What rpm power range for my 460 build
 

Where should i build my power band at for a 460 for my cobra build. I am going to build it for around 500hp and just need to know if my power should be low, medium or hi end of the rpm range. I am looking for a nice tame driver, my tire dia is 25.7 inches, my rear end is a curie 9 inch Detroit locker with 2:50 ratio, and my trans is a Richmond 5 speed with 3.27 1st and 1:1 fifth so technically no overdrive. Thank you for your help.
Greg

If you have a 2.50:1 rearend ratio, you better be building it for as much off-idle grunt as you can muster.

Those ultra short tire diameters make a 2.50 ratio seem like a 3.50 with no overdrive.

That 3.27 1st gear should support that diff ratio just fine

Yeah, if you drive around in 1st gear.

Come on, no one uses a 2.50:1 rearend ratio in a Cobra....or any other vehicle for that matter.

A 2.87:1 1st from a TKO with a 3.31 gear would still be an overall ratio of 9.5. He's way down there at 8.2.

With a 1:1 5th gear, he's at 2000 rpm at 60, 1800 at 55. If that's what he settles with, then a mild camshaft will be in order.

Interesting thread.

It might be instructive to ask what txcobra's car weighs with 1/2 tank of fuel and the driver installed.

I have two sorta similar cars, each weighing about 3200 lbs. Both use a C-6 automatic with a 2.46 first gear and 1600 rpm (pretty low) stall speed converters. The automatic is a difference; txcobra's 3.27 first gear might be similar overall.

My Cobra has a 2.88 and the other car uses a 2.75 axle. The engines are, um, a bit bigger: 521 and 557 respectively and are quite mild with hydraulic rollers and 9.8:1 compression. They have between them about 50K miles of hard street use with lots of track time at road race venues such as Sebring.

Each has over 400hp at the back tires giving tire-shredding capability from a dead stop up to whenever I let up using street tires - track tires seem to stop spinning at about 50-70mph thank goodness.

Torque curves are wide, flat and high, getting to about 500 foot pounds at the flywheel not long after 2500 rpm occurs, and keeping that level to above 5000.

I'd predict that on the street, if txcobra's car isn't too heavy, it will be fine.

The 385 can be built to produce a bunch of torque over a wide range with lots down low if needed. Unless it will be a race car I'd suggest going for mid-range torque (say 3000-4000 rpm) so the car can be tamer going away from a dead stop. If the red line is 5800-6000 rpm, the car will still run away from almost anything, easily.

Tom

I don't know what the overall weight will be as it is still in the parts collecting build stage. What little I can tell you is I weigh 275 and it will be a alum headed motor. Is there a calculator to put in this kind of info that I can play with. Thanks for your replies so far
Greg

That would be a nice cruising rpm on the hwy for me. I had a 57 chevy with a 400sb and a wc t5 that would do 60mph at 1500 rpm in 5th

Tom is correct, these engines have enough grunt to pull from about anywhere, but they have to be built with that in mind.

Aluminum or cast iron heads really have nothing to do with the overall package, but you will need a mild camshaft to make that package work.

I would take a look at what speed you will be doing the most driving and work around that. Cruising at a steady speed is just part of the whole experience, and IMO, that overall gear ratio is going to be lacking.

I have a 460 with the same transmission and a 2.75:1 FDR. It's real easy to get rolling in 1st gear and a "tame driver", but my cam is pretty mild. If I'm just cruising and taking it easy I'm often out of 1st gear before I get through intersections.

If your goal is 500 HP you'll be putting in a bit more cam than I have and moving the power band up slightly. That should be reasonably compatible with your 2.50:1 FDR and your "tame driver" goals, but it will take a wee bit more to get it rolling. Obviously a lighter weight car will easier to get rolling than my ~3,000 pound West Coast Cobra.

Just my $0.02.

I tried a 2.47 2.75 and ended up with a 3.00 as a compromise with a C-6. It buzzed more than I liked on freeway so speeds were kept down. I had the luxury of having lots of ratios on hand to try. 3.50 was no bueno on the hyway. With 10" converter 1st & 2nd was often a pedal fest no matter which of three different cams tried, 225 to 244 duration.

American powertrain has a good calculator under tech support. Click on speed analyzer.

The reason i mentioned the alum heads was for the weight not performance. Anything i can go alum on i will to make the front end as lite as possible.

Speeds will probably be ALL. Some hwy to go on power tours, and city and back roads for cruising.

Understood.

With a BBF, you'll probably save 100 lbs between cast iron and aluminum heads, but don't get carried away with weight reduction on the engine as the engine sits considerably behind the front axle centerline.

As I mentioned earlier, your camshaft requirements will be more towards the "RV" side than the performance hot rod side of things. You will need excellent off-idle and low rpm throttle response/power.

^^^^^ Agreed.

IMO your 500 HP goal won't be attainable if you want to have "a nice tame driver" with a 2.50:1 final drive ratio. In order to have the former you'll need a mild cam, and that mild cam will keep you in the 400-450 HP range, even with good aluminum heads. A bit more cam will get you to 500 HP with a BBF, but then you'll be a lot happier with a FDR in the range of 3.00:1, even with the stump-puller 1st gear in that transmission.

Just my $0.02.

My car with me in it tips the scales a little over 2900lbs. running a 3:73 gear with Tremec TKO a tad over 500hp 460. It took several tries to find the combo I liked the best which I now have. Incredible off idle torque the engine effortlessly spins to 6K funny thing is very seldom push it that hard because most of the time it's not needed. Sure nice knowing when that urge hits have no concerns other than the blue lights. Good Luck in your quest for the right combo.
Mike

Assuming the valve train hardware between the two heads is identical, and both heads are passenger car type (ie, not A460, etc) then the weight reduction will be about 60 pounds.

Just dyno'd an engine that made 1.05 hp/inch with a 233"@050 custom flat tappet cam, 4150 carb, as-cast dual plane, and unported Edelbrock heads, pump gas. The same results could have been fulfilled with ported OEM iron.

For a low rpm responsive 385 Series, I'd recommend stroking it. Even a little ol' 4.14" stroke 500-inch engine will meet the needs, desired hp numbers, on pump gas with a pump gas friendly compression ratio. And with the right cam the torque number will far exceed the hp number (the above noted engine made 1.22 ft-lbs/inch).

I note how you left out the contextual "if you want to have "a nice tame driver" with a 2.50:1 final drive ratio" from my comments. That context is an important factor in cam selection, as you well know, yet...

cycleguy55 to be clear: the 500-inch engine I suggested in my post above would be a "very nice tame driver," and absolutely "will meet the needs" as I myself stated. The 460 could be, too, depending on the exact needs (ie, the 460 would still idle below 1000 rpm, for example).

It was not my intention to specifically delete that particular portion of sentence from your post. On the contrary my intention was to streamline the quote down to the matter at hand and provide the relative anecdotal advice, that's all.

The engine's would indeed be "nice tame drivers," specifically tailored for good idle, great low end throttle response, and an excellent overall broad power band.