1974 C25 octane rating - The 1947 - Present Chevrolet & GMC Truck Message Board Network

MylilBowTie · 12-30-2009, 05:13 PM

I was looking around on Jeff's site look at some vintage ads. Noticed that for 1974 the recommended octane for the 454 was 91. But the compression ratio was pretty low like 8.25:1. Looking over the ad again all the engines are recommenced for 91 octane.

So does my 454 really need 91 or is 87 okay? I just got it and put 89 in it and it seems to run okay.

http://www.73-87.com/7387info/articles/74pu02.jpg

74 C-30 · 12-30-2009, 05:35 PM

I run 91 in my 74, cause it runs like junk if I don't, but I also only buy Mobil, I guess I'm just picky...

GMC Guy · 12-30-2009, 05:37 PM

i always put 91 in mine. i can really tell the difference between it running on 87 and 91. but that's just me

vtwinsport · 12-30-2009, 06:14 PM

I've been running 91 for about two months now and there is a noticeable difference. I'm logging my efforts and tracking gas mileage so we'll see if it really does anything else

GmtGmt · 12-30-2009, 08:23 PM

Well here when we have build a couple of street cars we ran 97 or 98 octane and there was a very big difference from the normal 91 or 95 octane both in power and fuel economy

rare86 · 12-31-2009, 03:04 PM

In my stock 454s, I havent seen any benefit for using 91 over 87 octane. The compression is low, and shouldnt really need it, also, the gas used today is different than it was in those days. I run 91 in my 468, but its pushing 10.5:1 compression. It may have to do with altittude tho because Im n the desert.

12-30-2009, 05:13 PM	#1
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	1974 C25 octane rating I was looking around on Jeff's site look at some vintage ads. Noticed that for 1974 the recommended octane for the 454 was 91. But the compression ratio was pretty low like 8.25:1. Looking over the ad again all the engines are recommenced for 91 octane. So does my 454 really need 91 or is 87 okay? I just got it and put 89 in it and it seems to run okay. http://www.73-87.com/7387info/articles/74pu02.jpg __________________ 1974 C25 LWB: 454 4bbl Carb / TH400 / 3.73 1992 Camaro RS 305 TBI

12-30-2009, 05:35 PM	#2
74 C-30 Dually Pride Join Date: Jun 2008 Location: NH Posts: 540	Re: 1974 C25 octane rating I run 91 in my 74, cause it runs like junk if I don't, but I also only buy Mobil, I guess I'm just picky... __________________ If I have to explain, you wouldn't understand. '74 Chevy C-30 350/4 speed/dually '94 Ford Ranger

12-30-2009, 05:37 PM	#3
GMC Guy Registered User Join Date: May 2009 Location: Sparks, NV Posts: 913	Re: 1974 C25 octane rating i always put 91 in mine. i can really tell the difference between it running on 87 and 91. but that's just me __________________ Greg 1974 GMC 1/2 Ton SWB Fleetside L33 5.3/4l65e .................__ ............._____l __\__ ..............l_(O)_ l___(O)]

12-30-2009, 06:14 PM	#4
vtwinsport Registered User Join Date: Nov 2008 Location: edmonton, alberta Posts: 293	Re: 1974 C25 octane rating I've been running 91 for about two months now and there is a noticeable difference. I'm logging my efforts and tracking gas mileage so we'll see if it really does anything else __________________ 76 Silverado, 2wd, long box, 350/th350, 3.42 posi, edelbrock performer 64cc heads, edelbrock 1405, 2101 intake, Hedman Headers, Comp Cam XE262 http://beerbreadbike.wordpress.com/

12-31-2009, 03:04 PM	#6
rare86 Extended cab fanatic Join Date: Oct 2009 Location: Gardendale, Tx Posts: 314	Re: 1974 C25 octane rating In my stock 454s, I havent seen any benefit for using 91 over 87 octane. The compression is low, and shouldnt really need it, also, the gas used today is different than it was in those days. I run 91 in my 468, but its pushing 10.5:1 compression. It may have to do with altittude tho because Im n the desert. __________________ If it has a motor, it has my attention.



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