If I were to replace the 76cc iron heads on my Goodwtench 350 with some 64cc Edelbrock aluminum heads, would that be an effective way to bump up the compression ratio in addition to increasing flow without messing with the bottom-end?...

 

Yes it will do both. You will probably have to get different length push rods with the aluminum heads. You also need to make sure the valves will clear the pistons.

 

It's not likely that you'll have problems with either of those things.

Yes you can definitely do that. The compression bump will be significant; assuming that you now have a std bore 350, 76cc heads, the usual .025" of deck clearance, .041" gaskets, and 12cc dish, the CR is right at 8:1. Changing to 64cc chambers will raise it to almost exactly 9. So yeah, YYYYYUUUUUUUUUUJJJJJJJJJE.

However, since aluminum heads conduct heat (energy) out of the chamber so much faster than iron ones, you pretty much HAVE TO raise the CR when going from Fe to Al, to keep the power output the same, all else being equal. Half a point is the usual rule of thumb so you'll be gaining somewhat more than the break-even. The Edelbrock heads are far from the "most power" choice, butt they're an excellent street head. Thing is, you can get a good bit more power out of many others than those, at roughly the same price. It's your call though.

 

I was not impressed with the machining on my Edelbrock Performer RPM heads. I would not buy them again.

 

Myth. Been disproven by engine masters (and others) at least once if not several times. Power stays the same w/the same head port, chamber, compression ratio....AL vs. Cast Iron.


W/in 1 hp and +5 lb-ft. with the AL head. So....IDK about that old tale.

 

I was just using Edelbrock as an example. Obviously I don't want to spend a ton of money on a trick set of heads just to put on a Goodwrench 350, so they would have to be in the general price range of the Edelbrocks.
I was just thinking about better flow and a bit more compression ratio.
Thanks for all the replies...

 

It's a solid plan. Plus you will get the weight savings.

 

Do you have the actual specs for a Goodwrench 350? I think there may have been some values assumed but to dial it in further, as in a cam spec, operating range, not to mention what you want out of it, details are nice.








Just about a full point as suggested.
Any street orientated SBC, especially one with aluminium heads, would give give a greater kick in the pants on the other side of 10:1. That's my personal opinion although I've learned that, tuning aside, compression is your friend. But as with friends, there's a limit.

 

Does a Goodwrench engine come with .041" head gaskets?
That would yield a .066" quench.

 

That I can't answer but quite possibly.
Throw in an .026" head gasket and you're at 9.26 with .051" quench.
If there's confidence that the deck surface is sound then there's always a shim gasket at .015 or so. Now it's 9.49 and .040" piston to head.

 

Definitely worth checking the geometry after the heads and gaskets are installed. No sense killing a set of guides by skipping a simple step.

 

According to the "specs", compression is 8.4:1. Head gasket thickness is supposedly .026" to .028" x 4.100".
Mine does not have the stock cam.
Why would a different length pushrod be necessary? ...

 

Any time you change some aspect of the valve train it will affect the relationship between the rocker arm and valve tip.
Let's say the geometry is presently good. That is the length of the pushrod places the rocker arm at the correct angle relative to the valve stem.
At the risk of sounding elementary, think of it as lever with the rocker arm as the beam and the stud as the fulcrum (which it is). The pushrod sets the angle of the rocker arm when on the base circle of the cam. If the geometry is properly set, the rocker arm will be at 90° to the valve stem when the valve is opened to mid-lift.
If a different set of heads has an overall shorter height, then to maintain that 90° angle, a shorter pushrod is required.
The same conditions might come into play if a different cam with a smaller base circle, rocker arms, block decking and or head milling have become part of the picture.
I've posted Jim Miller's Mid-lift valve train geometry paper before. I'll post it here should you be interested in what's going on. My explanation may have been a little clunky.

 

The engine has dished pistons. Therefore, has no "quench" to begin with. Not really an issue.

Not sure what gaskets those motors come with. I just used the Fel-Pro thickness (.041") to calculate with.

I've seen that Jim Miller write-up before, and the toy that goes with it. I don't agree. In principle, he's exactly right; butt details in how rockers are made, render his plastic toy a gross oversimplification. In theory, theory and practice may be the same, but in practice, they're not. First off, not all rockers have their 3 active points - pivot, push rod cup, and tip - in the exact same geometry. Imagine looking at a rocker from the side, and those 3 points being a triangle. If for example a given rocker has its push rod cup located higher or lower with respect to the pivot, or the pivot higher or lower with respect to the line connecting the other 2, then the triangle will be a different shape, and his toy won't match it, and it will "predict" the wrong push rod length.

