I have searched the board and I'm still not crystal on this issue. I have a early 90's 350, one piece seal 4 bolt main motor that needs a new crank and rods. I want to install a 95ish LT1 crank and PM rods. My questions are: 1) Do I need to run LT1 pistons 2) What compression will Lt1 pistons yield with 64cc heads 3) Can I use a regular harmonic truck balancer and iroc flex plate I know about changing the crank key and that the Lt1 crank is balanced for the lighter rods and pistons. What I don't understand is that if you replace the Lt1 pistons with say Sealed Power Hyper pistons, why would that throw the balance off? Thanks, Mike Jones

Mich,

1. If you use the factory PM rods, you should be able to use lightweight cast HE pistons without having any unusual balancing problems.

1A. If you ever wanted to change to 6" rods, the L99 crank and rods would work, or the LT1 crank with L99 PM rods.

2. Compression ratio won't change, since the LT1 has the standard 3.48 stroke and 5.7" rod length.

3. The standard balancer should work, although the truck balancer is a larger diameter inertia ring (6-7/8") which is closer to the diameter of the LT1 ring (7-1/2").

3A. The crank keyway is a standard Woodruff keyway, so just pull the cut-back key and install a standard one.

well your compression ration w/ the 64 cc chambers would be low as crap... as the LT1 cars had 58 cc chambers if i am correct...

changing the pistons will throw off the balancing a little... but they should be w/ a few grams of each other... so you could possibly be ok... the best thing to do is get new pistons and then get the rotating assembly balanced... to ensure the motor lives for a while...

i am actually doing the same thing you would be... i have a early 90s 4 bolt truck block that is bored .030 over and ready to go... and i will be using the LT1 crank, and PM rods... like vader said the only think that will need to be modified on the crank is to switch out the half woodruf key for a whole one...

Chris: The Lt1 had 10.3:1, so the 64cc should put it back in the L98 range of 9.5:1 shouldn't it? Without the reverse cooling and aluminum heads, I don't want to be in the 10's.

Anyone: Where can you get the Lt1 pistons? Are they hypereutectic?

Vader: Can a Lt1 balancer be used with my 88 iroc accessories sepentine belts and pulleys. Or will the old 305 LB9 balancer or the truck balancer be better.

Thanks guys....

Mike

i am not sure if that will get you to the 9.5:1 stuff... sound like it would be close if not around there...

oh yeah... and i have a set of LT1 pistons that are used that came when i bought the crank and rods... the short block had 30,xxx miles on it when i got it... they look to be in good condition but you would need to get them checked...

These are the pistons I was considering.

http://cgi.ebay.com/ebaymotors/ws/eB...category=33623

http://10lw.com/images/fmc/h631p.jpg

[quote]From Chris89GTA
...well your compression ration w/ the 64 cc chambers would be low as crap... as the LT1 cars had 58 cc chambers if i am correct...

LT1 heads are 54cc. The pistons are flat tops, so compression ratio wouldn't change from whatever he is making now.

The LT1/4 balancer uses the outer surface of the balancer ring as the drive sheave for the poly V belt. There is no other sheave bolted to the hub as in first generation SBC engines. I doubt that your accesories would line up.

I mentioned that you shouldn't have any unusual balance problems, meaning you shouldn't have to add heavy metal. You'll probably still want to balance the rotating assembly.

BTW - you can get those same pistons in any size or oversize, flat-top, 4-relief, 2-relief, .125" dome, or .275" domes, for $169.95 from Competition Products

You can get the same thing (cast hypereutectic alloy) in Badger Pistons for $99.95 from them ...

I want to be absolutely clear on this:

Since LT1 is internally balanced, a neutral balance harmonic balancer like a Streetdamper would work, right? In terms of balance, this should be just like assembling a regular SBC--having everything balanced would serve to remove minor imbalance stackups, and the main difference is a lighter rotating assembly.

To clarify, here is my situation: I have a 1993 LT1 complete minus wiring/computer that will be going into a 1991 T/A. I plan to run it with the 7730 ECM using a distributor, and am interested in using the LB9 accessories. I could have a spacer that would go between the balancer and the hub machined to bring the LT1 balancer in line with the rest of the accessories, but I'd prefer to just get a normal 87-92 damper with timing marks on it. Then all I'd need to do is rig up a timing tab and work out the water pump/belt idler issue.

Bottom line: can I use a neutral balance damper on an LT1?

Bottom line? The LT1 damper IS neutral balanced. You should be able to mount whatever drive sheave you need to operate the accessories, but the bracketry might get interesting if you don't use the LT1 accessories.

You're going to have to install an expansion tank for the cooling system (hopefully available from the donor car), and will have to somehow plug the distributor drive hole in the timing cover. The controls should be easy to revert to the earlier ECM. Make sure you use the detonation sensor for an older SBC 350.

The rest should be pretty straightforward.

Thats exactly what I needed to know. The only other hangup is if the old style balancer will fit with the LT1 front cover; I haven't looked at it. I'm hoping that the Front seal doesn't go over the balancer hub neck. I may need to make some custom bracketry for the accessories, thats no big deal. Either way I have several options on how to proceed and I appreciate the information.