IR vs. Plenum?, Bonafide dyno tests anyone? Options

[jhadler]

Hey all,

I realise that this may have been hammered at before, but I was currious if, on a stock 2.0L, there was any distinct advantage of going to IR throttles over the stock plenum (or some other single throttle plenum).

I know that the stock cam will limit the amount of air the engine can ingest, and that IR throttles will definitely NOT be the limiting factor on the top end, but with tall manifolds, and IR throttles, can a stock 2.0L run better than it could with the stock intake plenum. Assuming that both are running a programable fuel injection system that has been optimized.

Thought? Experiences? Test data? Dyno results? (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

-Josh2

[lapuwali]

Pure speculation and second guessing:

Several people who should know have stated that the stock 2.0 plenum setup is good for lots more than the stock 2.0 puts out, so a "stock 2.0" almost certainly won't benefit from changing the induction system. The numbers that get bandied about are 160-180hp is the upper limit for the stock setup. Dave Hunt is using the stock 2.0 plenum on a Raby 2270, and even Jake hinted that the stock setup would be, at worst, "marginal".

Now, if you're planning on changing the cam, and doing some headwork, and using an aftermarket exhaust, that's when you have to start worrying about the stock plenum setup.

From everything I've been able to glean, IR setups are primarily about throttle response (i.e., reducing the "throttled volume"), not about absolute flow. Plenum systems have the advantage of being easier to work with (no throttle synchronizing, easy to tap a steady manifold pressure signal, easy to make up efficient filtering for), but out of necessity have a fairly large volume between the throttle plate in the valves.

[jhadler]

Cool.

So, distilling this question a little more: If the target was a car built for competition (and no cams, the rules require stock motor internals), is there an advantage to running IR throttles or plenum?

If there's a top-end for mid-range trade off, it's maybe not worth it, but I'd like to get some ideas going here...

Thanks!

-Josh2

[DNHunt]

Josh

You say stock internals but, you didn't mention whether you would try to use D-jet or another system. I can't see D-jet working so I'm going to assume some other system.

I would have a hard time seeing much advantage with IR without internal changes. Throttle respose on the stock system is pretty good so no gain there.
I just have to believe that the cam is the primary thing holding things back.

Dave

[jhadler]

Yup, stock internals, but everything else (short of turbo-charging) is unrestricted. Kindof the opposite of production cars...

Already have the headers, and the stub pipes have already been matched to the heads.

So yeah, I'd be going with a programable FI system either way. I have hardware at my disposal for IR throttles, I also have a complete D-jet intake setup. The questions is, is it worth it at all to even try IR throttles or just stick with the D-Jet plennum?

-Josh2

[Bleyseng]

Definately the cam would hold you back as its setup so mild I don't imagine IR TB's would work very well or atleast be a pos to tune.

If you can, work on the valves, springs, lifters, pushrods to get more outta that end to get more hp and revs

[jhadler]

QUOTE (Bleyseng @ Jan 17 2006, 05:05 PM)

Definately the cam would hold you back as its setup so mild I don't imagine IR TB's would work very well or atleast be a pos to tune. If you can, work on the valves, springs, lifters, pushrods to get more outta that end to get more hp and revs

Geoff,

Not much I -can- do inside the motor... Like I said, stock internals...

It's sounding more and more like the IR throttle idea is only gonna yield positive results with a hot motor... that's not an option....

Anyone else? Jake?

-Josh2

[Bleyseng]

atleast better valve springs?

valve stem keepers?

[Jake Raby]

I did this test in October. On a 2270 "Daily Driver" combo the plenum was "Sufficient" for the powerband of that engine combination. I swapped it to a pair of 45mm TWM Throttle bodies and the engine made more power, and did increase efficiency (BSFC#s logged) and gained HP by 5% due to added RPM. Torque was boosted by near 10% at peak.

