4.1... maybe.

[80sportcoupe]

Well, we finally tore the engine down and the crank is destroyed Looks like there was was front to back play prior to the rod bearing spinning.

190K 3.8, RIP. You were a great mill.

Since I'll be pounding junkyards for the crank out of a 4.1 anywho, we figured why not just build a 4.1? They came with the rolled filleted crank and 8445s

Well, it'll be an interesting summer. I'll post as it goes.

 

[b4black]

I say go for it!

The only drawback to a 4.1 is the pistons. Quality pistons will need to be custom made which is expensive and takes time. Enough people are going to 4.1's that this may change soon.

If you find a good running 4.1, you may want to use it as is. At the HP and boost levels of a Carb/Turbo, you might be able to get away with the stock peices.

BTW, many 4.1's don't have 8445 heads. Just the 83 and later engines. The difference between 8445 and earlier heads is minimal. Don't worry about getting 8445's.

 

[Turbo-Rich]

Originally posted by 80sportcoupe

190K 3.8, RIP. You were a great mill.

AMEN

 

[80sportcoupe]

Found one.

OK- 87 junkyards later, I found a '82 4.1-VIN4 reasonably close to the shop. Mileage unknown, but tagged "good"... Wish me luck and a good crank.

 

[MY85pontiac]

ok whats the big deal about the 4.1 crank? i happen to have a 82 4.1 and a 85 3.8. i wanna know what the internal differences are between the 4.1 and the 3.8.


(i admit i'm clueless as to what a rolled filleted crank is, so explain it to me)

 

[Freddie's Buick]

According to forum members, the 4.1's crank is the same one used on the turbo 3.8's. It's an x'tra heavy duty crank having rolled fillet's on the rod and main crank journals. (Not that the 3.8 turbo, N/A or the 4.1 can go without it. They can still perform with the regular crank).

The regular 3.8 crank has the same rolled fillets on the crank's main journals. The differance is that the 3.8 's rod journals do not have rolled fillets.

Still, the regular crank has shown to take much punishment. If one has the HD crank, hold on to it! If it's toast......so what! Get a regular one.

I too do not know what the heck a rolled fillet is.....is that some sort of steak?

 

[80sportcoupe]

filleted mignon, judging from the price of a new crank.
$1K can buy a lot of steaks. And beer.

The guys in Junkyard Dogs have been chatting about this a lot, check out the 4.1=Turbo 3.8 thread. There's a good link to the gnttype site with pictures.

After this experience, I personally will try to stock a spare crank in Dexter's Laboratory, uh, my shed.

 

[mygrain]

b4black:
I say go for it!

The only drawback to a 4.1 is the pistons. Quality pistons will need to be custom made which is expensive and takes time. Enough people are going to 4.1's that this may change soon.



What about the speed pro pistons? I believe theyre 8:1 compression. I dont think a carbed car would put enough stress on them to do much damage.

 

[b4black]

I'd be willing to bet that even the stock NA pistons can handle modest (fairly stock) boost levels. If the 4.1 ws running I'd throw it in as is. But if I were going to rebuild it, with the idea of running as much boost as possible, I'd probably want the insurance of a good pistons. I'd build like it was going in a SFI/IC car.

Same with the crank. If it was a fairly stock car, the turbo crank is overkill. But if the plans are for the 12's, then the turbo crank is good insurance. Since it's not going to be a 9 sec cars, don't pay for a uncut turbo crank.

It's not HP/torque, but detonation to worry about. We may not have the power, but are probably more likely to have detonation problems. And the eariler ESC's aren't as good as the later designs ('83 TR have the same ESC as SFI motors).

 

[80sportcoupe]

Well, I'm considering investing in some detonation control measures such as alky, but the bottom line is if I'm going through the expense of having an engine built, I want it to last as long as possible. This project ain't cheap, and I ain't wealthy enough to do this again any time soon.

I plan on very taking the old TR to the strip mainly as a reference point, and do not plan on abusing it otherwise, unless to occasionally teach a kid in a riced honda a lesson. I do plan on running higher than stock boost. Since the old crank died so dramatically I suspect replacing the turbo is a really good idea- there must have been metal in the oil running through the turbo.

If I can't figure out an economically feasible way to make the 4.1 low end strong enough to last under boost, I will probably just take the crank and go with another 3.8 since forged slugs are available.