Inlet Manifold Design

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Duk
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Inlet Manifold Design

Post by Duk »

With my decision to go for some modified normally aspirated performance improvements, I've initally terned my attention to some of the external components of the engine.

The inlet manifold is 1 area that can be hugely influential in the outright performance of an engine and an area that I believe needs attention on the Alfa.

Some facts about the Alfa 75 V6 inlet system:
Small plenum chamber capacity of about 1.7 litres.
Number 4 inlet is quite close to the roof of the plenum chamber.
The inlet runner length is really too short for any road going engine.
There is about 20mm between the top of the plenum chamber and the bonnet in the 75.

From http://autospeed.com/cms/A_107771/article.html "David Vizard suggests that a runner length of 17.8cm at 10,000 rpm makes a good starting point. (In this context, "runner length" refers to the distance from the inlet valve to the plenum chamber.) Add to this length 4.3cm for each 1000 rpm less that the system is being tuned for. Tuning for peak torque (not peak power) is the norm, and so if the engine were being tuned for 4000 rpm, a runner length of 43.6cm would be required. You can see that for an averagely-sized engine bay, the longer the runner that can be fitted in, the better!"

I love to look at the way other manufacturer's have designed their manifolds.

Ford (Australia) apparently achieved 100% volumetric effecientcy when they added their 2 stage (long/short) inlet manifold to the EF model onwards Falcon (4ltr OHC 2 valve straight 6).

The Holden VL Commodore Walkinshaw (5ltr pushrod V8) used a large volume plenum chamber, relatively short runners and staged dual thottlebodies in it's configuration. Tho I can't see the staging of TB being anything more than an attempt to achieve better drivabillity than anything else.

The realworld performance differance wasn't as huge as the price gap was tho......

Nissan breifly used a V6 manifold design that had 1 TB but 2individual plenum chambers that were linked together at some point to achieve a broader torque curve.

So the new question is. Which way to go about achieving a better designed inlet manifold for the akward6 packaging of the V6?

The volume needs to be increased, that's a given.

Should I start from scratch and make a long runner manifold, possibly with individual volumes that get linked together at some point in the rev/load range?

Should I make tapered runners that attach to a modified factory plenum chamber?

Should I add runner length or raise the top of the plenum chamber, or modify the bonnet and do a bit of both?

I've got a mental picture of what I want, but any other sujestions are always welcome?
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GTV27
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Re: Inlet Manifold Design

Post by GTV27 »

option one: hows about the 164 type runners, extended over to the RHS to a custom (ie larger) plenum with a throttle body on the end - might be tricky to fit an aircleaner thou... :?

option two: velocity stacks sticking out through the bonnet - no that'd only work on a gtv6 :D

option three: curved runners, three one way and three the other, indivdual throttle bodies and two aircleaners (have to be map for the ECU, but that's the go anyhoo)

PS - the walky throttle was all about race homologation v's drivability - it did almost all of its street driving on the little one (they could've just left the big one disconnected and still got 180kw, but the FIA (then FISA?) prob would have called foul)
Jason
1983 GTV6 2.8 litre

Duk
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Re: Inlet Manifold Design

Post by Duk »

GTV27 wrote: option three: curved runners, three one way and three the other, indivdual throttle bodies and two aircleaners (have to be map for the ECU, but that's the go anyhoo)
This is similar to my current thinking :mrgreen: .
My method is with 2 individual plenums (left and right), but with them both joined together at the front of the engine with a common (standard Alfa) throttle body. The collector would be built so as to not allow direct left to right pulsation transfer.
At the back, near the fire wall would be a cross over pipe that joins the 2 together but it would have butterfly valve in the middle. At low engine speeds and low loads, the 2 plenum chambers will remain seperate. At higher speeds and loads, the 2 plenum chambers will be joined together via the opened valve. Similar to the Nissan system but the throttle body will have equal distance to each plenum chamber.

I'd take a photo of the crude mock up I have on the engine, but it's dark outside. And, I'm afraid of the dark............ :cry:

Incidently, your set up could be (sorta, kinda) done with 1 dummy airflow meter and 1 functional airflow meter, and was an initial set up idea. Just need to boost the signal from the functional AFM and that's not hard :D :D :D .

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GTV27
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Re: Inlet Manifold Design

Post by GTV27 »

refining that thought, how about 3 each way into separate plenums with separate throttle bodies and we throw the airflow meter(s) in the bin and use delco computer with a MAP sensor (airflow flaps are evil). Throttles would only need to be small (something like a 4cyl corrolla of some such) so should be cheeeep.

what's the idea with the cross over pipe and valve?
Jason
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Re: Inlet Manifold Design

Post by Duk »

At low revs/loads, a smaller volume plenum works better, but I can't say for sure why. Because the engine fires left bank, right bank, left bank, right etc, the engine can be thought of as 2 3 cylinder engines on a common crankshaft. At higher revs/load, the engine operates better with larger plenum chamber volume, so simply joining the 2 plenum chambers together achieves this.

