pump gas 460 and compression ratios

11220 Views 11 Replies 7 Participants Last post by Muddin, Sep 27, 2010

rhodes wayne

Discussion Starter · Jul 16, 2010

everyone of the articles from different sources say that you can run regular unleaded with 8.82:1 compression. So I built a junk yard 460 1974 ish year with a set of dove heads. no block decking or milling heads, just a resurface on the heads. with a .040 head gasket gave 8.82:1 static compression ratio so anyway built the motor and had to run 93 octane unleaded because the motor pinged with exceleration my theory is go a head and run 9.5:1 compression with cast iron heads and a 160 degree thermostat and at least 91 octane, here in the south we are lucky to have 93 octane. A lot of this has to do with the cam lobe centers, and cylinder pressure, and a good ignition system, such as MSD or accel or Mallory, with a hot coil will also make or break the pinging and detonation problems, and save the motor. Now we are talking street everyday driving ,or at least on the week ends with gas so high, now days most people including myself can not afford to drive, a gas hog everyday to work. I love trucks so I built trucks with 460"s anyway just a little food for thought WR

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HotRodLincoln

· #2 · Jul 16, 2010

Heat is what pushes the piston down, don't throw it away. Daily driving with a cold stat will just use more gas. Try decking the block, use the tightest quench you dare and if you feel like fiddlin' with stuff cut Singh grooves in the pistons. Be sure there's nothing like a sharp edge in the chambers or on the piston tops - no sharp edged valve pockets. That all won't let you run 87 by itself, but it'll run better than it does now.

Knock sensors are old tech now. GM ran 9:1 on iron headed engines in the '80s that way, on 87. Sensor setups have to be tuned to work with each engine.

And never believe anything you read ;-)

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MauriSSSio

· #3 · Jul 17, 2010

HotRodLincoln said:
Heat is what pushes the piston down, don't throw it away. Daily driving with a cold stat will just use more gas.....

but why do most cars run faster after cool down then??

i run 10.8 compression on my 533 w 91 octane gasolina.

I think something just as important is DYNAMIC compression and how efficient the combustion chamber is.

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2slow

· #4 · Jul 17, 2010

MauriSSSio said:
but why do most cars run faster after cool down then??

i run 10.8 compression on my 533 w 91 octane gasolina.

I think something just as important is DYNAMIC compression and how efficient the combustion chamber is.

getting the best MPG and the best performance con't use the same rules .

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Money-pit

· #5 · Jul 17, 2010

How is your dizzy set up ? Maby you could loose some advance to help out some.

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DanE

· #6 · Jul 17, 2010 (Edited)

In 1988 I built a .060" over 460 that was properly clearanced and 0 decked. It had professionally ported D3's with PI valves The forged pistons gave it 9.0 CR. I used a performer intake with a professionally calibrated 750 DP. The cam was 236*-242* at .050", around 525 lift and 112* lsa. The ignition was MSD with an in cab dial that would swing the ignition advance 15*. I set the ignition total at 38* at 2400 rpm with the in cab dial set at 7.5*. That way I could retard the ignition for nitrous (175 HP) or advance it for cruise. The headers were 1 3/4" long tube with 3" x 24" collectors ending in termination boxes and then into 2 1/2" pipes and 2 1/2 straight through mufflers. ( There was a 2 1/2" "H" pipe between the collectors) The transmission was a JPT C6 with a 2400 stall converter. In the rear was a 3.73 Detroit Locker with traction bars. On the dyno the engine delivered 518.5 ft lbs at 4000rpm and 451.4 hp at 5200 rpms. On the street it pulled strong to 5600 rpms. The vehicle was a 79 Ford 150 PU. It was built to be my wife's every day ride and she drove it hard. It was a great ride. That truck laid waste to many brand x's. The point of this is that I built it to run on 87 octane gas and thats all it ever ran on.

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HotRodLincoln

· #7 · Jul 17, 2010

MauriSSSio said:
but why do most cars run faster after cool down then??

i run 10.8 compression on my 533 w 91 octane gasolina.

I think something just as important is DYNAMIC compression and how efficient the combustion chamber is.

Cool air is denser, so you get more air and fuel into the engine by heating it less. It also helps control detonation. With a metal intake manifold plus the passages in the heads air picks up heat on the way into the engine, thus you lose some power at normal water temps. For racing you don't want a stock high temp thermostat but for anything that looks like normal driving you do.

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MauriSSSio

· #8 · Jul 17, 2010

HotRodLincoln said:
Daily driving with a cold stat will just use more gas...

but that sounds like there are ZERO benefits to a cooler running engine.

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MauriSSSio

· #9 · Jul 17, 2010 (Edited)

2slow said:
getting the best MPG and the best performance con't use the same rules .

i know they dont use the same rules, but hes talking about a vehicle hes looking to drive pretty much only on weekends. If the engine i detonating itself to death, MPG shouldnt be a big deal (wouldnt more heat make it knock/ping even more?) and getting it to perform on his desired octane should be the main priority of this discussion.

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DanE

· #10 · Jul 17, 2010

In my above post about my 9.0 CR 472cu. in. 460 that ran on 87 octane gas, the cam was a hydraulic flat tappet. and air cleaner was dual snorkel with 4" tubes bringing in air from behind the grill. The cam was a little bigger than usual for a low rpm engine, and that was an effort to bleed off some low rpm cylinder pressure. The engine pulled 15" of vacuum at idle.

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2slow

· #11 · Jul 18, 2010

MauriSSSio said:
i know they dont use the same rules, but hes talking about a vehicle hes looking to drive pretty much only on weekends. If the engine i detonating itself to death, MPG shouldnt be a big deal (wouldnt more heat make it knock/ping even more?) and getting it to perform on his desired octane should be the main priority of this discussion.

if you know the rules, then you know the answer to your question ...... why do they run faster cooled down

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Muddin

· #12 · Sep 27, 2010

good info.

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