Intake Rise

[gt1cooper]

This may seem a minor suggestion, but I can see it having a large effect on the ability to fit engines into various cars during the game, as well as creating performance engines for smaller cars.
Intake rise, as most of you probably know, is how high up the intake manifold extends up above the engine. This affects both power and height.
The affects of this are dual:

1. Increasing the intake rise will allow fuel to flow quicker, reducing the RON, hurting fuel economy, and increasing power. However, the height of the motor is greatly increased, making it more difficult to fit in the car, and perhaps requiring a functional hood bump or scoop to get to air or enough room.

2. Decreasing the intake rise will force fuel to flow slower, increasing the RON, helping fuel economy, and decreasing power. The height, obviously, is decreased greatly, and thus bigger engines can fit into smaller cars.

I do believe that this feature can contain a reasonable enough effect on gameplay to merit inclusion into the final game.

[Daffyflyer]

I can't say I've ever seen documented in any of our textbooks the fact that intake height has any effect on fuel flow or octane requirement. As far as I'm aware, fuel flow is defined purely by fuel pressure, carby jetting/design or injector size and ECU programming. I don't understand how intake height would change that?

Changing the length of the intake runners WOULD change the resonant tuning of the intake and potentially change the shape of the torque curve and give breathing improvements at different RPMs depending on length (this is modeled ingame, but is fixed per fuel system type). Different runner diameters and shapes could also give different torque curves, improve or hurt all out power and potentially make smalish economy differences depending on where it makes the engine breath most efficiently. We'd love to have the option to change intake runner length, but it's an art nightmare as well as more complication to find UI space for.


Also do note that at this point engine design features are basically locked down, the only things that are coming are more forced induction options (including superchargers) and more engine types (V6s, V12s etc.)

[gt1cooper]

I understand completely why you might not include it, it is a minor thing, but it can be a thing that will actually have an effect. High-performance, or high-rise, intake manifolds have wider, longer intake manifold ports with a higher vertical rise, all of which combine to increase fuel flow and fuel speed into a vehicle's engine, which in turn increases engine horsepower and performance. The greater amount of fuel, the lower the RON as you know, so that is how that effects the RON. Higher rise manifolds help mostly at higher rpm, when more fuel is being dumped in, while at low rpm, fuel molecules are not really obstructed by their predecessors. A higher valve lift will allow much more fuel into the combustion chamber when coupled with this. That is why, on my Mustang with it's 427 stroker, I had to pick between a low, mid, or high rise engine. I do not have the power charts available, but I picked mid rise for two reasons. One was because with the mid rise, a functional 2 inch hood scoop would fit the air filter for the dual 850 holleys, and the other was that with that intake, I had a flat torque band from 3000 rpm to 5700 rpm. The low rise intake's torque peaked at 4000 and dropped off at 5000, and the high rise had the same mid range power of the mid rise, plus an increase where the torque curve held steady to 6500 rpm, and did not fall off all the way to the limiter of 7750 rpm. However, the air filter would have stuck clean out of the hood, and I did not want to deal with the fabrication, forward visibility, and price of having such a setup. Resonance does also have an effect, and I understand the nightmare that is valve timing for the static Helmholtz resonance property of the air vs. the dynamic timing. Just, on carbureted engines, this is one of the many ridiculous things that, when you are building an engine for a car, must be considered. (It was a nightmare, trust me. I used to work for FoMoCo as an engineer and team manager focusing on the top end, from intake to valves.)

[Daffyflyer]

I still don't understand how it'd increase fuel flow, is this something about pulling more vacuum against the carby jets? Is that part of the effect any different than just jetting it a little richer? Or is it that vertical height helps fuel atomization in a way that other long manifold shapes don't? (If so, why?) If you could point me to somewhere with more information about this effect I'd love to find out more.

The only two major design parameters I'm aware of is runner length (mainly effecting the RPM and strength of resonant tuning) and runner diameter (mainly effecting air velocity/overall flow capability) so I'm not quite sure how the height of the manifold changes much (I'm assuming that's what you mean by rise), I guess it is one way of packaging longer runners in a V configuration though.

I doubt we will change much about intakes at this point, but I'd still be interested to know why high rise manifolds do all these things.

[xABSOLUTIONx]

Daffy as you are speaking about manifolds - will manifold choking will be a thing?

BMWs M50TUB25 and M52B25 - basicly the same engine, but there is a difference in power - 192hp v 170hp and the big difference comes from the manifold, torque stays the same at 245nm, M50 has wider/bigger runners and is a cheap way to rise power on the M52

[gt1cooper]

I like how absolution put it- manifold choking. It is difficult to explain in a chat room, but quite simply you are increasing your volumetric efficiency at higher rpm by either going to a high rise single plane manifold, and at a lower rpm by going to a low rise dual plane manifold.
http://www.edelbrock.com/automotive_new ... sion.shtml
In this chart, you can see the direct results of this.

