Porschefile

Well, I've been having some discussions with several Rennlist members lately regarding intake design. I must confess I'm not that technical of an individual, so the mathematics behind everything tend to hurt my brain a bit. I understand more from the point of view of what works and what doesn't. In general, desiging these components isn't really rocket science and understanding the physics behind everything is largely a matter of common sense. In my research I happend to come across a website that is about the best example I can find for a turbocharged motor. Unfortunately this manufacturer is only building this one intake for Honda motors as far as I'm aware. Regardless, the same concepts and physics apply so it is still an excellent example of how to do things right. Here's the link: Advanced Induction Research I highly encourage anyone that is considering an aftermarket or custom intake to check the website out. Check the "Performance Data" section to see some graphs of the changes this intake had. The most impressive thing is that every aspect was only improved. The intake flows more CFM over ALL valve lifts, has more airflow velocity over ALL lifts, the improvements resulted in a significant decrease in airflow temperature and the result was increased horsepower AND torque over the entire rpm range with excellent top-end curves. I'd encourage people not to simply dismiss this example due to the fact that it is a Honda motor, or the fact that the overall torque is relatively low (it's a 1.8l so that's to be expected). The overall power curve is what's impressive. Besides torque at higher rpm equals more horsepower, and after all it's horsepower that moves a car.

I see many people in our community using stock intake components even for higher power levels and larger displacements. I completely understand doing this for the sake of frugality, however IMO this is far from optimal from a performance perspective. I honestly feel that all of these stock intake components (IC end tanks, IC pipes, throttle body, plenum volume, etc) pose a definite restriction for moderate to high horsepower levels. Lets get the ball rolling and throw some ideas out there that might better educate our community. Although some will laugh, I might leave some of the more technical and mathematic areas of this subject to Drifto as he is a walking, talking science book and extremely well versed on subjects such as this regardless of what his obtuse personality might convey.

Guns951

This is similar to what Chris White is designing for my individual throttle body setup and custom plenum. The technology and know how is out there in the 951 world with the likes of Jon Milledge and Chris White - but the costs of producing such setups are substantial and nothing to be sneered at.

I agree that intakes have much to do with the characteristics of the car - especially the ITB setup and its influence on throttle response and top end power.

333pg333

Great thread Travis. Let's see what comes out of it? My guess is that it's no point just changing one or two of the above items, but that really you have to make it a complete system that works in harmony or concert with all of it's components pulling in the same direction. Conversely, the oldest way of increasing hp by just adding a larger turbo is equally dangerous and too basic as a true search for power increase. Now put these two things together, bigger pump and bigger lungs and just watch us fly!

Porschefile

I'm going to have to respectfully disagree with your first comment. To accurately and completely build the "perfect" intake for a setup, of course it will be necessary to used CAD/CFD design, elaborate calculations and tests to come up with an absolutely perfect design. That would take tons of time and money. Though, IMO, I think far too many people in our community get caught up in the mind game of over-engineering things. You can acheive probably 90%+ of the same effects of a properly "engineered" intake component simply by trial and error plus a bit of simple math and common sense. This stuff isn't rocket science and you don't have to pour cubic $$$ into your car to do this stuff.

You can get plenty of ideas from simple and common designs such as this Sr20 Intake. Hell, you could buy an intake like that off Ebay for $200-500, hack it up, modify it to fit a 951 and you'll still end up with a better than stock intake as far as increased power levels go, plus you could accomplish that under $1k pretty easily. Focus on the basics. You want more power, well that means you will be running more boost and flowing an increased volume of air. An increased volume of air means you are going to need a larger plenum, larger throttle body, larger IC pipes, larger intercooler, etc etc. You can elaborate from there by identifying potential issues and identifying solutions to those issues simply with a bit of common sense and a basic understanding of physics and/or fluid dynamics. For example, you need a larger plenum for your increased power level and that will result in decreased airflow velocity. To combat this, you can introduce a shallow angle taper to increase airflow velocity (much like the SR intake from the link above). It seems to me like many people around here are simply afraid to try some things like this out. You don't have to be an engineer to build a better part like this.

