boosted-lt1

Dear Engine Builders and Enthusiasts,

I was wondering what the recommended piston land thicknesses are for a turbo motor? I've been looking at rod length and stroke for a genII LT1 and a 9.010" deck. Considering the below, I don't see how you can run a 6.00" rod in this block with a 3.75" stroke. Or maybe a better way to state what I'm looking for: What is the longest rod you can fit in a 9.01" block with a 3.75" stroke while maintaining maximum piston durability for a turbo application?

Top Land - 0.18"
Second Land - 0.18"
Third Land - 0.11"
Bottom Land - 0.030"
Comp Ring - 1/16"
Scrapper Ring - 1/16"
Oil Ring - 3/16"
Pin Dia. - 0.927"
Deck - 9.010"
Stroke - 3.75"

I get 5.85" rod with 0.009" in the hole and a rod ratio of 1.56

What does a piston look like for a 6" rod in a 383? Would it work for a blower/turbo?

Thanks!
Scott.

streetbad

.3"

boosted-lt1

Please explain.

Thanks.

Injuneer

5.85's work fine in a 3.75" stroke engine, with a large hit of nitrous. Why do you have a concern with a 1.56 ratio over a 1.60? The whole "ratio" issue is really not as important as people would have you believe. Keeping the piston intact is much more important.

boosted-lt1

Injuneer,

Yeah your right. 1.56 is within 5% of a production SBC @ 1.64 so no big deal. Maybe the 'yuck' smilie was a bit too much.

Streetbad,

Did you mean a 0.3" top land and a zero deck?


How do the land thickness look in the initial example? Maybe a thicker top land and take some thickness out of the second/third? Anyone recommend a big block piston pin @ 0.990?

Thanks,
Scott.

rskrause

0.25" minimum.

Rich

streetbad

For strength in a Turbo Motor most go with a 5.7" rod so that the piston can be made stronger. .3" is just a general recommendation. As the rod becomes longer the piston becomes weaker (no room for thick ring lands). If you are building a new short block,put in boost specific pistons for best results.

rskrause

The above is true, but you really don't need that much compression height to have enough room for a beefy top ring land. The pin bore can intersect the oil ring groove provided you don't mind using an oil rail support. You don't need much more than an 1" of CH in that case. A 6" rod with a 3.75" stroke nd a 9.00" deck leaves 1.125" for the ring pack, which is plenty for a 0.25-0.3" top land. Now, I still prefer a short rod for a blower motor, but that is another discussion. A 3.875" stroke would probably not leave enough room.

Also, you do need to leave enough room for adequate piston crown thickness. If the piston is for a low compression blower motor, with a large/deep dish that can also be an issue. Another reason why a shorter rod may be needed. Just pointing out that it isn't the ring pack per se. If you re building a high boost motor, you had best talk to a good piston manufacturer before ordering the parts. Ross, JE, Probe, etc.

Rich

boosted-lt1

Thanks for the info. I didn't consider the pin interfering with the oil ring in my initial assessment. Now I see how you can get ~0.3 T/L and a long rod.

I had just begun reading a thread on rod length/ratio last night over at Gofast. For a street motor on pump I think I need to focus on durability - detonation resistance with varying quality of fuel.

Apologies for not making this very advanced, but thanks again for the info.

-Scott.

streetbad

What is "adequate piston crown thickness"? I may be intending to push over what is reasonable! ? Thank You -Tim

rskrause

About 0.300" for high boost or >150hp nitrous. Talking t the piston manufacturer is a good idea for anything other than a standard combo.

Rich

Clary

I agree with Rick that the shorter rods are a better choice, mine has 6" rods with 3.875" stroke crank 4.040" Diamond pistons.
I called Diamond and they said the pistons were good for 28 psi, i guess i,ll find out in a few months,now have Procharger D-1 instaled.

Clary PS if i get 15psi i,ll be happy.