FI Plenum Design, MS'ing my 2270 Options

[Tom Perso]

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

[DNHunt]

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

[maf914]

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.

[Jake Raby]

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..

[Tom Perso]

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

[DNHunt]

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

[Tom Perso]

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... (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

Thanks,
Tom

[914efi]

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.

[Jake Raby]

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.

[Tom Perso]

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. (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) Just like everything else I've done (IMG:http://www.914world.com/bbs2/html/emoticons/ar15.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/ar15.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/flipa.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/flipa.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/icon8.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/icon8.gif)

Thanks
Tom

[Jake Raby]

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.

[Tom Perso]

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

[Brett W]

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.

[Reiche]

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.

[DNHunt]

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

[Brett W]

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.

[SirAndy]

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 ...
(IMG:http://www.914world.com/bbs2/html/emoticons/smash.gif) Andy

[jwalters]

(IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif) 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!!! (IMG:http://www.914world.com/bbs2/html/emoticons/mad.gif)

[Reiche]

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.

[SirAndy]

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.

(IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif) Andy