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Old 07-06-2008, 05:42 PM   #1 (permalink)
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1.6 vs 1.7 rockers

Ive got a 512 lift cam with 232 duration in a 351w with 1.6 comp cam roller rockers. Would there be much of a gain if i were to put 1.7s on it or would it put added stress on the studs (theyre screw-in studs on afr's with guide plates)?
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Old 07-07-2008, 08:34 PM   #2 (permalink)
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Re: 1.6 vs 1.7 rockers

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Ive got a 512 lift cam with 232 duration in a 351w with 1.6 comp cam roller rockers. Would there be much of a gain if i were to put 1.7s on it
NO IMO
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Old 07-08-2008, 12:59 AM   #3 (permalink)
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Re: 1.6 vs 1.7 rockers

Quote:
Originally Posted by hepcat69 View Post
Ive got a 512 lift cam with 232 duration in a 351w with 1.6 comp cam roller rockers. Would there be much of a gain if i were to put 1.7s on it or would it put added stress on the studs (theyre screw-in studs on afr's with guide plates)?
YES
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Old 07-08-2008, 07:59 AM   #4 (permalink)
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Re: 1.6 vs 1.7 rockers

Quote:
Originally Posted by hepcat69 View Post
Ive got a 512 lift cam with 232 duration in a 351w with 1.6 comp cam roller rockers. Would there be much of a gain if i were to put 1.7s on it or would it put added stress on the studs (theyre screw-in studs on afr's with guide plates)?
Going to 1.7 rockers would increase the valve lift considerably. This can gain a lot of power in some combinations and not so much in others. Some people even stagger 1.6's and 1.7's if it works best for their particular combination. This is something you can do a little experimenting with if you have a set of each. However, you have to make sure that your valve springs are compatible with the additional lift. I think that 1.7's would put you somewhere in the .540 -.550 lift range. Maybe someone else can chime-in with the exact amount of increase.
With a .512 lift, going to 1.7's isn't going to create enough additional lift to "stress out" your screw-in studs. I was originally running .555/.576 lift on 3/8 studs with no issues. I now have 7/16 studs in my AFR's with the same cam.
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Last edited by kgordonl; 07-09-2008 at 01:37 PM.
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Old 07-08-2008, 09:12 AM   #5 (permalink)
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Re: 1.6 vs 1.7 rockers

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YES
So after he spends hi$ coin and his car ends up going slower are you gonna pay for his investmnet?
If your motor needs more lift you have the wrong cam and thats what I would spend my $ on. The afr 185's can could use and take advantage of more lift
The CC spec'd valve springs for the Magnum 280, if that's what you are using, are marginal at best. Your probably have valve float issue already. my 185 stock springs float bad

You may also, if you have not already, need to fly cut your pistons. I did with my 351w 280 Magnum cam. Check your IO BTDC measurement
Could be some more expen$e you will endure, but you can do it yourself.

The lobe measures .320 x 1.7 if you actually get that out of your rockers and pushrods=.544"

It just bothers me for people to suggest spending $$ on anything. But hey WTF do I know
The 351 I ran with the Magnum 280 got me into the high 12's with D0E heads, I liked that cam.
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Old 07-08-2008, 12:34 PM   #6 (permalink)
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Re: 1.6 vs 1.7 rockers

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So after he spends hi$ coin and his car ends up going slower are you gonna pay for his investmnet?
If your motor needs more lift you have the wrong cam and thats what I would spend my $ on. The afr 185's can could use and take advantage of more lift
The CC spec'd valve springs for the Magnum 280, if that's what you are using, are marginal at best. Your probably have valve float issue already. my 185 stock springs float bad

You may also, if you have not already, need to fly cut your pistons. I did with my 351w 280 Magnum cam. Check your IO BTDC measurement
Could be some more expen$e you will endure, but you can do it yourself.

