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More 4.1 questions

955 Views 16 Replies 9 Participants Last post by  Scottie-GNZ
Thanks guys, I was thinking of building up a 4.1 myself, I mean, you can get the right heads, crank and rods off the same block. All I need are pistons, who has forged pistons for a 4.1 that don't have to be custom made?
I also thought that if I got the %10 more displacement, I would need to cut the heads up a little bit to accomodate to demand on airflow. Is this correct?
As for the Har Blok,I wonder if it would affect the knock sensor though, I figure it would kill some of the vibration we've all come to know and love.
By the way, there seems to be an abundance of 4.1 motors in San Diego, maybe thats why I spend 6+ hours in the junkyard every Sunday. headbang
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Did you look at the link I provided? I think it covered pistons fairly well.

I believe that I would follow Mike's lead and use hypers as I don't believe there is is a over the counter forged.

I think J&E makes a set[I was offered some]. :)
They're great if you want to spend the money.
All I need are pistons, who has forged pistons for a 4.1 that don't have to be custom made?
I searched and searched, came up with nodda. Without going custom route you aren't going to find a forged piston. Some people say use a Ford Windsor piston, but once you start doing the math on what's available, I could never find a piston that had the correct dish AND pin height. Even going with Diamond (cheaper than most) you are still looking at $500+ for slugs.

I decided to buy the FM Hypers. They are the correct dish, correct compression height and look very beefy. My compression ratio ended up being 8.2:1. The box even says GM 4.1 Turbo pistons... although I can't think of a Turbo 4.1 application..

Again, you aren't going to get a straight answer on the hypers as the people against them are spouting heresay and wives tales. For less then $200 you can get a set of hypers AND the rings from Summit. They are however a very heavy piston compared to the stock 4.1 piston so a rebalance will be required. I have made about 450hp so far with this motor and Scottie (uses the 3.8 hypers) is close to 500HP.

I am building another 4.1 for the permanent motor in the Buick and I already have another set on the shelf waiting to be installed...

Again, just something you will have to try for yourself... powersix
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I get a ton of questions about the magic piston to install. There isn't one. The worse that you can do is buying the Speedpro "hyperujunkit" pistons. They may be fine in that 455 in the your Electra, but they have NO business in a turbo charged anything!
Here is some text that I find interesting in that link Steve provided. When statements like these are made you have to wonder what experience this guy had with a Hyper. You also have to wonder which actual piston he is talking about and from what timeframe. I believe the Hypers in the early 90's DID have problems. How old is that article? Was there a failure? How much boost and timing? I think once you start some official investigation you'll find the hypers aren't a bad choice.

Again, you'll never know until you try it for yourself! poon

I get a ton of questions about the magic piston to install. There isn't one. The worse that you can do is buying the Speedpro "hyperujunkit" pistons. They may be fine in that 455 in the your Electra, but they have NO business in a turbo charged anything!
Phil had a lot of experience, but, it was back in the early 90;s as I recall. I saw a number of broken hypers from that period...in 3.8s as well.

As you guys, Jesse, and Red have had good luck with them, I suggested them above.

I believe it was last summer that I spoke to Sealed Power or whatever they are called today, and they did not recommend them. Keith Black said hell yeah.

Yet, I think it was Reds that said KB were junk and SEaled Power/FM/TRW etc....were the way to go.


yup dat was me ...I have broke many KB hypo pistons for double the $ of sealed powers then I desided to try sealed powers and loved em

I have broke one in a nitroused sb motor but that was after I had swallowed something down the carb and it beat the piston up bad but being in a hurry I didnt change it and it came apart at 7500 rpm with a 250 shot of noz going in it silly

all the other ones looked good still

Im thinking of doing a 4.1 hypo motor but not sure just yet cant seem to blow up the 3.8 ...lol

<small>[ June 06, 2003, 03:34 AM: Message edited by: REDS HOT AIR ]</small>
is it really that hard to actually get a set of pistons for this engine?

several years ago i got in touch with a guy at weisco and was hoping to get some 4.1 slugs for myself at dealer cost. (i worked at a motorcycle dealership and we were weisco dealers). i figured they were in the automotive catalog which i didn't have. anyways they sent me a catalog and said that the low compression slugs for the 4.1 were no problem and they make a bunch of them. he said that he already had the combustion chamber specs so getting whatever compression i wanted was easy and the domes have a nice radius to them. he also told me they were made out of 2618 alloy (whatever that means, i ASSuME that's good) and that he'd design my lands around whatever rings i found in the oversize i wanted.
You can get pistons for anything, if you order them and don't mind paying the price. Cheap, off the shelf, pisons rather than custom jobs was the discussion, I think. :)

Wiseco, Diamond, etc. will make just about anything for you....pistons for your Cushman or your 4.1.

