Originally posted by sixgun86gn
I plan on putting GN1s or the new T/A heads I have been reading about.Also Is there anything I have to do to the heads to mate them to a 4.1?Im also thinking of a cam of about 218 duration at.050.Any cam suggestions?Intercooler ,I will e-mail you.
Your e-mail kept bouncing back so here is what I wrote. Some may be off slightly as I can't remember all the numbers:
I got all my parts back from the machine shop before leaving for Texas for 3
weeks. It is still sitting in the wrappers so over the T-day Holiday I plan on
putting it together. The 4.1 gains benefits of everything a 3.8 does. Have you
looked closely or done any research on a 4.1? Let me tell you what I know from
doing research and measuring:
-The lifter valley of course is open style without bridging from one side of
the block to the other. Excellent idea to grab a Dremel and knock the sand-
casting flash (roughness) off the valley holes so they can never chip off and
fall in the motor. Also helps in preventing some of the stress risers in this
area.
-The rear main actually mics out a little thicker than a 3.8 but it is
marginal. Not a problem area in either but thought you may want to know.
-I had a 3.8 109 block sonic checked compared to a 484 casting (best 4.1
production available)and the deck of the 4.1 is .125" thinner to start with.
This is a known problem area as some of the 4.1's are cracked before even
turboing them. Have your block magged! If nothing else the decks and cylinder
walls. The 484 casting has a couple of extra reinforcement ribs like the later
109 3.8 blocks which make them stronger.
-All 3.8 109 blocks have their anchors for the head bolts down deeper in the
cylinder. The 4.1's threads are right up top at the deck surface. Great idea
to chamfer the top of the thread to help prevent a crack starting there.
-The cranks, rods, cams are the same. The 4.1 takes different cam bearings
with all together different oiling holes than the 3.8. Pistons are much larger diameter. I think 3.965" for standards .
-You can get Speed-Pro rings or a set of Total-Seal second rings but they
don't make a top ring Total-Seal to fit a 4.1.
-Your 14 bolt oil pan will not be baffled like the GN 20 bolt oil pan. You
will have to get one. They only come on the 84 GN with a 14 bolt pan and you
will pay dearly for it. I got one from a close friend for $65.00. It was
rusted so I had to blast and powdercoat it. I have since picked up a mint one
off of E-Bay for a steal at $35.00 as a spare. I flipped the oil plug to the
outside before doing this so all the oil will drain. If you don't about 1/4
quart will still be there with any metal or debris.
-They make a girdle to fit a 4.1 to add strength just like the 3.8 20 bolt.
The caps are the same if you want to go billet.
-The 4.1 takes different head gaskets than a 3.8 to accomodate the bore.
-You will need a universal or 14 bolt front cover to fit the oil pan.
-The turbo drain back hole in the front of block is not drilled. You will have
to have the 3/4" NPT thread put in for this.
-Without a doubt check your pushrod length because it will differ if using 3.8
pushrods.
-The 445 casting heads are better than the 293 casting 4.1 heads. Use them.
-The 4.1 has a different flywheel with weights. Use it.
-The siamese bores of the 4.1 leaves thinner cylinder walls. Bore just what
you need.
The production 4.1 is nothing like a Stage 2 4.1 motor and to push 600 HP or
low 10's is asking for trouble. If you do the girdle and other things it may
last a while if the block doesn't split in the valley. I don't plan on going
past 10.8 with mine so here is what my 4.1 build consists of:
-Studded bottom end with billet center caps. Line bored .005" with
a .010"/.010" turbo crank.
-.020" bore with Hyperutectic pistons. I catch grief all the time over them
but I like them. They have worked well for me. Shelf 4.1 pistons are none.
They are custom so $600.00 is what J&E gets for the forged 4.1's. Lee Thompson
had/has the fastest hot-air 4.1 known and ran a production 4.1 with Hypers to
11.2 hot-air and didn't lose one. Up to you. Hypers are $150.00. Polish the
tops and you are golden.
-Total-Seal second ring setup
-Chamfered deck
-Head studs. A must on a 4.1. It will help a bunch to equal the load exerted
on the deck and will help keep it from cracking.
-ARP Pro-Series rod bolts
- "H" series bearings with wide rods
-Fel-Pro 1000 head gaskets. Never tried them but that is what fits and that is
what Lee liked. The 1007's would work nice too but I am not set up that way.
About all I can think of right now. If you have more questions just ask.
