Any issues with swapping from 396 to 454 HO in 67-72 Trucks?

[Jonlopes]

A few months ago I posted some questions and a video about the knocking sound in my 402 big block.

Preparing my-self for the worst case scenario I started calling around to the machine shops in the area. The strange thing is every single one of them were completely flabbergasted with the insane notion that I was hoping to drop off the truck and have the engine rebuilt. Apparently this simply is not done. They all want me to pull the engine from my only truck and somehow transport it to them so they can do their thing. Then the prices they are quoting also seemed high in the $3500 range. I guess this is a good sign for the economy since they are able to pick the low hanging fruit and turn away the rest. To me this seems like too much work (rent a truck twice, etc) and money for an engine that has already been rebuilt once.

In my youth (25 years ago) I pulled and replaced a couple of engines so I started looking at alternatives and I ran across the Chevrolet Performance 454 HO. It costs a little over $5k but it has all brand new parts and puts out 425 horse power which is more than I will ever need, a 2 year warranty, AND shipping to my house is included. Costs a little more than rebuilding my old engine but the parts sound like they are not only new but better quality (4-bolt mains, forged crank, etc). I will have to buy or rent a cherry picker and an engine stand but Harbor Freight always has them on sale.

I am hoping someone has the experience to answer a couple of questions:

Does anyone have experience with this swap (stock 396/ 402 for new 454 HO)? I am hoping it will be a simple unbolt everything from the old engine and bolt it to the new one. Are all of the bolt holes drilled/ tapped in the same place?

My truck has the short water pump, I can buy a correct one and swap out the long one with no problems but after I change the pump can I just bolt up all of my pulleys and accessories and have them line up correctly? Is the distance from the engine to the pulley mounting surface of the Harmonic Balancer universal or are there different sizes? Or in other words is the harmonic balancer different in long water pump applications than short? I am assuming no but it would not be fun to get to that point only to find that my pulleys do not line up.

The stock oil pan is like 4-5 quarts where the 454 HO has a 6 quart “truck” pan. I would rather have the extra capacity, will the 6 quart pan fit?

I know this question has been debated for decades with no firm answer but am I silly to want to keep the stock exhaust manifolds with an engine that makes 425hp? I have had several cars with headers and hated them every time with the starter heat soak, leaky flanges + gaskets, not being able to get to all of the spark plugs, etc.

[engineer_gregh]

I had my 402 rebuilt a couple of years ago and it was expensive. Machine shop costs are crazy high. I've often wondered if I wouldn't have been better off buying a crate big block myself. I went with headers and they sound great but if I had it to go over again I would have stuck with the stock manifolds. Does your truck have stock A/C? I believe that makes a difference in long vs short water pump and which valve covers you can use if you stay with the A6 compressor. Does the crate motor have the alternator on the drivers or passenger side of the block? I would think Summit or Jegs can answer a lot of these type questions. There are several board members here running 572's and so forth that are a wealth of information. Good luck and please keep us posted on the direction you take.

[hugger6933]

If the crate doesn't come with a flexplate/flywheel that is the only difference I can think of off hand between the two motors. Yes you should be able bolt the acc and water pump[new of course] on to the fatter rat. the motor won't quite make the full 425 with manifolds but you won't lose over 25 hp I would think by not using the pain in the rump headers. I've NEVER seen or even heard of a machine shop that pulls and does rebuilds. For the most part either it is a auto shop that can do that or a machine shop to do the rebuild. I think the crate motor is a smart plan that you should enjoy. Jim

[68 CRACKERBOX]

only big thing is I think you will hurt the valve of the truck by putting a 454 in place of the org. 402. 402's are worth a lot more than a 454.

[ss454conv]

I suggest you do a 454HO oil consumption search before you purchase. Unfortunately there are tons of posts to read on the subject.

[Valarius_Starchaser]

Originally Posted by ss454conv

I suggest you do a 454HO oil consumption search before you purchase. Unfortunately there are tons of posts to read on the subject.

I have seen and heard more recent engines having much less of a problem on top of that with it being a drop in and not a buy and build before he drives it would still be in the warranty I vote let her rip if you've got the green and the drive

PS: I have also never heard of a machine shop pulling an engine

[Jonlopes]

Originally Posted by engineer_gregh

I had my 402 rebuilt a couple of years ago and it was expensive. Machine shop costs are crazy high. I've often wondered if I wouldn't have been better off buying a crate big block myself. I went with headers and they sound great but if I had it to go over again I would have stuck with the stock manifolds. Does your truck have stock A/C? I believe that makes a difference in long vs short water pump and which valve covers you can use if you stay with the A6 compressor. Does the crate motor have the alternator on the drivers or passenger side of the block? I would think Summit or Jegs can answer a lot of these type questions. There are several board members here running 572's and so forth that are a wealth of information. Good luck and please keep us posted on the direction you take.

