Please advice: Maximum RC with CIS.

[zarpoxx]

Hello,

firstly, let me introduce myself: My name is Gisleno and I'm from Madrid (Spain) . I have a 964 3.3 turbo with the following modifications:

Sc cams (Option X33 )
K27 HFS (for sell)
1 bar
GSF headers
Cat bypass
LFW
Bypass waste gate
KN air filter
Forge Diverter valve


With the original turbo (K 27 7200) gave 415 hp at the flywheel.

I intend to make deeper changes, but keeping the CIS which I have the following questions:

I would like to improve the off boost mode (performance and response), but I do not know what the RC I must to go (taking into account a maximum pressure of 1 bar blowing, but if you say that is too risky could lower it to 0.7 or 0.8).

You see dangerous operation at 8.5 RC? And a 8.0 RC?

My choices would be:

1. Install only 97 mm pistons of JE Pistons RC 8.0 to 1
2. Install only 97 mm pistons of JE Pistons RC 8.5 to 1
3. Install Mahle pistons and cylinders with 3.4 RC 7.5 to 1 or 8.0 to 1.
4. Install Mahle pistons and cylinders with 3.3 RC 8.0 to 1 ( I donīt know if this option is possible)

What option for you is most advisable? Do you recomend JE pistons? I have read that JE pistons with Mahle cylinders cold make noise (due the different tolerance between materials), but that means I will have problems? They will have durability?

What is the real gains that I could expect from these changes? It is worthy? What is the total amount of horse power that I could expect?

which is the theoretical limit between CIS and RC?

Which is the theoretical limit between RC and 1 bar boost (with CIS)? And with 0.8 bar?

On the other hand, as I will do a complete review, could you say to me what pieces should change (valve springs, ect ...)

Thank you very much in advance

P.D: A picture of my car:

[RarlyL8]

Welcome and nice car!

What are you goals?
Do you have to tear down the engine or just want to?

Changing your C/R (compression ratio) will help driveability but is not necessary to help power. CIS is capable of handling up to ~430WHP at 1.0bar with mods. Making your engine capable of producing 430WHP does not require a C/R change.
Adding twin plug ignition will allow a small bump in C/R or boost.

[David]

Given the choice, I'd go with Mahle, but I couldn't find any in the right CR when I built my engine.

I have 98mm JE pistons in Mahle full fin cylinders running the Mahle clearance (I forget the actual clearance) as recommended by EBS. So far so good.

Unless you're running 0.8 bar boost or less (or race full only), I'd stick with 8.0 CR or less.

[zarpoxx]

Upss, sorry for the mistake (RC means CR, compression ratio).

Rarly8, my goals are maybe a little more power (450 at the flywheel) but my main interest is make my car more responsive at low speeds (off boost mode). That is why I am very interest in higher the CR, but I donīt want to spend money in a mod that is not good for the engine (too much pression) or in a mod that I couldnīt feel (I want worthy mods, like the headers).


125shifter, how do you running with the mahle clearance with JE pistons (how do you did it)? I said that because in all the threads that I read, all the people said that it is very noisy (Je pistons in Mahle cylinders) due to diferents materials between JE pistons and Mahle cylinders.

Who is EBS?

Do you running with CIS? Did you feel the higher CR Instantaneous when you drove at first time the car with the new CR?

Thank you in advance.

Bye!

[David]

In the past, JE recommended more clearance than Mahle, so they had a bit of cold piston slap.

EBS is www.ebsracing.com They did my valve job, crank work, and cylinder replating (although I'm sure they outsourced the plating). I also bought my pistons and rods from them. I don't remember the exact clearance, but 0.0015" or 0.04mm comes to mind.

I'm running EFI. I did so many modifications during the rebuild and EFI conversion that I couldn't tell how much the CR added to the off boost power.

Our biggest problem with CR is the air-cooling. We just can't run the CR that modern engines can.

Here's a chart from A. Graham Bell's, Forced Induction Performance Tuning book:

This is for a watercooled engine, so I wouldn't exceed these numbers.

[lucittm]

Gisleno,
I have a similar car without the X33 option. It is interesting to me that you want better off-boost performance and response. I believe the purpose of the X33 option was to provide better top-end performance and a sacrifice of some off-boost power.

I think the X33 cams (and heads) cause your manifold vacuum to be lower off-boost (The reason for variable cam technology). The cylinders will not fill as fast under the lower vacuum and the performance suffers slightly. On boost, which is really at higher RPMs, the power is greater because you are "on the cam" and forcing the air through the manifold.

According to Adrian Streather's book, Porsche Enthusiasts Companion, the X33 option also changed the valve timing. You could advance (increase) the valve timing to improve your bottom-end performance. I would be curious what the factory recommended for valve timing with the X33 option. Mine is .60-.65mm.

Could you also explain your item: Bypass waste gate?

I am afraid if you increase your C/R above 8.0 and run at 1 bar, your street car (from the picture) may not be too reliable. For track purposes it would be fine.

As fas as CIS and C/R, I don't think there is a relationship there. CIS just controls the AFR and regulates how well the engine can flow air to the intake side of the head.

The graph that 125shifter provided is useful if you assume a 50% efficiency for the intercooler. At 1 bar, your C/R should be below 7.0 with premium fuel. With racing fuel, you might be able to push a C/R of 7.5.

