Mongo

If some of you remember since I've been posting on Pelican since the year 2000, I've been hungering for power gains on my old 84. 3 years ago I put the idea to sleep after I had lost 6-7 HP on the dyno with a cone filter and Dynomax straight through muffler, Bursch header and 2.5" piping.

However, something got me thinking last night; what if that straight through setup I was running was too straight through??? I am talking to the point where I was losing exhaust density because of the piping and the cone filter was contributing even more to the loss.

This morning I gave the sound issue a thought. Perhaps it's possible to run a cone filter (NO POWER GAIN, YET NO LOSS) and still maintain the factory 2.25" piping with no catalytic convertor and a factory muffler? I think I'm gonna give it a wack this weekend and see if I feel any loss of power here like I felt on dyno day a couple years ago...

Hmmmm....

Skunk Workz

Bigger,more open pipes and cone filters etc will usually result in a net loss of hp unless you add more gas to the increased amount of air...and an 2.25-inch exhaust is enough until atleast 220-230 hp. Add the gas necessary for maintaining your previous A/F,and a cold air intake cone filter could possiby give you one horse or so... so no enourmous gains just like the Ricers state from their "rear-end-dynos"..

M758

Here are some comments I made related to stock vs no cat 2.25" pipe. Both with stock airbox. I have not seen a cone car increase power from the cone. I have heard of tests where power is either not gained or is lost from a cone.
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This is not a apples to apples test, but I dynoed my 944-spec car on dyno dynamics dyno couple weekends ago. I came to 134 RWHP.
Another driver dynoed his 86 944 spec car also. I came out to 118 hp on the same dyno about an hour later.
Differecnes between my 944 spec and his.

His car was a completely stock untouched motor. Stock chip, air box, Cat, Muffler

My motor was just rebuilt. Rings were original 150k rings. Head had combustion chamber cleaned (carbon removal only) and light machine work done a couples years ago. All to stock specs. Not blueprinted or anything. Stock 9.5:1 Compression. Stock paper filter, air box and muffler
Non-stock items I was running were a Steve R chip and no Cat.

Differencing in HP = 16 rwhp. I am guessing that most comes from removing the cat. Next chunk comes from the cleaned but still stock head, 3rd chunk from the chip. The ower of the other spec car was going to pull the cat and re dyno to get numbers, but I have not heard from him.

Geo

OK, the issue of mixture is real and should be worked out on the dyno. Short of a user programable ECU, the easiest way to make changes here would be with an adjustable FPR. If I were building a street car, and going all out I'd switch to a MAF and sequential FI, but that's another story. An adjustable FPR should get you where you need to be. What you really want to be using to tune is a Horriba wideband. Even the ones that come with dynos are not all that great according to a friend of mine with more time on a dyno than probably everyone here (he has been doing aftermarket development work for 20 years, is an OEM automotive engineer and used to work in TRD's GTP engine program).

As for the gains from a CAI, they are not from Ricers "rear-end-dynos." The results are real, documented, and reproduceable. The problem is, nobody here wants to listen to how a CAI makes power (hint, little to none is actually from the cold air). The SE-R Cup racers have done considerable testing and found they get 10-12whp. Documented and repeatable under controlled dyno testing. The thing that may prevent big gains from occuring in a 944 is the barn door AFM is a big restriction. Still, a properly engineered CAI should work nearly as well on a 944 as a Honduh or a Nissan.

As I have said a number of times, the power from a CAI is gained from resonance tuning. AEM actually tests prototype CAIs by starting with a set length and cutting the length by a half inch and retesting (keep repeating). They configure their final product at the length that makes the most HP. Length, diameter, and even placement of the AFM within the length of tube can affect power production (I watched a friend gain an honest 2 hp by moving his MAF 6"). The trick, IMHO for our cars is to fabricate an adapter that tapers smoothly from 3" round to the square opening of the AFM. So far the only one I've seen that really comes close to doing this correctly is a plastic piece sold with a worthless filter on eBay. I will be having a one-off adapter CNC machined before I start tuning my car. If I get the gains I think are available, we (NISsport) will produce a kit.

I agree with Pepe (reference the screen name thread) that exhaust tubing shouldn't be a big factor, and in fact, it's possible to go too big. However, exhaust can be tricky and can depend a lot upon the header. The Bursch header doesn't seem to do much. A $600 header from JME is supposed to be much superior to anything else out there.

My question would be the muffler. Too many poor ones out there. Dynomax doesn't blow my skirt up. Magnaflow might be a good one to try. Remus seems to be a superior product, but you pay for it and if no one has figured out a proven set-up, there are no guarantees. Absolutely stick with a perforated straight-through muffler. No chambers, and for God's sake, NO louvered mufflers. They backpressure worse than a chambered muffler. The so-called "turbo" mufflers suck too.

Mongo

of course I'm not speaking in ricer terms, but I liked the sound my '84 produced when I had my design on it. It sounded mean!

nine-44

I've been pettling the thought, I'm slowly getting my tools aquired to get some fab work done. The problem would be the dyno time. I was kinda thinking just for fun try the butt-dyno and a few ft of pipe, see where I get? I know, it's not proven, but I do want to play with it, heck, my little project isn't proven either for that matter.

Campeck

ok...i have a gutted cat. a FR wilk chip. and almost brand new rebuilt engine. why oh why am i only at 127 rwhp?????

