I am going to put a vinci 210/218 .551/.551 in my truck and was looking at using the com 918 springs. My question is do I need new retainers for them or are the stock ones good enough? Also, do I need to change the pushrods too?

 

stock retainers will be fine if you don't go all out draging with the truck. most people usually upgrade the pushrods though. harden 7.4" pushrods (comp, thunder, manley)...

 

i went with the comp steel retainers with the 918s. not a requirement, but more of a peace of mind thing. i would suggest getting pushrods that are at least .025" longer. the base circle of this cam is .043" smaller than the stock cam. 1.507" vs 1.550". using the stock length pushrods will unload the lifter slightly making for a noisier top end. the less pre-load won't hurt anything just a little more noise.

 

I just put a Vinci 045 in my 5.3. I would suggest getting stock length pushrods.

This cam has a smaller base circle radius of .027

My stock pushrods all measure about 7.392, the comp 7.400 pushrods checked 7.408 So you gain .016 lifter preload with the pushrods. This will get you within .010 of factory preload.


I had some comp cams 7.425 pushrods from my Lingenfelter GT2-3 cam setup (.080 smaller base circle diameter or .040 smaller base circle radius) that I thought would be good for the Vinci cam but they would have given me more preload than factory. The comp 7.425 pushrods checked 7.442 (.050 longer than stock).

 

not meaning to hi-jack the thread, but wanted to clear up the pre-load issue.

ideally one would check pushrod length prior to installation to determine the proper pushrod to use.

with that being said, using a pushrod on a cam with a reduced base circle radius will net you a reduction in lifter pre-load by amount equal to original base circle radius (-) reduced base circle radius.

depending on who you ask the ideal pre-load is anywhere from .020-.100. VHP recommends a pre-load of .060-.100" when using the crane adjustable rockers.

so if using the stock pushrods with an approx length of 7.4" on a cam that has a .043" smaller base circle radius, assuming an approximate factory lifter pre-load of .060", will net you a less than desireable pre-load approx. .017" which could contribute to a noisier than normal valvetrain. to compensate for this loss of pre-load using non-adjustable rocker arms a longer pushrod is required. in this case a .043" longer rod. but since they don't generally make a .043" longer rod, the more common approach is to use the 7.450" pushrod, which will net a .007" increase in lifter pre-load well within the ideal lifter pre-load range.

 

I'm not so sure you cleared up pre-load issue.

Your cam has .043 smaller base circle DIAMETER which would be a .0215 smaller base circle RADIUS and resulting .0215 reduction of preload.

 

A quote from Tin Indian on tech back in 2003:


The aftermarket cams being installed today will usually have a smaller base circle than the stock LS1 cam they are replacing.

Base Circle is actually the distance accross the cam's lobe. This is 90 degrees from the top of the cam's lobe at the point of highest lift.

You can easily measure this distance with a micrometer. Measure across the cam's lobe (the lobe's smallest distance across). You will find that it is 1.552” That is actually the cams “base circle”. You will need to cut this distance in half in order to get the cams "centerline to lobe heal" distance. The stock LS1 cam has a .776" centerline to lobe heal distance (19.7mm).

This centerline to lobe heal distance is what is important to you in determining lifter preload.

By the way, someone posted a while back that the TR-224 actually was measured to have a .030" smaller centerline to lobe heal distance than the stock cam.

If your aftermarket cam has lets say a .746" centerline to lobe heal distance, that would mean that it is .030" (30 thousands inch) smaller than stock. Remember, the stock cam was .776"

To be very accurate, you would then need a pushrod that is .030" longer than stock to achieve the same spec lifter preload as you had with your stock cam.

These aftermarket pushrods come in .050" length increments, so in this case, a longer 7.45" rod would get you closer to your factory spec lifter preload than using the stock 7.40" pushrod.

Remember, hydraulic lifters, due to there design have a + - preload variance that the lifter can operate within. It don't need to be exact. Just get it as close as possible with the various pushrods that are available (in .050" increments)

Be advised, milling the heads will change all this and require shorter pushrods equal to how much is milled off the heads.


So, to re-iterate all this:

1. If your cam has a .030" smaller centerline to lobe heal distance than stock, you would need a .030" [longer] rod.

2. If you just milled the heads .030", you would need a .030" [shorter] rod.

3. Combine the two, and your stock 7.40" pushrod would be perfect … It then becomes “tit for tat”

Hope this info helps a little.

Ron,

 

So which pushrod should I go with? 7.4, 7.425, or 7.450

 

Get Thunders rods. They will work for what you need.

7.430" is ideal for a pushrod with an aftermarket cam.

 

Go with stock length 7.400

My comp cams pushrods #7955-16 were about .016 longer than my factory pushrods.

I'm running a Vinci 045 cam that checked about .025 smaller base circle radius. The 7.400 got me w/in .010 which was good enough for me.