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Old 08-20-2010, 05:58 AM
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3/8 or 7/16 rocker studs on hot 383?

I just bought a set of ARP 3/8 rockers studs for my 383 build, but now I'm thinking that maybe I should've gone for 7/16 instead. I can easily return the 3/8 studs (not even opened the pack yet) if necessary. I'll be running a Comp Magnum 294S solid FT cam with 1.6 ratio rockers (.560" lift) and revving to max. 6,500. Car will be used 99% on the street.

Should I go for 7/16 rockers? There's very little extra cost involved, but I don't want to goto the hassle of returning my 3/8 studs if there's no need.

Thanks.

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Old 08-20-2010, 06:28 AM
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7/16" studs are a LOT stronger, I'd recommend it, for sure.
IMHO, it's always a good idea to go for the extra strength once you get past .500" lift,
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Old 08-20-2010, 06:31 AM
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7/16 rocker studs

Absoutely, you should always use 7/16" rocker arm studs with 1.6:1 ratio rocker arms and especially with more than 0.500" valve lift. I am assuming you also have full roller 1.6:1 rocker arms, if that is correct, you must also return those rocker arms and poly-locks for a set of 1.6:1 ratio full roller rocker arms and poly-locks for or 7/16" rocker studs. All BB Chevrolet and Pontiac V8 engines that used 1.6:1 ratio rocker arms also used 7/16" rocker studs because of the increased side loading on the studs. You have the opportuntity to uinstall valve spring that have the load that will follow cam lobes with 0.560" valve lift, if you do not already have them. I suggest that you use valve springs with at least 150 lb. seat pressure and 350 lb. open pressure at 0.560" valve lift with GM Engine Oil Supplement. You should also use 0.080" wall chromemoly pushrods because stock or stock replacement mild steel push rods will fold up like wet spagetti.

High lift flat tappet cams and low-ZDDP (zinc) motor oil can be a problem these days if you use valve spring loads that are designed for those cams. .
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Old 08-20-2010, 07:07 AM
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Quote:
Originally Posted by v8hed
Car will be used 99% on the street..
What ya going to do with the other 1%?
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Old 08-20-2010, 07:14 AM
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Yikes

The camshaft, rocker arms, rocker studs, valve springs, and pushrods are for the other 1%.

BTW, the camshaft you have will float quicker and at a lower RPM if you don't have valve springs with adequate valve spring load. Unlike stock cams with low valve lift, high lift cam profiles can float the valves prematurely if you have stock valve sprimngs. For example, the engine may pull hard to 5500 RPM with a stock cam and stock valve springs before valve float occurs but will float the valves at 4500 RPM with a high lift cam and stock springs. Radical high lift camshafts tend to "toss" the lifters off the nose of the lobe if the valve spring load is inadequate.

High spring loads and low-ZDDP motor oil is why factory and retro-fit roller cams are so popular today. You can use high spring loads with roller cams without any break-in or worrying about your cam going flat.

Last edited by MouseFink; 08-20-2010 at 07:29 AM.
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Old 08-20-2010, 07:29 AM
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Why would anyone ever use 3/8 studs if buying all new parts? The 7/16 are considerably stronger and the rocker arms cost the same.
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Old 08-20-2010, 08:16 AM
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Quote:
Originally Posted by lmsport
Why would anyone ever use 3/8 studs if buying all new parts? The 7/16 are considerably stronger and the rocker arms cost the same.
I think he realized his mistake. That's what this thread is all about.
At least he hasn't installed them yet!
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Old 08-20-2010, 08:44 AM
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Thanks guys, I'll return the 3/8 studs and go for 7/16. The reasoning behind taking the 3/8 studs in the first place was that 3/8 rockers are a little easier to come by and I didn't really stop to think about the amount of lift I'm going to be running.

I'm going to be using Comp 986-16 dual springs (280lbs open pressure / 132lbs seat pressure). These are the springs recommended by Comp Cams for this cam.

Oh, the other 1% is in case I goto a Run What Ya Brung event down at my local track
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Old 08-20-2010, 08:54 AM
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7/16" studs always preferred

There are uses for 3/8" rocker studs if the other valve train components are carefully selected.

