402 Experts... Tell me what you know

[Grit dog]

So not like I don’t have enough to do, but thinking about building a 402 motor or maybe just a refresh.
I can get a good running 72 402 truck motor basically for nothing. What little I’ve read, they’re torquey but pretty anemic in stock form as big blocks go.

I’m not an engine expert. I know how to do all the work but not “what works”. Especially with this engine and not just throwing the whole checkbook and a couple credit cards at it, lol.

Let’s say I wanted 400hp min and a good smooth torquey engine for the 86.

what would I need to do to this engine?

 

[HotRodPC]

Cam and scrap the 72 denutted truck heads. Try to find some 70 or earlier 396 heads for it.

 

[BillK]

Let’s say I wanted 400hp min and a good smooth torquey engine for the 86.

I would stick with the 454 that you have. A little bit of camshaft and maybe some work on the heads or a different set of heads and you should be able to easily get 400 HP.

With the smaller 402 you will need to build a much more aggressive engine to reach the same goal. I would imagine you will spend an easy $5000 to build a nice reliable 400HP 402 engine.

Another thought would be to get a bolt on Procharger kit

 

[Grit dog]

Cam and scrap the 72 denutted truck heads. Try to find some 70 or earlier 396 heads for it.

That's what I was figuring as well based on what I read about the heads.
Not that it mattes for a mild engine but do you know if they're 2bolt mains in the late 396/402 engines?

 

[Grit dog]

I would stick with the 454 that you have. A little bit of camshaft and maybe some work on the heads or a different set of heads and you should be able to easily get 400 HP.

With the smaller 402 you will need to build a much more aggressive engine to reach the same goal. I would imagine you will spend an easy $5000 to build a nice reliable 400HP 402 engine.

Another thought would be to get a bolt on Procharger kit

LOL, that's a thought.
So they're that anemic eh?

This is only hypothetical at this point since the 454 is running well, but part of the motivation is the 454 is a Vortec engine with no fuel pump boss for a mechanical fuel pump and the expense and butchery to do the right job for electric fuel pump(s) is not attractive with the current engine. Currently running a little sucker pump ahead of dual tanks. Engine is carbed.

I do like the thought of an old 396 or "400" though. But sounds like this old 402 engine may be best served to be dressed up, re-sealed and just run as is. Probably a stout motor I'd think?

 

[BKING33]

I Have a 69 Chevelle with a 396 .030 over. They are great torq motors. I had it rebuild about 30 years ago. All stock except for a mild cam.
Biggest draw back that I can think of is limited options for pistons.

 

[Bextreme04]

LOL, that's a thought.
So they're that anemic eh?

This is only hypothetical at this point since the 454 is running well, but part of the motivation is the 454 is a Vortec engine with no fuel pump boss for a mechanical fuel pump and the expense and butchery to do the right job for electric fuel pump(s) is not attractive with the current engine. Currently running a little sucker pump ahead of dual tanks. Engine is carbed.

I do like the thought of an old 396 or "400" though. But sounds like this old 402 engine may be best served to be dressed up, re-sealed and just run as is. Probably a stout motor I'd think?

You can get just the Gen Vi block from GM with a fuel pump boss. Or just drop in TBI sending unit/pump into the factory fuel tanks with an adjustable fuel pressure regulator on the frame rail. Then the only aftermarket non-GM item would be the regulator. Just camming that Vortec motor with no other changes should put you up over 400hp. The ZZ502 cam will slide right in with no changes at all. I'm running a custom regrind on the factory cam and upgraded to the 454HO dual valve springs with rotator eliminators on mine.

There's lots of videos of junkyard dyno runs. This one is pretty good with the stock EFI vs Carb vs Cam plus a nice nitrous shot at the end.

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Considering that's on a bone stock motor that he probably paid $500 or less for... its hard to beat. I paid $500 for my whole donor truck with a 454/4L80E and about $2200 for the machining and rebuild parts to put it back to new. With the head rebuild, cam, 454HO valve springs/retainers, fuel injectors, ECU, and new pushrods... I'm right around $3,000 in the motor. But... it will be better than brand new and should last another 288,000 miles like it did in the donor.

