Computer Modeling of the 3.2 Liter 911 Engine

[dkirk]

I've started this thread as a continuation of a previous thread entitled "3.2 Cylinder Head Info" as it better describes my project - that is to construct a computer model of the Porsche 911 engine. I chose the 3.2L as it's the engine in my car and the one I'm most familiar with.

I'll be using Virtual 4-Stroke by Optimum Power as the computer code as it is this software that I'm trained in using. Once the model has been created, running and showing realistic results, it's straightforward to make changes in induction and exhaust systems, cam timings, and displacements. I'm hoping that this may be a useful tool to us engine guys.

I may have to occasionally request info on engine specifics and already many readers have contributed some excellent data - I thank you!

Here is a major request - does anyone have a valve lift file for 964 camshafts? I would need both intake and exhaust valve lift numbers, taken at the valve, with .1mm valve lash setting? Every 5 degrees of rotation would be fine, but every 1 degree would be preferred. This can be lift (in inches or mm) vs. camshaft (or crankshaft) angle. Preferably an Excel file would be desired.

Please send to my business e-mail at dkirk@milwpc.com. Thanks very much for your interest and contributions. This will take some time to prepare but with this COVID thing and the fact that we're practicing anti-social behavior, plus the driving season being finished here in WI, it will be an excellent project for me during the winter months.

[Mr Beau]

Cool project. His some info for E cams... looking for 2.7RS CAM BODY EVALUATION

[dkirk]

Thanks to all that have sent technical info to me - greatly appreciated. Working on assembling this engine model every day and things are shaping up.

The initial model will be of my 3.2L engine equipped as follows:

Steve Wong Chip
964 Camshafts, timed per Porsche specs
SSI Exhaust system
Dansk 2-in, 1-out sport muffler

I plan to get a chassis dyno session conducted next Spring and thus will have some actual test data to compare model results to.

[robcf]

2010: An EFI Hot Rod Odyssey

[dkirk]

Thanks robcf - some interesting airflow information in that chart that will be useful.

In creating a virtual engine model that will accurately represent the real machine, duct lengths are vitally important to replicate the tuning pressure pulses. Their strengths and arrival times in conjunction with valve events and engine speed are the ingredients for accurately calculating engine output at a given rpm. Thus the lengths and diameters of the ducts that comprise both the inlet and exhaust system are critical.

In concentrating on the exhaust system, I was able to get this picture from the SSI website showing the header pipe arrangement.



Using this picture, I measured the header pipe length then applied a scaling factor based on measurements from the same system on my car. From cylinder head flange to the exhaust system merge point, I arrive at a 47 inch (1195 mm) header pipe length. All header pipes are designed to be the same length which is the goal. The ID of the pipe is 1.438 in (36.5 mm), which incidentally, is the same as the factory exhaust.

If anyone sees an error here, or can contribute more accurate details on the SSI system, please let me know.

[Peter M]

Originally Posted by dkirk

The ID of the pipe is 1.438 in (36.5 mm), which incidentally, is the same as the factory exhaust.

Mr Kirk,
I don't have a set of standard 3.2 exhausts handy but I think you'll find the primaries are larger than the SSI's. I would expect the standard exhausts to have 1 5/8 inch OD primaries or something around 39mm ID.

I can measure for certain in a couple days if you would find this helpful.

[dkirk]

Peter M - yes, please measure the stock exhaust system pipe ID's if possible. I measured the ID at the cylinder flange end on the stock 3.2 exhaust system and found it to be the same as the SSI. I'm making the assumption that all tube diameters are the same, but this may not be correct.
.

[dkirk]

If one of you kind souls with a spare 3.0 or 3.2 cylinder head lying around could supply the following information, I would be very grateful. Please refer to the image below. Need the following, within +/- 1/8 of an inch (if possible), and units of inches or millimeters are fine.

Exhaust port pathlength to manifold mounting face, Leh
Exhaust port diameter at manifold mounting face, Dem

Intake port pathlength to manifold mounting face, Lih
Intake port diameter at manifold mounting face, Dim

Thickness of intake manifold thermal isolator, with gaskets (not shown)



I have all the valve dimensions measured from the old valves I kept from the top-end overhaul.

[Peter M]

Originally Posted by Peter M

Mr Kirk,
I don't have a set of standard 3.2 exhausts handy but I think you'll find the primaries are larger than the SSI's. I would expect the standard exhausts to have 1 5/8 inch OD primaries or something around 39mm ID.

I can measure for certain in a couple days if you would find this helpful.

Dave,
For standard 3.2 headers, I measured:
41mm OD - Equivalent to 1 5/8 or 1.625"
38mm ID

[dkirk]

Peter M, thank you for the stock header dimensions. I measured my stock header tube ID at the cylinder mounting flange and got 37.5 mm or 1.48 in.

Still hopeful that someone will respond with the port dimensions requested in a previous post.

[racing97]

Intake port dimensions for 3.2 carrera 3.8 inches intake and 2.54 exhaust

[dkirk]

Thanks to DJ and racing97 for answering cylinder head port length question. I'm getting close to having a single-cylinder model ready to run...this is the first step in creating the full multi-cylinder virtual engine.

[dkirk]

I now have a single-cylinder version of the 3.2L engine running on my computer. Best to start simple and work up to the more complex 6-cylinder with all the interconnected ducting. This baseline, virtual single allows verification of valve timings and piston motion, just to be sure everything is representative of the real engine. Right now, at 6300 rpm, power output from this single, multiplied by 6, yields about 225 bhp. The interaction of gas dynamics in the inlet and exhaust systems on a 6-cylinder version will hopefully up the output to around 245 - 250 bhp.

Thanks to all that have contributed to this endeavor. Hope to have some power and torque curves to display in a few more weeks.