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Discussion Starter · #1 · (Edited)
I have been frustrated by valve train noise for 10 years on my 350... I changed cam & lifters, rockers, & pushrods and adjusted and re-adjusted valves about 10 times.... Inevitably I end up with one randomly tapping again before too long. I have adjusted them a full turn past zero lash... but the noise keeps coming back. The cams have been relatively mild. I have had a Comp XE268 cam in it but switched to a Howards Street Force 2 hoping it would be easier on the valve train and be quieter....

The heads I have on the engine have 76cc combustion chambers and PRESS-IN STUDS. RE: pushrod length, I had checked with both Comp and Howards if stock length pushrods were ok. In both cases they said stock length was fine.

Other than a surging issue under minimal load that I am working through, engine runs strong...

QUESTIONS:
1) Is stock pushrod length okay? Cam is 455/465 lift Rockers and push rods are stock and only a few yrs old...

2) I'm wondering if the Z28 valve springs I have (good for.55 lift) are pulling the stock press-in rocker studs out little by little and that's why the rockers keep loosening up. My heads are reworked heads--one cast in 73 and the other on 75...with what I assume are original press-in studs. Any thoughts on this?

3) I'm considering these heads from Summit that are similar to what I've been using for 10 yrs except they have screw-in studs that can't pull out and 72CC combustion chambers slightly smaller than my 76cc chambers. My current static compression ratio is 9.1:1 with the 76cc chambers. Any idea how much the slightly smaller chambers would affect the compression ratio? Still want it to run good on 91 or 93 octane..

Summit Racing SUM-152123 Summit Racing® Cast Iron Cylinder Heads for Small Chevy | Summit Racing
 

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I would do aluminum heads too, but not sure I would jump to a 62 cc chamber depending on what piston you have and if the block has been decked. You always have some adjustability via head gasket thickness. There is an almost infinite variety of head gasket thicknesses availability for a small block chevy, but you want to be careful to maintain a good quench area. I would aim for 10:1 compression with an aluminum head. The 72cc heads are a good choice if weight is not a concern. Some more info would be helpful. How heavy is your car, trans, rear gear ratio, tire size, cam, etc.. All these things play into how much compression you can comfortably get away with.
 

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I have been frustrated by valve train noise for 10 years on my 350... I changed cam & lifters, rockers, & pushrods and adjusted and re-adjusted valves about 10 times.... Inevitably I end up with one randomly tapping again before too long. I have adjusted them a full turn past zero lash... but the noise keeps coming back. The cams have been relatively mild. I have had a Comp XE268 cam in it but switched to a Howards Street Force 2 hoping it would be easier on the valve train and be quieter....

The heads I have on the engine have 76cc combustion chambers and PRESS-IN STUDS. RE: pushrod length, I had checked with both Comp and Howards if stock length pushrods were ok. In both cases they said stock length was fine.

Other than a surging issue under minimal load that I am working through, engine runs strong...

QUESTIONS:
1) Is stock pushrod length okay? Cam is 455/465 lift Rockers and push rods are stock and only a few yrs old...

2) I'm wondering if the Z28 valve springs I have (good for.55 lift) are pulling the stock press-in rocker studs out little by little and that's why the rockers keep loosening up. My heads are reworked heads--one cast in 73 and the other on 75...with what I assume are original press-in studs. Any thoughts on this?

3) I'm considering these heads from Summit that are similar to what I've been using for 10 yrs except they have screw-in studs that can't pull out and 72CC combustion chambers slightly smaller than my 76cc chambers. My current static compression ratio is 9.1:1 with the 76cc chambers. Any idea how much the slightly smaller chambers would affect the compression ratio? Still want it to run good on 91 or 93 octane..

Summit Racing SUM-152123 Summit Racing® Cast Iron Cylinder Heads for Small Chevy | Summit Racing
1: Pushrod length is a combination of things, but if your heads and block haven't been heavily machined/milled, you're using a hydraulic flat tappet cam, and you're using stock style, stamped rocker arms... you're probably okay. I would probably check to be sure.
2: "Z28" valve springs don't tell us everything. You need to know what the cam wants for seat pressure and open pressure, bind height, and retainer clearance as well. At a quick glance, most "Z28" style springs are 125lbs closed, 325lbs open. Comp Cams suggests the 981-16 valve springs to use with that cam, which are a 370lbs open pressure; you may be under-sprung for the cam alone. Considering most pressed-in studs can pull out at stock seat pressures, it wouldn't surprise me if you're starting to pull the studs out. For peace of mind, I wouldn't stick the 981-16 springs in ANY head without doing screw-in rocker studs.
3: Without knowing your deck height, how far the pistons are in the hole, what the volume is of the pistons (dish, eyebrow cuts, dome, etc.) and how thick your head gasket is, it's really hard to determine your static compression ratio. If you wanted to know what your dynamic compression ratio is (which is even more important in my mind), then all of those things come into play, on top of cam timing events as well.

