Does the 964 motor really need it’s crank damper?

[Duc Hunter]

I have a 964 3.6 in my ‘75. For year I ran the stock crank pulley. It has 3 grooves and is a vibration damper too. These can die over time as the rubber part of the damper degrades. A few year ago I went to a Rothsport crank pulley without a damper. It’s lighter weight, cleaner look, and its new (vs a 31 year old rubber damper).

Is there an issue running the 964 motor without a damper? It;s been a nagging question in the back of my mind, and laying under the car recently I was staring at it thinking hmmm….

I almost went with the Fluiddamper when I changed things up. I love those things from my muscle car days.

[Bill Verburg]

Originally Posted by Duc Hunter

I have a 964 3.6 in my ‘75. For year I ran the stock crank pulley. It has 3 grooves and is a vibration damper too. These can die over time as the rubber part of the damper degrades. A few year ago I went to a Rothsport crank pulley without a damper. It’s lighter weight, cleaner look, and its new (vs a 31 year old rubber damper).

Is there an issue running the 964 motor without a damper? It;s been a nagging question in the back of my mind, and laying under the car recently I was staring at it thinking hmmm….

I almost went with the Fluiddamper when I changed things up. I love those things from my muscle car days.

I don't know

But every 964 crank factory motor that I have seen, including RSR and Cup has the 3 sheave damper pulley.

I have seen engines where the owner has put a non damper pulley on they claim no issues.

I tend to go w/ the factory

I believe that Neil Harvey developed the ATI Super Dampers for the GT3 crank used in most probably all the late 4.0 air cooled motors


Last I heard He was working on one for the 993, maybe 964 too. He sometimes responds over on the Engine building form so maybe ask there.

the 964, 993 and GT3 all have different snouts so the pulleys and by extension damoers are not interchangeable.

[Duc Hunter]

Bill, great advice. That looks like the Clewett serpentine conversion as well. Any idea which ATI that is though? They don't list a Porsche as a fitment.

[winders]

I've seen a zillion non-Factory race engines built on 964 and 993 cases. 3.6L up to 4 Liter....I can't recall one I have seen with an ATI damper ...and an only a few with the Clewett serpentine setup. 90% have an aftermarket pulley setup instead of the Factory 3 groove pulley.

[Bill Verburg]

Originally Posted by Duc Hunter

Bill, great advice. That looks like the Clewett serpentine conversion as well. Any idea which ATI that is though? They don't list a Porsche as a fitment.

That engine is a buddies, it is a Gamroth built 4.0 w/ w/all the goodies.
AFAIK you need to buy from Rothsport or Neil Harvey.

Again these currently(to my knowledge, are only available for GT3 cranks

[Duc Hunter]

Bill, well I know Jeff so I can just give him a call. That motor in your pictures has no disti, runs off a crank trigger, etc. Right now my motor is pretty stock (though Jeff would like to change that for me….and some $$).

[PeteKz]

My advice: Do not run without a damper if you want long engine life. For the racers, who will rebuild motors every season (or more often), fine, do whatever makes you fast. For hot rod street cars that won't see 10,000 miles the rest of their lives, do what you want too.

But for street cars that you want to last 100,000 miles or more, there are good engineering reasons engines have harmonic dampers. I'm sure Porsche would not have spent the extra dough to put a damper on the 964 engine if their durability testing didn't justify the expense. Furthermore, if you change to a lightened clutch/flywheel, you better use the damper.

[Bill Verburg]

Originally Posted by Duc Hunter

Bill, well I know Jeff so I can just give him a call. That motor in your pictures has no disti, runs off a crank trigger, etc. Right now my motor is pretty stock (though Jeff would like to change that for me….and some $$).

Correct, no dizzy, Extreme heads,, the best of the best and all of it

As i said all the 964 crank factory motors use a damper of some sort, either the 964 3 sheave or the later RSR serpentine/

Here's the best pic I could find of the damper used w/ the serpentine, this is a 993Cup engine which uses a 964 crank(they all do), most have the 3 sheave pulley but this one was upgraded to the RSR serpentine setup. the damper pulley part # is 964.102.150.20

[group911@aol.co]

Bill. Here is the pulley I came up with for a cup and I don't believe it is dampened.
I'll see if I can find the part number.

[Bill Verburg]

Originally Posted by group911@aol.co

Bill. Here is the pulley I came up with for a cup and I don't believe it is dampened.
I'll see if I can find the part number.

I/m sure that there are several different pulleys that enterprising builders have come up w/ but the fact is the 993RSR factory serpentine pulley is is damped, as I stated all the factory motors that use the 964 crank use one form of damped pulley or another.

993Cup which uses the 964 crank used the stock 3 sheave,

Here is the page of the'97 RSR parts book that best illustrates the point

[group911@aol.co]

Correct on the RSR. Interesting that the damper also had a v-belt groove and your parts list actually shows the v-belt part number. Wonder what that would have driven?

[Bill Verburg]

I've seen some running a v-belt
964 RS l/wt


93Cup


993RSR sprint motor

[group911@aol.co]

I'm a little slow but I think I'm getting it now. The serpentine portion of the balancer goes on after the v belt portion which has all the timing marks on it and is therefore necessary. Sorry I didn't pull the serpentine pulley off of that rsr engine to see how the two halves were mated.

[Tinker]

I would agree that it's probably there for a reason. I removed mine (964) when I swapped the motor to an early car in the mid 1990's. It also has a lightweight flywheel and clutch. I removed mine mostly because it was a pain to get to the crank pulley to rotate the motor to adjust the valves. I understand the harmonics could potentially break the crank so proceed at your own risk.

Not to hijack the thread, but on the above posted pictures I note that the heater ducks are mostly vented to the atmospher. I guess it's not critical to have that duct sealed?

Curious.

Tinker

[Duc Hunter]

Wow you guys are a wealth of knowledge! So I guess I am going to source a serpentine and that ATI damper....or a fluid damper. Hmmm.......

No I'm not going over 7k RPM, but still.

[wallra]

I called API about getting a damper made for a 964 crank they wanted an order of 10 at $1000.00 each. the one you see in the picture is for a GT3 crank. I run with clewett setup. patrick motorsports make a serpentine belt kit also. https://patrickmotorsports.com/collections/all-products/products/eng96410615180rsrpms The thing that get me with the stock 964 crank pulley is the rubber is only on the ac pulley. not like a true damper. I have one here I took apart.

[Duc Hunter]

Clewett wants wants $625 for the non-A/C (out of stock…….and Patrick wants $1700. Wow. I know Rothsport uses them, but dont see it on their site. Might be worth a call. Hmm.