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Would you install 1.6 or 1.7 rockers? |
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rang-a-stang 
AMC Nut 
Joined: Sep/25/2018 Location: Camarillo, CA Status: Offline Points: 272 |
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 Topic: Would you install 1.6 or 1.7 rockers?Posted: Sep/27/2018 at 12:24am |
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I'm pretty new hear; I usually live over on the IFSJA.org forum. So have mercy on my soul.
 I am mostly done building a 401 for my Cherokee Chief and am at the point of buying my rockers. Part of me says get 1.7s now so I have them but another part says I won't see any benefit with them compared to 1.6's on mostly stock heads. Here are my stats: 401, .030 over, Wiseco 27cc pistons, moly rings Heads: 3216090 castings (intake and exhaust port matched but no other intake/exhaust work), 3 angle competition valve job, heads were surfaced but not really milled, Comp Cams 940-16 single valve springs (1.464" O.D., 1.080" I.D) Comp Cams High Energy 268H (Duration 268/268, Lift .456/.456) Edelbroke performer intake (also port matched) with EGR I plan to run a 454 TBI on top of it and long tube Hedman headers This engine is pushing a 4500# Jeep, TH400, with occasional towing and lots of highway driving. I am already planing to buy new push rods so that is not really a concern. I also plan to install 7/16" studs. I REALLLLLLLY want to keep my stock valve covers on it. I am looking for a long lasting engine but also don't want to leave HP/TQ on the table. So, if'n it was you, would you buy 1.7 or 1.6 rockers? Why or why not? The cost difference seems negligible. Here's my engine as I left it. Alot of the items (like dizzy, valve covers, heater hose fitting, etc.) are on there just to keep dust/dirt out of while I am on travel for the next month. |
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WesternRed
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Joined: Aug/03/2010 Location: Australia Status: Offline Points: 5799 |
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Posted: Sep/27/2018 at 1:23am |
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I would really see no need for 1.7 rockers in your application other than as a band aid for not choosing the right cam in the first place.
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I've finally given up drinking for good...........now I only drink for evil.
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Trader
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Joined: May/15/2018 Location: Ontario Status: Offline Points: 6881 |
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Posted: Sep/27/2018 at 6:47am |
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I would go with 1.6 rockers because the higher lift will not provide the lower end torque you would want for occasional towing.
The cam you choose is not bad for what you state as you desired application, street, occasional towing and the 401 has enough "performance" for your Jeep. WesternRed, what would be the cam recommendation? The duration looks good for low RPM torque and I admit a little more lift would not hurt but going over 0.485 would be loosing low RPM torque for towing, would it not?
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WesternRed
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Posted: Sep/27/2018 at 8:20am |
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GreyhoundsAMX is the cam guru, download his spreadsheet and have a play, it has provision for 1.6 and 1.7 rockers.
When I was playing with the numbers, 1.7 rockers give you a couple more degrees duration @ 0.050" lift compared to 1.6, so it's almost half a cam size. The extra lift might be beneficial if you head flow can actually support it. The increased rocker ratio might give you a slight improvement in performance without the loss of low end torque that might come from going the next cam size up. If you look at the Comp Extreme Energy cams, they try to do something similar to increasing the rocker ratio with more aggressive ramps to open and close the valves more quickly and have more lift with less duration than the traditional Magnum cams.
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I've finally given up drinking for good...........now I only drink for evil.
