I recently blew up the LT4 in my C4, and I'm not sure what to do for pistons in the new motor. The car will be used exclusively for road racing/auto-x, and it will NEVER see spray or boost. EVER. What it will see is a lot of hard use between 4,000 and 6,500 rpms for long periods of time (like 20 mins at a time, maybe longer).

Currently, I have a stock, used LT1 short block in need of freshening. I can't decide if I should try and use the stock LT1 pistons or get some hypers to replace them. I think I would want my compression somewhere around 11.0:1 to 11.3:1 (it must run on 93). LE is doing my heads (valves and port job), and the custom cam he spec'ed is going to have an LSA around 108, which I think means it will have a very high dynamic compression ratio. I really don't want to lose compression from the smaller dish LT4 pistons I have, but I'm not sure what kinds of pistons I should be looking at or if it is worth it to replace the LT1 pistons at all.

I'm hoping I can get by without going .030" over, but I will have to if my block needs it.

Anyone got some tech/suggestions?

 

I've been following your story here and over on CF. Hated to see the results of your last trip. Were you able to salvage anything from the LT4? I'd hope that at least the heads were salvagable.
I dont know what your budget is but if you could swing these http://www.cnc-motorsports.com/produ...D=16076&CtgID=
and for rods
http://www.cnc-motorsports.com/produ...25&CtgID=21452
They have the same valve reliefs as your stockers and should net you similar CR. Dont be too cheap on the bottom end, at least as it relates to rods/ARP bolts/pistons or it could very easily come back to bite you. I understand the whole broke college student budget though.
FWIW, I've got 97k miles on my LT4 with in excess of 200 trips down the 1/8th or 1/4 mile track as well as 3 seasons of autox and maybe a half dozen HPDEs. All so far on the stock stuff with my rev limiter set at 6700 which I bounce all the time.
It'd really be nice of you could locate a good used LT4 crank rather than the stock LT1 though. Keep us updated.

 

The heads were salvageable. They are at Lloyd's place right now. The entire bottom end was trash. Block had lots of damage to several cylinders, the 5-6 crank journal was toast, timing chain broke, cam was messed up, etc.

Balancing up front cost and reliability down the road is what I have been struggling with. Part of me wants to throw in a fully forged 383 setup, and another part of me wants to run the stock rotating assembly. So the stock LT4 pistons are -5cc? I have been trying to find that info for the LT1 and LT4 pistons and thus I haven't had any luck. I'm not really sure I need forged pistons since this motor will never see spray or boost, but I'll definitely keep them in mind.

What are the advantages of a 6.0" rod? I seem to remember that the longer rod reduces the side load on the piston, but I'm not 100% sure.

The stock motor had 150K on it when it let go, and the last 4K or so were me beating the crap out of it. I was hoping it would live a bit longer so I could plan ahead and start on a new motor first, but oh well.

 

Hey Mohave,

I work at Wiseco, but I do not work in sales, I work in the custom auto division as a machinist. I own a LT1 so I have seen all different combos come through for big name race teams and engine builders plus I am in the process of building a 396. If you are going to run a motor that high of rpms, just for a short period of time, the stock pistons will hold up but not that long. You may only see 20,000 miles on a motor rebuild then. Buying hypers are a waste of money, don't do it. Do it right the first time!! The stock LT1 crank is not made for durations of high rpm for more the 30 seconds at a time, they heat up too fast, seen it happen in r&d. You may be 1 of the lucky ones that it lasts forever, or you can spin a bearing like I have seen from a couple of f-bodys the first time out to an autocross. I recommend atleast getting a good cast crank at minumum or go on ebay and search for a eagle forged crank. There is a machine shop that buys eagle remans for cheap and resells them with a eagle factory warranty for the same cost as a cast crank from summit or jegs.
If you are staying with the 355 format, go with a 6" rod, You will see a 800 rpm jump with the LE heads and a good cam due to better rod to stroke ratio.
As for pistons, there are many manufacturers that make a good piston. At wiseco, we have a newer ring package that will suit racing and street driving, it is the one I am using. If you decide to go with a 383, you can use this ring package and still have a + pin to oil ring and it has a nappier 2nd ring and a moly top ring. We sell alot of ls1 pistons with this ring package for big strokers to companies like late model and mallet. I highly recommend a forged piston, forged I-beam rod, and new crast crank at minimum. But to cancel any probs, in the future, go all forged, break it in correctly, and beat the hell out of it for years. If you have any ?'s, just ask, I am willing to help in anyway.
steve

 

My suggestion is to do more research. How on earth did you miss the fact the stock pistons are hypereutectic. Time to rethink what you thought you knew.

 

Rather, I meant is it worth it to replace my used stockers with new hypers, since I don't think I really need forged pistons for this application.

So are the ~$200 cast cranks that much better than the stocker?

 

Just to update this thread, since a lot of people kept telling me to do it once, do it right, I decided to man up and go 383.

Mahle PowerPak -5cc .030" over for 6.0" rod
Childs and Albert 6.0" rods (found a deal)
Scat 9000 crank


Anyone have a recommendation for bearings or lifters? Nex max RPM of 7K, with a shift point of 6400-6500.

 

Morel lifters are nice pieces, and should be considered.

There are new OEM offerings that I do not know much about that
you should check into though. LS7's should be made to see some major RPM's

Lloyd did my LT4 heads, and they came out nice. I stuck with the stock valves.

 

That's exactly what Lloyd said. He runs the Morels, but the LS7's could work too.

I got bigger valves, mostly because 1/2 of mine were bent (and 1 leaked sodium).

 

If you have not bought already I also suggest the Mahle pistons, and at CNC you can get the piston and rod (eagle H beams) for @ $800.
I also like to encourage folks that are using their engines in a high performance capacity to utilize all forged components in the bottom. Just good insurance and it reall isan't all that much more.
6" rods do help as you stated above. Also note as stated above the pin height in relation to the ring lands. If the two are too close together or overlapping you could run into frequent rerings. You also want to pay close attention to quench!

 

not atall, if staying stock stroke I would sooner reuse a stocker than put a $200 crank in the car. The $200 stuff does seem to work fine but I would not throw out a stocker in favor of one.

 

I already picked up the Mahle pistons, and I found a deal on some Child's and Albert 6.0" rods. Just need to get the Scat 900 3.750" crank (and ARP main studs).