250 bhp from CIS ?

[911st]

I think most the power difference was exhaust.

Also playing w the SC cam timing can get you to a bit higher peak HP number which was the 3.0 Carrera trick.

Porsche has been suspected to play w HP numbers at times.

I am rusty but if I recall, 1 point increase in compression is about 3+% more power at that level.

On a 72 911S I had we got the 8.5 CR up to about 9.2 by decking the case. Every motor is different.

[afterburn 549]

Reading the numbers posted by Porsche...makes wonder alot about their HP figures Eruro or what
same cams, same crank. same C/r and they claim diff Hp for ROW (more) I am thinkin they water the figure for US market or Hype it for ROW

[davidbir]

OK, let's have 3 more beers each and talk about fitting MFI....

[911st]

Porsche may have been under pressure to build a car to equal the 2.4 911S at 210 hp so there could have been some of that.

However, aggressive cam timing, no cat, no air pump, more aggressive tuning, of A/F ratios and ignition could take one from a smog motor 185 to 210.

I think the USA Carrera had its cams timed for TQ and the ROW 3.0 Carrera was timed for HP. Latter the 3.2 Carrera split the difference

I suspect we got the small port motor for smog reasons as it helps with achieve a better air and fuel mixing. Rember w CIS fuel is being sent to the intake port all the time and it just sits there until the air start rushing by. The small ports helps along with the shape of the CIS piston to complete the mixing.

[Gary.H]

Originally Posted by afterburn 549

Reading the numbers posted by Porsche...makes wonder alot about their HP figures Eruro or what
same cams, same crank. same C/r and they claim diff Hp for ROW (more) I am thinkin they water the figure for US market or Hype it for ROW

All UK SCs make at least stock power on reputable dynos, usually more. It's not uncommon for stock 204 SCs to make 207/208. I don't know about the US figures but the Euro SC power figures are definately true, if a little conservative to tell the truth ! Definately no hype

[safe]

Originally Posted by afterburn 549

Reading the numbers posted by Porsche...makes wonder alot about their HP figures Eruro or what
same cams, same crank. same C/r and they claim diff Hp for ROW (more) I am thinkin they water the figure for US market or Hype it for ROW

All ROW SC engines has the same big ports as the US 78-79 cars.

[Rick V]

Intake port size and length help to determine what the engines strong points will be. They can be figured as exhaust. Long, narrow= torque, and are better on the bottom and mid. Short and big are better for HP and come to life in the midband and upper end. 78-79 US cars are better on the upper end and don't fall off at 6k, the later 3.0's pull better up to 5500-6000.
Depends on what you want from your car.

[Mothy]

That would make sense.

I have a US spec engine 83SC which had its cat converter replaced with a bypass about a year ago and has had most of the other emmisions stuff disconnected or removed (eg. Oxygen sensor)

A couple of weeks ago it was on a dyno and they found it was leaning right out - so it was recommended I fit a ROW fuel distributor. Now, the car is like something else new - the difference is dramatic. At a recent track day I was over 4 seconds faster per lap and I can feel the difference in the torque in the 2k to 5k range. My lap times are now on par with ROW spec SC's.

When I bought the ROW fuel distributor, it came with the complete CIS system including larger runners - when I asked the mechanic if we should fit them as well he recommended not to as the inlet valves would still be smaller ones and it would be better to have the smaller runner to keep the velocity of the mixture high.

Tim

[911 tweaks]

does anyone know the "best" combination to extract the hi rpm end performance benefits of the 78-79 lg port and the sm port low end torque?
Maybe a totally (larger displacement) different engine ?
Bob

[afterburn 549]

to Quote Bruce Anderson loosely He said (and the info is now old) that his exp @ adj. cam timing did little - retarding or advancing
On the the Sc cams I put in from EBS there was a recommended number for performance and a other number for ..what ever................. DUAHH , you know what I went with

[davidbir]

Originally Posted by Mothy

That would make sense.

I have a US spec engine 83SC which had its cat converter replaced with a bypass about a year ago and has had most of the other emmisions stuff disconnected or removed (eg. Oxygen sensor)

A couple of weeks ago it was on a dyno and they found it was leaning right out - so it was recommended I fit a ROW fuel distributor. Now, the car is like something else new - the difference is dramatic. At a recent track day I was over 4 seconds faster per lap and I can feel the difference in the torque in the 2k to 5k range. My lap times are now on par with ROW spec SC's.