The same test was done in December with a bit more dense air on a 2270cc "Performer" combination. The results proved that the plenum was absolutely maxxed out as the individual runners made a solid 20% more power than the plenum did on the same engine- the plenum also required altered ignition timing to retain the optimum power numbers, something that was not a characteristic of the "Daily Driver" combo and certainly not conventional.

remember that plenum systems are seriously impacted by camshaft and vacuum signal dictated by the cam. This is the magical part of the combination (and between the Daily driver and Performer combos) that separates the men from the boys with designing an engine for a plenum, or Ind. runners- totally different schools of thought must be used to build each engine the best it can be.

Based upon what I have seen so far, the stock plenum is dead after 155HP, BUT it's "All in the combo"

Anyone serious about making a plenum based system work the best of it's ability is not very wise if they don't consult with me and use one of my cams to get the job done- period.

[Brett W]

Josh
For what you are needing, IR will be much better. The constant changes in throttle position will require a system that reacts very quickly. LIghtened flywheel, clutch, fan. etc will help the engine rev much faster in addition to the TBs. A plenum system will have some inherent lag in relation to throttle position as the column of air that has to stop and start is much bigger with the plenum setup.

I would have a set of the shortest manifolds you can find, attached to the engine and tune the exhaust system accordingly. This would be a very strong combination for autocross.


In all situations transient response is much more important than maximum HP. the faster you can recover from a shift or change in throttle position the faster your car will be. In an autocross you have a minute maybe two and have very little room for error. The better your engine recovers the more likely you will win or can correct a slight error that might eliminate you from the finals.

[lapuwali]

However, the original point was that the cam could NOT be changed. Stock has to be used. So, with an internally stock 2.0, having nothing more than a header on it, would the TWM throttle bodies do any good? Is the stock plenum good enough for this?

[Brett W]

Yes, IR will have it over the stock plenum. Measure the distance from the valve to the throttle plates. Now measure the distance from the throttle plates on a IR setup and you will see the reason why IR will be the best for his application.

[Bleyseng]

I thought that only mattered at wide open throttle. I thought one of the benefits of a plenum was the other cylinders were keeping the air flow into the plenum so it is "forced into" past the valve some. You don't get that with IR so you lose some torque.


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

[Dead Air]

QUOTE (jhadler @ Jan 17 2006, 03:10 PM)

there was any distinct advantage of going to IR throttles over the stock plenum (or some other single throttle plenum).

what's IR (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)

"Independent runners"?

[jhadler]

QUOTE (Bleyseng @ Jan 17 2006, 07:19 PM)

I thought that only mattered at wide open throttle. I thought one of the benefits of a plenum was the other cylinders were keeping the air flow into the plenum so it is "forced into" past the valve some. You don't get that with IR so you lose some torque. (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)

Right, but there's the other side of it too...

With an IR setup, you develop a "stack" of air fuel mixture above the intake valve before it opens (the injector has sprayed two squirts of fuel into the manifold), and the air has a straight shot down to the valve instead of having to turn throgh the manifold. Gravity assist if you will...

I really don't know however if the IR is any better than the plenum with a STOCK motor.

Jake, I have no doubt that the IR setep is better with a hot motor and more aggressive cam. My question is regarding a stock motor with a stock cam.

The plenum intake can generate intake pulses that can help draw in more air, but the IR can drive it into the combustion chamber better. So, what's better with the weak-ass stock cam in the 2.0L motor?

So, given that, will an IR intake be any better than a plenum under those conditions?

-Josh2

[Jake Raby]

QUOTE

Jake, I have no doubt that the IR setep is better with a hot motor and more aggressive cam. My question is regarding a stock motor with a stock cam

Can't help you there.....

Stock cams are against my religon!

[ChrisFoley]

I agree with Brett that throttle response will be better with an IR setup and tunable fuel injection, compared to the stock plenum and the same fuel injection system. Peak torque and HP won't be significantly improved however, and I doubt you would "feel" much difference between the two.

[Brett W]

Build a high butterfly injection system and you will pick up about 10% over a standard below butterfly system. If you are using a decent FI system, I would build a staged injector setup and really increase the torque curve.

[Bleyseng]

So what happened to Muellers IR setup that he was building? That would be a good test mule. (IMG:http://www.914world.com/bbs2/html/emoticons/mueba.gif)

[Jake Raby]

I'm also with Brett, based on my findings.