Thoughts On 4.1 Liter Based Builds?

[Cool Guy]

How well does the 4.1 liter Block perform / hold-up as compared to the 3.8L 109 Block?

Is there a date range or model of the 4.1 that is more desirable than others?

Will the 4.1 oil pan fit the Regal?

I understand the 4.1 Block will require machining for a turbo oil return port. What other modifications are needed?

[earlbrown]

How well they hold up depends on the loose nut behind the steering wheel.

The oil pan's aren't the same. The 4.1 is an early block so it's a 14 bolt block.

[Scoobum]

I cracked two separate cylinders and went into the water jackets in a .030 over 109. I'd want as much 'meat' between the cylinder wall and water jacket as possible. I currently run a standard bore 109...for good reason.

[Scoobum]

If I was gonna build a 4.1, I'd be calling Nick Micale.

[TexasT]

The "291" casting is regarded as the one to seek though I have seen where people have used a "484" casting also.
Drilling and threading a block isn't that big of a deal. Or you could rig it up where it dumps back into the oil pan if that would seem easier with a welded on nipple or something.
Chamfering the head bolt holes seems to be a way to keep the deck from cracking. Over on the TBS.com there was a sticky of how one person did his. ill look for a link.

Found link
http://www.turbobuicks.com/articles/4point1ForCheap/

Some other links for those looking for something to read
http://www.turbobuicks.com/forums/showthread.php?t=28069

Not sure if you will see it or how Photobucket goofed up the pix but here goes.

Maybe you can see the casting number ending in 291 toward the top of the pic about a third of the way from the right.
I've been planning a 4.1 build for well over a decade. Pistons have been my hurdle, or more correctly the cost of nice forged pistons. And with the advent of good forged Chinese cranks I think that is the way to go. My theory is that the flex of the stock crank has torn up more stuff just behind detonation at the top of the I tore it up list. And a forged crank minimizes the flex so it cam stay together and not bust out the webs in the block.
I want to go to a 4" bore as the sbc offers pistons and rings in that size. And with the advent of "less expensive" forged pistons available in what ever compression height you want it is easy to get where you want with a zero deck to help with the detonation. And a set of aluminum heads a 9:1 compression ratio becomes real streetable or at least I'm going to find out.

Good ness this escalated quickly. Sorry it turned into a novel. I have big dreams.

[earlbrown]

Pistons have been my hurdle, or more correctly the cost of nice forged pistons.

I want to go to a 4" bore as the sbc offers pistons and rings in that size. And with the advent of "less expensive" forged pistons available in what ever compression height you want it is easy to get where you want with a zero deck to help with the detonation.

It's be nice if 4032 forgings would quit going up in price. They're almost as expensive as 2618's now.  I still like the 4032's better for street builds.

There's no reason to go straight to 4" if you don't have to.  Even though that's 'only' .035" over.  The block will dictate how far over it takes to come clean, no reason to go screaming past that if you don't have to. My first block wouldn't come clean at .060". I wish I still had it, I would have sleeved all 6 holes and build a backup.

Keep in mind those pistons don't use the thick factory style rings, so ring availability is different animal since mine can go either 1.5mm or 1/16"  (or 1.2mm, or whatever...).



This link shows my 4.1 build (with the crappy FMO pistons that caused me so much grief and the reasons for designing my slugs).  http://www.turbobuicks.com/forums/buick-v6-turbo-tech/88129-day-life-earl.html

Notice it looks just like any 'normal' 3.8 build with only a couple exceptions.   Granted I ran my drain to the pan and I lowered my rocker shafts but everything else was the same as a 3.8.

[Cool Guy]

Thanks for the info. I've seen the "4.1 For Cheap" write up before. It's a bit dated & I was wondering if there is newer info available.


Knew about the Oil Pan bolt pattern difference. Does the original 4.1 Pan have the same shape as the 3.8?


Is the "291" casting found in any certain year, make & model?

