I need help deciding what to do...4.1 built or 3.8 built

[coldair85GN]

Both blocks are sitting here staring at me fully disassembled. The 4.1 is a late model (probably an 84) and the 3.8 is an 87 turbo block. I can go either way at this point. My goal is mid 10's. My build is in my sig which was done with this 87 block. Opinions?

 

[CTX-SLPR]

3.8L would be cheaper since the pistons are off the shelf, 4.1L would make more power with the same parts.
3.8L is arguably more durable with thicker decks and lifter valley, you'll break anything if you try hard enough or detonate.

I'd build the 4.1, just realize its going to be a bit more expensive with its custom pistons.

 

[Lee Thompson]

Imo

3.8--109

 

[Grumpy]

3.8--109

X2

 

[SHADOWII]

4.1

Why? I ask myself that same question! I guess just because you can and if you don't, you will always be wondering "what if!" I have both setting on engine stands now w/the same haunting possibities. 206 or 224, TE-70 or 71GTQ? girdle or caps or both? HELP!.....lol:biggrin:

 

[Kid Turbine]

Well I am building a 4.1 (about done) because my friends dad had this motor wrapped up sitting on a tire and it was a 291 motor with gn heads, rods, and crank for $40.00. But the pistons dont have to be custom cause at Flatlander Racing - High Performance Engine and Racing Parts you can get hyper/ coated pistons for $36 a peice. bur for the 3.8 you can get forged for $60 a peice or hyper for $39. I went hyper because i have never had a problem with that type of piston before in racing. It is all in the tune!!!!!



I have an 357 S-10 with hypers with 250hp shot of nitrous and its been together for awhile!!

But before that the S-10 I was driving for a guy had trw pistons (cast i believe) with 225hp shot of nitrous, and it was drag raced for 4 years before it went. (one cylinder had 90# compared to 120#, cracked piston)

But if this motor fails me for some reason that a buick will destory a hyper faster then a chevy motor.

My sbc will be waiting for its chance to release some hell through a s475 (currently building also)

 

[Brer Rabbit]

109

Build a 109 especially if U dont mind buying a stroker kit.

 

[dlafont]

4.1 vs 3.8

I did quite a bit of research before deciding on a 4.1. From what I've seen (I might be biased a little) i'd say 4.1 is better for street manners with good track capabilities. The 4.1's extra cubes give it better performance and response down low. A girdled 291 block has proven to go to as much as 700HP without trouble (staying out of detination). As long as your OK with the 700HP then youre in proven territory. For >700HP there are more 3.8's that are proven to go further but I cant tell you if any of the 4.1's have been pushed farther than 700HP or have blown up that I know for that matter. Maybe somebody can chime in with this.

The 4.1's are also nice with some race ported champion gn1r's. The valves are more unshrouded with the bigger bore and have more potential of producing more HP at lower boost than the 3.8. The regular gn1's also do better on the 291 4.1 block because of the unshrouding benefit.

The hyper pistons seem to be the choice if you don't want to go with custom pistons.. Customs can be quite expensive.

I've also heard of some people looking to stroke the 4.1 but I don't know of anybody who has succeeded yet. They use the same stroker parts as the 3.8 stroker kit except the pistons are custom.

I've attached a picture of my 4.1 and I'm going to install it and tune in the comming weeks.

D

 

[49-blues]

Very nice job - im working on a 4.1 stroker also. What bore did you go with? stock crank? billet caps? stock rods?

 

[CTX-SLPR]

I have a mostly complete 4.1L motor. The poop on it:
Block: 484, 3.995in bore
Caps: Billet first 3, stock rear, girdle won't clear the chassis (Hybrid)
Crank: Eagle 3.400in forging
Rods: K1 stock length (if it gets opened it's getting 6.0in since the pistons are 0.031in down)
Pistons: Diamond customs that I messed up the deck and compression heights when ordering
Heads: Champion CNC irons
Fel-Pro 1000's and ATR steel headers (rumored off of Jay Carter's old car) Yet undetermined turbo.

 

[87GNSteve]

I did the 4.1. Love it.
You can get away with using a larger cam and turbo w/ a lesser stall converter.
Also have plans for a more serious one in the future.
Im in the parts acquision stage.
I have:
291 Block
CAT crank
K1 Rods
BHJ balancer
BHJ flexplate
Waiting on: pistons and billet caps, GN1 heads.

 

[boostingbuick]

4.1 here. Not looking back. If I had to do over, I would do a 4.1.

 

[dlafont]

Hey boostingbuick,

Do you have any HP or ET numbers? I'm in the process of building a very similar combo.

D

 

[49-blues]

what is the Comp/Height of the diamonds- i have a new set of diamonds 4.00" and i think the CH is: 1.640."

 

[Black Power]

I am doing a 4.1 production block with ported stock heads, a big turbo and intercooler, and a shot of nitrous. Budget build for my street car :biggrin: I think if I blow up the 4.1, my next "turbo 6" will be a turbo 6 liter :biggrin:

Do the 4.1, I think it will be fun...oooh that rhymed :redface:

 

[boostingbuick]

On 93 my car put 550 to the tires and has gone 10.90's on a 26 slick. I have not put the 72 on it yet. It's in the assembly stage right now. I am hoping to get into the 10.50's this year, but on a 28 slick.

 

[87GN_70GS]

The 4.1 blocks have a history of cracking with enough hp.

 

[dlafont]

4.1

I heard that certain blocks crack around the headbolts sometimes however there have been mods that have been recommended to reduce this such as drilling out the first couple of threads in the head stud locations so that the headstuds pull from deeper into the deck, etc. I've also heard that it depends on the blocks... 291's seem to be the best to use because of the appearant deck strengh improvement near the head studs around the water jacket.

My source for the info on this build was:
TurboBuicks.com - Build a Budget 4.1 Motor!
and
4.1 Recipe

Some of the postings indicated that even with these types of cracks the blocks still seem to be OK.

Maybe somebody can chime in with their experiences such as:

Where did they crack? What block did they have the problem with?

Has there been any other catostrophic failures that can be attributed to some root deficientcy with these blocks. What are the opinions of where these deficientcies are?

Anyways... would be nice to get some feedback as I've seem more and more looking at using the 4.1 blocks.

D

 

[49-blues]

How much is enough horsepower and on what kind of build up?

 

[87GNSteve]

Do a search on the TBs.com site.
The search here is limited to 4 or more characters and you should search there under:
484
291
4.1 etc there has been tons of discussion and photos.
That 4.1 recipe seems very doom and gloom and seems pretty old.
Unless you have a block in your hands it might be hard to find one.
and if you have one use it!
There is plenty of us out there just bring it to the right shop and it will hold together.
Claims that the 109 is stronger are just that--claims. there has been no test to my knowlege of a 109 and a 484, 291 all being built to exact standards and tourture tested until failure.
From a visual the 109 looks stronger but by how much? 10 HP ? 20 HP?
and why would someone run their car at the terminal horsepower/RPM level anyway?