If you change out your cams, heads, etc. (X33 option) let me know, I may want to buy them.

Good Luck,
Mark

[cole930]

I got a real kick out of this particular thread as it is so typical of us fanatics and
our constant quest to wring the last drop of quickness out of these old sleds.
I grew up in the 60's street racing best 2 out of three for $20 to keep buying
parts to make the old small block Chevy a little faster. Now I'm older than dirt
and still have never owned anything I thought was fast enough.
I've got an old 80 Row 930 I've owned for almost 20 years and still continue
the quest. A couple years ago I took the old girl out and tried to see just how
fast she would go. I have all the usual bolt on mods, just about everything short
of efi. As I shifted from 3rd. to 4th. I past the 140 mark and she was still digging
and about 160 I shut her down. On my way home I thought why in the hell do
I need to go over 160 MPH and where would one do it safely. I can't afford to
track the car and I do all my driving on the street. I just want really quick and
about a 150 top end.
Hence it came to me that we always overlook the obvious, gearing. I called
Chris Fisher, original owner of Powerhaus and renowned mad man in a Porsche.
We had a conversation about 930's and gears and I ended up horse trading him
out of a 934 short track trans that he had used in the infamous Powerhaus
"White Car" featured in European Car April of 1996. The trans has a 8:37
ring and pinion and FE,HQ,QQ,WL gear set. I also added the original 934 short
track headers and a K28 11/11 turbo used on the "White Car"
Did this ever wake the old girl up !!! I have to be carful because the rush
wants set my defibulator off. The car will still run nearly 160 but gets you there
very quickly and it definatly addresses any off boost acceleration issues.

[RarlyL8]

Cole - can you post or send me a picture of those short track headers?

Gisleno, the build sheet you listed should get you close to 450CHP. If you are having off-boost lag something is wrong. Your setup is pretty close to optimal for CIS driveability.
Have you checked your AFRs and ignition?
Can you describe how it runs now?
How do you like the sound of your stock muffler with no cat? There are some improvements that can be made there but will not help off-boost.

[cole930]

Brian.

I'll get pics. of to you.

Cole

[zarpoxx]

125shifter, thanks for the chart and the info. It is very useful.

lucittm, thank you for your imputs. The valve timing that the factory recomends for the x33 option is 0.9-1.1 (Mine is 1.1)

Bypass waste gate (sorry if it is not correct) is a empty tube from waste gate to the tail. No mini-silencer, no mini-cat. It was made by Scart exhausts.

If I change this items, I will let you know.

Cole930, I agree 100% with you. Many times we are ridiculously obsessed with more power or speed, perhaps when the solutions are as simple as you say.

I think that sometimes we have to say: Stop. But you know, we cant and the spiral goes on...(thinking in new cams, new Pistons, new...)

Rarly8, I will check my AFR and ignition, but I think it is ok.

Now the car runs fine, but I would like more off boost response, thatīs all.

My stock muffler (the right side), is a little empty (open and a little modificated), and with a cat bypass the sound is great. Maybe not too loud (I had to take off the bypass muffler made by scart (Gooseneck) because this was VERY noisy, but with the stock muffler it was very soft...So I think I have the perfect combination.

Thank you for your help.

Regards,

[RarlyL8]

The setup you have now is pretty good.
If I were to make one change it would be to dump the HFS for a turbo with a lower boost threshold.
Other than that, time your cams for torque and get your AFRs perfect.

[9dreizig]

Zarpoxx, are you running a stock IC ??

[lucittm]

Zarpoxx,
Thank you for sending the valve timing with the X33 option. You might be able to go to 2-2.2mm for more torque, but I would check the piston to valve clearance first because I don't know how much there is at factory spec settings. Although I do think the turbos have a bit more room than the Carreras in the combustion dome area.

We refer to your bypass waste gate as a "zork tube" or a straight pipe. A zork is really the pipe that comes off the outlet of a turbo. Why do we call it a zork anyway. Does it sound like zork when you blip the gas? Then zork is an onomatopoeia. And who came up with THAT word?

I would follow RarlyL8's advice (dump the HFS) and look for someone who could create a custom turbo application that would increase boost at lower engine RPM. I think that has to do with the AR ratio in the compressor and turbine sections. By specifying a turbo with greater AR in the compressor and lower AR in the turbine, better low engine speed turbine performance will result and this will give you quicker boost at the expense of peak engine power.

One more thing, can you determine that you have no leaks in your intake system? I found a leaking intercooler hose with a smoke test done at a SAAB/Volvo dealership who had the smoke machine. The car ran great off-boost because there was not a vacuum leak (the hose was pulled in). But on-boost , there was a leak and I was probably only getting .2 bar at the top of the RPM range. The machine indicated a leak and the smoke showed where it was. It was fixed in 2 seconds and they only charged me for an hour of shop time.

BTW, I run the same exhaust as you (cat bypass to almost stock muffler) and the sound is good. I hope I can lean my AFRs enough to pass smog.

Enjoy,
Mark

[jryerson]

I have heard you can get up to 500hp with CIS, there are some shims you can remove the will make the dist run more fuel, my car 77 930 has great low end and is very fast, SC cams, RSR Flywheel, SSIs, K27 11, 1 bar, bored out TB with euro dist, K N filter, all emission stuff removed including AAV, used SC cam timing so it pulls quicker than a SC from a stop till boost then hold on