[oldman]

I checked all gaps on my factory rings and there were "fine", maybe I got lucky. I have the GPI drop-in stuff, outside of the rod bolt, there is really NOTHING wrong with the factory rod... that said IMO I think the stock weight stuff is iffy over 850 engine HP, I tend to be conservative. Just IMO if I were building a 1000 HP engine I would do some super thick I beam rods and some heavy forged pistons with the deep ring lands... and runs some big clearance on the rings too. Of course, this would need a rebalance, we ARE talking 1000 HP.. I know vendors say what they are doing with stock weight stuff, IMO material is material and the more of it the better, call me old fashion. Just like a Tiger tank has flat armour but it is THICK and a T34 has angled armour but thin, what tank do you want to be in?

The only thing I went cheap on was the LS7 lifter and as luck would have it, it failed about 1000 miles or a couple of months before I was going to drop in the forged stuff. bummer. I talked to my several builders and buds and decided that at my HP level and cam size, it was time to go with Manely Pro-Flow valves due to :
1) bounce under boost on the intake
2) heat running WOT on fat E85 / meth mixtures on the exhuast.

I would run inconel or taitanuim if I was going over 850 engine HP. I should add I drop my lift .596" for many reasons and keep my Texas Speed twin spring with titanium retainers, I forget the weight difference, of the Manley valve, but if was going to keep something like .640 to .650 lift I would go for a stiffer conical (single spring)....

[oldman]

Originally Posted by Eldi Z

120 seconds would probably be an exaggeration...Agreed.
I am practically thinking in the direction of "road course" applications, when talking about this maximum allowable WHP figure.
1/4 Mile runs have been pretty much proven to be "safe" at 600 WHP...

As to setting the gaps on the stock pistons - Again, this means going into the motor and this I am trying (hoping) to avoid.
Moreover, it is rumored that there is no replacement for the reliability of a motor, that has been torqued correctly with the robots (man-assisted of course) at the factory...
Once opened, it looses some of the reliability attributes, even if the machine shop torques back to OE spec. - It is simply not like the process at the engine factory.
Again, I am not an expert, so this may also be a myth...

Torque to yeild bolts are working here (the secret magic), they need to be replaced yes, but a new set in an old block will yield factory results, no magic... Aftermarket rod and head studs are even better / stronger.

For me I think it would be crazy to pull the pistons / rods and NOT install at least the GPI stuff... That is a lot of work.

[Eldi Z]

Originally Posted by oldman

Torque to yeild bolts are working here (the secret magic), they need to be replaced yes, but a new set in an old block will yield factory results, no magic... Aftermarket rod and head studs are even better / stronger.

For me I think it would be crazy to pull the pistons / rods and NOT install at least the GPI stuff... That is a lot of work.

Exactly! So obviously, having pulled the engine, then an Aftermarket Forged Drop-in Pistons-Rods set would be installed.

Exactly because of this work, I am still playing with the idea to leave the motor stock untouched, not go over 8 PSI @ 93, not go over 570-580 WHP and add Meth for cooling purposes only (without the temptation to advance timing).
Stepping on it for more than 1/4 mile runs would also have to be avoided (which is my main concern, since I would like to have the "freedom" to push it for longer periods - similar to what I would do if it were a stock LT4 engine => No Fear)
Must still learn and think about which path to take...

[KingLT1]

The man assisted robots at the factory assembling these engines are only more reliable from a mass production standpoint. You are building 1 engine...with the proper tools, torque wrenches, and attention to detail, you can build a engine just as if not more reliable by hand.

[Eldi Z]

Attention to details and taking your time is probably key and using new bolts...

Wish I were confident enough to leave the engine stock, while being able to enjoy boost. I guess that the gamble with the LT1 is higher than it is with I.E. the LS2/3s...

[oldman]

like I said mine checked out, I think many guys are running like autox or road race with boost and this is pushing the expansion. At 8 PSI and some 1/4 miles I really don't see an issue. I have maybe not kidding 1000 WOT runs on the stock pistons... 4 set of rear tires and I dont' "burn out"...

[Eldi Z]

I

Originally Posted by oldman

like I said mine checked out, I think many guys are running like autox or road race with boost and this is pushing the expansion. At 8 PSI and some 1/4 miles I really don't see an issue. I have maybe not kidding 1000 WOT runs on the stock pistons... 4 set of rear tires and I dont' "burn out"...

Your experience is encouraging. If you indeed boosted so many times on WOT at ~ 8 PSI without failure and probably so many others boosting the stock LT1 successfully at such level, then I might just take my chances and wait with the forged material, until I decide to go into boost and WHP levels that truly require this investment (or I encounter a failure, that will force me to do it...) .

