beast69camaro

iTrader: (14)

Hey all,

So the other night I was looking at PTV clearance after measuring pushrod length on my 383 build.

Now, I'm running a .378" lobe lift on my cam which should give me a .604" valve lift with a 1.6 rocker ratio. However I noticed valve lift to be .635" which corresponds pretty closely to a 1.7 ratio.

These are part# 1305-16, 1.6 ratio for 7/16 stud, non-self-aligning. Each rocker body definitely has "1.6" stamped on the side even though they clearly have a larger ratio. Has anyone out there had problems with rocker ratio accuracy with the comp pro magnums?

Thanks...

AChotrod

iTrader: (17)

Mine were right on. Are you sure your cam specs are not figured with 1.5 rockers? My cam spec card is done at 1.5 and you have to do the math for 1.6 rockers. Kinda sounds like thats what happened to me

beast69camaro

iTrader: (14)

My cam card listed the lobe lift numbers, no math required.
I measured the lobe lift myself to +/- .001".....more than one time on more than one lobe....and my measurements agreed with the cam card.
I also measured valve lift myself to +/- .001"....more than one time on more than one valve.
I am 100% positive that the rocker ratio is off (nearly 1.7 instead of 1.6).

So I ask again.....has anyone else had similar problems with the comp pro mags?

Thanks.

Jditlfm

iTrader: (26)

If the push rod is too long wont that give you more valve lift? Im not 100% sure but that seems right maybe they are .021 to long? Like i said not sure just throwing out idea's.

beast69camaro

iTrader: (14)

Theoretically no, the only thing a longer pushrod length SHOULD do is move the rocker trunion (pivot point) higher on the rocker stud and screw up your valve tip sweep pattern.

However, I guess it's possible that rocker ratio could increase through the rocker's angular travel on the way to max lift (ie. slightly variable ratio). This could happen if the line connecting the center point of the rocker-end pushrod ball and point of valve tip contact passed slightly above the rocker pivot point. If this is the case with my rockers, then pushrod length could indirectly affect valve lift by making the rocker end at a different angular position (and thus different rocker ratio) at max lift. That would still screw up my valve tip sweep pattern though.....so either way, it's crap.

I'm off to the garage now to test this out.

beast69camaro

iTrader: (14)

After playing with pushrod lengths to test for a variable ratio in my rockers, I found only mildly interesting results.

- Increasing pushrod length .100" increased valve lift ~.005" (negligible)
- Decreasing pushrod length .100" decreased valve lift ~.005" (negligible)
- As expected, such changes in pushrod length severely screwed up the valve tip sweep pattern.

Conclusions:

- The pro mags are not variable ratio, and the measured changes in lift caused by differences in rocker angular position at max lift are probably due to trunion hole machining tolerances
- As expected, my lift issues are not due to valvetrain geometry error (pushrod length)
- I am still 100% certain that my rocker ratios are larger than advertised on their body stamps.

I'm going to call Comp tomorrow.

Jditlfm

iTrader: (26)

good to know.

Mighty Whitey

I've got the SA 1.6 pro-mags on my car. but never bothered to check their actual lift.

where are you sticking your indicator to produce these valve lift numbers? on the rocker body? or on the retainer?

LTBANDIT

iTrader: (3)

did you measure the lift of all of your valves?
i thought i heard they were actually closer to a 1.65 rocker but i may have heard wrong...

i would think the cam would be off before the rocker... where is the cam from?

blackz93

iTrader: (2)

If I had the clearance and the springs for it, I wouldn't be complaining!

BALLSS

Beast:

AChotrod points out that typically the 'cam card" states lift with a 1:5 RR, if you run a 1:6 than the 'math" you need to do would then show what the lift is with a 1:6 RR.

given the variances you stated, they are very close if not exact the difference in lift between 1:5 & 1:6 RR

Certainly not saying there isn't something wrong with your specific set of COMP's...FWIW I run the same ones

Ironically my cam card (COMP XFI) states lift using a 1:6 ratio. Other cam cards I have including a COMP custom grind note lift with 1:5 ratio

beast69camaro

iTrader: (14)

I shipped the rockers off to COMP before Christmas.....they JUST got back with me last week or so.

The warranty guys measured the rocker ratio and confirmed the larger ratio. They measured ~1.66 ratio (on a dinky >.300 lobe lift) while I measured 1.68 (on my .378 lobes). THEY SAID THIS IS TYPICAL.

My guess is most people just install these things and don't check resulting lift.....my advice is be careful if you are close to spring bind with advertised numbers. Chances are you'll have problems when the actual lift numbers are greater than advertised.

Comp says their "high tech" stainless versions of the pro magnums are true 1.6 ratio (we will see), so I'm gonna pay the difference and have them ship me some of their stainless replacements.

ss.slp.ls1

iTrader: (36)

^Win.

beast69camaro

iTrader: (14)

A) My AFR Eliminators (195 comp ports) go into port stall if you go much above .600" lift.....I don't WANT .637" lift

B) My trick flow 5/16" pushrods are already going to see some abuse with springs that are already >400 lbs @ .600" lift over the nose......opening the springs further AND multiplying that force by ~1.7 instead of 1.6 just means higher loads and more wear and tear. >1.6 rocker ratio puts me outside the balance point that I established between performance and reliability for my application....

C) The point here is not me asking for advice. This post was only for fact finding.....Comp advertises this part number as 1.6 ratio, when they aren't, plain and simple. It's great if you want the extra lift, and crappy if you don't.

You're welcome for the information.