[GUS00]

Have A 454 With Flat Top Pistons ,SLR Cam. Lift Is 532-522 Duration Is 282-292,with Roller Rockers . Had Some Head Trouble, They Were 702's Now Have 336781 Open Chamber Heads . 206-172 Valves Will This Combination Work Just As Well ? Thanks....................gus

[matts37chev]

flat tops and 781s make a pretty low CR
i dont know what cc the old heads were
have the 781s and/or the block been cut/milled ?

but it will probably work ok with that cam



*I am no expert
there are a few guys on here that know more than me
maybe they will chime in

[GUS00]

The 702's Are 98 Cc . The 781 Are Supposed To Be 113 Cc. The Block Has'nt Been Decked ,but The Heads I'm Not Sure About As They Are Still At The Head Shop &the Bore Is Still Stock. Thanks For The Comeback...........gus

[matts37chev]

Originally Posted by GUS00

The 702's Are 98 Cc . The 781 Are Supposed To Be 113 Cc. The Block Has'nt Been Decked ,but The Heads I'm Not Sure About As They Are Still At The Head Shop &the Bore Is Still Stock. Thanks For The Comeback...........gus

the 781s are more like 118 - 120 cc

[topwrench]

I dont know what the deck height or the volume of piston or head gasket thickness is gonna be but the flatops with those heads will make that big block sick (wont go!) compresiion,Ithink ,will be in the 8:1 range at best...
Try to get some closed chamber heads or change pistons.

[GUS00]

How much can I mill the 781s down .They have 219 188 valves now .I want to try them on a 454 with a comp extreme marine cam - lift-544-547 duration 226-236 & flat top pistons. stock bore & deck. .......

[F-BIRD'88]

It won;t matter. You won;t get the cr up high enough with a flat top piston and those heads.

Get a supercharger or different pistons with a 18-26cc dome or different heads with a small combustion chamber.

A modern gen VI 454 vortec BBC head will work well. Any of the good old 96 to 100cc closed chamber oval port heads work well with flats tops in a 454. like 063, 215 castings etc.

the 781's will work well with a piston swap.
heads will work well.

[F-BIRD'88]

If you want to use the big valve good 781 ovales it will be well worth it to do it right and get the right dome piston
for this combo. The right pistons are not that much money.
A KB hyper or speed pro hyper or probe will get it done.

You want a 18 to 26cc dome depending on the desired cr, actual measured head volume and assembled piston to head clearance @ TDC. (deck height)
Piston dome to chamber wall clearance must be checked. minor chamber wall clearanceing grinding may be required.

This is a really good combo when done right.