# Motor HP/torque thread, build info!



## jetstang (Nov 5, 2008)

What does it take to get 400 HP, and 500 Ft lbs out of a 75 400 with 6X-4 heads on the cheap, or reasonable?

I got a good 400, cam rounded a couple lobes, ran great. Put a 350 in with a cam and it's a dog. Just want to freshen the 400 up, small stall and get some good HP/Torque for $1000 or so. Just cam, pistons, no exotic stroker stuff for now.. Already got headers, duals, Edelbrock dual plane, Holley 670, 3.36 gears and HEI. I am running AC, power brakes and want some MPG.
I plan to take the 70 on the Power Tour next year, so it has to be a streetable motor with Oomph and mpg, injection is an option.


All the motor talk, figured this would be a good place for Bear and others to talk the talk about engines..:cheers
This is a jackable thread, feel free!


----------



## yammiman (Apr 19, 2009)

I would put the bulk of the money into the heads - have them ported - possibly milled to get a 9.5-1 compression - go with a cam with around .480 lift and keep the duration under .280 and you will easily be at 400hp - pretty tall gear for that set up - might want to consider at least a 3.55 - probably have a hard time doing all of that on $1000!!!


----------



## 66tempestGT (Nov 28, 2009)

i guess this is a highjack already. what am i missing? if you have a complete 455 what do you have to gain by buying a stroker crank and gaining 6 cubes?


----------



## jetstang (Nov 5, 2008)

66tempestGT said:


> i guess this is a highjack already. what am i missing? if you have a complete 455 what do you have to gain by buying a stroker crank and gaining 6 cubes?


For Stroking the 400 to 461, the 400 has a smaller crank journal, 3.25 compared to 3.5 for 455s, so the 400 is a stronger block, can handle more horse power and better oiling on crank-so more RPMs. I asked the same question for a long time..
I don't know why you would stroke a 455 to 461, doesn't sound like much of a stroker kit..


----------



## geeteeohguy (Feb 2, 2008)

Jetstang, from what I've learned: zero-deck the block, get your compression right at 9.0--9.5 to one, get the heads dialed in to flow correctly, and do your homework on a cam. I'm a fossil when it comes to today's builds, as I built my 389 in 1981 (still runs great in the '65) and my 400 in 1988. I have to run additives/race fuel in the 389 due to 10.75 compression, and I just put some 87cc iron heads on the '67 two years ago so I could drive it on crap gas. Guys like Bear and other folks over on the PY forums are up to date on modern cam grinds, pistons, and head porting. There is a whole world of excellent pontiac parts out there that was not available when I went through this. If you do your homework, you can get good results and keep the price reasonable. If I were in your shoes, I'd spend the money on headwork, get the chambers to about 82-85cc (with flat top pistons...or use dished pistons with smaller chamber heads), zero deck it, and get a compatable roller cam so you can run any oil. Roller cams seem to be the way to go these days, and make a ton of power with good driving characteristics. I would leave your 3.36 gear alone, as in my opinion, its an excellent all-around gear. If you go "big" on the cam, be sure to upgrade the valvetrain accordingly, with good springs, good rockers (roller), etc. If you elect to go flat tappet hydraulic on the cam, you can use Rhoades lifters which bleed down at low speed, allowing wild profile cams to idle well and pull hard low in the rpm range. They pump up as rpm increases, and you make killer power on the top end, too. Most good runnning combos seem to be a direct result of homework, research, prep work, and a few choice parts that MUST WORK IN HARMONY with each other. Hopefully, others with more information will chime in.


----------



## BearGFR (Aug 25, 2008)

jetstang said:


> What does it take to get 400 HP, and 500 Ft lbs out of a 75 400 with 6X-4 heads on the cheap, or reasonable?
> 
> I got a good 400, cam rounded a couple lobes, ran great. Put a 350 in with a cam and it's a dog. Just want to freshen the 400 up, small stall and get some good HP/Torque for $1000 or so. Just cam, pistons, no exotic stroker stuff for now.. Already got headers, duals, Edelbrock dual plane, Holley 670, 3.36 gears and HEI. I am running AC, power brakes and want some MPG.
> I plan to take the 70 on the Power Tour next year, so it has to be a streetable motor with Oomph and mpg, injection is an option.
> ...


