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Better aftermarket heads for my 77 L48

stevolwevol

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I am considering replacing my stock heads to a good flowing aftermarket heads. I'm looking for better flow, and higher compression. I don't really know where to start, but I want to replace the cam also. This is for street use. Any suggestions would be appreciated.
 

Tom Bryant

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1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
Do you want to go to aluminum or stick with an iron head? To run premium pump gas about 9.5 with iron and 10.5 with aluminum would be your max cr. The Chevy Vortec iron head would be a good upgrade for a mild build. I think GM still sells them drilled for both a Vortec intake pattern and traditional small block pattern so you won't have to change intake manifolds.
 

stevolwevol

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I have considered Vortec heads. You say GM still sells them drilled for my intake? I didn't know that..I have a Edlebrock performer I put on last spring, and would like to keep it. So do I contact a dealership for that? Do you know what compression that would give me? I've heard that used vortec heads from days gone by are often cracked. What say you?
 

Tom Bryant

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Well they used to but I can't find them now. They must have discontinued them. They require a Vortec manifold and if you are going to use an upgraded head I'd switch to a Performer RPM Intake. You can always sell the old one. They also require center bolt valve covers. I'm not sure what piston you have in the L48 but I suspect it's a dished one. CR will depend on dish volume, deck height, head gasket volume and combustion chamber volume.

My combo in my '69 stepside is a .030 overbore, flat top pistons and ported smogger heads that have been milled some and cc'd to 73 cc chambers. The block isn't decked and I run a .018 shim head gasket so with the deck height figured in I arrive at just over 9.3:1 cr. That would be a premium fuel engine with a performance timing curve. Cam is a 214/224 @ .050, .442/.465 lift with a Turbo 400 and 3.73 rear gears.

We would need the dish volume of your pistons to roughly calculate the cr with the Vortec heads. I suspect you would be safe though. These Vortec heads came stock on the L31 engine used in light trucks in the late 90s and up a few years. I had a L31 in my '99 Tahoe and it was strong. Leased it for 3 years and never had a problem so I can't speak to the cracking thing. For less than another $200.00 you might consider the aluminum Edelbrock E-Street heads EDL-5073 (70cc) or EDL=5089 (64cc) in the Summit catalog. They are a little bigger in runner volume but not too big for a mild build. I'm pretty sure they use the standard Chevy intake and valve covers so you can use what you already have.

If you have flat top pistons I'd run the 70cc with a thicker composite head gasket or the 64cc with the dished pistons and in either case, the gasket Edelbrock recommends.

Tom
 

stevolwevol

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1977 light blue
Hey Tom, thanks for the info. I may look into the EDL 5073 heads from Summit. My guess is they will breath best, and give me better performance than vortecs anway. BTW, can you suggest a nice cam to complement the heads?
 

Tom Bryant

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If you are running a stock exhaust you want to stay mild with the cam. Looking at the charts Edelbrock shows the 2102 Cam as matched to your intake and the E-Street heads. Power increases up to 5500 rpm which they also list as the limit for the E-Street heads. Says major improvements in throttle response and torque from off idle to 5500 rpm. If you have dished pistons you will be in the 8'5 range with the 70 cc heads and might still be able to run regular. E85 would also work well.
 

stevolwevol

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I called Eckler's, they and the EDL 5073 heads you described for a little over 1000 dollars. They also had Promax heads for about $800. My compression would be about 9.3 for the more expensive heads, and I would be under 9:1 with the Promax heads. Ya get what you pay for. As far as my exhaust I have full length headers with "1 5/8 primary tubes. They should be fine for the upgrades I'm looking at doing. The tech told me; if I have too much cam, my vacuum will be too low operate the headlights etc. Now back in 1970 the L46, and the LT-1 put out 350 hp, and 370 hp. Both had vacuum powered headlights, and 2" diameter ram horn exhaust manifolds. Shouldn't I be able to put out that kind of power with my engine without making it less drivable?
 

Tom Bryant

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Well both of those engines had higher compression but you make a good point. You could go with a bigger cam than what we were talking about and still have enough vacuum. The Performer cam is matched to your heads and intake so it should be a nice package. Even better with the exhaust upgrades.

Tom
 
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Changing the cylinder heads is the single best bolt on upgrade you can do to an engine. While the standard 882 GM castings had the same port design as the old fuelie heads, they also got terrible 76cc combustion chambers. Then GM put them on top of dished pistons. To make matters worse, GM really never cared to zero deck the pistons. They were often .025 to .050" down in the hole. All of these issues combined to give the 70's era 350's terrible quench. The real compression could be closer to 7.5:1 than the advertised 8:1. This is also why you could run near 60 degrees of timing (initial, mechanical, and vacuum advance) without detonating. Even on crummy 87 octane pump gas.

There are a ton of great aftermarket heads out there now. Many are less $1000 now. Here at BluePrint, we have seen upwards of 65 to 70 hp increase using our heads over a factory casting. This is on a 350 with a fairly mild hydraulic flat tappet camshaft.

I would look at heads with smaller combustion chambers than the original 76cc heads to bump up the compression. This will also help increase horsepower. With a 64cc head, you would be closer to 9:1 compression. Also check out heads that have heart shaped combustion chamber designs similar to GM's Vortec heads. This design really helps increase quench with a dished piston.

There are many choices to look at for heads. Stay away from the bigger port designs, anything over 195cc intake runners, to keep port velocity up and the resultant increased torque. The bigger intake runner designs will make a near stock 350 pretty lazy in the lower rpm range.

For even more power, look at going to a bigger camshaft. If you don't want to go to a new higher stall converter, keep the duration measured @.050" below 230 degrees. Comp Cams Xtreme Energy line is a great start. They will produce good vacuum, for your brakes and headlights to function, but also increase cylinder pressure for better performance.
 

stevolwevol

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Messages
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1977 light blue
Yes, chambers are way too big. I do believe also the 882's can be prone to cracking, but not as bad as the 624 series that came a year later. It's 624 I believe, and they were very crack prone.
 
Joined
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Yes, chambers are way too big. I do believe also the 882's can be prone to cracking, but not as bad as the 624 series that came a year later. It's 624 I believe, and they were very crack prone.

Yes, those 882's are crack prone. We had to discontinue one of our crate engines that used those heads because we just couldn't get them not to fail during the build process.
 

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