[phil400]

I was just reading the 400 stroker vs 455 thread, great thread, great info.

My question is what is it about pontiac engines that allow them to make so much power at relatively low rpm compared to other engine family's( ford &chevy).

Is the the port shape or port velocity? Or what? My car is slow compared to the cars on this site, but in my youth when I gave a ride to my friends( with Camaros ) or my cousin who had a 5.0L mustang they always commented on how hard the car pulled low in the rpm range.

[Tom Vaught]

Comparing a 302 (5.0L) Mustang to a 455 Pontiac is basically about stroke.

A 5.0L Mustang has a 4.00" bore and a 3.00" stroke.

A 455 Pontiac has a 4.151 Bore and a 4.21" stroke.

1) First off there is 153 inches different in the displacement of the two engines.
(That is a 50% bigger Engine).

2) The 455 has a 4.151" Bore vs the 4.00" 5.0L Mustangs bore. So the bore is roughly 4% bigger on the 455 engine. Not much of a change really.

3) The 455 has a 4.21" stroke vs the 3.00" stroke so the 455 has about a 40% bigger stroke. The torque difference with the same rough compression ratio, piston area, and the 455 just excels in torque output at the same rpm.

Pulling hard in the lower rpm means more torque to more the same mass weight of a vehicle.

Now if you let that Mustang 302 have a Vortech Supercharger and they put 15 psi of boost on the engine it was a whole different ball game. Now the 302 thought it was a 600 cubic inch engine.

Just saying.

Tom V.

Put 13 psi of boost on a 455 like Luhn Performance did and their engine made 863 HP at 5300 rpm and almost 900 lb/ft of torque at 4800 rpm.

[phil400]

Ok, I get what your saying, but take a 400 or 383 stroker sbc and a 400 pontiac, they all have a 3.75" stroke, but pontiac engine seems to start making power lower in the rpm range, and capable of more low and mid range power,why is that?

I guess I just mean, with a pontiac there seems to be no delay, you hit the gas and bang it takes off where as other makes it doesn't kick in till higher in the rpm range.

[gtofreek]

Port velocity has a lot to do with responsiveness. Port velocity and crankshaft weight have a lot to do with torque production. The main difference between a 400 SB Chevy[4.125 x 3.75], a 396 Chevy[4.093 x 3.766], and a 400 Pontiac[4.120" x 3.750] is the cylinder heads. The 400 Pontiac has a much heavier rotating assembly versus the 400 SB, but is pretty close to the 396 Chevy. The 400 SB makes 410 ft. lbs. of torque. The 396 makes 415 ft. lbs. of torque. The 400 Pontiac makes 445 ft. lbs. of torque. The main difference hear is the heads, and cam design. The extra torque is mainly from the port velocity, I would say. The 396 has really big ports for the engine size, when compared to Pontiac. The SB also has larger ports, so velocity in either engine is lower than the Pontiac. Also, Pontiac used 30° intake seats in most of their performance engines heads, and the 30° intake seat, compared to the 45° seat of the Chevy's, flows much better in the low to mid lift range. This also helps responsiveness, and torque production.

[GRX]

You pretty much nailed it there Paul. The low end power is what has always drawn me to the Pontiac v-8's. Have seen so many guys go wrong trying to apply their high RPM small block chevy thinking to them.

Concerning the 400 comparison, in addition to seat angles the pontiac 400 typically has 2.11 & 1.96 diameter valves where the chevy 400 has 1.94 & 1.50. And let's not forget the Pontiac double valve spring thing.

[steve25]

Also the fact that once Pontiac settled on the open combustion chamber in mid 1967 Pontiac motors then had a much better burn rate than any other production motor but the Hemi and that is a factor in better torque production for any givin RPM or Intake air flow level!

Getting back to the title of this string of post, HP is derived form Torque X RPM. The higher in a motors rpm range you make peak Torque the more HP you will make even with the same level of intake air flow, and since peak Torque takes place pretty much at the same point that the motor has tapped out its breathing ability the only ways to kick up the rpm point of peak Torque is with more cam duration, greater Intake port area, shorter Intake runners or a combo of all three and if these three things can also add more total air flow to the game than the HP increase can be huge!

Ho Jeez, we may need to get back to the discussion of cylinders heads and VE, lol!

[phil400]

Great info! Thanks.

[pastry_chef]

Originally Posted by gtofreek

The 400 SB makes 410 ft. lbs. of torque. The 396 makes 415 ft. lbs. of torque. The 400 Pontiac makes 445 ft. lbs. of torque. The main difference hear is the heads, and cam design. The extra torque is mainly from the port velocity, I would say.

Those torque numbers are dismal!