When I bought the ROW fuel distributor, it came with the complete CIS system including larger runners - when I asked the mechanic if we should fit them as well he recommended not to as the inlet valves would still be smaller ones and it would be better to have the smaller runner to keep the velocity of the mixture high.

Tim

This is the first mention I have seen of different fuel distributors--can anyone else provide info/experience on using ROW fuel distributors in US spec SCs?
Is it possible this car was just in need of a good tune up?

[Rick V]

JMO, If I was looking to make a monster 3.0 I would ditch the CIS. I love CIS but if you are gonna try and make a monster, you should have a fuel system that will handle it. A stand alone fuel managment, with a sequential injection system. That will cover anything you can throw at a 3.0. High CR, wild cams, twin plug, done. The cost isn't very nice though. a 3.6 swap would yeild much better results.
I for one don't like engines that are built on the ragged edge of staying together, and a monster 3.0 would be such an engine. The best part of a 3.0 is the fact that they are 300k engines. Why ruin that durability?
This is all my opinion.

[911st]

Putting large port runners on a small port head will not change the velocity of air flow much at all into the cylinder head. The small ports will still act like a spray nozzle. The air flow will accelerate when it comes to the small port and create more swirl in the head when is bounces off that funny bump on the CIS piston.

The added disturbance might reduce total flow and fill rates at certain RPM’s.

I met a guy that ran a 2.8 race motor in the SCCA. Everyone else was running big 40mm =/- ports on there motors. He ran a well developed 35mm port and it had no problem supporting 260-290hp. He was the class leader. I would think that a properly cleaned up and polished small port head at about 35-36mm would be better than a stock 39mm large port head on a 3.0 motor. The large port SC heads did not have a good reputation for air flow for a long time so I am surprised to see them so popular now. I am suspect of any single dyno run supporting large port heads as the best as there are other factors that can effect HP when the heads are changed.

I saw a results of bench testing the air flow of small port and large port heads and the small ports were concluded to flow better???

Also, I would not expect the euro head to have much effect on the A/F curve.

The shape of the cone around the metering plate and the control pressure determined by the WUR is what affects the AF curve.

I suspect just setting the base CO at the best point and maybe using a euro WUR might make most of any gains available here.

Running a lower control pressure will progressively richen the motor w increases in air flow. Thus this is the source of fuel tuning along w base CO setting.

If more is needed, S-car-go Racing modifies the cone around the metering plate and that could be looked into.

Is the CP of a euro WUR different and what are its specs compared to the US unit?

Taking the cat off and dyno tuning a CIS motor cold be the best investment and produce the most gains I suspect. I would play w the base CO, control pressure, and ignition advance to achieve the best performance/HP.

Having ones injectors cleaned and balance checked at the nearest diesel repair shop along w a new air cleaner can help to.

Sport Cams might add up to 10HP. An increase in compression from 8.5 to 9.5 might be good for up to another 10hp if one is lucky. Headers might add some HP in the 2500-4000 rpm range. Adding a sport muffler might extend HP near red line some. The stock heat exchangers are not as bad as some like to think.
The 930 guys are just starting to play with a digital or electronic WUR to tune there A/Fs through out the rpm and boost range. This device should make solid gains on SC's and enable a near perfect A/F curve and better throttle response.

I did these years ago on a C2 Turbo. I had used a frequency valve that bypassed the WUR so I could lower CP along with a modified additional injector controller. Made a big difference on my A/F rations. I also used a drop and catch strategy I came up with to lower CP a bunch with acceleration and picked up a lot of throttle response. This could translate to the SC's.

If I recall BA concluded that setting the cams to Carrera specs was the best compromise. If ones total goal was to build a CIS race motor, there should be some increased efficiencies available at high RPM by playing w the cam timing. For everyone else, the Carrera specs makes for the best of breed setting with little compromise.

I am not an expert, this is just my opinions.

CIS is a great system.

