Ok, first off, I realize there's already a helmholtz theory discussion open a few threads down, I could have posted this in there but its kinda OT and didn't want to screw up that thread. I would like to discuss intake manifold design theory itself, runner lengths and plenum volumes have already been calculated and decided.

I've noticed on OEM intake manifolds for mitsu evo 9's there's some odd stuff going on where the runner meets the plenum. Not really odd but I have yet to see it in any aftermarket intake manifold. Basically the short side and long side of the intake runner in the head are taken into consideration on runner lengths. The roof and floor of the intake manifold runners is staggered in such a way that the airflow/pressure waves are "square" with the plenum all the way to the intake valve. I had actually discussed this with a local tuner a few times but more recently his shop of 20+ years has taken a turn for the worse and I can no longer get in touch with him. I will attach a pic of this moreso explaining what I'm talking about.

Now on to my specifics, I'm trying to build a max effort LS2 that will spend a considerable amount of time between 6700-7200 rpm since I want to do Big Bend open road challenge and Texas Mile in this car. 240+ in dur @ .050, 250+ ex dur @ .050, 106 lsa. Static compression will be dictated by dynamic compression as soon as I can get the valve events figured out, would prefer if it ran on 93 octane though since I do drive it on the street about once a week. Exhaust will be 1 7/8" Kooks headers with a y-pipe and boom tube.

I would prefer to build this intake with 2 plenums and a crossover tube between each bank. Similar to an OEM viper intake manifold. As a mechanical engineering studen I can't say I agree with the 180+ degrees of bend in an LS1/LS6/FAST intake manifold and would like to straighten out the runners. I can understand in OEM packaging concerns the need for it.


I'll stop here so I don't pollute anyones opinions. Would love to hear some from OldSStroker or anyone else I can't think of off the top of my head who might have input on this. Keep in mind it will be manufactured out of carbon fiber with chemical resistant resin and I already have a jig built and head flanges. I'm about to start cutting a buck/mold to get the plenum/runners built any day now.

Here's a quick explanation of my crappy sketch, Green lines are intake runners in the head, blue line is head flange. Red lines are intake manifold runners and plenum, orange circle is a throttle body. I only drew up one bank to keep it simple. Sorry folks, I'm on my home computer right now and don't have solidworks here.

 

Drew,

Skip over to CamaroZ28.com and search for any posts by SStrokerAce. Look closely at the engine in his avatar. It's a 4xx cube LS engine with a one-off manifold which is much like what you are discussing. The heads are a rectangular port LS variant, and what is inside the plenum I can't discuss here. The engine was on display at PRI. Too bad we didn't meet there.

I can say the runners are not bent, and are about the right length for the rpm range you mentioned. Twin plenums (plena?) don't really float my boat on this size engine. Packaging and availale TBs may have driven the Viper design, as it may with your racer. I think you'll be leaving horses on the table that way, but that's just my $.02. Otherwise I like your ideas.

Jon

 

I'll jump over to that other forum here in a few and check it out. I think I might have an idea what was going on inside the plenum but I'll keep my lips tight about it. Was probably something similar to what we had on our FSAE car. I'll send you a PM with a drawing of our intake manifold on that car. Seems like it might be useful if I can implement it properly. I don't care too much for the twin plenum Idea either but with a total induction length of ~18" I'm out of room under the hood for a single plenum. Cowl hoods are out of the question.

*edit* I don't have any drawings of that FSAE plenum on my work computer, will have to send that PM later tonight/early tomorrow.

 

Details?

 

The engine uses GM heads tweaked by a great head porter.

Rectangular port intake choices:

1. C5R

2. C6R

3. LS7

4. L92

 

I believe the viper intake should be completely ignored in this case, as the firing order (2 at a time) dictates completely different dynamics than an LS based V8.