Jon@Texas-Speed

iTrader: (18)

That's fine if he recommended that. We sell and install a ton of them and there seems to be a little variance in the cam cores recently. We installed the exact same cam in a car last week with stock heads that took a 7.350" pushrod and setup with .065" preload. That's why we stress so much to measure each setup!

Jon

Paul 75 L82

iTrader: (1)

I used the 7.4" rods in mine with great results. No noise and great power.

Patrick G

iTrader: (14)

Guys, it's pretty simple math. The stock LS1 cam has a base circle radius of .7755" and runs a 7.38" pushrod. This gives a lifter preload that offers low noise and good long term performance. When running a stock LS1/LS7 lifter, I prefer to run a preload that's the same as factory.

A 228R cam has a base circle radius of .7265". That means the 228R cam has a .049" shorter base circle radius than the stock cam. If you are trying to maintain stock lifter preload with the 228R cam, you will need to run a .049" longer pushrod than stock .7755"-.7265"). Adding .049" to the stock 7.38" pushrod length gives you a 7.429" pushrod. The 7.425" pushrod comes closest to maintaining factory preload with the 228R cam. If you run a 7.400" pushrod, it will work, but you will be running .029" shallower preload than stock. If your LS1 is at the shallower end of lifter preload tolerance, you may get some lifter noise with a 7.400" pushrod. With the 7.425" pushrod, you will have a better chance of having a quiet setup because the lifter is more in the middle of it's plunger travel (like the stock LS1).

Jon@Texas-Speed

iTrader: (18)

I understand the math. But what I'm trying to to tell you guys is we have seen some variance in base circles on the cams we have installed lately. Joseph knows a thing or two about these engines. If he comes to me telling me there is something different in the cams and the last couple he installed were different, I am inclined to believe him and I try to pass that info. along here. All I'm saying is to measure the length. At the end of the day, it's your car and you can do whatever you please. Just trying to give you a heads on something to look out for! Good luck with it!

Jon

z99ls1

iTrader: (12)

So the cams are that much out of spec?

01ssreda4

iTrader: (96)

Measure to be sure....and read and understand Pat Gs post because its spot on.

bonethugluv

iTrader: (10)

Pat sounds like he knows his stuff very well. I used a 7.4 in my 228r for a couple yrs and car was always quiet as stock too. but like they say, measure to be sure.

01ssreda4

iTrader: (96)

I know Pat G is correct because i measured my stock cam and my TR224 that went in years ago and did the math to compare. I ran 7.425 pushrods with that and it was silent. Aftermarket cams are cut on a smaller base circle.

DUSTYWS6

I followed Pat G's logic when I put my 228R in. I got a digital caliper and measured my stock cam base circle and 228R base circle and determined that I needed 7.425" pushrods. I was pretty impressed with GM's quality control on the base circles, each one was identical.

z99ls1

iTrader: (12)

So pretty much if I measure my 228r and get .7265", than I know I need the 7.425 pr's

z99ls1

iTrader: (12)

Sorry to bring up an old thread, but I would like to pick my pushrods based on how pat g said to do it above and measure my stock cam and aftermarket cam lobes to see what I need. So how do you measure the base cicle of a cam lobe?

ZeeOSix

Measure across the top peak of a lobe to the base circle, and then subtract the lift spec of that cam lobe (depends if you measured an intake or exhaust lobe) to give you the base circle diameter. Then divide that diameter by 2 to get the base circle radius.

Do this measurement on a couple of lobes and see if you get the same answer. You should, as the base circle radius should be the same for every lobe. But be sure to subtract the lift spec for the intake lobe if you're measuring an intake lobe because intake and exhaust lobes will have different lifts.

z99ls1

iTrader: (12)

Ok so if you have to subtract the lift spec from the cam and you have an intake lift of .598 and an exhaust lift of .650 than technicly wouldn't you need a different pushrod for the intake and exhaust sides?

ZeeOSix

No ... because when you measure lobe to base on an exhaust lobe it will be a larger number because the lift is larger on the exhaust lobe.

So when you subtract 0.650 from an exhaust lobe measurement it should be the same as when you subtract 0.598 from what you measure when you go across an intake lobe. The cam's base circle is the same on all lobes, and all 16 pushrods will therefore be exactly the same length.

z99ls1

iTrader: (12)

Ahh alright. Well if we could get some accurate base circle numbers from our cam supliers, getting pushrods would be a cake walk. I am just about thinking of calling up tsp or thunder racing (wichever will do this for me) and asking them to measure the base circles of some of these cams and see what there getting.

ZeeOSix

True on that.

Better yet ... if you know who actually designs & makes the cam, then give them a call, as they should know the exact base circle and the IN/EX lift dimensions of all their cams.

z99ls1

iTrader: (12)

I think me and you are on to something here lol

01ssreda4

iTrader: (96)

Or you could measure where there is no lobe, that's what I did.

z99ls1

iTrader: (12)

Like from side to side on the cam lobe? Im not sure if that would be accurate or not...

ZeeOSix

As you can see in this photo, the base circle at the lobes is not the same as the base circle between the lobes.