Just interested in some discussion on this. As some of you may have seen, my engine has post box plenums on top of a shortish runner with the injector spraying directly into the port.

Ive just had a look at the "new project car" pics and the manifold is long runners with the injector up high spraying straight down the runner (looks awesome).

I dont know whats right and/ or wrong (if either) and I dont have any real world experience as to either set up. Im no fluid dynamics expert either...

From what I have read about turbos, non nitrous assisted - the diameter of the inlet runner fixes the rpm at the engine will make HP, and the length will rock the HP curve around the peak - ie long runners will up bottom end HP, but will fall over past peak HP, short runners kill the bottom end but make HP way past the peak. Ideal length from the valve to plenum about 270 - 300 mm and .9 x valve diameter in diameter (for a race car).

A balanced plenum - ie air entry into the middle, nice bell mouthed runners exiting, around 1 - 1.5 times the engine capacity in volume will help equalise airflow into the cylinders. Problem with a flat engine is getting equal distribution to a dual plenum set up, or coming up with a central plenum design.

Im just interested in ideas and thoughts on this, runners, plenums, injector positions etc... Most of the above is borrowed from Forced Induction Tuning by A. Graham Bell.

Some other designs and info. Im liking the twin plenum design, but havent seen one on an aircooled VW ?

http://www.bufkinengineering.com/intake%20manifolds.htm 

this is a great topic as there is some conjecture about the different styles of intakes. Me personally i lean towards the straightest paths theory, shortest is best!

I WOULD SAY THAT AS WELL SHORTEST AND STRAIGHTEST
BUT SOME TIMES YOU SEE TURBOS WELDED TO THE SIDE OF A MAINFOLD WITH NO FLOW DESIGN
AND YET THEY WORK GREAT

This was the pleniums I had on my street car, I think it also depends on what your doing, street driving or race

I've been looking at this for sometime with my own engine.... Marty Staggs and Shag Leone in the US have been very helpful with advise, but as yet, I still have not made a solid decision.... Systems like the ones suggested so far and the one that Troy hard on his Fasty seem to be the most popular with street/strip cars, but I have seen systems that offer long runners into IDF style manifolds and a central plenum are becoming increasingly common in the race world.... Chuck into the equation the various fuel deliver methods ( blow, draw, carb, efi) and the challenges amplify....

It'll be interesting to see what the more educated minds around here will have to say about all this.

Troy, nice plenum, single throttle body set up, what sort of boost were you running on that beast.
I don't think shortest and straightest is the "ideal" turbo inlet manifold but more so the shape, volume and design of the plenum/s and runners.

Back when F1 were running the small 6 cylinder turbo there were experimental intake designs by at least four teams, Renault and Ford being the most adventurous, ok I know that some of you are thinking what's F1 got to do with our antiquated flat 4 design, but trust me it's all relative.

Their research on variable vane and expandable intakes created power through a wider RPM range than previously possible for engines of that design.

I would hope that someone with direct physical R&D background can chime in on this topic, maybe connected to a rally team......

Bikes not cars (well, no cars for a while anyway), but then hey,engines don't know that!

Intake runner "tuned length" is as important in boosted as in NA, a lot of gains can be made for free in that area if the packaging and space constraints allow it.
0.9 x times valve is more for MCSA of port for a turbo motor than intake runner sizing. Intake runner volume is important for complete fill, off-boost response can be affected though from making the runners short and fat rather than long and thin, although overall total power and total volume may be the same. Most tuners are aiming for 100%-120% of cylinder capacity per runner for volume, then using the longest intake tuned harmonic length possible to reduce intake diameter and fine-tune.

Injectors at the start of the runner will promote extra intake cooling and further atomisation, but at the expense of fuel droplets at low rpm (like Ducati's shower-injectors causing "hunting" under 4000rpm). Injectors aimed straight at the valve can sometimes end up with distribution issues and chamber burn problems at some rev ranges (like Toyota JZ motors). I would avoid both placements on an ACVW for those reasons, find a spot to shoot at the inner curve wall of the manifold just as it enters the port possibly, to aim for the high-speed area of the intake?

Boosted engines aren't as critical as NA to plenum volume, but again off-boost a big plenum can cause response issues. Most plenums are designed with curved walls to reduce internal turbulence, volumes ranging from 100% for NA to 600% for boosted and pure top-end. The bigger the plenum the less mixture variation between cylinders due to internal turbulence.

Having said all that, bolting a big 4" round tube on top of an IDA intake manifold each side, put the injector on top for easy servicing and access, then joining them up to the turbo output will also work very well. Are you chasing a National Index record, or just aiming to get down the track fast and get your Anandamide fix? Do you need all the extra plumbing and tuning grief for a few extra tenths or the "cool factor"?

Have fun man!

