Stock CIS system - Power Capability?

[mikedsilva]

Someone has asked me to build his 3.0 Carrera engine with a bit more oomph (chasing 230-240)

It has the stock low compression 8.5:1 pistons so these will go in the trash.

He wants to keep it at 3.0litres so a modified piston will be required; not sure if they are available off the shelf or if have to be made (still waiting on a set from CP for 3 months and counting....) In my mind, if we are using a new 95mm piston then the cylinders will likely need to be recoated, in which case, why not open them up a little or find some decent 3.2 barrels along the way?

But he also wants to keep it with the stock fuel system.

So the question is, how capable is the stock CIS?

He requires heat so is looking at SSI - they make the normal 1.5 inch primary but I'm inclined to use the 1&5/8 primary. Would the larger primary hinder torque down low?

As for Cams, maybe something from John D or W Knight but what?

I guess I'm trying to find the 'sweet spot'....

[porschedude996]

Interested responses.

[panama911]

With stock CIS, I'd say about 70 DIN HP per Liter is a realistic goal for a streetable car with some torque down low...

[Henry Schmidt]

Over the years we've built many of these projects.
9.5:1, DC 21 or Web 2021, 1 1/2" SSI, sport muffler (Dansk makes a few options) stock distributor curve and clean up the CIS. Generally that means removing everything except WUR, AUX air valve, cold start injector, stock euro fuel distributor and go back to venting the air box (fitting next to the air filter) to the oil tank instead of venting the a air bellows between the throttle plate and the air flow meter. The hose for this is available on the 74-77 CIS.
This combination should should performance in the 230 range. Very driveable, great acceleration, go fuel mileage and reliable.
The cams can at times seem lumpy but it's a hot rod, live with it.

There is a poster on this forum who had one of these engines who might give some insight as to how they perform.
Fintstone

[fintstone]

Yes, I can vouch for Henry's approach. Mine replaced a 2.7 that ran well but left an oil smoke cloud. Henry used the Web cam 2021s which were popular at the time. As he noted, plenty of power/torque. No cam issues in this case...very smooth.

I wanted the car to look and feel like it did from the factory, just have more horsepower....so I asked Henry for something not too radical that I could use for a daily driver (bulletproof and good gas mileage on pump gas). I did not want to use carbs but still wanted more hp...and wanted to keep my heat (so he used SSIs and a Dansk stainless steel muffler that I already had).

The car was a '74 so the engine was mated with a 7:31 gearbox and 15-inch Fuchs which made the acceleration even better. Henry used a later 3.0 engine but earlier, free flowing top end from a 78...and polished/increased port size. Of course, he also used his own Supertec head studs and put his shop's massive expertise in every tiny detail (which may well account for what a great engine it is/was). Henry's engines are magic. He is the best.

My intent was to add a state-of-the-art AC system later (and did). The engine was powerful enough that it really did not notice/care that it had to run the compressor. I found a used Sanden on Ebay which was/is a bit lighter and better designed than the original (consumes a few less hp). Here is a thread on that: https://forums.pelicanparts.com/porsche-911-technical-forum/288251-obligatory-32f-ac-vent-image.html#post2644484


Henry built this engine way back in 2003. If you click on my garage, you can see photos of the work of art (in my black 911). I will post a couple below. Note the powder coated AC bracket and zinc plated double pulley that Henry added for me/my future AC plans. That car was later totaled, and the drivetrain was transplanted into another (yellow) '74 that I still own. The engine is bulletproof. The engine and working with Henry was my best experience/performance upgrade ever.

My butt dyno tells me at least 230 hp (maybe more). The car accelerates much better than other SCs (or other 3-to-3.6-liter cars I have encountered) ...and my pristine '89 3.2 Carrera (at least within legal speeds). The gearing is a bit restrictive at very high speeds. Every 911 fan/owner that has ridden in it or driven it has been quite impressed. In fact, I think even Henry was surprised when he took me out for the initial test run as he could really smoke the tires at will (serious smoky burnouts in a midyear 911). I later increased the wheel width and put better rubber on it so as to better take advantage of the extra torque. I upgraded the suspension in the yellow car as well (torsion bars/sways/shocks/struts) during the drivetrain swap.

