Where do i go from here?

[zinser72]

i know this subject has been beat to death but ive asked so many people and everyone tells me something different. im looking for a hardcore tech guy to steer me in the right direction. i have a 318 with factory forged crank, scat rods, and kb167's. i will be at zero deck. i acquired some RHS LA-X heads for it (62cc closed chamber w/ lots of quench but cast iron) my cam is a XE285HL per comps recommendation. int closes 68* ABDC. it has .545 lift and 241/247 dur @ .050. i ran all the numbers and with a .051 thick gasket my static compression is 10.7 and dynamic is 8.7. with such a low dyn cr wouldn't i be fine on 93oct? no one can tell me. please let me know what i should do from here. i already have all the parts so swapping is not an option, how can i make this work? KB recommends .040 quench and i'd already be over. i know im not the first one out there to build this combo so it has to be possible. please let me know what you think. block oiling is fully modded for sky high rpms just going to limit it to 7000 because of pistons. please let me know if i did my calculations wrong or what i need to do to make this 93 oct friendly!!

 

[273]

This is a little above me but I'll get the ball rolling, dynamic ratio 8.7 isn't low and anything above .040" quench is starting to lose its effectiveness. Every point of CR is worth about 4%hp so say your engine would make 450hp now and if you went down to 9.7:1 CR you would 430hp. I go with a 0.040" gasket to get more quench and open up chambers and deshroud valve to a larger cc.

 

[273]

You sure about your CR I just typed in your spec's with the KB CR calculator
Zero deck
0.051" gasket
62cc cambers
I guessed at
0.040" overbore
4.07 gasket dia
5cc valve notches
And I got 9.55:1 static CR

 

[crackedback]

Run a .040 gasket.

 

[MoparAnglia]

You sure about your CR I just typed in your spec's with the KB CR calculator
Zero deck
0.051" gasket
62cc cambers
I guessed at
0.040" overbore
4.07 gasket dia
5cc valve notches
And I got 9.55:1 static CR

As above, you'll never get 10.7 static with a zero-decked flat top, without serious milling or a steel shim (and mashed valves).
You fluffed your original calculations by putting the valve reliefs in as a negative number (if using the kb calculator).

Run a .040" gasket, it will come in around 9.7-9.8 static and your motor will run happily on 93 or less. Those closed chambers with decent quench won't need much total advance anyway.

 

[Dodge74]

I don't think those pistons really sit at a real Zero Deck. Somebody needs to get out a feeler gauge and a straight edge and check the clearance, because i came up with 9.52:1 with a 0.40" Quench and 9.54:1 with a 0.39"............ hope this helps .........

 

[MoparAnglia]

I don't think those pistons really sit at a real Zero Deck. Somebody needs to get out a feeler gauge and a straight edge and check the clearance, because i came up with 9.52:1 with a 0.40" Quench and 9.54:1 with a 0.39"............ hope this helps .........

He said 'I will be at zero deck'. I had assumed that meant the block had been decked to get it there...

As for the oiling mods for sky high rpms, I'm curious as this being a hydraulic flat tappet, 7k is way optimistic anyway.

 

[zinser72]

As above, you'll never get 10.7 static with a zero-decked flat top, without serious milling or a steel shim (and mashed valves).
You fluffed your original calculations by putting the valve reliefs in as a negative number (if using the kb calculator).

Run a .040" gasket, it will come in around 9.7-9.8 static and your motor will run happily on 93 or less. Those closed chambers with decent quench won't need much total advance anyway.

you guys were right i put -5 in figuring negative would be reliefs. anyway now i get 9.7 static with a .039 gasket. sounds good for 93 oct correct? just wanna be totally sure before it goes together. thanks for the responses