Register now to get rid of these ads!

Technical Ford FE pistons

Discussion in 'The Hokey Ass Message Board' started by sunbeam, Aug 28, 2023.

  1. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,382

    sunbeam
    Member

    Has anyone built a 390 with using 352 rods and cut the tops of pistons enough to zero deck
     
  2. Dan Timberlake
    Joined: Apr 28, 2010
    Posts: 1,576

    Dan Timberlake
    Member

    How much has to come off the pistons?

    I'd think not many are thick enough to handle even .100 ", and getting too close to the top ring groove could also be a problem.
    Clearance of the skirt to the crank counterweight when near BDC may need to be checked too.
     
  3. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,382

    sunbeam
    Member

     
    seb fontana and Deuces like this.
  4. The stroke is different on those 2 engines. The pin placement in the piston must be known to do a proper calculation.
     
  5. Boggus Deal
    Joined: Dec 27, 2012
    Posts: 27

    Boggus Deal
    Member

    There has been a couple people built them. Scott Foxwell at Foxwell motors for one has built a couple.
     
    mgtstumpy likes this.
  6. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,382

    sunbeam
    Member

    the stroke difference is mostly made up by the rod length why Ford didn't use a a piston around 1.60 and the 352 rod only Ford knows
     
  7. jaracer
    Joined: Oct 4, 2008
    Posts: 2,906

    jaracer
    ALLIANCE MEMBER

    If I remember right Ford used the same piston pin placement and used shorter rods on the 390.
     
  8. Pontmerc
    Joined: Jul 13, 2013
    Posts: 436

    Pontmerc
    Member
    from Finland

    Nothing wrong with piston coming proud of deck.
    Thick fellpro head gasket and there are probably enough clearance.
     
    seb fontana and Deuces like this.
  9. jaracer
    Joined: Oct 4, 2008
    Posts: 2,906

    jaracer
    ALLIANCE MEMBER

    No, but we had a truck 360 at the dealership that had a bad rod, the pin on the crank was bad so we ordered a crank and bearings from the local NAPA. The mechanic put it back together and it started and sounded like a diesel. He came and asked me if you could put a 390 crank in a 360 and get it to turn over. Since I was kind of the Ford guru at the Dodge dealership, I told him that I didn't think it was possible. Well it is possible. Called NAPA and their machinist said it wasn't possible. We pulled one head and measured the stroke, then the machinist measured the stroke at least 3 times. They sent us a correct crank and paid the labor bill.
     
  10. Marty Strode
    Joined: Apr 28, 2011
    Posts: 9,579

    Marty Strode
    Member

    I knew a guy that replaced a rod and piston in a T-Bird, had the wrong parts, ended up with the piston sticking out of the bore. No problem, he used a body grinder and ground it down flush with the deck, and put it back together !
     
    jaracer, RMR&C and deadbeat like this.
  11. The 352 has a 4" bore. A 390 is 4.05. The difference in stroke is .284. One half of that is the difference in compression height if the rod length was the same. The .052" difference in rod length leaves .09" in compression height difference in the pin location. A 360 is the same bore as a 390. Is that the piston you are wanting to use?
     
  12. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,382

    sunbeam
    Member

    The 352 rod Length 6.54 compression height 1.816 The 390 rod 6.488 compression height 1.77 The idea is to take a 352 bore it to standard 390 ( I have a set of NOS dished pistons) use a 390 crank zero decking it by cutting the tops of the pistons to reduce the dish for compression
     
    Last edited: Aug 29, 2023
    Deuces likes this.
  13. FrozenMerc
    Joined: Sep 4, 2009
    Posts: 3,325

    FrozenMerc
    Member

    Given a nominal deck height of 10.17, you would have to cut 0.040" off the top of the piston to get it back to 0 deck, when using the longer 352 rod and standard 390 piston.

    6.54+1.78+(3.78/2) = 10.21"

    Depends on the piston as to whether or not that is feasible, but I would be concerned about the strength of the ring land after hogging that much off the top.
     
    Last edited: Jul 3, 2025
  14. Relic Stew
    Joined: Apr 17, 2005
    Posts: 1,237

    Relic Stew
    Member
    from Wisconsin

    A 390 truck/410 piston has a 1.66" compression height, correct diameter, for 10.09", .080" below deck.
     
  15. What is the dimension from the top ring land to the top of the piston? Are they cast, forged or hypers?
     
    Deuces likes this.
  16. theHIGHLANDER
    Joined: Jun 3, 2005
    Posts: 10,590

    theHIGHLANDER
    Member

    This idea has teeth. A long rod 390? Is that the plan? I see a higher rev limit coming...o_O
     
    Deuces likes this.
  17. 34 5W Paul
    Joined: Mar 27, 2020
    Posts: 401

    34 5W Paul
    Member
    from Fresno CA

    I know this is an old thread about a 390 with 352 rods, but there's a current 352 rebuild that has this subject at the top. I want to link this info over to that current thread. Mostly because this has a solid thread title.
    My calculator shows the stack height in your example at 10.21" for .040 out of the hole. Pistons I'm looking are for the 360 FE and they have 1.760" deck height. That would go 6.54+374+(3.78/2) = 10.19 for .020" out of the hole. Seems much more feasible than skimming seventy thou off of any piston.

    The other issue frequently raised with FE rebuilds is getting a 352 piston anywhere near deck.
    This addresses all those issues. I researched this b/c I bought a $50 360 and a $45 390 crank and was curious. FE Calcs.jpg
     
    Last edited: Jul 2, 2025
  18. FrozenMerc
    Joined: Sep 4, 2009
    Posts: 3,325

    FrozenMerc
    Member

    Yep, looks like I mathed my math wrong and it should have been 0.040" off the top, much more feasible than 0.070". I corrected my previous post. I agree, if you can get your hands on 1.76" compression height 360 pistons, that is even better, assuming 0 deck is your target.
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.