Why does NHRA underrate Mopar so much? 426/365 etc?

DeuceCoupe · 10-27-2016, 08:33 PM

Well I don't want to be a pest but just have to ask.
As we all know NHRA has been prone to "factoring" or modifying factory rated horsepower since the late-1960s at least.

It used to be for obvious reasons, like the "425 horse" Hemi, "290 horse" z28 and Boss2, "335 horse" 428cj, etc. Usually engines were factored UP cuz they were obviously or intentionally underrated from the factory..

Looking thru the NHRA online classification sheets today though, it seems almost mandatory to fiddle with the factory ratings. Often NHRA still factors the ratings UP, eg they still factor Fords 428cj/335hp up to 375hp which is pretty close to what it actually makes.

But for the big B/RB Mopar, NHRA wants to ding the ratings WAY down below factory. Why?

The worst one is the 426/365 Street Wedge.
NHRA rates it at 291 hp, 74 hp below its rating.
This is the all-time record NHRA de-rating of the ones I have checked.
Although, NHRA de-rates the early 1962-65 383/330afb down to 280 hp, a ding of 50hp and almost as bad percent-wise.

Were these engines REALLY that bad?
Or is NHRA just playing?

For example, circa 1970:
Ford rated its vanilla 429 Thunderjet at 360hp.
Ford rated its 429 SCJ at 375hp, only a 15hp difference for:
*Bigger carb and intake
*Bigger heads, way bigger
* Higher compression
*Bigger (and solid) cam
*Bigger exhaust.
Having had both, and later Gonkulated both, the 429SCJ was 8-10mph faster than the 429 Thunderjet which is a whole lot more than 15hp.
Yet, NHRA keeps the ridiculous factory ratings on both those engines.

Similar for the Pontiac RamAir-4=370hp vs RamAir-3=366hp. There is a whole lot more than 4 hp difference in reality and it shows up in the timeslips once the exhaust is uncorked. But NHRA actually rates the RA4=365 hp, and keeps the RA3=366 hp. So a RA4 makes less power than a RA3.

There are some other goofy things about today's NHRA factoring, but the worst I found in computing things lately was that 426/365 street wedge example -

Does anybody know NHRA's basis for dinging that 426/365 down 74 hp to 291 hp?

Thanks again, I can see why the Presidential Candidates avoid all this tedious math.
"It was my understanding that there would be no math"
- Chevy Chase as Gerald Ford in the 1976 SNL Presidential Debate.

Albert Lee · 10-29-2016, 05:23 AM

The answer lies in the NHRA Automatic Horsepower Factoring System. A few years ago I thought it might be a decent combination to run both NHRA Stock and NMCA NSS with the same car. I built a 426 street wedge, small carb, small exhaust valve motor and put it in my '64 Plymouth. I ran it slow a time or two and the AHFS dropped the hp. The car wasn't fun to to drive and I abandoned the project.

Al Corda

10-27-2016, 08:33 PM	#1
DeuceCoupe Member Join Date: Feb 2016 Posts: 271 Likes: 97 Liked 46 Times in 42 Posts	Why does NHRA underrate Mopar so much? 426/365 etc? Well I don't want to be a pest but just have to ask. As we all know NHRA has been prone to "factoring" or modifying factory rated horsepower since the late-1960s at least. It used to be for obvious reasons, like the "425 horse" Hemi, "290 horse" z28 and Boss2, "335 horse" 428cj, etc. Usually engines were factored UP cuz they were obviously or intentionally underrated from the factory.. Looking thru the NHRA online classification sheets today though, it seems almost mandatory to fiddle with the factory ratings. Often NHRA still factors the ratings UP, eg they still factor Fords 428cj/335hp up to 375hp which is pretty close to what it actually makes. But for the big B/RB Mopar, NHRA wants to ding the ratings WAY down below factory. Why? The worst one is the 426/365 Street Wedge. NHRA rates it at 291 hp, 74 hp below its rating. This is the all-time record NHRA de-rating of the ones I have checked. Although, NHRA de-rates the early 1962-65 383/330afb down to 280 hp, a ding of 50hp and almost as bad percent-wise. Were these engines REALLY that bad? Or is NHRA just playing? For example, circa 1970: Ford rated its vanilla 429 Thunderjet at 360hp. Ford rated its 429 SCJ at 375hp, only a 15hp difference for: Bigger carb and intake Bigger heads, way bigger * Higher compression Bigger (and solid) cam Bigger exhaust. Having had both, and later Gonkulated both, the 429SCJ was 8-10mph faster than the 429 Thunderjet which is a whole lot more than 15hp. Yet, NHRA keeps the ridiculous factory ratings on both those engines. Similar for the Pontiac RamAir-4=370hp vs RamAir-3=366hp. There is a whole lot more than 4 hp difference in reality and it shows up in the timeslips once the exhaust is uncorked. But NHRA actually rates the RA4=365 hp, and keeps the RA3=366 hp. So a RA4 makes less power than a RA3. There are some other goofy things about today's NHRA factoring, but the worst I found in computing things lately was that 426/365 street wedge example - Does anybody know NHRA's basis for dinging that 426/365 down 74 hp to 291 hp? Thanks again, I can see why the Presidential Candidates avoid all this tedious math. "It was my understanding that there would be no math" - Chevy Chase as Gerald Ford in the 1976 SNL Presidential Debate.

10-29-2016, 05:23 AM	#2
Albert Lee Member Join Date: Apr 2010 Posts: 256 Likes: 106 Liked 273 Times in 50 Posts	Re: Why does NHRA underrate Mopar so much? 426/365 etc? The answer lies in the NHRA Automatic Horsepower Factoring System. A few years ago I thought it might be a decent combination to run both NHRA Stock and NMCA NSS with the same car. I built a 426 street wedge, small carb, small exhaust valve motor and put it in my '64 Plymouth. I ran it slow a time or two and the AHFS dropped the hp. The car wasn't fun to to drive and I abandoned the project. Al Corda