RKD in OKC

Okay, so I checked out the honda intake. If I were going to monkey with intakes here is what I would do...

Get the Lindsey Racing intake. It is similar to the that Honda one. It has a larger plenum, but needs longer runners for the lower flow performance spectrum.

Stage one.
Re-do the runners so they extend about 1.5 inches into the plenum like velocity stacks. This is similar to how the runners work on a 928 dual plenum intake. It would still have a bias towards higher rpm and flow because of the large plenum, but the lower rpm/flow performance would be increased due to the longer runners.

Stage two.
Make the plenum even larger and separate the plenum into two halves, 1,2, and 3,4. Put a connector between the two halves with a choke type valve that opens around 3400 rpm. This would give a smaller plenum at lower flows then open to a larger plenum for higher flows. Again very similar to the 928 intake. The main problem with this design would be fitting it under the hood.

Just an idea.

Porsche-O-Phile

My understanding is the exhaust system on the 944/951 represents a lot bigger of a choke point than the intake does.

KuHL 951

While on this subject has anyone had any luck with ExtrudeHone on the stock intake? I've read about flow imbalance on #4 and I wonder if this helps or is just another trick to throw money at? Has any other internal surface treatment shown improvements in overall flow?

reno808

Has anyone tried the jonh mildage carbon fiber intake?

evil 944t

Travis,

I agree whole hearted. I actually called A.I.R about 6 months ago and they were to busy to start anything new at that time. A basic design starts around $10k and goes up from there. Which in the R&D world, isn't that much money.

Like Patrick said, a complete system will allow you to run less boost. The problem is nobody cares, they just turn up the boost. Its cheaper than building a good system.

I drew up the 968 manifold in solid works and I need to continue that project but the problem is, people have so many different goals that its not cost effective to design and produce 5-10 or 20 of these. I will still do one for myself but probably not offer it to other people. It will cost to much money for most.

Also because nobody really designed one(lack of knowledge(no offense) and costs involved), you see people accepting stock IC,boost tubes,T-body, etc. and thinking its ok to run 2-3 times more air through it.

Raceboy

I'm going to test-fit a new dual-plenum intake that I fabricated for my friends 3.0 8v. I used stock intake flanges and very nice trumpets. I fitted 65mm TB from BMW also. When everything checks out, I'll weld it finally together.

IMO stock 951 plenum is WAYYY to small for optimum, especially on 3.0 engine. Not to mention unequal flow to cylinders.

tommo951

Sorry I disagree on this one. It is a fallacy to think that a bigger exhaust is the solution to the problem. I have posted this subject on here a few times and it never ceases to annoy a few people with 4" straight throught systems.
The example I always quote is the Renault 1.5 litre Turbo formula 1 cars of the 1980's. They had 2" exhaust Straight through and produced 1000bhp
In fact if you look at a modern F1 Ferrari producing over 700bhp the exhaust is less than 2.5"
I have seen Audi Quattro Turbo's that have lost a considerable amount of low end power by fitting 3"+ Exhausts. By the time the power has come in they could have been long gone.
For racing and track where your power is high in the rev range a larger exhaust is a worthwhile conversion. I still believe from experience that 2.5 is ideal for the front pipe graduating to 3" at tail pipe. I always get slammed on this one., usually from peoplke who have spent money on a 3"+ system.
When I convert my car to track racing I will go 3" from the turbo back but for now I seriously believe that what I have is optimum for road.

Waiting for the flames!!!

evil 944t

No flames here. If that supports your engine, great.

IMO if you upgrade to a larger turbo, I feel all the stock hardware will work but not as efficient as it was designed. In my book, if you upgrade the turbo, you must address everything else to keep it from working so hard.

tommo951

I agree, but for a road car its not necessary just delete the CAT. For race car definately a good step forward. Most of the mods we all use are race derived and thats where the best is extracted. I'll see if I can dig out any pics of the Pro Drive Suburu WRC cars. The pipes on these are less than 3"

SoloRacer

tommo: If I'm not mistaken the Ferrari F1 engines are normally aspirated - not turbo. On normally aspirated engines having too big of an exhaust can lead to lower power - something to do with reversion I am told.

reno808

the max on a na is 2 1/2