Personally, if I were you, I wouldn't waste the money on iron heads if you're going this deep. You can pick up a set of really good aluminum heads for a few bucks more, and you'll have more bandwidth for avoiding knock, while having a motor that runs harder. Take the motor apart, measure everything methodically, and make a decision from there. We're here to help.
 

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Discussion Starter · #6 ·
Here is more info on my engine/car. I am pleased with the performance (although more power is always nice). Again my main issue is the rocker noise that keeps returning. Also, When I adjust valves, with engine off with proper procedure, the nuts are at different depths on the studs. Should this be?

Current Cam Installed October 2017

Howard CL-112571-12 Street Force 2 Hydraulic Flat Tappet

RPM Range 1200-5500

Duration @050 in lift Intake 215 Exhaust 225

Adv Duration Intake 269 Exhaust 279

Lift Intake .455 Exhaust .465

Lobe separation 112 centerline 108

IVO 26.5 degrees IVC 62.5 degrees

EVO 75.5 degrees EVC 23.5 degrees

ESTIMATED HP = [email protected] RPM

ESTIMATED TQ = 387 @ 4000RPM

Block

The short block is 78 L-82 out of a Corvette . It had been rebuilt by someone who didn’t know enough about what they were doing… very dirty inside (not metal) Pistons were on rods backwards so all valves had hit the pistons (see pictures at bottom). So other than some minimal milling of the heads, I don’t believe block was decked. Block is stock bore #3970010 4 bolt main. Factory pistons are actually forged TRW with single valve relief. With 76cc chambered heads and these pistons compression ratio rated at 9.1:1 . I used Fel Pro head gaskets either .037 or .039 (can’t remember).

Heads

#3932454 Heads used on 69-79 350 heavy duty trucks with 350. One was cast in December 1973 and the other in December 1975.They have 76cc chambers and originally came with 1.72 intakes and 1.50 exhaust valves but reworked to allow 2.02 intake and 1.60 exhaust valves; Pocket Ported; milled to ensure straightness; New stainless steel swirl polished valves; New umbrella valve seals; New hardened exhaust seats; Hardened valve keepers; New .550 lift valve springs; and bronze valve guides.

With each cam, I had checked with both Comp and Howards about my valve springs and they said the spring rates were fine for these cams. Don’t remember (probably wrote it down somewhere & can't find) what the readings were but I did verify by bringing one to machine shop to have tested.

Rockers are Summit stamped steel stock style with Summit hardened pushrods
Also did a compression test 4 yrs ago...All cylinders between 174 and 183...

Gearing…

Tremec 3650 5 speed 1st 3.38 2nd2.00 3rd 1.32 4th 1.00 5th .62

Rear 3.73

Rear Tires 27”

Car weighs about 3400# without me in it and a full tank of gas.

421604


421605
 

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If you haven't put screw in studs yet , I think you are pulling the pressed in ones thus your adjustment is loseining
 

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If you haven't put screw in studs yet , I think you are pulling the pressed in ones thus your adjustment is loseining
I agree with your conclusion 100% I would just machine the heads for screw-in studs, as I recall I bought the tool to do it (still have it) from Summit Racing or 1 of those type of places years ago for that exact issue.
 

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With the rocker nuts at different locations on the studs, I'd strongly suspect pulling studs or a cam going out slowly. Given that it's happened with two different cams, my guess leans towards the studs. I'd pay a few bucks for a nice set of heads and move on!

Kev
 

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Discussion Starter · #10 ·
With the rocker nuts at different locations on the studs, I'd strongly suspect pulling studs or a cam going out slowly. Given that it's happened with two different cams, my guess leans towards the studs. I'd pay a few bucks for a nice set of heads and move on!

Kev
I also forgot to mention that the original L-82 heads had screw in studs... I did not re-use them because all the valves had hit the pistons and condition was unknown--plus the original 624 heads were said to be crack-prone. I doubt the original valve springs were stiffer than what I have and the cam was a little milder with less lift... I wish I had done screw in studs before I originally put engine together...
 

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Discussion Starter · #11 ·
I have decided to go with the Summit cast iron heads. They are on order...should be available about a month from now.
My current heads have 76cc combustion chambers and have been milled slightly to assure straightness and using .039" thick Fel Pro gaskets.
The Summit heads are new castings but have 72cc combustion chambers. Would there be any problem using the .039" gaskets?
 

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I try to avoid Summit Racing when it comes to heads. I had a bad experience with them a few years ago back when they still had the "Summit Engine Shop". I bought a pair of cast iron Dart heads from them that were CNC port-matched backwards. In other words some numbnut there machined the ports as-if the intake gasket was upside down. Subsequently it created such a huge mismatch between the heads and the intake runners that they were unusable. When I approached Summit with the problem they told me I was SOL and screwed me bigtime.

Then they went on to say due to so many customer complaints they were shutting down the Summit Engine Shop permanently. Total incompetence. Probably for the best but I was still out over $1,000 and was mad as hell.
 