[Old H2S]

Look up ICARP on here and talk to him about set up for adjustable fuel distributor.. I got rid of all the CIS junk except for the CSV that I have hooked up to the rear window defroster switch but do not use. I have an adjustable fuel pressure regulator with fuel pressure gauge and a AFR gauge. When it is cold I set the pressure to 1.2 bar and the car starts down to 23 F so far without the CSV. As soon as it starts I bump it up to 1.5 bar. and it will idle at 12.5 AFR, drive off and turn the pressure up to get any AFR you want.. Hooning around set it at 13.5 , want big MPG set it to 16.
I do not know what the max HP the set up will pull is but I built a 3.2ss with max ported heads, Nikies, Carillo rods, Carillo 9.8 compression pistons with the M1 cam and DLC coated everything that moves, Stomski solid chain tensioners so I quit dealing with factory junk, SSI exhaust with what's his names 2 in 2 out muffler. Total HP ? Haven't a clue, maybe Henry, Ian or William can guess, but turning the fuel pressure up to anything I want says I can support more than I've got. What is the limit of the tubing going to the injectors?
I do a lot of silly stuff.. and am retired so I have time to fool around and see what I like and what to change when I pull down the engine for a change or a look see. See my thread on the rear main seal.
I would like the thank Henry for all the great ideas he spills and Ian and William and Neil and and ...

[panama911]

A properly set up, tuned and maintained CIS in these fine cars doesn't need nor deserve such a hack job...

Also, it is not advisable to have the driver monitoring AFR and fiddling with manual control pressure adjustments at speeds these cars are built for ;-)

[Old H2S]

Then why the added junk yard from the beginning of CIS to the end?

[Old H2S]

Pearl clutching ensues..

[Henry Schmidt]

Originally Posted by panama911

A properly set up, tuned and maintained CIS in these fine cars doesn't need nor deserve such a hack job...

Also, it is not advisable to have the driver monitoring AFR and fiddling with manual control pressure adjustments at speeds these cars are built for ;-)

Seems a little harsh for a guy looking to have fun with his own project.
The old hot rod guys would welcome the self expression.

Then to add safe driving tips......."thanks dad, can I have the keys now"

Back to CIS performance

The challenge with CIS is the metering plate.
On acceleration the vacuum (turbulent air) pulls the plate up pretty aggressively.
As soon as you start to cruise the air across the plate goes laminar.
This reduces the pressure needed to lift the plate and as a result, the fuel mixture leans out.
We found that putting a small 1/16" (.062) lip on the metering plate breaks up the flow and keeps the mixture more consistent.
A 2.5" semi-circle (looks like a smile) silver soldered to the bottom edge of the plate (top on a turbo) will make your fuel ratio smile.

If you have an old piece of engine tin laying around, that will do just fine.

[panama911]

Sorry Henry, I didn't intend to sound harsh or to offend anyone by using the term 'hack job'.
It's just because Mike was asking for the limits of stock CIS for an engine he builds for someone else (customer?) - and for this, I think having to manually adjust control pressure and AFR is a workaround at best... it should be possible to get satisfactory results without having the driver constantly dialling in what is needed?
As you indicate in your posts, there is ways to optimize CIS performance, starting e.g. with deleting emissions stuff, using the right vacuum assisted WUR etc... could you elaborate on your suggestion to modify the metering plate some more?
Again, I didn't mean to offend anyone and of course old hot rod guys may do whatever pleases ;-)

[Old H2S]

Henry great idea.. I have a very expensive laser welder sitting here that will do this job quick.
All yours FREE, everyone else 20.00 plus shipping, one day turn around.
Micrometrics
P.O. Box 262
Buxton, NC
27920

