Titanium Valves in SS

[BBF67]

Originally Posted by Alan Roehrich

When they refactored the aluminum head combination to 411 a few years back (that's 16HP over the iron head combination, which is a natural SS/D car), they allowed the aluminum head combination to move to SS/C, from SS/D.

From the 2018 NHRA rulebook====NHRA-accepted aftermarket cylinder-heads carry a horsepower penalty that is calculated to the weight of the vehicle and does
not change the class of the vehicle.

[Billy Nees]

Originally Posted by BBF67

From the 2018 NHRA rulebook====NHRA-accepted aftermarket cylinder-heads carry a horsepower penalty that is calculated to the weight of the vehicle and does
not change the class of the vehicle.

The BB Corvettes had an aluminum head option. Always been there and it stands by itself. The head that they use is a GM head OR a GM REPLACEMENT head not an AFTERMARKET head.

[BBF67]

Originally Posted by Billy Nees

The BB Corvettes had an aluminum head option. Always been there and it stands by itself. The head that they use is a GM head OR a GM REPLACEMENT head not an AFTERMARKET head.

Correct starting in 1967 with no penalty. Prior to that the GM or 401 aluminum head gets the horsepower penalty.

Where does the class guide show the 396 Corvette with a natural class of SS/C?

[Billy Nees]

Originally Posted by BBF67

Correct starting in 1967 with no penalty. Prior to that the GM or 401 aluminum head gets the horsepower penalty.

Where does the class guide show the 396 Corvette with a natural class of SS/C?

It doesn't. I didn't say that it did.

[Greg Hill]

I don’t think the 65 Corvette had an aluminum head option. Looking at the classification guide the aluminum head is listed as a replacement head and the weight break is 7.67. Hard to get to 6.5.

[Dwight Southerland]

Originally Posted by BBF67

Correct starting in 1967 with no penalty. Prior to that the GM or 401 aluminum head gets the horsepower penalty.

Where does the class guide show the 396 Corvette with a natural class of SS/C?

According to the class guide, the P/W factor is 7.65. That is SS/D.

The confusion may have started because of the two different methods to determine class when replacement heads are given a different power rating.

Method 1: If you say that the calculation is based on shipping weight, then the classification for the aluminum head is calculated by the different power rating divided into the shipping weight and results in a new P/W factor not listed in the Class Guide. (65 Corvette 396 shipping weight is 3022 lb / 411 = 7.35 or SS/C. The car can run in SS/B, C or D. This may be how Jimmy is getting the car classified in SS/B.)

Method 2: If you say the calculation is based on the P/W factor listed in the Class Guide, then the classifications stay the same as indicated in the Class Guide, but the weight changes. (65 Corvette 396 P/W factor is 7.65 SS/D so it runs SS/C, D or E. The minimum weights for the classes is based on the power factor with aluminum heads aluminum heads.).

I have had this ongoing conversation with people from NHRA tech for several years and the opinion/answer changes. The last statement from them was number 2.

[fredjohnston]

Dwight - with all due respect, there is only one method and that's to look at what it says in the NHRA classification guide, see that it says 7.65 @ 411 and to abide by it. No need for a calculator.

Now if anyone feels the 7.65 was put in the guide by error, then take it up with NHRA and hash it out. In the mean time, this combo should be raced at 7.65 with a HP rating of 411.

Originally Posted by Dwight Southerland

According to the class guide, the P/W factor is 7.65. That is SS/D.

The confusion may have started because of the two different methods to determine class when replacement heads are given a different power rating.

Method 1: If you say that the calculation is based on shipping weight, then the classification for the aluminum head is calculated by the different power rating divided into the shipping weight and results in a new P/W factor not listed in the Class Guide. (65 Corvette 396 shipping weight is 3022 lb / 411 = 7.35 or SS/C. The car can run in SS/B, C or D. This may be how Jimmy is getting the car classified in SS/B.)

Method 2: If you say the calculation is based on the P/W factor listed in the Class Guide, then the classifications stay the same as indicated in the Class Guide, but the weight changes. (65 Corvette 396 P/W factor is 7.65 SS/D so it runs SS/C, D or E. The minimum weights for the classes is based on the power factor with aluminum heads aluminum heads.).

I have had this ongoing conversation with people from NHRA tech for several years and the opinion/answer changes. The last statement from them was number 2.

[Dwight Southerland]

Originally Posted by fredjohnston

Dwight - with all due respect, there is only one method and that's to look at what it says in the NHRA classification guide, see that it says 7.65 @ 411 and to abide by it. No need for a calculator.

As I said, I have been having this conversation with a variety of people at NHRA Tech for a long time and the method/opinion has changed back and forth depending when and who you talk to. I agree that the current consensus is to use the P/W factor found in the Class Guide to determine the class, and use the power factor to multiply to find the race weight.

It has not always been that way.

[Andrew Hill]

Straight from the rule book, "The power-to-weight factor is the shipping weight of the vehicle divided by the advertised, or when applicable, the factored horsepower for the OEM-assembly-line cylinder heads. NHRA-accepted aftermarket cylinder heads carry a horsepower penalty that is calculated to the weight of the vehicle and does not change the class of the vehicle."

I'm not sure when this verbiage was added, but it's in the 2017 and 2018 rule books.

Edit: just realized this quote was already posted on the last page, oops.

[Race Clean]

Originally Posted by Dwight Southerland

According to the class guide, the P/W factor is 7.65. That is SS/D.

The confusion may have started because of the two different methods to determine class when replacement heads are given a different power rating.

Method 1: If you say that the calculation is based on shipping weight, then the classification for the aluminum head is calculated by the different power rating divided into the shipping weight and results in a new P/W factor not listed in the Class Guide. (65 Corvette 396 shipping weight is 3022 lb / 411 = 7.35 or SS/C. The car can run in SS/B, C or D. This may be how Jimmy is getting the car classified in SS/B.)

Method 2: If you say the calculation is based on the P/W factor listed in the Class Guide, then the classifications stay the same as indicated in the Class Guide, but the weight changes. (65 Corvette 396 P/W factor is 7.65 SS/D so it runs SS/C, D or E. The minimum weights for the classes is based on the power factor with aluminum heads aluminum heads.).

I have had this ongoing conversation with people from NHRA tech for several years and the opinion/answer changes. The last statement from them was number 2.

I bet if it had been another make the tune would be different..