Plans for a 478 build.

[TJ's GMC]

Originally Posted by beerman

I don't think there is a compromise either go lower RPM and boosted or higher RPM and Naturally Aspirated.

My thoughts exactly.

[Charon]

The biggest problem with the v6. And the main reason it's made so heavy is it's design can't be balanced. The rotational mass can. But the firing pulses can't counterbalance each other. The engine actually shakes front to back. Kind of like a rocking chair. This is why they don't feel smooth at higher rpms. The faster you turn it the more violent the rocking becomes. You could lighten up the rotational mass. And the rocking motion would be worse as the speed increased. Its the weight that makes these engines feel half smooth.

[bigblockv6]

I've got the custom cam specs for my 478. I'll have to send you a copy of the custom cam specs for my 478 along with the part number for longer valve springs from Comp Cams , they are actually Ford 390 valve springs

[turbobill]

The cost of making a 478 (or any other GMC big block V6) make power at high revs will be much higher than making the same power at low revs by boost. I can certainly see the limited breathing of any of the V6 heads nullifying some, if not much of the gains made through headers, 4 bbl carbs and cams.

In addition, to make power at high revs will require tons of money to be spent on either making the heavy parts in the bottom end live, or be replaced with custom/aftermarket stuff. Aside from that, you'll still have to buy/source/make the headers and intake as well as pay for a custom ground cam.

Under no conditions would I try to make a 478 run at over 3600 RPM with the stock bottom end or valves, even in new condition.

[bigblockv6]

I would say 3700 rpms is max for the 478, mine is good for 4500 but only if I get rid of those hollow stem sodium filled exhaust valves which I will absolutely have to do. Some 478's back in the day had the governors blocked and would get over revved and end up sucking valves.

[Charon]

I thought you used cat valves in your 478. Not sure which. I looked at all the cat specs and none are close to a v6 gmc

[bigblockv6]

Never used Cat valves, someone else on the site did and gave me the part numbers which I can't find, so I'm thinking of going with some custom stainless steel valves from Manley.

[beerman]

Are these the ones?

http://6066gmcclub.com/showthread.php?t=38705

[bigblockv6]

Beerman, those most likely are the valves, thanks for digging it up

[TJ's GMC]

I never rev my 305 past 3500! I wouldn't dream of reving a 478 past that either. haha

Another thing I was considering was fuel injection. The MSD injection is spendy, but a sweet unit. Be great on a motor that size. I've been wanting to make headers for my 305 for the cool factor, but haven't gotten around to it.

Maybe I'll just do nitrous on the 478.