What kind of data logging do you have on the car?

the design for the pics you gave, are purely to make sure there is no favoured cylinders,air is slowed down and fills the chamber area evenly.

individual plenums each side or triplets like troy had work,but not well.
air likes direction.not brick walls and T junctions.
troy's new manifolds are proberly what you should try to copy,flow will work well,ask him to post a pic or 2.
if it has fuel suspended in it,different question,it will like some sharp edges to re-spray fuel particals .
i have seen stock manifolds work better that big dollar billet or waterformed manifolds in boosted cars .
if you have rounded edges and flowing bends.equal length runners you can't go wrong.
injector placement depends on the injector and the spray pattern.

for example...vl turbo manifold with a small mod and a xf falcon throttle body ,standard runners and injectors that shoot at the back of the valve(so close as possible,but factor) with a second set put where ever you can fit them.
1500hp.
no rocket science there.
dont just stick plenums anywhere,
if the pipes going to them are uneven in flow or different lengths your just sticking bandaids on a bad design.
hope that helps.
you have an awesome fabricator buy the looks of your extractors,now just do that in reverse.if you know what i mean.

I knew you couldn't resist to comment, have you got the fabricators # for future reference?

I had a look at a few photos of the Baron and Paradise Hater Maker - and they basically seem to run what you describe Westi. The injectors on Hater Maker look like they are in a really similar spot to where T3 Kings injectors are. No doubt those cars make a shit load of HP. I guess the difference with my set up is it will see some (not a lot) street time. When I look at Ferrari, koenigsegg, audi etc supercars they all run the dual plenum set ups, I can only guess that these guys have spent millions on R and D, and these plenums must work. Im really surprised that no one has tried anything anything like this on a VW.

Basically a plenum feeding a plenum through a slot to get even air distribution over all intake runners.

I think Troy ran about 16 psi in the fastback. His new manifolds are much much better in design than the old ones. But again the room you have to play with also depends on how you manifolds are designed as well. If its a race car you should have plenty of room!!

For reference this is what mine has now - untested, not even here yet.


Fan housing in front which is why everything heads back. Will run it how it is regardless.

Hatermaker inlet - crap photo but all I could find...

I have little turbo experience but I'm with Westi, those Audi V8 (and earlier versions) dual plenum designs are purely because of design constraints where the incoming air is at 1 end feeding 4 or 5 cylinders so it's done this way to get an equalisation of charge accross all cylinders. I think with only 2 cylinders per side, it makes it easier (like Westi designed for Troy) depending on fuel delivery/type.

Looking at the pic I posted, that made 1025 HP at the treads with that inlet, Im not arguing wether or not it does work, it plainly does !! Im starting to think its a horses for courses thing, out right HP i think thats the answer, driveability - street and circuit, almost all run a plenum of some description. The audi pic is lemans egines - circuit racing, maybe there are some design constraints, I dont know. Pretty much all super car manufacturers use a plenum with individual runners out of it, and all enter from one end and have a diminishing cross section the further away from the inlet the plenum is.

So I dont think the plenum I have is very efficient, unless there is a shaped floor - like an A - under the inlet splitting and directing the air flow too the inlets like this - http://img230.imageshack.us/img230/8600/plenum3tz1.jpg  - although even then air is slamming into the ends ... or do the one end entry and design the plenum to flow equally to both cylinders... wonder how much gain there is to be had, probably off boost only I reckon ?

Where our cars differ is that we are rear engined with a high roofline so the necessity of a low profile design is pretty well out the window. The other plenum designs are in a front engine configuration so low profile becomes a high priority, therefore the plenum designs are developed. IMO the increased volume must take away engine response, ie longer off boost.

as you said,horses for course.totally agree.
it all depends on what you want from your car and turbo size with response time.

wrx standard manifold,which is a flat 4.
delete plenum and bigger runners ,put in y pipes 1 into 2 into 4.(ruebs has a pic somewhere)help a nigger out rueb's.
made 60kw more atw 5 pounds less boost,can't argue with that.came on earlier and power was gained everywhere.
sometimes people just take the easy route because of a lack of imagination or skill or budget.
but there is always more than one way to skin a cat.
troys injectors are up high to cool inlet charge.because of no intercooler.
hope that helps.
a bend one the way into a plenum also has a high speed and low speed air path,so sometimes even plenums can have uneven cylinder filling properties.

put some thin strips off paper taped at the ends of the ports ,with the whole set up on the bench and blow through the inlet from the turbo with compressed air.
then block of a cylinder at a time with your hand to see what happens.
i have a flow bench so its easy for me to test,but thats just one to test if you want to have a stuff around at home.
cheers

Cheers for the insight Brad.... I have seen what you have talked about around the the place, but the clarity you have offered in your words, makes it so much easier to understand.

Cheers.

Hi all, I have read this post and thought I would post mine up including how I blended the intakes. This is built for the street and sprints.








T54