Originally Posted by Heypops
Will try the 87 octane trick !
About to visit our son at college, a good 6 hr trip by interstate.
Hopeful this trip will help clean the fuel system and give info about the knock.
I keep you informed on the progress.
thanks a ton for your help !!
The octane rating of fuel is really it's ability to withstand compression and the advanced timing of the engine.
The octane rating has to do with the amount of compression it takes to make the fuel spontaneously combust. Lower octane takes less compression to combust than higher octane. This is why high compression engines need higher octane fuel, to get their full power potential without causing "preignition." Preignition is when the fuel in your cylinder spontaneously ignites before it is actually sparked. That is really the only reason to use high octane fuel so it can withstand higher compression.
Unless you are running like 10.5:1 or higher compression ratios, or a advanced timing program in your PCM, then you are gaining nothing from using premium octane fuels. I don't even really understand why those aftermarket computer chips or programmers tell you to use higher octane fuel once they are installed, they don't change the compression of your engine. That is literally the only reason that their are higher octane fuels, higher compression and there also programmed to detect any detonations to adjust the timing. I have my self altered the timing program on my PCM's engine timing and engine temperature setting to run cooler then the stock 195" with changing the rocker ratio's to 1.6:1.
Actually, if you want to get real technical, using higher octane fuel in an engine that does not actually need it could potentially take some power AWAY from the engine. They get higher octane fuel by changing the ratios of certain chemicals in the fuel mixture. This basically means that higher octane fuel means a little less gasoline, and a little more of additives.
Say, just hypothetically, that 87 octane fuel is 90% gas and 10% octane chemicals. 91 octane may then be 85% gasoline and 15% octane chemicals. Using those imaginary figures there, that means that using higher octane fuel = less usable gas.
Just a little food for thought, and for those who are interested in swapping out your rocker ratio from the stock 1.5:1 to 1.6:1. There are 4 variations of rocker setups on the Chevrolet 4.3L V6. The difference is in the stud base and in the rocker adjustment and alignment. The first thing you must determine when starting this project is what variation you have.
The first starts in 1988 and lasted until 1992. This setup uses a press in stud with a 10mm diameter and a rocker that is fully adjustable and NON self aligning. The second used the same stud but was a self aligning rocker arm.
The third appeared on Vortec motors in the early 90's and also on some non Vortec motors and lasted until 1999.
This setup uses a screw in stud with a 10mm base thread and a shouldered stud on top. The shoulder on the stud served as a stop on the adjusting nut. This setup is NON adjustable and is know as a Net Lash Rocker system. In 2000 and up model years GM introduced a roller rocker. This rocker sat on a guide plate and was bolted down with an 8mm bolt.
Key points in determining what rocker setup you have in your engine.
* 1988 to 1992 all used press in studs, were NON self aligning and fully adjustable
*1992 to 1995 Vortecs ALL used a net lash system with screw in studs and self aligning rockers
*1992 to 1995 Tonawanda* Engines used a net lash system with screw in studs and self aligning rockers
*1992 to 1995 Romulus** Engines used press in studs and were full adjustable. The rockers were self aligning.
*1996 to 1999 All engines used a net lash system with screw in studs and self aligning rockers
*2000+ All engines used roller trunion rockers. They were a net last system and self aligning.
If you have a Tonawanda engine, it will have a "T" stamped on the machined surface on the block just in front of the right cylinder head.
If you have a Romulus engine, it will have an "R" stamped on the machined surface on the block just in front of the right cylinder head.
1988 to 1992 with press in rocker studs, NON self aligning
On this type of engine you have basically one option. Remove the studs, drill and tap the head to accept a 7/16" rocker stud, install a 7/16" bottom X 3/8" top stud and use a set of narrow body rocker arms. This procedure should only be done with the heads off the block which makes it one of the most difficult procedures.
All the rockers below are NON Self aligning they will all require the use of push-rod guides.
Below are just a few of the rocker arms available.
Comp Rockers 1017-12, 1.5 ratio Aluminum
Comp Rockers 1018-12, 1.6 ratio Aluminum
Crane Cams 10750-12, 1.5 ratio Gold Race
Crane Cams 10759-12, 1.6 ratio Gold Race
Harland Sharp S1001, 1.5 ratio Aluminum
Harland Sharp S1002, 1.6 ratio Aluminum
Harland Sharp S1003, 1.65 ratio Aluminum
Scorpion SCP1037, 1.5 ratio Aluminum
Scorpion SCP1038, 1.6 ratio Aluminum
Below are some rocker stud options :
7/16-14 Bottom X 3/8-24 Top
7/16-14 Bottom X 3/8-24 Top ------- but a longer stud and a better option for full roller rockers.
