An interesting look at CIS

[rdane]

I was at the local speed shop today discussing EFI. Because most of us run the same dyno and the owner was kind enough to allow me a look at his 3.2 dyno numbers, I had Alex run a comparison from the computer logs. The A/F ratios were also very comparable fwiw..



The Varioram/Motec 3.2 in BLUE
"911 with US 3.2L, 9.5:1 , stock longblock that has been balanced and fitted with adapted 993 Varioram, MAF. K&N, Magnecore, 951 injectors, SSI, Sport muffler - all controlled by MoTec CD and Fuel management and mated to a early mag 7:31 915 box. I had the 993 Varioram adapted to my stock longblock 3.2L (now sadly history, due to a recent rod bearing failure after 200 track hours).... We did gain 20 hp and 30 ft lb of torque at 3500 rpm. Varioram starts to help the torque curve as low as 2500 rpm, then fills out that curve to about 5000 rpm. At 5900 the resonance flap acts to extend the HP another 500 rpm to about 6500. It is an amazing piece of technology that actually works."


CIS 3.4 in RED
3.2 crank, Puater rods and bolts, Mahle 98 P&Cs @ 9.8 for a 3.364l, SFL Piston skirts, Ceramic coat on the Pistons, EBS valve spring, TI retainers, APR case studs, New injectors, new exhaust valves (which is why I tore the engine down), boat tail the crank cases and half moon the cylinders, Bored throttle body
match and polish the intakes, 20/21 webcams, SSI, sport muffler
light flywheel.

It shocked me! Motec and CIS comaprable? I would have never believed it.

[jpnovak]

Dane, I just noticed that you coated your piston skirts and tops. Who did the coatings for you?

You are still running single plug right? Any problems with detonation at 98mm and 9.8:1? Are these a CIS type dome or a wedge dome?

[geof33]

Just proves a well dialed CIS is just fine. Hard to justify the cost for the performance. On the otherhand, the reliability MIGHT outweigh that some!!! Great info either way

[rdane]

EBS did the coatings for me Jamie. 8000 miles ands still single plug on mostly 92 octane Chevron. Having a hard time justifing finishing the twin plugs.

Costs? I believe the Motec and Varioram alone cost a LOT more than my full build.

[jpnovak]

Thanks. My 3.2SS using RSR pistons should come out to be 9.8:1 based on emcon5's measurements. I have not torn down the engine to CC on my own. I think I could get by with single plug but am always looking for other examples.

Now if Aaron (burn-bros.) gets his twin plug rotors in production...

[rdane]

Jamie, sorry I missed that the first time. I am using the Mahle, Max Moritz wedged shape pistons. They were specifically designed for single plug in 98mm. Lot of difference between that an an RSR dome for single/twin plug applications.

I wouldn't

[geof33]

Jamie,

Definately do the Moritz/mahle 98's. You can get away with a bit more comp ratio with a single plug system.

[Jeff Alton]

Hmmm, Rdane why go with the efi you seem to be collecting parts for?!?!?! Or are you just like me, not happy unless you are tweaking! How would that 3.4 go with some PMO's??

Jeff

[jluetjen]

I'll try not to rehash (ohhh, but it is sooo hard!!!! )

You keep giving the CIS credit whenever you compare your oversized 3.4 to a 3.2. If you were to say that it makes more sense (and fewer cents) to invest in capacity then in sophisticated injection systems -- I'd agree with you!

But you always start with the premise that it is the CIS by some magical properties which allows you to get the performance that you are -- and this just ain't true!!!

If you were to compare a CIS'd 3.2 to your Varioramed 3.2 (as you off handedly did) you'd find that the Varioramed engine would outperform the CIS version every single time. Will a Varioram'd engine outperform a CIS'd engine by more then (3.4/3.2 - 1 = ) 6.25%? No.

So if the choice is increasing the engine's capacity by 6.25% or buying a Varioram system -- the question would be which is cheaper? If the P&C's plus any headwork is cheaper then a Varioram, get the extra cc's. If the Varioram is cheaper, get that.

As far as the CIS is concerned, you can see the strengths and weaknesses of the system in your charts.

Strengths: It self-adjusts for any changes in capacity (which by definition means changes in torque output).

