What pushrod size would be used for a TR 224/224 112LSA cam with LS1 heads (241 casting) that have been milled .040? I know the TR cam has a smaller base circle, so I was wondering if stock length pushrods would be OK?

 

Truthfully u have to check it but I would guess a 7.35 might be the one...

 

Well.. TR 224 cam is .030 smaller base circle I believe, so technically you'd need a 7.430" push rod, but milling .040 then you'd technically need a 7.390" push rod so you should be fine w/the 7.400" stockers...

hmmm... was just rethinking... I think my above calcs are flawed... if the base circle is .030 smaller, then you would only need a .015" longer pushrod right? In which case 7.415 - .040 = 7.375 in which case I believe the stockers would still be ok...

 

I'd still check it...

 

I think 7.4 would be ok. I would check with Thunder racing. Let me know what you find out because thats the exact cam I'm going to use with my stock heads..

 

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 base circle distance with a micrometer. Measure across the cam's lobe (the lobe's smallest distance across). You will find that it is 1.552” on a stock LS1 cam. 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.

A TR-220 cam has a 1.502” across the lobe base circle. Cutting this number also in half will equal a 0.751” centerline to heel distance. This is a 025" smaller centerline to lobe heal distance than the stock cam. (Your TR224 may be around .027" smaller)

To be very accurate, you would then need a pushrod that is .025" 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 stock 7.40” pushrod would be ok.

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 (see below).



So, to re-iterate all this:

1. If your cam has a .025" smaller centerline to lobe heal distance than stock, you would need a .025" [longer] rod.

2. If you just milled the heads .025", you would need a .025" [shorter] rod.

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

Ron,

 

One other thing. We measured the Thunder Racing 7.40" rods. They actually measured .015" longer than stock. If you use these, you can apply that number in order to figure lifter preload.

IE:

TR224 cam = .027" smaller cam centerline to lobe heal distance. Needs a .027" longer rod

Heads milled .020" Needs a .020" shorter rod

Combine these numbers, and you will have .007" [less] preload than you had before with stock GM rods.


Now install Thunder 7.50" rods = .015" longer than stock. Now your lifter preload will be .008" (8 thousands) more than it was when stock.

Again, .008" is nothing. No problems at all...

See how this all works?

Ron,

 

From what I've seen I would say 7.35's for your setup.I run LS6's milled .030 and found 7.40's were .010 preload.So I went 7.35's and had .005 preload.
Also seen a 01 LS1 with .030 shaved that needed 7.35's.These cars run a TR224.
I would rather have .020-.050 preload than .080 anyday.Less chance of floating the valves.