Long Pushrod Length, preload ?
02-02-2010, 08:42 AM
#21
Great topic.
I am all for overkill, especially in the area of valvetrain, but just not convinced even at a 7.500" length that a 3/8 push rod is needed in these hydraulic cam engines.
I am wondering if at only 450# of open spring pressure there is any 'measureable' advantage, if any at all, of a pushrod bigger than 5/16 .083" or even .110" wall. I can understand the use of a larger diameter in a SR application, but I am not really convinced they are needed, or are the culprit to valve spring and lifter failure issues. I tend to believe the lifter issues some have are more related to improper pre-load from the get go, along with excess RPM. And valve springs, that is more related to some of these crazy fast lobes that people try to street drive and get thousands of miles out of.
I am always willing to learn something NEW, but my past experiences with SBC's, SBF's, and small block Chryslers tell me differently. I've run much more than a measely 450-475# OPEN pressure (common LS upgraded spring) on a 5/16" diameter push rod with no valvetrain instability at longer lengths than 7.500". A stock SBC length is 7.796". Have done many late model dirt SBC's with a 5/16 push rod that ran 5000-7500 RPM all season with smaller SR's running 240# on the seat and 650# plus open pressures showing no signs of deflection. Valve springs still tested good at the end of the year, keepers looked good, lifter rollers were good, etc. Again, I think in many cases it is setting up the rocker geometry properly to avoid some of these mysterious valvetrain failures.
I am aware of all the spintron testing that gets done too, and I will say a bigger pushrod won't hurt a thing, but to say it is needed in these street LS engines?? Although, I guess with some of the lobes out there today getting a little crazy, maybe?? Depends on your definition of a street cam I suppose.
As a side note I do know the TFS heads will accomodate a large push rod.
Have you LS engine builders really seen this problem on XE, XER lobe style street hydraulic rollers?
I am all for overkill, especially in the area of valvetrain, but just not convinced even at a 7.500" length that a 3/8 push rod is needed in these hydraulic cam engines.
I am wondering if at only 450# of open spring pressure there is any 'measureable' advantage, if any at all, of a pushrod bigger than 5/16 .083" or even .110" wall. I can understand the use of a larger diameter in a SR application, but I am not really convinced they are needed, or are the culprit to valve spring and lifter failure issues. I tend to believe the lifter issues some have are more related to improper pre-load from the get go, along with excess RPM. And valve springs, that is more related to some of these crazy fast lobes that people try to street drive and get thousands of miles out of.
I am always willing to learn something NEW, but my past experiences with SBC's, SBF's, and small block Chryslers tell me differently. I've run much more than a measely 450-475# OPEN pressure (common LS upgraded spring) on a 5/16" diameter push rod with no valvetrain instability at longer lengths than 7.500". A stock SBC length is 7.796". Have done many late model dirt SBC's with a 5/16 push rod that ran 5000-7500 RPM all season with smaller SR's running 240# on the seat and 650# plus open pressures showing no signs of deflection. Valve springs still tested good at the end of the year, keepers looked good, lifter rollers were good, etc. Again, I think in many cases it is setting up the rocker geometry properly to avoid some of these mysterious valvetrain failures.
I am aware of all the spintron testing that gets done too, and I will say a bigger pushrod won't hurt a thing, but to say it is needed in these street LS engines?? Although, I guess with some of the lobes out there today getting a little crazy, maybe?? Depends on your definition of a street cam I suppose.
As a side note I do know the TFS heads will accomodate a large push rod.
Have you LS engine builders really seen this problem on XE, XER lobe style street hydraulic rollers?
02-02-2010, 11:14 AM
#22
FormerVendor
iTrader: (2)
Join Date: Dec 2001
Location: Baton Rouge, LA, USA
Posts: 1,954
Likes: 0
Received 3 Likes
on
3 Posts
I agree, in many cases there is no need for larger diameter pushrods. In this case, the OP has a very aggressive camshaft with large diameter intake valves and fairly heavy rocker, he and I both felt the 11/32" .120 wall pushrods would definitely not hurt and are cheap insurance. The problem is, most new cam profiles these days are not XE or XE-R. In many cases, we are using spring pressures much greater than you cite in your post and I have seen issues both on the dyno and at the track. My point is, if you can overkill this one component slightly, its one less thing to worry about if or when you do have problems.
