Thom

"Perfect world" formulas have the merits to give a base to start with. People who pretend the opposite probably have never taken any engineering courses, or are so obsessed with their real world results that they may not be able to understand anymore why what is happening.

I wouldn't have posted that stuff if I had not found accuracy in it considering what I have experienced using different intakes.

I see no interest in some one-click programm that gives instant 10000hp per spare wheel, but I see some in understanding how (part of) the physics work just by looking through straightforward mathematical facts. Sorry for trying to get started without even having reached destination first (!).

Ok, runner diameter effect on pulse wave... anyone?

67King

Honestly, this is NOT the place to learn about this. I did engine development for 7 years, and it was really only in the last couple did I start to more fully understand all the stuff that went on (granted, my proper function was more about getting something in production on time, under budget, and meeting targets - I wasn't a technical guru until I started trying to learn more).

But if you wnat to learn, I have three books you need to buy and read:

I found Taylor's books more useful, but it may interest you to know that Heywood runs the auto labs at MIT. He also occasionally teaches to engineers at Ford - I was fortunate enough to have his class.

Again, to design an intake, you need to pick RPM for peak flow. This may be peak power, but it'll likely be slightly below peak power. Then back calculate. Go buy those books, learn what Z-factor is, then figure out your necessary valve OD. Once you have that, factor in the size of your seat, and your taper to the choke point up in the bowl area of the runner. I use about 10% taper from throat diameter (i.e. valve OD - seat geometry). That is your diameter.

From there, go after runner length. Pick an RPM point for peak TORQUE. Not power, torque (in reality, peak VE, which will be slightly higher in RPM than torque, but close enough). To determine runner length, run the calculation: 642^2 * Vel,sound * Port Area / RPM^2*Vol,cyl*CR-1/CR+1. Which is a turned around version of the Helmholz equation, which is RPM = 642*Vsound*(Port Area/(L*Vol))^0.5*(CR-1/CR+1)^0.5. Speed of sound is a function of gamma and temperature. I used 1.4 and 570R, and got 346m/s.

All that said, did I mention that a freakin' web forum is not the place to learn about this crap? You can run equations all day long, but if you don't know how to apply them, it doesn't do you much good. For example, you may find out your runner ID needs to be 40mm, which turns out to be pretty close for a 2.5L at 6500 RPM (this is off of memory, been a LONG time since I did that one and it was a stroked Ford 2.3 Turbo). Good luck finding a source for 40mm ID pipe. So now what do you do?

Now, you may not mind dropping thousands and thousands of dollars on materials, fabrication, and dyno development work. If you do, fine. You'll still end up with a suboptimal result. That chart I showed earlier was from a SINGLE change. I modeled it, found out what options we had, adjusted the model, and gave Karl the parameters to fab the intake to. Same cam, and I designed the intake outside of the cam events (which is not to say they aren't important, they are, but again, you have to know what you are doing). Ironically, what started it was a request he made of me to evaluate some cams that were recommended to him. The cams were too big, but a simple equation wouldn't tell anyone that.

gruhsy

Thank you for posting this Always wanted to have some good reading material but never knew what was worthwhile reading.

refresh951

Just ordered Volume 1, thanks!

Raceboy

It's always funny to see peoples reactions when when someone asks opinions about something out of ordinary, in that case ITB's.
There are always people who whine about it being impossible, hard to do, expensive, not gonna work etc.

Guess what? I have done ITB's on several cars, both NA and turbo, inclusing several Porsches (911, 924, 944).
Here in Nordic countries we just think it throgh and just do it, not over ANALysing, naysaying and whining.
Also, can't you guys search? https://rennlist.com/forums/924-931-...31-gulf-4.html

I guess it does not work: from 931 engine (head is completely stock), 270hp/370 Nm at 0.8 bars of boost. Does not work, riiiight.

Thom

There will always be some overly-academical engineers who feel better when they know very accurately why something does not work at all than when they can't quite figure out why something else works just pretty damn well.
It's all the fault of these boring frictional losses! ;-)

Joking aside, thanks for the link on the books, I will have a look.

