402 Experts... Tell me what you know

[Grit dog]

@Bextreme04
Some great info on the mark vi. Thank you.
The engine is also carbed so that’s a lot of stuff to get gas to a carb and not planning on fuel injection.
Looks like a little work to the existing engine would wake it up though. Basically just a cam.

 

[Bextreme04]

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.

He wont need heads for the engine he has now. The heads he has now are the best low end torque heads you can get, that aren't aftermarket. He can get over 400hp just with a cam... per the video I linked above and many, many real world experiences by GMT-400 owners.

I have my reciepts for my L29 rebuild. Cleaning, boring, new pistons, balancing, and all new parts including lifters/pushrods/waterpump/gaskets/harmonic balancer came out to just over $2000. I live an hour or two south of the OP.

 

[Swearbody]

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.

I think A 396/402/454 whatever is gonna put out more torque than hp in stock form. So a small cam,intake combo will be smooth like stock and easily make 450+tq. Thats pretty Smooth and reliable IMHO.
As far a cost well you get what you pay for thats true. However if your paying over 2k just for labor you better be getting waaay more than a simple rebuild. Are they assembling it for that price too like cam install,intake,timing cover,oil pump and pan,etc. Even if so at 2k labor your talking maybe 1k parts...still not horrible
But thats not the point. You DO NOT have to go crazy building a 402 to get 400hp 450tq and it be smooth and reliable. Thats simply not true regardless of where or who you are. You dont need aftermarket heads and big compression to make 400 on ANY big block..just a few more rpm's.
And since the OP want torque and not hp he can opt to stay with the stock intake, have the heads worked for larger valves, a small cam with longer exhaust duration, and have a torque monster that drives like a stock truck all day. and pulls like a NA diesel.

But you are right...he can do that with the 454 and have better results regardless of whatever is being said about the 402.
Its really about when and where its puts power down that seems to matter to the OP. Anything outrageous is gonna move the power band into an unusable for daily situation pretty quickly anyway. Keep it as close to stock as possible with a small cam and maybe some head work and you'll make 400 no problem. And it will run as long as you treat like any other stock motor. But ...I still think I could build 2 400hp 402's for 5k

Anyone wanna give me 5k and 2 402's PAweeeze.

 

[Catbox]

I will eventually be putting a L-29 into my truck or Bel Air.
It will have a carb and the only real change will be the ZZ-502 cam and a set of Crane roller rockers that I have.

It should be around 450hp and 500lbft from what the internets have told me.
More than enough for what I want to do with it.

The fuel system should be pretty simple to set up in either vehicle I choose.

As it is, I have a set of the L-29 heads in the garage next to the whole L-29 engine.
Those heads will be going on the MarkIV 454 that is in the truck now.
With those in there and a aluminum intake under the Quadraje

 

[Bextreme04]

I think its very telling that the stock L-29 with the EFI intake was hitting 356hp and 486tq in bone stock form. The intake and carb just shifted the power band up and had 10 more hp and 10 less tq. They never mentioned that the factory injectors are basically tapped out in stock trim. Any basic power improvements run the injectors up above 80% duty cycle and they are notoriously inefficient to boot.

There are reports of 10-30hp improvements just from an upgrade to a more modern 4-hole bosch injector with the same flow rate as the stock ones. Stock injector rating is only 19lbs/hr.. which on paper is only good for 225-290hp. That's why most people with the L29 in the GMT-400 trucks say to do a cam swap and put in the Bosch 30lbs/hr injectors as the main upgrade. They are then probably very close to that carb and cam dyno run that was giving 428hp and 528ft-lbs. They are also reporting between 10-14mpg at those power figures, which is pretty awesome.

@Catbox you should just put the whole motor in there with the fuel injection and everything. My tune should be able to just go right in with the dual electric fan control and everything. You can even bring it down here and we can get the wiring and programing out of the way over some beers. Unless you want to sell the intake and fuel injection stuff to @Grit dog to go with new fuel injection tanks and senders

 

[Shorty81]

I have the old 781 heads on my 496. They work well. Monster torque.

 

[Catbox]

@Catbox you should just put the whole motor in there with the fuel injection and everything. My tune should be able to just go right in with the dual electric fan control and everything. You can even bring it down here and we can get the wiring and programing out of the way over some beers. Unless you want to sell the intake and fuel injection stuff to @Grit dog to go with new fuel injection tanks and senders

We just pulled the long block when we yanked it out of there.
No FI stuff to be had here.
If I was to do the FI goodies, it would be the Edlebrock Pro Flow set up.

I did find a 0411 computer the other day in the junkyard though...
It was the one that didn't look like it was submerged when the yard flooded a few weeks ago.

If I put the whole thing into my truck, I told junior that he had to find me another one for my car.
As putting it in the truck benefits him...

 

[Turbo4whl]

Some little know 402 info: The 402 was actually 3 years of production not just 2. In 1970 Chevy listed the 402 as a 396, which basic it is, 396 .030 over. In 1970 Chevy listed the 402 as a 400, which caused confusion since there was, also in 1971, a 400 small block. The last year of it's production Chevy finally called it a 402.

The heads on the '71 and '72 for sure were the same heads used on 454 engines. Better than the previous heads they have fully quenched valves, no hot spots that would cause pre-ignition. The 402 stock pistons filled this quench area to bring up the compression. This also means it is not a free wheeling engine, failed timing gear/chain set will bend intake valves.

Also supplied with the pink rods the 402 is ready for a different cam and timing curve, and you have a torque machine. The large oval port heads are just fine for torque! If you want high horse power, you might want the square port heads.

 

[Grit dog]

I’m just soaking up the knowledge here. Keep it coming.

 

[BKING33]

I agree on the heads. big square ports are best for race cars and smaller oval ports are for making torque in a street engine.
my engine in my Chevelle isn't a powerful engine, probably in the 360 hp range. But I have had no problem destroying many tires and multiple clutches over the years of having fun.

 

[Mark Jones]

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?

A good stock but blueprinted rebuild with a hyd roller. Feel free to send the 402 heads my way!

 

[Mark Jones]

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.

I would never do this. The bore is not big enough to utilize a 2.190/1.880 combination. The 049 - 781 head has to big of a chamber for a 4.125 bore, you would need a big dome to make this work, then heavy metal to make it balance.
]The best combination IMO is to use the 292 head (402) with a 2.100/1.780 valve combination with mild port work. Way more than 400 steetable HP.

 

[Mark Jones]

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.

I use a Racetec in my 396/402 builds, they build me anything I want.

 

[Mark Jones]

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

"bolt on Procharger"



You sure get around Bill...............

 

[Ricko1966]

Freshen up the 402 change the cam use the stock heads and go with a roots type blower, not a centrifugal blower. Boost cars don't need great heads to work.