GT/KA ? What class?

[trmnatr]

With 3,700-3,800 pound race weight what class would a 327/275 or 327/300 fall under? GT/KA ?

What ET would it have to run and would would be a record ET ?

It will consist of a TH400 Automatic with a Transbrake and the engine will be SS legal rods, GM crank, Bill Miller pistons with .031" rings and -291 heads at the min 57.5cc chambers

Some other questions are being it is Super Stock and not Stock, Can you run like a Holley double pumper with a choke tower or do you have to run a Q-Jet or is there a specific Holley you have to run or what?

[Adger Smith]

As posted on GT Thread
Looks like the 327 275 has been gifted with HP. (NHRA.com) The 1966 275 is now at 299 HP with OE heads & 304 HP w replacement heads. The 327 300 HP is at 285 w OE heads & 290 W Replacement heads. Might make the 300 a better choice, depending on the differences in the engine combos. If you know the shipping weight of the heavy car you want to use you can use Bill's GT calculator to figure out what classes it will fit. You have to know 3 things to figure the class w/GT calculator. 1. Shipping weight of the car you want to use. You can get the factory shipping weight from the NHRA classification guide. http://www.nhra.com/tech_specs/classification/ 2. The factored HP of the engine. (get the same place) 3. Either Auto or Man. The program works. It even gives you choices of which classes you can move to by adding or subtracting weight & the HP required to run. Pretty nice tool.
No Holley with choke horn removed. Carb must be type listed in classification guide for engine & correct bore size. The engine has to be built using the specified parts sizes & types for the HP claimed. You must use the base weight as listed in the classification guide for the body you use. You can't just throw weigh in a car & start out calling it heavy. Hope this helps.

[Adger Smith]

This is a stab at what class. In the PM you sent me I still didn't get enough info. I'm going to assume the car is a 2 dr cpe. If it's not that changes things. The 1970 Chevelle 2 DR Cpe has a NHRA factory shipping weight of 3372. That appears to be the heaviest small block in a 2 Dr Cpe. The 1966 300 HP 327 has a NHRA rated HP of 285 with the legal OE 291 casting head. According to the GT calculator the lightest class the car will fit in is GT/FA @ 3162.5 It will take 462 HP to run the index in that class and 613 to run 1 sec under. The heaviest class the combo can fit is GT/JA @ 3732.5 lbs. It will take 478.3 Hp to run the index & 626 to run 1 second under. The weight for those 2 classes includes the driver. The combo will fit GT/ G, H, I with the weight adjusted to fit those classes. Better check on those pistons. I'm not sure if the 300 hp 327 had 2 or 4 valve notches... A little CRS on my part. If I didn't miss any thing most of the other specs you gave me looked good. The carb on the 1966 300 HP 327 is listed as a Holley 3367A with throttle bores of 1.562 & venturi's of 1.25 and 1.313. You don't have to use the original part #, but have to use the correct bore sizes. It has to be built to SS legal specs. I hope I didn't screw anything up and this info helps you.
GT calculator
http://www.employees.org/~bhracing/g...ulator_1p1.xls

[Mike Voth]

Adger - Where do I find Bill's GT calculator?

[Chris DeGidio]

Mike,
It's in the other GT post that I started about how to configure GT class.It works real well.

[SSDiv6]

http://www.employees.org/~bhracing/g...ulator_1p1.xls

[trmnatr]

Originally Posted by Adger Smith

This is a stab at what class. In the PM you sent me I still didn't get enough info. I'm going to assume the car is a 2 dr cpe. If it's not that changes things. The 1970 Chevelle 2 DR Cpe has a NHRA factory shipping weight of 3372. That appears to be the heaviest small block in a 2 Dr Cpe. The 1966 300 HP 327 has a NHRA rated HP of 285 with the legal OE 291 casting head. According to the GT calculator the lightest class the car will fit in is GT/FA @ 3162.5 It will take 462 HP to run the index in that class and 613 to run 1 sec under. The heaviest class the combo can fit is GT/JA @ 3732.5 lbs. It will take 478.3 Hp to run the index & 626 to run 1 second under. The weight for those 2 classes includes the driver. The combo will fit GT/ G, H, I with the weight adjusted to fit those classes. Better check on those pistons. I'm not sure if the 300 hp 327 had 2 or 4 valve notches... A little CRS on my part. If I didn't miss any thing most of the other specs you gave me looked good. The carb on the 1966 300 HP 327 is listed as a Holley 3367A with throttle bores of 1.562 & venturi's of 1.25 and 1.313. You don't have to use the original part #, but have to use the correct bore sizes. It has to be built to SS legal specs. I hope I didn't screw anything up and this info helps you.
GT calculator
http://www.employees.org/~bhracing/g...ulator_1p1.xls

So if we do the engine as a 327/275 we can run GT/JA ?

