1.7 to 1.8 ratio BBC rockers much diff...? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 04-27-2005, 08:24 PM
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1.7 to 1.8 ratio BBC rockers much diff...?

Have a BBC 427 (.030 over) forged TRW L-88 (ZL1) pistons that make 12 to 1 with closed chamber heads but am running 781`s (open chamber) so its about 10.8 to 1 and have the larger 2.19/1.88 valves and some bowl and port work... Also the intake is a Performer RPM and BG 750 Speed Demon... It has Hooker SuperComps (35" long tube) with 3" exhaust 2" H pipe and a pair of single chamber Flowmasters The cam is a Lunati 00026 with .549/.558 lift & 232/239 @ .050 (293/310 adv. duration)


I am thinking of switching to the 1.8 ratio rockers over the 1.7`s how much is to be gained if any...? Also what estimated HP/Torque is this setup...? I punched in all the numbers incl the cam (direct from the cam card) and DD2K gave me a pretty healthy number but would rather hear from the BBC boyz...

thanks in advance...

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Old 04-27-2005, 08:36 PM
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Whats the Difference?

Going to the 1.8 rockers will give you a 6% increase in valve lift, which will translate to about 1-3 hp max gain at each measuring point along your power curve. Higher ratio rocker arms will not effect duration, only lift.
In my opinion, going to higher ratio if you already have aftermarket rockers isnt worth the money, unless you are after that last final hp you can possibly gain from your setup.
The question is whether they are worth the money for the gain.
Another consideration, is will it effect your valve to piston clearances?
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Old 04-27-2005, 09:40 PM
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The gains will vary. If your heads were being held back by the cam, the higher ratio will make a bigger difference.
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Old 04-28-2005, 02:35 AM
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Mutiply Rocker Ratio by cam Lift (Not cam and Rocker lift)

so

INCORRECT ANSWER (CAM + SET ROCKER RATIO) (Also known as Lift @ Valve or GROSS LIFT)

1.8 x .549 = .9882" Lift
1.8 x .558 = 1.0044" Lift

You can see how these Figures would be Incorrect, because theres already a Rocker Ratio Added to the Cam Lobe lift.

CORRECT ANSWER (CAM) (Also Known As Lift @ Lobe)
Intake
1.8 x .323 = .5814" Lift With 1.8 Ratio Rockers
1.7 x .323 = .5491" Lift With 1.7 Ratio Rockers

Difference = .0323" Lift

Exhaust
1.8 x .328 = .5904" Lift with 1.8 Ratio Rockers
1.7 x .328 = .5576" Lift with 1.7 Ratio Rockers

Difference = .0328" Lift




Your cam is Part #16478 / 00026

HYDRAULIC, Rough idle. Needs 3000 stall converter. Great street/strip cam.

RPM RANGE
2500-6500

Advertised Duration
293° / 310°

True Duration (at .050")
232° / 239°

Lift @ Rocker (Rocker Ratio + Cam Lobe Lift, Rocker ratio is a set Rocker they Choose)
.549" / .558"

Lift @ Lobe (CAM)
.323" / .328"

Lobe Seperation
110° Sep
104° Int C/L

When The Valve Opens and Closes at .050" Lift
12°BTC 40°ABC / 55.5°BBC 03.5°ATC

This Cam was best suited and was specifically made by Lunati for Bracket Racing. But can be used as a Street cam as well... All these Figures came Straight From Lunati's Official Website, and The Math Above is Something I figured out after studing cams for a few years now... The Math is correct.


http://www.holley.com/ProdLine/Produ...CC/Chevy7.html

Your cam is Found on the Second Section Under "Street / Strip" and is Midway Down.
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Old 04-28-2005, 02:38 AM
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Hope that Helps

Mike
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Old 04-28-2005, 12:41 PM
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Incorrect Answer?????????

Who gave an incorrect answer?

Last edited by Max Keith; 04-28-2005 at 12:58 PM.
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Old 04-28-2005, 11:41 PM
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Eh, no one I guess.. Well theres good info there anyway. It never hurts to share
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