Compression ratio ?
11-16-2012, 10:51 AM
#1
Compression ratio ?
I’m in the process of piecing together the engine for my Excalibur project .
Im starting with a Dart Big M tall deck block bored to 4.560 and a 4.25 stroke crank.
Future plans for this engine involve either a Procharger or twin turbos but it’s going to have to run N/A for a season or so ‘till I come up with the funds…
I plan on using AFR Aluminum heads (most likely the 325cc) which can be ordered with either 117cc chambers as cast or 121 cc cnc.
I figured the compression ratio with a 0 decked block and .041 head gaskets..
I’m trying to stay with a JE “shelf” piston but am having a hard time deciding between going with a flat top or dished…
Using the Flat top (-3cc) pistons with 121 cc chamber heads I come up with 9.4:1 compression.
Would run great N/A but how much boost could it handle on pump gas ?
Using the dished piston (-20cc) with 117 cc chamber heads I come up with 8.6:1 compression.
Would work good on boost but will it run ok N/A ?
Any input would be greatly appreciated..
Doug
Im starting with a Dart Big M tall deck block bored to 4.560 and a 4.25 stroke crank.
Future plans for this engine involve either a Procharger or twin turbos but it’s going to have to run N/A for a season or so ‘till I come up with the funds…
I plan on using AFR Aluminum heads (most likely the 325cc) which can be ordered with either 117cc chambers as cast or 121 cc cnc.
I figured the compression ratio with a 0 decked block and .041 head gaskets..
I’m trying to stay with a JE “shelf” piston but am having a hard time deciding between going with a flat top or dished…
Using the Flat top (-3cc) pistons with 121 cc chamber heads I come up with 9.4:1 compression.
Would run great N/A but how much boost could it handle on pump gas ?
Using the dished piston (-20cc) with 117 cc chamber heads I come up with 8.6:1 compression.
Would work good on boost but will it run ok N/A ?
Any input would be greatly appreciated..
Doug
Last edited by Boatally Insane; 11-16-2012 at 11:02 AM.
11-16-2012, 08:02 PM
#2
Registered
iTrader: (3)
If your truly thinking about a twin turbo setup(which is huge money compared to the procharger), I'd go with the -20CC blower piston. Actually, either blower, I'd go with that piston.
When you get the pistons, I'd consider getting a upgraded wrist pin. The standard JE blower piston will come with a good pin, but with a procharger or turbo, you'll have the capabilty to make some big power. Hence a even better pin than what comes with them.
http://www.trendperform.com/index.ph...ts&type=piston
As for N/A with 8.6:1, the cam will make or break it. Over cam it and it will be a turd without a blower. With the right cam, it can still make decent power and run well. Youll want to go with a blower friendly cam. Nice thing about a blower cam, is they are normally 112-114LSA, which will help build some cylinder psi with the lower compression.
Mercury's HP500 was under 9:1. You'll have much better heads, 50 more cubic inches, a better cam profile, I dont see why you couldnt make 600HP all day on 87 octane.
When you get the pistons, I'd consider getting a upgraded wrist pin. The standard JE blower piston will come with a good pin, but with a procharger or turbo, you'll have the capabilty to make some big power. Hence a even better pin than what comes with them.
http://www.trendperform.com/index.ph...ts&type=piston
As for N/A with 8.6:1, the cam will make or break it. Over cam it and it will be a turd without a blower. With the right cam, it can still make decent power and run well. Youll want to go with a blower friendly cam. Nice thing about a blower cam, is they are normally 112-114LSA, which will help build some cylinder psi with the lower compression.
Mercury's HP500 was under 9:1. You'll have much better heads, 50 more cubic inches, a better cam profile, I dont see why you couldnt make 600HP all day on 87 octane.
11-16-2012, 10:16 PM
#4
Registered
You have a few options. I would certainly use the inverted dome pistons with an SC engine, if you plan on running any appreciable amount of boost. They have a thicker crown, lower ring land, anti-detonation groove,etc. You can mill the heads down to probably 115 cc's or so. If you start with the 121 CNC heads, you will have to cut .025-.030 to get to 115 cc's. With a .041 gaskets and the 20 cc piston, you will end up with 8.8:1. This will work just fine for both the NA and SC. As Mild mentioned, the cam will be the deciding factor.
The other option is to fly cut the piston some. You can take around .050 off of the piston to reduce the volume of the dome. The other option is to run a thinner head gasket. You can drop down to a .030 Cometic. That gasket has a volume of around 8 cc's, instead of the 11 cc's of the .041 gasket. You may not want to go that route if you are shooting for 0 deck. That will put your quench a little low and may make it susceptable to detonation. Ideally, you want between.040-.060 quench.
Eddie
The other option is to fly cut the piston some. You can take around .050 off of the piston to reduce the volume of the dome. The other option is to run a thinner head gasket. You can drop down to a .030 Cometic. That gasket has a volume of around 8 cc's, instead of the 11 cc's of the .041 gasket. You may not want to go that route if you are shooting for 0 deck. That will put your quench a little low and may make it susceptable to detonation. Ideally, you want between.040-.060 quench.
Eddie
