It's a different world above 7500!!!!
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From: Walker County Alabama
It's a different world above 7500!!!! Spring surge..... that's what I've got. Intake valves bouncing on the seat when they close due to harmonics in the spring. This is the same valves and springs that are on the SAM 375 inch motor and it has no problems. The only difference in the motors is mine is a 6 liter block and 5 ci less. The problem didn't show up until I started turning the motor 8000 on the nitrous. It's not valve float. We'll see what's up in a few days.
Re: It's a different world above 7500!!!! Sounds like it's going to blow up and you should back it down 400 rpms. I don't think the stock pcm makes adjustments above 7200 I think it freezes and just does whatever it was doing at 7200.
I'm going to spray at TR Shootout and just take it up to 6600 on 28" slicks.
I'm going to spray at TR Shootout and just take it up to 6600 on 28" slicks.
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From: Walker County Alabama
Re: It's a different world above 7500!!!! </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Pro Stock John:
<strong>Sounds like it's going to blow up and you should back it down 400 rpms. I don't think the stock pcm makes adjustments above 7200 I think it freezes and just does whatever it was doing at 7200.
I'm going to spray at TR Shootout and just take it up to 6600 on 28" slicks.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">John if it blows up I've already got another one in the oven. Also the PCM adjust right up to 8000.
Fenris the springs are OK.... done did that....
<strong>Sounds like it's going to blow up and you should back it down 400 rpms. I don't think the stock pcm makes adjustments above 7200 I think it freezes and just does whatever it was doing at 7200.
I'm going to spray at TR Shootout and just take it up to 6600 on 28" slicks.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">John if it blows up I've already got another one in the oven. Also the PCM adjust right up to 8000.
Fenris the springs are OK.... done did that....
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Re: It's a different world above 7500!!!! Joe, how do you figure spring harmonics are causing seat bounce? Seat tension is what controls bounce, you might have proper open tension thats why you dont have valve float, but valve seat bounce is more likely from lack of seat tension. If im wrong im curious how you came up with this diagnosis?
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Re: It's a different world above 7500!!!! I was under the assumption that on nitrous you should shift at the same or lower RPM's since nitrous makes so much torque. If that is true. Then I would think you might be ok not spinning the motor so high.
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From: College Station, Tx
Re: It's a different world above 7500!!!! Can you loose any valvetrain weight (Ti retainers? Star shaped retainers (crower sells them for SBC - you could convert yours with a dremel - instead of a full circle they have "notches" cut in them so they kinda look like a starfish), etc.
If it's a harmonics issue then changing the weight of the springs mass will change the rpm at which you have the problem.
A different spring will also help if it's harmonics - doesn't even have to have more pressure - just a different construction/cross section, etc.
I agree with the above though - are you sure it's harmonics? It could simply bee not enough spring pressure, or a lobe profile problem?
I would tend to think that it's a lobe problem if it's really valve bounce - remember, while your cam lobe profile has a constant radial velocity/acceleration/jerk, etc. at any given point as your rpm increases so does the factor that translates this radial acceleration to linear (what the valve sees). A profile that's good at 6000 rpm could be to agressive at 7000 rpm - infact if it's near the edge at 6k it would have to be at 7k. To agressive means it is closing the valves to fast (setting them down to hard) and the spring is weakest at this point.
Chris
If it's a harmonics issue then changing the weight of the springs mass will change the rpm at which you have the problem.
A different spring will also help if it's harmonics - doesn't even have to have more pressure - just a different construction/cross section, etc.
I agree with the above though - are you sure it's harmonics? It could simply bee not enough spring pressure, or a lobe profile problem?
I would tend to think that it's a lobe problem if it's really valve bounce - remember, while your cam lobe profile has a constant radial velocity/acceleration/jerk, etc. at any given point as your rpm increases so does the factor that translates this radial acceleration to linear (what the valve sees). A profile that's good at 6000 rpm could be to agressive at 7000 rpm - infact if it's near the edge at 6k it would have to be at 7k. To agressive means it is closing the valves to fast (setting them down to hard) and the spring is weakest at this point.
