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Thread: Oversize valve thread

  1. #1
    Moderator Turbo Mopar Staff Force Fed Mopar's Avatar
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    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
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    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

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    Slugmobile & MeanMini Caretaker Turbo Mopar Contributor wheming's Avatar
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    Re: Oversize valve thread

    Thanks for sharing that info Todd!
    Wayne H.

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    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
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    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

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    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....

  7. #7
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    Re: Oversize valve thread

    I used to have a company called Techuvance make custom guides Mang-bronze guides for me. They were bought out by SI valve. Lee, new owner contacted me introducing himself and was looking for business. He was wanting me to place an order, but then told me he won't "do" custom guide work anymore. It wasn't like I was ordering 8 guides at a time. I placed orders for between 100 to 150 at a time. Need to find someone else that wants my money I guess... BTW on my exhaust guides, I taper them in a lathe prior to installing.

    The +1mm REV valves that Rick D. had made up used a very undercut stem on the intake. When I saw them they scared me a little, they were REALLY undercut! They are 7 mm stem size, but obviously a much smaller (lighter) valve.

    Sometimes going with something that should be a gain winds up not being a gain. For example that same Masi 16V REV +1mm undercut intake valve actually flowed less than a stocker until the ports were enlarged quite a bit. My point is you may not know the answer to your questions until you try, but I'll offer you my opinion. IMO, 5/16" stem size is not hurting the 2.2/2.5 heads flow, & don't think I would want to go much thinner stem diameter than that besides. The factory Masi exhaust valves had a bad habit of being bent even on bone stock low mileage 10-11 PSI cars. Rick went with a strong but heavy Inconel exhaust valve for that reason.

    Todd

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    Re: Oversize valve thread

    That's kinda what I was thinking.
    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....

  9. #9
    Supporting Member II Turbo Mopar Contributor
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    Re: Oversize valve thread

    I don't think it was the physical design of the Masi exhaust valves that caused them to "bend", but poor material. I don't think they held up the the heat cycling. (just a note, my Masi head I just had done, NONE of the stock exhaust valves appeared to be "bent", but ALL of the guides were worn. That head has ~130k miles on it)

    I *just* spoke with Rick D. last night about my one Masi head that he's working for me. ALL of the guides were worn. Apparently replacing guides all together is becoming a thing of the past unless totally needed. What is current tech/practice is guide liners that are reamed to the correct diameter. I have mixed feelings about this. Part of me thinks it's fine because it doesn't stress the head nearly as much as replacing guides. The other part of me wonders about heat transfer due to different materials.

  10. #10
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    Re: Oversize valve thread

    Chris,
    Bronze guide liners is nothing new. Been doing that for decades. I bought a frame off 69 Vette years ago that had liners in heads. The two rear cylinders (furthest from the waterpump) ejected the liners because machinist didn't quite give them enough clearance, and when things heated up the valves seized in head and ejected liners. As you eluded to, the beauty of Mag-bronze liners is they expand and contract at close to the same rate as aluminum. You can then run clearances slightly tighter than with cast iron or steel guides, which makes your valve job last longer.
    I bought in on the RD valve package many years ago. Came with nicely made guides with stops that were easy to install. Rick must not have any new guides left and maybe his source for them like mine, dried up. I've seen plenty of cast iron guides actually cracked in the head from when bronze liners are installed. The liner was okay though. If you ask me, that would seem to suggest it puts more stress on cylinder head.
    If you performed a leakdown test, you can immediately tell if you have some bent or warped exhaust valves on that particular cylinder. My masi engine just had one warped exhaust valve.

  11. #11
    Supporting Member II Turbo Mopar Contributor
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    Re: Oversize valve thread

    Thanks, Todd. I actually hadn't heard of guide liners until recently (though I did know about them before this job, but barely). As for the cracked guides with liners...I'd say that the guide probably had something wrong with it, then the added stress of being bored out, then a liner pressed into it (I'm assuming that's how it's done), if the press fit was a little too tight I could see it causing an issue. The only reason I infer that the liners would put less stress on the head is that you aren't having to subject the head to the brutality of removing the old guides.

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