Steve Cattaneo

Greg,

Speaking of the S4 intake manifold, mainly the resonance plate (floppy) when closed it divides the intake manifold chambers, at a speed of about 3500 RPMs under a load, the vacuum diaphragm opens the resonance plate causing a boost in torque.

With an open resonance plate it allows more airflow through the intake chambers, giving the engine a boost in power. What if someone supplied a constant vacuum to the diaphragm allowing it to remain open at all times, that should increase the overall performance of the engine. The resonance plate could be the airflow restriction in the S4 engine, if only I had an S4 to play with.

John S,

I’m running custom dual 21/4 in pipes with a high performance free flow muffler. No cat and no rear muffler. My car sounds like a big block, when I pull up to a red light all eyes are on my car. It’s an awesome sound. You can hear the valves popping through the exhaust system and you can feel the 310 plus horsepower on acceleration. Do you know anything about Reher-Morrison racing engines? They are located in Arlington, Texas.

Jay,

I’m rethinking my first thought of bigger valves. The 2/37 mm intake and 2/33 mm exhaust valves should provide more then enough airflow for an engine producing 550 HP. Those valves are the equivalent of a 2.914 intake and a 2.60 exhaust valve on a 16-valve engine.

Jim, Jay,

What size valves are you running in your 944 head?

Increasing bore (cylinder diameter) or stroke (length of piston rod travel) will raise compression. I read somewhere that a longer stroke will increase compression ratio more effectively then increasing bore diameter. Dome piston also increase stroke and compression ratio.

928 GTS 5.4L engines have a HP rating of 350 Hp/365 Ft.lb or torque. The compression ratio is 10.4:1 with a longer stroke 85.9 mm; the bore is the same as the S4 100 mm. The GTS pistons have a small dome. This combination could be a consideration. I want to keep my super charge option open, if my NA engine does not meet my HP expectation. I need to speak with Mark R the super changer king for some recommendation on compression ratio. Does anyone have the cam, specks for a 5.4L engine? Duration, lob lift, separation, valve timing. Jim, I will continue my research. Thank you.
Steve C
The Great White

Jay Wellwood

Steve-

I think you'll find that the Throttle Body is the culprit on the S4+ intake.

The GTS and the S4 share the same cams - while the GT is a stand alone beast with higher duration and lift (this is also the reason the GT's are all 5 speed - impact on the vacuum while idling). When the GTS was produced - had Porsche installed the GT cams - the GTS would have produced more HP than any other stock Porsche in those year models (well, NA anyway).

I am in the process of obtaining the parts to go the 968 Intake route - and then maybe a bit more (if I can find a reasonably priced donor 87+ block). First the heads though, and then from there. I decided to not perform the SC mod at this time. However, Marcus has developed a great base engine IMHO for the SC to work beautifully.

Donald

Steve-
If I understand the basics (emphasis on basic ) of intake manifolds, the reason for the crossover, which is effected by the flappy valve, at 3500 rpm is to tune the intake vacuum for low rpm torque. This is why quarter milers use hi-rise tunnel ram intakes because they only run at idle, or full throttle (like some on this board ). If this is correct, you will have a huge bog at rpm below 3500.

FWIW
Cheers,
Donald

Steve Cattaneo

Jay,
I would be careful installing those bigger valves (968). If you look at the S4 head combustion chamber, where the original valves lie, there is no room. You will have to machine into an area that’s known as the squish band. That area has a purpose. It accelerates all of the air on the compression stroke to the center of the chamber. Thus allowing the combustion process to occur faster. Reducing it can cause a loss of torque or worse, detonation.

Research this a little bit more.

Donald,
Racing tunnel ram manifolds are for all out racing engines. They have very large volume runners. They flow 3000+ CFM’s. That’s a lot of air. That’s why these cars have hood scoops on them. The S4 intake manifolds are tune-port injection. The runners are smaller in diameter to optimize low speed power. But, By having the floppy open all of the time, it could detune the manifold causing a bogging condition. You maybe right, for I am no expert on engines or manifolds. Thanks for the insight, the more information the merrier.

PS. Would you like to use your car as a test platform?

Steve C
The Great White

Mike Schmidt

The intake flap opening doesn't allow for more airflow through the intake. What happens when the flap opens is that the resonant frequency of the intake is changed. The intake is tuned to take advantage of the Helmholtz effect at one RPM with the flap open, and a different RPM with the flap closed. The length and volume of the intake runners determines what RPM is tuned for. What happens is that the air flows through the runner into the cylinder when the intake valves are open. When the valves are closed, the momentum of the air that's still moving towards the cylinder creates a pressure pulse that now moves away from the cylinder through the intake runner. When this pressure pulse reaches the higher volume of the plenums, it reverses again, moving through the intake runner towards the cylinder. Think of the way a toy Slinky pulses back and forth. The trick is to have that pressure pulse moving through the intake runner towards the cylinder, and getting there at the exact instant that the intake valves are open. This will allow air that's actually at a higher pressure to be rammed into the cylinder. In a way it's like having a slight amount of boost. As engine RPM increases, the pressure pulse gets out of sync with when you want it to be at the open intake valves. When the flappy opens it's like having a second intake manifold tuned for the higher RPM range. That's why there are two torque peaks on the cars with the flappy. Putting a constant source of vacuum on the flappy wouldn't give you any additional top end, but would reduce the low end power.

