|"This information represents what worked for the author(s) with their combinations. It may not work for you. Be aware that anytime you increase the performance of your car you run the risk of damage. Be smart about modifications: take them one at a time and keep a close eye on vital tuning indicators such as knock counts, O2 volts and RPM. This Recipe assumes you are using adequate octane RACING fuel for best performance. -editor"|
|In an effort to help you guys out on building a 4.1 or whether or to build a 4.1 production block (NOT a stage block), I put this little FAQ together to answer some common questions I get.
First, if you have a GOOD 3.8 block from an 86-87, then stop thinking 4.1 and build your 3.8! The advantages to running a 4.1 are definitely apparent, but hardly worth the price of custom pistons if it can be avoided, IMHO.
So despite my advice, you've decided to build the 4.1. You want the low end torque your 3.8 seems to lack. Here are a few things that I've found after building SEVERAL 4.1 motors. These observations are from my experiences. Like anything else, there will be different opinions out there.
|You've got 4 years to choose from, 80-84. 81 and 82 blocks have small oil pump feed gallies. The 83 and 84 blocks have the same size feed as the 86-87 Turbo 3.8s. This means that if you do pick up the earlier block, You need to machine that galley to the larger size to ensure adequate oil flow. You must find a block that has no cracks on the deck surface. MANY of them do. I found that a lot of the castings were poor on the 4.1 so sonic checking is a must for the long haul. You'll probably have to go through a couple blocks before you find one that has consistent casting thickness throughout the cylinder walls and deck surface.
For block preparation, you will first notice that you need an oil return line for the turbo. I did the tap and drill method in the stock 3.8 location. A better suggestion would be to run the return line to the oil pan. Think about a good strategic place for a boss to be welded to the pan (i.e. no interference with the crank). The advantage here is to keep the blistering hot oil away from the seemingly vulnerable cam and to avoid that oil dumping on the rotating masses below.
You should polish out the casting slag in the bottom of the lifter valley. That is a common place for cracks to start. Anything beyond that is at your own discretion. Use head studs. They put less load on the vulnerable 4.1 deck surface. Obviously you would be wise to run at least the center two mains in steel. I like girdles too. The less stress in any engine casting the better for that long haul. Go ahead and "surface" the deck. This means tat you're not removing any notable material, but you're putting a good finish on it and taking out any inconsistencies from past heat warping, etc.
[Comments from Jim Frankovich -- another tip when junkyard diving for either the whole 4.1L motor or the crank from it...IF you are pulling it for the whole motor AND the rolled fillet crank, while still at the salvage yard, pull the oil pan and a rod cap to double-check that the rolled fillet crank is still in there...those motors are now almost 20 yrs old and many have already been rebuilt...and if it was rebuilt by a major remanufacturing company, chances are that the original rolled fillet crank has been replaced by a std N/A 3.8L crank without the rolled fillets and also the blocks may already be bored out to +.060 over. Pull a head and check for overbore stamping on the tops of the pistons...Those companies usually epoxy some type of tag somewhere on the block with their name and some type of serial number so they can keep track of them for warranty purposes...thats a dead giveaway for a rebuild and chances are REAL good that the turbo crank is MIA...I have already been through at least 3 of the 4.1L motors looking for cranks and was lucky that I thought of checking before I grabbed the whole block and went home...BTW, they are becoming harder and harder to find in the salvage yards...and I never did find a good rolled fillet crank in the salvage yards...I finally got one from a local machine shop that had a stack of 3.8L cranks on the shelf already machined and he dug through them and found 1 with the rolled fillets(010/010) in the whole bunch of them...]
|Do the same to your heads. Stock Turbo 3.8 heads will work fine. Keep in mind the stock Turbo 3.8 heads are already undersized, and a 4.1 flows about 10% more air so they will be that much smaller. Will they hurt performance, no, but they may not allow you to utilize the extra cubes fullest potential.
