I have a 454 BBC out of a 1990 GM truck..and I want to put into my 86 c-10....I feel that the DZ is to stressed as I dropped a valve a while back

I have yet to take the intake off of the BBC because its sitting in my friends garage,my question is, is it a square port head or oval.Whats the difference between the two?Whats better for a street/strip engine?Does it really matter that much?

I have some parts sitting around and Im looking to make 1.3hp/per C.I or right around 600hp at the flywheel

276/ 284 Lift .554/ .572 flat tappet cam

BG race demon 850CFM carb

merlin intake ....dont have it yet

I will be using a little n2o ....10lbs per minute

also I have heard that BBC's dont like a lot of compression like a SBC does...I was told not to go more then 10:1 on pump fuel...however I will be using 110 on the juice

thanks guys for the help....also is there anything I should know about BBCs,this is going to be the first BBC that I have built...looking for some advice from the CZ28 motor heads

 

if it has the heads on it that i'm thinking it does, they arent good for much of anything. they will be what is refered to as a "peanut" oval port. theres room to open em up to the large oval port size... but... yeesh thats a lot of time with a grinder BTDT. i also just really hate flat tappets in bbc's, but we've already had that talk on this forum.

 

.The large oval ports can work well in a relatively low rpm street performance application. The small oval parts (sometimes called round or peanut ports) do not. The rectangular port heads work best for larger displacement/higher rpm setups. Most trucks had the small oval ports.

Rich

 

You will not make squat for power with those heads, like said above they are the peanut port heads, I am actually doing one of those motors this week for an '86 1 ton. It will have world heads(I hate world, but they have an EO #) with some clean up work, should make good power for a smog legal hauler.

 

Find some 781 heads. They'll work a lot better than what's on that engine. Put some 2.19/1.88 valves in it, clean up the ports and bolt them on. Don't overlook a set of aftermarket heads. Even cast Iron Merlin heads are cheap and work well right out of the box. Depending on how much work needs to be done to the 781 heads, valve job, new springs, guides etc, it can be cheaper to just buy some aftermarket heads. Oval port heads and an aluminum dual plane manifold will work very well. You don't need rectangular port heads. I have small rectangular port heads on my car and wish they were larger. The bigger engines need a lot more air at 7000 rpm.

The majority of all good BBC heads have large 119cc combustion chambers. GM offered many different BBC head castings with a lot of different combustion chamber sizes. 119cc just stuck and the majority of all the aftermarket heads also use that size. The 119cc chamber is big enough for larger valves and still won't shroud the valves. Unlike a SBC where compression ratio increase is preferred with a flat top piston and a small combustion chamber, the BBC works better with the large chamber and a dome piston. The domes on my pistons are huge making my compression ratio around 13:1 but I also run alcohol fuel.

Back when I had a very similar 469 (454 + .070) to what you want to make, it was enough to push my car into the low 11's at altitude on 92 pump gas (no NOS).

 

I agree - I have several sets of 781 and 049 heads on the shelf all setup with 2.19/1.88 valves, the boat guys love them and they make good power with a proper valve job and matching chamber work for the bigger valves.

 

Keep in mind if you start looking for an old set of heads that the real early heads had "closed chambers" which require a different piston when a dome piston is used. The chambers on these heads are smaller though, which brings up the issue of CR. The allowable CR is still mostly a function of the fuel used and the cam selected. Obviously, issues like cooling and CC design play into it as well. But generally speaking, there isn't much difference between big block and small block CR. Like the small block, combos are pretty well worked out for this ubiquitous engine. Chose your CR accordingly and don't try to reinivent the wheel.

Rich

 

rskrause, I would think that the huge 118 cc open chamber heads would be a little more sensitive to detonation than the SBC heads. The big chamber and a dome needed to obtain decent compression should produce long burn duration.

My old 10:1 compression iron head 468 ran great on 92 octane back in the 80s, now it rattles like shaking rocks in a tin can. I suppose the gas they make these days is not what it once was.

 

I agree to a point. Typical BBC street combos are ~ one full pojnt lower CR than you see in aluminum head small blocks. That's why I suggested staying with what has been proven to work.

Rich

 

Ok...so stay away from the peanut ports...

I think it would be cheaper to find some 781 or 049 heads around town..I was looking at some Jegs heads or some brodix but I dont know if I want to spend 2,000 on some heads that are going into a farm truck..

whats wrong with a flat tappet cam in a BBC?

 

I'm confused. I thought it was a street/strip motor and now it's going into a farm truck

Rich

 

yeah..I call it a farm truck...and thats what the LP says..

3,000 rpm stall
Art Carr 700R4
Strange Axles ,Auburn Diff and gears
ET streets on Centerlines
twin holley blues

you know....standerd farm truck parts

 

Im runnin 781 ovals and a flat tappet cam,ET in sig.

With that big of a cam your prob. gonna want to run rectangular port heads...my motor doesnt like to turn more than 6300 RPM's.

 

Then you have other problems. Maybe weak valve springs. I had a flat tappet cam around .630 lift with oval port heads set up for a high lift cam and easily spun the engine to 7000 with a single 850 carb and 92 pump gas.

 

Yeah - rectangle ports would be a bad decision for that motor.