tomcat

I was reading some comments about using the 500EFI intake on larger displacement engines. Guys found the power to fall off after 5000 RPM on a 540. Is this because the runner is too long or too small? I also see that sheet metal tunnel ram intakes can now be ordered with "long" runners.

The small and dangerous amount of information that I have says runner volume has to go up with cylinder displacement. The runners in the 500EFI intake appear to narrow quite a bit where the crossed runners touch.

I have also read that runner length determines the time it takes for the pulse from the closed intake valve to travel to the plenum and back to the valve again, where that pressure pulse can help fill the cylinder when the valve opens again, a kind of acoustic supercharging. Therefore runner length has to be coordinated with cam timing and engine RPM range.

Any rules of thumb for runner length vs RPM range? For example sheet metal tunnel rams for drag racing often have runners about 6" long and are being used on engines that reach 8000 RPM. What should runner length be if maximum RPM is 6000 RPM? If I say that the port in the head is 4" would this get you close?

8000/6000 X 10" = 13.3

13.3 - 4 = 9.3"

Raylar

Tom: Not sure how expert I am having designed a couple of intake manifolds but I can give you the formula for calculating optimum runner length.

L= ^ ((ECD x .25 x V x 2) divided by (RPM x RV)) - 1/2D

Where:
L = runner length
V= velocity of air ( use 1250ft./sec)
RV= reflective value ( pulse number -use 4th wave= RV=4)
D= intake runner diameter
ECD= effective cam duration= 720-(adv.intk. duration - 25)

This should give you a length in inches which includes valve to plenum.
Hope this helps
Ray @ Raylar

vtec

F1 engines rev to over 18000, and have short intake runners. The runner length is variable, but is generally short. These engines don't make any power at lower rpms, and have relatively narrow power bands.

vtec

Drag racing engines such as pro-stock (not nitro) have relativley narrow powerbands complemented with a 5 speed gearbox. F1 cars have a 6 or 7 speed gearbox. Runner length has to be optimized with rpm range and thus is a compromise. Ford and others have designed variable length intake runners to increase the powerband range.

articfriends

GPM,looks like you used this post to show off those BIG HP NUMBERS!!(I'd do the same thing ). Now that you teased us with that wild dyno sheet,you might as well hijack this thread and give us details,Smitty

GPM

I'm not trying to show off, I know there are other people out there doing a lot better,
I run a tunnel ram.

articfriends

Gpm,I wasn't trying to slam you or anything,your dyno numbers were outright AWESOME and i'm sure ALOT of us,including tomcat who started this thread,are eager to hear your combo!!!PLEASE re- post them and tell us about your combo,even if you start your own thread,We all (including myself) have turned tomcats threads into 4 pages before ,i'm pretty sure he likes to get as much publicity on his supercooler as possible , We want details,specs,etc,Smitty

rmbuilder

Ray,
Do you factor the back of the valve to the flange?
Bob

open87

dayummmm!!!

articfriends

GPM,what kind of fuel injection are you running,what are you controlling it with,who programmed it?What are you running for a innercooler and what kind of plumbing are you using to get air into intake,can you post a pic? I am upgrading my heads this winter and am looking for induction ideas to replace my 502 mag intake and fuel injection. I am running m-3sc on 540 blowing thru stock 502 mpi intake. What size injectors are you running and what kind of fuel pumps? What kind of hull are you running this in and what kind of drives? How good does it idle,are you running dry exhaust? Thanks,Smitty