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Old 05-07-2008, 11:17 AM   #1 (permalink)
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Need advice on 1.6 to 1.7 rockers

I need some input on whether or not it's worth it to step up from a 1.6 to a 1.7 roller rocker

My street/strip 67 fairlane is a equipped with a 347 with out of the box Edelbrock RPM heads & manifold and a Holley 650 VS carb, MSD billet dizzy with a 6AL box.and hooker comps. The cam is a Comp XE268H and it will rev to 6,200rpm and through the lights at 5,800 rpm. The car weighs 3,400 lbs with me in it and has run a best of 12.90 @ 105 mph with a 1.8 60ft. on M/T drag radials and a 3.89 locker. I tried a Holley 750 VS and played with the timing and jetting on both, but it ran the same.

I am avoiding putting a bigger cam in it, because this combo just recently went into the car and I don't want to tear it apart again.

The question is how much of a gain in performance and powerwise will I see by stepping up to a quality 1.7 rocker? Am I wasting my money? I'm not looking to make a quantum leap in ET and MPH. If I picked up a couple of tenths and MPH I would be satisfied for now.

Thanks
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Old 05-07-2008, 12:23 PM   #2 (permalink)
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Re: Need advice on 1.6 to 1.7 rockers

Simply put, swapping 1.6 ratio rocker arms for 1.7 ratio rocker arms tricks your engine into thinking you have changed cams to one with a slightly different profile. Whether or not it will help or hurt your engine's performance depends on what your engine needs in order to produce more power where you need it. It may even be possible, for example, that you need 1.7's on the intake only...or visa-versa. All you can do it experiment with the two sets and see what makes you engine the happiest for your application.

If you will use a different brand of 1.7 rocker arm than your 1.6 rocker arms, you may need new pushrods too.

Paul

p.s.: By the way, I have a few sets of 1.7's....
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Old 05-07-2008, 01:06 PM   #3 (permalink)
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Re: Need advice on 1.6 to 1.7 rockers

The biggest gain will come from increasing the duration.

A Lift only change may gain you a little, but it also increases the stress on the valve train, (maybe lower peak RPM power) and possibly wear out the valve guides if you don't get the correct length push rods to match.

Picking up 20 HP, may not be worth the expense and possible risk to the heads. May not even notice it is any faster....

I see lots of folks selling thier "slightly used" 1.7's must be a reason for that....
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Old 05-07-2008, 01:39 PM   #4 (permalink)
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Re: Need advice on 1.6 to 1.7 rockers

This pretty much covers it:
http://www.fordmuscleforums.comall...o-rockers.html

Last edited by secport; 05-07-2008 at 01:41 PM.
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Old 05-07-2008, 02:43 PM   #5 (permalink)
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Re: Need advice on 1.6 to 1.7 rockers

Completely different engine. Different heads, compression ratio, and cam profiles will resullt in different effects.

It is a gamble if this mod will do anything, or help.... at $400.00 for a set of good 1.7's and new push rods, a cam change is a much better bet on making more power.
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Old 05-07-2008, 03:41 PM   #6 (permalink)
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Re: Need advice on 1.6 to 1.7 rockers

If you look at the link that "secport" added you'll see this debate there too. I understand that with the lower flow heads like I have right now (iron GT40's) the 1.6 to 1.7 ratio swap is a waste of time and money. However, AFR advised me to swap my rockers to 1.7 and not change my cam as they prefer short duration, higher lift cams with their heads (ARF 165's at least) once I get them.

I still may go that route just to keep it simple and not have to get into the bottom end of the engine right now.

For what its worth I've seen 1.7 rockers in the Summit and Jegs catalogs for $200-250 made my several companies like Crane & Comp Cams.
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Old 05-07-2008, 05:16 PM   #7 (permalink)
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Re: Need advice on 1.6 to 1.7 rockers

I've heard the 1.7 rockers don't start to show any extra hp increase over the 1.6's till your over 6500rpms. The 1.6's provide a more "dead on" geometry on your valvetrain. Maybe try a 1" 4 hole spacer if you don't already have one or spark plug indexing. The Victor Jr intake responds well to the 347 too.
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Last edited by Spali32; 05-07-2008 at 05:20 PM.
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Old 05-07-2008, 05:48 PM   #8 (permalink)
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Re: Need advice on 1.6 to 1.7 rockers

Ford used Crane 1.7's on the Cobra engines. They did not have a lot more power but it added. Look on AFR's web site for the 400 HP 302 Car craft article. They were close to 400 with a stock cam and used the 1,7's to get over the 400 mark. You could look at the power curves and see where it came in. I know of a few Cobra mustangs with over 100K on them with stock 1.7's. If you do it make sure your springs are OK. I think a lot of people use them as an interim measure to get 10 HP and sell them when they get a new cam.
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Old 05-07-2008, 05:57 PM   #9 (permalink)
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Re: Need advice on 1.6 to 1.7 rockers

Dont waste your money, IF ThATS IF, it makes any differance, it would be so little you cant even tell the differance. I have done this test on the dyno at least 20 times, and when there is a gain, it is like 5 to 8 HP up at max RPM, down at 3000 it will LOOSE power.

JOE SHERMAN RACING ENGINES
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Old 05-07-2008, 07:01 PM   #10 (permalink)
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Re: Need advice on 1.6 to 1.7 rockers

Looked at the Car Craft article....23HP and 12 FT LBS. That was with a stock cam and good heads. If Joe was testing with a well designed set up to start with his results make sense. If you have more breathing than cam it looks like it could be a consideration.
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Old 05-07-2008, 07:03 PM   #11 (permalink)
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Re: Need advice on 1.6 to 1.7 rockers

You have to remember, there is a lot of hype in the magazines. They are there to sell a product. So numbers can be inflated to meet their mission. Be skeptical when reading magazine articles. Like Joe said, maybe 5-8 hp but the 1.7's generally start to produce power(shine) 6500rpms and up.
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Last edited by Spali32; 05-07-2008 at 07:25 PM.
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Old 05-07-2008, 09:36 PM   #12 (permalink)
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Re: Need advice on 1.6 to 1.7 rockers

We did this on a dirt late model engine on the pump, made a whopping 6 hp. Big deal, NOT worth the money
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Old 05-08-2008, 09:21 AM   #13 (permalink)
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Re: Need advice on 1.6 to 1.7 rockers

Thanks to all for your replies.

I think I'll hold off until I decide to make a cam change and get the most bang for my buck. In the meantime, I may look to gearing and chassis changes to try to lower my ET's.
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