Regardless, since the SBC has adjustable rockers, the stock push rod length usually works fine on almost any heads, with a near-stock cam. Since the rocker is adjustable, the height of the valve stem tip is the only significant variable in the system, under that condition. As long as the rockers that are used have close to the same geometry as stock per the above, then nothing else needs to change to retain the stock geometry. With a "bigger" cam all that goes out the window of course. Butt I don't think Jim Miller's toy is ever a dependable answer for what the push rod length needs to be.

 

You may have "seen" his paper but it would appear you haven't read it.
There in NO plastic toy. ALL of the geometry is calculated via measurements.
With respect to SBC's, and SBC's only, we can only deal with one side of the "triangle". That being the side with the pushrod. The only way to effect a change on the valve side is via different rocker arms.
The measurement method, and no fancy springs are needed nor does the rocker need to be tightened down, works for any cam and any rocker arm. The full roller rocker is easier to work because the axis' are well defined. It's a little different with a shoe type rocker.
The perfect SBC arrangement is a shaft type rocker system. Then both sides of the rocker arm are included in the geometry. But that's another matter altogether.

Stock cams? Who cares? The O.P. doesn't have one apparently.

No plastic toy has ever entered the conversation.

 

Yes I've READ his paper. Yes I've SEEN the little plastic toy based on it; https://www.summitracing.com/parts/pro-66789 for example. Yes I've SEEN rockers that are different in ways that render that whole idea moot. I think that while it sounds and looks GREAT on paper, out here in meatspace, it's an oversimplification and NOT a true "solution".

Now if you measure the rockers you ACTUALLY HAVE, and can set them up like he describes, then you can get pretty close to the "ideal" push rod length. Butt as far as any kind of "universal" anything, not so much.

AFAIK the OP has a Goodwrench 350, that still has the cam in it that came in it; although I could be mistaken about it still having the original cam. It would probably be a 929 if so.

 

For the life of me, I can't find any reference to any kind of gizmo used as a universal checker.
I'm aware of the toy you're referring to and agree it's junk butt, it's not referenced in the write-up anywhere that I could find.
The only tools discussed are a straight edge and means of measuring distances such as a machinists ruler. An adjustable pushrod as well.

Not much more to say on it.

 

It has a mild Comp cam with .440" lift...

 

Sorry about that, for some reason I thought it still had the OE one.

 

One variable in the geometry is the cams base circle. I/we have no way of knowing what they might be other than measuring or finding someone that has.
Even a custom cam such as my own, it was explained to me by the cam grinder/designer that any given base circle he comes up with is determined by the maximum lobe lift and what will fit into the cam tunnel. So it that regard, each may be unique. Between the OEM and Comp? I couldn't say.
Would it be much and would it have much impact? I think it was mentioned that at this level as stock or nearly so, there's probably not much that would go sideways.
But, if you drag a new set of heads into it, things get complicated.
Take two Edelbrock heads (as an example). When they offer two chamber sizes, how is that achieved? Two different castings? Maybe but it seems unlikely. The easiest thing ( in my mind) would be to take the 76 cc head and mill it to arrive at 64 cc. Generally (a dangerous word) it takes .006" for 1 cc.
12 x .006" = .072". That's within the .050" pushrod length selection. Maybe the base circle difference adds to that? You can see where it's going. How about the difference between the OEM and the aftermarket heads in general?
All that said, it's not difficult to measure.
Or you just have at it and see what the outcome is after a few thousand miles.
I'd done an extremely poor job when I first set up my Vortec heads with an aftermarket cam and rockers. I mistakenly went for a centred contact patch on the valve tip rather than trying to achieve the narrowest contact sweep. The saving grace was that the Vortecs had cast iron guides. My machinist said those suckers last forever.
But when I kept all of the above components and went to an aftermarket Vortec with bronze guides, I wiped them out in short order having incorrectly setting up the geometry in the first place.
I learned the hard way.

 

So bottom line: Check pushrod length...

 

I would.

