Devil's Advocate on my Cold Air Intake Theory..
#16
Originally Posted by TheStig
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.
#17
Originally Posted by 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.
Unfortunately the rules require me to source air either from under the hood or the stock location. The stock location fortunately allows me to use a CAI.
Originally Posted by Skunk Workz
Even though you can't share it,I'm willing to bet it's not the biggest header pipes in the entire world..
Originally Posted by Skunk Workz
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.
#18
Originally Posted by GlenL
Porsche not run by gods? Whatever. The engineers there do seem to be blessed, though.
Originally Posted by GlenL
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.
Originally Posted by GlenL
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.
#19
Originally Posted by Geo
Blessed? Nah. They just have a different mission from engineers for other manufacturers (Porsche has slightly different priorities, namely performance). It's funny how people get defensive about Porsche though.
Originally Posted by Geo
An open airbox is just a noise maker.
Originally Posted by Geo
Larger filter is not the problem. Cooler air is a very small part of the equation. But now I'm repeating myself.
Less drop across the filter can be nothing but good. Perhaps the existing filter size good enough. I won't waste my dyno time on this one, but try a comparison between a new filter with an old dirty no-light-gettin-through filter. I know which will have more power. How about no filter? Anyone run that?
Air temp is an important part of the equation. Does the term "intercooler" ring a bell? Now the equation does use the absolute scale (Rankine or Kelvin) so a few degrees are not important. If you can start with 70F air instead of 180F air it does produce more power.
There are several parts to engine power level:
Getting fresh mixture into the cylinder. (This includes evacuationg the burned charge.)
The mechanics of the cylinder (CR, head shape, crank arm)
The fuel/air ratio
When the mess is ignited
If you're not going to change the cams or other engine mechanicals, there's just a few things to alter. Allowing the parts of the intake above the throttle to breathe better is a good approach.
Unfortunately for us, the blessed Porsche engineers have already got the N/A cars tuned fairly strongly. This makes it hard to get cheap easy extra ponies out of it.
Reminds me of another US car story:
Had this 1976 Olds Ninety-Eight coupe (RIP) with a 455 V8. Lots of torque off the line, but the small exhaust manifolds, cat and single exhaust held it back. Once I put headers and dual exhaust on it, the thing had a completely different top end. Bizarrely and unexpectedly quick acceleration. Added a switch in the ashtray to hold the kick-down switch on for high-revving stoplight action. Now that was a few hunderd well spent.
#20
Believe me, at speed the underhood temp on the 944/924S is not that much higher than ambient. I know this to be a fact as I took measurements last summer and will repeat the experiement this summer to confirm my findings.
On the other hand, with the car sitting still (read no airflow) and at operating temperature the engine compartment temperature goes up quite a bit.
I have also posted before that on a dead cold engine I found idle performance and throttle response to be far better with the stock airbox and snorkle than with an MSDS cone filter setup. Heat in the engine bay was not a factor since, as I mentioned, the engine was cold when I did the comparison. Unfortunately no dyno info.
On the other hand, with the car sitting still (read no airflow) and at operating temperature the engine compartment temperature goes up quite a bit.
I have also posted before that on a dead cold engine I found idle performance and throttle response to be far better with the stock airbox and snorkle than with an MSDS cone filter setup. Heat in the engine bay was not a factor since, as I mentioned, the engine was cold when I did the comparison. Unfortunately no dyno info.
#21
Originally Posted by GlenL
Repeating how? Looking back at your first post I see an idea to change the intake tubing.
Originally Posted by GlenL
Less drop across the filter can be nothing but good. Perhaps the existing filter size good enough. I won't waste my dyno time on this one, but try a comparison between a new filter with an old dirty no-light-gettin-through filter. I know which will have more power. How about no filter? Anyone run that?
Originally Posted by GlenL
Air temp is an important part of the equation. Does the term "intercooler" ring a bell? Now the equation does use the absolute scale (Rankine or Kelvin) so a few degrees are not important. If you can start with 70F air instead of 180F air it does produce more power.
Where a properly designed CAI makes power is not through the cooler air, but through resonance tuning. The cooler air is a tiny part of the equation. Proper resonance tuning can greatly improve VE however.
#22
Originally Posted by Manning
Believe me, at speed the underhood temp on the 944/924S is not that much higher than ambient. I know this to be a fact as I took measurements last summer and will repeat the experiement this summer to confirm my findings.
OK, make that 4 people with 3 different cars have confirmed this!
#23
Originally Posted by 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.
#24
Originally Posted by Serge944
Performance =/= peak hp
#25
Hey;
You lost HP because you lost volumetric efficiency. More air flow than the engine could use. Less back pressure than it needed to maintain that flow. To make more power, you first have to be able to process the air that's there. The filter/air box is likely not the limiting facter here. Ever measure the surface area of most cone filters?
Once you get more air in, you have to process it better. Throttle bodies, intakes, heads, and cams are what make power. That and associated RPM.
$$$$$$$$$$$$$$$$$$$ame old $$$$$$$$$$$ame old.
You lost HP because you lost volumetric efficiency. More air flow than the engine could use. Less back pressure than it needed to maintain that flow. To make more power, you first have to be able to process the air that's there. The filter/air box is likely not the limiting facter here. Ever measure the surface area of most cone filters?
Once you get more air in, you have to process it better. Throttle bodies, intakes, heads, and cams are what make power. That and associated RPM.
$$$$$$$$$$$$$$$$$$$ame old $$$$$$$$$$$ame old.
#26
Originally Posted by Geo
What does a dirty filter have to do with a larger filter? If nothing else, a larger filter box will just slow down the intake charge. That will make matters worse. Air flow will stall. Not what we're looking for.
I my opinion, the air box is too far from the valves, with too many bends and restrictions in between, to affect system resonance. The runners from the plenum to the head are clearly designed to do produce resonance for each cylinder.
Originally Posted by Geo
We aren't talking about forced induction here. Do you think you're going to see a 110* reduction in air temps on a NA? Hell no. In fact, I know three people who have conducted instrumented testing with thermocouples on two different cars and all three found that temps under the hood of a car moving at 50 mph or more was nearly ambient.
The underhood temp issue depends on the situation. Standing start or straight-away? Those el cheapo cone filters sit directly behind the radiator. Can't be good. Removing the cold air duct leaves open that the air will be similarly heated.
Originally Posted by Geo
Where a properly designed CAI makes power is not through the cooler air, but through resonance tuning. The cooler air is a tiny part of the equation. Proper resonance tuning can greatly improve VE however.
If you're going to make comparisons the base and new conditions have got to be defined. I'd like to see real numbers on what the changes upstream from the AFM are doing.
#27
I have been reading this post closely and have seen that you are all well educated on the subject. What I not seen is anyone in this thread or any post state how a na 944 can get substantial power gains in the lower RPM. I have also wondered how can I get more low end "take off" HP in my 84 NA?
Turbo? No, because of the $ to value, better to just by a factory 944 turbo.
CAI? Already has one of sorts from Porsche.
Rebuild? Maybe it would make like new HP, but is that enough?
I think so far the only real answer is to drive it on twisty roads and enjoy it as a sport touring car like it was made.
Just my two cents guys, but if you have a better idea and answers let me know.
Turbo? No, because of the $ to value, better to just by a factory 944 turbo.
CAI? Already has one of sorts from Porsche.
Rebuild? Maybe it would make like new HP, but is that enough?
I think so far the only real answer is to drive it on twisty roads and enjoy it as a sport touring car like it was made.
Just my two cents guys, but if you have a better idea and answers let me know.
#28
Originally Posted by my84-944
I have been reading this post closely and have seen that you are all well educated on the subject. What I not seen is anyone in this thread or any post state how a na 944 can get substantial power gains in the lower RPM. I have also wondered how can I get more low end "take off" HP in my 84 NA?
Turbo? No, because of the $ to value, better to just by a factory 944 turbo.
CAI? Already has one of sorts from Porsche.
Rebuild? Maybe it would make like new HP, but is that enough?
I think so far the only real answer is to drive it on twisty roads and enjoy it as a sport touring car like it was made.
Just my two cents guys, but if you have a better idea and answers let me know.
Turbo? No, because of the $ to value, better to just by a factory 944 turbo.
CAI? Already has one of sorts from Porsche.
Rebuild? Maybe it would make like new HP, but is that enough?
I think so far the only real answer is to drive it on twisty roads and enjoy it as a sport touring car like it was made.
Just my two cents guys, but if you have a better idea and answers let me know.
The other thing you can do won't add hp per se, but will feel like you did... a low mass flywheel. Some people aren't impressed with them, but most people are. I love 'em. A low mass flywheel will help all the way through the rev range.
A good header should help. The MSDS and Bursch aren't so hot. The Milledge header is supposed to work well with an IT race engine. Don't know how it would do with a street engine. There is another commercially available header that is supposed to work well, but I cannot remember which one it is. It's a relatively common name though.
#29
Originally Posted by GlenL
"it's pretty easy to size the intake plumbing to the needs of the engine".
Unfortunately for us, the blessed Porsche engineers have already got the N/A cars tuned fairly strongly. This makes it hard to get cheap easy extra ponies out of it.
#30
Originally Posted by my84-944
What I not seen is anyone in this thread or any post state how a na 944 can get substantial power gains in the lower RPM. I have also wondered how can I get more low end "take off" HP in my 84 NA?