refresh951

An age old battle, engineer vs tech! Two camps, two ways of thinking. My experience says both ways can work. You can design an intake without math...how...trial and error and experience. And some are pretty darn good at it (Vic Edlebrock). Some really cool things have been developed this way and the math followed after. The engineering however can avoid a lot of wasted effort and many times can achieve unbelievable results. My experience has always taught me to respect both camps. In my opinion the best solutions always occur when both approaches work together rather than insult each other which accomplishes nothing.

gruhsy

Agreed

67King

A rough estimate is fine, you can make improvements. But fabbing an intake is not as cheap as you'd think, and if you are going to put forth the effort, why not try to optimize it, at least as much as possible?

Shawn brought up a good point, which is kind of what I was getting at, though he didn't use the term. Applied theory. There are plenty of desk jockeys out there, aren't going to do anything. I rebuilt my first engine when I was 14. And oh yeah, I used to do this stuff for a living. So there's a little more than just throwing theory out there.

But anyway, actually doing it can be educational, but then you get so many parameters that you just can't afford to optimize the system without using some sort of a guideline. I couldn't do it on Karl's engine, but we "lucked" out a bit in that my modeling showed a 35 horsepower increase, rather than a 50 horsepower increase.

You'd be amazed at how many rules of thumb there are for designing intake systems. Radius of curvature 1.5*ID or greater. Bellmouth radius at 0.2*ID or greater. Etc, etc, etc.

I've written enough stuff in the thread to give you a good start. Seriously, though, look at your biggest constraint. If you can't change the valve sizes, then to back and calculate how many RPM it can sustain (FWIW, a 34mm valve size w/o tearing up the head for much bigger seats ended up being our constraint on that BMW engine). Another rule of thumb, average flow velocity through an intake port (not valve, but the port) is 100-110 m/s. Figure out your RPM at peak horsepower. Then figure your peak torque will be, say 1250 or so fewer RPM. Figure out runner length, then see what kind of mandrel bent pipes are available in that size. Then redesign it based on that. THEN go back and figure what you can package.

To get a GOOD system, you have to be iterative. But, you can iterate most of it wihtout building stuff.

SirLapsalot

I 3-D printed a small intake manifold to be used as an adapter between a briggs and stratton engine and a throttle body from a EFI kit once and the 3-D printed adapter melted within minutes on the engine dyno. Of course this was a piece directly attached to the engine but its something to keep in mind. Especially with the high under hood temps we see in 951's

333pg333

Well clearly you could put together a large can and some tin runners to cobble together an intake system and it might even work. The thing is, unless you’re going to do some half decent testing with half decent equipment you’ll never know quite how much better or worse it is vs what you’ve started with. With many modern ECU’s you can trim individual cylinders and possibly make the ‘Tin Cow’ work. There’s many cases of people welding up a box with runners on some Supra and getting 800whp. On the other hand, if you can do the math beforehand and then test and tune, you’ll more than likely get a better system than stock…depending on what you’re after. The stock intake on many cars is as much about packaging as it is efficiency…well at least on 30 year old cars. I think the stock intake is holding my motor back but we’ve still achieved a pretty good result and car is fast. Will be looking to move forward from this in the future.

Raceboy

to robstah: I have never blown up my project cars engines you know I have been into car modding for quite a few years and out of ~80 cars that I have tuned (yes, including some very high power BMW's) I have blown up one engine, a Mercedes 5.5liter AMG supercharged V-8 (3valves, twin-plug) and that was on the engine dyno due to the fact that the owner had brought a canister of year oled 95octane fuel with him even though I stressed earlier that he should bring 98.
Regarding your notes on the cage, the seat was in upper position after my brother drove the car and no need to lecture me. Go and 3D print the V8 ITB's (I have 3D measuring machine, 5axle CNC and 3D printer at my work facility also, you know lol ).
And BTW, in summer we have a month where temperatures reach 30-35C, it's not a North Pole you know.

to 67King: we took a completely stock S50B32 engine and just installed standalone ECU, better exhaust (headers are fine already stock) and reached 388 hp on the engine dyno with some tuning and playing with cam timing. Did the same with completely stock Honda H22 (only put GSXR1000 ITB's on it, ECU and headers) and got 260 hp @ just 6900 rpm. Stock is 183ish hp.