As you know, increasing the cfm of your carburetor will increase fuel delivered, help higher rpm power but hurt drivability, etc. Increasing rise follows the same trend and allows the fuel to flow in a straighter line, faster, directly to the valves with no curves to slow it down. Single planar manifolds do the same thing. Dual planar lower rise manifolds will slow down the flow of fuel, but take up less room and are far better for lower rpm engines; thus why a Chrysler 426 hemi has a low-mid rise manifold (revving only to about 5500 rpm) while a 427 side oiler ford cammer has extremely high rise manifolds (revving to far above 10000 rpm). The cammer has 900 hp, but at about 8700 rpm, while the 425 gets it's 400+ at about 4700.
Fun fact: at 427 is the only engine banned from nascar because Chrysler complained that it was unfair to compete against with its 426.

[Daffyflyer]

But unless I'm mistaken, a higher flowing carburettor won't increase the richness of the fuel mixture, just the total amount of intake charge inhaled (still improves power, of course!)

Also as far as I can tell, the gains from "high rise" manifolds are because they have longer runners with smoother curves in the runners, yes? If so, that's already somewhat taken into account with the different intake/carby setups, although admittedly there are not different manifolds available for the same carby setup.

I'm still not understanding how fuel flow comes into it though. Surely the only thing that'll change fuel flow as a percentage of air flow is carby jetting? (I'm assuming there must be a property of carby fuel systems that I'm failing to understand here)

[gt1cooper]

The reason fuel flow is affected is that, as you know, the fuel flow in a carb and down through an engine is entirely regulated by gravity.it is quite simple, not having anything to do with the Venturi effect (but that will have to be re-tuned after switching rise), but simply having to do with the fact that a steeper slope allows the fuel to experience a greater acceleration due to gravity. The engines do not need that increased fuel at any point until you get to a certain consumption figure, at which point the increased fuel speed and thus availability with less in the middle of the runner at one time leads to better power in this range.

[WizzyThaMan]

Way too complex for me IMO. Not sure this will contribute anything to gameplay value than being able to get a certain increased HP after RPM XXXX, something which can be achieved by VVL already anyway.

[gt1cooper]

It does something very similar to cams, however, it is more linear, space reliant, and important for higher revving engines. It makes a huge difference. Luxury cars have a very low rise, for low down power and drivability. It is not any more complex than ignition timing or cam rise. I understand that it will probably not go in now.


This is also cheaper and requires less man hours, as well as determining the powerband, not just more power after a certain rpm.


However, it is also cheaper to do, and requires less man hours. It also has a greater affect on size, as well as affecting the ron.


Edit: My apologies, mod. My internet is slow, and did not regester that I had posted it the first time.
Mod edit: merged triple-post into one. Given warning for unneccessary triple-posting.

[Daffyflyer]

OK, that is an interesting one, I assumed that gravity would have such a tiny effect on the fuel charge compared to the very high speed air it's being carried by, but perhaps not. Anyhow, whilst I'd like to have a bit more variety in intake designs I don't think it'll happen. Thanks for the discussion though, intreging concept

[JohnnyOnTheSpot]

I have never heard anything about the acceleration of fuel due to gravity?

I think you are talking about tuned length? The harmonic wave that in present in the runner syncs up with the opening of the intake valve at a certain RPM and causes a ram effect. This is why some well-tuned naturally aspirated engines can achieve a VE of well over 100%. Ideally the 1st order harmonic would be harnessed, but this would require a runner several feet long - usually 2-4th order is used to prevent an excessively long intake tract. (here is how NASCAR engines get so much power out of unequal length runners - very cool stuff! http://www.stangtv.com/tech-stories/com ... echnology/)

This same effect is present in exhausts and is why a flat-plane V8 is more desirable from a power-standpoint. (cross-plane harmonic is compromised at the collector)

[Daffyflyer]

^Mmm, that's exactly how I understand the advantages of long manifold.

Any change in the way fuel acts due to the direction of the runners relative to gravity seems like it'd have a minimal effect on anything, and I've not seen it in any of the literature we've worked from. But i'd love to read more about it if it is indeed a documented effect.

[Killrob]

Well, the effect of gravity is easy to determine. Just comparing two of the factors should give a pretty good, rough estimate.
1) Air/Fuel mixture speed / acceleration
2) Free-fall speed of droplets speed / acceleration

Let's assume we run at 3000 RPM, i.e. 3000 / 60 = 25x BOOM per cylinder per second. That is 0.04 seconds per 4 strokes, 0.01 seconds per stroke.

For 1) we know that some engines get into breathing problems when they reach the speed of sound for the intake flow. Let's halve that to be a bit more modest and produce a reasonable figure. That gives us 170 m/s. What acceleration do you need to get from ~0 to 170 m/s in 0.01 seconds? 170 = a * 0.01 which gives us an acceleration of 17000 m/s^2 or about 1700g.

For 2) it's simple: gravity is 1g.

Comparison: The effect of gravity on this system should be more than a factor of 1000x smaller than that of other forces involved. So naively, I would think it doesn't matter.

[WizzyThaMan]

Dr. Rob strikes again! Badum tisss!!

interesting read, KillRob.