Mortec says 336781 heads are 118cc chamber heads, if you mill .012 off of them how much does it drop the cc size?
Im running 30 over 454 flat tops with .030 deck height now with peanut heads at 122cc and i need to boost my compression a little, im pretty sure with this setup im at about 7.75 to 1 and i'd like to get it up at least one point to run the cam i want and stay on pump gas..so i found a set of 781 heads (listed above) for $400 already rebuilt.
Thanks guys

I'm pretty sure for an open chamber head .006"=1cc. You can mill them to 118cc and probably zero deck the block and still be below 9-1 compression.

Sheet I've got shows .005" per 1cc on the 118cc chamber.
Did you cc the heads to see what your actually starting with ?
A 100cc head will get you to 9.2 with your pistons and deck height and a 109cc head would be 8.6.
Both calculations are with .020 gasket.

Sheet I've got shows .005" per 1cc on the 118cc chamber.
Did you cc the heads to see what your actually starting with ?
A 100cc head will get you to 9.2 with your pistons and deck height and a 109cc head would be 8.6.
Both calculations are with .020 gasket.


No i have not found the cc flask thing in town to measure the cc.. but the heads i have on it now are stock and never milled and mortec says 122cc..
IF these 781 heads would bring it to 8.5 it will work, but then again for 400$ i could put in pistons too..weighing my options ?? ? ? 781's flow better too..
Maybe i should hold out for closed chamber heads...
What do you think?

I'm pretty sure for an open chamber head .006"=1cc. You can mill them to 118cc and probably zero deck the block and still be below 9-1 compression.


I really dont want to mill the block.. so thats out.. SS402 already schooled me on quinch.

Hold out for some closed chamber heads. The 781's are good heads and $400 is a decent price, but even if you mill them a little you'll probably be barely over 8 to 1. Find some closed chambers, put them on, and leave everything as is it'll be right around 9 to 1.

I really dont want to mill the block.. so thats out.. SS402 already schooled me on quinch.

Ok, did he tell you that about .040" is where you want to be for a quench number. You have to add the .030" in the hole plus the head gasket. Unless you are using a .010" head gasket, you have room to deck the block.

Ok, did he tell you that about .040" is where you want to be for a quench number. You have to add the .030" in the hole plus the head gasket. Unless you are using a .010" head gasket, you have room to deck the block.

yes he put me on a site that explained it all, i just dont want to get that deep in this motor, im on a budget...i understand i can do all that milling and still have peanut heads too... i figure if i can put some closed small chamber heads on it it would do the trick until these 781's came along and i know they flow better so i could gain a little better performance there... but close chambers are hard to find... i called the engine builder here and he said he could mill my peanut heads for 50 each and port them and by that time i could have these 781's..

Unless you cc the heads when you start, you're spinning your wheels. I've measured 781's at anywhere from 117cc's to 125cc's. See of you can locate some 215/290/063 castings, they're semi-open chambers and generally come in around 106 cc's.

Unless you cc the heads when you start, you're spinning your wheels. I've measured 781's at anywhere from 117cc's to 125cc's. See of you can locate some 215/290/063 castings, they're semi-open chambers and generally come in around 106 cc's.

Busted Knuckles,, hahahaha,, that a good name, been there too, and my temper makes me throw my wrenches,, if they ever go to seed ill have some wrench trees growing in the pasture but one thing about it those wrenches wont bust my knuckles again....sorry back to subject,, i also have some 6272292 located but i cant find out much about them.. Ive got a buddy in the shop with some 215 heads but i cant talk him out of them they go in the boat...hes got 12.1 compression with those heads and i tried to convince him he cant run pump gas on those...he thinks he can...

The 292's are decent heads. They were on the LS-5's I believe. Kind of a middle size chamber around 112 IIRC, probably bet you around 8.5 to 1.

My 454 has the pistons about .030 down the hole too. I went with .020 thin gaskets, it's not the ideal .040 but without milling the block, what can you do?

I got a free 50 cc plastic syringe from the Hospital/Nursing Home my Mom was in years ago before she left us and use it along w/ a small piece of picture frame glass!

Works like a charm but you need to angle it and put the sawed off needle in from the high side. You will see what I mean.. It's easy, but take's some time...

pdq67

PS., you can probably get one from a Drug Store or maybe a feed store in the Vet Supplies for CHEAP??

yes he put me on a site that explained it all, i just dont want to get that deep in this motor, im on a budget...i understand i can do all that milling and still have peanut heads too... i figure if i can put some closed small chamber heads on it it would do the trick until these 781's came along and i know they flow better so i could gain a little better performance there... but close chambers are hard to find... i called the engine builder here and he said he could mill my peanut heads for 50 each and port them and by that time i could have these 781's..

If that's the case, a smaller chamber head is a wiser place to start. The 781 is a better flowing head than a smaller chamber head, but this only comes into play if it is a higher rpm engine. I don't think you could raise compression enough to be valuable by milling a 781 head alone. You have to mill off like .070" to get down to a 109 cc head, and then mill the intake to fit. I would agree if budget is the driver, and it usually is. Look for a smaller chamber head to start.

I made a list from mortec on the closed chamber heads is it safe to say if i can find any of these it will work for me?
Gen IV Closed chamber heads according to Mortec
206 97cc
208 109cc
213 ??cc
260 ??cc
702 98cc
858 109cc
390 98cc
391 107cc
392 Alum 107cc
215 101cc
802 101cc
063 101cc
840 107cc
842 107cc
290 101cc
291 109cc
198 ???cc

I wish W/P's would make a cast-iron Merlin 290 cc large oval port head that had 100 cc chambers and also used stock, 2.19"/1.88" valve train stuff.

Somebody finally verified that they did at one time make a 290 cc large oval port Merlin type head, but it had big chambers instead of 100 cc's jobbers.

I wanna say 290 Merlin VR's????

pdq67

I wish W/P's would make a cast-iron Merlin 290 cc large oval port head that had 100 cc chambers and also used stock, 2.19"/1.88" valve train stuff.

Somebody finally verified that they did at one time make a 290 cc large oval port Merlin type head, but it had big chambers instead of 100 cc's jobbers.

I wanna say 290 Merlin VR's????

pdq67

Combustion Chamber Volume: 119cc ALL IRON AND ALUMINUM
http://www.worldcastings.com/documents/instructions/head_merlin.pdf

Let me ask you guys this, casting number 3935401. One date code is D25-8 and the other is C5-8. They are “large oval port” intake port 240cc, and milled to chamber volume of 110cc. They were originally on a 427 truck engine. These heads have been completely rebuilt with all new valve guides and new exhaust seats, and both have been surfaced and new valve seals installed. Valve bowls have been pocket ported and large 2.19” intake valves and 1.88” exhaust valves have been installed, with a 3 angle valve job. New Crane 13308-1 springs and retainers and set to proper spring height. small 240cc intake ports professionally tested on a Superflow tester and i have the test papers.
My question is Will i have trouble with these tall deck heads as far as push rods length or intake fitting or anything else put on my 454 short deck. Im at the point of maybe changing my pistons out to gain a little better head than my 236's.. I pulled one of my rods out today and they are the thumb rods. end product is i want street pump gas and high performance street car, may be 8.5 to 1 compression maybe even 9 to 1,, i dont want to go too high because i may put a blower on it later down the line..

Input please, thanks

No one ?? ? ? ? ?

Heads from a tall deck engine are no different regarding external dimensions than those from a standard deck.
Pushrod length may vary due to the cam/lifter combo ,not the heads.
Stock intake on standard deck block works as well.
Those 240 ports are smaller than the normal oval port heads.
See Pg 11 - http://racingfeed.com/downloads/chevy_flow_data.pdf#search=%27cylinder%20head%20fl ow%20data
These heads will be restrictive in a blower application.

that didnt work.. i cant paste the results of the flow test..
http://pics.ebaystatic.com/aw/pics/s.gif (http://contact.ebay.com/ebaymotors/ws/eBayISAPI.dll?ShowCoreAskSellerQuestion&requested=motorhead0922&iid=130296058496&redirect=0&SSPageName=PageAskSellerQuestion_VI)

Compare them to the ones in the link I posted.

Compare them to the ones in the link I posted.

Here is the flow test. they have been worked..

http://img403.imageshack.us/img403/3008/401flowtest.jpg