Roller Rockers...

foxmustangman

Member
Jun 20, 2007
196
1
16
Idaho
So I'm looking at getting a set of roller rockers for my 'Stang. What's the difference between 1.7 and 1.6 ratio rockers, and also what's the difference between 7/16 and 3/8 stud mounts?

Thanks,
-FMM
 
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7/16 is bigger than 3/8.....

A 1.7 rocker will give you more lift and slightly more duration at the .050 lift measurement, but nothing to write home about. 1.6 is stock. I would recommend 1.7, but they don't work with some heads so I would just use a 1.6

Basically, a 1.6 rocker takes the cam profile and multiplies it by 1.6 while the 1.7 does the same thing, but you end up with a "bigger" result.
 
3/8" is the smaller of the 2 available stud sizes on a stud mount rocker head, 7/16" is the larger. If you have a stock head it requires a pedestal mount rocker... You can put any ratio on ANY head, it will only depend on the spring pressure. Most cams unless noted are made/designed for a 1.6 rocker.

The 1.72 rocker will add .031" lift to the cam numbers @ .050, so a cam with an advertised .500 lift will have .531" at the rocker now.

Ped mount style head
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Stud mount head
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Fast63 and Rick are both correct, except 1.7's will NOT give you more duration. just more lift in the same duration. the camshaft determines your duration, not the rocker arms.

to determine how much lift you will gain going from a 1.6 to a 1.7, take your current lift number with 1.6's, divide by 1.6 then multiply by 1.7. example:

stock cam is .444 with factory 1.6 rockers.

.444/1.6= .277 (actual cam lift)

.277x1.7= .471 (new lift with 1.7s)

.477 if you have 1.72s

hope this helps!
 
Fast63 and Rick are both correct, except 1.7's will NOT give you more duration. just more lift in the same duration. the camshaft determines your duration, not the rocker arms.

Yes, your total duration will not change and is determined by the cam only. However, your duration at .050 is a LIFT measurement, and if LIFT changes from a different ratio rocker, your duration measurement at .050 LIFT will be different.

And 1.7's DO NOT work with all heads. Try running some on windsor jrs like I did and you will have problems unless you machine the pushrod openings larger so the pushrods won't rub on the castings.
 
Yes, your total duration will not change and is determined by the cam only. However, your duration at .050 is a LIFT measurement, and if LIFT changes from a different ratio rocker, your duration measurement at .050 LIFT will be different.

And 1.7's DO NOT work with all heads. Try running some on windsor jrs like I did and you will have problems unless you machine the pushrod openings larger so the pushrods won't rub on the castings.


:nice: duration at .050" will be different, nice to see someone else know's.

How old are your Juniors?? I had a set here last month (brand new set) with 1.72" and a 5/16" pushrod no issues.
 
Just so you know......1.7s on the stock valve covers will mildly scar the tops of the rockers. Nothing too serious though.......I would still recommend them. Especially if you're upgrading your cam you'll experience a NICE increase in power. :nice:
 
:nice: duration at .050" will be different, nice to see someone else know's.

How old are your Juniors?? I had a set here last month (brand new set) with 1.72" and a 5/16" pushrod no issues.

:nice: Excellent, I find few other that know it!

My windsor jrs. are from 2003 I think, back when they came out as Roush 180's. Have they made adjustments to the casting that allow 1.7's now? I know world products had this problem with chevy heads as well, maybe they realized their blunder and fixed it?
 
I'm personally against 1.7s...i don't see the need. If you want more lift, get a better cam and leave the valve geometry alone. The size of your rockers (3/8 or 7/16) will depend on what your heads are set up for, unless you buy them bare or want to run 7/16 for the added strength and buy a set of studs and swap them in the heads.
 
I don't think it would hurt. There's lot of serious race cars out there running the stock pedestal mount setup with ported stock heads. Unless you plan on running extreme RPMs you should be ok with 3/8. I happened to find a set of Comp Cams Pro Magnums that were 7/16 for only $160 and they even came with ARP studs to match, so i'm switching the studs in my heads. I really don't know what you can do with pedestal mount, if there's even a 7/16 option, as i've never worked on them.
 
