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And most people would have just re shimmed these valves and moved on with it. But given my previous experience with these parts, I knew that would not fix what was actually wrong here.
2 of the 8 intakes had closed up ~ 1.5 thousands of an inch. When I got the head disassembled they were starting to exhibit the same failure pattern as I had previously experienced. For a "normal person" these two valves which were now at .0085" would have been re-shimmed and then would have ran it for another year or more.....When you have the volume of data that I have....there was no question what the cause of the movement was.....and if I want my car to continue to be at the front of the pack...It needs valves that don't leak. As a side note....the same exhaust valves have been in the motor since 2012 FWIW. |
Originally Posted by patsmx5
(Post 1352943)
There is no doubt we have two completely different cars, hell I'm pretty sure we've done this same BS conversation about our cars being different already, haven't we? .
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Originally Posted by bbundy
(Post 1353015)
point of reference my flyin miata super tech 1mm oversized valves have been in use since bought in 2006. Head was rebuilt FM ported casting replaced with one ported from replika after ARP torque specs cracked it after needing the bottom end rebuilt, valves were re-used. I then burned exhaust valves twice running it on the track and melted a piston and did some knock damage to the head once. Im on the third rebuild of the bottom end, still reused the intake valves. 2013 I blew the freeze plug out of the front of the head and thought it might have been damaged too much during the melted piston event had it checked out real good and couldn't find any evidence of catastrophic damage so I re built it again and added Inconel exhaust valves, shim under bucket lifters, and went from super tech single to medium double springs still reused the intake valves. 2016 I broke an intake camshaft and replaced it. I still have not seen intake valve seat wear like others are seeing.
Current config is 2.0l stroker motor. bp4w head. with bp5a intake. makes ~330hp setup for the track ~400 setup for everything else. II holds all the TT2 lap records on northwest tracks. It does pretty good set up for SSM autocross as well and is nationally competitive. rev limit is set to 8600 rpm and it sees that on many autocross courses. I think there is something to the supertech intake valves of much older vintage being better. mine are in 10 years of abuse now.
Originally Posted by TNTUBA
(Post 1353045)
And most people would have just re shimmed these valves and moved on with it. But given my previous experience with these parts, I knew that would not fix what was actually wrong here.
2 of the 8 intakes had closed up ~ 1.5 thousands of an inch. When I got the head disassembled they were starting to exhibit the same failure pattern as I had previously experienced. For a "normal person" these two valves which were now at .0085" would have been re-shimmed and then would have ran it for another year or more.....When you have the volume of data that I have....there was no question what the cause of the movement was.....and if I want my car to continue to be at the front of the pack...It needs valves that don't leak. As a side note....the same exhaust valves have been in the motor since 2012 FWIW. Every motor builder I spoke to keeps saying it's spring pressure causing the problem. I am not 100% sure of that myself. The quality of the nitrated valves are in question as well as required spring pressure. Sure Bob has gotten away with light pressures (both single and double) but his cams are very mid stock ones. Eric had problems with stock cams IIRC as well as his aftermarket ones. Overall I find the spring pressures quite low vs what I am use to dealing with. Sure this is a DOHC 4V head vs SOHC 2V head but still I think creeping up in spring pressure is not a bad idea. I opted to go pretty aggressive on my last head refresh and shimmed the intakes to 85lbs seat pressure. When I start running it again later this year I'll keep a close eye on clearances and report back. If I gotta pull the head again I am going to push for fully nitrated valves. Anyway great info guys! Lots of relevant info to help put this problem to rest. Thanks!!! |
My current seat pressures are between 92 and 96 psi on the intake side and 64-71 on the exhaust side.
That was as close as I could get them with the available shims. I saw no reason to increase the seat pressure on the exhaust side because they seem to be living a happy life. So. Over .060" seat witdh, fresh bronze guides, over 90 psi seat pressure, 8,500 rpm redline, 11.5:1 CR, 26psi boost, C16 leaded fuel, VR1 oil.....and they still started to tighten up after 13 races (That equates to just over 3.5 hours running at "race pace" and is the longest life I have yet to achieve with Supertech Parts) The new parts I have will fix the issue. The new valaves are 3.3 grams per valve heavier than ST stainless valves and with the coatings they were only 4.5x's as expensive as ST valves......and if they fail....I'm taking up golf again. |
FM has some ST inconel intakes out being tested. There are a lot of us having the same issue with the ST stainless intakes. Also I have had no issues with the inconel exh. valves. I would rather pay for the inconels if they prove to work.I have tried all diff spring pessures including singles, light dbls and hvy dbls and diff seat widths all to no avail with msm intake and stock exh cams. Have no issues with OEM intake valves, and that is what I've been running this season along with the oversize exh. ST inconel valves but would like to be able to run the larger ones on the intakes also.
