apw964

Folks,

There has been a lot of posts about the Dist Belt failure problem. Does anyone know exactly how much HP is lost ? and how the torque figures are effected.

Has Porsche ever released any figures (I can't imagine they have), or would anyone like to make a guess ?

IMPI2001

Hi APW,

I can't give you actual numbers, maybe someone else has actually tested it on a dyno, but it was very obvious when the belt on my C4 964 went. Power was down significantly. It idled just fine , but on acceleration there was an obvious jerkyness and also quite noisy preignition "pinging". It felt scary, as if harm was being done. Which indeed it is doing harm if you carry on pressing hard! The local official dealership were convinced it was fuel pump problems and replaced that with no effect. I got fed up and went to another (non official) shop who took all of 20 minutes to identify the problem. Once the belt was replaced everything is just fine again.

Good luck

Randall G.

Hi apw964,

Well, perhaps the loss of power varies on a case-by-case basis? When the belt failed in my car, I thought something was amiss, but it wasn't blatant.

The night before my belt was diagnosed as failed, I got tangled up with a last generation RX-7 in a stop-light drag. Even with a 250 lb. passenger, I almost beat 'em. But, fact is, I lost at two consecutive lights. Felt better when I found out the next day my car was not running at full strength, whatsoever. Oh, and I should add that if I had any idea the distributor belt was broken, I certainly wouldn't have been working the car for all it had .

Oddly enough, it was losing the race to the RX-7 that convinced me something was wrong with my car, and that it wasn't my imagination .

Bill Wagner

Randall's correct in implying it's on a case by case basis. In the BEST CASE, the secondary distributor wiper will settle between two distributor contacts and be far enough away from both of them that no spark really gets sent to any plugs. This will lead to a decrease in horse power, which is often not noticeable until some, as Randall did, pushes the car a little. In the WORST CASE, the secondary wiper settles right on top of a contact and that spark plug will fire for every stroke of the engine on a single piston when it should be getting distributed to the pistons in their proper order. In this case, the problem is actually counter acting power generation, and if left unfixed will likely end up damaging the engine. Notice these are the two extremes.

Good Luck,


Bill Wagner

Adrian

There is no data of this subject. It would require some form of testing using a dyno. Any volunteers.
What I can tell you for a fact is the knock sensors if they detect what we call "pinging" will kick in and retard the timing. How much, up to 6 degrees on the crank.
This belt problem is obvious to someone who "knows" their 964 and drives it. It will be less obvious to the new owner or to those who just sort of commute. Of course if it was broken from purchase, then this owner would not know any difference.
It is a good idea and in fact it is a servicing requirement to check this belt. If it is broken, get it fixed. If you do not have the vent kit installed, get it installed.
Only six spark plugs will affect starting as well as running. It will normally not affect idle values but it may affect the time taken for the idle to settle.
Anyway, thats enough for now. If you know you can tell. Like anything else the 964 has a learning curve.
Ciao,
Adrian
911C4

Adrian

Based on the data I have just read. The power (HP) loss caused by the loss of the six secondary spark plugs will be minimum. These spark plugs are designed to aid in combustion efficiency to help with emissions and fuel economy. There is going to be some power loss but I would estimate 10-20HP simply based on what the 3.2 carrera put out with only six plugs. The PRIMARY IGNITION SYSTEM is from the Primary Distributor and its six spark plugs,
Ciao,
Adrian.
911C4

das

My distributor belt was probably broke since I purchased my 90 C4, and there was never any noticable problems or lack or power. In fact, before I realized this from my own inspection, I was getting 5.1 s to 60 on my g-tech. It does seem to run smoother and slightly more power with the belt replaced, but there is very little difference.

Adrian

Dear Das,
Thanks for the information. Very helpful for my research. After I posted yesterday I found some info where a claim of 10% power loss caused by the secondary belt.It seems we have a lot to learn about this system. Most people who have contacted me report similar experiences to yourself. Never really knew it was broken and when fixed, the changes were not that evident,
Ciao,
Adrian
911C4

Randall G.

Well, I'll add that--in my case--even though the side effects of the broken distributor were not blatant ... the engine felt much nicer after the belt was replaced.

It wasn't like a turbocharger had been slapped on, but definitely one of those things where you realized what you were missing, once the problem was fixed. Again, this was in my case ...

Adrian

Dear Randall,
What we have to work out is how to avoid this situation in the first place. It is too late when a 964 owner works out that something is missing when it has been fixed.
I will be posting more on this subject when I get some more data and when I conclude my discussions with some of the engine rebuilding facilities and the authorities. The fact is, that in general, the average 964 owner will never know the belt is broken. You will feel nothing. If you purchase with a broken belt you will never know. I will be including some servicing recommendations as well.
Ciao,
Adrian
911C4

Bill Wagner

Adrian:

"The fact is, that in general, the average 964 owner will never know the belt is broken. You will feel nothing. If you purchase with a broken belt you will never know."

You've finally convinced me. You're a very dangerous man.

Jacks911

I receintly repaired my broken belt and can say the difference is significant at speed. I am still learning about this Carrera having only owned it since last fall. It is Very different from my '76 2.7. I believe my belt broke on a mountain drive. Accelerating at 4000 feet was smooth but almost nothing left at 90+ mph. With the new distributor belt and back at sea level a freeway ramp was enough to see red line in third with out feeling winded (this should be about 120mph with the Tiptronic).
If you want to see the difference just snap off the coil amp plug, the forward one on my car was the secondary distributor. You won't have as bad a drop because with out any detonation (no spark in Secondary dist.) the DME should give full advance. By the way, snaping off that amp connector is alot simpler than pulling the cap on the dist. to check your belt.
Regards, Jack S in Seattle - '91 C2 Cab Tip

Adrian

Dear Bill,
I think you really need to take some time off. This discussion is getting to you.
Five of the six US based engine re-building companies answered my question and I quote for the record one of them.
My Question: Am I correct in understanding (which is fully supports your statements by
those who have had belt breakages) that the loss of the secondary
distributor is almost silent.

Answer: Yessir.

My Question: There is no real loss of anything.

Answer: Just a power loss and most people are not sensitive nor knowledgeable enough to
notice. They do perceive "something" is wrong but mentally chalk it up to
outside air temperature or a fuel variation issue.

My Question: The average driver cannot pick up the difference between 12 spark plugs and
only six or
seven working.

Answer: Not at all. They will notice a change but be unable to account for it.

My Question: The vast majority of people who have contacted me on this
problem report that they felt nothing and when the belt was replaced they
noticed no improvements anyway.

Answer: Normal.

Respondent is a well known and respected member of the rennlist community. Four others answered the same way out of the USA as did all the Europeans. Only one stated a different story,
Ciao,
Adrian
911C4