93 Octane Pump Gas

6hypo5conv_old · November 26, 2009 at 7:13 AM

Can I expect my K engine to run as is was ment to on todays 93 octane pump gas?

It was completely rebuilt to stock specs (had to be bored .030) and heads were cut about .015, other than that its all stock.

I don't plan on any all out racing or anything like that, just some spirited driving on Sunday afternoons.

66KGT_old · November 26, 2009 at 8:45 AM

I hope you put hardened valve seats in. Yeah, 91 - 93 will be fine.

zray · November 26, 2009 at 8:59 AM

mine ran well on 93 & 91 when stock. Took a 1500 trip and used Shell premium. No problems.

However when I added a vintage Paxton I began to have some pinging (still using the Hi-Po 10:1 pistons). Retarding the timing, adjusting the advance curve, and the jetting has eliminated most of it.

Z. Ray

66gtk · November 26, 2009 at 10:17 AM

You will be fine! Try and use non oxy fuel if you can find it. Especially with the last tank of gas before winter. Glad to hear you will be driving the car. It's time for you to enjoy it!!

6hypo5conv_old · November 26, 2009 at 12:25 PM

Thanks Guys!!! I understand I can get NON Ethinol gas at a couple of marinas here locally-(our current gas is all the 10% Ethinol)(of which I have in the tank right now) I believe that the very first gas that was put into my car's tank was regular 87 octane stuff, so I have put 5 gallons of Sunoco 93 in it with a whole bottle of octane booster, and a double dose of Sta-Bil, and will go th just straight 93 octane when I need more gas.

Yes, We put hardened valve seats in as the originals were trashed anyway, so I'm good to go on that.

BTW: any estimates as to how the .030 bore and the .015 cut to the heads has changed the cubic inch size of the engine or the compression? has this washed each other out?

zray · November 26, 2009 at 1:19 PM

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>

..............." BTW: any estimates as to how the .030 bore and the .015 cut to the heads has changed the cubic inch size of the engine or the compression? has this washed each other out?

doesn't a 302 go to a 306 with a 0.030 overbore ?

Z.

289kford · November 26, 2009 at 1:59 PM

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>

BTW: any estimates as to how the .030 bore and the .015 cut to the heads has changed the cubic inch size of the engine or the compression? has this washed each other out?

I think both changes will raise comp ratio. cutting the heads made the chamber smaller, the over bore made the volume of the cylinder larger, to be compressed into the same (relative)area, unless the pistons were designed to compensate for that.

earlyk_old · November 26, 2009 at 9:09 PM

K's run fine on 87 too

rr64_old · November 27, 2009 at 9:07 AM

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Can I expect my K engine to run as is was ment to on todays 93 octane pump gas?

It was completely rebuilt to stock specs (had to be bored .030) and heads were cut about .015, other than that its all stock.

I don't plan on any all out racing or anything like that, just some spirited driving on Sunday afternoons.

Not exactly the same but my black Cobra's HP289 engine had its heads milled in the 1960s (a very common occurrence). The heads are the small chamber small valve 1963 design. Nothing is ported. I measured, "cc'd", everything when I overhauled the engine in circa 1986 and came up with just under 11.5:1 static compression ratio. The engine still has its original HP289 cam, standard bore, and is stock specifications otherwise except for the COBRA KIT 1-4V induction system and later C5 design distributor. I run 36° total advance at the factory recommended curve and the exhaust is its stock original back to the mufflers. The engine normally runs around 180°F to 200°F in the summer and cooler in milder weather. I have never checked hot compression.

93 octane (any brand) fuel without ethanol runs just fine until about 5,000 rpm. I will start getting preignition break up about that time unless I either run an additive or high octane racing fuel. The engine was optimized years ago for doing open track events at the Tulsa Mid-America event. In that configuration it had a K&N filter element, K&N “stub stack”, BTF1 or BF12 racing spark plugs, and highly leaded racing fuel in the 110 or higher octane level. With that set up running 7,000 plus down the straights was no problem. For street and play, putting a gallon or so of NASCAR leaded racing fuel in a tank of 93 octane street fuel made a big difference, 7,000 rpm short runs being no problem. In lieu of the racing fuel as additive I have also used commercial octane boosters. With 91-93 octane fuels believed to contain ethanol I still use the commercial octane booster, a lead substitute, and a fuel stabilizer (since I don’t get to drive the car as much as I wish). I was running through the gears into the 7,000 rpm range at Bearun at SAAC-34 during this summer and detected no issues.

The static compression ratio (SCR) “as built” is not the one that always gets you into trouble long term. Cylinder pressure when running is a major player. It is determined by not only SCR with every other variable that affects cylinder filling, air fuel ratio, mix quality, ignition timing, ignition efficiency, ring seal, valve seal to head seat quality, et ectera. Fuel producers include detergents in their blends but they are not all the same or were they even meant to. A marine engine has different considerations than an aircraft which has different ones from cars and trucks. Running a high ash fuel with a meets minimum requirements detergent package can lead to a signifciant layer of carbon and ash on every fixed surface inside the combustion chambers and exhaust ports. I am sure you have seen ash fouled spark plugs come from some type engine, now imagine that layer everywhere inside the combustion chambers. Thick deposits in chambers do a couple of significant things, one the raise your SCR because deposits reduce the chamber volume. Thicker deposits mean more volume loss. The other is create irregular surfaces with raised protections that can become red hot during high load engine conditions. These hot spots can ignite the air fuel mix in the chambers before the spark plug does. The SCR that was okay when you built the engine may be more significant later, so keep that in mind. Changes you may make over time that affect running cylinder pressure should also be considered.

