4.1?
- Thread starter CORNFEDGN
- Start date
If it's really an 85 it'd be one of the last ones built. Supposedly werent offered after 84. Damn sure worth grabbing for free, they are getting scarce. Post up the casting number off the block.
Off the shelf forged pistons do not exist, have to have custom forgings or run hypers. Head gasket is pretty thin between cylinders, the ones I know of running around are using cometics. Check the deck for cracks from the head bolt holes to the water jackets but I've heard of people running them with the cracks and not having any problems with it. Not as beefy as a 109 block but it takes a lot of HP to break a block without detonation.
Off the shelf forged pistons do not exist, have to have custom forgings or run hypers. Head gasket is pretty thin between cylinders, the ones I know of running around are using cometics. Check the deck for cracks from the head bolt holes to the water jackets but I've heard of people running them with the cracks and not having any problems with it. Not as beefy as a 109 block but it takes a lot of HP to break a block without detonation.
- Joined
- May 26, 2001
Ask anyone that has gone from a 3.8 to a 4.1, especially in a street car, and they will tell you they would never go back to a 3.8! 
I personally have 2 4.1 production block engines, and 3 more in the build process.
A couple visiting Canadians were completely blown away with a "test" drive yesterday at 17 psi. on e-85!
Forged pistons for a turbo 4.1 must be custom, but are priced similar to the 3.8 forged pistons we use.
I personally have 2 4.1 production block engines, and 3 more in the build process.
A couple visiting Canadians were completely blown away with a "test" drive yesterday at 17 psi. on e-85!
Forged pistons for a turbo 4.1 must be custom, but are priced similar to the 3.8 forged pistons we use.
The biggest (expense) lesson I have learned is when builing a 4.1L build what you want and then spec out custom pistons. In the end it will be a ton less expensive and then you get what you want and not have to compromise on the combo. I started a build with a set of pistons and tried to build around them. What a huge mess. I ended up not using them and had to get customs anyway. It turned out alright but would have prefered a stroker crank. Anyway, don't be afraid of cusom pistons. The cost is not much more than any off the shelf stuff for a 3.8. Get with a good builder and let er rip.
Thanks guys! I've been working on my Gen5 Camaro and I'm calling it done. Now I'm looking at my 60K GN that I've had for 23 yrs. to maybe build a engine for it. I want to take out the original engine (which is in great shape) and build one that has a little more HP I've been running E85 for 3 Yrs. and having great luck with it. I'm going grab the 4.1 and go for it!
ek02
Well-Known Member
- Joined
- Jan 31, 2008
Good decision! I run N/A with nitrous, and the 4.1 with a 3.625 stroke has so much more torque than a 3.8, there is no comparison. Be sure you countersink or recess the head bolt threads in the block. It will at least need billet caps on the center mains. I like the RJC girdle myself. It's a pain to have it machined and to assemble it, but I think it holds the bottom end together better than just caps. Just my opinion for my setup. There is a car in my area with a 109 block with a girdle, and it regularly runs high 9's with a stock crank and a girdle, and lots of boost on E85. That helped me decide on the girdle. A steel crank and center caps seems to hold up on the turbo cars with good tuning as well. You will also find that the ring packages that are available will determine the bore size. Usually standard bore is not a problem and .030-.040 is also available from JE in file fit.