Weakness: It is airflow limited and so at engine speeds above the peak torque point, the CIS will ultimately limit HP since it can only flow so much air through the system. Take a look at the higher end of the RPM range (5200 RPM and above) where the torque and HP for the CIS'd engine falls off a cliff while the smaller 3.2 engine keeps on pulling.

Basically it is not a fair comparison to compare engines of two different sizes and conclude that the performance is due to the CIS. Using the same logic, you could say that aluminum cases are comparable to magnesium cases because the aluminum 3.4 liter has comparable performance to the magnesium cased 2.7 RS engine. Imagine that, aluminum cases make just as much HP as magnesium cases!!!

That statement completely ignores the fact that the RS engine is significantly smaller then your 3.4 liter, but also weighs significantly less. The reality is that they are two different approaches to solving a problem (how to hold the cylinders and support the crankshaft) with each have different strengths and weaknesses. There is nothing special about either aluminum or magnesium that allows it to produce more HP.

So the premise of this thread -- "An interesting look at CIS" could have just as well been "An interesting look JE pistons" or "An interesting look at aftermarket pistons" or just about anything else and been equally valid.

[Elombard]

Mr. Dane

Sorry to change the subject but I am anxiously awaiting your detailed running reports on the WEVO gateshift you recently purchased. I really appreciate the analytical way you evaluate products/changes that you make on your car.

Take care

[rdane]

Good morning Mr. Lombard,

The Wevo gate is the second one I have purchased. I have about 9000 miles now on my first WEVO setup. This one is for a second tranny with longer gears I am doing as a spare for long road trips. (Seattle/NYC) I sent you a PM on the details.

John, I made two simple comparisons. Dyno numbers are the most clear. Easy enough to read that for us simple guys. I have a reasonable idea of the money involved in both conversions so mentioned that. My real point is CIS gets a bum rap IMO, not that is superior. When a Motec and Vario ram engine doesn't blow a similar CIS engine away I have to say much of what has been said over the years about CIS has to be questioned if not just chit canned. Magical? NO. It is decent system we can live with in a street rod, seems a fair statement.

You make a number of assumptions that are incorrect, John. The HP and torgue are actually even more comparable than the graph shows. The drop of the CIS that looks like "falling off a cliff" is just simple throttle lift. That should be obvious.

Running the CIS car to the 7K rpm rev limiter would show a similar graph relationship to the 3.2.

The Motronic 3.2 is actually a 3.164 liter engine. My 3.4 actually a 3.356 liter engine. That is a 5.72% gain of the 3.4 CIS over the Motronic "3.2" in displacement. Some would argue this 3.2 used the very best engine management and induction. I was more than surprised that a "super" 3.2 didn't thrash a wheenie 3.356 CIS with only a 5.72 gain in displacement.

The 3.4 torque numbers are 5.53% higher than the 3.2. Not the 5.72% one might expect. But then a 0.19% loss to CIS would seem to be an easy choice over the costs of Motec let alone Varioram for most of us. With the facts more clear I think we are comparing apples to apples here on induction and not apples to oranges as you want to imply John.

The numbers are what they are. Helps to have some hard data to make good choices.

I know what my car will do. Just trying to share some info for the other CIS owners out there looking at options.

BTW I think a 3.356L, 98mm piston, Motronic injection engine would beat both of these engines for costs and in performance.

It will also be worth noting the changes a EFI system and twin plugs make to my 3.356L engine. That info will be available shortly as well.

[lendaddy]

Is the VR Motec owner happy? Are they still in the tuning stages ar have they concluded "mission accomplished" and this is the final result?

When I was looking into EFI I found lots of guys would have eureka moments when they were doing final tuning.

On edit: I see his run was done a couple years ago so if he hasn't made any changes since........

[smestas]

Whats with the Varioram/Motec big dip from 3,500 to 4,00 rpm in the torque curve?

It also seems that the CIS has alot nicer area (table top) under the torque curve then does the Varioram/Motec.

[rdane]

My impression was yes, he was very happy with the end results. (engine was recently destroyed by a spun bearing)

He won at least one national title and many regional titles with that engine pretty much "as is" on the dyno sheet from our recent email exchange. Car was featured on the cover and in an article, in EXCELLENCE several years ago.

