Higher compression by shaving heads?
07-29-2003, 01:57 AM
#32
I always understood that shaving the head screwed up the chain length more than the tensioners could cope with.
It seems odd to go cheap when the cost of "doing it right" is so small compared to the labour cost of pulling the heads off.
Every time I try to save money with this car I end up hurting myself...
It seems odd to go cheap when the cost of "doing it right" is so small compared to the labour cost of pulling the heads off.
Every time I try to save money with this car I end up hurting myself...
07-29-2003, 02:01 AM
#33
Rennlist Lifetime Member
LOL, I understand. Normally if you are going for only a half a point there are not really any issues. It is when people start to get greedy and do more that the problems occur. Also the easiest way is the pistons as if you want to go back to stock simply yank the pistons.
07-29-2003, 02:37 AM
#34
looking at your pics of Cylinder heads, two comments I wish to make.
First, the 911/930 head, the Exhaust Valve looks very low. On my engine, the exhaust flow was very poor, until the porst were opened up and massaged, and the seat height was critical. Have you found the same.
Second, the race head, is it not a 956 head. 962 heads 2V were similar to 930 heads, and 962C heads 4V were water cooled along with the cyclinders. I think 956 heads were water cooled only, and the cylinders air cooled. It looks like you have finned cylinders.
First, the 911/930 head, the Exhaust Valve looks very low. On my engine, the exhaust flow was very poor, until the porst were opened up and massaged, and the seat height was critical. Have you found the same.
Second, the race head, is it not a 956 head. 962 heads 2V were similar to 930 heads, and 962C heads 4V were water cooled along with the cyclinders. I think 956 heads were water cooled only, and the cylinders air cooled. It looks like you have finned cylinders.
07-29-2003, 10:49 AM
#35
Rennlist Lifetime Member
Yes, We have found that the heads really flow pretty poorly and benefit from a little work. To be honest displacement and CR are great additions, however there is free HP in the heads. I have also found that 90% of the heads we do require new valves. They take a beating form the head and the general design of the valve train and ether wear the stems out or when faced have such little material left I wouldn't use them in my lawn mower.
On the heads types, I apologize I wasn't paying attention to my typing. Yes, the 962 head used a single plug 2 valve set up. They also had a very unique squish area un like the 930 head to accommodate for the lack of twin plugging I suspect. The cylinders were not welded on.
The 956 heads were welded together as you can see from the picture and used two 35mm intake valves and 2 30.5mm valves on the exhaust.
Sorry for the confusion
On the heads types, I apologize I wasn't paying attention to my typing. Yes, the 962 head used a single plug 2 valve set up. They also had a very unique squish area un like the 930 head to accommodate for the lack of twin plugging I suspect. The cylinders were not welded on.
The 956 heads were welded together as you can see from the picture and used two 35mm intake valves and 2 30.5mm valves on the exhaust.
Sorry for the confusion
07-30-2003, 01:46 AM
#36
Actually, the 962 heads were twinplugged and 2V. The head material was different to that of the 930 heads, and did have some small design differences, port/intake flange, and some other very small changes. They all ran the second distributor off the back of the camshaft. They were really a follow on to the 935 heads. Only in the US were the 962 engines run. There may have been a few others in other countries, but in general most were run in IMSA. The Europeans ran the 956. Air cooled cylinders with water cooled heads. It wasn't until the 962C engine came along that all cars run similar engines. Along with these differences, I think there was some displacement differences. IMSA ran 3.0L and 3.2L and the 956 ran 2.8L and I think some of the early 962C engines ran in Europe with 2.8L.
From your pic's, the 930 head looks to have the exhaust seat very low. I have seen many repairs on Porsche heads where the seats were recut, without regard to seat height. In some cases, the seat is so low that the chamber is blended back into the top angle. Flow is always compromised, and the seat height can never be higher than the chamber chamfer. Most Porsche shops just want the seats recut. When asked if they want the seats replaced, the answer is typically no. As a customer, I'm glad I was asked, given the reasons as to why and shown the difference in flow. As a point for all to know here, the difference is huge. Flow loss can be as much as 20 HP. Yes it cost more to do, but the difference in cost is the cheapest 20 HP you will ever buy.
From your pic's, the 930 head looks to have the exhaust seat very low. I have seen many repairs on Porsche heads where the seats were recut, without regard to seat height. In some cases, the seat is so low that the chamber is blended back into the top angle. Flow is always compromised, and the seat height can never be higher than the chamber chamfer. Most Porsche shops just want the seats recut. When asked if they want the seats replaced, the answer is typically no. As a customer, I'm glad I was asked, given the reasons as to why and shown the difference in flow. As a point for all to know here, the difference is huge. Flow loss can be as much as 20 HP. Yes it cost more to do, but the difference in cost is the cheapest 20 HP you will ever buy.
07-30-2003, 02:14 AM
#37
Rennlist Lifetime Member
m42racer,
Please don't take this the wrong way, but the 962 may have had a twin plug version, but all the early versions I have seen were a single plug aircooled design with a modified squish area to accommodate for the lack of the second plug. I have a picture somewhere that I can show you. There were obviously differences in the material as well as the intake/port sizing. You are also correct they are a close relative of the 935 head. Another version of the 962 was air cooled and the later water cooled. The 962C was actually a 4 valve 956 engine or at least based on it and watercooled heads with single plug driven by a dist off of the pass cam. Displacment from 82-84 was 2.8, 84-87 was 3.2 and 1992 was 3.3.
