Rod length and compression height of 3500's

[Will'sFiero]

Both VVT and non-VVT.

Anybody know?

I'm looking at Summit and they have some pistons for various applications in the general vicinity for bore, from flat tops to modest dishes, but of varying compression height. Knowing the rod length & compression height for the 3500's would help me figure out if there is a substitute out there.

94 mm bore = 3.701"

305 Chevy has 3.736" bore and 1.560 comp height (comp height is a little high)

The closest thing I have to a 3500 is the 3400 at 1.46 comp height.
Thanks!

[Superdave]

the LX9 uses a 5.9" rod and i have 1.25" written down for the compression height. I'll grab my better set of calipers from work and double check that though... unless someone can confirm.

I found that the Buick 3.3 used the same bore pistons as the LX9, but going .030" overbore and using 305 SBC pistons seemed to be the better option considering the aftermarket.

[bszopi]

Non-VVT 3500 rod length is 5.9" (http://60degreev6.com/content/3500_E...Specifications)
Compression height could be reverse engineered from the numbers in our CR calc (http://60degreev6.com/content/CR_Calculator) and using the deck height from the Specs listed previously.

As far as the 3500 VVT goes, I dunno...

[bszopi]

By definition, compression height is the distance from the center of the wristpin to the top of the piston, not including domes. This distance needs to change depending on the engine's stroke, rod length, and block deck height. Here's the formula to find out what compression height you need.
(1/2 stroke + rod length + desired piston-deck clearance) - block deck height = required piston compression height.
Here's an example for a small Chevy with a 3.5-inch stroke, 5.850-inch rods,
a desired deck clearance of 0.005 inch, and a deck height of 9.00.
(1.75 + 5.850 + 0.005) - 9.00 = 1.395

http://blogs.carcraft.com/1005722/editorials/how-to-properly-calculate-compression-height/index.html

Therefore, compression height = (1.655+5.9-.01)-8.818 = 1.273"

If I have the piston-deck clearance backwards, then it would be 1.253", like Dave said.

[Will'sFiero]

Ok, 5.900 conrods. Sweet.
Do the non-VVT engines still use 0.927" piston pins?

If you go to www.summitracing.com and look up pistons for small block Chevy with 3.736 bore, 6.000" conrod and 3.48" stroke (Basic 305 but with 6" rods), you'll get three results.

There are two Keith Black Hypereutectic P/N's, both with 1.261 comp height (.0035" in the hole). One has 5 cc valve reliefs (Summit # UEM-KB153) and the other has valve reliefs and dome that net -2.80 cc (UEM-KB179).

There's a KB forging with a comp height of 1.265 (.0005" out of the hole) and 3.20 cc valve reliefs.

The 5 cc valve reliefs will get you 10.8:1 compression with a .037 head gasket for .040 quench.
The 3.2 cc valve reliefs will give 11.1:1 compression with a .041 head gasket for .040 quench.
The -2.8 cc dome will yield 12.25:1 compression, again with a .037 head gasket.

[Joseph Upson]

MEASURE THE ROD LENGTH before you buy pistons! The 3900s rod length is advertised as 5.9" but it is actually 5.827" per my measurement and another members measurement by the machine shop prepping his engine components.


I saw those KB pistons on Ebay today when checking for shelf available forged pistons for a possible 3.6L build up one day. They also have some nice ones for the 3900 already at stock LS1 bore (3900 has the same bore), they'll probably be much better priced on Ebay. I found a set of forged MAHLE pistons with rings for under $500 just .010 taller than the stock C/H which can easily be turned down for the 3900.

[Will'sFiero]

Rod length is 5.827? Ain't that a pisser.

I hate marketing pukes who don't get that you NEED the extra numbers when you talk about engine dimensions.

Do the non-VVT engines have piston oil squirters?

[bszopi]

The 3500 only has oil squirters on pistons 5 & 6.

[Superdave]

i measured with the manual calipers that i "borrowed" from work and got 1.252" for compression height.

[Will'sFiero]

MEASURE THE ROD LENGTH before you buy pistons! The 3900s rod length is advertised as 5.9" but it is actually 5.827" per my measurement and another members measurement by the machine shop prepping his engine components.

i measured with the manual calipers that i "borrowed" from work and got 1.252" for compression height.

These can't both be true (well... if they were both true, the piston would be .085 in the hole).

Is the piston pin diameter .927?

What's the stock head gasket thickness?

[Superdave]

the piston i measured was the Gen3 LX9 3500, not a gen 4 3900.

[Will'sFiero]

http://blogs.carcraft.com/1005722/ed...ght/index.html

Therefore, compression height = (1.655+5.9-.01)-8.818 = 1.273"

If I have the piston-deck clearance backwards, then it would be 1.253", like Dave said.

8.818 - (5.900 + (3.307/2)) = 1.2645
8.818 - (5.827 + (3.307/2)) = 1.3375

There are a couple of pistons with 1.338 comp height on www.summitracing.com
I think they're 3.740 or so bore, however.

I wonder how much a Gen III 3500 rod costs... I could order one and measure it myself to verify.

[Joseph Upson]

8.818 - (5.900 + (3.307/2)) = 1.2645
8.818 - (5.827 + (3.307/2)) = 1.3375

There are a couple of pistons with 1.338 comp height on www.summitracing.com
I think they're 3.740 or so bore, however.

I wonder how much a Gen III 3500 rod costs... I could order one and measure it myself to verify.

Upon returning home I have to clear up or confirm my perceiving that the cylinder heads for the 3900 are left and right due to a difference in the coolant passages from one end to the other that I'm certain I observed but didn't take a picture of, in addition to one end with the appropriate coolant passage pluged from the factory.

The wrist pins are about .942" but that's a non issue, I just had a set of .927" bushings made for the stock 3900 rods to fit my forged LS1 pistons.

The problem with the rods among other things is the suspicion that GM may have changed some things about the later 3900 that may very well have resulted in two different rod lenghts, as there are year cutoffs for the engine for some parts and two different lenghts measured.

The later engines also produce less power than the first production engines. It was also discovered that the 3900 was not the only engine to receive the steel crank as advertised in which case I would expect some adjustments would have to have been made for engine balance due to the weight difference in the cranks. There's no telling what's correct about the specs and what isn't without actually measuring yourself.