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Originally Posted by TNTUBA
(Post 1353158)
My current seat pressures are between 92 and 96 psi on the intake side and 64-71 on the exhaust side.
That was as close as I could get them with the available shims. I saw no reason to increase the seat pressure on the exhaust side because they seem to be living a happy life. So. Over .060" seat witdh, fresh bronze guides, over 90 psi seat pressure, 8,500 rpm redline, 11.5:1 CR, 26psi boost, C16 leaded fuel, VR1 oil.....and they still started to tighten up after 13 races (That equates to just over 3.5 hours running at "race pace" and is the longest life I have yet to achieve with Supertech Parts) The new parts I have will fix the issue. The new valves are 3.3 grams per valve heavier than ST stainless valves and with the coatings they were only 4.5x's as expensive as ST valves......and if they fail....I'm taking up golf again. IIRC boost x surface area of the valve is about 1:1. Since I only run 12 PSI I should in theory have more effective seat pressure than you. I cap red-line at 8k. I'll be sure to share the results ASAP. I had about 9 race hrs on the old setup before I lost all of my intake clearances. Again thanks for sharing. Would love to hear more about these uber valves you're gonna run. I hope for your sake it puts the problem to rest cause your too young to hang up your hat for golf. |
Originally Posted by k24madness
(Post 1353364)
I share your logic on the exhaust side. I did not increase pressure either.
IIRC boost x surface area of the valve is about 1:1. Since I only run 12 PSI I should in theory have more effective seat pressure than you. I cap red-line at 8k. I'll be sure to share the results ASAP. I had about 9 race hrs on the old setup before I lost all of my intake clearances. Again thanks for sharing. Would love to hear more about these uber valves you're gonna run. I hope for your sake it puts the problem to rest cause your too young to hang up your hat for golf. Can you explain when it is that you have significantly more manifold pressure than what is in your cylinder? (Shouldn't the pressures be near equal when the valve is attempting to close?) |
Inconel
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Originally Posted by Alternative
(Post 1353370)
Can you explain when it is that you have significantly more manifold pressure than what is in your cylinder? (Shouldn't the pressures be near equal when the valve is attempting to close?)
If you don't have a net force acting to push the valve/lifter against the camshaft at all times, you will loft the intake valve off the camshaft and break stuff. The most likely time for that lofting to happen is right at/around max lift. If you want to get really crazy with valvetrain design, google "valve loft". Some race engineers are designing cams for "max valve lift" rulesets that are actually designed to throw the intake valve further open than what those rulesets intend :) |
Originally Posted by Savington
(Post 1353375)
Some race engineers are designing cams for "max valve lift" rulesets that are actually designed to throw the intake valve further open than what those rule sets intend :)
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Originally Posted by Alternative
(Post 1353370)
Can you explain when it is that you have significantly more manifold pressure than what is in your cylinder? (Shouldn't the pressures be near equal when the valve is attempting to close?)
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How do they handle valve seat recession after "lofting" the valve.. Isn't that especially hard on the seat and part of why matching the spring to the cam is essential?
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Originally Posted by mx5-kiwi
(Post 1353488)
How do they handle valve seat recession after "lofting" the valve.. Isn't that especially hard on the seat and part of why matching the spring to the cam is essential?
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As a former national MX racer, this is a very easy description for me to comprehend, thank you :)
Very clever, I wonder how long that has been a "thing" ? |
Not sure how long it has been going on in the automotive industry, but this was going on in go-kart racing engines in the late-90s.
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I just built a head with a set of ST +1 mm inconel intake valves to put through a season of being run hard. FM had a set built so well see what happens?
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Keep us posted jmann. I was unable to find a strength difference between stainless and inconel. Most articles spoke of strength stability of inconel at elevated temps.
TNTUBA what type of valves to you end up going with? Knowing your past cam decisions I imagine it's something from the U.K. Without getting all exotic maybe retreating the valves after the machine work would be a good idea. It seem ST is cutting right through the nitrate treating during final finishing of the valves casing them to be weakened. |
So a little update on this. I build a few heads a year and from what Iv experienced with Supertech they are trying to resolve the issue and we might have a final solution. the old valves that were junk were ss and ground. They didn’t last. Then they started leaving them unground with the nitride coating. This seamed to last according to bbundy. Currently they have added a stelite face to the valves and grind them. This should be even harder than the nitride surface. Time will tell |
FM has the inconel intakes now and I test ran them last season and they looked like new when I checked them this winter..
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Thanks for the heads up jmann. I’ll pursue the FM inconel valves next time around. Not feeling optimistic these Stainless ST valves will last much longer (10-15hrs) than the last set. How do they compare weight wise? Are they hollow or filled with sodium? |
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