cylinder bore vs chamber bore
10-12-2006, 11:07 AM
#1
On The Tree
Thread Starter
iTrader: (1)
Join Date: Oct 2006
Posts: 103
Likes: 0
Received 0 Likes
on
0 Posts
cylinder bore vs chamber bore Hello, I tried to search but search is down. I am trying to find out if the following setup would be a problem.
I have a stock bore LS1 out of a 02 Camaro. I purchased a used set of CNC ported heads from a local guy who had them ported by a top end porter in St Pete. The runners are 225-227cc. they have 2.05 int. and 1.6 exh valves. They were on a 408 and it look as though they had some port work in the chamber to unshroud the larger valves. I get 3.935 with a digital caliper measuring the width of the chamber from side to side across the valves. I would also venture to say that the extra porting in the chamber increased the cc's. They were also just recently freshened up and received a 10thousands mill. On the side of the heads reads 64.6cc. So after milling they ended back at the stock cc for a 243 casting.
My question is, will the larger size chamber(3.935) vs the stock bore(3.898) present a problem even thogh the cc's are back to 46.5. I assume the compression should be around 10.4-10.5 like a ls6. I just don't know if the wider chamber is a bad thing.
Also should I consider milling them some more to bump the compression or possibly run a .040-.043 head gasket.
The cam I am going to be running is a Comp XER 232/236 .595/.601 114+4.
I wonder what my DCR will be and also need to check PTV.
Mike
I have a stock bore LS1 out of a 02 Camaro. I purchased a used set of CNC ported heads from a local guy who had them ported by a top end porter in St Pete. The runners are 225-227cc. they have 2.05 int. and 1.6 exh valves. They were on a 408 and it look as though they had some port work in the chamber to unshroud the larger valves. I get 3.935 with a digital caliper measuring the width of the chamber from side to side across the valves. I would also venture to say that the extra porting in the chamber increased the cc's. They were also just recently freshened up and received a 10thousands mill. On the side of the heads reads 64.6cc. So after milling they ended back at the stock cc for a 243 casting.
My question is, will the larger size chamber(3.935) vs the stock bore(3.898) present a problem even thogh the cc's are back to 46.5. I assume the compression should be around 10.4-10.5 like a ls6. I just don't know if the wider chamber is a bad thing.
Also should I consider milling them some more to bump the compression or possibly run a .040-.043 head gasket.
The cam I am going to be running is a Comp XER 232/236 .595/.601 114+4.
I wonder what my DCR will be and also need to check PTV.
Mike
10-14-2006, 09:17 AM
#3
On The Tree
Thread Starter
iTrader: (1)
Join Date: Oct 2006
Posts: 103
Likes: 0
Received 0 Likes
on
0 Posts
I've been doing some more research now that the search is working again 
It seems that going with a comp cam will give me a .025 shorther centerline to lobe heel length. this will make my pushrods too short by this amount assuming all else is the same. If the heads are milled 10thou, using a .40 cometic should put me right back at stock lentgh. (7.4 +.025-.010-.015= 7.4)
I am using Jesel J2K 1.7 nonadjustable rockers and want to make sure my preload is correct. I am also looking into the new GMPP ls7 high RPM lifters that just came out. They are supposed to be stock drop in. Anyone have any experience with theese.
Mike
It seems that going with a comp cam will give me a .025 shorther centerline to lobe heel length. this will make my pushrods too short by this amount assuming all else is the same. If the heads are milled 10thou, using a .40 cometic should put me right back at stock lentgh. (7.4 +.025-.010-.015= 7.4)
I am using Jesel J2K 1.7 nonadjustable rockers and want to make sure my preload is correct. I am also looking into the new GMPP ls7 high RPM lifters that just came out. They are supposed to be stock drop in. Anyone have any experience with theese.
Mike
10-14-2006, 04:36 PM
#4
On The Tree
Thread Starter
iTrader: (1)
Join Date: Oct 2006
Posts: 103
Likes: 0
Received 0 Likes
on
0 Posts
Ok I found out that the heads had been milled twice. I measured from the top of the head where the valve cover seats to the bottom of the head. I got .020 shorter than stock spec. This would make sense as the heads have been off twice and got 10tho cleanups both times. I am going to use some cometics at .040 which will give me a push rod length of 7.39 to keep the stock preload. so stock 7.4's should work fine offering .001 more preload.
Now the only issue is PTV and what bore size gasket to use with the above mentioned head chamber size. Somebody pleas advise.
Mike
Now the only issue is PTV and what bore size gasket to use with the above mentioned head chamber size. Somebody pleas advise.
Mike
10-14-2006, 04:43 PM
#6
You'll want to lay a head gasket you would run over the deck surfaceof the head and carefully check to see if the gasket will protrude into the chamber anywhere. If it does, you may end up with dead spots in the chamber, or worse yet, a hot spot that could lead to detonation. Anything that disrupts the swirl in the chamber is gonna be bad.
10-14-2006, 08:54 PM
#7
On The Tree
Thread Starter
iTrader: (1)
Join Date: Oct 2006
Posts: 103
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by hammertime
You'll want to lay a head gasket you would run over the deck surfaceof the head and carefully check to see if the gasket will protrude into the chamber anywhere. If it does, you may end up with dead spots in the chamber, or worse yet, a hot spot that could lead to detonation. Anything that disrupts the swirl in the chamber is gonna be bad.
These are the things that worry me. The stock bore of the bottom end is 3.898-3.90. This opening is smaller than the opening in the heads (3.935). This indicates that the width of the combustion chamber is 30thou wider than the bore. this means 15thou to either side of the cylinder wider. So the chamber is wider than the bore. if I put a stock gasket 3.91 it will be fine for the cylinder but slighty exposed to the inside of the combustion chamber as looking down from the valves. If I use a 3.95 this will be wider than both the chamber and the cylinder bore. Which way should I go and what problems if any might I encounter?
