Hang on boys, That KB399 looks exactly like a 167 with a Q-pad,
In order for KB to call it a 6cc dome They musta cast it with about an 11cc pad, which is ~.050, am I right?
At 9.600, the flat part of the piston would already be getting close to zero deck, being just .0095 below, which would put the dome at .0405 above deck, right?Let's talk about the Q; Since the 70cc head is about .080 deep and adding .028 for the gasket
I get; .080+.028 -.0405=.0675Q;smack in the middle of the detonation-prone zone, which I have heard is .050 to .080. Am I wrong?
I like that piston, but I'd Mill the tops off them, to .009 above deck; then use it with a 58cc closed chamber head, and the 1008 FelPro at .039 .. Now your Q will be .030, and your Scr at 58+8.8+5-2for the pop-up=69.8...... (662.3+69.8)/69.8 =10.488Scr
Then with a 56*ICA and 7000ft, Mr Wallace says:
#1) Static compression ratio of 10.488:1.
Effective stroke is 2.74 inches.
Your dynamic compression ratio is 8.84:1 .
Your dynamic cranking pressure is 148.68 PSI.
V/P (Volume to Pressure Index) is 119 ................................ 119
Not very potent but that's pretty good for 7000 ft
But if you're gonna do that, you might as well use the KB 167s and shave the heads .009 for similar results.
Just so you know, here is the stock 69-318 at 9.2Scr and at 500ft with an ICA of 48*
Static compression ratio of 9.2:1.
Effective stroke is 2.89 inches.
Your dynamic compression ratio is 8.15:1 .
Your dynamic cranking pressure is 164.89 PSI.
V/P (Volume to Pressure Index) is 137 .......................... 137
You are already 119/137=87% or 13% down in low-rpm power.
Any combo you build wants to end up at 137VP to feel like the stocker at 500ft, and to use the stock TC and gears. Without that VP, you will be looking at a TC for sure, and probably more gear depending on your needs and wants.
_____________360s from here down____________________________
How about:
A 360 with the 62cc iron closed-chamber heads, and KB107s which drop in at about .012 in the holes, and the .028 gasket; might have a Q of .040, and might be
62+2.5deck+6.3gasket+5pockets=75.8 total chamber volume, and
(744.6+75.8)/75.8 =10.8Scr, and
Static compression ratio of 10.8:1.
Effective stroke is 2.97 inches.
Your dynamic compression ratio is 9.13:1 .
Your dynamic cranking pressure is 156.35 PSI.
V/P (Volume to Pressure Index) is 141 ........................ 141POW!
Check it out; 141/119= plus 18.5% more bottom end; that's the equivalent of about 2 gearsizes or from 2.76 to 3.23s
In other words this 360 with 2.76s will perform similarly the#1) listed 318, with 3.23s. So if mileage is important to you.......
But if it isn't, then the 360 with 3.23s would be a real good mover at 7000 ft. 141 VP is a lot of VP,and the 25x* cam is a stump puller.
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Still 360
But lets say you can't afford heads. How about putting your 70cc heads onto a KB167 equipped 360 short, still at .012 deck clearance. now we get:
70+2.5+6.3+5= 83.8, with a Q of .120 or better; and
(744.6+83.8)/83.8=9.885, and
Static compression ratio of 9.885:1.
Effective stroke is 2.97 inches.
Your dynamic compression ratio is 8.37:1 .
Your dynamic cranking pressure is 136.38 PSI.
V/P (Volume to Pressure Index) is 123 ........................... 123
Well that sucks; IMO, not worth the 3.4% improvement in VP.
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So how about the KB190s with the .050 pop-ups. the Q works out to .081 so just barely out of danger.Ok we can mill the heads to work with the 190s. So take .040 off the heads for a Q of ; (.080 less .040 mill)+.039+.012-.050Qpad=.041 Nice Q but that's a lot of milling.
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>How about the KB 191s with .200 pop-up, well, no, that's too much.
We only have ~.080+.039+.012=.131 less .040target =.091, so .200 means milling the pistons.109...I vote back to the KB191s and mill the pistontops; it will be way faster, make the heads fit better. and probably cost less.
Now again the heads ~.080, the pistons are down .012 and the gasket .039 and totals .131 and we might as well target a tight Q of .031 so we have an allowable pop-up of .100. And that means a cut to all pistons of .100.
Ok so that's working; what does this get us for Scr?
Heads at 70cc, gasket at 8.8cc, and 2.5cc in the deck clearance,plus 5cc for the eyebrows, and less (guessing) 6cc for the domes ; totals 80.3 total chamber volume; I think that's right.
And (744.6 +80.3)/80.3=10.27Scr
Static compression ratio of 10.27:1.
Effective stroke is 2.97 inches.
Your dynamic compression ratio is 8.69:1 .
Your dynamic cranking pressure is 144.74 PSI.
V/P (Volume to Pressure Index) is 131 ............................... 131
Not real good but still 131/119=plus 10% bottom end performance over the best the 318 could do. That's worth one gear size easy on the startline, and getting closer to the 137 of the stocker at 500ft.
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Ideally this 360 combo wants
Static compression ratio of 10.95:1.
Effective stroke is 2.97 inches.
Your dynamic compression ratio is 9.25:1 .
Your dynamic cranking pressure is 159.55 PSI.......................... 159.5
V/P (Volume to Pressure Index) is 144 ......................... 144 POW!!
To get 10.95, would take a total chamber volume of 744.6/9.95=74.83cc.
This would require a bit of milling to the heads and and adjustment to the Q, to achieve.
Bottom line is this:
Any combo you build wants to end up at 137VP just to feel like the stocker at 500ft, and to use the stock TC and gears. Without that VP, you will be looking at a TC for sure, and probably more gear depending on your needs and wants.
By the time you add up the COST of all the machining,the port matching, and assuming the intake will still seal, and the new installed TC , and probably new installed gears; IMO, you couldda had a 360 for same/similar/bit more, bottom end, tons more midrange and a big fat power power hit on top. Don't lose sight of the
DOLLAR per smiles ratio.
Jus trying to help
