Block replacement

Mart u

Not stock anymore!
Nov 11, 2001
Hello all,
Here is my problem I need a new block! I removed my engine at last for a spun rod bearing( I was right) only to find two of my wrist pins had badly scored the cyl. They look like they have been that way for a while. I dont even need to mic. it to tell it's shot. Crank looks OK a 10/10 should take care of it. 2 rod & pistons??? I 'll replace all just to be sure. What are the best parts to use. Street car stored alot,79k I was getting ready to take care of some blowhard and his TA at work! I will be needing all your help in the future-I have till spring and it is cold in MI anyway. This will be slow to do,working with what I have left after setting the EX!! up for awhile.
Getting to my question- what blocks can i use with my current engine parts. such as--
85 block
4.1 from what cars?
87 block/with mods
N/A block?
After getting some input I'll go junk yard searching around here first. I want to keep this car a hot air. I've owned this car since new in 84. This is my set-up-
te49-new, 4mi-spun rod bearing on first outing!
36# injectors-new
ATR SS headers & crossover-new
340 Walbro
valve springs,rocker shafts
boost & knock gages
I will listen to everyone, I want it to be done right,even if it takes longer.
Thanks Marty U
First off, there is no such thing as a turbo block or turbo rods. You could find an 84-87 3.8L in any G-body car. Any of the blocks, rods, and heads will work. If you luck out and get an 86-87 109 block you will have to use different headbolts and composition headgaskets or stacked steel shims. The turbo crank came in every 4.1L which was available in the G-bodies and Cadillacs I believe but I'm not totally sure about the years, I think from around 80-84.
If you just have a couple of cylinder walls damaged, have them resleeved. I'm sure everyone has heard of horror stories with resleeving, just be sure to use a competent machinist that knows how to do it correctly. I've had a few done with no problems.
Well I think I found a engine It's a 4.1 in a buick 4dr,auto. but I believe the yard man said it was a 79'? It was sitting right there at first he said it was a 3.8 then his helper said the 3.8 didnt have a 4v carb,which it had. It fired right up no smoke and ran smooth.they want 375 for it.I'm thinking as long as I must rebuild one I'll do the 4.1.
I would like to make sure of a few things first, Can i use the newer front cover with good seal,and my current cam sensor?Can the oiling system be improved?
After reading all about the blocks on the web site am I correct in thinking the junkyard is wrong about the year? I think I even found a good machine shop to do the machine work,even though he said he didn't want to build another one --some one else smoked one with bad oiling.
I also have a 4.1 block. The hang up I have is the cost of the pistons if you want forged. I know guys use the hyperatic ones. They either love them or hate them. So I don't know if I should use them or not. I would also have to get a crank and rods for it because I don't want to steal them from the orginal 3.8.
The only thing about the hypereutectic pistons I would worry about is detonation. It will kill a hyper piston quickly. They aren't as strong as the factory 3.8 turbo piston. I do have a set for a chevy 4.3 project that I have yet to finish, so I am not against them. Best bet in a 4.1 is to go with the forged and not worry.
I read on this board quite awhile ago, that the stock pistons ARE hypereutectics...but I'd suggest asking in the tech section, because like I said, it's only what I read!
I read the 4.1 build up by Phil Verhaeghe in the tech section,and I do like the idea to bore to 4.000 and use a common full floating piston. I lost the press on two of my wrist pins leading to badly scored walls. Clips for the pins NOW looks like a good thing. This isnt going to be a race motor but I do want a strong depenable one for the street! I also want to do the best I can on the oiling system. I going in search of info from Buick power source for tip in that area.
Again, I am listening to ALL input.

