Intake Port Size Affects - CIS
 

What are the real world affects on performance of the CIS 930 engine as you increase intake port size?
I understand the principals and am looking for specifics as they apply to our engines and CIS. I know many of you have opened up the pancake manifold and bored out the injector blocks. How big did you go and what was the effect on driveability and power? Is 38mm a better compromise than say 40mm?
Thanks!

I went to 40 mm for intake on head and pancake manifold
stock compression
CIS
Turbo Kraft S camshaft
rs fly wheel 11 lbs
currently with a zork

drive-ability off boost is like stock , may be better

on boost is ....well ...crazy

I still have not completed Tuning, I have a safe -conservative , 0.8 bar tune.

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/767012-forced-deal.html

How big did you go on the exhaust ports? I'm thinking 40mm intake and 38mm exhaust.

stock size ported & polished

I just wrote a long detailed post and hit a wrong key and lost it... i'm too pissed off now to rewrite it all.

Mine has 40 mm intake ports, manifold holes, and 40mm aluminum injector blocks with CIS Flowtech 20% over stock fuel head and the short version is it runs GREAT!

I had a very long phone conversation with Chris Carroll about this topic not too long ago. Conventional wisdom holds, but there is indeed some nuance with CIS.
The short story: 38mm and 40mm are a better choice than stock for all but stock motors.

Regarding my case, I was planning to stay stock, with some mild upgrades to maintain off idle performance. I was going with 98mm 8.5:1 JEs, and DC15 cams, maintain CIS via a Leask WUR. Chris said I was nuts, as with the upgrades I was planning, I’d be doing nothing but choking the motor.

I asked about 38mm I/E and he still felt 40mm I/E, and even 40I/38E, consistently performed better than 38mm I/E, given this spec. Shortly thereafter, I committed to a set of 3.2 Carrera HEs (38mm ID) as my exhaust. Although I wanted your headers, the slippery slope had already eviscerated my wallet and the $100 price tag was a compromise worth making. Otherwise, would have gone 40/40.

There's a MUCH longer story, but my fingers got tired while typing. If anyone cares, I might finish it - but there's a second level of depth around the fuelling resolution and control CIS provides.

Good info, thank you guys!
I'm thinking now I may go 40/40 and port my header flanges to transition from 40 to 38.
What is this "second level of depth" you speak of for CIS? I don't anticipate any issues but am always open to ideas.

Maybe I should mention mine also has a Brian Leask adjustable control pressure regulator, CIS Flowtech 20% over stock modified aluminum fuel head with lambda removed, and 964 cams timed at 1.26mm intake valve lift TDC before the intake stroke.
It has B&B headers, Garret GSX 61 ball bearing turbo (Hybrid TO4Z) with billet compressor wheel and a very low restriction baffle gutted B&B muffler.

Idle AFR is around 13:1, 3000 rpm steady cruise is around 15:1, and under boost it is never leaner than 11.8:1 and that's with E10 93 octane Florida pump gas.

The front and rear fuel pumps are both Bosch 044.

Good info Jim. You have no lean surge at 15:1 cruise? That's great!

As someone who's battled acceleration/transient enrichment with EFI, does CIS's strategy change with faster velocity/higher volume intake flow?

Meaning, if you went from stock heads and cams, then went to ported heads and say 964's, does the larger volume of air ingested during throttle movements maintain OEM AFR's or does the engine exhibit lean spikes?

CIS is mechanical, you simply tune the mixture when a change is made.

Right, but what about the "step up pump" system?

Not sure what a step up pump system is.
The volume of air follows the throttle and does not change significantly until on boost. You tune on 4 planes and all is fine. The early Euro system has no Lambda so idle CO% is set manually. I have seen no significant tuning changes until on boost with the big power engines. With those the extra fuel head flow and control pressures need mesh up.

I'd like to hear what this "second level of depth" is because I know CIS real well and have no clue what you're talking about.

What is this "step up pump" system?