I figure I see 2 to 3 threads a day on here with issues regarding valve bounce. Most of the time, I can see something obvious in their setup such as improper rocker arm choice or ratio for a given lobe or engine family. Sometimes, the issues are not so easily solved. We have actually put together a kit which allows the use of stock rockers with TFS or ETP heads. It includes 3/8" pushrods. GM uses 3/8" dia 7.8" pushrods in the LS7. Many "street" builds these days would have been considered aggressive race engines 5 years ago. If there's one thing I've learned over the years (the very hardest way, BTW) is that it is MUCH harder to build a high horsepower street engine and have it live through multitudes of driving situations for many years than it is to build a pure race engine to operate in a very specific RPM range for a specific period of time.
Thanks,
Shane
I figure I see 2 to 3 threads a day on here with issues regarding valve bounce. Most of the time, I can see something obvious in their setup such as improper rocker arm choice or ratio for a given lobe or engine family. Sometimes, the issues are not so easily solved. We have actually put together a kit which allows the use of stock rockers with TFS or ETP heads. It includes 3/8" pushrods. GM uses 3/8" dia 7.8" pushrods in the LS7. Many "street" builds these days would have been considered aggressive race engines 5 years ago. If there's one thing I've learned over the years (the very hardest way, BTW) is that it is MUCH harder to build a high horsepower street engine and have it live through multitudes of driving situations for many years than it is to build a pure race engine to operate in a very specific RPM range for a specific period of time.
Thanks,
Shane
02-02-2010, 12:24 PM
#23
I agree, in many cases there is no need for larger diameter pushrods. In this case, the OP has a very aggressive camshaft with large diameter intake valves and fairly heavy rocker, he and I both felt the 11/32" .120 wall pushrods would definitely not hurt and are cheap insurance. The problem is, most new cam profiles these days are not XE or XE-R. In many cases, we are using spring pressures much greater than you cite in your post and I have seen issues both on the dyno and at the track. My point is, if you can overkill this one component slightly, its one less thing to worry about if or when you do have problems.
I figure I see 2 to 3 threads a day on here with issues regarding valve bounce. Most of the time, I can see something obvious in their setup such as improper rocker arm choice or ratio for a given lobe or engine family. Sometimes, the issues are not so easily solved. We have actually put together a kit which allows the use of stock rockers with TFS or ETP heads. It includes 3/8" pushrods. GM uses 3/8" dia 7.8" pushrods in the LS7. Many "street" builds these days would have been considered aggressive race engines 5 years ago. If there's one thing I've learned over the years (the very hardest way, BTW) is that it is MUCH harder to build a high horsepower street engine and have it live through multitudes of driving situations for many years than it is to build a pure race engine to operate in a very specific RPM range for a specific period of time.
Thanks,
Shane
I figure I see 2 to 3 threads a day on here with issues regarding valve bounce. Most of the time, I can see something obvious in their setup such as improper rocker arm choice or ratio for a given lobe or engine family. Sometimes, the issues are not so easily solved. We have actually put together a kit which allows the use of stock rockers with TFS or ETP heads. It includes 3/8" pushrods. GM uses 3/8" dia 7.8" pushrods in the LS7. Many "street" builds these days would have been considered aggressive race engines 5 years ago. If there's one thing I've learned over the years (the very hardest way, BTW) is that it is MUCH harder to build a high horsepower street engine and have it live through multitudes of driving situations for many years than it is to build a pure race engine to operate in a very specific RPM range for a specific period of time.
Thanks,
Shane
That is spot on! Seems today's street engines are very aggressive, but they aren't really street engines, are they? lol I suppose we can pretend they are.
So I would agree, overkill is the best policy in these instances.
I get soaked into that argument all time.
BTW, I didn't know the LS7 had 3/8" PR's, never been in one. It is too rich for everyone's blood I know.
I really like that signature you have....that could be a full time job on this forum.
... I'm sure NOT in this business for the money!!!
