10-1 427 Build

[78Bu88SS]

We picked up a 427 shortblock with TRW dome'd pistons, forged crank, and thumb rods stuffed into a 4 bolt block for cheap money. We plan on freshening it up with new rings, bearings, and a good balance, ARP rod bolts, and main bolts.

Anyways, its going into a full weight 69 Chevelle SS with a M22 and 4.30 geared 12 bolt. Car is being built for a good street/strip car with enough power to have some fun with.

To keep this within budget, we are looking at a solid flat tappet (no money for roller) and a set of cast iron rectangle ports. Many guys keep telling us to look at aluminum ovals but my buddy is dead set on iron rectangles (his motor, not mine) plus he doesnt want to spend that much on heads. The Summit/Dart heads are right at $1250 for the pair and have 308cc intake runners, 2.25/1.88 valves, and 119 chambers. With that big of a head, how will the 427 go? I remember hearing the stories about the L88 and would be interested in seeing a 7000 rpm 427 in his car. He will drive the car hard....

Any input would be great.

 

[LS6 Tommy]

You're gonna need a stout cam to go with those heads. If your buddy already has factory iron rectangle port heads, you can build good power with some bowl & port work. A lot of APBA super stock 427 engines run them with an unported stock dual plane intake & make well over 600 hp at around 7000 rpm.

Tommy

 

[SuperShop]

check the piston to valve clearance b4 he throw them on cause i was told that whenever you've got a dome and its not SRP's that you will have to fly cut the pistons if you go bigger than a 2.19 valve 8)

 

[78Bu88SS]

You're gonna need a stout cam to go with those heads. If your buddy already has factory iron rectangle port heads, you can build good power with some bowl & port work. A lot of APBA super stock 427 engines run them with an unported stock dual plane intake & make well over 600 hp at around 7000 rpm.

Tommy

He doesnt have the heads yet...the last bbc he ran was a 427 with factory rectangle ports. That was back in the mid 70s. I gotta imagine cam and head technology has come along way and more power can be made.

What size were factory, say LS6 rectangle ports? How about the L88s? I believe no bigger than 320cc correct?

Even factory rectangle ports in runnable shape are about $1500 in my area, and I can't imagine they flow better then out of the box Darts.

 

[LS6 Tommy]

You're gonna need a stout cam to go with those heads. If your buddy already has factory iron rectangle port heads, you can build good power with some bowl & port work. A lot of APBA super stock 427 engines run them with an unported stock dual plane intake & make well over 600 hp at around 7000 rpm.

Tommy

He doesnt have the heads yet...the last bbc he ran was a 427 with factory rectangle ports. That was back in the mid 70s. I gotta imagine cam and head technology has come along way and more power can be made.

What size were factory, say LS6 rectangle ports? How about the L88s? I believe no bigger than 320cc correct?

Even factory rectangle ports in runnable shape are about $1500 in my area, and I can't imagine they flow better then out of the box Darts.

I'm sorry. I misread the port volume in your post. 308 is a good volume. Yeah, the LS6 "good" intake port is around 325 cc. The L88 & the LS6 heads were basically the same port configuration, just that the L88 was a closed chamber & the LS6 was open. They're good running heads. Many people say "Don't get factory rectangle ports heads. The port volume is too big & they have sloppy driveability becuase of the low port velocity at low RPM." I won't argue that in many cases the smaller, modern ports outperforms the older, bigger ports, but I will say my out of the box LS6 pulled from 25 MPH in 4th gear just fine in a 69 Chevelle with horrendous 2.XX gears.

Tommy

 

[78Bu88SS]

Thanks for the help. I think we are going to go with a set of Dart/Summit 308cc rectangle ports, 10-1 compression, and a good solid lifter cam. I may go for a custom grind at the same time. I gotta see how the powerband will be which will determine whether we go with a dual plane like an RPM airgap or a single plane like the victor jr.