My old BOSS 429 did not run well at all on anything less than 110 octane fuel but so far all my HP289 cars (formerly 1965 GT350, formerly 1966 GT350, currently Cobra) have done acceptably octane wise during ordinary street cruising with whatever I found at the pump. For high load high rpm play, especially during an open track road course event I would recommend doing something to increase your octane rating.

6hypo5conv_old · November 27, 2009 at 12:11 PM

Thanks Guys for your replies!!

I think I'm going to take rr64s advise and put at the very least some commercial octane booster in my 93 octane Sunoco gasoline.

or possibly get a gallon or 2 of Sunoco racing fuel that we have here locally-its about 8.50 per gallon.

289kford · November 27, 2009 at 2:15 PM

Since octane numbers of today are not measured as they were in the 60's, what would a 91 octane number gas from today equal in 65 numbers? now we use R+M/2 but in 65wasn't it just RON?

rr64_old · November 27, 2009 at 4:49 PM

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Thanks Guys for your replies!!

I think I'm going to take rr64s advise and put at the very least some commercial octane booster in my 93 octane Sunoco gasoline.

or possibly get a gallon or 2 of Sunoco racing fuel that we have here locally-its about 8.50 per gallon.

Your fuel requirements depend a lot on how the vehicle is used. If you are going to drive over to the next town for a show and run at posted speed limits you can get by with lower octane. If you are going to run wide open throttle corner to corner in an open track event for 30 minutes at a time I would run straight racing fuel. Shelby American kept their SCRs low and their cam shafts mild for internation racing and generally didn't run over 6,000 rpm because they had no idea what kind or how bad the fuel the European tracks would have available. If they could race in Europe on crummy fuel with SCRs around 10.5:1 you should be fine on today's premium unless you are doing "spirited" driving. I run additive because I am likely to run my Cobra wide open throttle at any time.

RalphJr · November 27, 2009 at 6:07 PM

RR64,

Nice to hear of another Mid-America attendee - it is a GREAT show.

I started going to that event in 1981 and attended every year until I moved to Georgia in 1999. I really miss it!

In fact I think we spoke in person the year you "traded" 2 cars for your Cobra. If it was you that is. Seem to remember you were cleaning it for the Sunday show when we spoke. As I remember it was an AWESOME car!

Edited by - RalphJr on 11/27/2009 18:08:28

zray · November 27, 2009 at 9:43 PM

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>

Thanks Guys for your replies!!

I think I'm going to take rr64s advise and put at the very least some commercial octane booster in my 93 octane Sunoco gasoline.

or possibly get a gallon or 2 of Sunoco racing fuel that we have here locally-its about 8.50 per gallon.

"................... you should be fine on today's premium unless you are doing "spirited" driving. I run additive because I am likely to run my Cobra wide open throttle at any time.

what additive do you use ? I've had good luck with the "race" NOS octane booster letting me run more advance with my Paxton set-up. Without it I have to dial back the advance to 32 degrees (from 40, which is stock). What I don't like about it is the red deposits it leaves on the inside of the carb & the spark plugs.

Z. Ray

rr64_old · November 28, 2009 at 6:25 AM

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote> RR64, In fact I think we spoke in person the year you "traded" 2 cars for your Cobra. If it was you that is. Seem to remember you were cleaning it for the Sunday show when we spoke. As I remember it was an AWESOME car!<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

Good memory, I actually just used my Boss 429 in trade (see orange car on the cover story December MM). A friend and I drove the Boss 429 from Decatur Alabama to Vinita Oklahoma one day and then drove the Cobra back home then next. Two twelve hour road trips back to back with staying up pretty much all night talking parts and cars with Jim and Terry Wicks. Yes, you can sleep in a Cobra (riding passenger) while on the move.

I separated myself from this list of vehicles to end up buying Cobra CSX2310.

Model Model V.I.N.

Year Designation

1965 GT350 SFM5S446

1965 GT350 SFM5S142

1965 Falcon Ranc. 5H27T145793

1966 GT350 SFM6S2070

1967 GT500 67402F8A00468

1969 GT350 (Hertz ?) 9F02M481476

1969 BOSS 302 9F02G189080

1970 BOSS 302 0F02G160803

1970 BOSS 429 0F02Z124202

1970 BOSS 302 0F02G126674

rr64_old · November 28, 2009 at 6:29 AM

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what additive do you use ?

Z. Ray

I have tried several different ones but I like one best and I think it is one of two products from one company. Before I make a mistake I'll go out an look at one of the bottles before saying which one.

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