Chris
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Re: It's a different world above 7500!!!! If I remember correctly, I think Joe runs a spring without a dampner. It's double, but without the dampner. He is changing that and installing a dampner.
Tim
Tim
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From: Walker County Alabama
Re: It's a different world above 7500!!!! LS1derful it is not valve float because the valves have not touched anything. You're right about seat tension that could be the problem. Again it's only the intakes.
Crash 02 with the gear I run it really don't matter because it's on 8000 in first gear before you can
shift it anyway.
Chris you could be right. The intake lobe profile is very agressive (254 @ .650) and the roller might have a problem following the lobe on the closing side. The heads are being worked on in Texas as we speak.... As soon as we get an answer I'll let you guys know what's going on.
Crash 02 with the gear I run it really don't matter because it's on 8000 in first gear before you can
shift it anyway.
Chris you could be right. The intake lobe profile is very agressive (254 @ .650) and the roller might have a problem following the lobe on the closing side. The heads are being worked on in Texas as we speak.... As soon as we get an answer I'll let you guys know what's going on.
Re: It's a different world above 7500!!!! Joe, this is a long shot (since you're not running stock rocker arms), but what does your rocker to retainer clearance look like? I had minimal clearance between the underside of my rocker arms and spring retainers and it was coming in contact at high rpms. Motor lost tons of power up high (just like valve float). Judson's guys clearanced the rockers and I've been able to peg the rev limiter with ease. Like I said, it's probably a long shot, but this problem absolutely kicked my ***! <img border="0" title="" alt="[Mad]" src="gr_images/icons/mad.gif" />
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
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From: Houston
Re: It's a different world above 7500!!!! Joe ours runs too 8000RPM with out anysurge...
But I don't belive our springs and the 375 is the same. we are running diffrent springs ours is the same as the 418.
hey remeber that set of heads I was showing you while you where down here?? 330CFM set!!
man it's making some killer power.
Hope you get that spring line out. 8000RPM is fun.
Brent
But I don't belive our springs and the 375 is the same. we are running diffrent springs ours is the same as the 418.
hey remeber that set of heads I was showing you while you where down here?? 330CFM set!!
man it's making some killer power.
Hope you get that spring line out. 8000RPM is fun.
Brent
Re: It's a different world above 7500!!!! Joe,
I agree that changing the mass of the valvetrain components will change the frequency of the harmonics (hopefully out of your range of use) You should try the retainer'lock combination I'm using... each retainer is 4gm lighter than an equivalent non-convolouted/drilled titanium retainer plus, they supposedly allow your springs to run cooler due to the added oiling...
Shane
I agree that changing the mass of the valvetrain components will change the frequency of the harmonics (hopefully out of your range of use) You should try the retainer'lock combination I'm using... each retainer is 4gm lighter than an equivalent non-convolouted/drilled titanium retainer plus, they supposedly allow your springs to run cooler due to the added oiling...
Shane
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Re: It's a different world above 7500!!!! </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by XtraCajunSS:
<strong>Joe,
I agree that changing the mass of the valvetrain components will change the frequency of the harmonics (hopefully out of your range of use) You should try the retainer'lock combination I'm using... each retainer is 4gm lighter than an equivalent non-convolouted/drilled titanium retainer plus, they supposedly allow your springs to run cooler due to the added oiling...
Shane</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I agree, that is what someone told me to.
<strong>Joe,
I agree that changing the mass of the valvetrain components will change the frequency of the harmonics (hopefully out of your range of use) You should try the retainer'lock combination I'm using... each retainer is 4gm lighter than an equivalent non-convolouted/drilled titanium retainer plus, they supposedly allow your springs to run cooler due to the added oiling...
Shane</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I agree, that is what someone told me to.
