Is the 781 head oval or rectangle port? I am getting parts for the big block, and preparing to swap out my small block. I just wanted to get the proper intake.

oval.

On a side note, if you decided on a eddy performer, I believe the ports arent quite as large as a regular oval port. More like a compromise between the peanut port and large ovals. jim

any suggestions on intake? the bore, mains etc are stock 454. the cam is a comp 287t h mt thumpr. roller tip rockers, new springs, pushrods, lifters. not sure of carb yet.

dlo,

With all due respect, I think you need to slow down and do some research before going further. Not knowing one of the BBC basics like what exactly a 781 head is and you are already "getting parts" has me worried. I am glad you stopped in here for some advice.
Lots of How To BBC books out there, plus this site here. Please take your time. BTW, 781 heads are excellent street, street n strip heads.

What have you got for a vehicle?
Gearing?
Transmission?
What engine parts do you have?
What are you planning to get?
What is your goal? your budget? Mechanical skills?
Street, street n strip?
I saw the "Mother Thumper" cam, has me worried too...............
Burger stand hero?
what part number on the pistons? Forged?

edit
Take a look at the BBC INFO thread, top of the ENGINE SECTION. Darryl posted some stuff, I posted some more stuff....ongoing.

edit 2
Tell us what you have going on and I'll be happy to share ideas, etc for your project.
I have a youngster in his 20s at my work wanting me to make him a 350 for his late 70s/early 80s Cutlass. He's talking CRAZY about Victor JR intake when he has 2.something Bonneville gears and a low compression 350. I've talked some sense into him, RV cam and Performer intake will be far better for his intended use.

What George said. might want to slow up a little, get a handle on your goals for the car and the budget.

the vehicle is a 70 chevelle. gearing i am unsure, but was told 308. tranny has been rebuilt a couple months ago, it is a TH350. The motor is currently a 350. I bought the big block a month or so ago, the previous owner had already purchased the mother thumpr cam and lifter set. The block is a 78 959 casting. the heads have been refurbished according to the previous owner but are stock. The rotating assembly, and pistons are also stock. I have very limited mechanical skills. I have swapped seats, bumpers, and put a new starter on, but that is about the limit of my skill. oh yea i put a new header gasket on. I have no real goal as far as horse power or time slips etc. I am just looking for a streetable combo with a little more umph than i currently have in the 350, which is mostly stock except for headers, 650 carb, edlebrock intake. I have currently purchased all my parts from a local parts warehouse. i spoke to the warehouse manager, told him what i had as far as cam, block, stock bore etc. He matched the parts starting with a rering kit, comp pushrods, comp magnum roller tip rockers, and falcon springs. I have a cousin whom is going to do the build for me. sorry for the dumb post, but you guys have been very helpful in the past. thanx..

you cant go wrong with a dual plane intake, eddy rpm, old school wieand action plus, performer works too. jim

the vehicle is a 70 chevelle.

SWEET!

gearing i am unsure, but was told 308.

FORGET ABOUT THE MOTHER THUMPER, too big to work with that gearset. This is to say it will physically work but it will be far from optimal. For that cam, you need 3.55 gears or higher numerically. edit. See below for another reason to NOT run the Thumper cam with this engine. Low compression and a big cam is not a good combo. Do you have positraction in the differential?

tranny has been rebuilt a couple months ago, it is a TH350.

If stock, a healthy 454 will make fairly short work of it. Have a shift kit installed, you'll need something like a 2500 stall converter if you keep the Thumper cam

I bought the big block a month or so ago, the previous owner had already purchased the mother thumpr cam and lifter set. The block is a 78 959 casting. the heads have been refurbished according to the previous owner but are stock.

Very important, you do have the good 781 head casting, right?

The rotating assembly, and pistons are also stock.

Stock passenger car or stock performance? Like you are talking cast pistons and cast crank. The crank is a tough hombre, good for 600 horses. The rods with good rod bolts should be fine, especially if you have the HD Thumb rods (see the "BBC Info" thread). I have cast pistons, millions of others do too. Right when your Thumper cam gets going, your cast pistons will become an endangered species...with a 4" stroke, the max safe pistons speed is 5500 rpm.

I have very limited mechanical skills.

RUH RO

I have no real goal as far as horse power or time slips etc. I am just looking for a streetable combo with a little more umph than i currently have in the 350, which is mostly stock except for headers, 650 carb, edlebrock intake.

You'd have to try hard to do poorly with a 454.

I have currently purchased all my parts from a local parts warehouse. i spoke to the warehouse manager, told him what i had as far as cam, block, stock bore etc. He matched the parts starting with a rering kit, comp pushrods, comp magnum roller tip rockers, and falcon springs.