I bore to a full 4.000" (.035 over). Note that this is the same bore is a Chevy 350. Ring selection is enormous for this bore. I like to keep my stuff as easy to find as possible, hence the Chevy pin and bore size. Also, 4.000" is the MAX bore for the 4.1 production block. So you might want find two blocks to prepare for the unexpected.
|I get a ton of questions about the magic piston to install. There isn't one. The worse that you can do is buying the Speedpro "hyperujunkit" pistons. They may be fine in that 455 in the your Electra, but they have NO business in a turbo charged anything! I don't have available piston specs so please don't ask;-) With minimal homework you can find the info you need to build the piston of your desire. ASK THE LIST.
You'll need to know compressed gasket thickness, desired compression ratio, compression dome cc, etc. Call JE or Wiseco for your slugs. Keep this in mind. For the most part, lighter is better. Full floaters are better than press fit pins. Thinner rings create more sealing power and less friction. If you go full float then use the same size pin as a small block Chevy. You will have an almost infinite weight selection in pins that way.
Higher compression means MORE torque down low, BUT it also means that you will run into tuning nightmares that will keep you up weeks at a time. Believe me I know. I started at about 9.5:1 and ended up at 9:1, which is still too high for a car that runs primarily on pump gas. If you're going to the track and running good gas, that boost in compression WILL be an advantage. If your livelihood is smoking Stangs on Amoco 92 at stoplights, then stay with 8:1 not to exceed 8.5:1.
You'll also find, as I did, there are few chip burners out there that want to or know how to burn chips for high compression. This being the case, you will have to teach yourself hacker skills or buy a Felpro. Another very important detail: Never buy just 6 custom pistons. JE and Wiseco have minimum orders of 4. This means that when something catastrophic occurs in your motor and you burn an $85 piston, you can't just buy 1. You have to buy 4! So, buy at least 1 extra, and if you're smart you'll buy two more.
Rings: I tried both Total Seal Race rings and Speed Pro Race Molly rings. They both seemed to seal adequately. Neither seemed to better than the other. I ran 1/16" compression rings and 3/16 oil rings. These size rings are easy to come by.
Crank: Any good Turbo 3.8 crank is fine.
|Head Gaskets and Cam|
|Felpro 1000s are the way to go. They have a 4" fire ring so they are perfectly suited for the 4.1. I have never blown a 1000.
The "key" to keeping gaskets where they're supposed to be is block and head prep. Both sealing surfaces MUST be surfaced with the right finish, free of "cupping", and oil/chemical free. Keep in mind that a rough sealing surface is not necessarily the best surface for HGs to seal on. A Felpro tech will be able to tell you over the phone what finish the 1000s require.
The studs I mentioned earlier will also help to keep a good seal.
Cam: I have tried a LOT of cams in the 4.1. The result was every time I went bigger, the car felt and went faster, period. The 4.1 flows about 10% more air so the big cams for the 3.8 aren't so big on the 4.1. The biggest flat tappet I ran was a 218/218 @ .050 while the largest roller I ran was a 214/210 @ .050. I sacrificed some duration with the roller but gained ramp speed and lift. In theory the roller would net more torque and a flatter power band, but the motor pulled extremely strong from idle with the 218/218 as well.
|Turbo/Injectors and Exhaust|
|Again, 10% more air requires 10% more fuel. Keep this in mind when ordering a turbo and injectors.
Exhaust: Again, more air, means better exhaust. If your exhaust is marginal on the 3.8, then it will be proportionally worse behind the 4.1. I think that about covers it. The rest of the typical bolt ons apply. Front mounts, front cover, etc that bolts right up from the 3.8.
Obviously, the motor is only limited by the amount of money you want to put into it. While it is NOT entirely necessary to do these mods I mentioned (which are minimal) to run the 4.1, they will make better utilization of the larger cubes. I hope I haven't forgotten anything...Good luck!