Best Overall Intake? (ie plenum vs velocity stacks)

[RageRover]

For a vehicle that will be driven on the street 99% (realistically closer to 100%) of the time, what would be an ideal intake? (or plenum?)

Something that would have a wide power & torque band, not something that doesn't idle well or only gives it's power out at high RPMs?

I'm planning a full rebuild, using a 964/993 case and taking the engine out to 3.8-4.0 Ltrs. Crank, not sure yet. But sleeves & liners, most likely LM "Nickies." Maybe Carillo rods or something similar (rods may be from a different company & if budget allows, maybe a lighter metal, (titanium? or a lighter design, but still race spec) connecting rods.

Singer has been using a modified GT2/GT3/RSR intake. Any advantage over it? There are some modified versions, especially one made completely out of carbon fiber that has been used on recent "cup cars" and I believe was just used at Le Mans.

BTW: the carbon intake is 99% something I can't really consider (although an aluminum copy can be built), it has a price of over $5000!

Singer also uses velocity stacks on some builds.

I'm just using Singer as an example because plenty of pics exist and they must work well (or work alright) if they use them!

I would like (ultimately depends on cam) an engine that has a nice, smooth, torque curve all the way to red-line.

Something DRIVEABLE on the street and as a daily driver if wanted.

Although having a high red-line vehicle/engine makes for lots of fun, realistically, it can get tiring, it takes it's toll on the engine and DO NOT want most/all my torque at the top end. I'd like to have bottom end "grunt." Ultimately, that's what you feel and that's what gets you off the line!

Velocity stacks (with small cotton filters maybe fitted on the top of each one) also do look beautiful!

Part of me would like to go with EFI, but some of the aftermarket systems (unless I go with something like MegaSquirt, which I still have difficulty getting my head around!) can be costly. The stock EFI system I guess can be modified, chipped etc.

Depending on funds, I may go with something like Webers at 1st, for that clean, classic look.

I'm willing to give up a bit low or mid range power for upper-end power & for the ability to increase red-line. But overall, how are velocity stacks on a street vehicle?

And how are the GT2 RSR/GT3 intakes?

There are also plenty of modified stock plenums/intakes that look "trick" but do they improve or mess-up the power band?

Yes, there is also the the stock plenum and the "varioram" intake/plenum, which I think adds a lot of complexity, a "busy" engine bay and for what? 15hp at most?



The Promodest Japan GT3 carbon fiber intake is similar (or maybe the same? & is an OEM supplier?) that's used on the "cup cars", RSR and most likely last Sunday's Le Mans.



Lastly, one day I'd like to turbo charge (maybe supercharge) the engine, so I am keeping that in mind during the build. "Runners"/velocity stacks can (must) be "closed off" and welded air tight, to accept a "boost of air" from a turbo or supercharger, so I also have that in mind.

Here are a few plenum pics for a 944 and VW engines.




Maybe there is better performance to be had from enclosing the tops of the stacks/runners even if there is no "forced air system"/turbos/supercharger?

I'm sure there are mathematical formulas to give the ideal runner length. I know that longer runners are better for lower power/torque, shorter = better for upper rpm power and am engine that likes to rev.

I've included a few pics of Land Rover V8 plenums/intake manifolds. The 1st is sort of the original design, the plenum modified slightly over the years, becoming a little more squared off & taller on this 1997-1999 version. When you remove the plenum/intake cover, there are 8 "runners" or "trumpets" which can be modified depending on your application.

If you have a fast TVR for example, boring the plenum a bit and using larger diameter yet shorter "trumpets" can give you some better flow at higher RPMs, but at the expense of some low-down power. The factory also experimented with dual throttle bodies and plenty have made their own "factory copies" that have a throttle body at each side.

If you want low-end torque and power, use as long a runner that will fit inside the cast cover, although you have to be careful of airflow if the runners/trumpets/velocity stacks take up too much room and are squeezed in there!

