How could I not realize that....
 

... all 6 upper comression rings were broken?

I really wanted to believe that I was 'in tune' with my car, but if it weren't for the fact that the car was spewing/spraying/leaking oil from the pressure relief valve on top of the oil tank, I would have never known there was an engine problem. I thought that the engine was running great. I believe that I even did 2 track days with the broken rings, based on the over pressure oil leak, without noticing that the engine wasn't right.

Anyway, a leak down test showed very low compression in every cylinder.

So, does anyone want to guess how much I was down on power without noticing?

Stock 3.6L 964 = 247 hp
My 3.6L 964 with 6 broken rings = ??? hp

Erick
From a guy that runs a couple of early cars in the 140hp range I figured the 250hp range would be like a Canadian winter. When it gets below -20 doesn't really matter how cold it gets. Similary 200- 230- 250 what does it matter, how would you tell the difference. Don't get me wrong I'd give my right arm to be there so I'll take a stab at 200 HP that's a 20% loss.

LOL! That's funny. :D

I should have been more clear that I don't actually know how much I was down on power (didn't dyno the car before or after), but somehow I think that most people would notice power loss from 6 broken piston rings, regardless of what the starting hp was. If not, then maybe they don't need that 3rd ring after all. ;)

Re: How could I not realize that....
 

Erick:

A dyno test would have shown a loss in low & mid-range torque with all those broken rings. Peak HP is not affected very much depending on many factors,....:)

Bottom line: you & your engine will be MUCH happier with full compression, but I'd strongly suggest that you figure out WHY the engine detonated hard enough to break the rings and prevent that from recurring.

Re: Re: How could I not realize that....
 

Hi Steve,SmileWavy

Well, you've got me worried now. I had just figured that a 964 with 115,000 miles on it, and possible a decent amount of track mileage could experience broken rings. No?

Other than that, I'm not sure what causes that kind of detonation. My engine is stock, except for a 'chip' from Autothority. Have you ever heard of detonation problems with those chips? I always use Premium grade fuel (91-93 Octane in the NW). The distributor belt is intact. And the valves were adjusted within the last 10k miles.

I'm at a loss to explain it. :confused:

Erick

Erick:

Detonation in 964's is caused by several things including:

1) Insufficent octane fuels

2) Improperly programmed chip (common)

3) Broken distributor drive belt

4) Excessive carbon buildups on pistons and combustion chambers. This raises affective CR as well as generates hot spots

5) Excessively lean fuel mixtures (poor chip)

I have seen problems with their chips when operated on West Coast gasolines and the outcomes are all identical to yours.

Steve is right on the money (imagine that for such a rookie, haha). My first thought was crappy fuel, but I'd be wary of some of the chips out there... They get pretty damn agressive and won't tolerate marginal fuel with some of the high advance curves they use.

As Steve sez... definitely start to think about the cause, there is no reason all 6 should be broken by "normally" hard use.


Does your car have the distributor vent modification?

You've seen problems with Autothority chip on 92-93 octane West Coast gas? And I thought 92-93 was good! No? Well I'm taking that chip out then.

So how do I know what a good chip is, because I've heard that chipping these engines can make a decent power increases. Is there always a detonation cost? Should I only use chips that are burned to my particular engine on a dyno?

Yes, I have the vent mod... and the belt is still intact. Although I think that I'll replace it now. Just in case.

Yes, I have. IMHO, some of their software has been too aggressive in the low & mid range for the fuel we have combined with hot weather. Thats a sure recipe for detonation.

Indeed, a properly made chip enhances throttle response and mid-range torque but the software vendor must take into account the local particulars such as fuel grades and any engine modifications that has been done. Failure to do so creates the problem that you have.

A properly programmed performance chip does NOT trigger the engine into detonation. :)

Unless your engine is highly modified and therefore would require custom programming, a good chip provider should have software that will enhance the performance of your largely stock 3.6 on 92 octane fuel. I do recommend that people mix some unleaded race gas for DE events no matter what software one uses.

Steve,

That's interesting. What ratio of race gas to 91 octane gas should be used for track days?

Erick

FYI, I've got about 2900 lbs (after some weight loss projects) to haul around. What about your 140hp car?

SUMMARY
Detonation in 964's is caused by several things including:

1) Insufficent octane fuels - Use 92-93 octane for street and track

2) Improperly programmed chip (common) - Autothority chip

3) Broken distributor drive belt - No, it's intact

4) Excessive carbon buildups on pistons and combustion chambers. This raises affective CR as well as generates hot spots - Certainly there was a layer of carbon built up on the pistons, but it didn't seem excessive from what I've witnessed before. Anyway, that's been cleaned up now.

5) Excessively lean fuel mixtures (poor chip) - Autothority chip

Erick:

I would add one more thing; any vacuum leaks in the intake system introduces air that is not metered by the airflow meter. This generates a lean condition that can trigger detonation. I would go over the entire intake system, rubber boots, and ALL hoses to make sure that there is not a vacuum leak.

One tests for these issues using either a can of spray carb cleaner with a long nozzle or a bottle of propane and a wand. With the engine running, any introduction of these fuels changes the idle speed when they are sucked into any vacuum leak and a sharp ear can detect that.

You can find a fuel blending matrix chart I posted at http://www.rennsportsystems.com/2a.html.

AFR readings may indicate what's going on with the mixure and what the chip is doing with the fuel curve.
j.p.

All great points. Even Steve (the rookie) was on the money :D. I would recommend the NBD dual chip to get the best of both worlds. Run the stock setting for daily driving on pump gas and switch to performance for track driving when you have access to high-octane gas. Remember, in SoCal premium is only 91 octane. That is marginal to say the least.

BTW: My gaskets for the intake manifolds on my 3.6 were all leaking and hardened. I am sure yours will get replaced during the rebuild.

Cheers,
Ingo

http://sswl.di.com/~ingo/Chipping.htm

I broke the rings on cylinders 1, 2, & 3 in my 50,000 mile 930 because of clogged fuel injectors. Is this a potential problem on 964's?

Hm,

as soon as there is less fuel in the barrel than what the DME comanded (clogged injectors) or more air (intake leak) than what the DME metered and calculated the fuel required for you have a lean condition. This results in detonation (aka knocking) which hammers rod bearings and breaks rings.

So in simple works: YES but the Turbo's are probably more sensitive since boost adds more margin for the mixture to go out of whack.

Ingo

Thanks guys. I'm having the fuel injectors cleaned and rebuilt. And I'll check for vacuum leaks in the intake system. Does anyone know where to get a "wand" for a propane tank to test for leaks?

Thanks for all of the valuable info.

Erick

Erik, brake cleaner, carb cleaner, starter spray all work fine.