NHRA Pro Stock HP (1 Viewer)

[Buzzz Miller]

The chambers are so shallow in these beasts now, the ignition timing numbers are nothing really important to the standard world as there is nothing in most of our shops that can use the info learned by those numbers. Most normal racers just don't have stuff that shallow and that quick, so knowing a pro stock timing just does not help us. Then you get into timing retards and the initial number does not mean much anymore anyway. But how much they take out at what time and for what occurrences is where things get secretive. But most numbers for a standard ignition timing before retards is going to be just shy of 30* BTDC.
And compressions actually vary from racetrack to racetrack, (especially Denver.) But it is more about valve to piston clearance, and piston to head clearance than static compression. With the short stroke and large piston, the compression numbers are not as high as you would think them to be. But again, that is static compression, and when you get to the flow of these heads, they get more air in the cylinder than your really good top dragster heads, and thus, raise your actual compression, so again, a mute point.
But they are a thing of beauty! Engineering masterpieces.

 

[.]

Didn't you post something once about valvesprings that seemed to do one thing on a dyno and another in a car? LOL, don't give the vague answer you did above, either! Okay, let's cut to the chase. I KNOW you did post about that. I'm trying to get you to repeat it because it was interesting!

I also seem to remember you saying that some foreign engineers had a hard time believing that people were doing with pushrod engines over here what they were, that they said it would be impossible?

I remember that post, great info too. I'd like to read it again but no idea where to search. I wish Darin Morgan still posted here, he also posted some really great info.

 

[Nitrohaulic]

I remember that post, great info too. I'd like to read it again but no idea where to search. I wish Darin Morgan still posted here, he also posted some really great info.

I'm wondering if it was on the old mater?

Maybe it wasn't on a dyno, either. Spintron?

 

[.]

Thanx to everyone except Alan for the helpful answers.
I was only curious, that's all.

P/S is using 118 octane?

 

[Nitrohaulic]

I remember that post, great info too. I'd like to read it again but no idea where to search. I wish Darin Morgan still posted here, he also posted some really great info.

Did he maybe say that so many RPM on one would kill the valvesprings while they lived on the other?

 

[.]

I'm wondering if it was on the old mater?

Maybe it wasn't on a dyno, either. Spintron?

I bet it was on the old 'Mater. I was thinking it was both the dyno and the Spintron. It was with Nickens and I think the story was that they got some new springs that were supposed to be better but instead they made the valves float and the engineers didn't believe them.

 

[none]

The valve spring story covered the Spintron, the Dyno and the racecar. I'll tell it again when I have a little time to type it out. It's a LONG story but I still think it's a good one.

The compression ratio in a Pro Stocker isn't as high as you might think. Remember that they have a spec fuel and you can only go so high before detonation. I believe that a number of teams had to back it down when they made the fuel rule. I know that we did. The old fuel we were running allowed for more C/R than the C-25.

Just as a pump gas engine can't run as much C/R as one that runs race gas. you can only go as high as the fuel will allow. On the timing issue 30 is in the neighborhood. when the new HEMI came out it wanted less timing than the wedge. The spark plug being right in the middle of the chamber made it more efficient so the timing could come back some. For those of you as old as I am remember the chevy "Angle Plug Heads" they were the deal, and all because putting the spark plug in at an angle moved the firing point a little closer to the center of the chamber

Alan

 

[Bullet]

I believe that a number of teams had to back it down when they made the fuel rule. I know that we did.

Alan, who is the "we" you refer to?

It must have been cool getting to see the inner workings of one of these powerplants.

 

[Professor Dave]

Sorry I didn't get provide a reply-I've been ill (I can't say sick because Alan would say something like, yeah, what's new? LOL). Alan hit the nail on the head in terms of a dyno being repeatable so you can know what affect a change has on HP. Eight cylinder motors make more HP per cubic inch than four cylinder motors. We just dyno'd the motor in my altered and it was making less that 2.5 HP per cubic inch (how much less I'm not allowed to say). Eventually we'll probably look into replacing the splayed valve motor with a four valve motor and the HP per cubic inch should be considerably higher.

As for timing, what Alan said is right. Our motor has a pro stock truck head on it that was most recently updated by Tommy Slawko-he's the guy who really did important work that has gotten the V-6 to fly.

 

[none]

Alan, who is the "we" you refer to?

I worked for David Nickens when he was the Dodge factory team. We had Darrell and Scott, then Mark Osborne then Gene Wilson.

 

[Bullet]

Alan, who is the "we" you refer to?

QUOTE]

I worked for David Nickens when he was the Dodge factory team. We had Darrell and Scott, then Mark Osborne then Gene Wilson.

Cool! I didn't realize that you worked for the Dodge team. What stuff did you work on?

 

[.]

Thanx for the post Alan.

I know you were just horsing around earlier.