When we send the heads out we use a bloke that comes from the "old" IMSA days and worked with Bruce and Jerry. You can imagine that the work that is done is very conservative. By that I mean we never NOT recommend replacement of seats and valves. I would say that 90 % of the heads we do are fitted as such. He knows that if after cutting, facing etc the material is at minimum spec or even within a 1/4 % of that just replace them. As you mention heads are easy HP and often over looked. The type of work he does allows me to feel good about warranting these type of motors for a year when we build them. Odd for the industry I know.
Please don't take this the wrong way, but the 962 may have had a twin plug version, but all the early versions I have seen were a single plug aircooled design with a modified squish area to accommodate for the lack of the second plug. I have a picture somewhere that I can show you. There were obviously differences in the material as well as the intake/port sizing. You are also correct they are a close relative of the 935 head. Another version of the 962 was air cooled and the later water cooled. The 962C was actually a 4 valve 956 engine or at least based on it and watercooled heads with single plug driven by a dist off of the pass cam. Displacment from 82-84 was 2.8, 84-87 was 3.2 and 1992 was 3.3.
When we send the heads out we use a bloke that comes from the "old" IMSA days and worked with Bruce and Jerry. You can imagine that the work that is done is very conservative. By that I mean we never NOT recommend replacement of seats and valves. I would say that 90 % of the heads we do are fitted as such. He knows that if after cutting, facing etc the material is at minimum spec or even within a 1/4 % of that just replace them. As you mention heads are easy HP and often over looked. The type of work he does allows me to feel good about warranting these type of motors for a year when we build them. Odd for the industry I know.
Last edited by PorschePhD; 07-30-2003 at 03:11 AM.
07-31-2003, 12:16 AM
#38
Not sure about what you are saying here. My reference shows all 962 engines were twin plugged and all 962C engines coil packs with motronic 1.7. anyway we got off the subject here a little.
I do have a question about some 89 3.2L Carrera Heads. I have the chance to pick them up at a very low price. They were take offs with around 15K miles. These have the threaded boos for the temp sensor in every head. Single plug. Can these be twin Plugged? From looking at them, it appears the second plug may go thro the temp sensor hole.
I do have a question about some 89 3.2L Carrera Heads. I have the chance to pick them up at a very low price. They were take offs with around 15K miles. These have the threaded boos for the temp sensor in every head. Single plug. Can these be twin Plugged? From looking at them, it appears the second plug may go thro the temp sensor hole.
07-31-2003, 12:25 AM
#39
Rennlist Lifetime Member
LOL, I have a habit of doing that...Sorry.
I will finish up on the 962 stuff with this...The IMSA version was the 2V single plug version it was single turbo and air-cooled to boot. They ran this configuration for about 5 years. Toward the end they started getting their ***** handed to them. A little belly aching and IMSA let them run the Euro version with restrictors. They ran air-cooled, then water-cooled heads and then fully water cooled. The 962C was actually a four valve head that is more or less from the 956. The head I have, I ran the numbers and it is from a 962C. Personally
I would take any version and a street tag
The Carrera heads can be twin plugged. Keeping mind that if you are using them for a turbo the metal compound between the turbo head and the Carrera head are actually different. The turbo actually will disperse heat a bit better than the Carrera heads.
I will finish up on the 962 stuff with this...The IMSA version was the 2V single plug version it was single turbo and air-cooled to boot. They ran this configuration for about 5 years. Toward the end they started getting their ***** handed to them. A little belly aching and IMSA let them run the Euro version with restrictors. They ran air-cooled, then water-cooled heads and then fully water cooled. The 962C was actually a four valve head that is more or less from the 956. The head I have, I ran the numbers and it is from a 962C. Personally
I would take any version and a street tag
The Carrera heads can be twin plugged. Keeping mind that if you are using them for a turbo the metal compound between the turbo head and the Carrera head are actually different. The turbo actually will disperse heat a bit better than the Carrera heads.
07-31-2003, 10:06 AM
#41
Nordschleife Master
The temp sensor is in head of cylinder #3 at the back of the engine and will not cause a problem with the second spart plug. I did this to a set of 930 heads and used the 3.2 Carrera as a model. It provides just enough room for my aftermarket scavage pump.
07-31-2003, 11:38 PM
#42
Geoffrey,
I heads I am looking to buy have the threaded hole for the temp sensor in each head. My question is not about the sensor, but can the second hole for the spark plug be drill and tapped in the normal position(2nd plug), and miss this sensor hole. I am concerned about the spark plug hole breaking thro, and not having a complete plug hole.
I heads I am looking to buy have the threaded hole for the temp sensor in each head. My question is not about the sensor, but can the second hole for the spark plug be drill and tapped in the normal position(2nd plug), and miss this sensor hole. I am concerned about the spark plug hole breaking thro, and not having a complete plug hole.