Jay Wellwood

Steve-

The 968 and 928 S4 heads are nearly identical in all aspects with regard to the bowl size/combustion chamber dimensions.

DEVEK also sells this as a perfomrance enhancement (in both the 968 Intake and then another set with both enlarged Intake and Exhaust). I don't know of anyone (yet) that has used these items (maybe Sterling?).

Just a thought...

John Struthers

Herr Schmidt,
Wunderbar! You haf proven once again dat der Cherman race ist zouperior as teachers as vell as inovators. Das ist so stimm, ya?
Hey, I am impressed, Mike. Growing up with motorheads of the Ford, MoPar and Chev. persuasion
I was taught that to much intake valve and the wrong manifold lost you the omph down low and gave it back on the high end. Mopar came out with the Cross Ram - which as far as I'm concerned Chev. later stole. Ford had so many cam, head, intake manifold set-ups that it was damn near untrackable. Big Blocks took over though -no replacement for cubes - on the drag strip.
And thru all of that not one REAL explanation on something that was basically, SIMPLE!
I'd bet there have been 15 - 20 references to the intake resonance issue since may and yours was the first description of the event-Helmholtz-.
My hats' off to you. The Intake charge/Pulse wave timing explanation places you in that lofty, demi-God, nay, Guru niche.
I appreciate the PRIMER and I'm sure others do as well.
Thanks, (BTW you have to come in for a fitting -you know...the linen robes and the pre-requisite Laurel Wreath)
John S. and Pattycakes

Jay Wellwood

Sterling -

In as far as the cam info - this is what I apparently repeated in error - thanks for clearing that up. Also, a cerified (or is that certifiable?) P mech told me that the heads were nearly identical in the area of the combustion chamber. Guess I should research this kinda stuff a bit more before I pass it on.


Thanks for the calibration...I think.

Jay Wellwood

Talked with marc at DEVEK this evening - an interesting conversation regarding valves and the like.

Sure enuf - the 968 Intakes fit without any problems (not according to me here - per DEVEK). He mentioned that the really large bores use 42mm (read that again) Intake valves. Problems were not mentioned by Marc. He did not mention the exhaust valves in size specifically - nor did I ask (foolish me). One thing that Marc did mention was that only the Exhaust valves are the sodiuum filled variety (and here I always thought/was led to believe that every damm valve was sodium filled!).

Per Marc, the White Car to date has 155K on it since the build up...that speaks volumes to me regarding longevity/reliabilty.

hth-

Aaron Rouse

If the white car has 155k miles on it since build up then why does the ad for it on their page say it has 6-8k miles on current engine? I know it is a old ad, but it can't be THAT old.

Okay, to my question if one were to run a TECII on their car and do way with the need of a distributer(s) then could they run 944/951 cams? If so would those cams be any more agressive than the stock 928 16V cams(Euro or US)?

2V4V

Steve,

Definately would want to cc ANY head that I was thinking of installing, no matter which one it ended up being. As has been pointed out, squish area, and the airflow patterns developed by it, are important towards the higher end of NA horsepower. And if you're doing the heads, cc'ing is as important to smooth power production as having a good crank/piston match and balance done.

Head volume also determines compression ratio
in concert with the pistons. So, 10:1 pistons with one type of head, will not necessarily produce the same compression with a different head.

I have yet to decide on a supercharger - it will either be centrifugal or twin-screw. (Probably centrifugal.) They have the best efficiency of any type on the market (coolest output air, lowest parasitic draw on the engine) and are simplest for custom installs, especially with an intercooler.

Greg

Carlos

Guys if I was wanting head work done I would contact a head guy not a Porsche guy. As they say, physics is physics. A top notch racing head builder will have an understanding of flow & combustion dynamics than cannot be matched by most engine builders. The principles involved are not specific to a given engine so a talented head guy will produce superior results. He will also have the necessary answers as far as valve sizes, springs etc. I have given some thought to how much streetable power could be produced with heads, intake, cams and exhausts. I may be wrong but I think there is more than 100 hp available for an S4 with the "right" stuff. With flow #'s from the heads, clearance, comp. ratio, gearing, etc, custom cams could be ground for far less than the $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ usually asked for. Then with the dyno info custom exausts can be had for not much more than MSDS. I think a potent combo could be had for not that terribly much.

Aaron Rouse

Has anyone had custom cams made before for a 928 be it a 16V or a 32V and not just bought them through a performance shop(Devek)? Just curious how easy of a route it was to get done.

Jay Wellwood

Aaron-

When I first got my Shark - it came with custom ground cams installed. The cams had to be de-tuned to get the car running right (an automatic) due to the duration and lift. This detuning in effect negated the use of the cam and their original design (they were ground based on the 944 cam profile) and where originally obtained from Elgin Cams in California. (Dyno numbers of ~ 240Hp, 255 Torque at the rear wheels) I have no idea what the cost was originally - but in talking to Elgin - they indicated ~$1K/cam (yikes!).

Fortunately, the original Porsche S4 cams were provided with the car when I purchased it. I installed the original cams last summer - now I'm getting 271HP and 283 Torque.

hth-

Aaron Rouse

Yeah, Jay I recall when you switched back to the S4 cams. So if you had an aftermarket engine management setup then you might have been able to use those cams to their potential?

I have heard from others that the 944 cams are more aggressively spec'd. If one were to run something like a TECII or TECIII on a 16V 928 which would eliminate the distributer, could they then fit 944 cams on it? Seems like you could since the heads will bolt on with minor mods.