superchargedgp

iTrader: (9)

i currently have 224/228 112lsa cam with .534 intake .537 exhaust
avd dur. 277/ 281

will yellow LS6 LS2 spring be enough for it

or should i replace them with comp 918

thanks!

PREDATOR-Z

THey have a rate variance of 53 so mildly agressive.
The LS6 springs could be used if shimmed, but that reduces its lifespan.
Personaly, I would opt for PAC springs.

Sharpe

iTrader: (7)

What is rate variance, how do you determine it, and what importance does it play, if you don't mind me asking?

PREDATOR-Z

it is the variance between .006 lift and .050 lift. That value is an indication of lobe rate.
The lower it is, the more agressive the lobe.
XE-R are 49
The ones above could be XE lobes.

Sharpe

iTrader: (7)

I'm sorry, but I'm sleepy as hell winding down ready for bed.

The variance of what between .006 lift and .050 lift? What numbers in his above example are you using?

The rest my sleepy brain understood, and that's some cool knowledge! Thanks!

superchargedgp

iTrader: (9)

ok which model pac springs,, they are going on bone stock 241 heads

the cam is comp cams ls1 xr277hr-12


thanks!

SweetS10V8

iTrader: (4)

Im running the 918s myself and have ran them on many many engines. There isnt any reason not to run the new silver 918s in this application.

I also noticed that Comp released its lightweight tool steel reatainers for the 26918s. So I ordered a set of those too. #1772-16. Titanium cant be any lighter than these are!

superchargedgp

iTrader: (9)

so 918's would be more than adequate to use?

SweetS10V8

iTrader: (4)

Its honestly whichever you prefer. They will both work just fine, I just prefer the 26918s. Those are the tool steel retainers too.

PREDATOR-Z

PAC used to suppliy and make the 918s. Nowadays that has changed. I'm just more faithful to PAC.
Pac 1518 are the ones

PREDATOR-Z

Durations at said lifts

above:
277-224=53
281-228=53

superchargedgp

iTrader: (9)

whats the difference between 1518 and 1218

PREDATOR-Z

PAC 1218
Beehive LS1 Spring
OD: 1.290"
130 lbs @ 1.800"
318 lbs @ 1.200"
Lift: 0.600"

PAC 1518
Premium Nitrided Beehive LS1 Spring
OD: 1.290"
130 lbs @ 1.800"
337 lbs @ 1.150"
Lift: 0.650"

Mainly the 1518 is stronger, has more seat pressure and can handle more lift.

Both will work in your setup, I just prefer 518s

superchargedgp

iTrader: (9)

i'm not planning on changing the cam and if that happens i will get heads also, so PAC 1218 should be safe and reliable springs for that cam
thanks

PREDATOR-Z

Just check you install height on all valves and make sure they are correct.

01ssreda4

iTrader: (96)

i was gonna suggest the 1218....im running them on a tr-224 so far with zero problems.

Sharpe

iTrader: (7)

I see, I see. That's terribly interesting.

Is "Advertised Duration" always the duration at .006? Or is it always the duration at .006 when you're being given the duration at .050? Or...?

You say XE-R's are 49. So, if you have a 244 (@.050) grind, and you know it's on XE-R lobes, then you know that the advertised duration (the duration at .006) is 273 (224+49)?

If you don't mind me asking, How many different lobe types are there, and what are all of COMP's? Would you be so kind as to list them in order of "aggressiveness" from least to greatest including their "rate variance?" Is "rate variance" really the technical term?

If so, can I start a new thread with discussion about this?

Thanks a lot! I'm very fascinated!

PREDATOR-Z

If you go to http://www.compcams.com
You'll find Comp cams master lobe catalog
The advertised durations at Comp are .006 lifts (Rated lifts)
You'll also have .050 and .200 lifts

Overall this gives you an idea of the sharpness of the profile (now mind you the lobe is not straight otherwise you would have a triangle)
Cammotion uses those lifts as well.

So to read through the lobes (analyse them) with this method you get a basic idea what the lobe rate is doing in between each lift. To understand that better, you should read about lobe profile diagrams and understand where the lifts occur in the lobe.

Overall this basicaly helps you understand what the cam is doing while going through a full cycle of opening and closing the valves.
This info is 1 of the tools used to tailor a cam to your overall combo, but more precisely to the flow of the heads (helps you choose which lobe to use).
I also give you an idea why cam designers chose cams with dual lobe patterns and their effects on the powerband.

Yes that would make an excellent thread (but will be time consuming to put it forward in Lehmans terms). You would be getting deep into cam dynamics.

To make it simple, for reference, one could plot that on a linear plot. then just by comparing variation rates, you could basicaly find out the overall agressiveness of the lobe.

SweetS10V8

iTrader: (4)

No, different companies use different points for advertised duration. That's why .050" became a standard for everyone to use, because everyone used different point for advertised and it was hard to compare cams from different companies.

Companies started using lower and lower starting points to make their cams seem bigger because the lower you measure, the larger duration numbers you get.

Say two lobes were exactly the same; one was advertised at 268 and the other advertised at 274. The 274 would sell more because most people think bigger is better.

Jason 98 TA

iTrader: (4)

We stock & sell both the 918 & the pac spring. We've never had any issues with the PAC spring at all, both seem to be great for .600" lift applications.

We have the PAC & 918s are in stock incase you need a set!!