CanAmJohn

EGT's arnt fast enough for mapping, they are more a way of safety checking to peak loads. Multiple wide band mapping is probably the simplest method (it is expensive on a V8) to establish a pattern for the install, but once you have trimmed out the individual cylinder variances you can then get back to mapping the majority of the time by a single WBO2. It just takes a lot of time to build up the knowledge base so you can then get a position of knowing what the average AFR needs to be to keep the leanest cylinders safe.

atb

Definitely. The place is a wreck right now, but there is definitely a lot going on.

ptuomov

Adam --

A random intake thing that I just thought about last night. This applies to ITB's, which you have (but I can't afford.)

Suppose that you ever need more low end torque, for example for an automatic car with four gears, such as yours. This means installing longer and probably narrower runners to your ITB system, compared to for example Ott's short runners. Instead of just shooting them up thru the hood, one probably wants to have bends of sort and stay under the hood. This is what I've gathered from this thread, please correct me if I am wrong.

Here's the idea. The most efficient way to terminate the runners that I have been able to come up with is a circle in which the runners cylinders are in the order 1-7-6-4-3-2-5-8-1. Looking from the roof of the car:

8 1
5 7
2 6
3 4

Why in this order? The firing order of the 928 is 1-3-7-2-6-5-4-8-1. In the above circel arrangement, the currently "sucking" runner is always three steps away from the previously sucking runner and the runner sucking next. This should allow for a compact plenum / air box while minimizing interference between runners.

What do you think?

Best, Tuomo

atb

Tuomo,

Click here for the follow up thread on what I'm doing with my intake.

The "sucking" runner phenomena doesn't become a factor with my proposed layout. As far as compactness, since my runners are going to be inside the box (as opposed to having a box tying the ends together) it will be as compact as it can be given the size of the horns.

FlyingDog

Has anybody thought about runner lengths relative to firing order or exhaust runner length? Maybe Porsche wasn't as lazy as we think? Okay, yeah, they probably are that lazy.

Erik, related to Todd's thoughts on knock from 2-6 being the cause for bearing failures... How does that apply to 16V engines? I know Todd hasn't done much if any work with 16V engines. Does anybody know if 2 and 6 are also the lean cylinders on 16V engines? Is the fuel mixture variations also linked to cams (increased duration reduce variation? increased overlap increase variation?)?

Hilton

Worth noting that everyone seems to assume Porsche optimised the intake for maximum power/torque delivery.

Its also worth noting that they'd probably started investing heavily in developing the 964 at the same time, and that may have affected their decision making on power output and design.

soupcan

My old shop teacher was a Chrysler engineer in the 60's he used to say the shock towers and hood took all the fun out of engine development. He had said that most designs were compromises of packaging and maintenance. The 32v engine was developed in the 80's to fit in a car designed in the 70's, so I would assume a lot more engineering went into fit than into function. Why did they change from the 85/86 intake to the S4 design? I looked at the TSB's from 85/86 and there were a few revisions related to the cylinder heads/covers and camshaft end plugs, I wonder if the S4 intake was also redesigned for ease of maintenance.

hacker-pschorr

Don't forget assembly time. The 16V intake and 85/86 unit have 18+ hose clamps along with the rubber in between the pieces. I have a feeling this alone had more to do with the final design of the S4 intake than anything else.

We need to drop this fantasy that every design from Porsche is for maximum performance. By the time 1986 rolled around the 928 was already coming up way short of its initial goal (kill the 911). It was on the back burner of the engineering pool before the 32V engine hit production. Porsche knew how to make a better intake, they simply didn't care since the power goal was reached with this one, no further development was necessary.


Look across the pond to see what GM was producing in 1985, nice big long even runners:



Don't even get me started on the 1989 ZR-1 intake. Triple plenum design with two sets of runners for each cylinder. 405bhp from 5.7 liters. The skunkworks version pumped out 475+hp:

heinrich

GORGEOUS!!

heinrich

Dude.

The 928 was never ever to outdo the 911, that what the point. 911 is Porsche's flagship. The 928 engine had TONS more power potential that Porsche super-undertuned it. Just to protect the 911.

And 405 normally-aspirated horses from 5.7 litres ... LOL!!! Not impressive. Our 5.7 litre motors do better than that. Hell, a simple bolt-on supercharger does better.

hacker-pschorr

That's not saying much about the 928 engine then is it? 5 liters pumping out 320bhp.

ZR1 - 71bhp per liter
S4 - 64bhp per liter
GTS - 62.7bhp per liter

The ZR1 motor was also detuned (pick a reason...) which is where the skunksworks or "Black Widow" ZR1 option came into play.
Still 5.7 liters N/A motor pumping out between 475-500bhp back in 1991ish. I know two people who have Black Widow ZR1's.

Black Widow - 83bhp per liter

Every ZR1 came with a 6-speed transmission

heinrich

The difference is, the 928 was always detuned in favour of the 911. You make my point excellently.

heinrich

Whereas the Chevy was always tuned to its absolute maximum ... squeezing every dry drop of power out of it ... at the expense of longevity, reliability, etc etc.

hacker-pschorr

I've made that same point in quite a few threads, same goes for the 951.
1988 when R&T posted better numbers from the 928S4 and 951S it must have upset a few 930 owners.

I never said Porsche didn't have the ability to make a faster 928.


Far from the truth. Look back at the specs of the Black Widow ZR1 I posted. This was a factory (well, kind of) option back in the 90's. People also bolt superchargers & turbo's on these engines with excellent results. Callaway gave up on the 928 and switched to Corvette's, produced some very fast cars. One of them held the record as fastest production based car until the Veyron came along. 254mph from a twin turbo C4 Corvette. Not to shabby.


None of this changes the fact that the S4/GT/GTS intake is a questionable design for a top tier production GT automobile. Maybe Porsche initially designed the intake for a non-batch fire injection system that never came to be. Who knows.


/sorry, closet corvette fan.........most of my local car guys are Vette owners (with very fast dedicated track Vette's) - sure beats slumming with 911 owners.

heinrich

Boy Eric that has got to be the most disagreeable agreement I have ever heard. So we are agreed then