hacker-pschorr

IMO it's not even a big deal on a stock 928 if the end result opens up the top end and allows for a more equal tune across all eight cylinders.

With the tuning of Todd's motor with Autronic, it becomes very obvious how limiting the stock intake is (even with the flappy) due to the wide range of intake runner lengths.
Even with the shark tuner you cannot tune each cylinder individually due to the batch fire injection system. This means you are always tuning for the leanest two cylinders.
The advantages of having an intake with equal length runners greatly outweigh any negatives over lost low end.
It seams like the S4/GT intake was designed to have individual cylinder control that never materialized. Maybe the technology wasn’t there for a production car back in 1986, who knows.

I was doing some troubleshooting on my father 355 yesterday; this involved a few test drives. Absolutely zero low end torque with a 3.5 liter V8. I would take an 8,500 rpm motor with that top end over a big block stump puller any day of the week.

Brendan,
Have you chatted with Todd about the one he is currently making?

Louie928

It's not, and IMHO, desireable to limit the torque below 3500 rpm or so on a stroker. It could be a problem on a 5 or 5.4L engine with auto trans. If you have a 5.0 L 928 and want good low end torque, you can go to big cubes, or get a twin screw SC.

Louie928

Well then, it's settled. Do it.
It'll be difficult to get the 330 mm total runner length. That will be about 9" outside of the cyl head. Come out of the head at about 17 to 20 degrees in relation to the intake mounting surface which is horizontal. That'll get the runner pointed right at the valve heads. Use a bend, not straight pipe, so the runner inlet curves more inward. You'll have to angle the front runner inlets toward the rear herringbone fashion because of interference with the coolant bridge. The rear ones can't be angled back 'cause there is no extra room at the rear. The temp sensors on top of the coolant bridge will have to be moved. I put them on the rear of the bridge, but maybe you wouldn't have room. Most likely the coolant bridge mounting boss by cyl #1 will have to be milled down for clearance of that runner, but it is not a huge problem. Build a box around the air horns, fit a TB at the front. Piece 'o cake.

I think the intake pic you had doesn't have a large enough plenum.

Here is a couple pics of how mine looked as I was building it. Might help. The vertical height at the front of the air box is about 2.5". You'll probably need multiple bore TB because I don't think there is enough height to fit in a large one unless the TB is remoted from the air box inlet. The top of this air box fits tight against the foam pad on the underside of the hood and I have the motor positioned about as low as I can get it with the oil sump spacer.

https://rennlist.com/forums/attachme...1&d=1217782527
https://rennlist.com/forums/attachme...1&d=1217782527
https://rennlist.com/forums/attachme...1&d=1217782960

Lizard928

Louie,

If you wouldnt mind indulging us, from your calculations, what type of plenum volume are you thinking would be a min, and a max.

As well as for throttle body or dual throttle bodies?

BC

He mentioned one, but I only call him for an hour at a time, and we never get to the full published agenda.

BC

Thanks again Louie. I just measured, and from the seat, 300-330mm is like 12-13 inches! That, as you mention, is around 9" of runner length outside of the port. Thats huge.

I don't want to limit low end torque, but I more importantly do not want to limit the airflow above 3500rpm, which is where all gears will drop to after a redline shift from first.

Louie928

Brendan,
I think it will end up as you doing the best you can for runner length and taking whatever the result is as it is. Your blower will take care of the top end. The runners can't get too convoluted in an attempt to get every last mm of length either since bends do cost flow efficiency and disrupt tuning to some degree. Some of the BMW V8s have an intake like you want and use curved runners inside an air box. Maybe use some of their ideas in your design.

Here is one idea from a Maserati. Probably 180 deg crank though and complicated to fabricate.
https://rennlist.com/forums/attachme...1&d=1217790772

BC

I think it was the older M5. They actually had ITBs, I think, and then curved (90 degree) into an air box (all different directions, interestingly) I will try and find a picture.

Here is the "expansion manifold" intake from the new GT2:

BC

"We're gonna need a bigger hood"

BC

What I need to make sure about is that there is not the sort of torque loss as there is here (50lbft!)

Louie928

Yes, I envy intake design on a flat or V6 because the intake pulses are even on each side so you can have a plenum on each side. Also, the intake pulses are spread apart enough that a good plenum resonance can be achieved.

Louie928

Great intake design if you don't plan on operating less than 5000 RPM.

You could get a feel for how the 5L 928 would be without the benefit of the side plenum Helmholtz effect which makes the lower torque peak at 3200. You can bypass the flappy vacuum valve so vacuum is presented to the flappy actuator all the time. Connect the two vacuum lines together at the solenoid valve. That should keep the intake flap open all the time. Normally, when the flappy fails, it has a lack of vacuum, or failed actuator, so fails in the closed position. That keeps the lower torque peak, but reduces the top peak at around 4300 rpm.

I've done that when Sharktuning so I can see the torque curve with the flap valve open and again with it closed. That way I can see where the optimum flap operating point (RPM) is to get the best from both intake configurations. Then set the LH to open the valve at that RPM. The flap closes again at 5500 - 5700 RPM but doesn't make much difference there. Near as I can remember, the torque curve appears like it would if you drew a straight line between 2000 RPM and about 4000 RPM with the 3000 RPM hump missing.

BC

I am trying to make sense of this Louie. This will be a street driven car, as well as on the track. The centrifugal boost, while under load, will come on at 2500, but will not be on full boil until 4500.

Do you have the stock S4 in the engine analyzer pro?

Louie928

Brendan,
Yes I do have those files. EA Pro can't model the 3000 RPM intake resonance so shows lower torque in that area than you'd normally see. Also, EAPro only lets you have one runner length for all cylinders so can't accurately show the multi length S4 manifold. What cam did you want and what intake? Email me what specs you want. I gather that you have the EAPro program?

BC

Yes sir. I did some cams. They have 10 degrees and .025 more lift on both sides. The centerlines are the same as stock.

Intake is 263 duration at .417
Exhaust 246 duration at .379

Yes, I got the EA Pro

(can the intake resonance be done by the "secondary throttles" option at 4000? Probably not)