[earlbrown]

It's dated because Make had to settle for the crappy FMO hypers at the time.  When I built my 4.1 I cracked 2 and 4 in less than one second when it was new. I though I blew a gasket between the two cylinders. After shotgunning a new $100 Cometic in there and still had 40PSI, I tore it down to the bare block. Got another set of hypers and broke another one in less than a month....

Needless to say I have forged slugs now and they can take a freakin beating.

Basically the same shape on the oil pan. The 20 bolt pan is pointed on the front and as three 1/4 holes in the shape of a triangle at the timing cover area.   The 14 is blunt and has two 3/8 holes for that job. The 109 blocks are based on the earlier 14 bolt blocks so the architecture is pretty much the same. They just changed the timing cover for some reason and added more threaded holes in the pan rail.  If you REALLY wanted to redrill a 20 bolt pan and make it fit, I guess that's possible. I would definatly use The Right Stuff and no gasket (and still might get oil weeping).

If you look at the link I posted you can see my 14 bolt pan that I added a turbo drain and a baffle I made from a Sony VCR cover using my GN pan as a pattern.

[Cool Guy]

I'm only able to view page #1. Won't show the pages after that.


How about fitting the 3.6+" forged stroker cranks into the 4.1 block?


What length rod is available that won't push the piston pin into the lower ring land?


Is a reduced base circle camshaft required to clear the connecting rods?

[earlbrown]

I don't think there is a such thing as a reduced base circle cam for out engines.  Cam to rod clearance can't be a 'published distance' per se.  It depends on the exact shape of the exact rods in the engine.  The only way to know is to mock it up, measure, and grind if need be.


On the shortest CH you can achieve that's kind of a trick question.  First you have to know the EXACT numbers as far as deck height, head CCs, etc so you know what you want...    The other factors are the ring pack. Thinner rings leave more room for a pin. 

The way I start is take the deck height, and start with .040" off the had. That math will show a starting point for CH and static compression ratio.  Then adjust from there if needed.

Also, there's once get out of jail free cards that is a oil ring support rail. Obviously the pin can't get into the top rings, but it can encroach into the oil rings space if needed.

That being said, I made a set of slugs a couple months ago for a 4.1 stage stroker with a 6.500" rod.   I don't remember the exact compression height but it was short as hell.

[Cool Guy]

How about the imported forged stroker cranks?


Which make & model has the best quality steel & tolerances?


I think I would prefer to convert to internal balance, so would require a suitable flex plate & damper also?


I've been reading up on connecting rods & stroker clearance issues. Sounds like Molnar has a rod that provides more clearance than others. What happens when a longer than OEM stock rod is used?


All advice is appreciated. Thanks.

[Cool Guy]

I cracked two separate cylinders and went into the water jackets in a .030 over 109. I'd want as much 'meat' between the cylinder wall and water jacket as possible. I currently run a standard bore 109...for good reason.

Are you telling me that the 3.8L 109 block has thicker cylinder walls than the 4.1L blocks?


Is the 3.8L block more rigid?


What weaknesses does the 4.1L block have?

[TexasT]

the 4.1L is a Siamese cylinder arrangement like the sbc 400. This puts the cylinders quite close together and there aren't any cooling passages between the cylinders. The cylinder wall thickness would depend on core shift in the casting I would think. But finding a "thick" one out of the small numbers available would equate to a "needle in a haystack" if you ask me.


If you are that worried about it TA performance sells a right nice after market block.
http://www.taperformance.com/proddetail.asp?prod=TA_V3800


Wouldn't really fit the budget theme though.

[Cool Guy]

TA Performance has some nice stuff. Out of my price range though.


Familiar with the SBC 400 core shift.

[TexasT]

For those who want a little core shift info.
http://www.v8buick.com/index.php?threads/understanding-core-shift-in-the-455-block-why-sonic-checking-is-so-important.171953/


Applies to all cast engines. And gives some info on how to tell the thickness and such.


I would think if you do a little sonic testing to the cyl walls and they are pretty equal you will be alright for a street engine. If you are thinking 35psi and some alky/race gas, this might not be the best way to go about it.