ALFAGTV6.COM

[Micke]

When you say 15 hp I wonder how it is measured in both cases and how the measurements are normalized to same level/standard?

[MD]

Micke,

I'll give you a call on Skype..

[slyalfa]

Duk that looks like the GM quad4 1987ish



see http://en.wikipedia.org/wiki/GM_Quad-4_engine

It was a good motor 180hp 4cyl 2.3L
"For twenty years, 1989-2009, the Quad 4 held the title of being General Motors most powerful naturally-aspirated regular production 4 cylinder engine"

They went to a plenum on the latter types and HP went up but cams and such too.
I think the intake is good but cost more then a cast one.
I think you would not see that type now due to most intakes have tuned lengths. And I do not think you can do it with the header like tubes.

[Duk]

What is the benefit of longer intake runners and bigger plenum. How do you guys know what is the perfect size and lenth for each setup.
Arent individual TBs like the AHM from UK more efficient to gain power?

Longer runner improve low rpm torque. The longer the runner, the more the manifold is in tune to help the engine produce its peek torque lower in the rev range.
Why have a manifold that is theoretically tuned to achieve peek torque at 8000+rpm? What road going car has that?

Car manufacturers put so much more effort into making their engines as tractable as possible rather than make big outright power. Their power outputs may look rather dull, but their torque to capacity ratio is excellent and it's spread over as broad a rev range as possible.

Designing an inlet manifold for high rpm power and then using it on a road car is really quite a strange thing to do. You make the engine less drivable and annoying to use in the real world.

It's kind of like having a low compression, big turbo car. Outright power may be impressive, but it's real world usability is just so annoying that you leave that car at home and drive some standard, boring POS daily and then make claims about your modified car being for special occasions

[Duk]

Duk that looks like the GM quad4 1987ish

The pic I posted was of a Toyota engine.

It was a good motor 180hp 4cyl 2.3L
"For twenty years, 1989-2009, the Quad 4 held the title of being General Motors most powerful naturally-aspirated regular production 4 cylinder engine"

Honda, Mitsubishi, Toyata and Nissan all produced NA engines that made 100+hp/liter engines in that time, but credit where it's due, the GM engine probably had a broader torque curve.

They went to a plenum on the latter types and HP went up but cams and such too.
I think the intake is good but cost more then a cast one.
I think you would not see that type now due to most intakes have tuned lengths. And I do not think you can do it with the header like tubes.

Do you mean dual length? Packaging aside, the 'exstractor' style manifold should be just as tunable, but making a dual length version would be a big achievement, especially at a cost car manufacturers could stomach.
Tho #4 does look particularly tortured in it's shape and possibly to short compared to the others. A conventional plenum style manifold does seam to allow easier equal lengths of runners, but this doesn't guarentee equal performance of each cylinder. http://autospeed.com.au/cms/A_109725/article.html

[Duk]

Mats video: http://www.youtube.com/watch?v=0ft7W_2PbYI

[Mats]

About the "extractor style" manifold, the inlet of the runners look awful. Notice in my video linked above how the air in the plenum is pretty much standing still in between when the different intake valves are open and how the primary flow into the runners are from the volume right next to it. I noticed a big improvement in flow balance between the runners by moving the ends further away from the #1 and 4 runners. A 10mm move made a HUGE difference, imagine having a wall right next to the runner like in the "extractor", it will be bad compared to a larger volume and a proper bellmouth, also "crosstalk" between the runners will be a big factor when you cram all of them into a small area like that with a very small volume of air to work with.

The CFD plot above look typically like a static flow through all the runners, as in all valves are open the vhole time, not like any piston engine I know of. Quite useless as a design evaluation.

[Duk]

About the "extractor style" manifold, the inlet of the runners look awful. Notice in my video linked above how the air in the plenum is pretty much standing still in between when the different intake valves are open and how the primary flow into the runners are from the volume right next to it. I noticed a big improvement in flow balance between the runners by moving the ends further away from the #1 and 4 runners. A 10mm move made a HUGE difference, imagine having a wall right next to the runner like in the "extractor", it will be bad compared to a larger volume and a proper bellmouth, also "crosstalk" between the runners will be a big factor when you cram all of them into a small area like that with a very small volume of air to work with.

The CFD plot above look typically like a static flow through all the runners, as in all valves are open the vhole time, not like any piston engine I know of. Quite useless as a design evaluation.

I did notice the reverse flow from the adjacent runner on your video Mats and it had me thinking that maybe a 4 cylinder engine could bennefit from 2 individual plenums that have 1 & 4, 2 & 3 in each.
Also, any volume between the throttle body and the collector of an 'exstractor' style manifold would/should be considered plenum chamber volume at part throttle and any volume between the collector and the outside world plenum chamber volume at full throttle.

Ultimately I think the only real comparison would have to be exactly that, a real world 1.
The transverse engines looked very compromised due to packaging tho. I think a north/south 1 or even on my mid engined MR2 would allow a more even manifold design that just runs up and over the head, rather than trying to be squeezed into the very front of the car forcing them to use many tight bends on 1 or 2 runners.
I don't see a practicle way of making 1 for a 75 V6 tho, so I'll be sticking with my dual plenum set up.

This looks interesting:

[Mats]

Some of what looks like reverse flow or parasiting is actually bounce from the valve closing but yeah, they are definetly affecting each other.

[xrad]

some intersting stuff in the above posts.

My 968 has a variable length intake system that when rpms reach a certain point, you can feel a slight 'punch' from the 'ram' effect.

This puts a nice peak in power in the higher rpms with 'longer' runners while maintaing low end power with shorter runners.

additionally, the runner length is measured from the valve back and not just the part outside the head. Valve cut very important if you are looking for that little extra....radius?.


Also, the reflective wave that builds up behind the valve after it closes, and which reciprocates between the valve backside and the 'resonance chamber wall' of the intake plenum is a very important consideration. It is not just based on pure volume but close consideration to the reflective surface design as you don't want wave interference cancelling a possible gain.

In normally aspirated design, manifold pressure close to atm as possible AND slight increase of positive pressure at certain rpms can be had with close attention to your ultimate needs (broad band power or targeted power in sinc with the tranny gearing and track/road situation).

[Micke]

Are you sure the 968 has variable length intake?
I don't think so but I might be wrong.
It has variable cam timing though which can give the effect you describe.
Also my 944S had the same feeling when the runners hit their resonance frequency. The S2 didn't have a clear punch.

[MD]

This puts a nice peak in power in the higher rpms with 'longer' runners while maintaing low end power with shorter runners.

I think you got that back to front.

Short runners for high RPM torque and long runners for low rpm torque

[Zamani]

Later 993s had vario-ram, not the 4-cyl engines AFAIK. From what I was told (famous Aussie Alfa tuner, and an cam specialist here in the US), 164 runners are too long for best top end power. Ported GTV6 runners are the way to go.

JK cut the 164 Q runners short. But then again JK cuts a lot of things

[xrad]

Yep sorry..back to front on runner length, sheesh...thinking too fast on my lunch break...

as for the 968 manifold, mine has what looks like a set of upper runners and a lower runner, you can kinda see in the photo(not the water pipe, but beneath it). You are correct, these are not 'variable,' but seem to offer peaks a low and high rpms which coincide with the variable cams. It is called the 'dual resonance' design and is pretty advanced. This car definately has variable cams because I have changed the variable mechanism pads. Nice smooth power from a four banger.
Unfortunately, takes up MUCH room.

[MD]

But then again JK cuts a lot of things

Damn right.. wish he'd cut the crap and pay his bills. He's sending Greece broke according to the monetary fund..