I rebuilt my 225 Slant Six with 0.040 oversized pistons and 0.090 shaved off the head. My compression ratio is allegedly 9.69:1.0. It currently has a half a tank of 87 octane gase in the tank left over from before the rebuild. My question is, what grade of unleaded should I be running to keep from carboning-up my new engine? Or should I buy 87 octane and add a bottle of octane enhancer? This is a daily driver that I hope to get another 100,000 miles out of. The performance went from a tired old Slant Six to a small block V-8. A big improvement with just 87 octane. I am just worrying about the long term effects of low octane fuel on my engine.

bwhitejr

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'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

If you have no problem running 87, like detonation, or have to retard ign timing, run 87

Right now the initial timing is set at 12 BTDC and the engine is not completely broke in yet. The car has a date with a mechanic to set the idle mixture and hot lash the valves. I just want to be sure it is set up properly before I begin driving it daily. From what I have read recently, I may have too much compression for today's gasoline. I have put my foot in it a couple of times and it didn't ping. When I was setting the timing the RPM's went up while I was advancing the timing. I just set it on factory numbers and quit.

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

No pinging = no problem. Most of the negative stuff you read in the hot rodding press about "today's gasoline" is bunk written by those who've been sniffing too many exhaust fumes.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Even when it was a tired SL6, it was fun to drive. Now I can't wait to drive it everyday. And on Saturday night take it down to the local burger hangout and show off the SIX!

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

Put the 87 in it and doint use no octane boasters waste of money. Have fun . Thanks Ron Parker











Hey Has That Thing Got A Bagel Bamboozler In It

Don't even worry about the octane booster(waste of money), drive it like it is, listen for the rattle of 'ping' on slopes and during hard acceleration (this will tell you either back the timing off a bit, or run the next grade up, or play with the advance)...

If it hasn't appeared, then you are in good shape, or your gas station gets really good 87 octane (in Oregon, it's a crap shoot every week unless you buy 'plus' or better), sounds like you've done a great job on the rebuild...watch the power it gets 'addictive'!




-D.Idiot

I may have read it here a long time ago, but I remember a post that said something to the effect that an engine will be it's most efficient with the lowest octane it can tolerate.

If this is incorrect, someone please correct me.

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The Old Goat '83 D150 225-2

AKA Ice Titan

Oh, yeah, really retard your timing, so it runs like crap, then you won´t get so addicted

Lowest octane without retarding timing...................


I do remember seeing somewhere that higher octane fuel has less BTU's / gallon which would make it true.........

Also that higher octane fuel burns slower......


Not sure if that's always the case or not??????????

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Don´t use any more octanes than you need, it is just a waste of money

More octane can tolerate more temperature or pressure, before it ignites, and that is all that rating is for.

If you can run on 30 octane snowblower fuel, there will be no advantage in using 110+race fuel, it may actually hurt performance( but probably not the engine, just your wallet)

If it starts to ping under load, try to retard timing a little bit, if it doesn´t stop, go for the next step up in fuel, and see if you can get the timing back where it is supposed to be.

You could always try a search for timing curve, or similar, maybe your distributor has too much advance, and you may want to modify it to your needs.

Ah, don´t mess with stuff if it doesn´t have a problem, of some kind

Oh c'mon! Where's your sense of adventure? "If it ain't broke, fix it 'til it is."

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

I like to keep that to myself

Thanks for all the reponses.
I bought a set of springs (P2932675) to put in if they were needed. I guess the jury is still out. The service manual I bought with the truck says: Centifugal Advance
1.5 deg to 3.5 deg @ 650 RPM
2.0 deg to 4.0 deg @ 900 RPM
3.5 deg to 5.5 deg @ 2200 RPM

Vacuum Advance:
1.5 deg to 6.5 deg @ 7 in. vacuum
10.0 deg to 12.0 deg @ 12 in vacuum

My distributor is a 3874876 electronic model.

The GVWR of the vehicle is 4800 lbs. And I am sporting 213 horses at 4500 RPM and 267 ft/lbs of torque at 3500 RPM. I am running Champion RV12YC plugs. And at idle I have 20 inches of vacuum.

Can someone point me in the right direction? More advance? Less advance? Recurve distributor?

You guys have gotten me through this build and I appreciate what we have accomplished. The final tweaks are all that is left.

What a project!

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

I would play with recurving for a while...