For exapmle: Due clearance problems with the 2" stock center bolt valve covers on my stock Chevrolet 4.3L V6, I used ARP 134-7101 3/8" screw-in rocker studs, Crane short poly-locks and Comp Cams 1015-12 narrow body, self-aligning 1.52:1 roller aluminum rockers. I also used Comp Cams 5/16" High-Tech pushrods, Comp Cams 26981-12 beehive valve springs rated at 110 lb. seat load at 1.700" and 310 lb. open load at 0.500" valve lift. The 3/8" studs and 310 lb. open load will be more than adequate for a camshaft with 0.500" valve lift. This is a street/strip engine that is computer controlled in a '91 S10 Blazer with a 700R4 transmission and a 3.42 Power Trax No-Slip differential. The main clearance issues were with the rocker cover center bolt supports, the poly-locks, and the pushrod cup of the rocker arms.

However, I certainly would have used 7/16" studs, poly-locks and Pro Magnum rockers if the 2" valve covers would have permitted it, using 310 lb. valve springs. A camshaft with 0.500" is the maximum lift I could have used with the 4.3L V6 engine and remain compuuter compatible and still use stock roller lifter "dog-bones" (tie-bars). Eliminating the dog-bones and using a retro-fit camshaft with higher valve lift and taller high load valve springs would have required custom facricated valve covers.

Last edited by MouseFink; 08-20-2010 at 09:01 AM.
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Old 08-20-2010, 09:09 AM
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Studs and rockers

Quote:
Originally Posted by v8hed
Thanks guys, I'll return the 3/8 studs and go for 7/16. The reasoning behind taking the 3/8 studs in the first place was that 3/8 rockers are a little easier to come by and I didn't really stop to think about the amount of lift I'm going to be running.

I'm going to be using Comp 986-16 dual springs (280lbs open pressure / 132lbs seat pressure). These are the springs recommended by Comp Cams for this cam.

Oh, the other 1% is in case I goto a Run What Ya Brung event down at my local track

Usually,in the past it is a good policy to follow the cam manufacturer's recomendations. However, I believe the reason Comp Cams are reluctant to recomend 350 lb. open pressure at 0.560" valve lift is because they are trying to sell more camshafts for street driven engines that use no-lead pump gas. Owners of street driven engines are their "bread-and-butter" customers.

You will have to purchase or exchange the rocker arms if the one you have are 3/8" rocker studs. If you use 7/16" rocker studs, the rocker arms and poly-locks must be for 7/16" rocker studs.

BTW, Comp Cams 986-16 valve springs will have initial 312 lb. open load at 0.560" valve lift. be advised, a seat load of 132 lb. is too much for no-lead pump gas, especially if the car is driven for extended periods on the highway. With that much seat load, you should install stellite exhaust valve seat inserts or use expensive high lead racing fuel. Do not exceed 125 lb. valve spring seat load on a street driven engine using no-lead pump gas. With 9.7:1 compression ratio, I use Chevron 93 octane premium pump gas with Techron. Techron works! It keeps the fuel system clean, lubricates the in-tank fuel pump and that is essential with throttle body fuel injection. Techron is the only fuel additive that I have used that actually does what it says it does. I don't use the Techron additive in the plastic bottles but use Chevron pump gas with Techron. A carburated engine does not need additives such as Techron.

Last edited by MouseFink; 08-20-2010 at 09:38 AM.
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Old 08-20-2010, 09:11 AM
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Quote:
Originally Posted by MouseFink
You will have to purchase or exchange the rocker arms if the one you have are 3/8" rocker studs. If you use 7/16" rocker studs, the rocker arms and poly-locks must be for 7/16" rocker studs.
Yep, I haven't purchased the rockers yet
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Old 08-20-2010, 02:14 PM
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Guide plates?

If you are using pushrod guide plates, be sure the studs you purchase have a guide plate boss. Most screw-in stud kits have studs with a pushrod guide plate boss, but some don't. The rocker studs I used do not have a pushrod guide plate boss, meaning they are perfectly flat under the jam nut where it seats on the head. The guide boss is a little step under the jam nut that fits into the stud hole in the guide plates and it suposedly aligns the center line of the pushrod slot in the guide plate with the center line of the rocker stud. If you are using guide plates, the rocker arms cannot be self-aligning. You cannot use pushrod guide plates and self-aligning rocker arms because only a slight misalignment can cause the pushrod to rattle and bind against the guide plates as the rocker arm goes through its motion.

If you are not using guide plates, be sure to purchase rocker arms that are self-aligning. They have rails that the valve tip fits between. I used self-aligning rocker arms with my screw-in rocker studs because the cast pushrod holes in my 1991 V6 cylinder heads do not line up well with guide plate pushrod slots.
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