What gas needed to run 11.0 - 10.5 CR

[Ironbuilt]

Interesting. We get 5-gallon party balls of VP110 for about $75 here, close the same neighborhood in pricing...which is surprising because I'm sure our pump gas is considerably more.

Believe it or not, North Carolina is high for gasoline. Right now, unleaded gas is averaging $3.00 a gallon. South Carolina, on the other hand, is around $0.30 cheaper a gallon. Virginia, about $0.10 a gallon cheaper.

 

[67belvedere/225]

Please forgive my ignorance, but how does AV fuel differ from jet fuel? Jet fuel is basically kerosene, correct?

I heard AV GAS is drier so marvel might be a good thing . My older client (76) swears by marvel oil . he adds it to engine oil.

 

[Jerry Hall]

So that tank feeding your Dart is 110 octane leaded gas?
How much, roughly, a gallon in American dollars?

Last I bought here was $5.45 a gallon US in Alabama.

 

[Canadian1968]

Agree with that^^^^! I have run 440s with 11 1/2 and 12 1/2 pistons on pump 91. However, both those engines were really at least a compression point lower than advertised, and both had big/huge cams. The 11 1/2 engine, really 10 1/2, has a 252 at .050 cam, the 12 1/2 (really 11.25) had a 272 at .050 roller.
Now that I have access to 100LL avgas, I run at least two or three gallons avgas with five of 91. I might not need to, but it sure don't hurt.
With your cam that short, I surely wouldn't be bumping the compression up. Run a compression test on your engine. If you are at 170 lbs now, I would not swap 915s on. My opinion only. I wouldn't want to have to pay race gas prices for a street driver. (Unless like me, you can get relatively cheap avgas)

because of the cam I'm going to really increase cranking pressure with 915 is that what i am understanding ?

And that what I am trying figure out.... sounds like I would have to run AV gas or dedicated racing fuel.

 

[dadsbee]

So that tank feeding your Dart is 110 octane leaded gas?
How much, roughly, a gallon in American dollars?

100 Octane. I'm waiting for the truck to come fill my 500 gallon tank and might need vasoline for the invoice this round. Last year it was $1.74Cdn / liter all in.. so about $5.40 US/US gallon.

 

[67belvedere/225]

I just filled up a shell and it was 1.65 a litre (3.785 makes a gallon so 6.24 cad a us gallon)
so 4.95 a gallon for 91 supposed no ethanol. @dadsbee hide the gas bill from the wife!

 

[Curiousyellow71]

We have always run av gas 100LL as opposed to race gas. Just bought some a month ago about 5 bucks/ gallon... its pretty convenient w card reader pump at our small airport. We had used 100LL Straight up in a 440 13.4:1 stage VI w a big roller cam, and we will use av gas again because race gas made no difference in performance. Over the years I would say av gas shrunk the gaskets but it took years to see it happen.
In our charger when it was 11.5:1 w 452s 5 gallon 100LL blended with 14 gal of 89 worked well. We since changed to a cam w a wider lsa and lots of seat timing and lowered the compression to 10.5:1, but it runs on 87 no problem with a open chamber head.

You are correct a 274xe builds compression instead of bleeding it off. For sure your going to be blending some octane to make it work.

 

[dadsbee]

@dadsbee hide the gas bill from the wife!

I don't have to hide anything from my wonderful wife...

 

[Jerry Hall]

I don't have to hide anything from my wonderful wife...
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[Jerry Hall]

Last I bought here was $5.45 a gallon US in Alabama.

It won't run my Dart, I use 110 or 115 racing fuel in it. Supposedly 12.5 to 1.

 

[Dodge Bros]

In theory with a good quench and the closed chamber 915 heads the timing could be backed off some versus the 906s. But the smaller cc’s on the 915s are going likely jump the compression a bit to much. IRC the port shape and flow are pretty similar between a 906 and a 915. If the 915s jump to compression up to far I would think they will likely loose some power against the 906s on the same fuel… But..That is assuming both heads are totally stock. So what comes to my mind is what do you hope to gain?