New tanks and senders would only run you ~$250 per side for a dual tank setup. Nice, high quality adjustable fuel pressure regulator is maybe $100-150. You're still well ahead to just sort your fuel system and cam that motor you have.

 

[BillK]

but do you know if they're 2bolt mains in the late 396/402 engines?

99% of them were 2 bolt mains.

 

[Wumbo]

You don't need to worry about 4 bolt mains at that power level.

 

[Swearbody]

Somebody on the thread said the 402 would need a lot of work to get to 400hp. IM calling BS if we are talking about the 71-72 LS3. Cam,heads,intake.etc will easily gross you 500. The low ass 275hp rating was net not gross. In other words they changed over to rating the hp at the wheels in 72. Furthermore the 402 is a 396 as well other than block/pistons. Same crank,heads,etc with slightly bigger bore. The 402 block has slightly thinner cylinder walls but no so bad you cant build one.
Get some square port "396" heads for the better flow and the aforementioned accouterments will gross you 500+ and net over the 400 easily. And for 5000 this could be done twice over if you do it yourself. 5k for 400hp is BS

I know personally of one(402 block) in a rock buggy thats making some serious chooch. Guy beats the hell out of it and it been in the rig for years now. I can ask him what he did to make it perk up so much(other than the fuel injection) but I imagine it will be the same old story. Cam,heads,intake etc.

 

[Swearbody]

Cam and scrap the 72 denutted truck heads. Try to find some 70 or earlier 396 heads for it.

Yes sir. Ditch the oval port shitters and grab the square port hitters.

 

[idahovette]

IMO, the best thing you can do is find a good set of heads, maybe 049s or 871s? and hog out the valves 2.19 intakes and 1.88 exhaust. That and pick your flavor of camshaft and you'll get your desired affect. Got .030 over 427 with these heads and a comp cam, I'm happy.. Also it has a Quadrajet on it. Your gonna need more rpms with the rectangular port heads.

 

[Bextreme04]

I'm also going to point out you already have a strong factory 4-bolt 454 in there, with factory hydraulic roller cam(that is ****** and retarded by 7degrees from the factory) and can be easily reground or direct swapped with a GM ZZ502 cam with no other changes. It cost me $140, all in, to send the cam up to Delta Camshaft in Tacoma and they had it back to me in a week. They'll grind it to your specific wants. The factory L29 heads are large oval ports and have been compared to the 049's for flow. You can see in that video they were making well over 400hp at the crank with just the cam. Plus you'll get even more torque and keep the benefit of the parallel flow cooling that the newer generation BBC have. You're going to be way more into a 402, dollar and time wise, and still have an inferior engine in almost every way except for the manual fuel pump boss.

My donor truck had 288,000 miles and the 454 was still pulling like a freight train and running smooth when I drove it home. It was leaking everywhere from being abused, but was still holding in there strong. I don't know that I've ever heard of a 402 going that kind of mileage and still being strong. I had it apart and rebuilt, so I know that everything internally was original factory and the block had the correct stampings to show it was original. The pistons got a .020 over and the crank didn't need anything but a polish.

 

[BillK]

Somebody on the thread said the 402 would need a lot of work to get to 400hp.

Yes but he said he wanted "a good smooth torquey" engine for a truck. A true 400HP 402 is not going to be that.

I still say he is better off spending the money on the engine he has now. A set of heads and a cam will get him to 400HP pretty easily and he will still have a smooth running engine suited for a truck.

And I dont know what machine shop prices are in your areas but around here the bare minimum you will spend on machining for a good complete engine including doing the heads will be at least $2000 - $2200. That does not include parts. I absolutely hate the magazine articles that make it sound like you can do it for pennies They are not real life.

 

[idahovette]

In most magazine articles , who ever is doing it is getting the stuff free or low cost for the advertising, NOT the real world !!!!