K&N watershield vs stock performance

[eapcpa]

I plan on Chassis dynoing this thing "with" the velocity stacks and without. The stacks are 2.25" tall and the filters are 3.125". That is 7/8" clearance from the top of the velocity stack to the top of the watershield top cover. Some have written that K&Ns are less efficient than stock due to the proximity of the stack to the top filter cover . That causes a restriction or other disruption of the air flow. TWM makes a 12mm tall stack and a 35mm stack. Since I am using a 1" spacer plate on my MFI that doubles as the cold start system (see pic) I could run shorter velocity stacks to get back to stock length. As a side note, what effect does the intake runner length have on the power curve. I am running 2.7 liters w/S cams and 36mm ports.

[Henry Schmidt]

We have been unable to measure the restriction you refer to. If you are truly worried PMO sells short stacks for K&N filters.

A one inch spacer would have zero effect.
During a 2.5 IMSA engine development in the early 80s we discovered that you had to change the intake running length by 5 inches to see any difference on the dyno.

Runner length technologies were pioneered by Dave Long, an engine designer working for Chrysler back in the 50s. Chrysler had a slant 6 with long runners to develop maximum torque. That slant 6 leaned to the right and had a 4 foot intake runner that put the carbs near the left fender.
Even the Porsche Varioram technology changes the runner length by over 2 feet.

[911pcars]

It's no longer uncommon for manufacturers to use dual-chamber intake air plenums to maximize torque at various engine speeds. A set of throttle plates inside the plenum allows the intake air path to lengthen or shorten. Operation controlled by the engine control unit.

For example, the version used by MB is a scroll-shaped (think snail housing), magnesium plenum to reduce real estate under the hood while providing the needed intake tract length.

Sherwood

[eapcpa]

Thanks Henry. When you say you have been unable to measure any restriction problem, have you done the dyno work to show that? There was a detailed discussion on the GT40s web forum some time back. My buddy started the website so I will ask him to give me the link if anyone is interested in their findings. I don't recall the exact details of the issues. Just looking for a quick easy answer and sharing the knowledge.

[Eagledriver]

There are several calculators available on the web to compute intake runner distance for max resonance effect. The longer runners help improve torque at low RPM. According to the calculator that I used if you increase the intake length to 16 inches (1 inch spacer and tall stacks) you will hit a 4th harmonic torque peak at 4500 RPM and a 3rd harmonic torque peak at 6000 RPM. Each change of 1 inch results in a 500 RPM change of these numbers. I.E. no spacer means first torque peak at 5000 RPM and second at 6500 RPM. This seems to match the seat of the pants feel of an early engine where you get a noticable increase in torque as you approach 5000 RPM.

You can measure your intake length above the port and then add 3.5 inches to account for the depth of the port to the valve face.

-Andy

[Henry Schmidt]

It is my belief and experience (we tried, we were looking for 3 horse power on a 296 hp 2.5 liter engine and runner length couldn't produce one hp or change the torque curve any measurable amount) that you will never measure a difference in the real world with a one inch change in runner length.
Theories are wonderful on paper or a cumputer simmulation but the real world is niether.

[911pcars]

Henry,
Do you have any data on any discernible power/torque differences between the factory and tall Weber intake manifolds?

According to user reports:
Factory Weber intake manifold = 68mm high
PMO replacement manifold = 82mm
Factory tall manifold = 98mm
PMO tall manifold = 98mm

Sherwood

[Steve@Rennsport]

Sherwood:

I'd concur with many of Henry's finding but it bears mentioning that many of these discussions are without context to make all the information relevant.

Intake length changes become worthwhile when camshafts with narrow lobe centers and extended duration are used. For a street cam, it makes little difference.

FWIW, tall manifolds on carbureted engines and tall butterfly stacks on MFI/EFI engines when race-type cams are used and these things make a very measurable difference in mid-range torque & throttle response. We see big changes in the AFR values that helps these motors make more usable power. Its all about "area under the curve".

Exhaust systems make a huge difference with these kinds of race engines and thats an integral part of intake tuning,.........they cannot be separated.

[eapcpa]

So 7/8" clearance from the top of the stack will not significantly disrupt or restrict air flow at high RPM. The length of the stack will not noticeably change the torque curve or ultimate HP enough to be felt either given the small changes I am working with. Thanks for the input.