1993 to 1995 with press in studs, Self aligning
Follow the same procedure as above except use self aligning rocker arms listed below
1993 to 1999 with screw in rocker studs
These engines used a 10mm rocker stud top and bottom. The one problem with this is the lack of any available conversion stud to work with a set of narrow body rocker arms. Do not use a 60* V6 conversion studs They have the right thread sizes top and bottom but they are too short. All narrow body rocker arms on the market come with a 3/8" stud hole. So your option is to tap the head with a 7/16"-14 tap and use a screw in stud similar to above. However the tap does not bite in very hard so it is advisable to coat the threads with JB weld prior to installing the studs. If you go this route use the stud options above and the rocker options below.
Anyone reading this article should do the community a favor. E-mail ARP (www.arp-bolts.com
) asking them to produce a 10mm X 3/8" conversion stud that is long enough for use on a Vortec motor. The 60* V6 conversion stud would be perfect if it was 3/8" longer on top.
2000+ with factory roller rockers.
This year of motor is very simple to do a roller rocker setup on. All parts can be purchased off the shelf and bolted in. This setup requires the use of a SELF Aligning rocker. The following are some of your options on rockers.
On the left is an example of a self aligning tip. The "ears" keep the rocker tip on top of the valve stem. In a NON self aligning system this job is handled by push-rod guide plates.
Crane Cams 10751-12 1.5 ratio Gold Race
Crane Cams 10758-12 1.6 ratio Gold Race
Comp Cams 1317-12 1.52 ratio Pro Magnum
Comp Cams 1318-12 1.6 ratio Pro Magnum
Comp Cams 1015-12 1.5 ratio Aluminum
Comp Cams 1016-12 1.6 ratio Aluminum
Scorpion SCP1073, 1.5 ratio Aluminum
Scorpion SCP1074, 1.6 ratio Aluminum
All the above are self aligning rocker arms and will not require the use of guide plates. All will bolt on to your heads with the following rocker stud set
ARP # 134-7201 (16 pack) for heads with factory roller rocker M8x1.25 bottom 3/8-24 top
I would like to note one thing I did find a bit different.
The ARP conversion studs are part number 134-7201 as listed in this info. That is correct in that they are the right part number for the VORTEC heads. Hpwever that part is intended as a V8 setup and comes with the nessecary 16 count studs. Thats OK, but us V6 guys will have 4 left over.
ARP has since added part number 100-7201 which is the VORTEC V6-specific kit and has 12 count studs. Thats the only difference. The price may vary tho in your search.
Also note that the rockers are in the same boat. For instance, CompCams #1318-12 are ProMagnums of 1.6 Ratio, Narrow, Self-Aligning and are in a count of 12 for a V6 application. But the CompCams 1318-16 are the exact same rocker, just in a 16 count for V8 applications.
The reason I make this a point is since the V8's are more common and thus the aftermarket parts are as well, it may be easier to find the V8 parts new and used than the V6 kits. This will broaden your search a great deal. Especially in the used search. Only thing is you have 4 left over. Ive noticed on the rockers, most places price the -12 and -16 kits the same. Yet fewer places carry the -12 kits.
Another note on these years. A LT1 motor had stock Narrow, Self-Aligning rockers. And Ive seen the aftermarket list kits specifically for LT1's. But they are the same as the late model Vortec's use in that they are a 3/8, self-align and narrow body.
Too add to that, LT4 morors came stock with a 1.6 ratio full roller rocker arm. Like the LT1 (1.5 ratio) the LT4 is a Narrow, Self-Align rocker with a 3/8 stud. So you may find a decent used LT4 set to add to your search. The LT4 rockers were made by CraneCams after their Race Series. Most have the bowtie logo on the end. GMPP used to also sell them as well as a retro-kit for LT1 upgrades. I also read that the 'early' LT4 rockers had a recall and there is a 'late' kit. Check out some LT4/Vette sites for those part numbers and the TSB on that B4 you buy those.