m42racer

Compression ratio is a HUGE factor in a 930 engine. If any one thinks otherwise, build one and see. On the very best fuel, you are still limited to a more conservative CR. Comparing a 930 CR limit to a 996's, is absoluetely stupid! The 996 is a pentroof combustion chamber, not a hemi. For those who do not know their engine design, hemi spherical chambers are always limited to CR values and Valve timimg. The later pentroof is center plugged, and 4 valves. A major design difference.

If you run very high CR #'s, you will be limited to lower Ignition advance numbers, and lower boost numbers. Many other factors are also apparant. In many cases the engine becomes very peaky, as timing is retarded and boost is limited. In cylinder temps become very high, and Spark Plug design is an issue also. Many times you are required to pull back the nose of the plug to keep it cool, and to prevent plug induced detonation. Its been done many times before. The results are always the same. There is definetely a sweet spot in these engines for CR, timing and boost. with the pump gas available today, 7.50Cr will be near the limit. Anything higher will require lower boost/retarded timing. These two factors always compromise the overall engine performance to much.

Cylinder to head sealing is not an issue anymore. There are ways to seal the the joint today. The use of sealing rings and headgaskets works very well. Don't be confused with the nirosist ring application. This cast iron ring was first done to stop the fire torching effect of a mechanical fuel system when the throttle was lifted slightly. This design was never meant to seal the heads. As the ring was never installed under crush the gases can escape around. It was there to stop the flame from burning thro the same parting line.

Brent 930

Around $2600

Luke

which is why it would be silly to compare it to a 996 tt's CR of 9.4:1. The 996tt has much better engine mang.

actually i'm comparing it to the 2.0 talon motor my buddy is building for Scca pro rally. the only reason to bump compression there is because he needs to run a 34mm restrictor and w/ that in place, there would really be no point in spinning the motor over 6000rpm. He bumped from 7.8:1 to around 8.5:1. He isn't looking for a peaky motor, just power that will always be there.

just showing off his car















I figured you would have lots of charts..... that is why I asked. I'm genuinely curious, how much of a bump the average 930 owner would make, and what the before / after tq curves look like. But you still haven't told me what kind of a bump we are even talking about. It looks like you are trying to defend yourself, but nobody is attacking you.

I have not called anybody a liar or threatened anyone, I asked YOU if you had charts because I have always felt that you are 'the man' ( and the man to ask ) , but looks like you are more of 'the jerk'

PorschePhD

Wow, A Jerk??? I ask a series of questions to see exactly what you are wanting and I am branded a Jerk??? I have devoted my name, reputation and support to numerous boards and continue to share real world use and knowledge...My stance was not a defensive one. This is a first...

I made reference to the 996 so you can see every situation has an application. Stupid I think not. I have run 3.6 and 3.8 standard air-cooled motors without the heads I say have the Supra syndrome and have run as high as 8:5:1. Mind you this is all on after market injections and certainly with all my it's crossed and my i's dotted. The AFR is normally set at a modest 12.9s around 1.1, 1.2 bar. This makes for a nice strong motor. A 930 motor should not see anything more than a half point bump coupled with a slight bump in displacement to 3.4. The two make very little in the HP department. Maybe 15 on its best day, the the low end throttle response is certainly improved. Keep in mind that 1 bar is normally the max with this type of setup. That is with modifications to the furl head in some capacity. The 993TT is a prime example of what is possible with better management on the masses side. I shoved 1.2 as a low setting through mine for no less than 30K miles and never had an issue nor toppled the 13 mark even in the hardest of circumstance. Of course the sealing surface is not in the mark of the combustion strike and the OBDII was certainly tunable. This is what is attainable with a good EFI and well built motor. The most you can expect out of the CIS is 475HP. This is the norm not the exception. If you can hit this mark with 1 bar and added compression then why not have it all now rather than a twist of the ****? There are plenty of people that that run more than that on CIS and push the limit, then there are those motors we build knowing the owner will look for 1.4 bar. All in all a bump in compression is a positive that requires restraints depending on the application.

gsxrken

Seems to me that boost, which is measured within the intake manifold, is not the ideal metric to use here. Boost speaks indirectly to cylinder packing, but has no insight into the mechanical squish ratio that will take place on the compression stroke. Ideally you would want a "boost" gauge that took it's signal from the combustion chamber. Then, the more initial CR you had the less boost one would need to arrive at the safe limit of total combusion chamber pressure, but less manifold boost in this scenario wouldn;t mean the power trade-off Brent mentioned. I think I've convinced myself.

PorschePhD

A very loose calculation is for every 3 pounds of boost equal 1 CR. This is a very loose calculation, but will get you in the general area.

Talking about squish area....Look at these.
930 twin plug head


956 Heads
notice the water jacket ports
996 Twin Turbo head

Luke

So, roughly, for every 1:1 bump in CR, you must run 3 psi less... ? how soon before you get out of the efficiency of the k27? Do you have k27 maps, by any chance? I can't seem to find one that I could convert to lbs/minute for comparison's sake.

PorschePhD

I have to see if I still have the maps scanned. Maybe Kevin has them handy? I will look.

If you are trying to stay at a certain CR then this is a good rule of thumb. The K27 7200-7006 seem to run out of efficiently long before 6K rpm. The new development by Kevin has proven that statement to be an old characteristic of the K27. The new versions are pushing harder than the k29s and certainly have good low end response.

I will work on the maps.

Eric 930

Stephen

Are there any good turbos that will produce all the way to red line?

Eric 79 930

PorschePhD

The new high Flow K27 will do it. This turbo is simply awesome.

Eric 930

Stephen

Do you sell them? How much? Is it a k-27 housing?
Eric

PorschePhD

Yes we sell them as well. Drop me a call or email. Still cheaper than a K29 and better. They are based on a K27 housing.

Eric 930

Stephen

Whats your email address?

PorschePhD

porschephd@imagineauto.com

Peter Carroll/Toronto

I just bought a set of J&E custom forged racing pistons made to my specs - 8.5:1 and I paid something like $800 including new rings, wrist pins, hartware, etc. Why screw around when you can do it right for $800?