RandyS

I tried posting to the regular forum with no bites.

How much can the aluminum block deck be shaved? Assume I'm putting in custom length rods, custom compression height pistons and I will have a custom intake manifold. I would like to lower the deck a lot. Can I do .020? .200? .500?

I have a cutaway picture of a block and it looks like there is about 3/8" meat before hitting the coolant passage.

Surely someone on this forum has a bare block they can look at and measure or a bad block they can cut up

Randy

Nine Ball

iTrader: (38)

Randy, I'm curious about why you would want to chop the deck down so much? Most shops just do a clean-up pass on the deck, to get a smooth surface.

RandyS

I need a low deck height for race engine I'm thinking about. It will be a 311ci (4.8 crank and 5.7 block) to meet the rules. With the short throw crank I don't need the block height to keep a good rod ratio so I'd rather lower the CG.

If there is enought meat I'd like to shave about 1/2" but I suspect there isn't.

Let me know.

Thanks,
Randy

ls1290

iTrader: (20)

I assume that this is not a LSX based block....

RandyS

why? Yes, I will be using a LS6 block

DAPSUPRSLO

iTrader: (14)

4.8 crank, how is that going to work in an ls1. wow, that sounds interesting, good luck

ls1290

iTrader: (20)

How in the world do you plan on getting 511 CI out of it

Keith

RandyS

Why wouldn't the 4.8 crank fit in the 5.7 block? The LR4 is the same GenIII engine family as the 5.3/5.7/6.0

RandyS

3.898 * 3.898 * 3.268 * 8 * .7854 = 311.99ci

DAPSUPRSLO

iTrader: (14)

I'm not a machinist nor a professional engine builder so I have no idea if it will work or not. I just know that a 4.25" is about the biggest I've heard of. I would not think you would be shortening the deck with that big of a stroke, if anything I would think you'd want to add to it to fit in the proper rod to maintain some kind of rod to stroke ratio. Like I said I'm no professional and that is only a guess from seeing looking at other's combonations. Good luck, that should be pretty interesting.

you know what, I just realized you menat the crank from the 4.8 litre motor, never mind, ha ha. I thought you meant a 4.8" stroke.

ls1290

iTrader: (20)

Recheck the original post. It says 511ci and not 311ci

Keith

RandyS

Gotcha, Fat fingers. Sorry.

311

Steve - Race Eng

iTrader: (1)

Randy,

I measured one of my machined for MID sleeve blocks for you to see how thick the deck is. Measurements run between a minimum of .400" and a maximum thickness of .450".

I wouldn't take any more than .020" off the block. Much less than .400" causes gasket sealing issues.

Steve

Mike TexaSS

iTrader: (2)

In a real racing engine where big RPM is involved you want the short deck to 1) reduce the weight of the rotating assembly and 2) allow for use of a shorter pushrod, which is generally the weak link in a high RPM engine.

-Ben

Pro Stock John

iTrader: (34)

Norm Brandes from Westech Auto in WI built a 311ci engine for a Camaro show car for GM about five years ago. Motor was a 5.7 block with a 4.8 crank.

Anyway I would avoid majorly decking the block because the complications from changing the geometry far outweigh the downside of the rod size you are talking about IMHO.

I looked at doing this a while ago, even had a 4.8 crank, and I thought it was possible for me to run a 6.250 rod with custom pistons.

RandyS

Thanks all.

A couple of years ago I heard a rumor that GM was considering casting a 8.5" short deck LSx version for use in FWD cars. Factory displacement range was supposed to be 4.2-5.1 liters.

Now that the Grand Prix/SS comes with the regular deck 5.3 and GM is on the verge of chapter 11 I guess it got shelved.

I could always have the deck cut and welded but too much effort for me.

Back to the drawing board.

Randy

SStrokerAce

iTrader: (2)

Don't worry too much about it Randy... I get why you want to do it and I like it but just throw some rod length in there and call it good. Or just go run a short deck SBC (lots of $$$$) or a 302/5.0L block.

Bret

Pro Stock John

iTrader: (34)

What are you trying to accomplish Randy, a true 302ci or something?

MAC4264

That rod ratio is a bunch of crap IMHO. I have seen guys spend hundreds of thousands of dollars getting the right ratio and to many other variables help show power. My example is this: A pretty known name shop in extreme high performance told me that it matter more than ever and was worth about 40 horsepower on a NHRA pro stock truck engine. They took and engine that made 880 hp and did nothing but change the the rod ratio and new pistons with a tall compression height. Re assambled the engine and it made 920. He replyed to me that was even with a heavier piston. I think that the motor made more power because it had the tall compression height and stablized the piston in the bore keeping the rings sealed better in the engine at higher rpms. The magic number in rod ratio is 1.67 in some peoples mind. If the rod ratio works so well than how come the 302 ford is such a piece of s--t.
5.090/3.00 = 1.697 Look all you want and you will never find it there. I buiding a 311ci (4.060x3.00) C-5R headed LSX motor right now and our main goal is compression and head flow. If you use a stock head you need to be worried more about the compression than anything.