402 engine rebuild

[ho70]

OK.......Rebuilding my stock 402 for my 72 C10.
Want 9.5-1 compression, added 6223 forged crank, 2162 performer cam, performer 4711 carb and matching intake
I have two sets of heads
781-stock off LS5 270 hp, oval port 113cc
292-stock oval port
both 2.06/1.72
Machine shop states use 292 as smaller chamber easier to get compression
I just want to confirm these are OK heads as they were the stock ones on the truck, but don't want to go against machine guy to piss him off unless absolutely necessary
Also, will I need a new harmonic balancer as I have old one from cast crank and using forged crank.
Want a nice strong 402, not a race engine nor a dog. Anyone done this what pistons did u use?
thanks

[Coley]

Make sure the engine builder knows the vehicle this motor is destined for.
That being....a heavy vehicle, basically a 2 ton truck (yes...that is what most long bed 1/2 tons weigh, at least with a v-8 and a few options)
In my opinion which ever head helps develop torque better below 3000-4000 rpm is what I would be after.
If you have a good high lift cam and are developing good torque....and if this is a fun 'city' truck....then you will have fun power.
Let's face it...activity over 4000-4500 rpm happens pretty rarely for most guys, most of the time.... so designing a motor to live up there is a bit of a waste of time and money unless you use the truck for a lot of 1/8 or 1/4 mile racing.
....just my two bits and it will be interesting to see what the shop has to say and what some of the other members recommend.

All good
Coley

[cadillac_al]

I passed on a 1971 402 because I thought the 292 heads would be very low compression. I didn't find a lot of info to clarify or figure out the specs on those heads. I would like to know too. If your machinist says they are the best option then those 402's just may be good scores.

[Tom]

Both heads flow the same when stock basically. Smaller chamber is easier to get compression without large pop up domes, but the open chamber head unshrouds the valves better. If you can make the 049's work, I'd go with those. As for the machinest, he works for you. If it pisses him off to do what you want, just imagine how pissed he'll be when you give your money to a different shop that does as asked.

[Ironangel]

The 292 heads are a closed chambered head, the 781's are not. In stock form the 292's will have a higher compression ratio than 781's thus producing more power. I have a set of almost identical 290 heads on my .060" over 396 (408ci) with Speed Pro-L2240NF forged pistons. I'm inclined to agree with your machinist because a stock 402 piston with a mild 22cc dome will make some good low end power with 292 heads...Save the 781's for a future 600 HP build as they will out flow the closed chambered heads as they should because they are 454 heads. The 402 is a 396 bored .030" over so think of your motor as a 396 rather than a 454. The closed chambered heads kicked to the curb because they had inefficient burn characteristics, not because they didn't make extraordinary power. Most police and Super Sport applications had the 290, 291, or 292 heads because compression is power...

[cadillac_al]

That's some good first hand information there Iron Angel. I'm reviving my 402 deal again. Those Chevelles and police car 402's must have had a dished piston didn't they? Did the trucks get a bigger dished piston and lower compression? Is it possible to get any decent power with stock truck pistons or is compression way low?

There are plenty of 454's around for not much more money but i really don't need a ton of power for the convertible it is going in. I just need the big block look and sound. If I had to buy pistons for a 402 then I might as well build a 454. I have always wanted a nice 402 though and I'll bet a low compression truck engine would still work good enough for slow cruising and an occasional burn out. Thanks.

[Ironangel]

Originally Posted by cadillac_al

That's some good first hand information there Iron Angel. I'm reviving my 402 deal again. Those Chevelles and police car 402's must have had a dished piston didn't they? Did the trucks get a bigger dished piston and lower compression? Is it possible to get any decent power with stock truck pistons or is compression way low?

There are plenty of 454's around for not much more money but i really don't need a ton of power for the convertible it is going in. I just need the big block look and sound. If I had to buy pistons for a 402 then I might as well build a 454. I have always wanted a nice 402 though and I'll bet a low compression truck engine would still work good enough for slow cruising and an occasional burn out. Thanks.