The lobe measures .320 x 1.7 if you actually get that out of your rockers and pushrods=.544"

It just bothers me for people to suggest spending $$ on anything. But hey WTF do I know
The 351 I ran with the Magnum 280 got me into the high 12's with D0E heads, I liked that cam.
There is a limit to the lift and profile of a cam lobe, thats why in the Engine Masters Challenge they use rocker ratios ranging from !.8 t0 2.2 to 1.
They don.t do it for fun or to save money.
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Old 07-09-2008, 12:45 AM   #7 (permalink)
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Re: 1.6 vs 1.7 rockers

lift would change from .512 to .544 and your duration and overlap would also increase. Yes, it will put as much added stress on the struts as the increase in lift (about 16%). You may need different springs to prevent coil bind and to control the added lift of the valve. You may have to add clearance for the pistons at the valve reliefs and you will get a small increase in power throughout the rpm range.
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Old 07-09-2008, 10:23 AM   #8 (permalink)
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Re: 1.6 vs 1.7 rockers

Duration and overlap do not change, when the cam close the valve, it is closed at the same time with 1.6 or 1.7.
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Old 07-09-2008, 04:53 PM   #9 (permalink)
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Re: 1.6 vs 1.7 rockers

As a matter of fact, the valves dont float even up to 6500rpm. I ran 13.45 at 105 with a good bit of tuning left to do. Ive got triple valve springs and thats about all i know about em. What is the formula for determining how the lift will change with the change in rocker ratio?
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Old 07-09-2008, 09:34 PM   #10 (permalink)
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Re: 1.6 vs 1.7 rockers

I can tell you that we did this a few times on a couple of dirt late model engines and saw no real change in the engine. Joe Sherman touched on this subject earlier in the year and you need to look it up on the search function.
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Old 07-10-2008, 12:37 AM   #11 (permalink)
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Re: 1.6 vs 1.7 rockers

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Originally Posted by teyerdhal View Post
Duration and overlap do not change, when the cam close the valve, it is closed at the same time with 1.6 or 1.7.
teyerdhal,
the numeric duration only stays the same if you don't consider the amount of opening. Cams today are rated by the SEA duration spec of duration at .050" lift. The duration at .050" will change and so will the overlap. Since the valve lift is higher it will open further, sooner, and stay that way longer.
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Old 07-10-2008, 12:42 AM   #12 (permalink)
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Re: 1.6 vs 1.7 rockers

OK said like this, i am agree with you ;-)
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Old 07-10-2008, 02:30 PM   #13 (permalink)
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Re: 1.6 vs 1.7 rockers

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Originally Posted by PaulS1950 View Post
teyerdhal,
the numeric duration only stays the same if you don't consider the amount of opening. Cams today are rated by the SEA duration spec of duration at .050" lift. The duration at .050" will change and so will the overlap. Since the valve lift is higher it will open further, sooner, and stay that way longer.
From one retired mechanic to another, Thank you. You explained it more thoroughly than I did.
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Old 07-10-2008, 08:36 PM   #14 (permalink)
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Re: 1.6 vs 1.7 rockers

10 years of being an industrial safety instructor does help.... sometimes.
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Old 07-11-2008, 06:46 PM   #15 (permalink)
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Re: 1.6 vs 1.7 rockers

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Originally Posted by PaulS1950 View Post
teyerdhal,
the numeric duration only stays the same if you don't consider the amount of opening. Cams today are rated by the SEA duration spec of duration at .050" lift. The duration at .050" will change and so will the overlap. Since the valve lift is higher it will open further, sooner, and stay that way longer.
Cam specs are based on tappet lift (unaffected by rockers ratio pantograph effect), not valve lift. A 224/232 dur. @.050" cam will also have different duration #'s if measured at the valve with 1.6 rockers following the .050" lift spec. If you also look at the specs, how would duration be increased if the seat-to-seat specifications are unaltered + the valve centerlines are unaltered as well....... if the ICL is at 108 ATDC with 1.6 rockers, it will not change with 1.7 rockers.
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