Camshaft Timing... (or how to gain 20 hp...)
09-23-2010, 12:10 PM
#46
Rennlist Member
My Porsche mechanic said that he has never seen a 993 with the correct and balanced valve openings. He has done the measurement and properly set the valve openings for many 993s, even for 993RSs and he said that each time he notices the engine becomes lively and he thinks that about 20hp can be recuperated.
09-23-2010, 01:47 PM
#47
there was a huge scandal in Europe when the 993s first came out due to the apparant inability of stock engines to produce rated hp, Porsche has always been very good in this regard, many of the engines were retrofitted under warranty particularly the typically more demanding RS owners
09-24-2010, 10:20 AM
#48
Bill, really?
Living in the Uk and having owned 911's since the 993 came out I have never heard that in such terms.
Huge scandal?...Where do you get that from?. Thre are usually a few teething problems with new models etc..
It's just that once something is written on the internet it becomes the absolute truth for some.
Living in the Uk and having owned 911's since the 993 came out I have never heard that in such terms.
Huge scandal?...Where do you get that from?. Thre are usually a few teething problems with new models etc..
It's just that once something is written on the internet it becomes the absolute truth for some.
10-03-2010, 12:34 PM
#50
Bill, really?
Living in the Uk and having owned 911's since the 993 came out I have never heard that in such terms.
Huge scandal?...Where do you get that from?. Thre are usually a few teething problems with new models etc..
It's just that once something is written on the internet it becomes the absolute truth for some.
Living in the Uk and having owned 911's since the 993 came out I have never heard that in such terms.
Huge scandal?...Where do you get that from?. Thre are usually a few teething problems with new models etc..
It's just that once something is written on the internet it becomes the absolute truth for some.
10-03-2010, 04:09 PM
#51
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Hmm, missed this thread. A few comments that are likely old news right now:
1 - I think the woodruff keyway disappeared on the stock cams around mid 1996. My car had the keyway, so retrofitting backwards to the 964 sprocket sets was no problem. If you are retrofitting a cam that does not have the keyway, you can get a machinist cut on. The position of the keyway does not matter.
2 -Colin has nice equipment to time these cams, and the knowledge, but us mortals only have a lift gauge to go by. I timed using 1.0mm lift on both sides (double checking several time).
3 - The tension on the chains is important, but I tried more and less tension to double check my numbers. Once the chains are tight enough, you do not seem to get that much variance.
4 - The factory tools lock the camshafts and crank to a certain position, and then the cams are tightened up. I do not like this method, nor the price of the tools, nor the timing position of the cams, so I did it the old fashioned way.
5 - With the cams at 1.0 mm, the torque curve is a bit lower (checked on a dyno and my butt), and I really like the feel of the car.
6 - It can be done on the car, see the engine rebuild thread at www.pcarworkshop.com. Its not that hard to time them on the car, but lots of stuff has to come off the engine to do it right.
I doubt if I gained 20HP, but the car feels better than other 993's I have driven. i attribute a lot of that to the cam timing. Definitely something to look at during rebuild time, but I would not bother digging into it if you are not opening up you engine (unless you have time and $$ for the gaskets.)
Cheers,
Mike
1 - I think the woodruff keyway disappeared on the stock cams around mid 1996. My car had the keyway, so retrofitting backwards to the 964 sprocket sets was no problem. If you are retrofitting a cam that does not have the keyway, you can get a machinist cut on. The position of the keyway does not matter.
2 -Colin has nice equipment to time these cams, and the knowledge, but us mortals only have a lift gauge to go by. I timed using 1.0mm lift on both sides (double checking several time).
3 - The tension on the chains is important, but I tried more and less tension to double check my numbers. Once the chains are tight enough, you do not seem to get that much variance.
4 - The factory tools lock the camshafts and crank to a certain position, and then the cams are tightened up. I do not like this method, nor the price of the tools, nor the timing position of the cams, so I did it the old fashioned way.
5 - With the cams at 1.0 mm, the torque curve is a bit lower (checked on a dyno and my butt), and I really like the feel of the car.
6 - It can be done on the car, see the engine rebuild thread at www.pcarworkshop.com. Its not that hard to time them on the car, but lots of stuff has to come off the engine to do it right.
I doubt if I gained 20HP, but the car feels better than other 993's I have driven. i attribute a lot of that to the cam timing. Definitely something to look at during rebuild time, but I would not bother digging into it if you are not opening up you engine (unless you have time and $$ for the gaskets.)
Cheers,
Mike
