so hear is the deal. i have a late 70's 454 block that is .60 over. i have a solid roller cam set up with a 620 lift. i have sealed power l2349f60 pistons that are 11.81 to 1 with 100cc chambers.

my question is this i have 3 different set of heads and im not sure which ones to go with? im looking for the best performance i can get out of my motor so mayb someone will know a little bit more about this then i do.

i have a set of chevy 353049 heads with 122cc chambers in stock running order with my pistons i believe that will put me down at around 9.7 to 1 comp ratio. the thing is im looking to keep my comp. up around 11.5 and up. cause i dont want to loose to much hp.

the second set of heads i have are gen VI # 10141279 they are 100cc chambers but the have non adjustable rockers. im wondering if these heads will work on my old block? and if they are gonna flow better then the 049's?

the third set i have are GEN V 118cc chambers head # 14097088. rect port.

all my heads are stock running order and i dont know which heads will be the best bang for my motor or maybe i can get a certain set of my heads milled to raise the comp ratio if the chambers are too big.

im new to building motors so if anyone can help it would be much appreciated thank you

                  Garrett  

The #049 heads are arguably the best performance iron heads Chevy made. CHP documented that they flow very well for an oval port, or as they put it - they 'outflowed' any other OE iron oval port head they tested.

It's unlikely that the Gen V heads would even bolt onto a MkIV block - there are differences in the coolant passages that could result in leaking.

If I were you I'd stay away from closed chambers. Factory big blocks have flat valve angles and need a lot of room for the valves to unshroud when they open into the chamber. GM phased out the closed chamber 35+ years ago for a reason, because the open chamber just proved to be more efficient.

Your compression is an issue and the best solution would be to get a large open-chamber dome to regain the lost compression from the larger chamber volume.  

WHEN YOU SAY TO REGAIN COMPRESSION  and get open chamber dome... does that mean get new heads? or like i said im new to engine building so give me a little break if that ? sounded dumb
                     thank you
                          garrett  

The Gen V heads will NOT work on a Mark IV block.  

well ive been told by many that my 049 heads will b my best bet.. but i just dont want to loose my compression. I wont b able to afford to buy new pistons either. any suggestions?  

I don't know what to tell you, it seems like a lose-lose situation...

You will either lose power to a low compression ratio or to valve shrouding and poor breathing.  

what do you think i would loose more hp with low compression or valve shrouding and poor breathing?

do you think i could get my 049's milled to raise the compression?

or would it be better to just find some new heads? as in some nice new pricy aluminum heads?


i have a corection also my block is a 1978 to 1990
#14015445 also stamped "hi perf"  

049's can safely be milled to 118cc chambers. You will have to do the mathmatics with your piston dome volume, deck volume (if not zero-decked), and head gasket volume, to find a true comp. ratio.  

What are the specifications on your camshaft? Overlap, intake closing piont, and duration@.050 are some factors that need to be considered with compression ratio.  

If you do indeed get the combustion chambers down to 118cc you should have a minimum of 10:1 compression. Is that a lot? No, but it is it "enough," probably.

I would say losses from valve shrouding and a poor induction are going to be more severe than by lowering the compression ratio, especially at the high end of the rev range.  

the cam specs are as follow


620 lift int/exh
valve lash hot .30 on both
adv duration.. 290 on both
.50 duration 248 on both
and 108 lobe center
its a solid roller cam  

i have the sealed power l2349f60 pistons  

Are you giving a sort of net lift value or a gross lift?

If it is indeed .620" gross, take .030" off that and you have .590" lift which is pretty piddly for a solid roller of nearly 250° @.050! Why is your cam that tame? I would be expecting at least .660" lift gross with nearly half the valve lash. Shoot, Crane has a 250/282 profile with .715" gross!  

Are you running this on the track or the street? If the street, that cam will not provide any low or mid rpm powerband with a 10-1 comp. ratio. The dur.@ .050 is way out there, especially for the relatively low lift.  

this will b a streetable track car... i had a sit down with mike from jms racing engines also known as johnson machine service. he has been a huge help to my cause. we decided that we are gonna build the motor one step at a time.. first we are gonna start with the heads and mill them down to 188cc chambers.

now depending on some other issues i may b able to go to a bigger cam. i will have to do a valve piston check after we mill the heads. i am also going to a 2.19 1.88 set of valves.

thank you all for your help if you all have any more suggestions let me know or have ever run a similiar motor combo give me a lil insite