This is what I was referring to. More volume, same response time can make CIS a bit cantankerous, because more air, same fuel = bigger margin for error. You can tweak for pig rich at idle, but that isn't great either. Which is why we all love EFI's performance: a feedback driven, completely granular fuel curve solves this.

If you have a modified fuel head, CIS pressure gauge, AFR gauge in the car and know how to use them than it's easy to adjust around all that... even with bigger ports, 964 cams, headers, free flow muffler, and a higher flowing efficiant turbo.

^ agreed - it is just a little trickier. I am working on getting one of the FrankenCIS digi WURs working. I think this little bit of hardware is going to make a world of difference.

I have a euro CIS fuel injection system and understand it is desirable due to much larger fuel lines etc. If upgrading my turbo would any tuning be required to my fuel system or will the CIS compensate?

934 cis replica
 

Dear fellow Pelicanites,

we have done some 934 replica fuel heads and cone systems.

The fuel delivery is good for 700 hp plus.

Here are some pictures - best reg.

Dirk

http://forums.pelicanparts.com/uploa...1421430990.jpg
http://forums.pelicanparts.com/uploa...1421431099.jpg
http://forums.pelicanparts.com/uploa...1421431706.jpg
http://forums.pelicanparts.com/uploa...1421431885.jpg
http://forums.pelicanparts.com/uploa...1421431977.jpg
http://forums.pelicanparts.com/uploa...1421432053.jpg

I was wondering when you'd jump in, Dirk!

This isn't a debate on CIS tuning and modification to handle the extra power, only what the expected impact from ported heads will be on driveability and what the ideal size should be.
The CIS mods are handled.
It sounds like 40/40 porting is tried and true with no affect on driveability which is great news. If anyone else has input on porting sizes and driveability I'm all ears.

I guess I'm complicating things, I'm totally ignorant what acts like a "step up pump" (like a carb) in CIS.

From lots of novice tuning, I can tell you, adding a little extra fuel can make low end feel a lot peppier than leaner.

Was just wondering if extra flow hurt transient response of CIS.

Hi Kenik,

cis became sort of a passion - what a wonderful system.

By AFR result curves that we got from Porsche / Bosch Motorsport systems we where inspired to see where the limits are.

And you can go sky high with CIS....

When it comes to porting we found that CIS likes an anti reverse even more then other systems.

It should be integrated into the inlet plenum but also, as all capable exhaust builders know, is very effective on the ex side.

It gains power, torque, efficiency as well as drivability.

Also keep the flow velocity on a certain level since on this way ignition advance can be some deg. more which means a lot to our engines in overall performance.

Best reg.

Dirk

Dirk, anti reversion like a reed valve? Or an anti reversion step machined into the face? My motor is still apart, so there's still time. ��

Anti reverse
 

Yes you should get a step into the system.

Use a 40 mm inlet port together with a 37 mm or even somewhat smaller plenum.

A 40 mm inlet fits to a 37 or 38 mm exhaust port used with a 40 / 42 mm header which would correspond then.

On this way you achieve the following effects:

Inlet: the flow volume is moving laminar towards the valve where it is reflecting while the cam is on base circle and so the valve is closing. The flow then tends to move backwards and this happens 90 % on the port surface. At the anti reverse step it is partially stopped and reintegrated into the positive flow while the cam hits the ramp and the valve is opening. Also hold in mind that the gas volume is expanding into the port and this is influencing the load temp. on a positive way too.

Exhaust: here you minimise back flow which keeps exhaust gas out of the combustion chamber and you just want fresh gas there when it gets ignited to make the best possible mid pressure.

Best reg.

Dirk

Ah - bummer - I already opened the manifold up to 40mm. I'd have to machine a ring/sleeve to get there now - or it goes to reason that I could buy a set of 38mm injector blocks - or sleeve my 40mm set down to 38mm. Interesting.

Yes you can do it with the injector blocks - tapered from 40 mm down to 38 maybe 37 mm. On this way you get the best from all worlds....

Volume

Flow speed

Anti reverse

Best reg.

