Hey Guys,

I am designing a MS system for my 2270 (163.86b cam, 48x38 valves, future Triad header). I am looking at running stock intake runners and possibly making a new plenum to run my Ford TB (probably from a 4.0L Exploder/Ranger).

Are there any "design guidelines" that should be followed when making a new plenum, such as a certian volume required for engine displacement?

Looking at space requirements, I see running the TB on top of the plenum is the only way to go. That, of course - begs the question... Is the stock 914 2.0L plenum a good starting point to modify to allow for the Ford TB?

Here are some pics for reference... I had a Bus 2.0L intake system to borrow, so I am basing my measurements and ideas off of that.

http://www.qtm.net/~persot/MS/

Any ideas, suggestions, etc, are appreciated!

Thanks,
Tom

Tom

I haven't really run my car enough to tell but I was using the stock intake off of a 914 2.0 with the throttle body opened up to 50 mm. It seemed adequate for my 2270 but I only had 350 miles on it before I tore it back down. The stock system with the stock airbox has som real advantages. The large airbox act like a Heimholtz (sp) ressonator. Certainly installation is easy.

If it turns out that this is inadequate my plan is to contruct a riser on the stock plenum and use a larger throttle body. The riser will add to plenum volume and the larger throttle body will replenish it faster. I'd have to fab a throttle linkage, open up the top of the plenum to match the riser and the stock airbox would have to go. Also the riser will tend to aim a column of air at the bottom of the plenum so a diffuser may be necessary.

My feeling so far is that the stock system will work.

Dave

Tom,

Didn't Shad Laws build a plenum for a large T4 back in the days he and Charles were planning the Nickies? LN Engineering planned to make and sell the plenum in its final form, but I never heard anything more. Maybe you could search the TypeFour archives (where Shad described it) or ask Charles. Good luck.

With the cam that I set Dave up with, his plenum has a better chance.

Something with more volume would always be better, but I won't know how much better till mine is done.

Tom, You need a cam change badly to run a common plenum system. The cam you have opens on a 104 center and is very difficult to tune at idle. It makes gobs of power but totally depletes that plenum with its early openings.

Been there and done that with the same cam. It is one power making bitch for carbs, but I'll never use it for FI again.. If you change it to a 110 center it comes to life though with FI and the loss of downlow power isn't there because FI makes more power at low revs than carbs..

Lots of good replies - thanks!

I have seen Shad's plenum in person - he built it out of fiberglass and it seemed to work pretty good. If I were to build one, I would use mild sheet steel and weld it together. I might pick Shad's brain and see what he says.

Dave - thanks for the advice. I am thinking that the 2.0L plenum might be the way to go... I think adapting a domestic TB to it would be pretty easy.

Jake, you have an interesting point about the lobe center. I've noticed that I never have a lot of vaccum at idle when I T'd the vac connections on the 44's. I never thought much about it though.

Is the fact that there is little vac. at idle, so that is what makes it difficult to tune, or is it a vac. pulse (non-steady reading) at idle that makes it hard to tune?

Thanks
Tom

Tom

Don't give up on this. I believe there is an option in the MS and S extra code that allows you to run a combination alpha-N and speed density in the fuel map. Alpha-N plots throttle position against rpm and speed density plots vacuum against rpm. I have not looked into it but, I assume it allows you to tune the idle independent of vacuum and switch to vacuum at some defined rpm. I know there are some pretty impressive cars that run a similar system.

That might solve the idle issue but, you still need to find a plenum solution.

Dave

I heard that running a new-unused fuel filter inline with the MAP baffles the reading and can smooth out the idle. I have been looking into the Alpha-n and that might be a good solution.

I'm feeling a little sick at work today *cough cough* I may leave early and hit the junkyard up for a Furd TB.

I will make this run right...

Thanks,
Tom

SDS has an option for locking in a fuel value at a certain throttle position. I did this for while but gave up on it because as soon as you opened the throttle and moved off the locked value, it would revert to the MAP signal and cause a sharp jump in the fuel value. This made low speed driveability poor. If you need to have a very different idle fuel amount than is given by the proper tuning of the MAP signal, you will have this jumpy condition.

