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Chevy 454 Big Block, Mark IV, 7.4l - Rebuild and more Power.

The cooling issues that you’ve read about aren’t totally founded - cooling either aluminum or iron heads is the same.
Aluminum dissipates heat quicker but if the motor will overheat with iron heads it will do so with aluminum heads too.
Like said above, a proper cooling system is needed regardless of type of head.

Also, if your motor is actually from a mid-seventies Vette than it will have some of the better oval-port ever offered ( rectangular iron heads were last used in 1970 ) and will make great power with the right piston and roller cam.

Aftermarket aluminum heads are GREAT but if you want your budget to go as far as possible than don’t shy away from a good set of oval-port iron heads - they make power where a heavy truck needs it and can still obliterate a set of 40” tires at will ( assuming the correct parts are used ).

Earlier you mentioned that you would need to pull your motor to get the casting numbers off of the head - this is not accurate; all you need to do is take a valve cover off. Very easy to do.

Good luck with this engine build and be careful of everything you read on the internet - lots of misinformation out there.
Stick with truly knowledgeable data so you won’t waste time, effort and money.
 
The frame behind the steering box is prone to crack, it can happen to a mild or build truck.
I would soak in some knowledge here, a built rowdy big block will be fun on the street but might not be the best idling up a trail for hours at a time.
 
I just read back on your comments on what you read about the iron heads not performing and want to make certain that you understand which heads are which.

Factory iron heads come in three basic flavors:
Peanut-port - these are meant to mimic a diesel type powerband and are what a heavy tow rig needs. All low end power and absolutely no upper RPM power band.

Oval-port - these come in all sorts of combustion chamber sizes but if yours are 73~74 castings they should be the 049 or 781 castings and that is a very good thing!
These heads do everything well and have great potential with good power parts.

Rectangular-ports - these also come in several combustion chamber sizes and are meant for upper RPM ranges and NOT suitable for any form of towing or slow offraoading situations.
These heads make GREAT power but may not be what you need according to what you stated with what you want to do with your Blazer.

The aftermarket offers all sorts of options but that will take a nice chunk out of your budget.

Talk with FOLKENHEATH about your goals and he will set you up with the right combination of parts to make it all work.
 
RayzWorld said:
Well damn... let me try and answer
1. I want to change the heads with aluminum.
2.i want it to idle like it's about to die i want that classic vehicle that has power.
3.manifold I want a new one.
4. If I need bigger heads then I'll be totally fine with that.
5.EFI, no to the carburetor.
6.The torque converter i know nothing aabout and would like input into what I should get.
I guess what I'm trying to say is that if I need to replace everything but the block then I'm willing to go that route to accomplish the goal. I want a big cam and I read the compression should be high to achieve higher power gains.
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I really like your plan, it's essentially the BBC in my personal fun truck, new rotating assembly, aluminum heads and manifold, and EFI, although that won't be under 6K.

The guys here have a lot of sound advice, you can learn a lot from them.

Aluminum is better, you are correct, it's lighter (about 80 lbs for a pair of BBC heads) and it transfers heat faster, to the point you can run nearly a half a point more compression on pump fuel.

However, I don't recommend chinese heads. You can get away with a quality chinese crank and connecting rod forgings if you need on a mild build, preferably finish machined in the USA, but the heads I would stick with USA made. Brodix, Dart, Edelbrock, GM, AFR, etc. So I would rather see a set of refurbished GM iron heads than a set of chinese aluminum heads, just not peanut ports.

Here is what I recommend we upgrade in order of importance depending on your budget. This is slightly different since you are rebuilding the engine, but still similar as if you were just trying to get more power out of a current engine. For example, if you had a good engine, I wouldn't tear it apart to replace pistons or a stroker crank before I swapped the heads. The heads and cam are the most important part of the engine for making power, but the heads aren't always the most bang for the buck because of cost when rebuilding, it depends on what you have to start with.

1 - long tube headers
2 - intake manifold
3 - camshaft (hydraulic roller, along with valve springs if needed)
4 - pistons
5 - crank
6 - cylinder heads

With that said, if the heads need new valves, new guides, new seats, new springs, retainers and locks, and resurfaced, that can add up to quite a large expense where new heads aren't much more.

EFI is awesome, but it's not cheap. I specialize in EFI and can recommend what's best for you starting at a budget and working up to the absolute best, which most people don't need, usually somewhere in the middle.

The torque converter needs to match the cam, heads, CID, and pretty much everything else in the vehicle.

RayzWorld said:
Well I'd have to pull the engine out to see the casting numbers. The information I put together was from the front cast numbers. Which have told me the year and that it came from a 73-74 corvette.
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The casting number for the block is on the back left side, above hte trans bellhousing.

The casting numbers for the heads are under the valve covers.

No engine pulling needed, you might need a wire brush for the block casting number, hopefully not for the head castings.
 
Wes Harden said:
Here is the best place for K5 mods. If it's possible someone here has probably done it.
there are plenty of K5s with big blocks. K5 are not light race cars, yes the weight can add up, but new aluminum heads will be at least a 3rd of stated budget. Weight vs cost.
If your engine is truly an early 70s Vett engine and unmolested the heads will make 500hp easy. You may have an Ls6 or Ls7.
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I'll have to confirm as soon as I pull the engine, fingers crossed.
 