The last pic is the last development of the Rover V8 plenum (aka "Thor" plenum, used from about 1999-2004). It increased low down torque at a sacrifice of loosing a few hundred RPM at the top (engines didn't rev as high, thus a lower red-line). But since Land/Range Rovers are mostly driven around town the highway and MAYBE occasionally offroad, you want low-down torque (say 1200rpm-2300+), not a curve where torque STARTS to come on at 3,4000+ RPM.

Rover V8s had/have a redline I believe of 5350 rpm! (although that's a factory vehicle and conservative). Can be made higher (atleast another 1000rpm). And were and still used in everything from TVRs, Morgans, Marcos, lots of "kit cars" (Cobra replicas) & other sports cars to Land Rovers and Sherpa vans.



It was/is the UK version of the chevy small block "SBC", cheap and plentiful in the UK and relatively light (300ish DRY) (it's all aluminum) & compact. FYI: It was bought from GM and used in the 1960-1962/3 Buick Skylark and known as the Buick 215. Plenty of Buick & Rover engine parts are interchangeable. (so if you're on Jeopardy, feel free to send me a couple of bucks if the question comes up!)

Land Rover only made them up to 4.6 liters. But TVR and "JE" (John Eales Engineering) bored and lined them up to about 5.5ltrs I believe, they were turboed & supercharged and even used as a base for an F1 engine in the 1960's.

A lot of power can be extracted out of them and fine-tuned depending on the trumpet diameter, length, etc.

My point was to show the different plenums and how that can affect the power band assuming nothing else was changed/touched and what would work best on a (mainly) street driven 911?

Although ideally, you would try to match everything, such as runner/trumpet/velocity stack diameter and length to the cam, head (intake/exhaust valves & has it been ported/polished?).

The Rover Engine, other than slowly growing in displacement like the Porsche, the actually architecture of the engine did not change during it's lifetime - about 1963-1994 (the last time Land Rover used it in a production vehicle, although Mahle still makes/casts it).

[jmh61]

Rothsport makes a system that uses Jenvey ITBs combined with a 993 intake with a resonance chamber. Its supposed to increase power across the rpm range and help eliminate flat spots. I've heard claims of 20% hp increase on a good condition stock, other than headers, SC engine. I'm a little skeptical... It would certainly improve throttle response over a common throttle body intake. You would have to go EFI.

Welcome to Rothsport Racing - Engine Products

[HawgRyder]

Short runs to intake = power at higher RPM.
Long runs = power at lower RPM.
ALWAYS use a good air filter...unless you plan on rebuiling the top end every 5000Kms or so.
Some intakes look soooo great....carbon fiber...slide throttles...anodized parts....etc.
But....in the end are you looking for bling or go?
Speed costs money...how fast do you want to spend?....LOL
Bob

[psalt]

This is a complex subject and if you are interested in learning more about it, I can suggest Lumley's "Engines", a excellent book on the fluid dynamics of IC engines. The intake manifold in operation is a swirling mess of back and forth flow of air, fuel and exhaust. A fixed length runner has one ideal rpm for peak torque, which is why experiments with variable length runners have been tried since the 1930's. There are many designs, the rotating drum inside a sealed chamber is one of my favorites and it is over 50 years old. It is interesting that most of the original IC engine mechanical designs were already on the books before 1920. Most OEMs chose a single throttle common plenum for a road car because their design spec for a road car is 85% driving below 30% load. It all depends on what you want, the best tool for a job, or an expensive toy that make a cute noise at a certain rpm. Take a drive and record the % of time you spend above 4500 rpm and 50% throttle and you will get the idea.

[Raceboy]

OEM's choose common plenum not because they are necessarily better, but because they do 90% of the job for 40% of the cost of ITB's.
Common plenum can never be as responsive as ITB setup and you can use wider variety of camshafts with ITB's.
I installed ITB's onto otherwise stock 993 non-vram engine and the powerband is very nice, pulls from whatever rpm very strong. Driveability is almost like stock car.
http://www.youtube.com/watch?v=EUOWAjkTmVQ

[manbridge 74]

Very complex topic. I've always liked Audi's dual plenum IMs which would, in theory, give both torque and high RPM power.