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You need to know how far the piston is down in the cylinder and the volume of the piston dish to be able to calculate compression ratio. Fortunately there are many different head gaskets available so you can fine tune compression.
 

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Discussion Starter · #14 ·
As far as I know, my stock bore block hasn't been decked. Not sure about how far below deck the piston is but I've read stock L-82 was .025 below deck height The piston has one big trough relief with 3.5cc volume. With original 76cc combustion chamber heads and .040 head gaskets, the compression ratio was rated at 9.0:1.

I'm guessing by what I've read (here & other places) that with 72cc combustion chambers (like Summit heads I'm getting) and .039 head gaskets I should have 9.6:1 compression ratio. The Summit heads have smaller combustion chamber (72 VS 76cc) I am just wondering if these heads and .039 gaskets might allow valves to hit pistons... I'm thinking "no problem" but just asking for opinions on that.

Maybe this is a question I should be asking Summit. Anyway, I appreciate any input.
 

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I'm guessing by what I've read (here & other places) that with 72cc combustion chambers (like Summit heads I'm getting) and .039 head gaskets I should have 9.6:1 compression ratio. The Summit heads have smaller combustion chamber (72 VS 76cc) I am just wondering if these heads and .039 gaskets might allow valves to hit pistons... I'm thinking "no problem" but just asking for opinions on that.
The Summit head is made by Dart and is the same as the Dart Iron Eagle S/S Vortec.....just with no Dart logo.
The smaller chamber is from a better design and shape, not from flat milling a larger chamber head down to smaller size....so the smaller chamber has no effect on valve-to-piston clearance.

With that said, every non-stock build should have valve-to-piston clearance checked, but unless you are above 245°@.050" duration it typically isn't a problem with those pistons....in fact, chamber volume would be last on the list of things that might effect V-to-P clearance, and a very distant last at that.....typically take a ral heavy milling or angle milling to get that to be a problem.
 

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Discussion Starter · #16 ·
Thanks Eric! That answers my question. I didn't think it would be a problem but thought it was worth asking. Thanks for your help and everyone else's input. I will report back when I get further. I will be able to begin as soon as I get the heads and header gaskets which will come in early October. I'm guessing the new heads will require a different combo tuning-wise because of the different chamber design and and slightly higher compression. Below are pictures of my current head and the Summit head...

Current Head


Automotive tire Automotive exterior Automotive design Bicycle part Hood


Summit Head

Rectangle Line Auto part Font Audio equipment
 

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There is a .026" thick composite gasket available if you want to tighten up your quench a bit more than the .039" will have.
Mahle/Clevite Original/Victor-Rienz #5746, it's a stainless core graphite faced gasket, works really well even with aluminum heads. .026" x 4.100" bore
Mahle Original, Head Gasket, Chev SB, 4.100" Bore, .026" Compressed, Each - Competition Products

Are you sure about those compression ratio calculations?? Reason I ask is when I run all your numbers through the calcs it comes up to barely 9.0:1 WITH the new 72 cc head and .039" gasket.....3.5cc valve relief, piston at stock deck height of .025" down, 4.166" gasket bore(Fel-Pro)....9.02:1 to be exact.
The Mahle head gasket would bring that up to 9.31:1.
GM originally used an .015" thick shim gasket to make 9.1:1.
 

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Discussion Starter · #18 ·
I was not aware that the factory L82 head gaskets were .015"... Actually, never thought about it! So mine currently has less than 9.1:1. So it would make sense to run a thinner gasket.

If I ran the .026 gasket and it made 9.3:1 I would probably need to run less advance timing. Actually I think I'm currently running too much advance (12degrees) as I noticed a little pinging the other day after about 20 miles on a very warm day while in OD. I believe the specs for a stock 1978 L82 was 8 degrees advanced... My cam is a little more than stock and I have long tube headers and no smog stuff.
 

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Discussion Starter · #19 ·
I was not aware that the factory L82 head gaskets were .015"... Actually, never thought about it! So mine currently has less than 9.1:1. So it would make sense to run a thinner gasket.

If I ran the .026 gasket and it made 9.3:1 I would probably need to run less advance timing. Actually I think I'm currently running too much advance (12degrees) as I noticed a little pinging the other day after about 20 miles on a very warm day while in OD. I believe the specs for a stock 1978 L82 was 8 degrees advanced... My cam is a little more than stock and I have long tube headers and no smog stuff.
 

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Discussion Starter · #20 ·
Actually I assumed the compression increase from the 78 L-48 (8.5:1) to the L-82 (9.1:1) was due to the different piston design. I didn't realize there was a thinner head gasket. I did some research and I've read the L-82 originally came with .018 gaskets... Eric may be right about .015 also.
But the .026 gaskets interest me.
Maybe this is a dumb question but should I have a detonation problem with the Summit cast iron cylinder heads and .026 gaskets or should I stick with the .039 gaskets bringing it to about 9.1:1??
 
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