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VP C-12 #3062499
07/25/22 03:38 PM
07/25/22 03:38 PM
Joined: Jan 2003
Posts: 1,490
westerly, ri. usa
4
440lebaron Offline OP
pro stock
440lebaron  Offline OP
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westerly, ri. usa
is to much octane to much?
400, stk 452 heads t/quad stock intake, headers, 4:56 gears 4100 lbs

Re: VP C-12 [Re: 440lebaron] #3062506
07/25/22 03:54 PM
07/25/22 03:54 PM
Joined: Jan 2003
Posts: 30,133
Oregon
A
AndyF Offline
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Oregon
Yes. Too much octane slows down the burn and makes the engine sluggish. It also burns a hole in your pocket.

Re: VP C-12 [Re: 440lebaron] #3062512
07/25/22 04:30 PM
07/25/22 04:30 PM
Joined: Mar 2010
Posts: 956
Atlanta, GA
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mgoblue9798 Offline
super stock
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Atlanta, GA
You need to optimize dynamic compression, valve timing events, and ignition timing for a certain octane level -plus a little margin for safety. Any fuel with octane rating exceeding what the build is designed for is just wasted money.


Last edited by mgoblue9798; 07/25/22 04:32 PM.
Re: VP C-12 [Re: mgoblue9798] #3062525
07/25/22 05:07 PM
07/25/22 05:07 PM
Joined: Jan 2003
Posts: 5,590
Hot Rod Ridge
FastmOp Offline
master
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Hot Rod Ridge
Test
Test
Test ical

Re: VP C-12 [Re: 440lebaron] #3062529
07/25/22 05:13 PM
07/25/22 05:13 PM
Joined: Dec 2018
Posts: 66
IL
8
83hurstguy Online content
member
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IL
Octane and the burn curve aren't necessarily related. High compression engines need higher octane and also typically operate at higher RPM ranges, which requires a faster burn...

You'll find that fuels have varying Reid vapor pressures that will help with intake charge cooling more than others, which may help increase power via better atomization/distribution. A lot of stock eliminator guys will typically run C11 or C12, and those engines have less than 10:1 compression and huge cams that produce low cranking compression. Some fuels like hot vs cool engines (or hot intake charges from boost).

That being said, many people use race fuel for consistency in tuning run to run (or class rules) even if the engine doesn't require it. I have a big block iron headed engine here with 10.5:1 compression that doesn't care whether it's on pump or C12 (it actually picked up a tick on pump on the dyno). My stock 440-6 has some preferences that show up on the dyno in terms of fuel, but it's maybe 5 hp difference.

Pump gas is inconsistent but also oxygenated, which can help make power. You may also find that race fuel has lower specific gravity than the pump gas you're running, which means you need to jet up to get the same power input.

Overall - fuel testing and tuning takes a lot of time and effort. It's definitely not as simple as the guy at the cruise night spouting off "yeah she really runs good with the race gas!"

Re: VP C-12 [Re: FastmOp] #3062530
07/25/22 05:13 PM
07/25/22 05:13 PM
Joined: Jan 2003
Posts: 19,723
Park Forest, IL
slantzilla Offline
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Is that the spec gas in Stock?


"Everybody funny, now you funny too."
Re: VP C-12 [Re: slantzilla] #3062547
07/25/22 05:57 PM
07/25/22 05:57 PM
Joined: Jan 2003
Posts: 14,130
So. Burlington, Vt.
F
fast68plymouth Offline
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So. Burlington, Vt.
In nhra stock, you have to run a fuel that’s on the approved list, and it will get checked after you make a pass most of the time.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: VP C-12 [Re: fast68plymouth] #3062577
07/25/22 08:19 PM
07/25/22 08:19 PM
Joined: Aug 2003
Posts: 40,361
Bend,OR USA
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Cab_Burge Offline
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Originally Posted by fast68plymouth
In nhra stock, you have to run a fuel that’s on the approved list, and it will get checked after you make a pass most of the time.

how long ago did that start?


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: VP C-12 [Re: Cab_Burge] #3062587
07/25/22 09:24 PM
07/25/22 09:24 PM
Joined: Jan 2003
Posts: 19,723
Park Forest, IL
slantzilla Offline
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8 years or so ago.


"Everybody funny, now you funny too."
Re: VP C-12 [Re: slantzilla] #3062593
07/25/22 10:21 PM
07/25/22 10:21 PM
Joined: Jul 2022
Posts: 9
AZLIVN
S
SLO-KID Offline
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AZLIVN
13.5-1 439 small block 7800 shift point been on C-12 since dyno day.