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PHAT69AMX
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Posted: Sep/27/2018 at 1:18pm |
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Which Ratio regardless, but understanding is AMC Rocker Arms are closer to
Ford Geometry than Chevy, same 1.6 ratio of those two have different short side & long side dimensions. The Ford ones are closer to AMC 1.6 Short & Long dimensions. 12 years ago I got Harland Sharpe AMC Rockers ( Ford Dims ). They sat and rode, etc much better than the previous rockers, even had to change studs. Previous Rockers were Chevy Dims Crane Hi-Intensity, and only after switching them out for the Ford Dim HS Rockers did it become obvious the difference it makes. The old notes I have say, according to BullTear: 1.60 Ratio Rocker Arm Mounting Stud to Valve Tip Dimensions 1.455" = stock AMC/Ford Small Block 1.363" = stock Chevy Small Block Pushrod side is also different to maintain 1.6 Ratio Understanding is Harland Sharp AMC Rockers are Ford pieces but they add a healthy chamfer around the bottom slot to clear the Rocker Stud Hex where it mounts to the AMC cylinder head. Found a completely different length Pushrod was needed on the same assembled parts depending on if Crane Energizer Rocker Arms or Harland Sharp Rocker Arms were used to do the mock up and test. Even different length Rocker Studs were needed. Crane #99721-2 were used but removed the locking hex nuts to clear valve cover ledge on head. ( edit: I'm not even sure what that last sentence means... they're 10+ year old notes )
Edited by PHAT69AMX - Sep/28/2018 at 12:16am |
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Buzzman72
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Posted: Sep/27/2018 at 4:53pm |
This is kinda where my thoughts were headed. Since I'm not looking for a race cam, I'm interested in the Howards #310101-12. I think it would be ideal for a highway cam in a 304. My thought has been that stepping up to 1.7 rockers, vs. 1.6, might give you a couple hundred more effective rpm on the top side without killing the bottom end...provided you're not running an SP-2P intake. |
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Buzzman72...void where prohibited, your mileage may vary, objects in mirror may be closer than they appear, and alcohol may intensify any side effects.
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rang-a-stang
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Joined: Sep/25/2018 Location: Camarillo, CA Status: Offline Points: 272 |
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Posted: Sep/27/2018 at 9:15pm |
Wow. That's a really good point. I spent quite a bit of time and energy picking out this cam. SC/397 gave me some fantastic advice and I hit up Comp, Crane, and Iske right before I ordered. I was looking at the HS S4004-77s (7/16's stud, 1.7). I found them for $288 (which seems to be a steal). The same shop shop sells the S4004-7 (7/16's stud, 1.6) for $271. Once I get them I will install a couple and measure for new pushrods. On a related note, I have read my heads (casting #3216090-1, early 401 heads with screw in studs) don't need guide plates because the opening in the head acts as the pushrod guide (I looked down the hole and it's a slot and my rods have a clean spot where they pass through it). Anyone want to confirm I don't need guide plates?
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FSJunkie
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Posted: Sep/27/2018 at 9:49pm |
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Higher ratio rockers indeed give more valve lift, but they also increase load on the valve train, including the cam lobe and lifter face. This means increased wear and chances of failure. It is better to have a higher lobe lift cam with lower ratio rocker arms to result in the same valve lift but with less load on valve train components. Increased valve lift by itself without increased duration, overlap, LSA, etc. results in increased torque at all engine speeds, particularly high RPM. Unlike increased duration, it does not steal torque from the low end to give it to the high end. Increased valve lift is always welcome in my engine building book so long as the valve train is up to the task and there is piston clearance. |
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amxdreamer
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Posted: Sep/27/2018 at 10:36pm |
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The engine sounds very close to the build on the 360 in my AMX and I have the stock stamped steel rockers. The cam should work well for your application. It's a heavy 4x4 NOT a 1/4 mile racer. I doubt you will be reving an engine with the performer intake at 6500rpm.
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Tony
Vancouver, BC 1970 AMX 1972 Badassador AMO#10333 |
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junk yard dog
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Joined: Dec/20/2012 Location: Vancouver wa Status: Offline Points: 1170 |
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Posted: Sep/28/2018 at 12:12am |
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What compression ratio is that thing ? 27 cc cupped pistons and 58 cc head ? About 8.5 to 1 ? Its going to be a dog ???? JYD.
Edited by junk yard dog - Sep/28/2018 at 2:24pm |
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WesternRed wrote: