.125 milled head

[larry mcgrath]

This engeie is a 3ascv swirl control valve i live at 5500 ft in montana it has 60,000 miles on it , it runs real strong. I'm in the middle of rebuilding a 83 4x4 with 230,000 and this engine will run circles around it .It will get rubber in 2nd gear. Larry

[4wdchico]

Welcome to the forum, lots of very savvy t4wd tech heads here.

Sorry, but I don't fully understand what you are trying to say. Are you going to put the 3ascv engine into the '83 t4wd? If that is the case, what car was the 3ascv in when you drove it?

I did however get that you can slam shift into 2nd gear with this engine and "get rubber". Doing this on a t4wd 6 speed tranny with a strong running engine will very likely cause you to "get transmission", as in search for a replacement because yours is blown.

[tercel4wdrules]

I think what he means is that he has 2 T4WDs, the one that has the head milled is the one with the JDM 3A-SCV. In addition, he has another 83 with 230k which he's rebuilding the engine on, I think this is what he meant.

I'm surprised that engine is that strong at 5500 ft, mine feels way underpowered at that altitude.

[4wdchico]

I think what he means is that he has 2 T4WDs, the one that has the head milled is the one with the JDM 3A-SCV. In addition, he has another 83 with 230k which he's rebuilding the engine on, I think this is what he meant.

I'm surprised that engine is that strong at 5500 ft, mine feels way underpowered at that altitude.

Higher compression can make a big difference in performance at high elevation. Advancing the ignition timing helps, but not nearly as well as raising the C/R. The downside is that one needs to put high octane fuel in a car with raised C/R before heading down to the flatlands to protect the engine from ping related damage.

[tercel4wdrules]

With that much milled off the head I would think the compression ratio would be a bit too high, even for premium fuel at sea level. One would have to find the right compromise between C/R and running the engine safely on the available fuels. I wonder what the C/R is with that much milled off the head...

[ARCHINSTL]

Welcome to the Club!
I guess there must be JYs with lots of 6S trans up in Big Sky Country, huh?
Tom M.

[Petros]

Larry,

Welcome to the list, it would be nice if you clairfy exactly what you are trying to say.

I am running flat top pistons, over bored .040", and the head resurfaced 3 times (not planned-about .075"), all serve to raise the CR, and mine calculates out at about 11.25:1, it runs fine at sea level with premium. If all he did was mill .125 off you would have likely a similar CR. At altitude there would even be less of an issue.

One problem I see with taking that much off the head is the valve timing would be slightly delayed since it would have the effect of allowing the cam sprocket to rotate backwards a few degrees. I do not know how it will effect it, on twin cams you actually improve low end by retarding the intake, but you also want to advance the exhaust at the same time to improve low end. With a single cam you affect both intake and exhaust timing. You would need an adjustable cam sprocket to dial in the cam for optimum performance.

There may be other issues with making certain parts of the head that thin, though I do not know of any specifics except I think the FSM recommends discarding the head after only .040" is milled off. Probably has more to do with emissions and use of regular gas when the CR is raised.

[larry mcgrath]

This is the 2nd time trying to post a reply. here we go first i have 3 4x4 wagons 2-1983 1-1984. The 84 has the 3ascv with the milled head. When I first did this I thought it would realy screw up the valve timing but compansated for it with ignition timing. The engine will ping if luged in 4th gear . Living at 5500 ft on a 95 degree day the density altitude is like living at 9,000 ft . I'm in the process of a total rebuild of one of the 83s i'll keep you posted. Larry: