Alrighty, a while back I found this thread here, https://www.rx7club.com/general-rotary-tech-support-11/heres-how-figure-out-intake-runner-length-199788/

I've read through the whole thread several times, and answers seem to be ALL over the place, with nothing solid. So anywho, I have quite a few questions, but would like to start here... After I get some solid answers from these questions, I can get more to the point.

1. When "tuning" the length of the runners for an intake manifold, is the distance from the outside intake ports (side of the block), to the intake ports in the combustion chamber, part of the formula? In other words, if you don't add that distance when figuring out the length, will it change the rpm in which you was originally tuning for?

2. If that distance is needed, what is the distance from the outside intake port (side of the block), to the intake port in the combustion chamber for both the primary and secondary ports? (center to center)

-Alex

 

Bump!

 

Oh c'mon! I know someone atleast has a motor apart that could take the measurements!

-Alex

 

I'm guessing you're thinking of fabbing your own custom intake manifold (especially since you think fabrication is such an easy process ).

I believe so since runner length affects the powerband (short runners are good for top end vs. long runners good for low end; right?).

Quick google search brought up this custom IM fabrification and what a coincidence, it's for an RX-7.

http://www.sdsefi.com/techinta.htm

Good luck with the project.

EDIT: In the link it says that most street vehicles use runners of length 9 inches or longer. After looking at that thread you linked I don't think you'll learn anything new from the link I gave you.

 

I guess you don't know I own a machine shop do you?! I'll be machining everything rather than actually fabricating it from hand.

Correct. The shorter you make the runners, the higher your powerband will be. This will create the low end to suffer though. Also, if you make them to short, you could have the powerband so high, that your motor couldn't utilize it. (motor can't rev that high) Of course, if you make them to long, your top end can suffer. However, the turbo(s) can take care of that problem as long as they are still in their efficiency range. That all depends on the size of the turbo(s), and exactly how long you made the runners.

Yea i've already found that. Didn't really give me much info though. I've torn google apart, and havn't been able to find a damn thing! I'm pretty close to figuring everything out, I just need a few questions answered first.

Thanks!

I noticed that, but it doesn't state what rpm the runners would be tuned for. However, if I knew the distance of the "internal" ports, i'd be able to figure it out.

-Alex

Edit:
I know. I appreciate the help and free bump though!

 

Bump!

So does anyone know the distance from the intake port on the side of the block, to the combustion chamber, center to center? (both primary and sec.)

-Alex

 

Someone posted their senior project on here a while ago, which included some intake manifold calculations. I don't remember whose it is, and I couldn't find the post by searching.


It's too large to attach on these forums. Send me a PM and I can email it to you.


-s-

 

The lenght of the runner is intended from the valve to the intake plenum, on rotaries I guess from the intake port to the intake plenum

 

I crudely measured this on a FC motor today, just stuck my finger in the port and then measured the approximate length of finger that it took to reach. It's about 2.5" +/- 0.75," I hope that's something to get you started.


-s-

 

scotty can you email me that senior project... mono4lamar@hotmail.com