[oldman]

I had a lifter failure on a high lift / fast ramp cam, pistons were mint....

[DorkMissile]

FYI - after pulling my #1 piston today, I was able to obtain some rough numbers on the assembly. I have a decent gram scale that I use for reloading, I would say accurate to within 2-3gr

Piston and rings, no pin, no snap rings - 587gr
Rod - 683gr
Pin - 144gr

Rod Balance
Small end weight (Big end supported, small end on scale) - 193gr
Big end weight (small end supported, big end on scale) - 428gr

[Eldi Z]

Originally Posted by DorkMissile

FYI - after pulling my #1 piston today, I was able to obtain some rough numbers on the assembly. I have a decent gram scale that I use for reloading, I would say accurate to within 2-3gr

Piston and rings, no pin, no snap rings - 587gr
Rod - 683gr
Pin - 144gr

Rod Balance
Small end weight (Big end supported, small end on scale) - 193gr
Big end weight (small end supported, big end on scale) - 428gr

This is one amazing piece of valuable information that is really helpful to the community.
Thank you
Now there is a reference and when vendors like GPI, CMS and Vengeance claim for "Drop In" and "Exact same Bob-Weights" , a direct comparison can be made to the OE components.

[DorkMissile]

Well unfortunately the weight of everything goes completely out the window if you change rods. If the rod weighs the same weight in Grams as the OE rod, but it heavier on the little end, and lighter on the big end, it is pretty much a crap shoot without rebalancing IMO.

But if you are just changing the pistons, you could use the numbers as reference. I know one of the popular drop in piston only kits uses a 597gr piston, (and that weight includes a heavy pin). Most of the aftermarket piston kits are much lighter than stock (60-80gram) and should be balanced.

Once you have the engine down that far, you are looking at another $250-350 for new mains & to have it all balanced.

I myself am contemplating at this point switching the crank to a 4" stroke or just rebalancing the stock crank.

I will say that if you are into the engine this deep, it might be worth switching the bearings to TriMetal bearings vs the Bimetal under boosted applications

[DorkMissile]

FYI - using two different bobweight calculators, I get between 1785 & 1787grams.

Now everyone understand - my numbers are reference, using my parts on my scales. I have a rough setup to measure the big & small end rod weight, but its not a full blown rod balance jig. I wanted to get a rough estimate of what the factory bobweight was.

Standard automotive balance is usually +/- 1%, which means you would want a calculated BW between 1768gr & 1785 (basically up and down 17.5g). If you bought a complete rotating assembly from the aftermarket, it would probably be within 1%.

From there it is all about how close you want it. Some guys will tell you a 1% balance is good enough for a medium power street engine. Some will tell you to target 10gr, some will tell you to target 5gr, or 1gr. I guess Cup engines are balanced to under .25gr. And you guessed it - the tighter the tolerance, the more finesse / time it will take to get it.

Using my data, but lowering a piston weight down to 565gr would put you right at the bottom of that range. This is the kind of math that I am assuming that are advertised as "drop in". But there are sever variables to put into this number - lister pistons and heavier pins to get the weight back up.

FYI - according to the Wiseco catalog, their catalog drop in pistons are 555gr

For most guys running 10-12lbs of boost, and under 6800rpm, it should live there. But the whole balance thing is kind of a black magic, smoke & mirrors kind of thing. No real hard information out there on how close it should be, and how important it is.

[DorkMissile]

Well Point of Reference (use this info at your own risk)

Googling some readily available information on the web about a particular rod

(6.125" center, .927" small end bore, 643gr) measuring small and bigs you get a average:

Big End 452gr
Small 191gr

Using one of the more popular name brand pistons out there that is 11.5:1, that has a piston weight of 414gr, rings that are 34gr, rod bearings that are 43gr (FYI - my rod weight was WITH the factory rod bearing), a 138gr pin and 2gr for clips, you end up with a bobweight of 1782 grams. Right in the sweet spot.

If you could get the big & small end weights within 1gr of each other with that setup, and assemble each set and have them within a couple of grams, I would probably send it without having it balanced.

[Eldi Z]

DorkMissle, this is important data and can serve as a good yardstick for people who can decide between Aftermarket Pistons only and a Rods-Pistons Combo.
Asking the vendors, who claim to deliver "drop in" ,the right questions before pulling the trigger.
I hope that these vendors are also reading this thread and shall do the necessary, in order that their components actually meet the spec for the benefit of the community