Originally posted by smestas
Whats with the Varioram/Motec big dip from 3,500 to 4,00 rpm in the torque curve?

Wondered that myself. I have seen it on several stock 3.2s to a lesser extent.

John said: Basically it is not a fair comparison to compare engines of two different sizes and conclude that the performance is due to the CIS.

My conclusion was not that CIS out performed the Motec or varioram...but more like "what the hell happened to the advantages of Mortec and Varioram". I would have thought with all the hype on both sytems (and their costs) 5.72% on displacement would have been easy to make up.

IMO the better arguement for a street car would have been the differences in throttle response, not what happens after 6500rpm. and the factory rev limiters.

[jluetjen]

According to the dyno sheet the owner of the 3.2 is our own Randy Wells who posts here fairly frequently.

I would have thought with all the hype on both sytems (and their costs) 5.72% on displacement would have been easy to make up.

As they say -- "There is no substitute for cubic inches!". As far as deliverying a 5.72% increase in HP, I'm not aware of many modifications which by themselves will delivery that kind of improvement with the exception of pitching the pollution controlled exhaust systems. In fact if you told most engine builders that you could increase the performance of an engine by 5.72% just by tossing the CIS and bolting on Varioram system -- they'd jump at it. The issue of course is cost. But then again that's why a lot of people do pitch their CIS and replace with EFI. Putting a Varioram on your "3.4" will most likely also deliver some pretty significant improvements over what you have now with CIS.

Performance per $, I think that you've got a great engine. It shows that by adding capacity you can increase the performance of the engine across the rev range within the limits of the CIS system. The biggest constraint of the CIS system is in the total amount of air (read HP) that it can flow. Up until you reach that limit life will be good. Just quit banging on this CIS thing because the CIS is not providing the performance. The cc's are providing the performance -- in spite of the CIS, or at least within the performance envelope of the CIS. I would like to see someone generate 250 HP from a stock 3.0 CIS system (without resorting to a Turbo or Supercharger). I don't think that you can do it. In fact I doubt that you could even get to 230 HP to be honest.

PS: The falling off the cliff was referring (metophorically) to the engine's torque curve starting at 5200 RPM. Of course I could recognize the shut-down at 6700 RPM. But your engine's torque curve was pretty well shot by 5500 RPM (6000 at the most) at which point it would make sense to shift to the next gear and drop the rev's to the 3700 RPM range and start again. To put it differently, your engine is within 90% of it's peak torque from 3500 to 5800 RPM. The 3.2 is within 90% of it's peak torque from 3300 to 6200 RPM. Hmmmm....

[beepbeep]

Is 3.2 pull done with Varioram? are HP-figures wheel HP or corrected crank HP?

[rdane]

Just quit banging on this CIS thing because the CIS is not providing the performance.

I have never claimed CIS provided any performance enhancements. To imply I have is silly. I have stated many times that CIS isn't as bad as many would like you to believe for a street car. I have also tried to show a reasonable option to a 3.6 transplant for SC owners.

There seems to be a lot of interest in telling us the limits of CIS.

What you missed in your "90% calculations" is have more torque low in the rev range with big bore CIS than the 3.2 does. Far away from the 5.7% gains would indicate. More like 15+% once you are below 3500. That makes a huge difference in daily drivability, and lauch, CIS limits and all. The dyno pretty much spells that out as well.

Be happy to post the numbers on a PMO 3.2 short stroke as well so you can point out the limitations of CIS there too
Not much of a limitation short of serious track time from what I have seen so far.

Goran the numbers are @ the wheels.
The 3.2 has Motec management and a complete 993 Varioram induction installed.

[jluetjen]

OK Dane -- We're in agreement. CIS is not "Bad" for street car performance. Not like air-pumps and smog legal exhaust systems are Bad for performance. So let's just let the CIS thing go.

What you missed in your "90% calculations" is have more torque low in the rev range with the 3.4 (so as not to bring up C?S again!) than the 3.2 does. That makes a huge difference in drivability. The dyno pretty much spells that out as well.