SDS is not good for low speed driveabilty with engines that have low idle vac (like my 2.2E). I think the 2D map like mega has is a better solution for these engines. You will notice that almost all of SDS projects posted are turbo engines. I am still running SDS and it works pretty well, but I would like to change to mega at some point. The SDS is so easy to tune that I am not looking forward to losing that. I would have to piggyback the mega onto my SDS crankfire system I think. I have not looked at what is involved in using the mega ignition.

There may be ways to help the situation at idle, but it will never idle as smooth as it did with carbs.

It is my duty to share what I have learned and thats early opening cams and FI don't get along at all at low speeds.

QUOTE (Jake Raby @ Feb 1 2005, 07:21 AM)

There may be ways to help the situation at idle, but it will never idle as smooth as it did with carbs. It is my duty to share what I have learned and thats early opening cams and FI don't get along at all at low speeds.

Point taken, Jake.

I can live with a lumpy idle. Plus, I look at it as a challenge. Just like everything else I've done

Thanks
Tom

AThe idle is also inconsistent with an early opening cam in my experience.. I have gotten past it with alot of initial advance and some richening up at low speeds.

Well, I've got the Mallory, so I can dink with initial advance... Plus, I have a 911 Carrara starter, so it should be able to turn it over.

So, getting back to the plenum, is the consensus that a 2.0L plenum should work with a different TB stuck on the top?

Thanks,
Tom

Tom
I will have to agree with Jake on this one. That cam (which is a barn burner) makes awesome power and I can make it idle glass smooth with Webers. But if you slap a common plenum on there I doubt it will idle at anything below 2000rpm. It will sound like a late model dirt track car at idle. V8s suffer from this problem when running big overlap race cams.

Why do you want to go to a common plenum? I remember Shad's plenum as well. His car was nice but I just wasn't impressed with it all that much. Maybe it was just a big heavy car that slowed that nice motor down, I don't know.

You should be looking at plenum volumns of 3.5-5 litres in volumn. A 65mm TB will probably be a little too big. I would try and find a TB from an integra 58mm or a prelude 62mm. Both should work well if you intend on going with a common plenum.

QUOTE (Brett W @ Feb 1 2005, 10:00 AM)

You should be looking at plenum volumns of 3.5-5 litres in volumn.

Those seem like huge numbers to me. I think I read on another thread that the stock plenum is a bit less than the engine total displacement. If you keep close to the same ratios you would only need a plenum size of about 1.8 liters or so and a TB of about 50–55 mm. Obviously the cam will play a huge role in the exact numbers but Dave got his to work with a stock plenum.

I think a more accurate statement is I got it to run. I believe it will work, idle was no problem and near wide open throttle was not a problem. Cruise and over run still need some work. Over run and decel are a problem because the large injectors are openning for such a short time that 0.1ms change causes a significant change in air fuel ratio and the engine flucuates between rich and lean. During cruise the MAP was flucuating and the car would stutter. I'm not sure what this was caused from and at the time I was more concerned about the amount of oil I was using.

I really believe that this setup will work on my engine but one of the considerations when the engine was designed was FI and a common plenum.

Dave

QUOTE

Those seem like huge numbers to me. I think I read on another thread that the stock plenum is a bit less than the engine total displacement. If you keep close to the same ratios you would only need a plenum size of about 1.8 liters or so and a TB of about 50–55 mm.

The numbers for the stock plenum and runners are for an engine that is operating at 70% VE in stock form. It was meant to run to 5500 making peak torque at a reasonable range and run all day long without overheating. When you change the stroke,bore, rod length, valve size, and valve timing, you have just changed all of the variables that went into the design of the stock plenum. (if VW put any effort into designing it to start with)

Your 2270 has a higher piston speed thus drawing more mixture into the cylinder, higher compression burns more mixture thus making room for more fresh mixture, you have to get that mixture into the motor. Designing a plenum will either be a cut and try affair or you need to spend sometime doing some pretty advanced math.

AS for the injection system, I would not use any parts from the stock D-jet setup. Toss that crap in the garbage and use more modern parts. Run a peak-hold injector and you will never have a problem with injectors that won't idle.