It is not worth changing to CIS but if the cost is $3k plus to go to somthing else or if you live in a smog state where a change will trigger problems with the visual inspection, it is not worth removing it for most.

Often, selling the SC motor as a runner or core an buying a plug in Carrera 3.2 is a more economic approach. Just chip it and add a cat bypass for a solid 230hp+.

[davidbir]

Thank you! That is possibly the best post I have seen

[afterburn 549]

Rick V, not for dispute but for info There is a P nut up here in Seattle area that puts dwn over 500 Hp to the wheels (turbo) with CIS . Saw it on the dyno in person.
He had the fuel head reworked by ??? he called the procedure a "V" or something. Anyway It is Impressive ! ( a reliable oldl CIS system)
He said you have to be real carfull with them B4 the fix, for they all go through a Lean spot on the climb.

[Rick V]

Originally Posted by afterburn 549

Rick V, not for dispute but for info There is a P nut up here in Seattle area that puts dwn over 500 Hp to the wheels (turbo) with CIS . Saw it on the dyno in person.
He had the fuel head reworked by ??? he called the procedure a "V" or something. Anyway It is Impressive ! ( a reliable oldl CIS system)
He said you have to be real carfull with them B4 the fix, for they all go through a Lean spot on the climb.

Ok point taken but is the cost of making the CIS worth it? For me I would rather go with the mega squirt or simular. Don't get me wrong I love CIS and have no plans to change mine, just playing the devils advocate. And your buddy is the exception not the rule. That must be a fun ride.

[911st]

Turbos are a different story and a slippery slope and quite adictive.

There is plenty of fuel in a SC to support 300 or more hp from what I understand.

And it for the most part automatically adapts to any exhaust, capacity change or mild cam you want to put on it.

Just needs a little dyno tune to get the most our of it or your own wide band O2. And for most, just setting the CO is all that is needed.

EFI definitely has the potental to be a better/best set up.

However, for the 10-20 extra Hp and mabie a bit better throttle response is it worth the cost effort to start from scratch, source all the parts, access the start up tables, get the ignition and fuel right for WOT, curse, transition. Then get the cold start and modifications for intake temperature right. Then end up w a system that only the builder can hope to understand and repair.

CSI is proven, trouble free, maintains resale value, is smog friendly, has a large pool of parts easily sourced, understood and can be worked on by almost any import mechanic.

It is all good but a roll your own system is a labor of love and the savings over buying a turn key conversion form a proven tuner (or just a full PMO kit) is earned in full.

Instead of the 100 hours rolling ones one, work a little overtime at the job, add to it the money saved sourcing IFI parts and just get the big jugs, exaust, and cam.

Been there done that.

[afterburn 549]

And another thing (in the voice of Yosemite Sam ) LOL There was a great big thread a while back......Sequential inj. is a big word, it stated rather then sequential...as once you reach any RPM to speak of there is not much squirting going on they are all pretty much continuous after idle...........makes sence to me

[javadog]

Originally Posted by 911st

If I recall BA concluded that setting the cams to Carrera specs was the best compromise.

Back in 1983, I played with cam timing on an '83 SC that I had then. Running the cams at the retarded spec was definitely better for acceleration. I never dyno'ed the car, as chassis dynos weren't available to me then, but I did perform a lot of carefully timed acceleration runs and there was a fair difference. No question is was quicker. I have no idea where my notes on that car are stored but it seems that in a second gear run from 3000rpm to 6000 rpm, it was .5-.7 seconds quicker.

JR

[Mothy]

Originally Posted by davidbir

This is the first mention I have seen of different fuel distributors--can anyone else provide info/experience on using ROW fuel distributors in US spec SCs?
Is it possible this car was just in need of a good tune up?

Try this thread back from 2002
Difference 3.0 vs. 3.0 Euro

It covers a lot of the info and some good discussion on this topic as well.

In my case the issue was probably more to do with the Frequency Valve not being used anymore, meaning the Fuel Distributor leaned it out at the top end. By going to the Euro (non FV version) it fixed the problem.

What I do know is that my driving has not got 4 seconds per lap better - and I know from another track day that the other mods done were only about 1 second a lap improvement - so lets call it 3 seconds a lap - thats still a massive imrovement on a 74 second lap.

Tim