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.