QUOTE (Tom Perso @ Feb 1 2005, 05:41 AM)

I am designing a MS system for my 2270 (163.86b cam, 48x38 valves, future Triad header). I am looking at running stock intake runners and possibly making a new plenum to run my Ford TB (probably from a 4.0L Exploder/Ranger).

i'm building the exact thing as we speak for myself and randal ...


assuming you want to stick with the single plenum setup, you'll need:

- 38mm (inner) dia. intake runners
- head port at intake side matched to runners
- TB with a dia. between 48mm - 50mm, preferably a 50mm TB with a 48mm venturi
- a (common) plenum with a volume of 1.2L

i'm already talking to a machine shop to get this fabbed. runners bend, custom plenum etc.
i still need to find a good TB and modern injectors ...

let me know if you are interested, the more of those we need the cheaper they will be ...
Andy

Just to add a little--common practice with the rice tuners and crotch rocketeers is to use as large of a plenum as possible will fit--with actually a smaller inlet opening into the plenum than the throttle plate---it is shaped into a venturi--

What the goal is, is to use the small venturi ( velocity increases magnanomously, with no loss of flow) which rams the air into the large plenum, changing the velocity to pressure---hence, " Ram Effect "

This is the only way turbines will survive at high speeds--just extropolate this practice into automotive--the practice is the same--but different--with turbines, the air has to be slowed down, or the engine will stall and flame out--piston engines are spark dependant, and never get to this speed, and hence can use this effect to an advantage--much testing has shown that when you increase the velocity of the air into the plenum beyond supersonic--and then have a large plenum to extract the velocity and turn into pressure--truely significant HP gains are achieved!!! Sometimes on the order of 20%

I have read SAE papers, and bike mag tests ( when they actually did this kind of testing--this technology is actually very, very old ) on jap bikes that make as little as1.9 HP per liter-to as much as 3.5, normally aspirated--the key element that they always hit on was that the velocity of the air entering the carbs was over 900 MPH----and the areas in the tract after the carb were of much larger volume than the carb throat displacement itself.

God, I have sooo many ideas on plenum designs and exhaust design based on my experience with aviation that it kills me I am not in a position to actually design and test this shit!!!

QUOTE (Brett W @ Feb 1 2005, 04:56 PM)

The numbers for the stock plenum and runners are for an engine that is operating at 70% VE in stock form.  It was meant to run  to 5500 making peak torque at a reasonable range and run all day long without overheating.  When you change the stroke,bore, rod length, valve size, and valve timing, you have just changed all of the variables that went into the design of the stock plenum.  (if VW put any effort into designing it to start with) Your 2270 has a higher piston speed thus drawing more mixture into the cylinder, higher compression burns more mixture thus making room for more fresh mixture, you have to get that mixture into the motor.  Designing a plenum will either be a cut and try affair or you need to spend sometime doing some pretty advanced math.

I admit I am way out of my depth when it comes to knowing exactly how to calculate plenum volume (if it can be calculated accurately at all.) So I may be bringing a proverbial knife to a gunfight. However, it seems to me that just because engine parameters change slightly doesn't mean you have to start from scratch. I just don't see how you need a plenum that is 3-5 times bigger, and a TB that is 1.3 times bigger with an engine that is only about 13% bigger, even with the other changes you are talking about.

Look at the 944. Here's an engine (in its weakest form) of 2479cc, 9.5:1 CR, making 150HP and 137 lb-ft of torque, with a redline of 6500. Its engine was designed as an autobahn runner from the start--hardly the VW 411 and bus-pushing slug the type 4 started out as. I bet you a dollar its plenum/runners/TB come pretty close to SirAndy's numbers.

QUOTE (SirAndy @ Feb 1 2005, 05:24 PM)

- a (common) plenum with a volume of 1.2L

OOOPS, typo on my end ... sorry about that ...

you want a volume of at least 2.2L for the plenum, that is for just the plenum itself, sans any runner pipes sticking out.

Andy

Bringing this post back to life....

Any thoughts on plenum design? I see we have the size area covered (somewhat) but what about shape? Square box with 4 tubes sticking out for runners? 5" steel tube with runners? Any better places to stick the TB? Top, front, side, backwards, up my... ?

I found a Ford TB that is nice and simple, just has a TPS on it... But, 62mm in diameter. Sounds a little big?

Also, what injectors will fit into the stock runner injector bungs? Looking for something a little smaller than the 2.0L and bigger than 1.7/1.8.

Thanks,
Tom

For starters, lay a 1 gallon paint thinner can on top of the motor, flat with the long sides facing the runners. Thats a start, hell, fab something up that basic shape or alittle bigger.

Geoff

Try to make a plenum along the line of this one.

This pleneum is from a GT3RS. I have a feeling Porsche Motorsports knows a thing or two about sizing and designing plenums.. If I get a chance Ill measure the volume f this particular unit.

Anywayz... it a box with runners molded to it. It appears to be one ply of CF cloth

nuther

Tim, if you would be so kind as to take a tape measure and the external dimensions of the Porsche plenum. I roughed an estimate at 18x12x3, that should be about 10 litres. Close to my 2.5 rule.

QUOTE

However, it seems to me that just because engine parameters change slightly doesn't mean you have to start from scratch. I just don't see how you need a plenum that is 3-5 times bigger, and a TB that is 1.3 times bigger with an engine that is only about 13% bigger, even with the other changes you are talking about.

You are assuming the factory dimensions are correctly sized for a stock motor? My stock 1.6 litre Honda motor made 108HP from the factory at something like 6500rpms. It uses a 56mm TB. Although I believe the plenum volumn to be less that 3 litres though.

A smaller plenum will yeild good throttle response and drivability. The plenum should not have a flat bottom with defined corners. Airflow doesn't like corners. I would not bring the runners in at a 90 deg. angle like the manifold pictured in a previous post. Airflow does not like radical changes in direction. Notice how Porsche brought their runners out the bottom. You could do the same or you could bring them out of a rounded plenum at the angle where the corners should be.

Brett,
What are the valve sizes of that motor?

QUOTE

What the goal is, is to use the small venturi ( velocity increases magnanomously, with no loss of flow) which rams the air into the large plenum, changing the velocity to pressure---hence, " Ram Effect "

Sort of. The ram effect does not necessarily come from that. The reason plenums taper into the TB flange is that you can just bolt a flange to the side of an open box, you will kill the airflow. Air does not like radical changes in direction, it will seperate from the boundary layer and create turbulence, killing your flow. Airflow likes to "see" less than a 15 degree change in boundary conditions, anymore and it tends to seperate.

QUOTE

This is the only way turbines will survive at high speeds--just extropolate this practice into automotive--the practice is the same--but different--with turbines, the air has to be slowed down, or the engine will stall and flame out--piston engines are spark dependant, and never get to this speed, and hence can use this effect to an advantage--much testing has shown that when you increase the velocity of the air into the plenum beyond supersonic--and then have a large plenum to extract the velocity and turn into pressure ....

Turbine engines have to slow air down because it chokes at levels supersonic and beyond. When airflow through an orifice chokes it will stall. Supersonic airflow is a very different animal than subsonic flow. I have seen what happens when airflow goes supersonic inside an induction system. An engine I was working with last year would flatline at 11200, exactly the point at where the restrictor caused the air in the intake to go supersonic. It is a phenomenon know as choke flow. This engine should have continued to make power into the 15500 range.

Velocity is good to a point in an intake tract. Too much is just as bad as too little. The airspeed in the intake ports should not see any more than about 300-400 fps, any more and you run into problems. Remember High velocity does not create high pressure. High Velocity creates low pressure. In the intake you high pressure not high velocity.

The "ram effect" that you mentioned is caused by "wave" tuning. Air is a really cool medium. It is a fluid but it also behaves as a gas. A fluid has mass and direction, but you can't compress it. A gas on the other hand can be compressed. Airflow can not be stopped and restarted instantaneously.

When the valves in a cylinder are opened pressure drop moves air into the engine, it will keep flowing even when the piston is starting to move back up the cylinder. This inertia will draw more air into the engine. When the valve closes the column of air moving through the intake tract can't just stop and wait for the valve to open again. It bounces off the back of the valve creating a "negative direction wave". As this wave reverts back through the intake port it has a certian velocity and mass. It will hit the plenum and either proceed to disipate somewhat or it will flow into another cylinder. The size of the plenum will determine how much a dampening effect is applied to the "wave" . When the wave bounces off the plenum wall it is headed back for the intake port. If the cam timing is matched correctly to the intake characteristics then this wave will have some extra velocity and can help push more mixture into the cylinder. The problem with "ram tuning" is that it only works in certian rpm ranges.