Just for reference, I did not "just slapped" together the intake, I did some calculation and forethinking with it. There is always some hp/Nm on the table but with common sense, some knowledge and fabricational skills you can get 95% of the maximum result with reasonable effort. If you want all out, fine, its your money but the intake cost me ~400 euros total to make.

It is and always will be that way: there are guys who do, and there are guys who just talk. And then there are guys who do and tell other not to do.

Thom

Those high HP Supras have more than often peaky torque curves that suggest poor off-boost performance and limited real-world drivability.

A flat torque curve that hardly shifts up through the RPM range and keeps flat beyond peak torque should tell most about both the off-boost and the top end breathing ability of an engine.

NA engines need exhaust back pressure to make torque, so hardly surprising that that E30 M3 lost some if no other work was done to rebalance the different points of restrictions. Butt dyno is far more accurate on a nicely-derestricted turbo engine when (high) boost can highlight breathing restrictions one may not even notice off-boost.

67King

Can we all just call a truce? Sheesh, why the Hell do we have to go insulting each other because we fall in a different place in the very grey spectrum between theory and applies?

Look, I might as well finish this. The OP shot me a note, and I replied with the following:
"The 100-110 m/s is the AVERAGE velocity. In other words, for our 2.5L engines, you have 180 degrees of crank revolution to fill 0.625L. At 7000 RPM, that is about 0.0042 seconds. So at 110m/s, that means you need a 41mm port diameter to flow that kind of velocity. Figure your valves are 45mm, allow about 3.5mm for seat geometry, that puts you at 41.5. Allow 10% taper, maybe that takes away another 2mm or so diameter, that leaves you at 39.5mm. That puts your velocity at nearly 120m/s. So go recalculate. Honestly, I'd target 100 or so without some serious, serious work. Anyway, in those conditions, peak power at 6,000 RPM gives you 102 m/s.

And where was teh peak power for the 944 Turbo? 6,000 RPM

Now what goes on in the actual valve seat is different. It will start out well above mach using simple geometry, so it'll actually be flowing at mach, then taper down, and it will actually get pretty close to 0.3 mach for the remainder of the stroke,

Anyway, what I would do if I were you, is figure out what kind of valves you can put in there, then from there, figure out what kind of RPM that can give you for peak POWER. Use that to calculate runner diameter (again, using about 3-3.5mm for seat geometry, and another 10% smaller from there). See what kind of size that gives you, compare to what is available. Then go put those numnbers into the Helmholz equation, and see what kind of runner length you get for abotu 1250-1500 RPM lower."

But let me go ahead and run a few numbers, just because we are this far. If you want to make peak power at 7,000 RPM, which I would NOT advise due to the oiling system, (cue Georgia Tech "You're at Georgia Tech, you can do that!" meme.......and actually, I DID go to Georgia Tech, and I CAN do that......but anyway, likely no one other than Rob and Shawn know what I'm talking about).

So here's what I get. This is a rough cut without a full model, which should be pretty sufficient: 7,000 RPM, assuming an average port velocity of 105 m/s*, one needs a ~47mm intake valve. So if we do that, the back calculation gives me a runner diameter of 1.65". The closest thing on the shelf that I know of is a 1.75" OD tube with 0.065" wall thickness, meaning you are going to have 1.62" runners. That'll put you closer to a 46.5mm intake valve , but let's go with that, and revise peak power target to around 6800.

* For comparison, when I did these numbers, the F430 was Ferrari's latest, its average port velocity in those conditions is 104.5

So now to figure out runner length. Say, 5,000 RPM? We'll shoot for that. Okay, crunch the numbers, and bellmouth in the plenum to gauge line for valve seat turns out to be 13.05 inches. Probably 3" or so is in the head, now you need 10" long runners.

That'll be pretty hard to package, especially the rearmost cylinders. Which probably explains why the intake on our turbos looks like crap. At least the engineers at Porsche understood that tuning would give them more benefit than would all-out flow. You'd be amazed at how many people that is lost on.

So now what?

THAT is why I espouse the analysis, and using models, rather than iterations, before you start fabbing up parts. What do shorter runners do? Move up the curve. How can we keep the same peak torque point with shorter runners? Make them smaller. What does that do to peak power? Lowers it.

There are tons of other factors that come into play, as well. Cam events, exhaust tuning, temperatures (I assume intake charge temp of 570R, or about 110F). Actually........that's another thing, if you can use water/meth injection, that'll lower intake temperatures a fair amount, which will shorten the required runner length (speed of sound determines tuned length, and it increases as temperatures increase).