Stock pistons are a cast piston with a thicker top. It also has a steel plate cast into the top like the diesel pistons use. Hypereutectic pistons have more silicon content (18%) and are theoretically stronger than cast. I know they are stronger in the skirt area. Hyper's use a closer skirt to cylinder wall clearance than other pistons. They use around .001-.002 where the cast will use closer to .004. Forged use about .006. With hyper pistons, the top ring gap is widened severely to about .060" because the top ring takes a s**tload more heat than a forged or cast. The extra silicone content makes them more brittle than a cast and can fracture and break where the cast piston is more forgiving, to an extent.
Thanks GNeric,
I love this! Where else could I find such help, and info from people I havent met-YET. I have been more or less just been lurking all these years reading all these posts yet not really needing all this info untill now.
I will copy all these posts into a few diffrent files for ref. for my own and others to use when needed.
I guess I'm either getting old or simple but I'm still up in the air- Hyper or forged? Your pref.
What about Rings,some better than others brands,total seal or no?
I hope you folks got time because I've got the questions!
Anything you can do to "seal" the engine will make power. I have never used Total Seal rings, but have heard from others that they work well in turbo applications. I plan on using them when I do my 4.1 for my 85 GN since the less oil to contaminate the intake charge, the more lengths on the mustangs you make.
So will a chevy 350 standard forged piston work for the 4.1's bored to 4.000? Will they fit on the stock rods? If that were so and you could find the right compression pistons then it wouldn't be so bad in price. I just have a had time justifing 700 bucks for a set of custom forged pistons.
An off the shelf Chevy 350 piston will fit in a 4.00" bore. I "think" the Buick rods are longer but being a Chevy part, there's probably something already made that will work with our rods.
So anyone hear of doing this? Also anyone got that hyper link for the 4.1 buildup in gntype org? The site won't let me get into the tech area. If the buick rods don't work will something else work? Food for thought.
The reason for using the 4.000 bore is not to use an off-the-shelf Chevy piston in a Buick motor...It is for the huge selection of piston rings that will fit and probably be cheaper since they were originally made for the Chevy bore...You will still need custom forged pistons made for the motor...the rods in the Buick are off center, which means the rod, when pressed on the piston is offset to one side of center on the piston...I *think* the Chevy pistons are all on-center, meaning the rods are centered on the piston...

Here is the hyper-link to the 4.1L recipe on the gnttype website...

Hope this helps...

P.S...I know Phil V. He is a real sharp person...He has tried it all with the 4.1s...He has been through rebuild after rebuild and knows what works and what doesn't...Pay close attention to what he says...

It's like Phil said in the article..."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. "

3.8L blocks aren't that hard to find(at least in this area) could try your local automotive machine shop...Ask them if they could get a rebuildable 86-7 25526109 casting block core and rods for you...A lot of those places have sources that they use to get that kind of stuff...Or even a repair shop that rebuilds motors...DO NOT tell them it is for a Grand National...Tell them it is for your grandma's car or something, if you tell them it's for a GN they will charge you more...As has been said before, the N/A 109 blocks and rods are identical to the turbo'd ones with the exception of the turbo oil return hole in the front of the block...Heck, find a shop that works mainly with Chevies or something and they'll probably give you the block... ;)

'Nuff said...
4.1 rebuilt

Well I picked up my 4.1 today from the bone yard. tore it down and this is what I have--
crank rolled fillets -.010/.010 as per bearing inserts, bore +.030 as per pistons!
I knew there might be some thing up when I seen the orange RTV at pan gasket and intake so I told the yard man I couldnt use it. He put it on the trailer for $100. block,crank,rods are correct.
Now when you guys talk about 700+ for custom pistons is this because of the bore size or that they are forged? Can I get hyper slug at this bore+.035?
I have to rethink this process,on which engine to build. But now that I have a spare the direction is different! I DO NOT believe in doing this twice. I'm thinking about doing the 4.1 to a decent state if not cheaper now while sleeving the 3.8 so I can have the time to find a 109 block and invest most ov my funds that way.
I have all the other parts,turbo ect. for either moter blus a 2nd set of heads. os its down to the short block and how to save the 4.1. I want to but the 4.1 in to see what all the fuss is about!:D So I need input on the pistons first so I can talk it over with the engine machinist.
On the side-boy are all carbed motors varnished up inside? It looks a world apart from my 3.8!
Sleep then back to the garage in the morning to gather up more questions This will be nice when I'm done!
total seal rings are worth the money...

speed pro hypo pistons are tougher than people think they are i have used them in plenty of nos'ed sb chevy motors running deep in the 10's

i also used hypo's in my hotair motor and i tried all i could to blow the heads off that motor with detination so bad i could feel it and the pistons still look new and yea i didnt use a knock sensor ..:D

just curious, how much NOS were u spraying into that SBC with Hyper pistons? thanks.
on a 10 to 1 motor i went up to 300 shot with nos big shot system

but mid 10's were on a 225 shot with my cheater system..:)

cant go but so fast at the track cause id never make a profit at the hang out...:D

it was a 400 sb in my old 79 malibu mild motor.

i built another 400 sb awile back that is a true 12 to 1 motor and the guy that owns it has put a 125 shot on it now and its still going.

dont forget if you have carbed friends that like spray i have another nos big shot system for sale unused with both plates to use with regular holley or a dominator.

i got it for another 400 i was building for my elcamino but i ended up selling most all the parts off and spending the money on my ttype.