4.1 info and stuffs

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TurboJames

Member
Joined
Feb 8, 2015

hey guys I'm newer ( couple years) into the buick thing now, i have a 4.1l 291 casting.. the motor has hyper pistons .030 in it. This means its bored 30 over correct? My goal is to run mid 10s. turbonetics 6465, can 3500 stall, alky, turbotweak chip etc..

So, here in windsor canada, theres no buick specialty shops around this area, and the fact the US dollar is so much more than canadian, thats out of the question..... So, i will be bringing my motor to a reputable guy i know who is good with motors... anyway a couple questions here,
3.8 turbo crank and stock rods.... should these be attended to? as in, should they be replaced?
forged pistons in a must... how should i approach this? quality/ cost?
what are the specs and clearances for all the bearings and stuff like that.. .i might be missing something but i just want to have all the proper specs and information build sheet so i can bring my motor in and say this is what i want done, to these specs..


i appreciate the help, sorry it was so long ! lol any tips, or information i receive i am very thankful for!
 
That 4.1 block is the best one to use . Make sure you have the 2 dot rods and turbo crank with the rolled fillets . Also I would go with two center caps minimum and make sure they are installed properly line bore/hone ect. Or girdle . Yes .030 means the bore is .030 over . These days the nice cranks are affordable if in the budget I would go with a nice crank for another $ 500. What cam r u going with ? I would pay the extra and go roller they are hassle free and u don't have the risk of wiping a love as u do with a flat tapped . You can read up on vortex Buick about a bunch of other stuff . Good luck with your build bro .
 
I would get the block sonic checked. I have a 4.1 that is .040 over and the machine shop checked for cracks... It was good but the wall thickness on one wall was not within spec. Also check for core shift. Yes forged pistons are a must. Look into SRP forged pistons. The 3.8 turbo stock crank can handle lots of power. Be sure to use main studs and 2 billet center main caps. Use head studs and get an alky kit, and 18-20 lbs of boost can move you into the 10's with a decent roller cam. Google 4.1 recipe for fast proven combimations
 
marc daniels said:
I would get the block sonic checked. I have a 4.1 that is .040 over and the machine shop checked for cracks... It was good but the wall thickness on one wall was not within spec. Also check for core shift. Yes forged pistons are a must. Look into SRP forged pistons. The 3.8 turbo stock crank can handle lots of power. Be sure to use main studs and 2 billet center main caps. Use head studs and get an alky kit, and 18-20 lbs of boost can move you into the 10's with a decent roller cam. Google 4.1 recipe for fast proven combimations
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Im right across the border from you. We have several shops that know these cars. Our currency exchange is close to even with Canada (last time I checked). Automotive Machine on Garfield rd in Utica Michigan is maybe 30 mins from the border and build hundreds of these motors. They build for most of the performance shops in the area.
 
Well, i have alky and head studs, the 3.8 crank will suffice? the caps will be a must and so will the forged pistons... i will give SRP a call tomorrow....
so, is your shop charging with par exchange rates? lol as of 5 minutes ago 1000 US= 1397 CA lol id come right away!

thanks !
 
TurboJames said:
Well, i have alky and head studs, the 3.8 crank will suffice? the caps will be a must and so will the forged pistons... i will give SRP a call tomorrow....
so, is your shop charging with par exchange rates? lol as of 5 minutes ago 1000 US= 1397 CA lol id come right away!

You shouldn't run as much boost on the 4.1 but you will make it up with cubes!! 20-22lbs should be fine. That is a great exchange rate for you. I would exchange currency at the border, our banks will give you a hassle!!! Google the machine shop and give them a call. Tax season is approaching and they get swamped fast, plus Autorama is right around the corner....
Click to expand...
 
You will need to bore, or probably hone it, to 4" if you use a 1/16, 1/16, 3/16 ring set. There are no readily available rings of that thickness for a 3.995 bore. Most forged pistons will use that ring thickness and there are a lot of ring sets for a 4" bore. You will probably have to have pistons custom made, so you may want to consider a forged stroker crank. There are a few issues with a stroker, mainly clearancing the oil passage for #1 rod bolt. Rod to cam interference has to be checked and the rods modified to clear.
 
I just built a 4.1(291) budget motor with .040 hypers, .010 .010 turbo crank, and 2 dot rods. Bought a roller cam used from a member, and bolted on some Champion Irons with ARP studs. Had it all together last summer and found out the shop that did my balancing screwed it up. I ran it for only a couple miles before finding out there was an issue, but it definitely felt much stronger than my old 3.8. Just buttoning everything up for the second time now.

A couple notes:
• Make sure you balance the rotating assembly.
• Make sure you have a 4.1 timing cover/oil pump in good condition.
• Oil pan is 4.1 specific as well.
• Head studs are different between the 3.8 and 4.1 so make sure to get the right set.
• You'll need to drill a turbo oil return hole in the front of the valley.
• Felpro 1000 head gaskets work well.
• Stay with the valley pan style intake gaskets.
• The Right Stuff for oil pan sealant, rear main, and intake end rails.