True -- This because at any given rev level below the peak torque engine speed, a larger engine will ALWAYS have more torque then a smaller engine. This is simply a fuction of a larger engine consuming more mixture with each revolution and converting that fuel and air mixture into thermal energy. This is true with any motor.

If you want torque in the normal "driving" range, there is no substitute for cubic inches. Check out the torque numbers for these Ford 7.3 liter diesel engines. Would it be fair to say that these are an improvement over your 3.4 because they make more torque down low were people spend 90% of their driving time? (Note that the torque chart is the upper set of lines)



I bet you that if you could come up with a 6.8 liter 911 engine and hook it up to your C?S system that the torque curve would look pretty similar to the dashed blue line. Would that be a better engine then what you have right now?

Be happy to post the numbers on a PMO 3.2 short stroke as well so you can point out the limitations of CIS there too

Go ahead! It would be interesting to compare and contrast that with 3.2 with Varioram and a 3.2 with the stock CIS. That would be a fascinating comparison of the strengths and weaknesses of each of those induction systems. If you want to send me the data I'll plot them on the same scale and post the results so that there will be an "apples to apples" comparison.

[rdane]

John all I have really tried to do with my build and the on going data collection is give us CIS guys some options that show good performance gains and that can be had either a little at a time or for less than a professional 3.6 transplant costs.

The 3.2 Motronic cars are even a cheaper candidate for performance upgrades than CIS.

I think eveyrone agrees "there is no replacement for displacement". But seeing the numbers and pretty pictures helps those educationally challenged like myself

But that said you have to see comparisons to carbs, Megaquirt and Motec and other combinations to make good decisions. Thiose are most often 3.2s to date. If I had thought I failed in my 3.4 I would have already had a Varioram 3.6 put in.

Driving along side turbos and lwt 3.6s tells me I am still at the party and I want to share the info I collect. Be interetsing to see Ralph's 3.5 numbers when he gets it off the dyno.

Sorry John no complete graphs...

Here is the written material I have gathered:

From Randy Jones' Iris,
"46mm PMO, carbed 3.2 short stroke. with dual plugs, Iris:
281 H.P./ 244 ft./lbs. torque at the flywheel at 6700 RPM's.
(27% hp and 21.5% torque loss by these figures)
Changed muffler and put her on the DynoJet to rejet the carbs and this is what we received. S-CAR-GO Racing dual in/out stainless steel muffler change and we received 222.1 HP and 201.5 ft/lbs. torque measured at the rear wheels at 6500 RPM's"

From Randy Wells,
"911 with US 3.2L stock longblock that has been balanced and fitted with adapted 993 Varioram, MAF. K&N, Magnecore, 951 injectors, SSI, Sport muffler - all controlled by MoTec CD and Fuel management and mated to a early mag 7:31 915 box.
The difference between using the stock
extrude-honed 3.2 manifold and the Varioram was immediately apparent to Chris and I on our first test run. There is much more push from 3500 rpm on up and the engine wants to keep going at 6K. Chris Powell has dyno sheets on my engine and can share them with you. Basically, this is what we found: the Varioram did not change peak HP (214) at the wheels (actually went down 2 HP), but peak torque went from 193 to 203. All these figures are with Triad muffler and street gas. Flowmaster and race gas gives 5 more HP. The biggest difference was a 15 HP and 20 ft/lb increase with the Varioram beween 3300 and 4000 rpm and 20 HP and 25 ft/lb increase at 4500 rpm. By 5000 rpm the difference was down to 5. Peak HP occured at 500 rpm higher with Varioram and did not fall off as quickly (it was still 200 at 7000 rpm)."

215hp and 203# at the rear wheels. 220/203 with the Flowmaster and race gas.


DB's CIS 3.4, 20/21 cam, SSIs and a 2/2 muffler.
Also on the same Dynojet last dyno with 92 octane chevron
223 rwhp @ 6100rpm
213 rwt @ 4100

[jluetjen]

Unfortunately the peak HP #'s don't tell you much.

But let's throw this open to the others --- Who's got 3.2 Dyno graphs of different configurations? I know jpachard has posted his in the past, so we can look that up. Anyone else?

Come'on in! Now that rdane and I have stopped slinging bricks at each other it's safe now. Honest!!