Aluminum block growth

SMOKEmUP · Posted: Fri May 05, 2006 4:05 pm Post subject: Aluminum block growth

I've heard the aluminum LS1 blocks will grow approx. 0.010" from cold to hot. What would be a good way to measure this without taking the motor apart?

The reason I ask is if the block grows then this will affect the compression ratio and quech height. Therefore I want to determine how much the block grows so I know how much to mill the heads and which head gasket to run. Any thoughts or suggestions?

clay · Posted: Fri May 05, 2006 6:36 pm Post subject:

Never really thought about it, but I would guess it would be more than a 0.010" deck height change. Seems like a friend of mine that messes with Harleys says the cylinders get around 0.040" taller or more when they heat up. That's why you can hear one with mechanical lifters a mile away. That brings up another point - if the deck height changes much, it would affect valve adjustment also so maybe it doesn't change more than 0.010". Maybe the design of the casting reduces expansion over what you would expect of an aluminum piece of that size (I guess engineers get paid for something)? You could screw in a piston stop and check how many degrees it stops the piston from TDC cold and then hot. I think if you use the same cylinder the piston stop should be repeatable. If there is a difference, it could be mathmatically translated from degrees to an amount of deck height change. I would try it several times to see if it is repeatable or not. That's my first thought. Clay

af2 · Posted: Fri May 05, 2006 7:07 pm Post subject: Re: Aluminum block growth

disturbthepeace1 · Posted: Fri May 05, 2006 10:16 pm Post subject:

..............alunimum+rpm=unstable valvetrain..........at least in my VW motor. But honestly I dont know much about the LS1 blocks execpt that they are one bad mother..... These things make incredible street power.. And i see more and more of them on the track, I dont know if the switched over to the cast iron truck block or not but i do know that I want the next motor that i build for my camaro to be one.......

SMOKEmUP · Posted: Fri May 05, 2006 10:46 pm Post subject:

Clay... I was thinking of doing the exact same thing. Use a degree wheel and a piston stop recording the degrees where the piston stops and try to calculate it. I doubt I can get an accurate absolute number but since the hot measurement will be relative to the cold measurement it will work, all I need is the difference (growth).

af2... I've heard from some people that it will affect valve adjustment so if that's happening then the block is growing.

I guess the only way to find out is to try and measure it and see what I come up with. Should be interesting. I need to get a piston stop and a degree wheel so I won't have an answer just yet. I'll let you guys know what I come up with.

af2 · Posted: Sat May 06, 2006 4:55 pm Post subject:

Smoke what I said is the block and heads grow at the same rate or as a whole. That is why the valve train goes crazy because it is steel. I can't see why the squish would be affected because the block and heads are the same material.

clay · Posted: Sun May 07, 2006 4:38 pm Post subject:

I would think the block would expand and get taller from the crankshaft centerline to deck surface. The heads would expand also, but they can't expand below the deck surface. The rods, being steel in this case, won't expand as much as the aluminum block, so the squish should grow slightly. Now the amount might be trivial, and I don't think it will make a difference on street level stuff, but interesting none the less. Clay

af2 · Posted: Sun May 07, 2006 5:42 pm Post subject:

73RS · Posted: Mon May 08, 2006 9:50 am Post subject:

Do you think the reason they designed head studs going way down in the engine up to the heads would eliminate the squish changes you are thinking takes place. Just something to think about, i know those studs go way down in the engine to the bottom of the cylinders.
Just a thought? I would still be interested to know for sure please post when you do get some results on whether the squish changes or not.

SMOKEmUP · Posted: Mon May 08, 2006 9:59 am Post subject:

87calais · Member Joined: 19 Apr 2003 Posts: 206 5692.14 points

The studs going so far down was to help eliminate distortion of the bore as the engine warmed up, making it easier to have less blow by. At least in this massive writeup about the ls1 it said that, makes sense.

Big Dave · Posted: Mon May 08, 2006 7:47 pm Post subject:

If your running stock hydraulic rollers they would take up the increase in lash, so you won't hear a Harley style clatter. The whole engine was CAD designed to run at operating temp. Disposable head bolts were designed to obtain correct yield strength, not torque setting. The intake is plastic, and the liners in the cylinder are steel but they are all screwed together to move as a unit. Just be sure (as always) that block is final honed at operating temp, and not room temp.

Big Dave

af2 · Posted: Tue May 09, 2006 5:42 pm Post subject:

clay · Posted: Tue May 09, 2006 7:29 pm Post subject:

There was an article recently that covered the hot honing technique. As usual, can't remember the mag., probalby Chevy High Performance or Popular Hot Rodding, maybe Car Craft. The measurments that were taken showed the bore distorted substantially more by the block being heated to operating temperature than the torque plate installation did. As well as I can remember it was a cast iron block - Little M I think. I believe it was around 0.002ish" from the torque plate and 0.005ish" distortion from heating to operating temperature. The guy they use to do the test had a machine shop and he offered hot honing. I'll try to find the magazine and look up the price. Clay

The_Raven · Posted: Wed May 10, 2006 9:26 am Post subject:

Inetersting, I'd be down for more hot honing info. Never heard about that, or even thought of the possible changes in block growth or distortion from heat.

Now, there's other variables that might also effect things, like the pull from the crank as the engine is running, distortion would probably be higher in the lower part of the cylider than the upper part, compression/combustion pressures, twisting forces of the crank/cam, etc.