[Eagledriver]

I'm assuming that the engine in Henry's experiments (296HP, 2.5 litre) made it's peak power up around 8000 RPM like the factory race engines did. The tall PMO manifolds are about perfect for that power band (no suprise since the factory chose that length). We, however are talking about an engine that makes it's peak power at 6600 RPM or so. I agree that the peak HP will not change much but as Steve says "it's all about area under the curve". The response of the engine in the 4-5k range will be noticably (and measurably) better.

I hope you run your dyno experiment both ways and give us some numbers on power throughout the RPM range.

-Andy

[Henry Schmidt]

Most of our work was done with MFI 2.5 both high butterfly and slide valve. We were looking for changes throughout the entire range.

Originally Posted by Eagledriver

...edit....The response of the engine in the 4-5k range will be noticably (and measurably) better. not with a one inch change

I hope you run your dyno experiment both ways and give us some numbers on power throughout the RPM range. We will not be retesting conclusions we reached over 20 years ago. If you doubt our conclusions you are more than welcome to do the engine developement work on your dime.

-Andy

Cheers

[Eagledriver]

Henry,

Sorry for the confusion. I'm not asking you to do anything I was talking to Ed. He was the poster talking about this mod.

-Andy

[freiherr]

Always fun to see two engine builders having a techie scrap on line... Handbags at dawn?
We were trying different trumpet lengths on my '65 SWB 911 FIA race car ( Solexes, Solex cams, legal small inlet valves etc) and the longer trumpets messed up the midrange bigtime even after rejetting. Most interesting thing was when we were swapping the trumpets back to standard: on a whim we did a dyno run with no trumpets at all, just to see how much difference proper factory ones made. The engine made 3 bhp more without trumpets than on any of the other runs... same ambient air temp / pressure etc, about 10 minutes between runs.
I think I could hear hollow laughter from the direction of Weissach...

[Eagledriver]

I'd forgotten about this thread. In October 2012 we did dyno testing of several spec 911 cars. Two of us have similar carburated 3.0 SC engines. Mine has 1.5 inch intake spacers. Mine measured 228 at the wheels and the other engine was 230 at the wheels. I had a 10 hp advantage at 5500 RPM and the other engine had a 10 hp advantage at 7200 RPM. Mine was falling off rapidly above that and the other was dropping less.

-Andy

[304065]

. . . science aside there is a very important question nobody has asked. . .

how tall can you go before you hit the engine lid?

[911pcars]

I'd forgotten about this thread. In October 2012 we did dyno testing of several spec 911 cars. Two of us have similar carburated 3.0 SC engines. Mine has 1.5 inch intake spacers. Mine measured 228 at the wheels and the other engine was 230 at the wheels. I had a 10 hp advantage at 5500 RPM and the other engine had a 10 hp advantage at 7200 RPM. Mine was falling off rapidly above that and the other was dropping less.

Always fun to see two engine builders having a techie scrap on line... Handbags at dawn?
We were trying different trumpet lengths on my '65 SWB 911 FIA race car ( Solexes, Solex cams, legal small inlet valves etc) and the longer trumpets messed up the midrange bigtime even after rejetting. Most interesting thing was when we were swapping the trumpets back to standard: on a whim we did a dyno run with no trumpets at all, just to see how much difference proper factory ones made. The engine made 3 bhp more without trumpets than on any of the other runs... same ambient air temp / pressure etc, about 10 minutes between runs.
I think I could hear hollow laughter from the direction of Weissach...

Before getting too carried away presuming modifications A, B, C, etc. results in increased power, remember that an equivalent reference point is usually required to understand mod A is an independent variable. Comparing two "similar" engines isn't necessarily equivalent.

In the air horn test, the engine produced more power w/o them installed - a surprising result. Can we conclude the wholesale removal of all 911 velocity stacks? Maybe there are other factors at work. ......? Maybe the Weber velocity stack shape isn't ideal....?

Here are some numbers to contemplate:





I'm open to learn something new every day.
Sherwood

[Tom Elder]

Good discussion, interesting subject

After reading this article

http://www.nsxprime.com/w/images/9/9e/%28Blair_and_Cahoon%29_Design_of_an_intake_bellmou th_Sept._2006.pdf

I modeled up what I think would be an improvement of the standard K&N setup.




Little more info here, on my thoughts. Post 97 and 104 Always interested in what the experts think. Pendulum Outlaw, Build, Adventures and Misadventures