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Was said 'sploding head with aftermarket valves/springs? I have +1mm supertechs all around with the single spring and titanium seats. I was told that'll do 8k without problems by a cam shop and I believe FM as well. Hammering through the head sounds like a lash adjustment issue to me. Either that or they cut the seats too much.
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IMO if there is no loss of cylinder wall material you can get away with a hone, get the crank polished, and have the head and block mating surfaces checked. That should come in pretty low on the price range to have done or like others said hone it yourself and have a shop check the head, block, and polish the crank.
For balancing if you shop around you can find a good price I would think. The shop balancing my rotating assembly (including clutch/pp/flywheel harmonic balancer) is getting $200. I really feel getting everything balanced is important for an engine that is going to be pushed hard but if it is just a toy that won't be tracked then you could pass on it. |
It was the RPM, not valve lash or something else. It was always the number 1 intake valves - same failure mode in 4 different heads with lots of stuff changed except the RPM.
Originally Posted by Reverant
(Post 699939)
We all know the story about Bill's car.
First, it was "overheating" each time. Then it was the VVT that was switched on at the setpoint with the TEC2, rather than progressively retarded and destroyed the head. The the Hydra was fitted and now its the sustained high-RPM operation that causes the failure. So what is it? -Jason Cuadra did 15 seconds of math and dispelled the idea that the rapid snap from full advance to full retard was increasing the cam RPM enough to pound the seats - IIRC he said that at most it was a 150rpm increase -Once they fitted the Hydra and had another failure, someone spoke with the old owner of Integral Cams, who said that there's a harmonic on the VVT intake cam at 7500. -Bill dropped the RPM to ~7400 and hasn't toasted another head that I know of. Maybe the EUDM VVT cam is different - I know the JDM VVT motors have higher compression. You can get away with just a hone - assuming the wall clearances are still within spec. You cannot just hone and slap slugs into a motor without confirming wall clearance. |
If your building a motor its worth doing everything you can to make sure its right, I'd much rather over build than build twice. Its cheaper that way and less time involved.
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Originally Posted by TrickerZ
(Post 699965)
Was said 'sploding head with aftermarket valves/springs? I have +1mm supertechs all around with the single spring and titanium seats. I was told that'll do 8k without problems by a cam shop and I believe FM as well. Hammering through the head sounds like a lash adjustment issue to me. Either that or they cut the seats too much.
The USDM VVT intake cam harmonic is one of the big motivators for me to get a set of "mild" cams into my motor - I could really, really use another 400-500rpm in 5th to avoid 5-6-5 shifts at a few tracks. |
Originally Posted by hustler
(Post 699874)
lol @ Canadia
lol @ spinning a Miata to 8000rpm. I'm just a layman, but I've seen my engine beat the turbo to death with vibration at <7k and would never go higher with this motor. I agree with the cost/benefit ratio. Hit the big stuff that make the engine reliable and take that last $1000 you'd spend on removing material and porting to the suspension fund because I promise you'd get more bang for your buck out of half a set of Xidas over 10hp from a p&p. And because your turbo system can't handle the resonance above 7k RPM doesn't mean the engine can't. I'll happily rev my motor to 8k+ with the Rotrex, and NA motors will run up there all day long. As for the head work, I agree. If I were to do my build over again I would have done the same stuff to the bottom end but on a 1.8L and throw a VVT head on it and call it a day. You can very quickly start spending too much money because "well I'm doing X already so I may as also do Y and Z while I'm there"... My head has supertech valves, stock BP springs, my own cams and MazComp SUB. Plus porting/polishing. |
Sav: re: "mild cam" - you may want more duration but with more gentle closing-acceleration profiles. You might want to talk to Dema Elgin at www.elgincams.com
Having said that, the problem may not lie in the cam profile... Did the dude who lost several heads, try stiffer or dual springs, or lighter valvetrain parts? Because a "resonance" is in the mass (valve+lifter) and spring combo, and is excited at a particular RPM (e.g. 7500). You increase the resonant frequency by reducing mass or increasing spring rate; dual valve springs break up the resonance into 2 smaller ones. Maybe you could do what Rebello does on some heads, which is to shim up the springs to get a bit more RPM capability. |
Side question whil i have a thread started... do the VVT oil pump gears have the same issue as the earlier pumps which suggest using billet gears to avoid shattering at high power levels?
