Results 1 to 6 of 6

Thread: Oversize valve thread

  1. #1
    Moderator Turbo Mopar Staff Force Fed Mopar's Avatar
    Join Date
    Dec 2005
    Location
    Greenville/Spartanburg SC area
    Posts
    7,371

    Oversize valve thread

    I know it's been discussed many times, and I remember even posting in various threads and linking to valve info, but I can't find half of the threads now, including the one I was really looking for. So, I figured I'd start a thread with an easily searched name that we can conglomerate all the info in.

    First, what's being used for the largest valve sizes? How large can we go before it becomes counter-productive/unfeasible? I remember linking to some Nissan L28 valves and Toyota 3TC valves, 3TC having the largest options. Of course, custom valves are usually available in any size you want if you want to pay, but sometimes it's nice to have off-shelf options. Also, what size seats to use with these?

    2nd, and this is what I remember discussing before but can't find, does upgrading the intake as large as possible and leaving the exhaust stock or at +1mm give an advantage? Or vice versa? Does boosted vs NA build factor into this decision at all?

    Lastly, anything else to do with oversize valve choice lol. Those are the 2 main questions I had in my head, but I'm sure there's more. Does casting type (IE swirl vs bathtub) make a difference? How much do oversizes increase compression/change chamber volume? Etc etc...
    Rob M.
    '89 Turbo GTC
    2.5 TIII swap is here!

    Project LookOwt
    '91 Daytona ES, 61k original miles, Rick Lozier's old 3.0 nitrous car
    Back to basics, then the mods go back on....

  2. #2
    turbo addict
    Join Date
    Dec 2006
    Location
    MPLS, MN
    Posts
    3,127

    Re: Oversize valve thread

    Rob,
    What I have found is you can't really put a cc number on combustion chamber volume from various valves available. For example the custom Manley valves combined with fresh seats could actually net you a gain in compression (less cc's)! Then of course after doing all the unshrouding in a typical HP build, and surprisingly, chamber volume doesn't change a bunch. Some exhaust valves are tuliped a lot more than other valves, while nailhead designs (intakes) can range from flat to dished. I typically don't worry whatsoever about chamber volume until all my chamber work is done, and then can adjust to desired volume by resurfacing head & deck of block, dish of pistons, headgasket thickness, and compression height of pistons.

    One issue I have run into lately is when running "stocked" forged pistons from vendors is the valve reliefs on 8V applications are not always machined quite in the correct location, and valve relief diameter & valve relief depth is not consistent from one piston manufacturer to another. I have also found this to be the case also with Masi 16V valve reliefs. Usually not an issue unless you are using a BV head combined with a .500+" lift camshaft. THEN, you might very well NOT have a non interference engine anymore! Lots of variables out there, so the point of this story is CHECK THIS during assembly.

    Not really sure who is making oversize valves these days for our applications besides Si valves. I'd be willing to bet the Si valves are import valves. I typically use Manley custom valves (made in N. America from SBC LS blanks) for all HP builds. I have used some of the MP stainless exhaust valves P4876670 with success too. These were manufactured in Argentina. Those valves were made pretty nice, and rival the Manley exhaust valve. I've also seen some MP +1mm intakes that were of poor quality. Probably flow not much better than a stock sized valve. IMO, a waste of effort putting such a low quality valve in.

    I use the typical +1mm on both intake and exhaust, and on BV applications I use 44/38mm ( 1.730" & 1.650"). My fully ported swirl or G-heads will both flow pretty close to each other. The swirl typically requires a bit more porting time. On my heads the swirl intake port usually is a bit better than the g-head on the flowbench, while the g-head exhaust port usually out flows the swirl on the flow bench by a similar small amount. Chamber and port work is a MUST when using oversize valves to get the benefit of the larger valve.

    IMO, the exhaust port flow is low on all 8v applications (better than Ford's 2.3 liter engines though), especially when you compare it to our 16V applications. Max effort ported exhaust flow #'s between 170-180 CFM @ .500-.550 for 8V's pale in comparison to even a STOCK Masi 16v & at much lower valve lifts. Most 8V exhaust ports will not even come close to the #'s I just posted. In fact, many intake flow #'s won't even make it to those #'s unless one knows what your doing (lol)! So my point is, anything you can do to help the exhaust on a 8V is going to be a gain. That doesn't mean bolt on a ported OEM or aftermarket exhaust manifold and think you have it covered.

    Todd

  3. #3
    Slugmobile & MeanMini Caretaker Turbo Mopar Contributor wheming's Avatar
    Join Date
    Nov 2010
    Location
    Raleigh Area, NC
    Posts
    3,963

    Re: Oversize valve thread

    Thanks for sharing that info Todd!
    Wayne H.

    '91 Dodge Spirit ES 2.5L turbo 5spd
    '05 PT GT 2.4T HO autostick
    '89 Plymouth Acclaim 2.5L turbo auto, "Slugmobile" yes, THE Slugmobile!
    '89 Dodge Caravan SE 2.5L turbo auto, "Mean Mini" yes, Gus' Mean Mini! (Current best 11.7786@113.04 mph! - Jan 15th, 2017 Fayetteville Dragway, NC)
    MeanMini dragracing videos: https://www.youtube.com/playlist?lis...URZLB1RxGYF6vw
    and other cars, trucks and motorcycles
    https://www.youtube.com/user/SlugmobileMeanMini

  4. #4
    Hybrid booster
    Join Date
    Mar 2014
    Location
    Toronto Canada
    Posts
    837

    Re: Oversize valve thread

    Lastly, anything else to do with oversize valve choice lol. Those are the 2 main questions I had in my head, but I'm sure there's more. Does casting type (IE swirl vs bathtub) make a difference? How much do oversizes increase compression/change chamber volume? Etc etc...

    I believe the stem length changes between the two style combustion chambers/heads

  5. #5
    turbo addict
    Join Date
    Dec 2006
    Location
    MPLS, MN
    Posts
    3,127

    Re: Oversize valve thread

    Yeah the g-head stem length is approx. 075-.080 shorter than a swirl. Sorry bout the no quotes, no workie for me anymore...
    Todd

  6. #6
    Moderator Turbo Mopar Staff Force Fed Mopar's Avatar
    Join Date
    Dec 2005
    Location
    Greenville/Spartanburg SC area
    Posts
    7,371

    Re: Oversize valve thread

    Would it be worth finding a guide that would allow 6mm or 7mm stems instead of 8mm? How much flow is a smaller stem size worth, vs any side effects of going smaller (if any)? Any long term reliability downside to thinner stems? I know it would reduce operating mass, but how much advantage would that give?
    Rob M.
    '89 Turbo GTC
    2.5 TIII swap is here!

    Project LookOwt
    '91 Daytona ES, 61k original miles, Rick Lozier's old 3.0 nitrous car
    Back to basics, then the mods go back on....

Similar Threads

  1. A/C expansion valve mounting screw thread size
    By 135sohc in forum "I need help!"
    Replies: 5
    Last Post: 03-24-2010, 01:50 PM
  2. T-3 valves - oversize?
    By glhs727 in forum FWD Performance
    Replies: 0
    Last Post: 02-07-2010, 09:11 PM
  3. Where to get oversize t2 pistons?
    By stormy69 in forum Engine - Block, Piston, Heads, Intakes
    Replies: 15
    Last Post: 08-05-2008, 02:53 PM
  4. 1.00mm Oversize Pistons
    By BadFastGTC in forum Parts Wanted
    Replies: 0
    Last Post: 10-21-2006, 10:11 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •