Thread: BBC 336781 Heads?

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Building a 468, going in an 84 Chevy Pickup, 454, bored .060, 4 bolt main, with stock crank and rods with flat top pistons and a set of ported 781's cut for 2.19/1.88 valves. Dual plane air gap and a 770 street avenger. Anyone have any info on these heads? I have heard good things about them other than my compression won't be very high. Any cam suggestions? Will have a 2800 stall or so and has 3.08 posi 10 bolt rear end. TH400 w/ shift kit. Not lookin for a dragstrip terror but more of a " I'll smoke just about any truck on the road and some rice burners. Maybe even some stock Camaros? Let Me Know.

yep i have used them heads .i am doing a build right now with a set but i am going to 2.250 1.880 with 11/32 stems will be a 496. why flat top pistons ? you not going to put much cam in it that point .no need for the 2800 stall ? no gear in a heavy truck??? the cam that i use alot i would not use in your build with low CR if hyd roller cam some thing like 225/235 @ 050 600/600 on a 108 you will need more gear or this is abit mild but would work good in a heavy truck you will need a 2000 stall 218/226 @050 588/588 on 114. if your sold on flat tops .i tru- deck the block with BHJ i then deck the block to O or in the hole a wee bit 005 thats about it that will help . you can give the heads a good hair cut as well

Yeah the deal was a 4 bolt main block (454) already bored .060 with the stock crank and stock rods that already had the brand new flat tops on them. It also came with a set of peanut port heads and my cylinder head guy said they would choke out after 4,500 rpm or so. So I found the 781's for $200 complete and i'm gonna cut them for 2.19/1.88 valves and get them a basic port job. They look as if they have been milled before but look stock other than that. I was planning on at least a .550 lift cam but I want a nice flat torque curve throughout the rpm band. I know the gears gotta go, and they will as soon as I can afford them. I don't know how to install them myself. I really just want it to be fun and powerful, And it will see some midnight drags as well. So lower the stall and be conservative on the cam, right? I will have to use Flat tappet for now so what would you recommend, keeping in mind the gears are next in line. I was considering comp extreme 4x4 cam with more exhaust duration.

well the small cam will work better with the low CR . and the small ports may slow you down BUT .... you need more cr to go with more any thing as i see it .so i not shure how nuts your going with port work there no need for it. good 4 angle on intake valve seat. full radius one angle on ex seat with some short side radius on the port that about it .you could use bigger valves 2.190/1880 .but porting work may hurt low speed tq less he has numbers to back up the work . i like the ideal of a smaller port with a bigger valve to pick up port speed on a lower rpm engine . the cam that marine bbc used with small port heads low pro intake .and iron log ex was the 500/500 222/234 @050 on 115 and this engine made 330 hp so it a great cam for low cr and small heads .so with headers and intake should not be hard to get it to 375+ hp or could try Erson e120020 232/239 549/558 110 adv 6 so on 106 or i may think about this cam kit elign e1117pk 549/558 232/239 110lc 440 hp marine cam looks alot like erson # 120020

I'm not planning on hogging out the ports, its basically focusing on the short side of the ports, he said i could gain up to 30cfm by doing this. This is not going to include a gasket match on the heads, which he said i'm not really going to gain a whole lot from that anyway. Plus I plan on milling the heads and decking the block to get it as high as i can. I can also use a thin head gasket too. Surely with decking, milling, and thin head gaskets i can get around 9:1, right? Will this be enough compression to have a .550 lift cam? Thats not really that big for a big block right? I had a .480 lift cam in my 350 and it was very streetable, in fact i wish i had gone bigger. I ended up hurting that cam anyway so it doesn't matter.

Originally Posted by slammed84

I'm not planning on hogging out the ports, its basically focusing on the short side of the ports, he said i could gain up to 30cfm by doing this. This is not going to include a gasket match on the heads, which he said i'm not really going to gain a whole lot from that anyway. Plus I plan on milling the heads and decking the block to get it as high as i can. I can also use a thin head gasket too. Surely with decking, milling, and thin head gaskets i can get around 9:1, right? Will this be enough compression to have a .550 lift cam? Thats not really that big for a big block right? I had a .480 lift cam in my 350 and it was very streetable, in fact i wish i had gone bigger. I ended up hurting that cam anyway so it doesn't matter.

yes it can be 550 lift is not bad but it the DUR and lobe sep + lift that can added up to no piston to valve . you taking better then a total of.040 off heads .gasket and deck .thats less pv room

Originally Posted by pat mccarthy

yes it can be 550 lift is not bad but it the DUR and lobe sep + lift that can added up to no piston to valve . you taking better then a total of.040 off heads .gasket and deck .thats less pv room

I think the duration will be somewhere in the 230-240 range. What is the thinnest head gasket i can use if I zero deck? Shouldn't I keep at least .040 for piston to head clearance? I've heard of people going lower than this to maximize the quench area. I've also heard that the quench is sometimes more helpful than compression, but will it help even if the compression is low? In other words, can you have a very effective quench area even though your chamber size is big? Quench is always going to be there as long as you get the pistons close to the heads, right? I could be wrong in this matter. Also won't it help that its bored.060. over? That will increase compression too?

well i would not run it any more then .038 from deck . big pistons can rock if you have some piston to wall .you said you were going to a thin gasket . you can used a gasket with a smaller bore size like felpro f 1037 thats a 9.7cc some of the one size fits all have a bigger bore size 4.500.if a race flat top if will help at 060 bore but if not some piston builder mover the ch down to lower the ch and to deck the block so you need to check the ch and deck to that .you asking if quench vs CR ? well both is good by that you shure in the hell do not want a piston way down in the deck with hi CR but a flat top work better if the quench is tune in better then a hi cr engine ? no both engine work better both engine tuned in the same CR make s power it lets you run more cam for more power. if you can get hi cr with a flat top all the better i have a flat top i am building it will be 14.7 or so .all bbc engine have quench a open chamber still has some like said its nice to have it right

how will you come up with 14.7:1? those gotta be some tiny chambers! Lets say hypethetically, If I zero deck, use that small gasket, and end up with a 110 cc chamber what would the compression be? I tried to do the math but it just confuses the hell outta me. So many variables. Would that put me some where in the 9:1- 9.5:1 range? What kinda numbers would you say I could see from this rat? Please tell me I will hit the 500 ftlbs. mark. I appreciate all the info Pat.

do the 781 heads have screw in rocker studs?

all bbc heads have screw in studs and guilde plates

Originally Posted by slammed84

how will you come up with 14.7:1? those gotta be some tiny chambers! Lets say hypethetically, If I zero deck, use that small gasket, and end up with a 110 cc chamber what would the compression be? I tried to do the math but it just confuses the hell outta me. So many variables. Would that put me some where in the 9:1- 9.5:1 range? What kinda numbers would you say I could see from this rat? Please tell me I will hit the 500 ftlbs. mark. I appreciate all the info Pat.

no not to small of chambers 4.610 bore by 5.500 crank

9to1 will be hard O deck the block use a 039 head gasket with a 4.370 bore .heads will need to be 110 cc it will be around 8.6

Yeah I'm gonna try to get as close as I can. Thanks for all your info.