Anyway, I gotta get back to work. Anyone wanna buy some oil? :-)

On edit - I had told Doug for peak power to be 1250-1500 RPM lower. A larger delta would probably be a little bit better. The larger the delta, the flatter the curve and less total HP you can make, but it'll be more usable and drivable. The hgiher you shift the peak torque, the lower it'll be just because of the fact that frictional losses increase roughly squared with RPM, so even though your peak VE doesn't really change, usable torque does.

333pg333

All this stuff makes me go a bit cross eye'd when I think of trying to design a new intake for the new motor!
So many things to factor in and then there's space to consider. Having the turbo located where it is doesn't make things easier. To me it seems tricky to clear the turbo without having to alter the runner length/diamteter to suit. This is with larger aftermarket turbo. While collating information and opinion it's not hard to get differing theories. Harry, do you have access to the CFD computer at G.T. ? lol...

67King

Patrick, I got out of Tech a long time ago. I actually built my models from Excel to try to figure stuff out that was not program intent when I was at Ford. Kind of the whole "don't complain about something unless you have a better idea, and can show why it is better." And since I didn't have access to CFD tools for a non-program application, I had to come up with SOMETHING (it actually worked, too, as what I was working on became the new 5.0L aka Coyote). I used a crude one for the above calculations. I use a more involved one with others that takes cam events into place, and essentially does an FEA for flow over the whole intake event. I've not yet tied actual flow data into it, yet. I could, but I didn't have a ton of info to use to calibrate anything.

refresh951

Thank you for taking the time to write this up Harry Very informative.

Cheburator

If you have something useful to add to the discussion - then say it...

Otherwise, **** off...

Slow and simple...

333pg333

Agreed, thanks Harry....thanks for making me dizzy.

I would like to employ some methodology that falls somewhere inbetween NASA / MIT and what we term down here as 'Bush Mechanics'. Bush is Ozzie slang for out beyond the urban line, even beyond normal Country. This is where your wits can save your life but don't expect these mechanical examples to make it into Racecar Engineering. Conversely, without the aid of high powered computers and the people that know how to run them, or the ability to make endless intakes and compare them on the engine dyno, then we have to make a compromise. I see what Thom and others are saying too. Hopefully there is a level of intellect that can start at a point that is far from scratch. I have discussed intakes with Thom a bit recently and he has at least tried a few different ones on his 3L 8v motor plus done his own research. So I'm also prone to listening to someone like that who has more data than myself. I'm still intrigued by the LR version that seems to invoke polarity from the pack. Some have basically ridiculed it but Thom has found that it was a positive improvement on a friend's car I believe. A question that has been vexing me and sorry to keep throwing it back to my motor, but I think it's also in context of the greater discussion. Perhaps if I start it like this;

I have a friend who has a pretty highly developed 3.1 8v motor. It has a big cam and a worked head running at close to 250cfm on the flow bench with stock size ex valves and 49mm intake. It has a 700hp turbo with a smaller hotside to help with spool. It also has 4-1 headers which are larger than the SFR equivalent. Larger cooling core system and larger 66mm t/body. The components are all geared for about 7500rpm running on race grade E85 with static c/r of 8:0.1...however despite adding ign at the top end, the tuner's down here found that the motor just wants to nose off at 6k. Most fingers are pointing at the stock intake as the culprit. Sure, there could be backpressure occurring elsewhere and this friend hasn't had time/money or motivation to test it just yet as the car is proving to be pretty quick as is.

So....long story long...if this friend was to have a new intake made which has (simplified) shorter runners than stock, bellmouths and a larger plenum would the motor become more peaky by moving everything across say by 500rpm, or would it open the motor up to be able to run to 7500rpm therefore not only increasing the overall rpm but also dropping back into the turbo's efficiency range when shifting to the next gear, thus making the car more driveable??? Currently my friend has stated that the car is a little old school laggy. Not too bad but could be improved.

My friend is obliged by any thought put into his quandary.

thingo

I think your friend should measure the back pressure.

333pg333

Obliqueness aside, please clarify your thoughts.

I'm sure you're right, he should...and will. Doesn't want to hex the car at the moment as it's running well enough and just wants to get through the next few weeks. He would hope to see you at the final PC event on the 26th...et tu?