atb

Lots of talk about different intake designs taking place for 928's here on R-list.
Thought that I would start a thread of my own regarding my own venture into making our motors breathe easier.
This is for my stroker motor, and is basically my following through on Louie's concept from many many years ago. We were at DEVEK days, back in 2001 or 2002. Louie had brought an exploded view of an M5 intake plenum with him and was talking about the advantages of going to an ITB system . This was truly the dark ages of 928 development, there were no readily available stand alone engine managements systems that were being used on the 928, no sharktuners, nothing. Louie went on to develop his ITB system nonetheless, and the 5 or 6 sets he completed that are running power the highest horsepower N/A 928's out there.

Part of Louie's design goal was to create a freer breathing intake system to unlock more top end HP from the 928 engine. The stock manifolded strokers had a tendency to choke up at 5K rpms and fall flat. Further, despite their top end HP deficiencies, the stock manifold created truckloads of torque down low, more than what the then limited size width of rear tire you could fit on the back of the 928 could handle. (Louie later designed a fix for that problem too. ). All of that low end torque tended to break the 5 speed gearboxes, and so, Louie designed his intake horns (velocity stacks) to give away that bottom end tq to protect the tranny, and to further allow him more top end. The other strokers out there running Louie's set up have adopted the same design - they are all 5 speed cars, and don't want or need all the low end torque available in a stroker motor.

To create this kind of power curve, Louie went with a velocity stack that is very short in this design, only 4" tall. It also helped to facilitate keeping the stock hoodline.

My stroker is going to be backed by an A/T, so I didn't want to shy away from the big tq numbers. I'm pretty confident that a modified S4 box can handle it.

I did some calculations, and optimum length for the intake horn come in at 6.77". I didn't know how long the M5 horns were at the time, so I ordered one and it was a whopping 10.25" long, meaning I would have to short the M5 runner by 3.48" to get to my calculated optimum length. I wasn't deterred though, I had driven the M5 it was not lacking for any kind of top end with its 7K redline, so I ordered an entire set.

Later, Louie was kind enough to do some calculations for me on his EAP software, and I've posted the results below.

Here's what the M5 horns look like in their native habitat:



As can be seen, there are three different shapes. #1 and #5 are mirror images of each other, the other six are all the same. The six common runners have a single progressive bend. The first one I ordered was one of these, and I determined that these would not work for me because the bell of the runner would end up in position where they wouldn't interweave with each other. So I ordered up 4 each of the #1 and three each of #5 intake horns. They will need adapters to bolt to the ITB's, but here's the general layout idea:




It would take a lot of work to shorten these horns to the optimized length that I arrived at. Based upon Louie's EAP calculations, by leaving the horns in their stock length, I have a net advantage up to about 5400rpms, until they fall flat, much like the stock intake manifold. If I shorten them 3.48", I regain that nice HP arc/peak approaching redline. I've decided to run them as they are first, and if it turns out that I feel I'm missing out on that booster shot at redline, I'll shorten them. This graph shows the overlay of Louie's motor configuration with the three intake horn lengths.
Louie = 4" Horn
Short M5 = 6.77" Horn (Cropped M5 Horn)
Stock M5 = 10.25" Horn (Unmodified)

RyanPerrella

great post

which throttle bodies are you using? Those arent the M5's throttle bodies are they? I see blue at the base so i assume those are from Louie.

Last i checked the M5's throttle bodies were like $325 each x 8 and it gets really expensive.

Interesting to see you choose to use the runners, most BMW guys throw those away honestly when they tune the S62 engine and go with something else.

BUT i do believe the M5's TB's are also 50mm which i believe is what Louie runs.

hacker-pschorr

Wow, that looks awesome!!!!!

atb

Thanks Hacker. It's a little misleading in that all the tubes will be housed in a plenum box very similar to what Louie did, but yeah I definitely like the look.

atb

(Too weird-had a double post and then no post-here it is for a third try)


Hey Ryan, yup, this is one of the rare official Ott Engineering ITB set ups for the 928.


These are TWM's. I looked online and it looks like they go for about the same as the Stock BMW units. This intake system is not cheap when it comes to calculating HP/$$, but it is the only way to get to the high HP numbers with an N/A motor. (and besides, they just look cool. )

I haven't seen before and after dyno charts of an M5 that has gone with shorter horns. I've seen the claims by Dinan, etc., that their shorter horns make higher HP. There's no doubt that would be true, the above graph shows that to be the case, with the shorter horns making more peak HP. But up until 5.4Krpms, the longer horns put down the torque and HP, with a net advantage over the shorter horns over the majority of the powerband.

