# Valve clatter, low octane questions?



## acs1123 (Jul 17, 2009)

Recently purchased 65 GTO, 389, 4 bbl, 4 spd, etc. Has original 389 with I suspect 10.75 to 1 C.R. Has much low octane valve clatter when accelerating. Anybody have a fix for this?


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## jetstang (Nov 5, 2008)

Racing fuel, 50/50 with Premium. Take out a couple degrees of timing, but you are going have to run the best fuel you can find with substantial octane boost. I know guys that run moth balls to raise octane, although I haven't been gutsy enough to do it myself.


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## Flyboy (Sep 21, 2009)

acs1123 said:


> Recently purchased 65 GTO, 389, 4 bbl, 4 spd, etc. Has original 389 with I suspect 10.75 to 1 C.R. Has much low octane valve clatter when accelerating. Anybody have a fix for this?


I had same issue when bought my GTO. Each fill up I put in Sunoco 94 octane with a bottle of Octane 104 and a quart of Maxlead 2000 (tetraethyl lead) and never had issue again.


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## Rukee (Feb 8, 2007)

jetstang said:


> Racing fuel, 50/50 with Premium. Take out a couple degrees of timing, but you are going have to run the best fuel you can find with substantial octane boost. I know guys that run moth balls to raise octane, although I haven't been gutsy enough to do it myself.


:agree
Find a local circle race track and call and ask which gas stations sell the race fuel(if there's a track, some station sells the fuel). Run 50/50 with premium. There are 2 stations around me but each are about 20 miles away. Also, if there is a small air strip around you you may be able to buy aviation fuel. In my town I have to put it into gas cans then fill up at home as they won't let you pump it right into the car as they will with the race fuel. You will not believe the performance change with the race fuel. And it smells nice too. 
Also, like jetstang said, remove some timing, you don't want it to make that noise at all, if you have cast pistons it WILL break them over time. Ask me, I know personally.


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## Eric Animal (Oct 28, 2007)

:agree That isn't "valve clatter" it's detonation AKA pinging...little hot explosions caused by poor fuel quality.....it will knock holes in your pistons eventually. The gas at airports, that you want, is 100LL and is blue in color. Put a 5 gal. can of that in with some 92 or 93 octane pump pee and you will be fine!


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## geeteeohguy (Feb 2, 2008)

The guys are right! It's not valve clatter, it's pre-ignition: your engine is acting like a diesel, only the explosions are happening when the pistons are on their way UP the bore, not at the top and not on the way down. I broke 4 pistons in a 428 back in the '80's this way, running cheapo fuel and listening to the stereo too loud to hear my impending doom. Knocked the ring lands right out of them. Recently, I've had a hand in overhauling the 389 with dished pistons, which lower the compression to about 9:1 and allow the use of pump gas. If you're running stock 10.75 (like I am and Rukee, and others), you need to boost the octane.


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## 66tempestGT (Nov 28, 2009)

dished pistons! you wont be sorry. you wont be tied to a leash. you can drive anywhere you want and fill up at the pump. and if you think pump gas is high that racing gas will make new pistons seem cheap. the power difference will be minimal, especially if you are driving the high compression car around "detuned" to try to get by.


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## Rukee (Feb 8, 2007)

Sorry, but performance difference between race gas and high compression VS dished pistons and premium is minimal??? seriously?? Dude, come by my house, I'll give you a ride. You'll never say that again!!! cheers


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## 66tempestGT (Nov 28, 2009)

LOL we arent talkin 15:1. dish piston and tight deck clearance you probably still close to 9.5:1 vs. 10.75 whats that 20 hp maybe? :cheers


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## Rukee (Feb 8, 2007)

pfft! There's more then 20 HP just adding the race fuel to the premium for the high compression(that's n0o crap!! Come for the ride!!), then deduct for the dished pistons......


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## 66tempestGT (Nov 28, 2009)

i would like to go for a ride in that car of yours, maybe someday. but i would really rather drive! :cool arty:


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## Rukee (Feb 8, 2007)

66tempestGT said:


> i would like to go for a ride in that car of yours, maybe someday.* but i would really rather drive!* :cool arty:


Yeah, that ain't gunna happen!!!:shutme


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## jetstang (Nov 5, 2008)

11:1 is 400 HP, 8:1 is 200 HP.. If you go 70 to 74, pre to emisions years. They had 455s turning out 180 HP in 78, but that was cam, heads and compression. It was the muscle car era for a reason, no compromise motors. Yeah, the cars ran 14 second quarter stock on little hard 14" 6" wide bias plied rock tires, traction compromised. Put a gear and some slicks on there and they were low 12 second cars.


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## geeteeohguy (Feb 2, 2008)

:rofl:I wanna go ride with Rukee!!!


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## Eric Animal (Oct 28, 2007)

Boys, boys........Uncle Eric will take you all for a ride....someday!!!arty:


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## acs1123 (Jul 17, 2009)

I appreciate everyone input. I am familiar with all the options mentioned. I will likely buy a barrel of 110 leaded racing fuel.


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## 66tempestGT (Nov 28, 2009)

you sound like a rich man!


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## 66tempestGT (Nov 28, 2009)

jetstang said:


> 11:1 is 400 HP, 8:1 is 200 HP.. If you go 70 to 74, pre to emisions years. They had 455s turning out 180 HP in 78, but that was cam, heads and compression. It was the muscle car era for a reason, no compromise motors. Yeah, the cars ran 14 second quarter stock on little hard 14" 6" wide bias plied rock tires, traction compromised. Put a gear and some slicks on there and they were low 12 second cars.


1983 camaro "HO" 305 165 hp
1978 pontiac 455 180 hp

those pontiacs kick a**
:rofl::rofl::rofl::rofl::rofl::rofl::rofl:


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## jetstang (Nov 5, 2008)

I wanna go for a ride too!!
Now, Butler performance and others-read Erics threads, they are turning huge numbers with Pump gas Pontiacs, but they have aluminum heads and roller cams and all the good stuff. Butler Performance - Specializing in Pontiac Engines Heads and Performance Parts
Technology has allowed big numbers with crap gas, but you are going to pay. At 10 MPG, I am willing to compromise some power to get reasonable fuel costs, 50/50 race fuel is about $6 a gallon, thats 60 cents a mile to cruise your car around!! At $4 a gallon, it was costing 40 cents a mile to use my 454 as a work truck, that hurt.


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