I have the Hypers in my current 3.8 I am hoping to tickle the 9's with and also in my 4.1. I have a set of .030" J&E forged pistons I may use in the 4.1 at some point but I have had good luck with Hypers. My old motor that has been in Banning's car for several years now I put together with Hypers. I don't know how fast he is going now but I know it is bottom 11'[email protected] MPH or so. If you set them up right and don't detonate them hard they will hold up fine. They will even take detonation but try to keep it in check. Any piston can fail but I think you will like them in the 4.1. A set of forged like I have on the shelf runs about $600.00 from what I am told.
Wow. Tickling the 9's with Hyper pistons! I have a lot of faith in them but in my mind I wasn't planning on pushing more than 600HP with them. Is this is a full weight regal? Please do tell the details! :) Great to hear some positive feedback on them. All we ever hear is they will shatter like glass under boost and usually the people knocking them have never even seen them! poon
Full weight except fiberglass front and rear bumpers. I have also heard the stories too and I believe some of it. Early on I think problems existed but that has changed. The KB Hypers had a problem with ring placement and would fry the top ring. I think this has been corrected. I always use the Federal Mogul Hypers which are the best! Very high quality piston. I haven't had the car to the track yet but ran it on my test road to 20-22 PSI with some slight detonation and the pistons are still there. If it doesn't go low 10's with 4-5 more PSI I would be real surprised. I should have everything in order to make a few track passes in a couple of weeks so we will see. I guess I will be the test mule because I don't know anyone that has tried for the 9's on a stock bottom end with only caps, stock crank, rods, hyper pistons, intake, iron heads and 200 trans using a stock ECM. I have heard of some 10.40 passes on Federal Mogul Hypers but nothing faster.
Two failure modes I have seen too:

- Cracked skirts. Actually a friend of mine bought a GN that had Hypers in it but he didn't know it until he had a problem and pulled the motor out. The car always detonated heavily and upon tear-down (due to excessive smoke!) he had melted #6 piston in the top ring gland. This never did any damage to the cylinder, just allowed oil into the chamber and hence severe smoke. Also all his pistons had cracked skirts. Who ever set up or built the motor made piston to wall way too loose and caused this. They can't tolerate forged piston specs due to expansion differences. Something in the ranged of .0015"-.0022" works best depending on how much heat you think you will generate. I have .002" on both my motors.

- Pulling the piston apart. This I have seen too at the top ring gland. What happens here is if you run the normal .018" or so gap on the top ring and are putting a ton of heat in their is a good chance of the rings butting in the gland and pulling the piston top off. It is like putting a noose around the upper portion and makes a clean break at the gland. Here you should loosen it up to .023"-.030". I have both my motors set at .027" top ring.
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Sounds good! :)

I am sure you are absolutely correct on the wall clearances, top ring, and minimum detonation. I believe they are strong, but, brittle. Brittle would seem to be a problem only if detonation was the rule rather than the exception. I also bought an engine some years ago with some broken hypers. I am sure that it was run under heavy detonation conditions.

Factory top ring specs are .013-.023". Given that that was for something more akin to 14# of boost, it would seem that your number is much more fitting given the egts that we run at much higher boosts.

Send me an Email on the pistons, I believe we have a set here that were custom made by JE a few months ago....for exactly this purpose! wink

Some like JE, use JE, etc....we usually run Wiseco or Diamond components if its our choice.

[email protected]
I always use the Federal Mogul Hypers which are the best!
Recommended to me by Jack Cotton a couple of years ago and as Orlando says, "tickling" 500rwhp and still going strong. Not sure I have the cajones to push it as far you are doing but my confidence keeps growing.

You are definitely pushing the envelope and as long as you avoid detonation, who knows how far you will go.
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