3.5L Piston Measurements - DodgeIntrepid.Net Forums - Dodge Intrepid, Concorde, 300m and Eagle Vision chat
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post #1 of 25 (permalink) Old 08-10-2016, 08:47 PM Thread Starter
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Post 3.5L Piston Measurements

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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post #2 of 25 (permalink) Old 08-10-2016, 10:12 PM
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post #3 of 25 (permalink) Old 08-11-2016, 08:11 AM
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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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post #4 of 25 (permalink) Old 08-11-2016, 08:42 AM
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Quote:
Originally Posted by WarlockSyno View Post
...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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post #5 of 25 (permalink) Old 08-11-2016, 09:18 AM
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Wrist pin to Crown won't do you any good unless the diameter is correct.
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post #6 of 25 (permalink) Old 08-11-2016, 12:43 PM Thread Starter
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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.
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post #7 of 25 (permalink) Old 08-11-2016, 10:11 PM
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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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post #8 of 25 (permalink) Old 08-11-2016, 10:51 PM
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Quote:
Originally Posted by WarlockSyno View Post
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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Last edited by Daytrepper; 08-11-2016 at 11:00 PM.
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post #9 of 25 (permalink) Old 08-11-2016, 11:04 PM Thread Starter
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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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post #10 of 25 (permalink) Old 08-12-2016, 03:32 PM Thread Starter
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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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post #11 of 25 (permalink) Old 08-13-2016, 04:50 AM
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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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post #12 of 25 (permalink) Old 08-13-2016, 07:24 AM
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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.

Last edited by peva; 08-13-2016 at 07:31 AM.
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post #13 of 25 (permalink) Old 08-13-2016, 11:31 PM Thread Starter
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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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post #14 of 25 (permalink) Old 08-13-2016, 11:55 PM
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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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post #15 of 25 (permalink) Old 08-13-2016, 11:57 PM Thread Starter
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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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