canvanner
10-18-2017, 09:40 AM
This is my first post on here so I would like to start out by thanking everyone for the wealth of knowledge I've gained from this forum. I have a Mitsubishi van with a lot a engine and drivetrain similarities to the MM's and it's been invaluable!
That being said, van has a 4G64 SOHC 8V that I'm looking to gain a little more cruising power out of. I've caught up on all the maintainence on the motor, put in a Uni foam filter, opened up the exhaust, put in a Jacobs high energy ignition (which I had kicking around), stretched the plug gaps as much as I could, and advanced the timing a touch with very good results. Buuut she needs a little more oomph on the highway.
In the coming months I want to pull the head, has a cracked exhaust manifold that the previous owner snapped a few studs off of, will do the valve stem seals and lash adjusters as well, all new gaskets/bolts and such sooo I was planning on doing some light port matching through the intake/exhuast ports and manifolds, possibly some shaping through the ports too after I do some more research.
What I was also considering was milling the head to bump the compression a bit, obviously I will CC the heads and piston dishes (if there is any, not sure about that one) and try to measure out how much I can take off before I run into valve/piston clearance issues. Ideally I would like to bump it to 9.5:1.
What I would like to know from anyone out there with experience is;
1: What would be a safe compression to run on 87 octane and stock or slightly retarded timing?
2: How much can I take off the head and still avoid valve clearance issues? Based on 8.5:1 and 69cc heads I calculated milling 1.1mm for 9:1 and 1.5mm for 9.5:1. Just an on paper estimate I'll have better numbers once I have it apart.
3: Any idea what kind of gains I should realistically expect from the the porting/compression increase? Percentage wise or HP/TQ?
Any input or ideas would be much appreciated!
That being said, van has a 4G64 SOHC 8V that I'm looking to gain a little more cruising power out of. I've caught up on all the maintainence on the motor, put in a Uni foam filter, opened up the exhaust, put in a Jacobs high energy ignition (which I had kicking around), stretched the plug gaps as much as I could, and advanced the timing a touch with very good results. Buuut she needs a little more oomph on the highway.
In the coming months I want to pull the head, has a cracked exhaust manifold that the previous owner snapped a few studs off of, will do the valve stem seals and lash adjusters as well, all new gaskets/bolts and such sooo I was planning on doing some light port matching through the intake/exhuast ports and manifolds, possibly some shaping through the ports too after I do some more research.
What I was also considering was milling the head to bump the compression a bit, obviously I will CC the heads and piston dishes (if there is any, not sure about that one) and try to measure out how much I can take off before I run into valve/piston clearance issues. Ideally I would like to bump it to 9.5:1.
What I would like to know from anyone out there with experience is;
1: What would be a safe compression to run on 87 octane and stock or slightly retarded timing?
2: How much can I take off the head and still avoid valve clearance issues? Based on 8.5:1 and 69cc heads I calculated milling 1.1mm for 9:1 and 1.5mm for 9.5:1. Just an on paper estimate I'll have better numbers once I have it apart.
3: Any idea what kind of gains I should realistically expect from the the porting/compression increase? Percentage wise or HP/TQ?
Any input or ideas would be much appreciated!