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Discussion Starter #1
Hey guys,

I was wondering if anyone had the measurements of the 3.5L piston. I'm looking to see if I can find some factory parts to put into my 3.8L OHV engine. It looks like the 3.5L has the same length connecting rods and the same big end.

I'm wondering if it would be a good upgrade for the 3.8L, since (I'm pretty sure) the 3.5L has forged pistons and rods.

However, I'm figuring the top of the piston to the top of the connecting rod is closer on the 3.8L pistons than it is on the 3.5L. I bet it will either be flush with the block or stick out a few milometers.

Let me know if anyone has information! Because I am having the damnest time finding this stuff out! I did find this info though:
http://www.turbododge.com/ forums/f11/f196/376000-connecting-rod-length.html#post2398617 (remove the space)



Thanks!
 

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Woober Goobers!
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From the FSM as Dan suggested looking at.......


Type Material Aluminum (Full Floating
Pins)
Piston Diameter 95.98 ± 0.019 mm
(3.7788 ± 0.0008 in.)
Clearance at Size
Location
–0.007 to +0.047 mm
(–0.0003 to +0.0018 in.)
Piston Weight
—A Size 438–443 grams
(15.45–15.62 oz.)
—B Size 433–438 grams
(15.27–15.45 oz.)
Piston Ring Groove
Diameter
—No. 1 87.4–87.6 mm
(3.441–3.449 in.)
—No. 2 86.3–86.5 mm
(3.397–3.4055 in.)
—No. 3 85.8–86.0 mm
(3.378–3.385 in.)
 

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...However, I'm figuring the top of the piston to the top of the connecting rod is closer on the 3.8L pistons than it is on the 3.5L. I bet it will either be flush with the block or stick out a few milometers...
I looked at the FSM specs. too, but I don't think it has that dimension.
 

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Wrist pin to Crown won't do you any good unless the diameter is correct.
 

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Discussion Starter #6
Does any one have a piston to measure the distance from the center of the wrist pin to the top?

Ronbo, does it look like the diameter of the 3.5L piston is the same as the 3.8L OHV?

I'm thinking the distance between the two will be further because of the short stroke of the 3.5L compared to the 3.8L.
 

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Don't have a clue on the 3.8L. You need to do some research yourself on that.
 

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Does any one have a piston to measure the distance from the center of the wrist pin to the top?

Ronbo, does it look like the diameter of the 3.5L piston is the same as the 3.8L OHV?

I'm thinking the distance between the two will be further because of the short stroke of the 3.5L compared to the 3.8L.
3.5 pistons will not work on a 3.8 connecting rod due to a different style wrist pin; although they are the same diameter.

It would be pointless to use a 3.5 piston and connecting rod assembly if you could bolt it in (not sure if journals are the same), because you would end up with less compression than you originally had with the 3.8.....the only other unknown is the piston height, but if it works out equal to the 3.8 (3.5 piston and con rod) which I doubt, there is also nothing to gain there. I am speculating here, not knowing the piston heights, but I doubt any taller piston height would be enough to make up for the shorter stroke on the 3.5.
 

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Discussion Starter #9
No, no, no. I don't want to put the 3.5L on the 3.8L connecting rod. I want to use the connecting rod and piston together. I know you can use the 3.5L crank on the 3.3L connecting rods and piston because they were being used in swaps for the Can Ams. So I know the reverse will work. (Also look at Chewy's build. He got it to work, although needing to figure out how to make the oil pickup work)

If it's less compression than the 3.8L was before, that's okay. I'm building this for boost so that's not too bad. However, like I said, I bet this would actually make the piston stick out of the block. That's how it is with the 3.3L connecting rods, although they are slightly longer. If the distance from the top of the piston to the wrist pin is the same as the 3.8L (doubt) than it will be all good in every way.
 

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Discussion Starter #10
The two blocks have the same deck height, right? If so then this all hinges on the travel of the crank journal and the wrist pin location. If I could have some one measure their piston and I can measure mine and compare.



3.3 rod:

  • 6.1811" center to center
  • 2.4101" large end bore
  • .900 small end bore
  • big end width .855"
3.8 rod

  • 5.945" center to center
  • 2.4101" large end bore
  • .900 small end bore
  • big end width .855"

3.5L

  • 5.936" center to center
  • 2.4101" large end bore
  • .98375" small end bore (no bushing)
  • .94535" small end finished ID (with bushing)
  • big end width .855"
 

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I no longer have a piston to measure off of, but what I see in your specs is that the small end bore is going to be off and making it a no-go. With the 3.3 and 3.8 having a small end bore of .900", the 3.5L having a small end bore of .984" is going to be pretty far off. The wrist pins are designed to be free-floating which means they are a slip fit. If a wrist pin is slip fit in a 3.3 or 3.8 rod, then it is going to be SLOP fit in a 3.5 piston.
 

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Maybe a dumb question but can you make press-in adapter bushings to take up the slop? If I'm thinking right, the bushings would press onto the wrist pin so the circlips would keep the pins from rubbing the cylinder wall.
 

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Discussion Starter #13
Lol, I don't think you guys understand what I'm saying.

Imagine I threw away my rods and pistons. So the 3.8L ones are in the trash. Now, I go down to the junkyard and find a '96 or something Intrepid and throw some 3.5L rods and pistons into my 3.8L. I just want to know how far out of the block the pistons will stick. The rods are the same exact length as the 3.8L, so that's all good. However, because of the shorter stroke on the 3.5L, it may have made up for the shorter stroke by making the wrist pin lower down on the piston. The distance between the top of the piston to the center of the wrist pin is what will determine if this will work or not.

Know what I mean?

It's either:
A. Going to lower the compression so low that the engine barely starts
B. Stick so far out of the block that it'll smash the head
 

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You never answered what the piston diameter is on the 3.8L? Are the bore sizes the same?
 

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Discussion Starter #15
Yup.

Size | Bore | Stroke
3.8 96 mm 86.9 mm
3.5 96 mm 81 mm

The 3.8L is a bored and stroked 3.3L.
The 3.5L used the stroke of the 3.3L and the bore of the 3.8L.
 

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ZeroKool just did a 4.0L stroker build on his damaged 2nd gen 3.5L. Maybe look him up on here and send him a message asking if he has an old piston laying around.

Also you're talking about using 1st gen 3.5L parts. 1993-1997. I think most everyone assumed you were talking about 2nd gen parts. Zerokool's build was a 2nd gen 3.5L 1998-2004. Not sure if there are any differences between the 1st and 2nd gen 3.5L pistons. Something else to consider.
 

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Discussion Starter #17
Yeah, I was thinking about that too. How many gens are there? Three? I remember the second gens are somehow weaker or something. The there is whatever is in the LX platform. I'm not sure which one would be best but I'm going to check out his 4.0L build first, been meaning to read up on it, I'll shoot him a message too!
 

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1st gen 1993-1997
2nd gen 1998-2004

3rd gen? LX 2005-2016. Chrysler still uses the 3.5L in the LX and LC cars.
 

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Discussion Starter #19
So, from what it looks like, do 1st gen pistons have valve reliefs? Looks like they're +.2 or .3 bumps of compression too. So, would the 3rd gen pistons and rods be what I want. I know those are forged and easily putting up with 370whp. Way above what I'm looking to do.
 

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So, from what it looks like, do 1st gen pistons have valve reliefs? Looks like they're +.2 or .3 bumps of compression too. So, would the 3rd gen pistons and rods be what I want. I know those are forged and easily putting up with 370whp. Way above what I'm looking to do.
Why don't you buy one from rockauto? About tree-fiddy.
 
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