Dirk

That is interesting.
I have always focused on volume and velocity and did not think anti reversion on a boosted engine to be significant enough to warrant the effort. During this build I can possibly work in an easy way to test that setup and measure the difference in my application. Is it more a drivability feel or does it show up as significant on the dyno?

Anti reverse
 

On na engines it is common tech and used on more or less all modern sport / race engines. The effect is always in direct relation to some basic configuration just as cam profile, TDC overlap and plenum design. For example it is a huge difference if open air horns are used or there is an air box with an intelligent specific design.

For sure there are some effects dominating others.

And for sure there is no out of the box solution - it is the knowledge and experience of the engine builder to get a working package close to the optimum right away.

Always picture the system and make all components work in a package.

The effects are very beneficial to charged engines too.

Best reg.

Dirk

Which is why I question the effects of using a enrichment delay solenoid on a mildly tuned engine (SC cams and headers).

That's the trick; finding someone who knows how to do it.
It's possible that a professional builder who has experience in building racing engines could do this.
Can anyone recommend someone?

Builds are a package/system which is the only way to do it IMO. You have a goal, this is the formula, you can't just use what you have or like.

Thank you very much Dirk for sharing your information.
I'm going to try anti-reversion on the R&D engine we are building. Never done this on a boosted engine before and will have to devise a way to detect and measure the difference while using the same heads. Inserts or sleeves for the injector blocks and header primaries might do the trick.

The "trick" there is to enrich that sweet spot corresponding to peak torque, but not too much. It takes a few dyno pulls to find it. If tuning from stock you have to lean it out as stock gets into the 10's. This number changes depending on the build, some turbos transition slowly some very fast.

Rich creates quicker spool from what I've found.

Here is a plot of flow verses valve lift. I can't remember where I stole it, but I have seen several others that agree with at least the 3.2L data, so I have no reason to doubt it at this time.



http://forums.pelicanparts.com/uploa...1421710202.jpg

An all out effort with 40mm ports gets you around 18% more flow over the 3.2L. The issue is that, beyond a certain point, the intake valve is becoming the restriction, not the port. I think that point is pretty close to the 3.2L 40mm.

Here is a reference chart to give an idea of port, valve, and cam relationships.

I see no reason that the lower port velocity would mess up the CIS fuel delivery, especially at WOT. At part throttle there is probably considerably more wall wetting, but I don't think you can tell from a performance standpoint. It is more of a flow consideration than a fuel system consideration.

http://forums.pelicanparts.com/uploa...1421710613.jpg

Cfm
 

Dear Sirs,

please hold in mind that cfm numbers are rising automatically when you open a port.

So as this is simple arithmetic it should be clear that on na or turboed engine it isn't that simple in real life.

An open port and a cfm number is just a part of the story.

Other effects are dominant and so it very often happens that better cfm numbers are making less power.

Just for a good orientation have a look on port sizes of the last 3,6 l Monoturbo 965 - this ports are making easy 650 plus HP on relative low boost.

In this case also a good relation between inlet and exhaust port diameter.

Best regards

Dirk

That is the heart of what I am trying to determine: the best size to port the intake and exhaust.
The intake port size on 3.3T compared to 3.6C2T is HUGE along with lift difference.
I'm going to use the suggestions from post #26 and also machine a set of injector blocks to taper from 40mm-38mm. The intake manifold will be ported to match the top of the injector blocks. I can stagger the intake/exhaust port sizes and header primary ID 1.5mm for anti-reversion. All these parts have be machined so one-off. Will be very interesting to see how it all comes together.

It would be interesting to see how much the stepped port helps with the reversion problem using CIS and a camshaft with more duration and overlap.

The pulse
 

There is a coherence but:

Backflow by valve reflection and pressure pulse inside the system are connected in timing but two different effects.

Anyhow we found the anti reverse positive on all kind of CIS application - starting with Golf GTI MK 1.

Best reg.

Dirk

There is one more consideration. What is the collective wisdom regarding increasing the throttle body dia. I changed my son's 3.2L with DC cams, headers and Wong chip. My son was following a thread on boring out the throttle body so he had it done. I didn't expect much as the change was not significant however the engine loved this change. No dyno data.