You dont need to pull the engine to see the numbers…
Taking the valve covers off will allow you to see the casting number (6 to 8 digits) and casting date on the heads.
On the bell housing flange on the rear of the engine drivers side, you will find a casting number, and on the passenger side a casting date letter and numbers. On the front of the engine a suffix number and letter combo which tells the application originally built for.

Look them up here…https://www.corvetteforum.com/forum...-4104940/lime_book_2018-48257239d1519196818dl

Location of block numbers….

A0280645-1590-4F5A-9EEC-68C96C5510A3.jpeg
 
As somebody that has run an 8.1 big block for quite some time, don’t stress on the weight if you have to run iron heads. My 8.1 is stock with the iron heads and giant cast aluminum intake and I’ve yet to have a problem with the frame that was caused by the weight. Keep in mind the same basic front frame section is pretty similar across the board from the 1/2 ton up to 1 ton that came with big blocks. The 6.2L diesel was no lightweight either.

You should use a ORD tubular engine cross member for a little extra strength and better oil pan clearance. The steering box brace and or plating should be mandatory for every square body build but the issue there is not engine weight induced at all.

Oh and by the way, even with a heavy big block up front I still have a tendency to wheelie on steep climbs off road. It might have more to do with the house on the back, but the weight of my 8.1 didn’t seem to hold the front end down as much as I thought it would.

Don’t stress on the weight. I’ll let the much smarter guys on the engine build combo continue but I wanted to toss that perspective in there.
 
ZooMad75 said:
As somebody that has run an 8.1 big block for quite some time, don’t stress on the weight if you have to run iron heads. My 8.1 is stock with the iron heads and giant cast aluminum intake and I’ve yet to have a problem with the frame that was caused by the weight. Keep in mind the same basic front frame section is pretty similar across the board from the 1/2 ton up to 1 ton that came with big blocks. The 6.2L diesel was no lightweight either.

You should use a ORD tubular engine cross member for a little extra strength and better oil pan clearance. The steering box brace and or plating should be mandatory for every square body build but the issue there is not engine weight induced at all.

Oh and by the way, even with a heavy big block up front I still have a tendency to wheelie on steep climbs off road. It might have more to do with the house on the back, but the weight of my 8.1 didn’t seem to hold the front end down as much as I thought it would.

Don’t stress on the weight. I’ll let the much smarter guys on the engine build combo continue but I wanted to toss that perspective in there.
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I had a 1200 lbs engine on my front and I still had a little lift on a hard launch.
Blazers have a short wheelbase so it doesn't help.
I say had because that frame ended up cracking in 6 places, mostly from the 410 ft lbs of torque from the turbo diesel engine
 
The 8.1L makes that kind of torque everywhere below 4500RPM and any good modified 7.4L will also make that kind of torque somewhere.
 
Yeah I know, but that was a 1967 Perkins 5.8 L
And I am assuming you know the vibration of diesels just rattles weak frames, my k5 frame didn't stand a chance also because someone cut the crossmembers off to fit the engine.
I am designing crossmembers to work with that engine on my crew cab build
Blue85 said:
The 8.1L makes that kind of torque everywhere below 4500RPM and any good modified 7.4L will also make that kind of torque somewhere.
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imiceman44 said:
that frame ended up cracking in 6 places, mostly from the vibrations of a heavy unbalanced old engine with hacked crossmembers.
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imiceman44 said:
someone cut the crossmembers off to fit the engine.
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FIFY.

I mean, possibly. There are way too many big blocks in K5s to say that "torque cracks frames". On a long enough timeline every frame cracks, but we haven't discussed durations.
 
Blue85 said:
FIFY.

I mean, possibly. There are way too many big blocks in K5s to say that "torque cracks frames". On a long enough timeline every frame cracks, but we haven't discussed durations.
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Oh I know it's all of it that's why I mentioned it all.
Especially that when I bought it it was a street queen and I took it immediately to Hollister hills, then frank raines, to Pismo then on snow runs, and finally to the Rubicon trail where I broke the frame at the steering box.
Fixed that then took it to Sierra treck and dropped the transmission and tcase when all the bolts on the crossmember vibrated loose.
After that trip I was tightening and inspecting and saw multiple frame cracks so I parted it
 
76zimmer said:
@RayzWorld
Any progress on finding those numbers?
Thought any more about the build plan?
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I haven't jumped into it just yet, I'm in the process of getting concrete slab indtalled so I can pull the engine. Thanks for asking. The whole conversation helped me understand what I needed to look for. Once I get the numbers where should I look them up?
 
82355 said:
As has been said multiple times. You 100% do not have to pull the engine to see the numbers. Use a 7/16" socket to remove the 1/4" screws holding the valve cover onto the head, and remove it.

Martin
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Thank you for the response I appreciate it. I wasnt pulling the engine to just see the numbers, I was pulling it because I dont trust the work the previous owner did to the truck. I also am getting a lot of fluctuation with the temp and oil pressure. On top of that I seen a lot of oil all over the underside where it seems the rear main seal is out. I already planned for a rebuild since I want to take the truck overlanding and I don't want to be have to worry about the engine falling out. There is so much more on the list that I have concerns about and I'm not sure you want the list. Lol.
 
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