power dies at 6400rpm.
10-08-2010, 09:37 PM
#21
Could be your 231/239 cam (that's what I saw in your sig) just isn't up t it and or their lobes are just too aggressive to continue to make more power up top. The more aggressive the lobes the harder it is to control the valves up top. Comp cautions that either better springs are called for or the rpms lowered when running an aggressive lobed cam.
AirFlow Research has written about this. GMHIGHTECHPERFORMANCE magazine's cylinder head shoot-out showed much the same thing at about the same RPM 6200-6400 (both are on their sites). GMHTP was running a 230/236 HR, close to what you're running.
Popular HotRodding had the same experience at about the same rpm point. I'll try to find the link to see if they ever solved it - I usually save links to things like this.
Could be cam, springs, valve train dynamics, harmonics setting in, ignition or something else entirely. I still feel you're expecting too much from your combination. Just getting the engine to rev higher doesn't mean the power hasn't taken a nose dive up there.
I'm sure the cam card shows the tested rpm power range of your cam. What does it say?
Taking a HR above what you're now seeing isn't the norm. Heavy lifters, more aggressive lobe ramps, limited spring pressures, pushrods, etc., all conspire to work against rpms higher than what you're now seeing. Especially rpms where the engine is still making more power.
One series of dyno tests I read about in one of the better known mags said something to the effect "It was like the engine hit a brick wall. Repeated tests and it wouldn't even go 25 rpm higher".
So my thinking is that if you're really determined to make more power at rpms higher than you're now seeing, you're looking at changing some valve train parts. If it were me, I'd immediately go with a solid roller. Starting in the mid 240 @ .050 range with the required springs, etc.
Jake
AirFlow Research has written about this. GMHIGHTECHPERFORMANCE magazine's cylinder head shoot-out showed much the same thing at about the same RPM 6200-6400 (both are on their sites). GMHTP was running a 230/236 HR, close to what you're running.
Popular HotRodding had the same experience at about the same rpm point. I'll try to find the link to see if they ever solved it - I usually save links to things like this.
Could be cam, springs, valve train dynamics, harmonics setting in, ignition or something else entirely. I still feel you're expecting too much from your combination. Just getting the engine to rev higher doesn't mean the power hasn't taken a nose dive up there.
I'm sure the cam card shows the tested rpm power range of your cam. What does it say?
Taking a HR above what you're now seeing isn't the norm. Heavy lifters, more aggressive lobe ramps, limited spring pressures, pushrods, etc., all conspire to work against rpms higher than what you're now seeing. Especially rpms where the engine is still making more power.
One series of dyno tests I read about in one of the better known mags said something to the effect "It was like the engine hit a brick wall. Repeated tests and it wouldn't even go 25 rpm higher".
So my thinking is that if you're really determined to make more power at rpms higher than you're now seeing, you're looking at changing some valve train parts. If it were me, I'd immediately go with a solid roller. Starting in the mid 240 @ .050 range with the required springs, etc.
Jake
10-08-2010, 10:36 PM
#22
Magazines write articles based on cookie cutter crap from companies that put money into advertising instead of R&D.
I have a valvetrain with beehives that is good to 7000rpms and with GM lifters to boot. The rules from a couple decades ago no longer apply.
I have a valvetrain with beehives that is good to 7000rpms and with GM lifters to boot. The rules from a couple decades ago no longer apply.
10-09-2010, 11:02 PM
#23
I have admitted and stated that the power goals are not my first worry at the moment, but the fact that a high revving camshaft dies at 6400 IS.
Lastly, your comment on going solid roller is, no offense, ridiculous. I have 2500 miles on my current setup that I just spent ~$2500 doing less then 6 months ago. Going solid roller before honestly chasing the problem around anymore is just stupid. A solid roller setup, done right (which is the only way I'd do it) would cost another $2500-3000. I don't have that kind of money.
I am going to look into swapping springs, perhaps that is an existing issue. After that, maybe it could be opti. I know I'd rather do an LS1 PCM swap, rather then go solid roller...
10-10-2010, 07:36 AM
#24
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Regardless of what lift the springs could handle it would probably be a good idea to either have those springs pressure tested or get new/different springs. Not sure if these are suggested by the cam manufacturer, if not then call them and ask what spring would work well that would fit in your spring pockets.
10-13-2010, 12:24 AM
#28
No offense but that its a garbage valve train and I suspect it could use some attention to detail in the setup as well. Get some good springs and rockers on there and make sure its set up well.
I vote for 7/16 ultra pro mags and patriot extremes...
I vote for 7/16 ultra pro mags and patriot extremes...
10-13-2010, 01:13 AM
#29
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it could just be maybe too much preload??? Just throwing out an idea for an easy fix... I probably run more than necessary preload, but I'm more worried about my rockers coming loose on my SA setup so I go 3/4, but maybe you just try 1/4 or 1/8 if you're revving that high with a NSA setup. Maybe the lifters are getting overly pumped?
10-13-2010, 08:50 AM
#34
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The only other thing I could think of is that maybe whoever you bought your cam from sold you a smaller cam than what it really was on accident or something. The only way to know for sure would be to take it out and measure it though.
10-13-2010, 12:40 PM
#35
That's kind of what I was thinking too. When you say hit a wall, does it just simply not rev higher than 6400 period? Or do you just mean, it's not continuing to make power over 6400rpm.
The only other thing I could think of is that maybe whoever you bought your cam from sold you a smaller cam than what it really was on accident or something. The only way to know for sure would be to take it out and measure it though.
The only other thing I could think of is that maybe whoever you bought your cam from sold you a smaller cam than what it really was on accident or something. The only way to know for sure would be to take it out and measure it though.
I bought the camshaft direct from Summit. Brand new Lunati, it's not the cam.
Also, I'm assuming when you say preload, you mean on the rocker arms? If so they're at 1/8 turn.
10-13-2010, 05:53 PM
#36
918s are a decent spring, they are however often missused. Cam intensity has a LOT to do with necessary spring specs not just lift.
Scorpion is fine.
People OFTEN mess up preload by screwing up "zero lash" How did you find "Zero Lash"? If you "spun the pushrod" you probably got it way too tight.
Scorpion is fine.
People OFTEN mess up preload by screwing up "zero lash" How did you find "Zero Lash"? If you "spun the pushrod" you probably got it way too tight.
10-13-2010, 06:00 PM
#37
918s are a decent spring, they are however often missused. Cam intensity has a LOT to do with necessary spring specs not just lift.
Scorpion is fine.
People OFTEN mess up preload by screwing up "zero lash" How did you find "Zero Lash"? If you "spun the pushrod" you probably got it way too tight.
Scorpion is fine.
People OFTEN mess up preload by screwing up "zero lash" How did you find "Zero Lash"? If you "spun the pushrod" you probably got it way too tight.
10-13-2010, 06:09 PM
#38
I had the same issue on the dyno but mine hit a wall at 6k @ 390hp. Not too sure if the swap to Patriot golds got me the 10 hp but my wall wasn't at 6k anymore, honestly I don't go higher 6200 on the stock bottom end. This was on hooker shorties no LTs. I won't waste my coin on dyno now, just getting my 383 ready for next year.
10-13-2010, 06:35 PM
#40
Problem is there is more poor or outright bad information out there than good. That leads people who try and do the research to do things wrong despite attempts to learn how. So a lot of the clueless guys probably made an honest effort they just made the mistake of listening to the 8 dimwits instead of the two knowledgable guys.
Sometimes it pays to listen to the minority voice over the popular one.
Sometimes it pays to listen to the minority voice over the popular one.