Remember all engines are a compromise. Factory stock engines will have compromises made in order to:
make the engine fit the engine bay
Meet emmisions and noise regulations
Make the car easy for grandma to drive to the grocery store
ETC.

Assuming that Porsche built it right from the factory is not the way to settle an argument. Porsche made the 3.0 litre S2 with 208 hp. Not really impressive if you ask me. Yes it is good but hell the 1.8 litre Intergra engine made 180hp from 1.8 litres. The first production car to make 100Hp per litre.

My SOHC 1.6 has 29mm intakes and 25mm exhaust. Not a great performance motor by any stretch but impressive for what is is.

QUOTE (Brett W @ Feb 3 2005, 09:41 PM)

Remember all engines are a compromise.  Factory stock engines will have compromises made in order to:   make the engine fit the engine bay   Meet emmisions and noise regulations   Make the car easy for grandma to drive to the grocery store   ETC. Assuming that Porsche built it right from the factory is not the way to settle an argument.  Porsche made the 3.0 litre S2 with 208 hp.  Not really impressive if you ask me.  Yes it is good but hell the 1.8 litre Intergra engine made 180hp from 1.8 litres.  The first production car to make 100Hp per litre.

Hey now, take it easy Brett W. Assuming Honda built it "right" isn't going to settle any arguments either, especially in a Porsche forum. And I doubt Porsche made many compromises for Grandma. Ever.

Back to the original question.

QUOTE (Tom Perso @ Feb 1 2005, 05:41 AM)

I am designing a MS system for my 2270 (163.86b cam, 48x38 valves, future Triad header). I am looking at running stock intake runners and possibly making a new plenum to run my Ford TB (probably from a 4.0L Exploder/Ranger). Are there any "design guidelines" that should be followed when making a new plenum, such as a certian volume required for engine displacement?

I never claimed to be settling any argument by what I wrote. I was asking how you figured a 300%+ increase in plenum volume for a 13% increase in displacement, given the stock intake runners. I'm still not sure. But I can respect what you know. Just don't read more into what I wrote than I intended. Like most here, I am trying to learn.

My suggestion was simply to look at something that works and start from there. You can look at Hondas, I am looking at Porsches (including type 4s.) Maybe Porsches don't work the same way your Hondas do, but I think I can assume Porsche's engineers know a thing or two about engine design. Did they build it "right?" I think you answered that yourself: "all engines are a compromise..." Not just factory stock engines. Yes, even Honda engines. So why dis the Porsche engineers for the compromises they chose? Don't agree with them? Fine. That hardly makes them wrong.

Speaking of compromises, just for fun let's look a little closer at the two engines you are comparing.
944S2 3.0: 208 HP @ 5800 RPM, 206 lb.-ft. @ 4100 RPM
VTEC 1.8: 178 HP @ 7600 RPM, 128 lb.-ft @ 6200 RPM
Obviously they are tuned for significantly different results. While the specific output of the Acura is impressive, that is only one of the many compromises that make the whole package. And those compromises may or may not have anything to do with the original question that started this thread.

I'm serious about that dollar. All good bro.

QUOTE (Bleyseng @ Feb 3 2005, 06:07 PM)

For starters, lay a 1 gallon paint thinner can on top of the motor, flat with the long sides facing the runners. Thats a start, hell, fab something up that basic shape or alittle bigger. Geoff

I have already fabbed something like that up. It was a cardboard box that was 10x4.5x5.5 and was 3.4L in volume (if I remember my math correctly). Looked like hell though

Half of me thinks to mount a Chebby 2.8L v6 TB on a stock manifold to get it running, then dink around with it. Hell, Tom Notch has the same setup on 2.7L T4 in his Notchback running Autronic and it works great. WTF.

And to put this in perspective, I'm not planning on getting this right the first time...

Later,
Tom

QUOTE

I never claimed to be settling any argument by what I wrote. I was asking how you figured a 300%+ increase in plenum volume for a 13% increase in displacement, given the stock intake runners. I'm still not sure. But I can respect what you know. Just don't read more into what I wrote than I intended. Like most here, I am trying to learn.

I am not working on ratios from the stock parts. I feel they are to restrictive. Based on the calculations I have done on some Honda engines and Suzuki engines I feel that the plenum on the 914 is too small for good performance in the range where a good high performance engine will make its best power. Although a plenum system will always offer less throttle response than an IR type system, it can make more overall power. Most guys with a 914 will want throttle response over maximum power.

