95 4.0 heads on a 91?

[Rightname]

I'm putting together a spare engine as mine is getting a lot of miles on it at present. I have read that the 95 head has a smaller chamber and the pistons had a larger dish than the 91. Has anyone tried to put the smaller chamber heads on the small dish pistons? What happend?

Thanks!!

 

[Alec]

It will raise your compression ratio about a point and it will be fairly hard to run perfectly without custom computer tuning.

 

[slow-demon]

I just did the swap. Installed a 95 cylinder head onto a 94 explorer. The 95's had a smaller chamber than the 91-94's as most of you know. I did the swap because I didn't want to purchase new 94 heads. Basically this is what happened. Bought a 94 explorer with blown head gaskets. Found out one of the heads had a crack. I didn't want to purchase new heads (pricey) so since I had some 95 cylinder heads laying around I decided to install them on. The truck started up fine and runs smooth. Power is good, I can't tell the difference. But what I don't like is that it pings like a raped ape. Especially going up hills. I new that it was going ping when the compression was increased. I was running regular 87 octane gas so I will be trying some super unleaded 92 octane. I also read that running a "colder" plug might also help. Right know I am sidelined with a broken rear driveshaft so I haven't had a chance to do some further testing. Has anyone else done this mod??????

 

[Rightname]

I understand there may be a plug in the wiring harness that can be removed that will retard the timing a few degrees. I have done this on an Aerostar and it worked fine. Not sure if there is one on the explorer. I'm fairly sure my 91 harness has it. After you get the driveshaft fixed, try that and let me know if it works. The plug looks like the timing plug on an older 2.9 that has to be removed to set the base timing.

 

[Rhett]

If you are referring to the octane shorting block, then I would recommend that you not do it. It might help the pinging, but it will cause a noticeable loss in power.

 

[slow-demon]

Are you talking about the "spout" connector that is used to check base timing. It is located next to the ignition module located in front of the battery. The spout prevents the computer from advancing the ignition spark. Regarding the driveshaft. I have a longer 4 door driveshaft that I will have shortened to fit. Only thing is that the shop can only "dial indicate" the shaft in. The cannot balance the shaft. Nobody in my area balances driveshafts.

 

[slow-demon]

Update

I didn't take out the gray timing connector as it will stop the computer from advancing the timing. It is used to check base timing only. And taking it out will not let the timing remain at 10 degrees all the time.

I have been running the explorer for 2 weeks now. It's running with good power. Engine runs smooooth. What I did to get rid of most of the pinging was install colder spark plugs. The stock specs recommend ford AWSF42PP's. I installed some Ford AGSF22?? plugs. It helped big time and got rid of most of the pinging. I kept running the fuel I had in the fuel tank (full tank) which as mostly 87 octane and only 2 gallons of 92 octane mixed in. I also installed a colder thermostat (180 degree). I recently filled up my tank with about 6 gallons of 92 octane. It runs so much better now than with the Awsf 42 plugs and 87 octane fuel. I couldn't believe how much difference changing the spark plugs made. The thermostat could have a little something to do with it too.I might just try and use the 89 octane and see what happens. My stupid fuel gauge is broken (too lazy to drop the tank and change the "float") so I have been estimating my fuel tank level. The super unleaded 92 octane is just too damm expensive here..$2.74 a gallon.