Good logic and a fair question.

However, the cross-tube that the flappy is in is not located in such a way to benefit from the harmonics as you would think. If it were located to maitain the pressure wave thru the intake runner, through the plenum, and to the other side - you'd have something.

As it is, we expect the improvement to be consistent with the CFM and air density curves, thats is, engines under boost (with higher CFM and Density) willr eceive greater benefit than the NA motors.

I have 3 sets of them out to Rennlist members who have promised to dyno them and send me the bill. they represent a stock motor, and 2 built strokers.

 

Carl -- Please ask them to record runs both with the flappy overriden open and flappy overriden closed. This way, we'll learn more about in which mode the spacer have most of their impact. Best, Tuomo

 

IMO the idea behind the spacer has more to do with trying to balance out a poorly designed intake manifold.

See this thread to familiarize yourself with the S4/GT intake manifold:
https://rennlist.com/forums/928-foru...ne-spacer.html

If you have any questions / comments about the thread I posted above, please post them in that thread to avoid hijacking this one.


If all goes well, we will be dyno testing these spacers on a supercharged GT and a supercharged automatic S4 sometime in April.

 

Hacker-Pschorr --

Thanks for the pointer. I was reading that very interesting thread yesterday, and that really got me thinking about the spacers. I will post my comments, if any, to that thread.

I would have to respectfully disagree with you one issue, though. You write "IMO the idea behind the spacer has more to do with trying to balance out a poorly designed intake manifold."

I wouldn't call the intake manifold poorly designed. If I have understood the history correctly, a large number of people have tried to modify the intake to improve it. So far, beyond simple port matching, I don't think anyone has succeeded. In face, I don't think anyone has been able to come up with any single throttle-body design that is better than the stock manifold, even for otherwise modified engines.

Is this a fair summary of the collective wisdom?

Best, ptuomov

 

That is the question I had..... ie will the fit on a 89GT with the Murph original Stage II SC install.

Seems to me I will have to rerout the oil seperator plumbing at the very least........ Let me know Hacker, 'cause if the fit, I want a set.

 

I have no doubt that a well designed modified intake would out perform the stock set up. by all accounts, it is very rough. extrude hone, and modifiying the intake runner horns, as well as the spacers, would give modest gains.
a nice round domed cover might help a lot more as welll, but there becomes problems in areas of fitting the fuel injector rails.

What I did was to run the stock intake with and without the flappy open. contrary to what you expected, having it open from beginning to end yielded the best top end HP by a slight amount. of course, the low end HP was killed , but again, thats below 3700rpm where i never use the engine in anger.

mk

 

Very interesting. Thank you.

So the closed flappy is either irrelevant or harmful after 3750 rpm. If I were consistently getting torque curves like this, I would leave the flappy open all the way to the end after 3750 rpm.

Why do you think the factory chose to open the flappy again somewhere around 5500 rpm? Could it be shifting for A/T cars? Does the rpm drop below 3750 rpm on A/T cars after a shift? If so, this may be simply to have the flappy already closed before the revs drop.

In any case, if the flappy open gives more high-end torque, then the spacer may very well work if it is combined with an ECU parameter update to not close the flappy again at higher rpm.

Thanks again for the dyno graphs.

 

I have no idea why Porsche would have the flappy close again at 5500 rpm , but I might speculate that a dimension other than all-out horsepower could have been involved. Maybe it impacts emissions, or fuel economy, or noise level, or wear-and-tear... lots of possible reasons other than hp to close it again.

 

Yes, I agree. Those graphs are a little off, in that I think I had some closed flappy runs near the same HP level. BUT, it makes the point that there certainly was no gain with the flappy closes. Now, why it was supposed to close after 5400rpm, is a mystery. maybe it was to protect from backfiring, cross talk on off throttle, who knows. I sure would like to have the answer to that question.

I did see this dyno run when i was having a hard time having the flappy open consistantly, given that if it didnt open, i lost big HP after 3700rpm to 5500rpm. So, I ended up just connecting the vacuum line to the flappy to the vacuum booster. now, if there is vacuum in the system, there is an open flappy, which is happy!

mk

 

Carl
I hope to have some results soon........ It might be the black widow 1st....but we'll see.....

 

lets see that dyno SOON! should be interesting.

 

MK
You know I have TWO sets right................................

 

Hi All, Carl F thought the info below would be of interest in this thread.
Adrian

From: 928racing@yahoogroups.com On Behalf Of adrian928@tesco.net
Sent: Sunday, February 01, 2009 1:58 PM
To: 928racing@yahoogroups.com
Subject: [928racing] Inlet manifold flow testing

Well with the weather pretty cold today, I went over to John Speake's today to flow test my modified 32v inlet v a standard GT. Apart from the polishing/porting, (see previous pics), I also added a set of Carl's side spacers.
We were unable to get up to max flow (as measured by voltage at the MAF), but results as follows:
1. Overall increase 1.4-2%, which at max flow should equate to 4-5% when I benchmark against data from other sources
2. The variations between cylinders was much better with the modified inlet - range 2% max on original down to 1.2% modified.
3. No measurable difference with flappy open or closed

Tests were with side plates on. (From other data I have no side plates improves flow by 3% at max)

So will have to see what this all means in the real world when the next race engine is finished. If the intake really is the restriction, then an improvement of 4-5% at max could equate to over 15bhp? For comparison the Phil Threshie carbon inlet flows 25% better than stock at max and can give over 60bhp more power.

My rough calcs suggest that with standard valves and my spec cams it will flow 237cfm standard valves per cylinder and 260cfm with the 968 valved/modified heads. Anyone got any comparable data? thoughts?

Rgds

 

Spacers are ON......should hit the dyno later today?

 

Good to hear.

Kibort: didnt you get a set of spacers too?