Yes, your total duration will not change and is determined by the cam only. However, your duration at .050 is a LIFT measurement, and if LIFT changes from a different ratio rocker, your duration measurement at .050 LIFT will be different.

And 1.7's DO NOT work with all heads. Try running some on windsor jrs like I did and you will have problems unless you machine the pushrod openings larger so the pushrods won't rub on the castings.

Now wait a second. DURATION is a measure of rotation the lobe covers on the cam base circle (degrees) and LIFT is a measure of the difference of the lobe peak and the base circle radius (inches). Maybe that is what you are trying to say, but it came of slightly confusing.

Duration measured at 0.050" is a popular method of measuring lobe duration from 0.050" lift (opening) to 0.050" lift (closing). Sometimes you can find specifications for duration on cams measured 0.010"-0.010" and smaller, though this is less popular, as the smaller numbers are harder to measure and do not significantly add any insight on lobe design over the 0.050" method (you don't flow much air with less than 0.050" lift, do you?). Notice it is still a degree measurement.

Roller rockers (or any type of rocker, really) will multiply cam lobe lift by their ratio. If you have a cam that has an intake lobe lift of 0.278" (stock HO) and 1.6 rockers (again, stock HO), then your effective valve lift is 0.278" * 1.6 = 0.4448". However, with the 1.7 rockers you will see 0.4726" valve lift.

The advantage of the 1.7 roller rockers (besides the reduction in valvetrain friction and wear) is that the desired lift can be achieved without using a cam that has more lobe lift, which results in steeper ramp rates and more aggressive grinds.

This being said, dyno reports I've seen indicate less than 10 HP gain from 1.7 RRs over the stock pieces on stock heads with stock cams. However, they may pay off in valvetrain stability, reliability, etc.

Sorry if some of this is redundant, I wanted to make sure none of us confused your original plans. I would say if you are going to buy RRs either way, go with the 1.7s.
 
Now wait a second. DURATION is a measure of rotation the lobe covers on the cam base circle (degrees) and LIFT is a measure of the difference of the lobe peak and the base circle radius (inches). Maybe that is what you are trying to say, but it came of slightly confusing.

Duration measured at 0.050" is a popular method of measuring lobe duration from 0.050" lift (opening) to 0.050" lift (closing). Sometimes you can find specifications for duration on cams measured 0.010"-0.010" and smaller, though this is less popular, as the smaller numbers are harder to measure and do not significantly add any insight on lobe design over the 0.050" method (you don't flow much air with less than 0.050" lift, do you?). Notice it is still a degree measurement.

Roller rockers (or any type of rocker, really) will multiply cam lobe lift by their ratio. If you have a cam that has an intake lobe lift of 0.278" (stock HO) and 1.6 rockers (again, stock HO), then your effective valve lift is 0.278" * 1.6 = 0.4448". However, with the 1.7 rockers you will see 0.4726" valve lift.

The advantage of the 1.7 roller rockers (besides the reduction in valvetrain friction and wear) is that the desired lift can be achieved without using a cam that has more lobe lift, which results in steeper ramp rates and more aggressive grinds.

The first part of what you said is true, but I made no mention of it. I thought that was just common knowledge, and I said nothing to refute that.

However, by saying that a higher ratio rocker increases the total lift is confusing without explaining, in conjunction, that the whole lobe's ramp rate is increased. That is why no one latches on to the idea that duration measured at .050 or .010 or whatever lift you want to measure it at, is changed.
 
the actual duration of the lobe will remain the same. meaning the valve will still be open for the exact same amount of time as it would be with 1.6s

but the valve has to move .030 ish (depending on cam) farther open in the same amount of time. so what results is a valve that opens and ramps up to max lift faster than it did before. so the valve is going to hit the .050 mark faster that it would before. and the valve will dwell longer in lift numbers exceeding .050"

so the duration at .050 does change

i'm no expert so if i am wrong on anything someone let me know, but that is how i see things.