Curiousyellow71 (my brother) and I with our 510 run 10.5 compression on 87 octane with with 452 heads. But the heads are very ported, uses a single plane M1 intake with no heat cross over, 1 7/8 headers with a 3 “ X full exhaust, plus it has a good sized cam with a fairly wide LSA and LOTS of seat timing. If we made a cam change to something like a xe274 I think we would have to knock a point or more off the compression. FWIW, We have a 440 on a stand getting a xe284 for a 440, it is set up for 9.5 compression for 87 octane, or a mix of 91 and 87, it has 906 heads milled .050 with minor port work 240 cfm, stock intake and small tube headers. I am sure it would be a better engine with 915s that are pretty similar cc’s and a better quench. Into the 10s is asking a lot though with a stockish iron heads and aggressive XE grind, 93 octane plus here, even with a quench.

I am guessing if you can make 91 work now with 906s, you could run the 915 combo on 93 octane or slightly higher, as long as it has a good quench. But it depends on where the compression ends up. We have a 383 with ported (250-260 cfm) iron 346s milled to have quench and it is at 10.3 compression with a Lunati hft cam sized between a xe 274 and 284. Our 540 engine is about 10.2 with 346 heads ported (300cfm) and a decent size bullet solid cam. Both those are intended to be 91-93 octane engines with dual planes and HP manifolds.

 

[Cojohnso1]

Jet fuel, diesel, kerosene all about the same. AV gas is gasoline...

Jet fuel is a high quality diesel. My stock 440 at about 9.5:1 runs good on non oxygen 91. (With hardened valve seats to accommodate.) But she sure does seem to like a gulp of the AV gas. Just starting and shutting off. No difference in performance. Actually AV gas produces less BTU's of energy than lower octane fuels. But not enough to make any noticeable difference. But because it does have some lead? And just a tad bit more oily? (For lack of a better word) The 440 just snaps better on start and off. I have no actual science measurements. But just what my ear detects.

 

[33 IMP]

I think i paid about $4.25/gal for the last 5 gallon can of avgas i bought here in arizona. About a buck more than az premium, at the time, and about 50 cents less than the california cat pee i mix with it.
Its been a while since i bought the avgas, we'll see how much it is now.

 

[33 IMP]

because of the cam I'm going to really increase cranking pressure with 915 is that what i am understanding ?

And that what I am trying figure out.... sounds like I would have to run AV gas or dedicated racing fuel.

Yes. The more camshaft you have, the more compression can be tolerated on a given fuel.
12 to one with 270° duration at .050 might run fine on pump gas. That same 12 to one with a 225° at .050 will detonate itself to rubble at half throttle, and have to have the timing dialed back so far it will barely run.
That combo would likely need straight 112 to run well.
With the cam you have, i would say you are probably on the edge now, and another half point, or more, from a 915 swap will be counter productive.
But thats just my opinion/guess.

 

[mrhemi]

The 100LL has more lead than you'll ever need for seat lubrication Jerry. More than premium leaded ever came with..

2 grams per gallon the last time I ran a spectrograph on some 100LL. It only takes approx. 1/2 gram per gallon for seat protection.

 

[BSB67]

There is some speculating as to what might work with different combinations. Here is what will not work:

440
915 head
222 degree @ 0.050 installed at 109
10.3:1 CR (Measured)
190-195 psi on the gauge
Good quench
93 octane
1000 ft elevation
160 degree thermostat
crossover blocked
NGK-7 plugs
No vacuum advance
Full timing in at 2500-2800.

The car is heavy, 3.23 gear, and stock converter. There was no reasonable ignition timing that would allow this motor to run well without detonation.

The detonation was significant.

 

[Dodge Bros]

We usually rough figure in a one point change in octane for every 5 pounds change of cranking compression. Going from 9.8 to 10.5 (rough figure for a closed chamber head swap) will be a minimum of a 15 lb change in pumping compression with the same cam and no other changes. Real life probably it is likely closer to 20 lbs…Which would be a 4 point octane increase. The quench style heads would lower it some, but for certain it will be at a higher octane threshold than before, would guess it will need 3 to 4 more octane fuel. FWIW.

http://race-gas.com/

 

[dadsbee]

2 grams per gallon the last time I ran a spectrograph on some 100LL. It only takes approx. 1/2 gram per gallon for seat protection.

Yep, why I run it at about 33% 100LL to 67% Shell 91. IE 5 gallons AV100LL + 10 gallons Premium.

 

[Curiousyellow71]

A little read about 100LL. It's certainly higher quality then what cars get. The octane rating is also different.
https://www.shell.com/business-cust...centre/technical-talk/techart12-30071515.html

 

[BSB67]

It's certainly higher quality then what cars get.

Well thank goodness for that.