462624 Heads - Stick with them, or move on?
I'm in the process of restoring a 1978 Pace Car. It will not be a show car, but rather a nice clean example that I can enjoy driving and taking to local events. I have the motor and transmission out of the car, as all of the seals need replacing. I noticed that one of the heads has a crack in it (a small crack in the rocker stud mounting boss). [Full disclosure - I had to replace that rocker stud because the original one had thread issues. So I may have cracked it myself.] In any case, I was looking to pick up another head or two but I have found countless examples on line where people have warned about these heads being prone to cracking. Many say "don't spend a dime on a 462624 head". So my question is, does anyone have any experience (good or bad) with 462624 heads, and what would you recommend? Is there another route I should be taking, or should I press on with a 462624 replacement? Thank you in advance for any help.
-
-
Re: 462624 Heads - Stick with them, or move on?
Mike
Welcome to NCRS Tech Board.
I've read/heard similar comments on these heads. I believe they were made using "light weight cast iron" as part GM's weight reduction program. FWIW, when tearing down my 1980, I found one head dated about 3 years after engine build date. (Other head was consistent with engine build).
Seems like these maybe are better as boat anchors. Have not decided just what to do with my original motor, right now it has a GM Goodwrench holding the chassis down. Lots of options, Vortec, aftermarket, GM Performance, etc.... Engine builder I talked with preferred to build up a head rather than use a prestuffed "ready to bolt-on" head. Some "ready to bolt-on" heads are not that ready.
DaveJudging Chairman Mid-Way USA (Kansas) Chapter -
Re: 462624 Heads - Stick with them, or move on?
Thanks Dave. Just joined NCRS this past year. Seems like a great organization. I'll continue to research the 462624 situation. What you mentioned makes sense. As we know the mid seventies wasn't exactly the heyday of Corvette performance and engineering.
MikeComment
-
Re: 462624 Heads - Stick with them, or move on?
Mike
it's great to have you on board with us.
DonComment
-
Re: 462624 Heads - Stick with them, or move on?
Mike------
I believe the main cracking problem with these heads is the result of the fact they have induction hardened exhaust valve seats. This process provides hardened valve seats without the need for inserts. But, at the same time, sets up prime conditions for cracking. This is not unique to the 462624 heads, though. It's shared by most of the 1975+ cast iron heads.
If you are not concerned about originality, I'd convert to good aftermarket aluminum heads. Edelbrock and AFR make excellent heads.In Appreciation of John HinckleyComment
-
Re: 462624 Heads - Stick with them, or move on?
I like Joe's suggestions but would add the option of the factory Vortec heads. Less money than the aftermarket heads but they also requires a matching intake.
Flow, swirl and power all are part of the better design of the Votec heads.Comment
-
Judging Chairman Mid-Way USA (Kansas) ChapterComment
-
Re: 462624 Heads - Stick with them, or move on?
Dave------
Some Vortec cylinder heads are dual drilled and can be used with original manifolds. GM #19331470 (complete) and GM #25534351 (bare) are some of these.
However, original 462624 heads have 75 cc combustion chamber while the above have 65 cc combustion chambers. So, a compression increase will result from using these heads. Most aftermarket aluminum heads also have approximately 65 cc combustion chambers.
In addition, I believe the Vortec heads and many aftermarket aluminum do not have heat cross-over passages. It may be possible to open up such passages if desired, though.In Appreciation of John HinckleyComment
-
Re: 462624 Heads - Stick with them, or move on?
Thanks Don. Bought my first Corvette (a 68 convertible) back in 1979. Figured it was about time.
Thanks for the note. Glad to be here.
- MikeComment
-
Re: 462624 Heads - Stick with them, or move on?
Joe, Richard, Dave, - Thanks for the info. I have been looking at some of the aftermarket heads at Jegs and others. I will look into the Vortec heads as well. Thanks for the info on the intake and multi-drilled heads. I definitely don't want an L88 style hood on my Pace car. Is the intake the only concern when switching out heads? Is the change in compression a concern? Is the stock cam okay? I'm a retired engineer, so I'm pretty confident in my ability to take things apart and put them back together properly. But not so confident in my knowledge when it comes to modifications from original. Thanks again. Really appreciate you taking time out of your day to help me out.Comment
-
Re: 462624 Heads - Stick with them, or move on?
Adding a question rather than an answer: What about aluminum vs iron? Aluminum heads are lighter but aren't they more prone to warping when hot and head gasket leaks?Mark Edmondson
Dallas, Texas
Texas Chapter
1970 Coupe, Donnybrooke Green, Light Saddle LS5 M20 A31 C60 G81 N37 N40 UA6 U79
1993 Coupe, 40th Anniversary, 6-speed, PEG 1, FX3, CD, Bronze TopComment
-
Re: 462624 Heads - Stick with them, or move on?
Mike------
The intake manifold is, basically, the only concern. However, some of the aftermarket heads have raised exhaust ports. Stock exhaust manifolds will usually work with these but an adapter may be necessary for exhaust pipe installation. I would stay away from these "raiser runner" heads, though. There are plenty of choices in standard exhaust port locations.
As far as compression ratio goes, most, if not all, of the aftermarket heads will have combustion chamber volumes considerably less than your stock 75 cc. So, there will be an increase in compression which you'll need to calculate based on the combustion chamber volume of the heads you use. If it's too high (above about 10:1), you can reduce it by using thicker head gaskets which are easily available. Some increase from your stock compression ratio may be beneficial. With 91-93 octane pump gas you should be able to go higher than your stock compression ratio of 8.5:1 if an L-48 or 9:1 if an L-82.
If you purchase complete cylinder heads, it's basically a bolt on experience. You can transfer your rocker arms and pushrods but I would carefully inspect them for wear before re-using. If you purchase bare heads, then you will need to separately purchase valves, springs, valve caps (retainers), and valve seals. Then, you'll need to have a machine shop do a valve job to seat the valves properly. Complete heads can be the way to go with one caveat: you don't want valve spring pressures, open and closed, much different from stock. Often times, complete heads will come with very high rate springs.
As far as cam goes, you don't need to change it. Your stock cam, whether L-48 or L-82, are excellent street cams.In Appreciation of John HinckleyComment
-
Re: 462624 Heads - Stick with them, or move on?
Mark------
I've never heard of a problem. Cast iron block engines with aluminum heads have been used in PRODUCTION for years for all sorts of applications. Some are even still made today although most engines have now gone to all aluminum construction.In Appreciation of John HinckleyComment
-
Re: 462624 Heads - Stick with them, or move on?
Awesome Joe, thank you so much.
MikeComment
-
Re: 462624 Heads - Stick with them, or move on?
Tell us which engine you have. L48 or L82? Manual or automatic? Do you really want to keep the low compression and lazy spark advance map so you can run unleaded regular or do you want five to ten percent more torque power across the range and ten percent better fuel economy for only about 5 per more fuel cost for modern premium?
Do you plan to have your car judged?
Do you have to have your car periodically emission tested?
Do you have a chassis service manual and chassis overhaul manual for '78?
There are other issues to consider, and the above are starters.
Web search the following for more food for thought:
"a tale of two camshafts"
"tuning vintage corvette engines for maximum performance and fuel economy"
The quotes will cause the search engine to look for the exact phase, so the articles should be at the top of the list.
DukeComment
Comment