 

[d'kid]

Alan,

Is that why WJ covers everything when you walk in?

d'kid

 

[5.0 Junkie]

Interesting stuff. I want to know what volumetric efficiency they are getting out of them. I'll bet that is more secretive than anything. 104% or higher?

 

[Todd]

Interesting stuff. I want to know what volumetric efficiency they are getting out of them. I'll bet that is more secretive than anything. 104% or higher?

I would assume that that number changes quite a bit when the car is moving verses sitting still on a dyno. I wonder how the compensate for that variable.

 

[jpee]

So you are saying: in excess of 2.8 HP/CI......What are the small Comp Elem. engines seeing?

I have seen a 290 ci GM small block make 721 hp on the dyno..

 

[mike]

I would assume that that number changes quite a bit when the car is moving verses sitting still on a dyno. I wonder how the compensate for that variable.

I've often wondered about this. The idea of the hood scoop is to provide a mild supercharging effect, but at what price? The intake flow rate and presumably the horsepower will be dynamic, ie. changing as a function of the car's velocity. My guess is that the air flow inside the hood scoop will be an aerodynamic mess when the car is really moving. I'd expect there'd be all kinds of density pockets, separation, and turbulent eddies as flow makes a right angle turn to the the carburetors. You've got to think that would produce different output than what is seen in an aerodynamically `quiet' dyno test.

In addition, the scoop represents a significant component of the car's frontal cross section and a very lossy one at that. I'd expect the aero drag to go up with the cube of the velocity -- does the supercharging effect of the scoop more than make up for the aero drag it introduces?

I'm sure people have thought about these tradeoffs for decades, but it sure looks like a non-trivial problem to me.

 

[Jude]

I think the scoops have more to do with intake manifold design, i.e. runner length and angle, plenum design, and carb position rather than any possible supercharging effect.

 

[scotty]

Very good observation about the scoops Mike. Just to clarify, the aero drag increases by the square of the velocity (not the cube). You'll notice that the hood scoops of today are much narrower than the scoops of even 10 years ago with much more profiled shapes (when looking from the top). Some are so narrow you will notice little "blisters" on the side to provide clearance for the carb linkage. And they also appear to have a more friendly cross section to help quiet the air and provide better flow distribution than before. There are many things they could do inside to help, but I have never been privy enough to actually get a close inspection of a real P/S scoop. I think they are a necessary evil that the racers have learned to live with. They are going to need some kind of hood blister to clear the carbs and manifold anyway so I guess they figured they may as well get something out of it. If you remember the P/S Trucks had no hood scoop and only raised center section in the hood. They took their air in from the center of the "grille" area. I thought this was a more efficient arrangement but I found out my logic was wrong. It was more aero on the outside, but the curves on the inside and reduced height above the carbs made for a tuning nightmare. It was not uncommon for the PST guys to have severely staggered jets and timing in each cylinder from front to back because they couldn't run a scoop. I'm sure the P/S guys still do this but not to the extent the PST guys had to.

To get the thread back on track, I agree with the 1400-1450 hp estimates and the fact that we don't race dynos so the number, while very interesting, is really only a point of discussion. I'd take a 1425 bullet with a nice robust acceleration curve over a 1450 engine that was "flatter" everytime. As Alan said, the dyno repeatability is important, but I also feel the dyno operator is another key. There are people who just know how to "read the sheet" better than others (Jason Line?). And then there is the drivetrain. I know the F1 guys do "full drivetrain" dyno tests (not the same as the chassis dynos you see around) and I have the feeling some very talented p/s racers have developed a method for this as well. We all know GA and company flog their cars over the 1/8th mile for days on end but what nobody is talking about is their timer arrangement. My feeling is that they are not only looking at 60, 330, & 600 ft. But maybe 10-15 clocks from 0-660ft? If you had 2-3 timers located right in the areas of your shifts you could get a much clearer picture of how your engine is responding to your chassis. And that's the name of the game.

Sorry for the long post, but as you can see I love P/S.

 

[mike]

Very good observation about the scoops Mike. Just to clarify, the aero drag increases by the square of the velocity (not the cube).

Thanks for the reply Scott. I don't want to turn this thread into a freshman physics class, but I do want to quickly clarify the difference between aero drag force and the horsepower needed to overcome that drag.

You are correct that the Bernoulli drag force goes as the square of the velocity. At steady-state (assuming the car is not accelerating) sufficient power must be made to overcome that drag. Power is the rate of doing work (work = force*distance), so you differentiate work with respect to time, and find that the steady-state horsepower needed to maintain constant velocity increases as the cube of the velocity. Accounting for acceleration, which is needed for a more realistic model, turns this into a nonlinear problem.

To get a rough idea of what this means: Assume 1400 HP is needed to attain 205 mph in the lights. Getting the speed up to 209 mph would require an additional 86 HP from the motor.

OK, back to your regularly scheduled programming.