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Originally Posted by Savington
(Post 699990)
It was the RPM, not valve lash or something else. It was always the number 1 intake valves - same failure mode in 4 different heads with lots of stuff changed except the RPM.
It's the sustained RPM. -Jason Cuadra did 15 seconds of math and dispelled the idea that the rapid snap from full advance to full retard was increasing the cam RPM enough to pound the seats - IIRC he said that at most it was a 150rpm increase -Once they fitted the Hydra and had another failure, someone spoke with the old owner of Integral Cams, who said that there's a harmonic on the VVT intake cam at 7500. -Bill dropped the RPM to ~7400 and hasn't toasted another head that I know of. Maybe the EUDM VVT cam is different - I know the JDM VVT motors have higher compression. You can get away with just a hone - assuming the wall clearances are still within spec. You cannot just hone and slap slugs into a motor without confirming wall clearance. |
Originally Posted by JasonC SBB
(Post 700046)
Sav: re: "mild cam" - you may want more duration but with more gentle closing-acceleration profiles. You might want to talk to Dema Elgin at www.elgincams.com
Having said that, the problem may not lie in the cam profile... Did the dude who lost several heads, try stiffer or dual springs, or lighter valvetrain parts? Because a "resonance" is in the mass (valve+lifter) and spring combo, and is excited at a particular RPM (e.g. 7500). You increase the resonant frequency by reducing mass or increasing spring rate; dual valve springs break up the resonance into 2 smaller ones. Maybe you could do what Rebello does on some heads, which is to shim up the springs to get a bit more RPM capability. AFAIK aftermarket valvetrain parts are not legal in CSP, so I don't think he tried anything because he couldn't. |
Originally Posted by DammitBeavis
(Post 700120)
I just keep running into new info here lately! I have experienced the hammered valve seats twice on my '99. The top end is all OEM except for some porting. I even decided not to rebuild that head again thinking something was wrong with it. I never could figure out what the hell was going on, and people looked at me like I was some sort of freak when I brought it up! And ... I've been running a 7500RPM redline with the need to ride it occasionally for autocross!!!
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Originally Posted by Savington
(Post 700262)
Again, only affects VVT heads.
What do you suppose is happening in my case then? I keep having to install smaller and smaller shims until the cam wants to hit the edges of the bucket. It's always the worst on #1 followed by #3, and always only the intake side. The harmonic issue is the closest thing to an explanation that I've heard. :vash: |
Originally Posted by shlammed
(Post 700092)
Side question whil i have a thread started... do the VVT oil pump gears have the same issue as the earlier pumps which suggest using billet gears to avoid shattering at high power levels?
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Is a hone required if you are just replacing rods and rod bearings (reusing pistons and rings)?
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Originally Posted by Savington
(Post 700261)
AFAIK aftermarket valvetrain parts are not legal in CSP, so I don't think he tried anything because he couldn't.
I vote for absolutely minimal machining if you are pinched for cash. Hone for clearance on the pistons, polish the crank only if it needs it, make sure the pins fit properly, and I'd even vote for just a valve lap to confirm seat. Spend your money on getting a good tune. I spent too much on balancing, line hone, bore and hone with deck plate, valve job, et al, then the fucking asshole knocked the thrust bearing out of place during assembly and the whole thing got scrapped. |
Originally Posted by dgmorr
(Post 700285)
Is a hone required if you are just replacing rods and rod bearings (reusing pistons and rings)?
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Originally Posted by falcon
(Post 700282)
No
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Originally Posted by Savington
(Post 699931)
Lol @ you, actually. There is a confirmed intake camshaft harmonic that will destroy the #1 intake valve seats if you run the motor at 7500+ for any sustained period of time. There's a local CSP car that destroyed 4 heads last year due to excessive sustained RPM - they dropped the rev limiter down and stopped hammering the intake seats out of #1 immediately.
My limiter is set at 7400 for a reason. You must hone the motor, that's not optional. It is HIGHLY recommended that you bore the motor, unless you are having custom pistons specifically created to match your bore sizes with the proper wall clearances. Start with a running motor and nothing else is needed, IMO - neither of my built motors had any additional balancing done beyond matched pistons/rods. any chance you could have a brass valve seat or something like that machine fit into place that would resolve this issue? i know that they do that for better sealing, but being softer i dont know if it would just fuck up faster.... |
Originally Posted by falcon
(Post 700282)
No
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Originally Posted by dgmorr
(Post 700285)
Is a hone required if you are just replacing rods and rod bearings (reusing pistons and rings)?
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