Putting together what parts I will use for a 355 rotating assembly. But, like many others, I am doing this on a pretty tight budget. I'll be using my LE1 heads and cam and the motor will not see nitrous or any type of FI. So it won't be seeing HUGE amounts of power, but will see the high rpm range, but thats just due to me being throttle happy.

Anyway, being probably around 400fwhp(maybe??) I don't see the need for a forged crankshaft, so the eagle 3.48 cast crank will be what i'll use there.

Being "throttle happy" sometimes, i'll be worried about my rods, so I was thinking some 5.7" scat forged I-beams. I just want to prevent this from happening again--

(it bent towards the crankshaft counterweight, and was hitting it as it went up and down...got a nice video of the sound too )

So that brings to me to where I really don't know what direction to take. Hypereutectic or forged pistons. I know this has been beaten to death, but i'm leaning towards the hyper pistons due to cost. Again, being in the power range that i'm expecting, I don't see the need for the forged pistons. Unless I am able to find a good set of forged pistons and rings for no more than $300, then i'll be using the hyper pistons(probably some KB pistons I assume) Unless I can scrounge up some extra cash for some SRP pistons and rings then i'll do that, but if not, would I be asking for trouble going to the KB pistons???

I don't see me making power above 6000rpms with my setup, and also dont expect to me making no more than around 400fwhp. That is why i'm not going with a completely forged setup. I'm just looking for any constructive criticism about my plans for this. Pointers, advise, etc. I'm open for anything

BTW, the car is an M6 and wont really be a daily driver as I have a truck I use for work. It will see around 50-75 miles a week at most.

 

check ebay for "LT1 rotating assembly" they have some eagle kits on there for around a grand(some for like 700 i believe) for a cast crank, forged rods, and forged pistons

 

hyper pistons a CRAP!
use a stock crank
get some decent rods (not alum.)
and get some forged pistons.. ANYTHING but hyper ones!

Do it wrong and you WILL be doing this all over again!

 

Hyper is exactly the right choice for the application you describe.

 

I know this is somewhat off-topic, but what happened that bent that rod?

 

I'm no pro but from A LOT of research I have to agree. There seems to be a lot of negative things from forged pistons..........heaver, distortion, piston slap, and cost more. The reason to go with forged is when you NEED it. I reused stock pistons and rods. I put down 370RWHP and beat the crap out of mine without EVER having an issue. I have been running it for 2 years to 6700 RPM's. That's just my experience, hope things work out well for you.

 

Keep the stock crank and have it touched up if it needs it. Spend what money you have on the rods and pistons. If it were me I would go forged pistons, just in case you change your mine and want to add a small shot later.

 

a good piston and rod is where I would put the money, stock crank is fine
have seeen them last years at 8k

 

Stock crank, good HE pistons like KB's. Nothing wrong with with stock rods with good bolts. They are as strong as the cheap aftermarket rods and have better QC. If you want cheap but good aftermarket rods, look at the Callies Compstar. Forged in China but at least inspected and finished here by a reputable company.

Rich

 

I have never heard of "lots" negative things from forged pistons. Heavier, maybe barely. Distortion, nadda. Piston slap, maybe a little but only at startup. And cost, yeah they do cost more. Forged are by far more popular with performance engine builders even if they are not super high performance. You will have more piece of mind with forged pistons. I think that hypers have their place in stock or slightly higher than stock applications but not LE1 which better be making over 400 FWHP.

Now lets hit the positives. Forged are far more reliable due to their resistance to detonation plus they also reduce detonation over hypers due to their ability to bleed off high temps. Anytime you are going to be porting and camming and raising CR this becomes a concern. Even traces of detonation will shatter the hyper piston like a beer bottle where forged will just absorb it and keep on going. Either way get a good dyno tune.

To the rods now. The stockers are decent once the dinky rod bolts are replaced. However you can get forged 4340 rods with ARP bolts from Scat for less than $200.00 shipped. This is simply cheap insurance and will help provide that wonderful piece of mind once again. The ARP bolts will run around $50-$6- or so, for a bit more go with the Scats. Guys are raving on these for 400-500HP applications.

