nismo502

iTrader: (2)

cant seems to find real stats or dyno comparison to substantiate long runners. Am fabricating another one with B series manifold with dyno comparison and post them here later.

emilio700

iTrader: (3)

Fundamental intake manifold design stuff. Just like you might have to search for a few minutes to substantiate a theory that rod ratio of 1.45:1 might make less power than 1.58:1 in a Honda B series.

The reason so many people build ultra short runner BP manifolds is twofold:

1. They start with B series manifold designed for a longer rod ratio engine that makes power between 7000-9000rpm and either don't know the difference or don't care. Boost tends to hide just how bad your manifold design is.

2. It's easier to make it fit in the bay without the plenum hitting the shock tower.

Regardless of high you rev a BP on the stock crank, an OTS B series manifold will have a hard time matching the area under the curve and peak power of a square top. I have a pile of Honda B series/BP flanged manifolds here. Our best one just matched a squaretop and barely cleared the shock tower. It has runners that are too short.

The ideal BP manifold has runners the same length as OEM average, about 1-2mm larger ID depending on cams, plenum 10-15% larger volume and most of all, a straight shot from the TB flange into the plenum. I say average runner length because every OEM BP manifold has 4 different runner lengths to work around packaging constraints (EGR, hood clearance, production line assembly). Fixing that one problem is worth a few %, and fewer blown F/I builds running one o2 sensor.

To get the correct runner length and still fit in the engine bay means starting from scratch or looped runners, sort of like the BEGI prototype. Honda B series based manifolds will always be too short because of the curve of the runners. I know of only one non-looped manifold in existence that is correct. It is sheet & tubular aluminum with some cool carbon trumpets epoxied inside the plenum.

Leafy

iTrader: (1)

^ Is exactly why I have 4-5 rough cad models of long runner intake manifolds of various types kicking around that arent going to get finalized because there was a difference of creative opinion between myself and the fabricator (who is a member of this forum) who contracted me for the modeling and cfd. One of us wanted to build long runner manifolds, and the other wanted straight runners.

Full_Tilt_Boogie

iTrader: (1)

Theory says that runners that short will move the peak resonance up to very high rpm. Just eyeballing it I bet it would show some good peak numbers above 7k rpm.
Theory also says that short runners will have more 2nd and 3rd order resonance within the power band, making it very flat. You can actually see gains at low rpm as well as high rpm when comparing really short runners with really long runners, but with big losses in the middle where the long runners are are having their strongest effect.

You will definitively have flow on your side though. So I will be curious to see your results.


Here is an interesting case study on the issue with a turbo engine.

VW R32 Turbo VR6 engine, the stock manifold has super long runners that stretch over the top of the valve cover:


Here is a super short runner aftermarket intake manifold:


and the dyno comparison:



In this situation it seems that flow is king. I can only assume the long runner manifold was optimized for the NA version of the engine.


Here is a possibly more applicable example in line with what emilio is saying about the history of using modified Honda B-series parts.
Edelbrock Victor X vs Skunk2 pro series on a turbo LS-VTEC.


This is why the effort is now going into modifying skunk2 manifolds and other Type R knockoffs instead of using the Victor X monster.

Leafy

iTrader: (1)

With a long runner manifold you're already putting the 2nd order in the powerband. A manifold that puts the first order at 8krpm puts the 2nd order at 4k rpm, and the 3rd at 2k. And super short runner manifold that puts the 1st order at 16k, puts the 2nd at 8k, the 3rd at 4k, remember the strength of each wave decays exponentially.

concealer404

iTrader: (3)

Some of the most powerful BPs in the world run 4g63 manifolds.

That said, obviously they're turbo motors running bigass turbos, so top end is important.

The FWD BG guys have been using 4g63 manifolds for.... a decade. Or two.

Me? I think i'll wait to see what the Skunk2 unit does. Then either buy it, a square top, or go ITBs because **** it all.