[Henry Schmidt]

I apologize for the crude drawing but here is the basic idea.
By rotating the x axis you change the way plate transitions through the metering body venturi.
The idea originated for me working on an Indy Car.
In the early seventy's INDY Car was having teething problem with wing deployment. The wing wasn't providing the desired down force without adding an inordinate amount of attack angle. This was developing some break-away drag so the aero guy added this lip to the top edge of the wing. This allowed for a reduced angle of attack without reducing down force. The down force was increased while the drag was reduced. It was eventually given the name Gurney flap after the car owner.

Keep in mind that this isn't some miracle HP bolt on. It simply helps to keep the engine from going lean on cruise/constant throttle.

Why is this important? With increased compression comes higher detonation possibilities.
If you're cruising under your maximum torque range (under 4500rpm or so), then accelerate aggressively there is a moment when the engine is in a lean running condition and your chances of detonation are greatly increased. Over the years we've seen a plethora on 9.3:1 and 9.8:1 pistons broken from a combination of lean running and poor octane fuels.
This little trick can reduce your risk....reduce mind you. CIS engines basically run their best on the edge of lean if you're tuning for performance, be careful.

[mikedsilva]

Getting back to the topic of piston choice.
Since we are staying with CIS, and upping compression, does the the absence of the Porsche designed pistons affect the compression ratio we can target with regular CP or JE pistons?

My understanding was that the special shape of the factory pistons was designed to encourage swirl and even burning due to the position of the plug. Does using a std symmetrical piston put me at a disadvantage? (not sure I'm asking the right question the right way...)

[Turbo_pro]

Originally Posted by mikedsilva

Getting back to the topic of piston choice.
Since we are staying with CIS, and upping compression, does the the absence of the Porsche designed pistons affect the compression ratio we can target with regular CP or JE pistons?

My understanding was that the special shape of the factory pistons was designed to encourage swirl and even burning due to the position of the plug. Does using a std symmetrical piston put me at a disadvantage? (not sure I'm asking the right question the right way...)

The major challenge with lean burn Hemi head engine is detonation.
The idea of the squish chamber piston it to ignite the mixture quickly and completely.
Hemi's offer a obstacle for that. If you want compression you need a domed piston. If the dome splits the combustion chamber, the flame front is obstructed and the fuel burns slowly.
So how do you make a piston that allows the flame front to burn all the fuel quickly. A flat top piston is best but given the Hemi chamber, that's impossible. Mahle's old remedy was to concentrate all the fuel in a confined space. Enter the squish chamber dome.
The next innovation was the wedge piston, in the Porsche world that was the Max Moritz piston.
The latest version of the Mahle high compression Hemi piston left most of the dome but created a flat area between the valve pockets.
One of our dear departed members took that design and incorporated it into a Porsche 911 piston. This is probably as good a design as you could want if signal plug, lean burn is your goal.
If you want to replicate the MM piston, CP already has drawings for that piston.

See the link:https://forums.pelicanparts.com/911-engine-rebuilding-forum/1120123-my-new-piston-3-0-a.html

Max Moritz (still available)



New Mahle Hemi piston



Fred's innovative design

[ahh911]

[QUOTE=Turbo_pro;12201300]

See the link:https://forums.pelicanparts.com/911-engine-rebuilding-forum/1120123-my-new-piston-3-0-a.html


Looks like more than a dozen sets of these have been out for maybe 1.5 years, I'd like to hear some feedback from someone who's installed them...

Phil

[Henry Schmidt]

Originally Posted by ahh911

See the link:https://forums.pelicanparts.com/911-engine-rebuilding-forum/1120123-my-new-piston-3-0-a.html


Looks like more than a dozen sets of these have been out for maybe 1.5 years, I'd like to hear some feedback from someone who's installed them...

Phil

Maybe post that question on the "My new piston 3.0+" thread.