what is the stock preload?
Originally Posted by cantdrv65
All lifters pump up at higher rpms....A rhoads lifter simply bleeds off more oil at low rpms those reducing valve lift/duration. If your valves float it is because you do not have enough spring tension for the valve/spring assembly mass. Assuming you have some, preload does not cause valve float. This is why you can set preload to a variety of values and never see a difference in power.
Thats my take on it anyway.
Thats my take on it anyway.
I will however say that many manufacturers do indeed suggest the shorter than stock preload claiming it battles pump up at high rpms. I dont see how its possible except that maybe the plunger spring will apply less pressure. All this assumes that youre setup is just barely able to keep things under control... running it right on the edge.Also, i want to state that while all hyd lifters do have a tendency to pump up, wether or not it happend depends very much on your setup, otherwise ever dyno graph would show a drop off in power.
Thread Starter
Joined: Mar 2003
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From: North Carolina
Originally Posted by cantdrv65
This is why you can set preload to a variety of values and never see a difference in power.
i just dynoed after a fast intake and pushrods, according to the airflow rate increase from the fast intake and then the pushrods (which was noticeable after the pushrods, 12 g/sec increase in airflow WOT, 15 with the fast). I gained 25 rwhp which makes about 11 of it from pushrods. the valve was opening sooner, and you can see that as i put the new pushrods on the car.
Originally Posted by WS6FirebirdTA00
complete BS
i just dynoed after a fast intake and pushrods, according to the airflow rate increase from the fast intake and then the pushrods (which was noticeable after the pushrods, 12 g/sec increase in airflow WOT, 15 with the fast). I gained 25 rwhp which makes about 11 of it from pushrods. the valve was opening sooner, and you can see that as i put the new pushrods on the car.
i just dynoed after a fast intake and pushrods, according to the airflow rate increase from the fast intake and then the pushrods (which was noticeable after the pushrods, 12 g/sec increase in airflow WOT, 15 with the fast). I gained 25 rwhp which makes about 11 of it from pushrods. the valve was opening sooner, and you can see that as i put the new pushrods on the car.
Of course that doesnt mean you didnt see any, you could have really been on the ragged edge. I just doubt it myself.
Ive actually been considering trying a slightly longer pushrod myself, then dynoing right after with that being the only change. It would be worth it to me if it just quiets the valvetrain a little.
Last edited by cantdrv65; Mar 26, 2006 at 04:42 AM.
Originally Posted by Viper
"This is why you can set preload to a variety of values and never see a difference in power."
The internet is great for opinions. Most opinions I've read on this site say it CAN affect power.
Not knocking what your saying, just pointing out the opinion is on both sides of the fence.
But if too much preload can hang valves open ( to the point the car won't start and it backfires through the intake ) then wouldn't it make sense that a little less than that ( enough for the car to run ) would be down on power too?
The internet is great for opinions. Most opinions I've read on this site say it CAN affect power.
Not knocking what your saying, just pointing out the opinion is on both sides of the fence.
But if too much preload can hang valves open ( to the point the car won't start and it backfires through the intake ) then wouldn't it make sense that a little less than that ( enough for the car to run ) would be down on power too?
Im going to add one of those disclaimers to my sig. I recall the post Tony has about his comp lifters and preload, so I understand why you would think that. And you're right, he wasn't at the edge ( top or bottom ). No worries, we're all learning.
Originally Posted by cantdrv65
Yes I totally agree with that... I wasnt referring to extremes either TOO loose or TOO tight. But hey Im full of **** anyway. Im going to add one of those disclaimers to my sig.
Im going to add one of those disclaimers to my sig. Thread Starter
Joined: Mar 2003
Posts: 8,319
Likes: 1
From: North Carolina
actually Tony is the one that told me about this. I am on stock lifters and if his test was with comps then I think it was just because they dont require as much preload as the stockers do.
I've been following this thread because I'm going to change to longer PR's this week also. Much of the confusion on the actual length of various PR's come from the different ways different manufacturers measure their PR's and how the oil hole comes into play. I don't have a 8" caliper to measure the length I but here's what I did to measure the difference between stock, Comp 7.4's and comp 7.425's.