Full_Tilt_Boogie

iTrader: (1)

Im no engineer but from what Ive read if the manifold puts the 1st at 8k, the 2nd would be at 4k, 8k, and 12k, and the 3rd would be at 2k, 4k, 6k,.. etc.
The short runners end up spreading the torque very evenly, for good or bad.

Madjak

What about something like this? Its designed around a 10" runner length so it would be pretty good for higher reving engines. I did this design a few months ago as part of my search for intake options for a Rotrex. The runner length could easily be tweaked to suit a specific engine.



The idea is I could fab this up myself from mandrel bent tube for the runners, joined once in between the curves. You can purchase the velocity stack / bell mouths online and the main plenum is made from sheet metal and a 4" pipe cut in half.

I'm really not sure it's worth all this effort over a square top manifold though.

bbundy

this is what I have been using. I'm guessing its not bad might could use slightly larger cross section for the runners.

bbundy

more pics

jpreston

iTrader: (4)

I haven't been able to convince myself to spend the money on a flattop manifold so I finally decided to give the Honda manifold a shot. I'm shooting for big N/A power for cheap for 2015 and then probably a JR rotrex on the car by 2016.

My B18B1 P75 manifold just showed up today... $50 shipped from ebay. Port size and spacing are almost identical to the mazda manifold. Runner length is a hair under 12" on the centerline. I don't think I'll be able to shorten it any because of how the 1 and 4 runners are curved. I already cut the flange off my BP6D manifold and can hopefully get one of the guys at work to weld them together next week.

It'll be a month or two till I get the car on the dyno, but here's the specs.

OEM 2001 bottom end
VVT head shaved .060"
Stock 2001 cams
B18B1 intake manifold with OEM B18 throttle body
RB header
Borla SM exhaust
E85
Megasquirt

Am I smoking crack to think I'll hit 170hp?

Savington

iTrader: (31)

I think so, yeah. The only stock-port 170whp car I've ever seen was Quinn from M.net and he had ITBs and high-lift cams. I'll guess 158-160whp, though.

jpreston

iTrader: (4)

Yeah, his setup is really the only data point I have for all stock internals with a .060" shave. My original plan was to basically copy all of his power mods, but trade cams for E85 and try to hit the same power numbers. I bailed on the ITBs after deciding to boost the car. The honda manifold won't be as good as ITBs while N/A, but it's cheaper and should be beneficial to both an N/A and a boosted setup.

240_to_miata

iTrader: (2)

And he just pulled his motor out for some upgrades in the shop i used to split with him...

hector

Stupid question since I know nothing about 1st order, 2nd order or manifold resonance/design.

Does what you are talking about show up as a kpa reading of >100 on NA engines when the order is reached?

hector

Again no expert here, but it has been mentioned in other posts that:
You want the air horns raised off the floor of the manifold.
You dont want flat areas so round tubing for plenum.
And go with bigger plenum if it fits.
You didn't mention runner diameter?

And just a guess but maybe 11" for runner length.

And another guess is that it will likely be about 5-7 lbs lighter than a square top so yeah it might be worth it.

Efini~FC3S

iTrader: (4)

Every proper STL Miata build has stock intake manifold, stock ports, and stock TB. My understanding is that 1.8L STL motors are making 170-195whp depending on how much $$$ the owner is willing to drop.

Leafy

iTrader: (1)

No, well I guess if you were measuring the pressure entering the cylinder. Now doing the same tuning for an intake could do that or at least higher than just a filter jammed onto the throttlebody.

hector

Im sorry but your answer is...... confusing?

Let me give some details and ask again.

Ok so its a CR.net ITB set-up:
4age AE 101 throttles, T3 manifold, T3 100mm horns, no filter(s)
DIY vacuum block plumbed to DIYPNP
01 VVT stock internals

On dyno runs there are two points where the kpa went to 107-108, 4200 and 7200 RPM.

Is this because of 1st/2nd order resonance? Or just dumb luck/coincidence?

Savington

iTrader: (31)

I'm quite aware of what an STL car makes. STL has cams. Doesn't change my point one iota: Stock cams + stock ports = not 170whp