QUOTE

My suggestion was simply to look at something that works and start from there. You can look at Hondas, I am looking at Porsches (including type 4s.) Maybe Porsches don't work the same way your Hondas do, but I think I can assume Porsche's engineers know a thing or two about engine design. Did they build it "right?" I think you answered that yourself: "all engines are a compromise..." Not just factory stock engines. Yes, even Honda engines. So why dis the Porsche engineers for the compromises they chose? Don't agree with them? Fine. That hardly makes them wrong.

I look at Honda because I feel that, as far a production NA engines, they are some of the most highly developed. I am not "dissing" Porsche engineers, I am making a statement about what I feel is some drawbacks to how Porsche does things. Please stop thinking of the T4 as a Porsche motor. Porsche would hardly have anything to do with this engine if it weren't for the original success of the early 70s cars.


All this being said I am stating my opinions based on my experiences and research. When VW decided to make the T4 an oversquare engine they had to do something to create torque. That is the part reason behind the 54+ inch exhaust primaries and common plenum design with very long runners and a small throttle body. Increase torque. When you modify the factory engine beyond the stock characteristics you move the powerband up in the rpm range. Thus creating the need for more airflow.

Not VW/Porsche but some tips on building a plenum here

I just think that a inline 4 plenum design doesnt share that much in common with a flat 4/6. The VW 4 has too long of runners to make real hp above 5000 rpms plus a small plenum but who in stock form needs it? I think Porsche's design shows where to head with the design.

Geoff

QUOTE (Brett W @ Feb 4 2005, 06:16 AM)

Please stop thinking  of the T4 as a Porsche motor.  Porsche would hardly have anything to do with this engine if it weren't for the original success of the early 70s cars.

Et tu, Brett?

It's bad enough when others NARP the 914, but one of our own?

QUOTE (Brett W @ Feb 4 2005, 06:16 AM)

Based on the calculations I have done on some Honda engines and Suzuki engines I feel that the plenum on the 914 is too small for good performance in the range where a good high performance engine will make its best power.

My input here won't be very scientific, but... When I was planning the turbo project I needed to move the TB to a location better suited for the turbo plumbing. This is on a 1.7 so the TB was horizontal on the driver's side. I cut my plenum neck off, rotated it 90 degrees, added about 1" to the length of the neck, hammered to shape, and rewelded it back together with the TB in the vertical possition. I estimated that I added about 5% to the plenum volume. The effect was a slight, yet noticable decrease in throttle response between about 2,700-3,100rpm. At other rpm's there was no noticable difference but it definitely lost some snap in that narrow rpm range. It was a little disheartening since that is typical cruise rpm and it's exactly the rpm I'm generally in when I decide to goose it. The good news is that for whatever reason, after increasing the plenum volume I was able to increase the timing advance by about 2 degrees (at that spot - not across the board) and got most of the snap back. I drove it like this for many months before the turbo was added.

-Ben M.

Turbo plenums are different. If you are going to go turbo I would copy the Subaru manifolds. They have really long runners and small plenums. I have a complete article on the Rally engine complete with pictures, but no scanner,

Tom, I still have the original plenum that we fabricated. Based on models with Engine Analyzer Pro, we found that a configuration or 130 cu inches and runner lengths of 10.5 inches would have the proper tuning characteristics for the flat four. It comes out to a very odd shape for the overall width of the engine, that's why it had a sweeping profile matching the top of the cylinder tin and case. I can post pictures when I return from CA next week.

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

I'd like to see that too Charles....I'm still on the fence debating between a single TB/plenum or dual Jenveys.

Going to have to make up my mind soon.

QUOTE

Tim, if you would be so kind as to take a tape measure and the external dimensions of the Porsche plenum. I roughed an estimate at 18x12x3, that should be about 10 litres. Close to my 2.5 rule.

I measured the (GT3RS) plenum today, it roughs out to about 18L the engine it was on is a 3.6L

Holy fuch! I'd need a plenum of 13L to follow the design of Tim's Porsche unit

BTW my /4 is going to be almost 2.7L

Thanks Tim, I knew it was big but not that big.