Here is a pump-gas SBC 388 on a totally honest dyno.
459 lbs-ft at 3500 RPM - TQ peak is much higher.

http://www.chevelles.com/forums/showthread.php?t=393589

---------------

A very mild BBC 408 - 9.5 compression
453 lbs-ft at 3300 RPM

http://www.chevelles.com/forums/showthread.php?t=310167

[Skip Fix]

Pastry Chef I bet Paul is usuing a milder set of motors and mayeb even a "real world conservative dyno" where the motors "run the numbers".

[54nomore]

I believe Paul is quoting factory advertised specs, most likely from a Chilton or Motors manual.

[gtofreek]

Originally Posted by 54nomore

I believe Paul is quoting factory advertised specs, most likely from a Chilton or Motors manual.

Bingo! Give that man a prize! Motor Manual.

[pastry_chef]

Originally Posted by Skip Fix

Pastry Chef I bet Paul is usuing a milder set of motors and mayeb even a "real world conservative dyno" where the motors "run the numbers".

Lewis Racing Engines is as "real world" and conservative as there is.
That was why I quoted torque values below 3600 RPM.

I have probably a half dozen other Chev dyno examples.
Most Pontiac guys stroke up to 463 plus and generally don't dyno.

I quickly found one example from April 1992 High Performance Pontiac by Pete Mccarthy.
400 Pont 0.035 over.
10.98 compression
Comp "super RA IV" grind

Torque was about 450 and 460 HP with a 108 LSA cam, they tried another cam at 104 LSA and torque went to 476

Pretty close comparisons I would say.

[pastry_chef]

Originally Posted by gtofreek

Bingo! Give that man a prize! Motor Manual.

Pontiac engineers deserve much credit in making the factory components work REALLY well as a combo.
Likely why a good old late 60's cast manifold is hard to beat for mid 11 street/strip ride.

[gtofreek]

I was quoting factory torque ratings. Of course engines with 40-50 years advancement in cam, and head technology are going to have an advantage, and make more power.

[PunchT37]

Basically, what Paul said is correct. So were the others. What Pontiac did was fill the cylinders at lower rpm`s better than most or all the others. That`s what they wanted to do with all their low po passenger car engines. Throw around heavy cars like the Bonneville, with as much throttle response and as little throttle as possible. Even 2bbl. Pontiacs ran well for most uses back in the day. To the average buyer, the engine felt baddass compared to what they were driving before. Especially for the 1`st time Pontiac buyer. Their deck height, stroke, rod length, port shape/volume, valve sizes, seat angles, cam selection, intake design did a damn good job of doing it. Course, it was over at 4500 to 5500 rpm`s. That`s why the rods were really not made for high rpm`s. The lower end and the upper ends were "tuned" together. When the rods couldn`t take more rpm, neither could the upper end flow more air to turn more rpm.

Hell, I had a `70 Executive 4 door, back in the day, with the YD, 290hp, 400, 2bbl. I remember that car could smoke the PISS out of that right rear tire. My friends used to love to ride in that thing.

SD engines and some of the others were dealt with by the engineers to make power at higher rpm`s. 4 bolt mains, better rods, better oiling, heads, cams, etc.

[paul s.]

good responses. Another factor which I don't believe has been mentioned is deck height. We have a very tall deck compared to other makes and it will effect the "line of sight" from the carburetor to the intake valve.

If one were to look at the engine from the front and visualize the path the air and fuel must make, the tight turns from vertical to horizontal (or nearly) as the air/fuel mix leaves the carburetor and enters the intake manifold and then later down the path where the small bores dictate a tight pushrod restriction and again where the mix must make a turn over an abrupt short turn radius and then enter into a flat floored combustion chambered area, it shows (like others have stated) the engineers had velocity and low rpm on their mind.

Now, for the sake of argument, if one could visualize a 1" shorter deck height, one could see the required path would change ever so slightly, leading to less acute angles under the carb and at the short side radius. Cut the deck another inch, leave the carb height the same and adjust the valve angles and you have made more "gains". But then, you've made a high end race small block!

That's one reason some guys were wanting a short deck race block casting.

[Skip Fix]

Originally Posted by pastry_chef

Lewis Racing Engines is as "real world" and conservative as there is.
That was why I quoted torque values below 3600 RPM.

I have probably a half dozen other Chev dyno examples.
Most Pontiac guys stroke up to 463 plus and generally don't dyno.

I quickly found one example from April 1992 High Performance Pontiac by Pete Mccarthy.
400 Pont 0.035 over.
10.98 compression
Comp "super RA IV" grind

Torque was about 450 and 460 HP with a 108 LSA cam, they tried another cam at 104 LSA and torque went to 476

Pretty close comparisons I would say.

Having dynoed a number motors on conservative dynos where they "run the numbers" including my tweaked RAIV 400 I would say those numbers are on a slightly generous dyno or the "super RAIV" is way bigger than any of the 4 cams I had in that motor and I had a big SFT, and a UD 304/312 HFT in it! That would put it in a 3800 car at 11.40s @ 117.

Maybe a 455 with a RAIV type cam like Jim Hand's combos-tough for a 400.