Making torque is all about air flow --- gotta get those cylinders full. If you can take advantage of Isaac Newton and use the inertia of the incoming air to fill those cylinders over 100%, even better. Next thing you have to do is burn it all effieciently and relatively quickly, to release all that potential energy while the piston is still "high enough" in the bore to take advantage of it. Combustion chamber design/shape is the main player here and remember that the top of the piston comprises half of the chamber. Generally, the faster the burn the better as long as you don't go TOO fast and get into detonation. You want peak cylinder pressure to occur "a few degrees" (I forget the exact number) past TDC to get the most bang for the buck, so to speak. Turbulence is good because it keeps things nice and mixed, also helps to prevent hot spots that lead to the nasty D word - and good quench area promotes turbulence. The faster the burn, the less timing advance you need, and the less timing advance you need, the less 'negative work' in the motor. Negative work occurs when combustion pressure starts to build before TDC - it's pressure that's trying to push the engine in the opposite direction. You're always going to have "some" because we have to light the fire before TDC, but the more you can avoid the better. The size, length, and volume of the intake and exhaust "ports" (includes the whole path from the base of the carb through the intake manifold to the intake valve, and from the exhaust valve out through the headers/manifolds) can help widen the motor's torque band by keeping flow velocity up. You want the ports "big" enough so that they don't choke the motor but not "so big" that velocity slows "too much", "stops' or ever reverses (called reversion). Lot's of otherwise good engines have had their torque potential "killed" by people running headers and/or intakes that were too big. 

Once you get torque output optmized, then the next thing is to "decide" where you want peak torque to happen, rpm-wise. Want more horsepower? Choose a cam that moves the torque peak to a higher rpm - its that simple. Want more torque? Gotta get more air/fuel into the motor and burn it - that means bigger displacement (bore/stroke), boost (turbo, supercharger), "oxygen supplement" (nitrous), improve volumetric efficiency ---- or some combination thereof. 

The fun part is trying to optimize tihngs while staying within whatever constraints you have, so it's important to identify what those are early on and be realistic. 

500 ft. lbs out of 400 cubic inches is just going to be tough - very tough. You've got two things working against you: cylinder volume and mechanical advantage (length of the lever arm --- stroke/2). A factory Ram Air IV 400 makes realistically about 440-450 lb. ft. peak - and there's not much more, if any to get out of 400 inches with that bore/stroke geometry. Keeping the motor at 400 inches, but with a 4.25 stroke and corresponding smaller bore (to keep it at 400) raises peak torque output by about 10-15 lb. ft. just because of the longer lever arm due to the longer stroke.

Horsepower's another story. Starting with that same factory Ram Air IV, but going with an even more aggressive solid roller cam (longer duration, more lift), horsepower figures around 450 to 470 at around 6000 RPM are attainable (but at the cost of lost low end torque, not to mention extreme risk to factory rods).

So, while 500 lb. ft. is probably out of reach unless you're going to run juice or forced induction, 440 is certainly do-able. Next step is to decide where you want it --- down low, or up high? Towards the low end, it's going to be a blast to drive on the street and will have reasonable manners for things like power brakes and a/c. It'll roast tires with ease and will definitely suprise folks, but probably won't be the quickest at the track. Up high is where the horsepower lives, and will be quicker at the track, but street manners will suffer --- and if you go too extreme you'll have to start worrying about factory rods and other stuff being strong enough.

Which way do you want to go?


Bear


----------



## jetstang (Nov 5, 2008)

I'm in Florida, and it is a cruiser with PS and PB, and AC is a must.. Premium gas is cool though. I'm thinking of putting 700R4 in it for OD, I have a TCI one in the garage that needs second gear fixed. The torque/HP #s I was talking was just to start the thread, not that important. I like the tire shreading torque with street manners. I have a 90 454 SS with 3.73s and the good stuff, so it's hard to race around in that, then jump in my muscle car and it's a dogggggg... I'm also doing a 66 Cloan that has a really nice 400 in it that should be my quick car and won't compromise as much on that one, picked up a set of lakewood traction bars for this one at the swap meet, cool stuff.


----------



## BearGFR (Aug 25, 2008)

jetstang said:


> I'm in Florida, and it is a cruiser with PS and PB, and AC is a must.. Premium gas is cool though. I'm thinking of putting 700R4 in it for OD, I have a TCI one in the garage that needs second gear fixed. The torque/HP #s I was talking was just to start the thread, not that important. I like the tire shreading torque with street manners. I have a 90 454 SS with 3.73s and the good stuff, so it's hard to race around in that, then jump in my muscle car and it's a dogggggg... I'm also doing a 66 Cloan that has a really nice 400 in it that should be my quick car and won't compromise as much on that one, picked up a set of lakewood traction bars for this one at the swap meet, cool stuff.


Alrighty then - that helps! So, to keep reliable vacuum for power brakes and factory a/c valves you don't want to go TOO nuts on the cam. My cam would be borderline --- it makes 12-13 inches on my 461 (it'd be a lot "worse" on a 400) and I've already decided not to chance the brakes and am converting to hydroboost power assist instead of the vacuum booster. Unless you plan to do lots of highway cruising, don't worry too much about an OD trans. Pontiacs make enough torque down low that 3.50 gears with a reasonable converter will still snap your neck yet retain very civilized street manners. 
I think you said you had 3.36's in it now? If'n it were mine, I'd forego the headache of tyring to convert to an OD tranny and instead "bullet proof" the trans that's in it now (TH400? TH350?) and get an appropriately sized converter for the motor. Choose a cam that puts the torque where you want it to be and have a blast. 

Bear


----------