Here is something you really need to look at. If you have stock pistons and 781 heads, the actual measured/calculated compression ratio will be around 7.9:1. The Big Mutha Thumper cam is gonna run like crapola with that kind of static compression. I pray inside your engine are some domed pistons.
Never heard of Falcon Springs.
3.08 gears and a low compression engine....you'll really want a smaller cam.
Look at the Summit 3101 cam with .500" lift.

I have a cousin whom is going to do the build for me. sorry for the dumb post, but you guys have been very helpful in the past. thanx..

You did the right thing posting here.
Got a name dlo?
If the pistons are good, the bores are good, and the valvejob on the heads is good.....I'd consider using the existing heads and a much smaller cam. A Performer intake would work fine. You could open the runners up to the cylinder head runner size. I avoided this situation by running an older Edelbrock C-396QJ that has the full oval port runners.
If the shortblock is good and the heads are tired, get some 1965-1970 closed chamber heads...get them freshened-up and install them on the shortblock...if you have flattops.
This will raise your compression ratio up to somewhere between 8.8--9.2:1 depending on your chamber size.
For a mild street engine, the 650 carb would work.

Build her like a stock LS5 at 9.75 to 10 to 1 CR or so, 454 and add a 268 for more grunt OR the 276 for more topend VooDoo cam or a good old CC 282S solid.

Run at least a good old tuned 3310-2, 750 or an 800 or 830 cfm Holley vacuum secondary carb. and high-rise oval port intake under her like the old Stealth 8019 and then, no more than a cheap set of 1.75" to 1.875" dia., 4-tube, long headers and go have more fun than John Law will allow!

You talk about waking the old motor up!!!!!!!!!!

He, He!!

What are we talking about guys?? 450hp easy???

pdq67

PDQ,
Probably about 425 horse but around 500 ft lbs torque.
The cool thing is that the torque is there from idle and it only gets better with more pedal pressure

I JUST finished this EXACT build!! This was a BUDJET build, goal was to have a nice SOUNDING motor with nice street manners. 454 with 781 heads and small BBC mother thumper cam...with cast pistons.............and it SOUNDS just like I wanted...Cant drive it yet.

I JUST finished this EXACT build!! This was a BUDJET build, goal was to have a nice SOUNDING motor with nice street manners. 454 with 781 heads and small BBC mother thumper cam...with cast pistons.............and it SOUNDS just like I wanted...Cant drive it yet.

'whenya' gonna drive it?

I'm sorry guys, but I don't drive "cam cackle"!!!

pdq67

I need a shortened driveline (Gearvendors installed already) and need to hook up master cylinder (been waiting on Hydroboost bracket 9 weeks-$100 up front and no bracket yet) and then interior and glass and electrical...about a year!!!

update..i had intended to finish this build and have the small block out and big block in by this time. however i have realized that there is no rush since the small block runs great anyway. as mentioned earlier i have no set horse power numbers, i just want a hot streetable setup. I need to add when the tranny was rebuilt i also had to have a new converter put in, 2500 stall. I got the bb performer 2-0 intake, a set of summitt headers part #g9010. the following specs are off the nitraded camshaft. gross valve lift .510-.495, .006 tappet lift 287-304. valve timing open int 40, exh 80 close btdc 67 abdc bbdc 45 atdc. duration @ .050 235-249, lobe lift .3000-.2910, lobe separation 107.0. I would like to leave the bore stock but have decided after input here that i need to change out the pistons. i have been told i should shoot for 10.5 or 11 to 1 compression. I have been advised to get a hyper piston. I would like advise from u guys on type of piston dome, cast, forged, etc, and brand and maybe a compression ratio i should look for. will it be enough to order the correct piston just using the casting numbers from the 781 heads? Also i have seen some post hear about changing to 2.19/1.88 valves. Any suggestions appreciated.

Cam's too big for pump gas and buy FORGED pistons!

And btw, check the cams advertised duration numbers for when the intake valve close's to keep me honest.

Please shoot for 9.75 to almost 10 to 1 CR. using .020" thick steel shim headgaskets to keep the quench tight for better burn, a 274/280 hy-cam or a 282 solid cam and don't forget headers so she can BREATH!!

Build her for max midrange T right at 4500 rpm and go have more fun than John Law will allow, imho..

pdq67

thanks for input. I wish i knew a little more about this, but i wanna get it right before i have it all buttoned back up..

[QUOTE=pdq67;2386711]Cam's too big for pump gas and buy FORGED pistons!

And btw, check the cams advertised duration numbers for when the intake valve close's to keep me honest.

valve timing close btdc 67 abdc, and bbdc 45 atdc.

And ebay the Ebrock 2-0 and ebay buy a good old Weiand 8005 instead!

Please read the late great Pat Kelley's dynamic compression ratio calculator site at least three time's to see what I'm talking about w/ respect to intake valve closing timing!

http://cochise.uia.net/pkelley2/DynamicCR.html

for starters...

I have!

pdq67