Now here is my setup which is currently in the works. I have a fully refreshed LT1 two bolt block bored 355, lightly decked and align honed and fully studded. I have LE2 heads with LE1.5 cam which I might trade up for the LE2.
I also have fully ported intake and all the bolt-ons.

I am going with Mahle .030" over forged flat top 6" pistons as well as Scat forged 4340 6" connecting rods. I have ground the stock crank .010"/.010" for reuse. I am hoping for around 400 RWHP or so. Compression ratio is going to be about 11.1 to 11.3 with Impala head gaskets.

You may be fine with hyper pistons if you nail the tune. Go on and reuse your rods plus ARP bolts plus the crank. If it were me I would go forged pistons. Plus you can expect the LE1 cam to make power all the way to about 6200 RPM making shift point about 6300-6400 RPM according to Lloyd. You will not like shifting at 6000 like you said in you opening thread, there is more power to be made above 6000 RPM.

I really think the key to high performance other than HP is piece of mind, build it reasonably strong to help ensure reliability and you will feel much better about your work and investment. If I built my new engine with hyper pistons I would feel like I am walking on egg shells, but with the forged I know I can beat on it a bit more.

 

My guess for the rod getting bent like it did was from over revving the engine. But it didn't happen one day while I was driving. I would assume that it got weak from the high engine speeds over time, because it didn't start making the sound until one day on a cold start up. And I know it wasn't from the time I dove it before because it was raining HARD and my a/c wasn't working so I had no defrost...so needless to say I was driving pretty slow. So with that I am worried about the integrity of the remaining rods. I'll have to buy new ones anyway, so that is why I was going to go with some forged i-beams, or maybe even a set with the 7/16" capscrew...unless someone can advise otherwise. But I will certainly look into those that you mentioned Rich.

I guess I can find a machine shop to look at my crank because the rod was hitting the weight of it and beat it up pretty good.

I understand how forged pistons can no doubt hold up to pretty much anything a normal person can throw at it, but like some said the hyper pistons may be good for my use. Once this thing is done I wont want to spend any more for nitrous and such(will be saving for a 5th gen) so that is why it won't see nitrous. I'm more looking to get this thing running again...not something that is going to the track every weekend. Though like I said, if the extra cash is there then forged pistons it is.

Guess my next goal is to locate a machine shop in the area who can look at the crank. Though i'm wondering how much i'll save just working the stock versus buying a new cast one.

 

you can get that same crank out of a truck or van....thats what I did, I get my rods and stuff inspected, had to get 2 cause they spun bearings and couldn't be cut down enough after polishing the crank checking all rods and 2 new ones I spent $50. I know the stock parts are pretty good, If you can afford to go with a good rods and piston go for it. I would not trust a set of rods that are less than 200 bucks...cost of bols plus inspection and resize is that much so i'm sure they are probly junk

 

i would think that hypers would be fine. i don't think that they are near as fragile as some seem to think as long as you get a quality set.. if you were looking at cast pistons then i would say hell no.. but lt1's come stock with hypers and how many people have strapped a 150 shot of nitrous on there stock bottom end lt1 car and never looked back. i bought a set of speed pro hyper lt1 pistons in my vette and i have no issues whatsoever and i have about 5000 miles on them without a glitch.. its got lt4 heads and a lpe 216 cam. so its in your power range. i don't plan on using nitrous on them but that is cause i have two other cars to race and my vette clutch probably wouldn't last too long with some juice. if you get some stock rods then i would totally suggest some new rod bolts. those kits on ebay are also a great choice.. if you can get forged for a price in your budget common sense go for it... but i don't feel that hypers will leave you stranded. call up KB or SRP and ask them what is a good piston for your setup... that will without a doubt set you in the direction you need to go in..

 

I agree completely.

And whatever caused that bent rod would have happened to a scat or eagle - looks like a hydrolock.

 

well, once my tune allowed me, it did see 6000-6500rpms a few times with a significant drop in oil pressure one time. Plus, if it was hydrolock, then wouldn't the top of the piston be steam cleaned? It was pretty dirty, though now its clean and is sitting on my shelf. Well either way I think i'm going to go ahead and go with a new set of forged rods.
I did find a set of forged KB pistons for $340-$400, and forged speed pro pistons and rings for $400