Yes the truck has AC and that is one of the reasons I am liking the 454HO because it is one of the only crate big blocks that have the short valve covers which are needed to clear my compressor.

[Jonlopes]

Originally Posted by Valarius_Starchaser

I have seen and heard more recent engines having much less of a problem on top of that with it being a drop in and not a buy and build before he drives it would still be in the warranty I vote let her rip if you've got the green and the drive

PS: I have also never heard of a machine shop pulling an engine

I read the same thing. I guess Chevy Performance pulled the engine in 2012 to re-do something in the manufacturing process and re-released.

[davischevy]

The only issue I have is I didn't go 454 while I had my 402 out.

Get the balanced flexplate for the 454.

[Rod Run]

They were all surprised by you wanting to drop your truck off because they are machinists, not mechanics. They don't have the time, nor are they probably equipped to pull & install engines.

It's just like if you went to a mechanic and asked him to bore and hone your block.

Good luck with whatever road you choose

[1972RedNeck]

To answer your original question, if you swap to the short water pump, your accessories will all work. I can't say for sure, but I would be willing to bet that the 6 quart pan will fit like a glove.

As for value, if I were looking to buy a truck, I would pay a fair bit more for a 454 than a 402.

[El Dorado Jim]

I agree with Rod Run, most machine shops that I have had rebuild engines for me had no way of pulling the engines, nor do they want to, they are machinists, not mechanics....anyway, I would go with the 454,better engine and great warranty...the only thing to check for is to get the one for your year or as close to it as they make, there were changes over the years, I bought a truck a few years ago that the owner had swapped in a new crate 454, only had 10,000 miles on it, I put that engine into my '73 Suburban,This engine was a gen IV , it did not have provisions for a mechanical fuel pump, so I have to run an electric one, that was the only problem I had,I run headers on my Suburban and my '74 pickup with 454's, the original exhaust manifolds always crack, because of too much heat and are very expensive to replace, I have had good luck with headers,except I have to put heat covers on the spark plug wires where they are next to the headers/ heads, bought the silver cloth ones from summit, they help protect the wires pretty good....hope this helps

[Jonlopes]

Originally Posted by Rod Run

They were all surprised by you wanting to drop your truck off because they are machinists, not mechanics. They don't have the time, nor are they probably equipped to pull & install engines.

It's just like if you went to a mechanic and asked him to bore and hone your block.

Good luck with whatever road you choose

LOL it makes 100% sense when you guys explain it. I just thought of it as "my car is broken and I was going to take it somewhere to get it fixed".

I think it will turn out for the best since it will be nostalgic to R&R and engine again.

[Rod Run]

Originally Posted by Jonlopes

LOL it makes 100% sense when you guys explain it. I just thought of it as "my car is broken and I was going to take it somewhere to get it fixed".

I think it will turn out for the best since it will be nostalgic to R&R and engine again.

Once you do it that way, you can always say the you have a punched out 396 under your hood and that sounds way cooler than a 402 anyway.

Last time I did a 396/402 I actually had it bored out another .030 (so it's now a 408) and for some strange reason (same dimensions), the .060 over 396 pistons listed for a lot less than .030 over 402 pistons.

[engineer_gregh]

Once your 402 is removed and disassembled you'll get a better idea of direction. I discovered that my heads were 396 325 HP car heads that were much better than the stock truck heads. The machine shop made sure my block and heads didn't have any cracks but also discovered my crank was too bad to turn and had to be replaced. Hopefully the truck is not your daily driver and you have some time to think through all possible options.

[Doug's68SS]

I saw a couple of post about the flex plate but you will need a Balancer also. the 396/402 are internally balanced and the 454 is external. the 454 Flex Plate has weights on it and the balancer has weight on it also.

[67 chevelle]

The availability of 396/402 pistons has doped to almost nill , you can get 11to1 and 12 to 1 vary easily , the last 396 I had built 7 or 8 years ago this was an issue , they fly cut the tops of the high compression pistons and ran a thick layered metal head gasket , unfortunately these things are getting obsolete , before I get flamed , check 396 piston availability

I like the 402 396 powerband better than a 454 , while the 454 has gobs of torque when built right , the 396 with shorter cranks rev faster
All 396/402s had good heads , some had excellent heads , some 454s had peanut port heads that had trouble making 250 horsepower

[kehstr]

With both of those motors being big blocks, you can unbolt the 396/402 and a 454 with drop right in it's place. The oil pan is the only thing i am not sure about, there are several different pans, some are deeper at the rear, and some are deeper all around, sorry can't help you with that.
What do you plan on using this truck for? is it going to just be a weekend driver? Race truck? Tow rig? Daily driver? These are all things you want to consider when building a motor for the truck.