The car is a two door coupe

[Adger Smith]

No. The 327 275 carries more HP(299). That is based on the 1966 327 300 HP(285), via the GT calculator.
I have personal experience with a couple of GT cars & the runs missed the GT Calculator a little. One I had on my dyno, the other went into the car with out a dyno session.

The list below is from the 70 Chevelle as it fit on the GT calculator in GT/JA
Mike,
I'm not sure about your dreamers HP figure comment. If you figure .060 overbore & + .013 stroke on the 327 it comes up 338 Cu In.
If you divide the Required index HP(478.3) by 338 you get 1.412 HP per cu in.
If you take the 1.2 under required HP (663.6) divided by the 338 cu in you get 1.96 Hp per cu in.
Just how far out of line do you think those numbers are. On the one I did my Dyno numbers only missed the 1 second under by a little. I know my dyno well enough to know it is calibrated on the conservative side. I feel it is best that way to work with simulation programs, torque converter companies & customers.

GT/JA
11.60 index
10.80
10.60
10.40 1.2 under

3732.50 min weight



478.3 HP to run the index
592.6 to run .8 under
626.8 to run 1. under
663.6 to run 1.2 under

[Mike Voth]

Here's another possibility to consider - If the car has been back-halved, and done right, you could drop between 100 and 200 pounds. If you put disc brakes on all four corners, you could drop another 150 pounds, or more. If the 327 is build right, it has the potential of making more torque than some 350 combinations, but still short. It has been my experience in the past that dropping weight and moving up in class gives you the potential of running further under the index with the 327. Our 275 horse 327 liked to get the weight out from under it. If you play your cards right, you might be able to drop under the GT/FA minimum, and be able to control the weight up via the weight box (up to 100 pounds). We have our car set up to adjust weight with the amount of fuel in the cell, and run 15 pounds over the 3120 limit. It works good, and the car responded better when the weight was removed. You might find that you like being a little quicker (ET), and not have to leave first all the time.

Just a thought. Since you've chosen to run a GT class, I believe your options for carbs are greater, too. But mainly, it's all about what weight you'll end up at, and what year engine you claim. A q-jet will cost you HP, and without looking, I think in the 299 range, depending on the heads. I think that Holley carb Adger was talking about is a 580cc carb (I'm sorry if I'm wrong, trying to go off memory), and an early style q-jet is 720-750, I think??? The Holley would be the way to go if you can make similar numbers compared to the q-jet.

I hope this helps a little.

[Bill Harris]

The HP calculator is just a ball-park since there really is no way to do an accurate estimate of the peak HP for a racecar. The Chrysler estimates were developed back in the '60s and are roughly based on a constant acceleration model that would give an estimate of power at the flywheel. The equation uses basic Newtonian physics to determine the power needed to accelerate a given mass to a given speed in a given time and then padded to account for observed performance. Anyone who has a data aquisition system can see at a glance that the acceleration of a racecar is anything but linear which makes a constant acceleration model a rough estimate at best.

There are other ET estimators out there that use similar equations but with some variation of the "200" constant. For example, the TCI website (www.tciauto.com/Products/TechInfo/Calculators.asp) has a calculator that is the same as the Chrysler estimates except that the constant is 193 instead of 200. It goes though the intermediate step of calculating the MPH and then the ET, but the end result is that the estimated HP is weight*193/(ET^3). These results are of course lower than the Chrysler results, but not by a lot. The difference is around 15 to 20HP for various weights and HP ratings.

The spreadsheet was originally developed to allow me to figure out which GT classes I could run with various engine/body combos when I was planning my adventures into the realm of super stock competition. The HP stuff was added to give a relative measure of how much power I would need to make at the different weights. It is more of a measure of which legal class is more attractive from a power standpoint than a target to shoot for in the dyno cell. I found it useful and thought that others trying to decipher the GT class mess might also benefit, so I shared it with the forum.

I am pretty certain that the classes that the spreadsheet reports are accurate given the NHRA indexes, rules and user input, but there are no guarantees. The HP stuff is for entertainment purposes only.. if you get my drift.

Enjoy, or not....