 

If the new heads are using guideplates, then you will need hardened pushrods anyways (assuming that yours are OE currently).

 

Yeah, I already knew I would need to get hardened pushrods...

 

I'm running a .066 quench with fel pro 501 sd's on a stock deck with 55cc zz4 113 aluminum angle plug heads at 9.8:1 and I don't have a lick of detonation or preignition on 89 octane gas with 32 degrees of total timing, haven't put 87 or more timing in it yet. I have TBI style dished pistons.


I think you can run whatever you want for a head gasket and be fine so long as the heads are aluminum

 

I think more accurately that at 9.8:1 and aluminum heads, you've little concern for detonation regardless of the head gasket used. You're correct in that regard.
That said, there's abundant evidence to support that a tighter quench will increase combustion efficiency as there's little lost to end gases not being consumed. The increased squish promotes chamber turbulence. All beneficial.
Although not to your point, now carry that further and bump the aluminum head compression to 11:1 or better, then the risk of detonation goes up and a tighter quench will be your ally. This is of course cam dependent too as well as piston crown shape.

 

I have a GM Goodwrench 350 in my 87 Monte Carlo SS with TPI conversion. The Goodwrench 350 had 76cc iron cyl heads. I removed the heads and calculated the compression ratio. I got 7.9/1 was supposed to be 8.5/1. I read in one of the car magazines that this is normal GM assembly line tolerances. I purchased a set of Trick Flow Super 23 175cc Alum heads. They have a 56cc combustion chamber. Trick Flow said that these heads would be best for TPI. Compression ratio calculated to 9.3/1 with a .023" thick head gasket. I also installed Trick Flow full roller rockers, I checked pushrod length and ordered the appropriate length hardened pushrods.

My cam is Comp 212/212, .444"/.444" lift and 112 degree lobe separation. Wish I had got a bigger cam.

Fred

 

I apreciate that information...

 

The GM Goodwrench motor I had bought is Part #10067353. That was several years ago.
If I knew then what I know now, I would have bought a Vortec long block.

Fred

 

The only reason I got the one I have is the price was super excellent. A guy bought it for his '63 Nova. It wasn't in that car very long before he decided to sell it and get a more powerful engine.
I needed an engine, and figured it's more powerful than the 305 that was available in '83, so still an improvement...

 

@sofakingdom you were right about that 66789 tool. It's useless. Perhaps it's meant for a bone stock cam but for the lingenfelter 74211, definitely not. I've been chasing a cold tick for quite some time. I used that plastic thing and it told me the correct length was 7.200. That's the tool flat on the valve tip and pushrod tip. That's also the stock pushrod length. I have flotek aluminum heads and scorpion 1.6 rockers so something wasn't making sense. Anyway this past week I took it apart... again. This time I did the mid lift method while using EOIC. That was an eye opener. Using the mid lift check I measured a pushrod length of 7.375. using the 66789 with that length, the valve side sits quite a bit higher than the valve tip. So that tool is very misleading. I believe I've solved the tick. Now it sounds like a sewing machine on the cold start instead of a jack hammer.

 

The midlift method is king in my books. And while I've never tried that plastic tool I knew enough about it to not bother trying.
All sorts of weird things can creep into the need for a different length pushrod. And sometimes it can't solved with just that. My RHS heads have .100" longer than stock valves. As such when getting the midlift geometry correct the longer pushrod was placing the roller tip right near the edge of the valve tip. Too close for my comfort level. The fix in this case was a roller rocker with a .050" backset trunnion. With the hole for the stud off-center towards the exhaust side, it drew the valve tip contact back. Result was a narrow sweep and practically dead centre.

 

That tool told me that my 7.200 pushrods were right. I think that was stock length to begin with, I had a rocker sweep over the tip of more than .100 wide. But the tool "indicated" I had the correct length. Live and learn. Now I'm running 7.375. I just wasn't sure if I was supposed to add the preload or an extra .020 to that using the mid lift method. I'm running around .035 preload on Hilift-Johnson lifters.

 

Live and learn indeed. And sometimes learning can be expensive. Expensive as in needing new guides and yet another valve job. The bronze guides don't appear to have the same durability as the OEM Vortec cast iron versions. That may seem like a Captain Obvious statement but those cast guides will mask a poorly setup valvetrain for many many miles. The bronze guides, in my experiences, are definitely less forgiving.