IMO
for a streeter
a 450 hp 360 with 3.91s may not be that street-friendly; been there done that. This will require something like the Mopar 292 cam,(248*.050) which makes peak power at about 5600. To get the 450hp number you will need it to be on a 108LSA or less. Which means a torque peak around 4100, and a shift rpm of about 6000. With a 727, that means on the 1-2 shift, the Rs will fall to 3540, which is well below the torque peak.
But 6000 in first gear with 3.91s and 27" tires is around 44 mph, and the 2-3 comes at about 77mph, dropping from 6000 to 4140, back into the basement as regards the torque peak. And 6000 in Third will be around 136 mph; so that would be a pretty long pull from 77 to 136; lol.
Restated; your powerband with a 292/108 cam may be from ~4100 to 5900= 1900rpm.
But your trans has a requirement of .59on the 1-2 and .69 on the 2-3 , which are 2420 in Second, and 1830in third.
Now, if you spin right thru first gear on the street, which with 450 hp is about guaranteed, then the 1-2 split is not a big deal. But if you also spin say half way thru second, which is from 44 to 77 so say she stops spinning at 60, that would be around 4600, lessee 5600 less 4600= 1000 rpm short of the power peak, and you are nearing the shut-down speed, which for me is 65 mph, cuz I don't get speeding tickets.
So My point is this; if your car is gonna spin the tires to 60mph with 450 hp, and trap at 60=4600; why do you want 450 hp? You can do the very same thing with 400hp; even 350 maybe even 300.
Now, the thing is this; assuming
an elevation of 900ft, and
the 292/108 cam in at 104* which then has an Ica of 70*, and
with an Scr of 10.5, and so
is predicted to make about 159 psi CCP, and a Dcr of 7.83
But the VP at 127 is only a lil more than a 5.2Magnum; so, it will take-off like one, and act like one up to about 3300 rpm
Read about V/P here
V/P Index Calculation
To get past all that, you would need a fairly hi-stall TC.
Or do what I did; With alloy heads you can run close to 200 psi on pumpgas here which is (R+M)/2, available in octanes of 87, 89, 91 and occasionally 93. I have run 185psi on 87E10
If you do that, then you can down-cam at least 2 sizes to say
[email protected] and still make say 380hp , but now with a power peak of say 5200, which will like the 3.91s. And it will have a super-fat low/mid range
Bumping the Scr to 11.3 with an Ica of 66*, will get you a Dcr of 9.0, CCP of 187psi, and a stinking wicked V/P of 157, all at 900ft elevation.
I have run this exact combination. It didn't make anywhere near 450 hp but it was way more fun to drive. By the car's trapspeed of 106mph in the Qtr, this was maybe 350 hp. Possibly a lil more cuz I was shifting at 7000, on a 5200 power peak, yeah so I did not know that I was that far out of sync..
Anyway, since you are at this early stage of the build, I thought I'd mention these things, before you get the lazy bottom end below 30 mph, that is so frustrating when you don't have one lower gear.....
The whole point is to decide at what roadspeed you want the power to be. What is most valuable to you? And then try to fit that in with the gears that you are willing to run. And then build only enough engine to make that happen, without excessive wheelspin.
Forget trying to build a street car to be competitive at the track. Those two, with a 360/auto, require completely different rear gears and stalls, and OMP, will need more gears. No matter which way you bias the combo, the other will always suffer............ until you consider supercharging.
Happy HotRodding
