Piston talk...3500 style

[Superdave]

I've been trying to find a piston that will work in the 3500 and give some better compresison, seem to have run into a possiblity... I found that the 3.3 90 degree V6 has a 3.7" bore like the 3500.

I measured a 3500 piston and got:

Compression Height: 1.269"
Pin Diameter: .935
Actual piston diameter: 3.67" < wtf? LOL
Piston dome volume -26.5cc

the measurements for the 3.3 piston are:

Compression Height: 1.310
Pin Diameter: .9054
Piston Dome volume: -11cc


Now (maybe my math is wrong) but if i shaved .060 off the tops of the 3.3 pistons that should bring them to 0-deck and ends up with around an 8cc dish. Judging by the pics i've seen of the 3.3 piston it should be ok to take .060 off the top. On a 3500 with .040" gaskets that's like 13.24:1.. 12.4:1 with .060 gaskets.

If .060 is too much then shaving .040" off the pistons brings them to the stock deck height and would still be around 12.7:1 range for SCR. Still very nice for a N/A application.

Thoughts?

[Monzsta]

What 3.3? GM? Dodge? Just for clarification.

[Superdave]

3.3 Buick '90-'95 or so

[95Grand-Am]

I wondered what you were going to do for pistons. Your Idea sounds good if there is enough material above the top ring. Wouldn't you also have to bore the pin holes out too,which shouldn't be a big deal. Where you also going to have valve reliefs cut into them? Have you taked to a engine machine shop to see if they could think of any problems with this. It's to bad that you couln't just get 3.4 pistons for a 0.08" overbore.

[sprucegagt]

Everything I've read tells me not to sacrifice good quench characteristics. Personally I wouldn't even look at using .060 head gaskets with a zero deck block.

[ForcedFirebird]

Everything I've read tells me not to sacrifice good quench characteristics. Personally I wouldn't even look at using .060 head gaskets with a zero deck block.

I agree. I recently changed my mind on using 3500 gaskets for my motor with 3.4 pistons.

Dave, what happened to the 3.6DOHC idea?

[IsaacHayes]

I think it's LS4 build up time LOL

[Joseph Upson]

Why don't you look into the 305 piston instead since that engine has a 3.735" bore, then maybe you can have the crank offset ground and find a proper length SBC rod to place the piston at the right height. There's a .170" stroke difference for starters. You can also find forged 305 pistons for much, much cheaper than a custom set for the V6. You would need valve reliefs cut though.

[ForcedFirebird]

Dave, what happened to the 3.6DOHC idea?

I should have said "What happened to the idea of using 3.6DOHC pistons?".

Form what I understood from Brad's thread, the 3.6 pistons are a direct replacement for the 3500 pistons, but have a much smaller dish (actually no dish, only valve reliefs).

This would be the easiest/cheapest way to rais compression significantly - in my opinion, anyways.

[Superdave]

I should have said "What happened to the idea of using 3.6DOHC pistons?".

Form what I understood from Brad's thread, the 3.6 pistons are a direct replacement for the 3500 pistons, but have a much smaller dish (actually no dish, only valve reliefs).

This would be the easiest/cheapest way to rais compression significantly - in my opinion, anyways.

They are still an option however i'd need a hookup from someone with a machine shop to cut me some valve reliefs.

I'd also have to actually buy one to get the measurements off of

[Superdave]

Why don't you look into the 305 piston instead since that engine has a 3.735" bore, then maybe you can have the crank offset ground and find a proper length SBC rod to place the piston at the right height. There's a .170" stroke difference for starters. You can also find forged 305 pistons for much, much cheaper than a custom set for the V6. You would need valve reliefs cut though.

Money i don't have.. lol

[Superdave]

did some digging on the 3.6 pistons, and now that i have measurements from the 3500 to compare them to.. they might work well afterall..

Bore 3.7"
Stroke 3.307"
Head Gasket Bore 3.79"
Head Gasket Compressed Thickness .06"
Combustion Chamber Volume 32 cc
Piston Dome Volume 1.2 cc
Piston Deck Clearance .008"
Displacement 3494 cc
Calculated Compression Ratio 13.74:1


3500 compression height is 1.269
(un-verified) Compression height of the 3.6 piston is 1.255

which sets them at .014 lower in the bore than the 3500 pistons.. by my actual measurements that means they'll be popping out .005.

[Joseph Upson]

did some digging on the 3.6 pistons, and now that i have measurements from the 3500 to compare them to.. they might work well afterall..

Bore 3.7"
Stroke 3.307"
Head Gasket Bore 3.79"
Head Gasket Compressed Thickness .06"
Combustion Chamber Volume 32 cc
Piston Dome Volume 1.2 cc
Piston Deck Clearance .008"
Displacement 3494 cc
Calculated Compression Ratio 13.74:1


3500 compression height is 1.269
(un-verified) Compression height of the 3.6 piston is 1.255

which sets them at .014 lower in the bore than the 3500 pistons.. by my actual measurements that means they'll be popping out .005.

So where is the adjustment made for the difference in stroke between the two engines? piston I'm assuming. If the rods have the same size big end you may want to consider using them also, GM addresses them as Sinter Forged Steel which appears to be different from those in the 3500 and since the 3.6 in the Cadillac has a 7000 rpm fuel cut off I would think they are stronger. GM parts direct had what appears to be a reasonable price on an assembly.

[Superdave]

the 3.6 rods are 5.9212" long, the 3500 rods are 5.9" long.

Connecting rod bore diamater on the 3.6 rod is 2.347
same on the 3500 rod is 2.376

they must have offset ground the crank slightly to gain the .1L displacement.

[Joseph Upson]

the 3.6 rods are 5.9212" long, the 3500 rods are 5.9" long.

Connecting rod bore diamater on the 3.6 rod is 2.347
same on the 3500 rod is 2.376

they must have offset ground the crank slightly to gain the .1L displacement.

In that case I would expect the 3.6L piston to be very strong given how far up near the top the piston pin has to be to accomodate the longer rod and longer stroke. Perhaps that's where the forged piston typo in the GM literature originated from, maybe some were at some point. Some camaros and trans ams received the initially corvette only LS6 block when it first debuted but, GM didn't tell the customers that, you had to check and find out if you were one of the lucky ones.