The key to this, from what I've seen from other manufacturers, is that any pulsations that move toward the throttle body can't go directly to the other plenum chamber without doing a 180 degree turn, like the Nissan set up pictured. But when the 2 plenum chambers are linked, any pulsations can flow between the 2 plenum chambers in the same way as they would flow down an inlet runner into a cylinder.

Probably not as effective as a dual length manifold arrangement, but it should help to broaden the torque curve and make an engine that will probably be tuned for more top end power be more drivable and fuel efficient when cruising on the highway and tootling around town.

*I just realised how badly I have repeated myself :oops: .

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Re: Inlet Manifold Design

Post by kevin »

Very interesting topic. Post some rough sketches.

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Zamani
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Re: Inlet Manifold Design

Post by Zamani »

For a road car, then I think the 164 setup is probably the most practical and cost effective. For a race car, I would use short runners. If you want twin plenum, then you will have to track down the Alfa 90 2.0 V6 Super. That's probably more rare than an Alfa Sei!!
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Re: Inlet Manifold Design

Post by Duk »

Zamani wrote:For a road car, then I think the 164 setup is probably the most practical and cost effective. For a race car, I would use short runners. If you want twin plenum, then you will have to track down the Alfa 90 2.0 V6 Super. That's probably more rare than an Alfa Sei!!
Z man, the idea is to try and reduce some of the compromise of the factory Alfa inlet manifold designs while still fitting under the bonnet.
It will be all custom made by yours truly and made from stainless steel exhaust pipe so it won't rust or form scale inside when I weld it together.
Straight out of the box I expect to see better torque every where because I'll be adding the best part of 200mm with decent internal bellmouths to the original factory cast aluminium runners and hopefully the new design will reduce some the cylinder to cylinder variations that tend to occur in most/all manifolds.
The larger plenum volumes should also assist with top end power too :D .

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Re: Inlet Manifold Design

Post by Duk »

Obviously a very crude mock up that's missing the left (in photo) mock plenum, has only 1 half of mock collector and missing rear inlet runner and crossover pipe, but hopefully it will give some idea of what I've been ranting on about.
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killaz
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Re: Inlet Manifold Design

Post by killaz »

It would be usefull to run flow simulation test before making new plenum... I will probably make new plenum based on AR164 but with extended intake pipes.

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Daniel
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Re: Inlet Manifold Design

Post by Daniel »

I went with the 164 style setup with a modified 164 plennum on Dads GTV and something similar but a little more modified (custom runners and bigger plenum) on my GTV

I was originally considering 2 x 164 plenums - 1 per head with 2 throttles and putting 3 pipes joining the 2 plenums (fills the spare 3 holes in each plenum and joins them to give a much bigger volume)

Headers are also a work in progress.
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Dads Plenum - fits under GTV 2.0 bonnet
Dads Plenum - fits under GTV 2.0 bonnet
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My Plenum 1 - fits under GTV6 bonnet, not tried under 2.0 bonnet
My Plenum 1 - fits under GTV6 bonnet, not tried under 2.0 bonnet
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My Plenum 2
My Plenum 2
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Zamani
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Re: Inlet Manifold Design

Post by Zamani »

Daniel,

Those extractors are WILD!!! Can you start a new topic and post photos and info on them??
Dr. Alban

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Re: Inlet Manifold Design

Post by Duk »

Daniel wrote:I went with the 164 style setup with a modified 164 plennum on Dads GTV and something similar but a little more modified (custom runners and bigger plenum) on my GTV

I was originally considering 2 x 164 plenums - 1 per head with 2 throttles and putting 3 pipes joining the 2 plenums (fills the spare 3 holes in each plenum and joins them to give a much bigger volume)

Headers are also a work in progress.
Nice work!
I'm liking the dual 164 plenum you sujested. It would be excellent to compare 2 dyno runs, 1 where the 2 plenums aren't joined and 1 where they are. If there is benefits with either, and I believe there would be, then the 3 joining pipes could be fitted with a butterfly valve each and at the preffered point, opened to join the 2 together.
That 24v plenum looks to be quite huge in volume :shock: .
Also as Zamani has sujested, prease be starting a new topic for the exstractors as this is some other work I'm under taking, but I'll really just be copying Jarle's design viewtopic.php?f=5&t=2116 :D .

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Re: Inlet Manifold Design

Post by darryl longley »

I know its off topic a little but what is the brake master cylinder set up on the 24 valve car
Mine is a uk car and that set up looks interesting it would mean doing away with the transverse tube

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MD
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Re: Inlet Manifold Design

Post by MD »

Darryl,

That set up is Daniel's street/race project in the making. It is a custom made pedal box. As you can see, no booster. He is a pretty busy guy and if he doesn't get around to seeing this post, send him a PM. I am sure he wil be happy to tell you about it and possibly even make you one..He made mine,for a special application that needed to clear a custom plenum on the race car!
Works great.
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Transaxle Alfas Haul More Arse

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