Here is a great page for rebuilding the motor. http://www.gnttype.org/general/rebuild.html

Most all of the information is in the article, or linked to places to find it.

These were my notes from my list of parts
Speed pro R93435 Plasma Moly Rings(4.005" bore-file fit)
E408K is a Moly Top Ring for the Buick 4.1-I didn't use these.
.018 on the top ring and .020 on the secong ring and have never had a problem.
ARP head studs part #123-4201
Main stud kit: ARP-123-5401
Felpro 1000 Head Gaskets-Need 2
Speed Pro 107M mains
Speed Pro 67120CH rods
Clevite 960P mains
1398H rod bearings
King main bearings - MB443AM
King rod bearings - CR6616SI
felpro BS40613 Rear main seal
Fel-Pro TCS45930 Timing cover set
Intake - Felpro MS96037
IF you're not going to use EGR order a MS96037 valley pan gasket and save a few bucks.
Dura-Bond High Performance Coated Cam Bearings BP-13T
The Right Stuff and do away with the oil pan gasket
Clock the front cam bearing 'wrong' so it injects the oil at 5:00 ish when viewed from the front. If your block has fully grooved cam bores do the rest of them that way too.
Roller cam button? Sealed Power, part No. MR-1874 Cam thrust button w/needle bearings 25532588
 
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There is a fellow in coburg, Ontario who does a fair amount of racing in his GN. I'm not sure how close that is to you but I do know he has a competent machinist he uses. Your guy should be good if he can follow directions. This isn't a Chebby motor. Buick need attention to detail. The info is out there you just have to find it.
 
czimpel - how did you realize that the shop made a error if it was running strong? My timing cover is in good condition, oil pan is correct, and so are the headbolts and studs. I am confused about drilling a hole for the oil return? This motor has been running before and running well at that, so I'm not sure maybe its already done? the right stuff works amazing! only stuff to use. I don't have a roller cam only a edelbrock flat tappet... for now unless i can find a deal on a roller setup.

Texas t - i would drive there, but unfortunately i live in the most southern part of ontario lol.. thats a 8 hour drive for me, But i am thinking about it. Thats exactly it, i am basically looking for a sheet for directions for him to follow. i have been starting to make one of my own, i just figured that someone would have already had one... the Gn Type site says its for a 3.8, rookie question, but is it still all the same for the 4.1?
i am just double and triple checking because i don't want any problems and have to spend any un necessary money.

Thanks guys!!!
 
Bad vibration when I got on it. Uploaded my balance card here and got the lowdown on how bad it was off.

Thought it was because of the HR mounts at first.

The oil return needs to be drilled to match how the 109 blocks are machined in the front of the lifter valley. It was fairly easy todo. If it already has a turbo on it, more than likely it's done.

Also, mine wasn't a stroker, not sure why I typed that in the previous post. It was just a budget 4.1 build with the stock crank and rods.
 
I have been debating on leaving the turbo crank in and just changing the pistons, would that make any improvements? i appreciate all the lists part numbers and everything a long with your post. i will be saving all of the info
 
If you are going to spend the money on new forged pistons, I would wait and collect enough to purchase a forged rotating assembly. I bought a forged stroker assembly from Dave Husek for my 044 4.1 block. Still collecting parts for that build. $$$$$$

It all depends on what you want to do and how much you enjoy fixing. I love the repair process, so I don't mind if I break things. I started with a 500 mile rebuild from a cookie cutter engine rebuilder. It was a .040" over 291 block. I disassembled it, used the turbo crank and rods from the 044 block. The 044 engine only had 40,000 miles on it. Turned the crank, balanced everything, honed the cylinders, new plasma moly rings, and clearance everything correctly for proper oil pressure. Bought a used RPE billet roller(pretty mild).

Haven't really drove it since fall of 2014 due to the balance issues. Hoping to get some miles on it this summer.
 
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I saw a guy post on the Facebook site, that Eagle makes complete forged rotating assemblies for the 4.1 now!!! Crank, rods, rings, bearings and arp bolts. I saw that post about 6 months ago
 
Have you been over to this link?

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

I wouldn't use hypereutectic pistons as they tend to disintegrate with detonation. Just a personal preference.

I would do the stroke crank if I was buying pistons any way. Get that block checked out and see if I needs bored. Might get by with honing it out to 4" as suggested. Lots of ring choices as pointed out above. I'd want the pistons on hand and fit them for each bore. It will come out tight and that is a good.
 
the specs from the buick power source and GNTTYPE for the 3.8 i can use all the specs and clearances etc for the 3.8 right? or is it all different??! ;/
 
Except ring gaps and piston clearance could be a little different due to the larger bore.
 
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