Campeck

If perry would come through on his dyno meet (peeeeerrryyyyyyy!!!!) i could test out the pipe length factor in the equation of hp from a cold air intake. ( i just got one)

Serge944

For street driving a a free-flowing intake and exhaust will hurt the performance of a 2.5l n/a. Afterall, its the low to mid-range that lacks power.

General rule: longer intake tubing = more low end hp; longer exhaust tubing = more low end hp
This is the same case with backpressure...but of course there are limits and plenty of exceptions.

It building a fast car was clear as day there would be no tuners...

Serge944

The wilk chip does very little to nothing for hp. However, it changes the torque curve so you get quite a bit more power in lower RPM ranges.

There are way too many factors which can explain poorer performance, so I wont bother listing.

Geo

I disagree. I have not seen a properly engineered CAI to lose power anywhere. It may more a greater % one place or another, but not lose. It is possible to lose power with too large an exhaust because the velocity of the flow can slow to the point that it kills scavenging. The backpressure thing is not totally true. It's true where there is a lot of overlap such that some backpressure can delay escape of unburned mixture, but generally what happens is flow slows too much and scavenging is lost or diminished. The backpressure thing is one of the widely understood myths.

Skunk Workz

Most CAI's I've seen done here have the guys themselves claim outrageous hp gains...until the dyno proves them wrong. But like you stated,it all has to do with actually testing for what works,not just bolt on some huge cone and imagine the "new-found hp". Properly sized, made and tested...they work.

Same can be done to make a proper intake manifold...to yield even bigger gains. But then you need to make the port the right size first...the best intake manifold in the world will only patch the problem if the head doesn't do it's trick.

Remember to keep an open mind about headers too...who says the stock header primaries are the perfect size? Who says they are too small? What if they are too big,making them not as efficient as they could be? Haven't done any testing on that,though...but I will...just remember that making parts bigger or just flowing more isn't always the way to go for your engine size and HP goal.

I've only seen one muffler yet that gave a substantional gain just by changing the muffler (and adjusting the fuel curve,as that was needed after the change). Not a fancy claim,I've seen dyno papers for it. Even posted them here in another thread.

And,Geo,that is just what it does...it sucks... by creating a vortex in the muffler,thus making a lower pressure zone in the middle...effectively making the exhaust go down the pipe into a lower pressure than atmospheric pressure...just like you would get behind the car at high speeds,if you placed the exhaust outlet exactly in the lowest pressure area behind the car. Like you should...but I guess your race car already has it placed there?

Geo

Yes sir. And simply blocking off the filter from the rest of the engine bay does not a real CAI make. Our cars are blessed with hole already for the stock intake. This is where a CAI should route. That's where mine will.

Oh, I agree with you completely. I'm definitely not one who said the Porsche factory is run by gods with faries for workers who spread pixie dust on the things. In my case, I have detailed specs from Jon Milledge Engineering for a header that has shown through dyno testing to be more effective than the others that are available. Since it's proprietary information that Jon sells with with other information to people who are building race car, it's not my place to share it here.

Actually, most dyno testing shows a shorter exhaust makes the most hp. Here we are allowed to dump it out the side. I never really thought about the fact that dumping out the back may take advantage of the partial vacuum behind the car. I may have to do some back to back testing of this. I'd prefer the exhaust to exit the rear for a number of reasons, not the least of which is to tuck the exhuast up into the chassis. I'm hoping to get away with not running a muffler, but I'll probably need a small one.

GlenL

Porsche not run by gods? Whatever. The engineers there do seem to be blessed, though.

Folks always want a few extra, and cheap, ponies. And I'm one of them, fer sher. However, it's pretty easy to size the intake plumbing to the needs of the engine. I tried a special open-top air box on my 928 and _lost_ horsepower on the dyno with it. Of course there are a lot of factors involved, but the intake was already sized right and letting in warmer air just caused a less-dense mixture to get sucked in. Here's the thread:
https://rennlist.com/forums/928-forum/146484-race-air-cleaner-top-project-2-a.html#post1453087

Since there has got to be a drop across the air filter a larger air filter would be better. Still duct it to cooler air and the easy way is using that carefully-provided hole in the fender.

It the buttometer-verification area, I know my '73 Riviera has more pull with a 3" open element filter than the stock 2" closed assembly. The closed unit still does not has outside air connection so there's no temp difference in the in-coming charge.

Skunk Workz

Are you allowed to make a ram-air box to that CAI? You could gain a little more hp on fast parts of the track by ducting air into the sealed box containing the CAI from the highest pressure region on the front of the car...effectively raising the atmospheric pressure in the airbox.And,decreasing the highest pressure in the car's frontal area also gives you more speed,as you have to push less air out of the way.

Even though you can't share it,I'm willing to bet it's not the biggest header pipes in the entire world..

Dumping it out the side can actually be a disadvantage at speed...dumping loads of hot turbulent gasses out the side will disrupt the flow of air around the car,giving it more drag,making the extra hp gained only compensate for the "dynamic airflow profile" of the car being killed by the plume of exhaust punching a hole out the side. Dumping it at the rear,in the lowest pressure zone,helps hp like a short exhaust would at stand-still in a dyno,and you also gain by having the exhaust "fill the void" behind the car,giving you even less drag,for even more speed.