I dont think the truck 402's got a different piston than the 396 motors other than being .030"' over which when used with an open chamber 110cc oval port head lowered the CR. The open chambered head got a more complete "cleaner" burn which is why GM went in that direction. There are lots of mitigating factors like cams, solid lifters, various head options, as well as crank and piston combinations used. Take the L78 396 for instance, it was the epitome of the "little Rat" motors making 425 horsepower. It had the 3964291 (closed chamber) cast iron oval port heads with an aluminum head option that ran the same numbers only lighter weight. I'm not sure what pistons the truck 402's got but I dont think they were a dished piston. I think if you went with a set of refurbished closed chambered heads set up with springs to match a CompCam 268H or the Voodoo 10110702 cam, you would have a very well mannered 402 with on the spot tire melting capabilities. Those two cam grinds have a mild choppy lope at idle and match the closed chambered heads perfectly because they're all in at 6000 rpm. Once more, the closed chambered big block sound is like no other especially when you run 3" pipes all the way...Heres a video of my 408 taking a first place trophy at last years Truck Nationals in Riverside, Missouri. Same motor as yours except bored .030" over to a 408ci with 3964291 heads and the 268H Comp cam... https://youtu.be/_jXxaOqm36M?list=PL...FwXZgV5iVEXyeB

[ho70]

Thanks for the replies. Gonna keep the small chamber heads with .300 30 over forged pistons.

[cadillac_al]

Yup, nothing wrong with that sound. that's the sound everyone wants and what I'm looking for the most. Cool burnout too! I see now that if you can find a running 402 it would be a nice fun project. If it needs to be bored and new pistons I might be better off going 454. I'll have to question my seller a little more about the running condition of his 402. It sounds like HO70 is going to have a tire melter too.

[alsriv2]

Originally Posted by Ironangel

I dont think the truck 402's got a different piston than the 396 motors other than being .030"' over which when used with an open chamber 110cc oval port head lowered the CR. The open chambered head got a more complete "cleaner" burn which is why GM went in that direction. There are lots of mitigating factors like cams, solid lifters, various head options, as well as crank and piston combinations used. Take the L78 396 for instance, it was the epitome of the "little Rat" motors making 425 horsepower. It had the 3964291 (closed chamber) cast iron oval port heads with an aluminum head option that ran the same numbers only lighter weight. I'm not sure what pistons the truck 402's got but I dont think they were a dished piston. I think if you went with a set of refurbished closed chambered heads set up with springs to match a CompCam 268H or the Voodoo 10110702 cam, you would have a very well mannered 402 with on the spot tire melting capabilities. Those two cam grinds have a mild choppy lope at idle and match the closed chambered heads perfectly because they're all in at 6000 rpm. Once more, the closed chambered big block sound is like no other especially when you run 3" pipes all the way...Heres a video of my 408 taking a first place trophy at last years Truck Nationals in Riverside, Missouri. Same motor as yours except bored .030" over to a 408ci with 3964291 heads and the 268H Comp cam... https://youtu.be/_jXxaOqm36M?list=PL...FwXZgV5iVEXyeB

Just got my 396 up and running this past week. It has the larger port 781 heads, a Lunati 50249 roller cam, Probe forged pistons, bored .060, (408 now). Compression estimated to be 9.5-10. Still have to create a good exhaust for it, but it does have a nice set of headers right now. I can't wait to get it on the road and start enjoying it. I really enjoyed your video. I am cautious about my Cam as my engine builder probably went a bit excessive. Dyno has it putting 469Hp at 6000rpm and 450tq at 4500. I tried to get the builder to understand I wanted a lower speed (50mph) type truck with lots of power and the ability to drive it at normal (65mph) highway speeds occasionally. They (the builder) are well known in the mid-Atlantic region for drag racing engines that win, so I might be in that category.
For now, your video gives me inspiration to "get-r-dun" and get a feel for a C-10 with a major attitude. LOL!