964 deck height

stevepaa · 04-01-2005, 06:42 PM

Putting it all back together. Measured my deck height at 1.20 mm using the crushed solder method. What was it stock and is this good to go? thanks

ChrisBennet · ChrisBennet's Garage

I looked in my notes. On the 964 motor I did (avg) deck height on #3 was 1.27mm and 1.03mm on #6. This was measured at the edge of the piston.
-Chris

stevepaa · 04-01-2005, 07:02 PM

Thanks Chris. This was at edge of piston on number 1. Should I do all of them? And what value is too low?

stevepaa · 04-02-2005, 10:51 AM

Okay, the solder method is good but not required for a 964. The OD of the piston is greater than the OD of the dome cut into the head. So you can just measure at the flat on the edge of the piston. Both solder and gauge are now giving me 0.76 mm of deck height. My machinist took off about .5 mm when he made all the heads the same total height and flat.

So do I need to get a custom shim to go between the cylinders and case?

350HP930 · 04-02-2005, 07:49 PM

Removing that much material could end up bumping your compression by about a half a point unless you correct most of it with the shims.

ChrisBennet · ChrisBennet's Garage

Quote:

Originally posted by stevepaa
Thanks Chris. This was at edge of piston on number 1. Should I do all of them? And what value is too low?

I'd measure one cylinder on each bank. I'd shim it back to 35-40 thou (.9mm-1mm). Competition Engineering has custom shims for earlier motors. I don't know if they have them for 3.6 motors.
-Chris

stevepaa · 04-06-2005, 01:43 PM

A well known shop has indicated that if I do not use a shim, but just assemble, then the increase in compression ratio may trip the engine computer to not run the ignition.

Anyone know anything about this?

350HP930 · 04-06-2005, 04:17 PM

Your knock sensor may kick in more if you have one and the timing will be pulled back accordingly, but thats not the same thing as not running the ignition.

stevepaa · 04-06-2005, 04:28 PM

Thanks, that's what I thought.

ChrisBennet · ChrisBennet's Garage

These are the figures for the only 3.6 (964) I've measured:
Left bank: 1.23mm deck height for 10.5:1
Right bank: 1.03mm deck height for 10.7:1

0.75mm deck height is 11.1:1

"350" is right. That's a compression increase 6 points (.6). 10.5:1 is about the limit for twin plugs. I suspect that more compression will cause knock (with street gas) which will cause the computer to retard the spark taking with it that extra horsepower or worse.

In my ignorance, I would be more concerned with the piston hitting the head. When I measured deck height in 4 places on the piston I got 4 different values i.e. some places on the piston are going to be closer than where you crushed the solder. Also, remember that when the engine is running, forces will be trying to fling the piston out towards the head.

Knowing just how small the deck height can be (for this flavor of motor) without wacking the head with a piston is one of those things that separates the "experts" from you and I.

A while back I think Dan Jacobs ("Dan J") indicated to someone that you could raise the true compression to the factory stated compression of 11.3:1. See this thread: 964 engine rebuild 11.3:1 compression
-Chris

350HP930 · 04-06-2005, 05:50 PM

Quote:

Originally posted by ChrisBennet
"350" is right.

Yup, rule of thumb for the big bore 911 motors is about one compression point per millimeter.

stevepaa · 04-07-2005, 07:26 AM

So any one know the minimum measured deck height so pistons don't hit heads when everything is hot and all parts grow?

350HP930 · 04-07-2005, 03:22 PM

The block will grow faster than the crank and rods so there's no issue with temp expansion.

The problem is stretch from the extreme loads of piston acceleration.

I will leave it to the experts to say exactly what it is but if memory serves me correctly I think wayne's book says you need 0.05" or more of deck height. I think that might be a generous number but I have not had a chance to personally investigate this detail yet.

stevepaa · 04-07-2005, 09:48 PM

My deck height is at .031". I guess I'll ask Woods tomorrow.

KNIGHTRACE · KNIGHTRACE's Garage

I try to keep these motors at .040 if it helps.

Steve@Rennsport · 04-10-2005, 04:17 PM

Quote:

Originally posted by Steve@Rennsport
I'd affirm Bill's suggestion;..........040 is the targeted spec for the majority of engines.

Under certain conditions, some race engines can use less deck height depending on the cam profile and ONLY if the piston to valve clearances are precisely measured,.....

stevepaa · 04-10-2005, 07:45 PM

So does anyone know of a .010 inch shim for 964 engines that have that green o-ring seal at the base of the cylinder?

The cam profile was standard 964.

I'll study up on valve clearance.

stevepaa · 04-12-2005, 07:35 AM

Talked to Woods and they suggested a base shim of .019 inch as they believed that .031 was just cutting it a little too close and the pistons might hit at high rpm. So he is making my shims which should bring this back to where I started. I will repeat measurements all around the perimeter to get a base value. Also they suggested DC730 as sealant to use around base of cylinders now with the added shim. So how does a projected deck height of .050 inch sound?

KNIGHTRACE · KNIGHTRACE's Garage

safe lots of stock motors are at about .060" .040 is my target but on a street motor it would be fine.