I put a piece of glass on the bench. Setup my dial indicater and put an old rocker arm on top of the PR's so that the dial indicater plunger didn't fall into the different size oil holes and set the other end on the flat surface of the glass. Measured the stock one and made that a zero point. Measured the comp 7.4...was .019 longer than stock. Measured the comp 7.425 which was .026 longer than the 7.4. Total difference in length from stock to a comp 7.425 was .045.
All this proves a comp 7.425 PR on a cam only swap (stock heads,stock head gasket) to the common 1.45x base circle cams is within ~.005 - .006 to having the stock preload assuming stock base circles are 1.553.
Something I found interesting is that when I adjusted the PR checker to what should be 7.40 it was .011 shorter than the comp 7.40 PR. One turn did equal .050 though.
I put a piece of glass on the bench. Setup my dial indicater and put an old rocker arm on top of the PR's so that the dial indicater plunger didn't fall into the different size oil holes and set the other end on the flat surface of the glass. Measured the stock one and made that a zero point. Measured the comp 7.4...was .019 longer than stock. Measured the comp 7.425 which was .026 longer than the 7.4. Total difference in length from stock to a comp 7.425 was .045.
All this proves a comp 7.425 PR on a cam only swap (stock heads,stock head gasket) to the common 1.45x base circle cams is within ~.005 - .006 to having the stock preload assuming stock base circles are 1.553.
Something I found interesting is that when I adjusted the PR checker to what should be 7.40 it was .011 shorter than the comp 7.40 PR. One turn did equal .050 though.
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TECH Senior Member
Joined: Mar 2004
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From: BFE
Originally Posted by AFTICA
I've been following this thread because I'm going to change to longer PR's this week also. Much of the confusion on the actual length of various PR's come from the different ways different manufacturers measure their PR's and how the oil hole comes into play. I don't have a 8" caliper to measure the length I but here's what I did to measure the difference between stock, Comp 7.4's and comp 7.425's.
I put a piece of glass on the bench. Setup my dial indicater and put an old rocker arm on top of the PR's so that the dial indicater plunger didn't fall into the different size oil holes and set the other end on the flat surface of the glass. Measured the stock one and made that a zero point. Measured the comp 7.4...was .019 longer than stock. Measured the comp 7.425 which was .026 longer than the 7.4. Total difference in length from stock to a comp 7.425 was .045.
All this proves a comp 7.425 PR on a cam only swap (stock heads,stock head gasket) to the common 1.45x base circle cams is within ~.005 - .006 to having the stock preload assuming stock base circles are 1.553.
Something I found interesting is that when I adjusted the PR checker to what should be 7.40 it was .011 shorter than the comp 7.40 PR. One turn did equal .050 though.
I put a piece of glass on the bench. Setup my dial indicater and put an old rocker arm on top of the PR's so that the dial indicater plunger didn't fall into the different size oil holes and set the other end on the flat surface of the glass. Measured the stock one and made that a zero point. Measured the comp 7.4...was .019 longer than stock. Measured the comp 7.425 which was .026 longer than the 7.4. Total difference in length from stock to a comp 7.425 was .045.
All this proves a comp 7.425 PR on a cam only swap (stock heads,stock head gasket) to the common 1.45x base circle cams is within ~.005 - .006 to having the stock preload assuming stock base circles are 1.553.
Something I found interesting is that when I adjusted the PR checker to what should be 7.40 it was .011 shorter than the comp 7.40 PR. One turn did equal .050 though.
Remember, pushrods are measured by Gauge Length, not OAL so you can't compare our measured length to that stamped on the pushrod. You must add the difference between the two measurements. Also, not sure if all manufacturers use the same gauge length either, Comp uses 0.140 diameter on the ball.
Last edited by vettenuts; Apr 5, 2006 at 05:32 AM.
Originally Posted by vettenuts
Remember, Comp measures their pushrod length differently than say Crane or Manley. Comp uses Gauge Length, Crane and Manley use OAL so you can't compare Comp lengths to the others as their method of measurement is different.
TECH Senior Member
Joined: Mar 2004
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From: BFE
Originally Posted by vettenuts
Remember, Comp measures their pushrod length differently than say Crane or Manley. Comp uses Gauge Length, Crane and Manley use OAL so you can't compare Comp lengths to the others as their method of measurement is different.