When you look at these horns up close it appears that a lot of engineering went into making them flow (their bends are graduated, not linear, etc.). The fact they they are so long I think shows that BMW was doing resonance tuning as opposed to just going for maximum flow that a shorter stack would allow at the cost of low end torque.

For my 928, which has the 2.20 diff and A/T, I don't know how often I'd be seeing that last 800rpm in my powerband where the shorter horns leave the stockers in the dust. I'm there a lot now with the stock 5L, but with the monster tq of the stroker, I may be able to live without it. If I had a GT with its close ratio box and short gears, it would a different story for sure.

They are. Without that match up it probably wouldn't be worth trying to make them fit.

hacker-pschorr

Similar to the Cobra R setup. Here is a custom job similar to what you are doing (except it's a one piece lower):

http://forums.stangnet.com/7637765-post7.html

Better shot of the lower sections here:

http://forums.stangnet.com/7638182-post13.html

FBIII

I'm surprised more tuners aren't sharing Adam's thoughts on developing a system that would sacrifice some low end torque for upper end power. With the stroker set that have gobs of additional torque that punishes drivetrains, I think this makes perfect sense.

RyanPerrella

thats a nice piece

can that lower manifold be adapted to fit 32V heads? I assume a simple spacer/adapter would work, but the runners need to be spaced apart to match the 928 intake port spacing.

I imagine that lower intake is what, less than $500?

atb

Sorry, can't take credit for this concept (especially since I'm not even implimenting it - I like my low end torque).

This was Louie all the way. Only he could take in all these concepts - replace a Stock S4/GT manifold with something that 1) Increases peak HP while 2) Decreases low end torque that 3) Provides better throttle response by getting the throttle plate as close to the intake valves as possible and 4) All fits under the stock hood line - and incorporate them all into one design.

I am merely lucky enough to be close enough to pick the fruit after its ripened, I didn't plant the tree.

Dennis K

Very creative, Adam. I like it. What cams were used in the simulation to produce those torque curves?

hacker-pschorr

I'm not sure about the price. The 2000 SVT Mustang Cobra R was a limited run (longer runner intake) model at 300 units. I'm not sure where the short runner intake came from.

As for using this on a 928, the bore spacing on the modular Ford SB is 3.937 inches. A 928 motor is BB size at around 4.9 inches.

atb

The model is based upon Louie's motor, which uses DEVEK B1 cams.
Our motors will be similar in displacement, run the same con rods, same valves and I've got the B1 cams as well. The differences are that I have the 6cwt crank to Louie's 8, I've got domestic pistons with nikasiled cylinders where Louie has the 104mm Porsche pistons and running the stock alusil cylinders, Louie's heads were ported by DEVEK, mine by a local machinest Gary Pugh, and Louie is running non-Porsche valve springs - I'm undecided at the moment as to what I'm going to use.

Other than the fact that the motors have different builders, physically they will have very similar specs. Louie has suggested a modification on the grind of the exhaust cams for my motor to better suit the A/T, so that may still be factor as well.

IcemanG17

Looking great Adam....should be quite a bit less expensive to make too.....

largecar379

an interesting discussion and tech results.

for the masses, however, I would be interested in what sort of air filtration box/routing/cold air package you intend to design---or not?








--Russ

atb

Hey Russ,

It will be very similar to Louies in appearance, but where Louie's has a rubber snorkel going over the rad/bulkhead, mine will have a pierce of oval tubing fitted with a (Super)MAF hot wire/venturi. I don't know what dimensions I'll use for the MAF. According the Burns Stainless, a 2.5" by 4.75" oval flows about the same as a 4" circle. Thats sounds pretty close to stock MAF dimensions, and I'd really like to go bigger so that the MAF isn't acting as a bottle neck.

Edit - I guess I should embellish a bit for anyone who is not familiar with Louie's set up. (Sorry, couldn't find the pic, I'll post it later) His plenum box is fed air through a snorkel that enters the front wall of the plenum. The snorkel extends over the rad into a custom made housing which holds an inverted OEM filter. The filter draws air from the space between the rad and the front bumper cover. The top of the space is closed off to forcing any air not taken by the motor to go through the rad.