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