70%? you want 2-3-4-5 times the size of the displacement of the motor.

fwiw stock IM runners are 16" long. I had used 6" runners on my design. I made peak torque at redline. Had it not been for my blown rings my dyno would have been bad ass, but i sold the thing to pay for a new block and parts.

Mine plenum was 14x4x4" making it a good 2.8L making it very close to x2 the size of the motor.

I only have one good dyno comparison cause the motor pretty much went during/after the first pull and only on wastegate.

http://www.boostedmiata.com/dynos/in..._wastegate.jpg

Thing had awesome potential up top and it was very apparent when driving around town. I'd like to fit it back on since my motor is back in good order, but another member here has it and will hopefully have good result with it soon.


For another good comparison, we can look at newbsauce's results with his BEGi IM. It uses a smaller 14x3x3" plenum, putting it right at 1.6L. He fitted a larger 70mm TB as well. I think it had runners closer to 9" long.

http://www.boostedmiata.com/gallery2...serialNumber=1


he lost a little low end, but the top end torque held MUCH better resulting in a great power boost.

wops saw my mistake.

so with an inch longer runners u'd had peak at about 6.5k rpm or so i assume

without seeing flow bench hard to tell. also what was this designed for drag, top speed, road race, this all goes into how you critique it lol. as far as the design it looks to be a very large plenum with short runners. seems to be fairly clean but like previously stated sharp into the runners i would recomend a v-stack into the plenum that is the common design for most race intake manifolds and works very well. intake manifolds are very tricky to make work its a guess and check type method without a flow bench.

i wish i had my manifold done, when i was doing this

Attachment 202223

As far as flow from one cylinder to another, I do not think that it will be a problem. Now if you try to enter some kind of liquid (meth ?), I could see how it would be a problem. But with a dry charge, you have a box that will preasurize equally. The preasure is not going to be higher on one side of the box, and lower on the other.

I will have to agree with the runner length issues. You could easily have it spit open and weld air horns in them. Other wise, to get the combination right with your current runner length, you will need a much bigger cam, and move your power band to a higher rpm.

I could critique the manifold using dynamics and race engine suggestions but without sold numbers it would be rather silly. I certainly agree with the #1 cylinder being lean but not for the same reason, the air simply cannot take that corner without getting flow disruption as it is too tight as well as being to close to the TB. #2 and #3 should see wonderful flow numbers while #4 again will be the bastard child in comparison because of the "equal" flow tactics rather than CFD tactics that should be employed but at least it will flow better than #1. At a guess, I would say your manifold will produce higher peak power with little difference in torque and a similar cylinder air distribution as stock but with cylinder #1 and #4 effectively swapping their respective values.

As for the ideas of the perfect manifold, NASCAR engine builder and copious engine building and designing book author A. Graham Bell suggests the follow attributes:
Butterfly 1.5x the inlet valve size
Plenum capacity should be between 0.8-1.5x engine capacity
After the TB the plenum entrance must grow to 1.5x the TB size to slow gases
Rear plenum wall should be 1.5x runner diameter away from the furthest runner

You can basically do a design of a manifold knowing the engine capacity and inlet valve size. However once the design has been done for dimensions, flow shaping MUST occur and then the dimensions go tits up. Good principle though.
Splittimes manifold is actually pretty good from what I can see I'd expect a better distribution than stock and therefore better power and torque (although I'm guessing #4 could use a slight richening if individual trim is available). Once again I am humbled by his DIY approach.

Dont you mean lean out the trim on 1 & 4 because if there not getting as much air, they dont need as much fuel.

get the trumpets off the floor to reduce the surface boundary layer effects.

Thanks for all the replies, keep them coming. A little more information about the manifold. The total runner length is 6.75" and the throttle body opening is 3.25" which will be used by an Infinity q45 throttle body. If I decide to use this manifold, I will be running up to 30# or so. With the exception of possibly changing my meth setup to run a port in each runner, I would be using this thing as is.

In my simple mind, it comes down to one thing, will I be better off running this manifold with known compromises or the stock manifold with known compromises?

Inlet Runner and Peak Torque Calculator

Intake Manifold Tech: Runner Size Calculations - Team Integra
Here are a few sites I used while designing mine,I also Have a great pdf. but I cant get it to post:jerkit:
(G)

Good links, there's so much information out there on manifolds yet it seems like such a black art. Wish I would have done this mod a long time ago since it's not just a simple bolt-on.

I've decided on a few things and will be installing this manifold and throttle body in the next month or so. Should have results shortly after. The meth setup will be changed to use individual runners using 2gph nozzles instead of the 10gph nozzle after the intercooler. To increase the runner length a little bit I will be using a .25" spacer between the manifold and the head.

The actual plenum volume is 2.8 liters and that should be fine if not even a little smaller than what I would like. This does seem about right according to all the links in this thread though. Any other thoughts, ideas, or changes before I commit to this?

Just do it and dyno it already! :P

What is this spacer made of? If you are getting it custom made, I'd suggest a phenolic material like G-10. Compared to the nylon/teflon insulating gaskets, G-10 wont sag. G-10 is basically pcb material. Who knows if it will make a difference, but it surely wont hurt.

--Ferdi

I'm going to start with just using a typical phenolic spacer that I've seen offered through a few vendors.

As for just putting it on and throwing it on the dyno, it will happen eventually. Just a lot of other things going on and I need to get rid of the other Miata first.

dynoz or ban.

Corrected!

Back off or the kitty gets it.

Don't worry. That pic is the exclusive property of Hyper Inventions Inc. All use of said avatar for commercial or entertainment purposes is strictly forbidden without written permission.

Wow it doesn't look like it's over 2 liters.

At the time of purchase, why did you go with this manifold instead of BEGI or Edelbrock (cut B16 mani with miata flange welded) etc?

As for individual runner WI, I'm considering that as well but I'm afraid of going dry in a nozzle and blowing a cylinder. Will you have a failsafe for that type of scenario?

I'm going to try and have some numbers on pump gas before Christmas.

As for the other manifolds, it's a long story. BEGI isn't an option. As for cutting another manifold and welding on a Miata flange, I would go with something from Magnus. Rob at Flipside was willing and ready to make these manifolds and he's local to me. If you called him today, he could probably have one of his standard manifolds to you within a month. He was also willing to make changes to his design to incorporate the throttle body that I wanted. That was enough for me to take a chance on it.

As for the individual runner WI, I'm not a big fan of it and feel it isn't necessary but I'm going to do it anyways. The more nozzles you run, the more points of failure, etc. I have a failsafe, but nothing is a guarantee.