2:91 or 3:55?
My '68 Dart has a carburated
5.9mag, stock bottom end, right now
stock cam, edelbrock air gap and a 1406 carb. Dougs
headers.
the stock install of
250/264/112-7/29 overlap (12 Effective)/116 comp./119 extr/64Ica
>
>A500 swap, and a cam swap to a
Lunati voodoo [email protected]
264/270/112+4/43 overlap(34* Effective)/122 comp/107 extr/Ica 58
>car currently has 3:23's but I have a brand new set of 3:55's I was going to throw in soon as well.
> My 225/60-15's are 25.5" (
80" roll-out)
>In my case, would you recommend just leaving the 3:23's in there till I get the cam and tranny swap done and see how it feels? Or go ahead and throw in the 3:55's at the same time?
>Note: I do a
lot more highway driving than in town.
>you are correct on the Lunati, it is the 20200715
>a stock 5.2 cam not the 5.9 cam.
It's 184/193 at .050 and its a 112 lsa.
>I"m at
5000' elevation
>Numbers are all between 139 and 144,
most were 140
Ok then
with the factory cam in at Ica of 64* as per the 119* installed centerline, and the stock Scr of 9.4; your pressure is predicted to be;
Static compression ratio of 9.4:1.
Ica of 64*, 5000 ft elevation.
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 7.55:1 .
Your dynamic cranking pressure is 125.52 PSI................ 125
V/P (Volume to Pressure Index) is 106........................... 106
So your reading of 140ish is telling a different story. I'm just gonna advance the cam until it lines up with your numbers
Static compression ratio of 9.4:1.
Ica of 53*. 5000 ft, factory cam
Effective stroke is 3.04 inches.
Your dynamic compression ratio is 8.13:1 ........................ 8.13
Your dynamic cranking pressure is 140.55 PSI.................. 140
V/P (Volume to Pressure Index) is 129 ............................. 129
So it looks like somebody has been inside there all ready.
A 53* Ica calls for
250/264/112+4/33overlap (32Effective)/127comp/112 extraction/53* Ica so that looks like someone already gave her the perfect cam-timing
.
So now lets see the Lunati, per their install,at 4* advanced.
Static compression ratio of 9.4:1.
Ica of 58*, 5000 ft
Effective stroke is 2.93 inches.
Your dynamic compression ratio is 7.87:1 .
Your dynamic cranking pressure is 133.78 PSI. ..................... 134
V/P (Volume to Pressure Index) is 118 ................................. 118
So looks like a bad deal below 3500rpm or so, she be needing more compression. How much?
here yago
Static compression ratio of 10.4:1.
Ica of 58*, 5000ft
Effective stroke is 2.93 inches.
Your dynamic compression ratio is 8.69:1 .
Your dynamic cranking pressure is 155.29 PSI. ..................... 155
V/P (Volume to Pressure Index) is 137 ................................. 137
now you got something!
Ok so now if the current engine is in fact a 9.4 Scr, then the total chamber volume will be 87.76cc. With your gasket swap of -4.87cc, the Scr becomes 9.89, lets check it out;
Static compression ratio of 9.89:1.
Ica of 58*, 5000 ft, Lunati cam
Effective stroke is 2.93 inches.
Your dynamic compression ratio is 8.25:1 ............................... 8.25
Your dynamic cranking pressure is 143.69 PSI........................ 144
V/P (Volume to Pressure Index) is 127................................... 127
So that compares favorably to the factory numbers of 140/129, as seen above. So now at least the bottom is as strong after the cam swap as before, Good deal. and the 213 @.050 compared to the
[email protected] is no comparison at all; the Lunati will rock with 29* more intake duration, which is 4 sizes, and I'll guess an easy 40 horsepower stronger,possibly more, at 800 rpm higher. The new power peak will be at about 4900, so yur gonna have to rev there to get the power. The peak will stretch out fairly flat with a 112 LSA cam so, with an automatic, your 1-2 shift rpm might be over 5500; you'll have to run some shift loops to see.
I see the Dcr has risen to 8.25, which might present a timing problem; But at most you might have to delay the All-in power-timing.
All in all, an excellent upgrade.
I say do-it
So again, the bottom end is pretty much the same so I would run the A999/3.23 combo, but I would first leave whatever is in there, in there. Cuz you said mostly hiway. Keep in mind that the power is not gonna be noticeably different until after about 3500, so don't get cranky!,lol. with A904/2.94s this will be 35mph in first. With the A999/3.23s it will come down to 28.5 mph. This is the beginning of the power increase. With the A904/3.23s it might be 32 mph.
You're in charge of maintaining the Piston to head and to valve clearances to prevent your engine from self-destructing.I think you'll be fine, but saying it doesn't make it so.
Ok so that's corrected to 5000 ft now.