Raceboy, any theoretical guideline on how you designed this intake?

Duke

I totally agree! Sure - to make the optimal intake it will require a lot of knowledge, calculations and testing. But usually it's not that hard to make something that works better than what you already have. And that's the point.

It's like saying: I won't even try to make a culinary 3 course dinner because I don't have the skills of a top chef, so instead I keep eating canned ravioli...

The funny thing is that the only real alternative on the market that most people recommend is the 16v intake manifold and 4-1 headers from SFR. And I can bet my car that I put more math's and theory into calculating my weekend beer purchase than SFR put into that stuff. But yet it works great compared to stock for most engines. Surely a better product could be designed, but I don't hear anyone complainging about them selling those products or think they are under achieving.

67King

Yes, and there are always people who come in here and tell people how to do something without reading or understanding what was being asked. The OP asked specific ENGINEERING questions that require ANALysis. He asked how to do that ANALysis.

You do realize I never said it didn't work, don't you? You do realize I said that I've done it, don't you? You do realize I showed how well it can work, don't you? 400 horsepower naturally aspirated from a BMW 3.0L, 50 from the intake.....that came from BMW making less than half that.

You don't get that kind of result from just slapping something together. Which is presumably why the OP was asking the technical details of how to do it.

And why did I warn him that this isn't the place to go looking for that kind of info? Because people who treat this kind of thing as a packaging exercise will come in here and tell him how to do it the wrong way.

lart951

easy on my brutish friend he kinda of slow.

Dougs951S

You guys all have valid points, and I appreciate all the input. I am studying mechanical engineering in school, but I REALLY value the honest and point blank input of people who have been doing the things that I hope to soon be doing for 30 years. Thom and raceboy basically hit my nail on the head though. I'm not trying to extract every last ounce of power out of this car because it is not economically feasible at the moment for me to do so first of all, and second of all I fully understand that I do not yet possess the requisite knowledge. However, my goal was simply to make something cheap which functioned better than the factory intake for my purposes, which I honestly think is WELL within my abilities. I realize the finer details are probably beyond me, so to clarify 67king I was basically just looking for a "rough" guideline which in engineer speak, doesnt really mean much.
Again everyone, I know I am greatly glossing over details so no need to try and bash it into my head, but I was basically looking for input along the lines of "obviously shorter runners will shift the power band to the right, as will a smaller plenum volume. If you are looking for roughly X amount of power/mass flow at peak VE RPM Y, than your runner length should be ~Z and the plenum volume should be ~W." Obviously in the real world it isnt that easy. Give me a break, I'm still in school and have not yet had a chance to explore any real world applications of the things I have learned/am learning.

A.Wayne

RPM and power level is achievable with stock items. Ported intakes, uprated boost pipes, cams and TB, is about all would be necessary with an HX35 @ 1.6 bar.

Looking good, how much @ 1.5 bar .....

Dougs951S

24 psi is really more than I'd planned on running with E85, and I know I can make that power with less boost if I have a better intake. Ideally I'd like to meet my power goals at less than 21 psi. I am convinced that I can make an ITB setup that will have better top end power and more importantly, better throttle response than any ported stock piece. This is more an exercise for me in seeing what it will do. Even if the power gains are marginal, I'm completely convinced it will improve the not-so-great throttle response. What is key here in my eyes is that even though you say the stock piece is "good enough" the design parameters that led to its birth and the design parameters that I will be taking into account are very different.

A.Wayne

That power output is safe with e85, just make sure you know when you have winter mix ( as low as E70). You may hit target with as low as 1.4 , 1.6 is worst case and not unusual .

A.Wayne

Some serious Irony there Robby .....

Dougs951S

It's peak 76% efficiency is at less than 2.4 PR, but maintains 74% efficiency up to a pressure ratio of 3.2 At 1.4 bar it is more efficient than say, a k27, a 60-1, or a 60 trim and it moves plenty of air at that pressure ratio.