Re: VP C-12 [Re: FastmOp] #3062609
07/26/22 06:18 AM
07/26/22 06:18 AM
Joined: Jan 2003
Posts: 1,490
westerly, ri. usa
4
440lebaron Offline OP
pro stock
440lebaron  Offline OP
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westerly, ri. usa
no fuel check yet, 8-1 compression

Re: VP C-12 [Re: 440lebaron] #3062628
07/26/22 08:26 AM
07/26/22 08:26 AM
Joined: Oct 2015
Posts: 561
UK
rb446 Offline
mopar
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UK
That'll run good on 87 prob, back in the day running my 440-6@9.8:1 with single 850DP I ran what we called 4 star leaded fuel, approx 97 octane, decided to add unleaded to it, and boy it sounded so much stronger, didn't go much faster but.


1969 'Cuda 446ci, best 9.96@133.9 in 1990
1971 340 'Cuda, best 11.01@122.8 in 1987
Re: VP C-12 [Re: rb446] #3062633
07/26/22 09:01 AM
07/26/22 09:01 AM
Joined: Jan 2003
Posts: 1,490
westerly, ri. usa
4
440lebaron Offline OP
pro stock
440lebaron  Offline OP
pro stock
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Posts: 1,490
westerly, ri. usa
YEP, no pump gas in stock, running in super street SST to break in car, illegal 383 still waiting for piston for 400

Re: VP C-12 [Re: 440lebaron] #3062639
07/26/22 09:10 AM
07/26/22 09:10 AM
Joined: Jan 2003
Posts: 14,130
So. Burlington, Vt.
F
fast68plymouth Offline
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So. Burlington, Vt.
“If it were me”, and I were running an 8:1 motor in Stock, I’d initially be using whatever was the least expensive legal fuel on the list.

After the car was sorted out and quite repeatable......... then you could experiment with some different fuels to see if there is a performance gain over the cheaper stuff.

Of course, I wouldn’t be messing around in S/St either.
Just put the 383 in the car, with the correct cam, heads, intake, carb and start making runs.
Swap the short block when the new 400 is ready.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: VP C-12 [Re: 83hurstguy] #3062643
07/26/22 09:17 AM
07/26/22 09:17 AM
Joined: May 2019
Posts: 516
Lake Villa Il
INTMD8 Offline
mopar
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Joined: May 2019
Posts: 516
Lake Villa Il
Originally Posted by 83hurstguy
Octane and the burn curve aren't necessarily related. High compression engines need higher octane and also typically operate at higher RPM ranges, which requires a faster burn...

You'll find that fuels have varying Reid vapor pressures that will help with intake charge cooling more than others, which may help increase power via better atomization/distribution. A lot of stock eliminator guys will typically run C11 or C12, and those engines have less than 10:1 compression and huge cams that produce low cranking compression. Some fuels like hot vs cool engines (or hot intake charges from boost).

That being said, many people use race fuel for consistency in tuning run to run (or class rules) even if the engine doesn't require it. I have a big block iron headed engine here with 10.5:1 compression that doesn't care whether it's on pump or C12 (it actually picked up a tick on pump on the dyno). My stock 440-6 has some preferences that show up on the dyno in terms of fuel, but it's maybe 5 hp difference.

Pump gas is inconsistent but also oxygenated, which can help make power. You may also find that race fuel has lower specific gravity than the pump gas you're running, which means you need to jet up to get the same power input.

Overall - fuel testing and tuning takes a lot of time and effort. It's definitely not as simple as the guy at the cruise night spouting off "yeah she really runs good with the race gas!"


Good post, agreed. thumbs


69 Charger. 438ci Gen2 hemi. Flex fuel. Holley HP efi. 595rwhp 475rwtq.
Re: VP C-12 [Re: Cab_Burge] #3062652
07/26/22 09:39 AM
07/26/22 09:39 AM
Joined: Feb 2016
Posts: 172
PA
S
Scully Offline
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Scully  Offline
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S

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PA
Originally Posted by Cab_Burge
Originally Posted by fast68plymouth
In nhra stock, you have to run a fuel that’s on the approved list, and it will get checked after you make a pass most of the time.

how long ago did that start?
More than 30 years ago.

Re: VP C-12 [Re: Scully] #3062789
07/26/22 03:38 PM
07/26/22 03:38 PM
Joined: Aug 2003
Posts: 40,361
Bend,OR USA
C
Cab_Burge Offline
I Win
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Posts: 40,361
Bend,OR USA
The last time my old M.W. race car ran in NHRA stock was in 1988, it ran better on VP C12 at that race than it had with the SO CA local race gas Daeco brand boogie
NHRA would check the polarity on gas in both SS and Stock but not in any of the Super heads-up classes back then shruggy
Both of those classes can be tough to do well in scope
good luck on your efforts up wrench grin


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: VP C-12 [Re: AndyF] #3062809
07/26/22 04:52 PM
07/26/22 04:52 PM
Joined: Jun 2008
Posts: 101
Colo
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PJ68RT Offline
member
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Joined: Jun 2008
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Colo
Engine masters octane testing

https://www.youtube.com/watch?v=ryqyTPfNj1Q







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