]

The question wasn't a general one though, it was a specific one. In this application, you can have a stock intake, or a Marine intake, a Carb'd intake, a Ram Jet, or the Edelbrock XT.

Out of those options, I choose the Edelbrock XT as the best mix of performance, price, capability, and ease of install.

There are many factors other than runner length alone in an engine. What if they are only 3" long, but 10" around? What if the plenum volume is very small? Or very large?

If you were to do nothing but swap an Edelbrock XT onto a completely stock engine otherwise, it would probably lose some low end. I bet you probably wouldn't notice it much though.

However, you put one on a mildly built engine, with decent compression and cam spec's, and it will walk that stock intake everywhere.

 

[Supercharged111]

The question wasn't a general one though, it was a specific one. In this application, you can have a stock intake, or a Marine intake, a Carb'd intake, a Ram Jet, or the Edelbrock XT.

Out of those options, I choose the Edelbrock XT as the best mix of performance, price, capability, and ease of install.

I was responding specifically to this:

Multiport fuel injection doesn't really work like that. With the injectors at the port, the runner's only have to carry air, so making them long, only restricts airflow.

This statement is incorrect.