[Raceboy]

Originally Posted by manbridge 74

Very complex topic. I've always liked Audi's dual plenum IMs which would, in theory, give both torque and high RPM power.

I made the very same thing and got inspiration from the very same source. But the main goal of dual plenum is not powerband, but equal air distribution. With ITB's it would be covered on part throttle, but not at WOT. So here's where dual plenum+ITB's come to play:

[HawgRyder]

Didn't Ford come out with a plenum that had moving plates or partitions in it for RPM control or torque?
I remember they had a difficult time making it work.
Bob

[RWebb]

I agree it is a complex area and involves hp and torque at various rpm, not to mention other desiderata for an engine - including the wt. hung out past the rear axle. I'm not sure I agree with raceboy's cost comments as applied to the 993 which modifies the size of the plenum by rpm.

This book?
Amazon.com: Engines: An Introduction (9780521644891): John L. Lumley: Books

[Raceboy]

Making a mold for VRAM dual plenum intake (which it essentially is) has zero to none more cost involved for OEM than equipping engine with ITB's that need syncronization and have plethora ofmoving parts. VRAM intake has only several.

[RWebb]

it's more than a mold

[dsfnctn]

Id go 3.6 with Motec M 84





Rothsport Racing Engine Dyno - Porsche 911 3.6L Engine - YouTube

[Bill Verburg]

Modern oem's use a central throttle body because it is cheap and works well w/ modern smog cams

Itb's better separate the intake tract from the valve events and are preferred for use w/ happier cams

Itb's can be used w/ velocity stacks of varying length's, as w/ exhaust the length is designed for the rpm window that is to be maximized.

variable geometry plenums in the 911 world were introduced in '84 and have been further refined on all 911, 964, 996, 997 model since.

The most flexible example being the 993 vram which is very successful at widening the power band if not the ultimate torque of that model.

current state of the art for maximizing power band is variable plenum geometry w/ itb's w/ variable cam timing.

for a 3.6 - 3.8 you can use use 964, 993, 996, 997, or anyof variouse GT3 plenums w/ itb's, the 996/997 plenums have a larger volume that is better for higher rpm/ larger displacement motors

Rothsport has been very progressive in developing these motors mostly for track use but certainly streetable. JMO but for street use on a 3.6-4.0 I'd want a 993vram(RS if possible, reg if not) OBD1 Motronics work great w/ these systems. I happen to have one and it is a wonderfully street motor, that is lacking for track use because of the limited rpms

The Singers are the best of both worlds, high rpm capability from GT3 crank/rods & l/w custom pistons, fairly happy cams, GT3 plenum on itb's all controlled by a custom efi(Motec or other like DTA works fine, Motronic will not work w/ theses systems))

[Bill Verburg]

The advantage of plastic or c/f over aluminum is the time it takes for heat soak to set in. The aluminum plenums hold a lot more heat than plastic or c/f, this is more a problem on a dyno than in use.

aluminum also tends to be somewhat heavier

[RWebb]

and don't forget, in modern engines you have direct injection, so we are only talking air flow (assuming we are talking 'modern'...)

[HiWind]

nice compact thread with lots of good info - thanks to Bill et al as ever
Just found this one which I think is the race legal 996 gt3 intake per grandam spec
ie you have to use the stock item but it can be modded ... hence all the pretty welds

anyone know more about it?
... looks to be stock 76mm intake size vs the later 82mm itnakes
.. but considering all the other opening up inside I;m not sure the 76mm is an issue, or is it?

[HiWind]

so this is the 3.6 world challenge intake.
Responds best to cup s /world challenge/ or clubsport cams.
Must use early throttle body from 98-07 cup or the one on a stock engine 996 cup.
Spins to 8800. Likes higher compression Pistons.

Not ideal for a 3.9+ big motor since one would want to use the "pigeon sucker" throttle body from the 997 cup for the better breathing needed by the bigger motor. ie 82mm butterfly diameter, not 76mm.