Getting ready to go back to the strip and need a little advice. I have a full weight 69 Dart with a 360/727. The 360 is about 12 years old and has about 40,000 miles on it. Dry wet compression tests show 170/195 except #6 Was 160/195. The motor has an edelbrock 650carb, edelbrock air gap, x heads, tti headers and a comp xe284 thats been advanced an additional 4 degrees.the 727 has a 2400rpm stall w/ a shift kit. 3.55 gears and 235's. The car has run 13.40-13.60 @102-104 on drag radials and 60 ft's were bad, 2.10's.
I have an opportunity to buy a 3.91 gear 3rd member for a decent price. Would it really help me much over my 3.55's? In a perfect world, I would buy a better converter and rebuild the 360, but I'm broke and wanna try and get into a high 12 before I rebuild this thing. Any advice or suggestions are appreciated. Thanks.
What gas are you running? And what power-timing?
To get the 168psi, I back-worked the calculator and came up with this
Static compression ratio of 10.2:1.
Effective stroke is 2.84 inches.
Your dynamic compression ratio is
8.30:1 .
Your dynamic cranking pressure is
167.70 PSI.
V/P (Volume to Pressure Index) is 145...........................................................145
You may be into detonation! A Dcr of 8.3 with no Q in the openchamber heads will/can do that.
Part of the problem is the 100* install.This brings the ICA to 62*.
Here is the same combo with the Ica @66*
Effective stroke is 2.74 inches.
Your dynamic compression ratio is
8.04:1 .
Your dynamic cranking pressure is
160.92 PSI.
V/P (Volume to Pressure Index) is 134..............................................................134
This is about the limit for pump gas and full timing
Notice tho that the VP has fallen to 134. This makes the bottom end with a 2400 very soft.
This increases your 60ft right there.
Then there is the small matter of the totally wrong gearing to tire size to trap speed. 103 calculates out to about 5100 with 5% slip. Your 4700/4800 means that 2400 is at about ZERO-slip, so the rest of my numbers will be using zero-slip. The problem is that 284 is just waking up at about that rpm. That cam probably power peaks around 5200, and will want the 1-2 shift at about 6600, and the 2-3 at about 6200, and I bet you weren't shifting it there?? So that means at 6200 in second gear you would be hitting 90 mph, and going into third this would be 4270rpm. where it has just woke up. It will want to trap at about 5700.
But I'll almost bet you short shifted both gears at 6000. If you did that, the Rs drop to 3540, and 4140, And with a VP of 145 She'll still be a lil soft down there.
So by my count, your combo is suffering in 5 areas
1) power-timing and possible detonation
2)the 2400 with the VP145
3) the shortshifting
4) trap gears.
5) the little 650 carb
I offer the following solution;
1)Check for signs of detonation and back up the cam to as far as 106 if you have to
2)More TC, a lot more
3)Increase your shift rpms to 6600 and 6200, and run some loops
4) the gear you want is probably 4.10s to get you 5700 on the nose at 104. The 3.91s might get you the same 104, but at 5450ish, IMO a hair low. But if the above mods pick up the trapspeed then 3.91s will work, and are good to maybe 109mph.
5) this would be my last mod, but that engine will like a 750
Now on a budget, numbers 1 and 3 are cheap,
>Detonation will kill your power, so that's the first place I would look. Easiest thing is to back off 4 degrees and see if you go FASTER in MPH. If yes, then go another 4 then start to work your way back.You can get around this for test purposes by running some anti-detonant in your premium. If she traps higher, you're on the right track.
>As to shift loops, work your way up from 6200 in first/5800in second, in 200 rpm increments atta time, and only work one gear atta time starting with the 2-3 shift. Anytime the car slows down, and it's not detonating, go back to the last shift rpm.
>But the TC is the big issue. I would drop that thing like a hot-potato. And here's why;
Your engine won't start pulling until somewhere near 4000, am I right, maybe even later. But with zero tirespin, 4000 is 34 mph. That's why. And the 2400 is making your hot-cammed 360 take off like a warmed up 318. That's why. That 2400 is putting the clamp on your engine at maybe 120ish hp, whereas a 3600 might launch you at 200ish hp ( yeah I'm guessing) but the point is you could be blasting off with a lot more horsepower. And that will really boost the 60ft, and that will knock down the ET, while not doing a lot for the Mph.
Try to get your combo working with the cam in at the current timing, cuz the drop from 145 to 134, will really be felt. And if the 2400TC is staying then the 145 is needed. But if you put a bigger TC in, then retard it!; Solving for detonation trumps everything else. A bigger TC would allow you to retard the cam without loosing the bottom-end cuz you're no longer stuck down there.
>As to the 3.55s, they are making your engine stay in the low-zone for just too long, and robbing you of putting down good average HP. But this is further down the list than the first three.Concentrate on the first three points first, and maybe it will be quick enough for you.
>As to the carb, I would do this last. I wouldn't be in any hurry to swap it out, cuz really it's only barely too small for this combo, and even then only at the very top of the powerband. Mathematically it's not too small at all; (360x6400)/3450 x.85VE(guessing)=568cfm. But mine
seemed so much sloower with a 600, and didn't wake up until the 750 or TQ went on it.
Any way, that's all I got,